Citation: Denis Avey, Brittany Brewers, Fanxiu Zhu. Recent advances in the study of Kaposi's sarcoma-associated herpesvirus replication and pathogenesis .VIROLOGICA SINICA, 2015, 30(2) : 130-145.  http://dx.doi.org/10.1007/s12250-015-3595-2

Recent advances in the study of Kaposi's sarcoma-associated herpesvirus replication and pathogenesis

  • Corresponding author: Fanxiu Zhu, fzhu@bio.fsu.edu
  • Received Date: 10 April 2015
    Accepted Date: 16 April 2015
    Published Date: 23 April 2015
    Available online: 01 April 2015
  • It has now been over twenty years since a novel herpesviral genome was identified in Kaposi’s sarcoma biopsies. Since then, the cumulative research effort by molecular biologists, virologists, clinicians, and epidemiologists alike has led to the extensive characterization of this tumor virus, Kaposi’s sarcoma-associated herpesvirus (KSHV; also known as human herpesvirus 8 (HHV- 8)), and its associated diseases. Here we review the current knowledge of KSHV biology and pathogenesis, with a particular emphasis on new and exciting advances in the field of epigenetics. We also discuss the development and practicality of various cell culture and animal model systems to study KSHV replication and pathogenesis.

  • 加载中
    1. Abend JR, Uldrick T, Ziegelbauer JM. 2010. Regulation of tumor necrosis factor-like weak inducer of apoptosis receptor protein (TWEAKR) expression by Kaposi's sarcoma-associated herpesvirus microRNA prevents TWEAK-induced apoptosis and inflammatory cytokine expression. J Virol, 84: 12139-12151.
        doi: 10.1128/JVI.00884-10

    2. Ambroziak JA, Blackbourn DJ, Herndier BG, Glogau RG, Gullett JH, McDonald AR, Lennette ET, Levy JA. 1995. Herpes-like sequences in HIV-infected and uninfected Kaposi's sarcoma patients. Science, 268: 582-583
        doi: 10.1126/science.7725108

    3. An FQ, Folarin HM, Compitello N, Roth J, Gerson SL, McCrae KR, Fakhari FD, Dittmer DP, Renne R. 2006. Long-term-infected telomerase-immortalized endothelial cells: a model for Kaposi's sarcoma-associated herpesvirus latency in vitro and in vivo. J Virol, 80: 4833-4846.
        doi: 10.1128/JVI.80.10.4833-4846.2006

    4. Arias C, Weisburd B, Stern-Ginossar N, Mercier A, Madrid AS, Bellare P, Holdorf M, Weissman JS, Ganem D. 2014. KSHV 2.0: a comprehensive annotation of the Kaposi's sarcoma-associated herpesvirus genome using next-generation sequencing reveals novel genomic and functional features. PLoS Pathog, 10: e1003847.
        doi: 10.1371/journal.ppat.1003847

    5. Arvanitakis L, Mesri EA, Nador RG, Said JW, Asch AS, Knowles DM, Cesarman E. 1996. Establishment and characterization of a primary effusion (body cavity-based) lymphoma cell line (bc-3) harboring Kaposi's sarcoma-associated herpesvirus (KSHV/ HHV-8) in the absence of epstein-barr virus. Blood, 88: 2648-2654.

    6. Ashlock BM, Ma Q, Issac B, Mesri EA. 2014. Productively infected murine Kaposi's sarcoma-like tumors defne new animal models for studing and targeting KSHV oncogenesis and replication. PLoS One, 9: 1-15.

    7. Bai Z, Huang Y, Li W, Zhu Y, Jung JU, Lu C, Gao SJ. 2014. Genomewide mapping and screening of Kaposi's sarcoma-associated herpesvirus (KSHV) 3' untranslated regions identify bicistronic and polycistronic viral transcripts as frequent targets of KSHV microRNAs. J Virol, 88: 377-392.
        doi: 10.1128/JVI.02689-13

    8. Ballestas ME, Chatis PA, Kaye KM. 1999. Effcient persistence of extrachromosomal KSHV DNA mediated by latency-associated nuclear antigen. Science, 284: 641-644.
        doi: 10.1126/science.284.5414.641

    9. Ballestas ME, Chatis PA, Kaye KM. 1999. Efficient persistence of extrachromosomal KSHV DNA mediated by latency-associated nuclear antigen. Science, 284: 641-644.
        doi: 10.1126/science.284.5414.641

    10. Bannister AJ, Kouzarides T. 2011. Regulation of chromatin by histone modifications. Cell Res, 21: 381-395.
        doi: 10.1038/cr.2011.22

    11. Bechtel JT, Liang Y, Hvidding J, Ganem D. 2003. Host range of Kaposi's sarcoma-associated herpesvirus in cultured cells. J Virol, 77: 6474-6481.
        doi: 10.1128/JVI.77.11.6474-6481.2003

    12. Bernstein BE, Mikkelsen TS, Xie X, Kamal M, Huebert DJ, Cuff J, Fry B, Meissner A, Wernig M, Plath K, Jaenisch R, Wagschal A, Feil R, Schreiber SL, Lander ES. 2006. A bivalent chromatin structure marks key developmental genes in embryonic stem cells. Cell, 125: 315-326.
        doi: 10.1016/j.cell.2006.02.041

    13. Bhatt AP, Bhende PM, Sin SH, Roy D, Dittmer DP, Damania B. 2010. Dual inhibition of PI3K and mTOR inhibits autocrine and paracrine proliferative loops in PI3K/Akt/mTOR-addicted lymphomas. Blood, 115: 4455-4463.
        doi: 10.1182/blood-2009-10-251082

    14. Bhatt S, Ashlock BM, Toomey NL, Diaz LA, Mesri EA, Lossos IS, Ramos JC. 2013. Efficacious proteasome/HDAC inhibitor combination therapy for primary effusion lymphoma. J Clin Invest, 123: 2616-2628.
        doi: 10.1172/JCI64503

    15. Blackbourn DJ, Lennette E, Klencke B, Moses A, Chandran B, Weinstein M, Glogau RG, Witte MH, Way DL, Kutzkey T, Herndier B, Levy JA. 2000. The restricted cellular host range of human herpesvirus 8. AIDS, 14: 1123-1133.
        doi: 10.1097/00002030-200006160-00009

    16. Borah S, Darricarrere N, Darnell A, Myoung J, Steitz JA. 2011. A viral nuclear noncoding RNA binds re-localized poly(A) binding protein and is required for late KSHV gene expression. PLoS Pathog, 7: e1002300.
        doi: 10.1371/journal.ppat.1002300

    17. Brinkmann MM, Pietrek M, Dittrich-Breiholz O, Kracht M, Schulz TF. 2007. Modulation of host gene expression by the K15 protein of Kaposi's sarcoma-associated herpesvirus. J Virol, 81: 42-58.
        doi: 10.1128/JVI.00648-06

    18. Brittany M. Ashlock QM, Biju Issac, Enrique A. Mesri 2014. Productively Infected Murine Kaposi's Sarcoma-Like Tumors Define New Animal Models for Studing and Targeting KSHV Oncogenesis and Replication. PLOS ONE, 9: 1-15.

    19. Brulois KF, Chang H, Lee AS, Ensser A, Wong LY, Toth Z, Lee SH, Lee HR, Myoung J, Ganem D, Oh TK, Kim JF, Gao SJ, Jung JU. 2012. Construction and manipulation of a new Kaposi's sarcoma-associated herpesvirus bacterial artificial chromosome clone. J Virol, 86: 9708-9720.
        doi: 10.1128/JVI.01019-12

    20. Budt M, Hristozova T, Hille G, Berger K, Brune W. 2011. Construction of a lytically replicating Kaposi's sarcoma-associated herpesvirus. J Virol, 85: 10415-10420.
        doi: 10.1128/JVI.05071-11

    21. Cai X, Lu S, Zhang Z, Gonzalez CM, Damania B, Cullen BR. 2005. Kaposi's sarcoma-associated herpesvirus expresses an array of viral microRNAs in latently infected cells. Proc Natl Acad Sci U S A, 102: 5570-5575.
        doi: 10.1073/pnas.0408192102

    22. Campbell M, Kung HJ, Izumiya Y. 2014. Long non-coding RNA and epigenetic gene regulation of KSHV. Viruses, 6: 4165-4177.
        doi: 10.3390/v6114165

    23. Cannon JS, Ciufo D, Hawkins AL, Griffin CA, Borowitz MJ, Hayward GS, Ambinder RF. 2000. A new primary effusion lymphoma-derived cell line yields a highly infectious Kaposi's sarcoma herpesvirus-containing supernatant. J Virol, 74: 10187-10193.
        doi: 10.1128/JVI.74.21.10187-10193.2000

    24. Carroll PA, Brazeau E, Lagunoff M. 2004. Kaposi's sarcoma-associated herpesvirus infection of blood endothelial cells induces lymphatic differentiation. Virology, 328: 7-18.
        doi: 10.1016/j.virol.2004.07.008

    25. CDC. 1981. Kaposi's sarcoma and Pneumocystis pneumonia among homosexual men--New York City and California. MMWR Morb Mortal Wkly Rep, 30: 305-308.

    26. Cesarman E, Mesri EA. 2007. Kaposi sarcoma-associated herpesvirus and other viruses in human lymphomagenesis. Curr Top Microbiol Immunol, 312: 263-287.

    27. Cesarman E, Moore PS, Rao PH, Inghirami G, Knowles DM, Chang Y. 1995. In vitro establishment and characterization of two acquired immunodeficiency syndrome-related lymphoma cell lines (bc-1 and bc-2) containing Kaposi's sarcoma-associated herpesvirus-like (KSHV) DNA sequences. Blood, 86: 2708-2714.

    28. Cesarman E, Nador RG, Aozasa K, Delsol G, Said JW, Knowles DM. 1996. Kaposi's sarcoma-associated herpesvirus in non-AIDS related lymphomas occurring in body cavities. Am J Pathol, 149: 53-57.

    29. Chagas CA, Endo LH, Sakano E, Pinto GA, Brousset P, Vassallo J. 2006. Detection of herpesvirus type 8 (HHV8) in children's tonsils and adenoids by immunohistochemistry and in situ hybridization. Int J Pediatr Otorhinolaryngol, 70: 65-72.
        doi: 10.1016/j.ijporl.2005.04.030

    30. Chakraborty S, Veettil MV, Chandran B. 2012. Kaposi's sarcoma associated herpesvirus entry into target cells. Front Microbiol, 3: 1-13.

    31. Chandran B. 2010. Early events in Kaposi's sarcoma-associated herpesvirus infection of target cells. J Virol, 84: 2188-2199.
        doi: 10.1128/JVI.01334-09

    32. Chang H, Wachtman LM, Pearson CB, Lee JS, Lee HR, Lee SH, Vieira J, Mansfield KG, Jung JU. 2009. Non-human primate model of Kaposi's sarcoma-associated herpesvirus infection. PLOS Pathog, 5: e1000606.
        doi: 10.1371/journal.ppat.1000606

    33. Chang HH, Ganem D. 2013. A unique herpesviral transcriptional program in KSHV-infected lymphatic endothelial cells leads to mTORC1 activation and rapamycin sensitivity. Cell Host Microbe, 13: 429-440.
        doi: 10.1016/j.chom.2013.03.009

    34. Chang PC, Fitzgerald LD, Hsia DA, Izumiya Y, Wu CY, Hsieh WP, Lin SF, Campbell M, Lam KS, Luciw PA, Tepper CG, Kung HJ. 2011. Histone demethylase JMJD2A regulates Kaposi's sarcoma-associated herpesvirus replication and is targeted by a viral transcriptional factor. J Virol, 85: 3283-3293.
        doi: 10.1128/JVI.02485-10

    35. Chang Y, Cesarman E, Pessin MS, Lee F, Culpepper J, Knowles DM, Moore PS. 1994. Identification of herpesvirus-like DNA sequences in AIDS-associated Kaposi's sarcoma. Science, 266: 1865-1869.
        doi: 10.1126/science.7997879

    36. Chang Y, Moore P. 2014. Twenty years of KSHV. Viruses, 6: 4258-4264.
        doi: 10.3390/v6114258

    37. Chen HS, Lu F, Lieberman PM. 2013. Epigenetic regulation of EBV and KSHV latency. Curr Opin Virol, 3: 251-259.
        doi: 10.1016/j.coviro.2013.03.004

    38. Chen HS, Wikramasinghe P, Showe L, Lieberman PM. 2012. Cohesins repress Kaposi's sarcoma-associated herpesvirus immediate early gene transcription during latency. J Virol, 86: 9454-9464.
        doi: 10.1128/JVI.00787-12

    39. Cheng F, Pekkonen P, Laurinavicius S, Sugiyama N, Henderson S, Gunther T, Rantanen V, Kaivanto E, Aavikko M, Sarek G, Hautaniemi S, Biberfeld P, Aaltonen L, Grundhoff A, Boshoff C, Alitalo K, Lehti K, Ojala PM. 2011. KSHV-initiated notch activation leads to membrane-type-1 matrix metalloproteinase-dependent lymphatic endothelial-to-mesenchymal transition. Cell Host Microbe, 10: 577-590.
        doi: 10.1016/j.chom.2011.10.011

    40. Cho H, Kang H. 2012. KSHV infection of B-cell lymphoma using a modified KSHV BAC36 and coculturing system. J Microbiol, 50: 285-292.
        doi: 10.1007/s12275-012-1495-9

    41. Clyde K, Glaunsinger BA. 2011. Deep sequencing reveals direct targets of gammaherpesvirus-induced mRNA decay and suggests that multiple mechanisms govern cellular transcript escape. PLoS One, 6: e19655.
        doi: 10.1371/journal.pone.0019655

    42. Dai L, Trillo-Tinoco J, Bai L, Kang B, Xu Z, Wen X, Del Valle L, Qin Z. 2014. Systematic analysis of a xenograft mice model for KSHV primary effusion lymphoma (PEL). PLoS One, 9: 1-9.

    43. Darnell RB. 2010. HITS-CLIP: panoramic views of protein-RNA regulation in living cells. Wiley Interdiscip Rev RNA, 1: 266-286.
        doi: 10.1002/wrna.31

    44. Darst RP, Haecker I, Pardo CE, Renne R, Kladde MP. 2013. Epigenetic diversity of Kaposi's sarcoma-associated herpesvirus. Nucleic Acids Res, 41: 2993-3009.
        doi: 10.1093/nar/gkt033

    45. de Wit E, de Laat W. 2012. A decade of 3C technologies: insights into nuclear organization. Genes Dev, 26: 11-24.
        doi: 10.1101/gad.179804.111

    46. Deng Z, Wang Z, Lieberman PM. 2012. Telomeres and viruses: common themes of genome maintenance. Front Oncol, 2: 201.

    47. Dittmer D, Stoddart C, Renne R, Linquist-Stepps V, Moreno ME, Bare C, McCune JM, Ganem D. 1999. Experimental transmission of Kaposi's sarcoma-associated herpesvirus (KSHV/HHV-8) to SCID-hu Thy/Liv mice. J Exp Med, 190: 1857-1868.
        doi: 10.1084/jem.190.12.1857

    48. Dittmer DP, Damania B. 2007. KSHV-associated disease in the AIDS patient. Cancer Treat Res, 133: 129-139.
        doi: 10.1007/978-0-387-46816-7

    49. Dittmer DP, Damania B. 2013. Kaposi sarcoma associated herpesvirus pathogenesis (KSHV)--an update. Curr Opin Virol, 3: 238-244.
        doi: 10.1016/j.coviro.2013.05.012

    50. Dollery SJ, Santiago-Crespo RJ, Kardava L, Moir S, Berger EA. 2014. Efficient infection of a human B cell line with cell-free Kaposi's sarcoma-associated herpesvirus. J Virol, 88: 1748-1757.
        doi: 10.1128/JVI.03063-13

    51. Ellison TJ, Izumiya Y, Izumiya C, Luciw PA, Kung HJ. 2009. A comprehensive analysis of recruitment and transactivation potential of K-Rta and K-bZIP during reactivation of Kaposi's sarcoma-associated herpesvirus. Virology, 387: 76-88.
        doi: 10.1016/j.virol.2009.02.016

    52. Ellison TJ, Kedes DH. 2014. Variable episomal silencing of a recombinant herpesvirus renders its encoded GFP an unreliable marker of infection in primary cells. PLoS One, 9: e111502.
        doi: 10.1371/journal.pone.0111502

    53. Feldman ER, Kara M, Coleman CB, Grau KR, Oko LM, Krueger BJ, Renne R, van Dyk LF, Tibbetts SA. 2014. Virus-encoded microRNAs facilitate gammaherpesvirus latency and pathogenesis in vivo. MBio, 5: e00981-00914.

    54. Flore O, Rafii S, Ely S, O'Leary JJ, Hyjek EM, Cesarman E. 1998. Transformation of primary human endothelial cells by Kaposi's sarcoma-associated herpesvirus. Nature, 394: 588-592.
        doi: 10.1038/29093

    55. Forte E, Raja AN, Shamulailatpam P, Manzano M, Schipma MJ, Casey JL, Gottwein E. 2015. MicroRNA-mediated transformation by the Kaposi's sarcoma-associated herpesvirus Kaposin locus. J Virol, 89: 2333-2341.
        doi: 10.1128/JVI.03317-14

    56. Ganem D. 1997. KSHV and Kaposi's sarcoma: the end of the beginning? Cell, 91: 157-160.
        doi: 10.1016/S0092-8674(00)80398-0

    57. Ganem D. 2006. KSHV infection and the pathogenesis of Kaposi's sarcoma. Annu Rev Pathol, 1: 273-296.
        doi: 10.1146/annurev.pathol.1.110304.100133

    58. Ganem D. 2007. KSHV-induced oncogenesis. In: Human Herpesviruses: Biology, Therapy, and Immunoprophylaxis, Arvin A, Campadelli-Fiume G, Mocarski E, et al. (eds). Cambridge: Cambridge University Press. Available: http://www.ncbi.nlm.nih.gov/books/NBK47373/.

    59. Ganem D. 2010. KSHV and the pathogenesis of Kaposi sarcoma: listening to human biology and medicine. J Clin Invest, 120: 939-949.
        doi: 10.1172/JCI40567

    60. Ganem D, Ziegelbauer J. 2008. MicroRNAs of Kaposi's sarcoma-associated herpes virus. Semin Cancer Biol, 18: 437-440.
        doi: 10.1016/j.semcancer.2008.10.006

    61. Gao SJ, Deng JH, Zhou FC. 2003. Productive lytic replication of a recombinant Kaposi's sarcoma-associated herpesvirus in efficient primary infection of primary human endothelial cells. J Virol, 77: 9738-9749.
        doi: 10.1128/JVI.77.18.9738-9749.2003

    62. Gao SJ, Kingsley L, Hoover DR, Spira TJ, Rinaldo CR, Saah A, Phair J, Detels R, Parry P, Chang Y, Moore PS. 1996. Seroconversion to antibodies against Kaposi's sarcoma-associated herpesvirus-related latent nuclear antigens before the development of Kaposi's sarcoma. N Engl J Med, 335: 233-241.
        doi: 10.1056/NEJM199607253350403

    63. Gavrilov A, Eivazova E, Priozhkova I, Lipinski M, Razin S, Vassetzky Y. 2009. Chromosome conformation capture (from 3C to 5C) and its ChIP-based modification. Methods Mol Biol, 567: 171-188.
        doi: 10.1007/978-1-60327-414-2

    64. Gorres KL, Daigle D, Mohanram S, Miller G. 2014. Activation and repression of Epstein-Barr Virus and Kaposi's sarcoma-associated herpesvirus lytic cycles by short-and medium-chain fatty acids. J Virol, 88: 8028-8044.
        doi: 10.1128/JVI.00722-14

    65. Gottlieb GJ, Ragaz A, Vogel JV, Friedman-Kien A, Rywlin AM, Weiner EA, Ackerman AB. 1981. A preliminary communication on extensively disseminated Kaposi's sarcoma in young homosexual men. Am J Dermatopathol, 3: 111-114.
        doi: 10.1097/00000372-198100320-00002

    66. Gottwein E, Corcoran DL, Mukherjee N, Skalsky RL, Hafner M, Nusbaum JD, Shamulailatpam P, Love CL, Dave SS, Tuschl T, Ohler U, Cullen BR. 2011. Viral microRNA targetome of KSHV-infected primary effusion lymphoma cell lines. Cell Host Microbe, 10: 515-526.
        doi: 10.1016/j.chom.2011.09.012

    67. Gramolelli S, Schulz TF. 2015. The role of Kaposi sarcoma-associated herpesvirus in the pathogenesis of Kaposi sarcoma. J Pathol, 235: 368-380.
        doi: 10.1002/path.4441

    68. Grundhoff A, Ganem D. 2004. Inefficient establishment of KSHV latency suggests an additional role for continued lytic replication in Kaposi sarcoma pathogenesis. J Clin Invest, 113: 124-136.
        doi: 10.1172/JCI200417803

    69. Gunther T, Grundhoff A. 2010. The epigenetic landscape of latent Kaposi sarcoma-associated herpesvirus genomes. PLoS Pathog, 6: e1000935.
        doi: 10.1371/journal.ppat.1000935

    70. Gunther T, Schreiner S, Dobner T, Tessmer U, Grundhoff A. 2014. Influence of ND10 components on epigenetic determinants of early KSHV latency establishment. PLoS Pathog, 10: e1004274.
        doi: 10.1371/journal.ppat.1004274

    71. Gwack Y, Byun H, Hwang S, Lim C, Choe J. 2001. CREB-binding protein and histone deacetylase regulate the transcriptional activity of Kaposi's sarcoma-associated herpesvirus open reading frame 50. J Virol, 75: 1909-1917.
        doi: 10.1128/JVI.75.4.1909-1917.2001

    72. Haecker I, Gay LA, Yang Y, Hu J, Morse AM, McIntyre LM, Renne R. 2012. Ago HITS-CLIP expands understanding of Kaposi's sarcoma-associated herpesvirus miRNA function in primary effusion lymphomas. PLoS Pathog, 8: e1002884.
        doi: 10.1371/journal.ppat.1002884

    73. Haecker I, Renne R. 2014. HITS-CLIP and PAR-CLIP advance viral miRNA targetome analysis. Crit Rev Eukaryot Gene Expr, 24: 101-116.
        doi: 10.1615/CritRevEukaryotGeneExpr.v24.i2

    74. Hassman LM, Ellison TJ, Kedes DH. 2011. KSHV infects a subset of human tonsillar B cells, driving proliferation and plasmablast differentiation. J Clin Invest, 121: 752-768.
        doi: 10.1172/JCI44185

    75. He M, Zhang W, Bakken T, Schutten M, Toth Z, Jung JU, Gill P, Cannon M, Gao SJ. 2012. Cancer angiogenesis induced by Kaposi sarcoma-associated herpesvirus is mediated by EZH2. Cancer Res, 72: 3582-3592.
        doi: 10.1158/0008-5472.CAN-11-2876

    76. Herndier BG, Werner A, Arnstein P, Abbey NW, Demartis F, Cohen RL, Shuman MA, Levy JA. 1994. Characterization of a human Kaposi's sarcoma cell line that induces angiogenic tumors in animals. AIDS, 8: 575-581.
        doi: 10.1097/00002030-199405000-00002

    77. Hong YK, Foreman K, Shin JW, Hirakawa S, Curry CL, Sage DR, Libermann T, Dezube BJ, Fingeroth JD, Detmar M. 2004. Lymphatic reprogramming of blood vascular endothelium by Kaposi sarcoma-associated herpesvirus. Nat Genet, 36: 683-685.
        doi: 10.1038/ng1383

    78. Hu J, Yang Y, Turner PC, Jain V, McIntyre LM, Renne R. 2014. LANA binds to multiple active viral and cellular promoters and associates with the H3K4methyltransferase hSET1 complex. PLoS Pathog, 10: e1004240.
        doi: 10.1371/journal.ppat.1004240

    79. Hurley EA, Thorley-Lawson DA. 1988. B cell activation and the establishment of Epstein-Barr virus latency. J Exp Med, 168: 2059-2075.
        doi: 10.1084/jem.168.6.2059

    80. Hyosun Cho HK. 2012. KSHV Infection of B-Cell Lymphoma Using a Modified KSHV BAC36 and Coculturing System. J Microbiol, 50: 285-292.
        doi: 10.1007/s12275-012-1495-9

    81. Iacovides D, Michael S, Achilleos C, Strati K. 2013. Shared mechanisms in stemness and carcinogenesis: lessons from oncogenic viruses. Front Cell Infect Microbiol, 3: 66.

    82. Jensen KB, Darnell RB. 2008. CLIP: crosslinking and immunoprecipitation of in vivo RNA targets of RNA-binding proteins. Methods Mol Biol, 488: 85-98.
        doi: 10.1007/978-1-60327-475-3

    83. Jha HC, Lu J, Verma SC, Banerjee S, Mehta D, Robertson ES. 2014. Kaposi's sarcoma-associated herpesvirus genome programming during the early stages of primary infection of peripheral blood mononuclear cells. MBio, 5. pii: e02261-14. doi: 10.1128/mBio.02261-14.

    84. Jin B, Li Y, Robertson KD. 2011. DNA methylation: superior or subordinate in the epigenetic hierarchy? Genes Cancer, 2: 607-617.
        doi: 10.1177/1947601910393957

    85. Jones PA. 2012. Functions of DNA methylation: islands, start sites, gene bodies and beyond. Nat Rev Genet, 13: 484-492.
        doi: 10.1038/nrg3230

    86. Jones T, Ye F, Bedolla R, Huang Y, Meng J, Qian L, Pan H, Zhou F, Moody R, Wagner B, Arar M, Gao SJ. 2012. Direct and efficient cellular transformation of primary rat mesenchymal precursor cells by KSHV. J Clin Invest, 122: 1076-1081.
        doi: 10.1172/JCI58530

    87. Kang H, Cho H, Sung GH, Lieberman PM. 2013. CTCF regulates Kaposi's sarcoma-associated herpesvirus latency transcription by nucleosome displacement and RNA polymerase programming. J Virol, 87: 1789-1799.
        doi: 10.1128/JVI.02283-12

    88. Kang H, Lieberman PM. 2011. Mechanism of glycyrrhizic acid inhibition of Kaposi's sarcoma-associated herpesvirus: disruption of CTCF-cohesin-mediated RNA polymerase Ⅱ pausing and sister chromatid cohesion. J Virol, 85: 11159-11169.
        doi: 10.1128/JVI.00720-11

    89. Kang H, Wiedmer A, Yuan Y, Robertson E, Lieberman PM. 2011a. Coordination of KSHV latent and lytic gene control by CTCF-cohesin mediated chromosome conformation. PLoS Pathog, 7: e1002140.
        doi: 10.1371/journal.ppat.1002140

    90. Kang JG, Pripuzova N, Majerciak V, Kruhlak M, Le SY, Zheng ZM. 2011b. Kaposi's sarcoma-associated herpesvirus ORF57 promotes escape of viral and human interleukin-6 from microRNA-mediated suppression. J Virol, 85: 2620-2630.
        doi: 10.1128/JVI.02144-10

    91. Kaposi M. 1872. Idiopathisches multiples Pigmentsarkom der Haut. Archiv für Dermatologie und Syphilis, 4: 265-273.

    92. Karlic R, Chung HR, Lasserre J, Vlahovicek K, Vingron M. 2010. Histone modification levels are predictive for gene expression. Proc Natl Acad Sci U S A, 107: 2926-2931.
        doi: 10.1073/pnas.0909344107

    93. Kati S, Tsao EH, Gunther T, Weidner-Glunde M, Rothamel T, Grundhoff A, Kellam P, Schulz TF. 2013. Activation of the B cell antigen receptor triggers reactivation of latent Kaposi's sarcoma-associated herpesvirus in B cells. J Virol, 87: 8004-8016.
        doi: 10.1128/JVI.00506-13

    94. Kedes DH, Operskalski E, Busch M, Kohn R, Flood J, Ganem D. 1996. The seroepidemiology of human herpesvirus 8 (Kaposi's sarcoma-associated herpesvirus): distribution of infection in KS risk groups and evidence for sexual transmission. Nat Med, 2: 918-924.
        doi: 10.1038/nm0896-918

    95. Kim KY, Huerta SB, Izumiya C, Wang DH, Martinez A, Shevchenko B, Kung HJ, Campbell M, Izumiya Y. 2013. Kaposi's sarcoma-associated herpesvirus (KSHV) latency-associated nuclear antigen regulates the KSHV epigenome by association with the histone demethylase KDM3A. J Virol, 87: 6782-6793.
        doi: 10.1128/JVI.00011-13

    96. Kornberg RD, Lorch Y. 1999. Twenty-five years of the nucleosome, fundamental particle of the eukaryote chromosome. Cell, 98: 285-294.
        doi: 10.1016/S0092-8674(00)81958-3

    97. Lagunoff M, Bechtel J, Venetsanakos E, Roy AM, Abbey N, Herndier B, McMahon M, Ganem D. 2002. De novo infection and serial transmission of Kaposi's sarcoma-associated herpesvirus in cultured endothelial cells. J Virol, 76: 2440-2448.
        doi: 10.1128/jvi.76.5.2440-2448.2002

    98. Lefort S, Flamand L. 2009. Kaposi's sarcoma-associated herpesvirus K-bZIP protein is necessary for lytic viral gene expression, DNA replication, and virion production in primary effusion lymphoma cell lines. J Virol, 83: 5869-5880.
        doi: 10.1128/JVI.01821-08

    99. Lei X, Bai Z, Ye F, Huang Y, Gao SJ. 2010. Regulation of herpesvirus lifecycle by viral microRNAs. Virulence, 1: 433-435.
        doi: 10.4161/viru.1.5.12966

    100. Li Q, He M, Zhou F, Ye F, Gao SJ. 2014. Activation of Kaposi's sarcoma-associated herpesvirus (KSHV) by inhibitors of class Ⅲ histone deacetylases: identification of sirtuin 1 as a regulator of the KSHV life cycle. J Virol, 88: 6355-6367.
        doi: 10.1128/JVI.00219-14

    101. Li X, Zhu F. 2009. Identification of the nuclear export and adjacent nuclear localization signals for ORF45 of Kaposi's sarcoma-associated herpesvirus. J Virol, 83: 2531-2539.
        doi: 10.1128/JVI.02209-08

    102. Liang D, Gao Y, Lin X, He Z, Zhao Q, Deng Q, Lan K. 2011b. A human herpesvirus miRNA attenuates interferon signaling and contributes to maintenance of viral latency by targeting IKKepsilon. Cell Res, 21: 793-806.
        doi: 10.1038/cr.2011.5

    103. Liang D, Hu H, Li S, Dong J, Wang X, Wang Y, He L, He Z, Gao Y, Gao SJ, Lan K. 2014. Oncogenic herpesvirus KSHV Hijacks BMP-Smad1-Id signaling to promote tumorigenesis. PLoS Pathog, 10: e1004253.
        doi: 10.1371/journal.ppat.1004253

    104. Liang D, Lin X, Lan K. 2011a. Looking at Kaposi's Sarcoma-Associated Herpesvirus-Host Interactions from a microRNA Viewpoint. Front Microbiol, 2: 271.

    105. Lieberman PM. 2013. Keeping it quiet: chromatin control of gammaherpesvirus latency. Nat Rev Microbiol, 11: 863-875.
        doi: 10.1038/nrmicro3135

    106. Lim C, Lee D, Seo T, Choi C, Choe J. 2003. Latency-associated nuclear antigen of Kaposi's sarcoma-associated herpesvirus functionally interacts with heterochromatin protein 1. J Biol Chem, 278: 7397-7405.
        doi: 10.1074/jbc.M211912200

    107. Lin HR, Ganem D. 2011. Viral microRNA target allows insight into the role of translation in governing microRNA target accessibility. Proc Natl Acad Sci U S A, 108: 5148-5153.
        doi: 10.1073/pnas.1102033108

    108. Lin X, Liang D, He Z, Deng Q, Robertson ES, Lan K. 2011. miRK12-7-5p encoded by Kaposi's sarcoma-associated herpesvirus stabilizes the latent state by targeting viral ORF50/RTA. PLoS One, 6: e16224.
        doi: 10.1371/journal.pone.0016224

    109. Lin Z, Flemington EK. 2011. miRNAs in the pathogenesis of oncogenic human viruses. Cancer Lett, 305: 186-199.
        doi: 10.1016/j.canlet.2010.08.018

    110. Lu F, Stedman W, Yousef M, Renne R, Lieberman PM. 2010. Epigenetic regulation of Kaposi's sarcoma-associated herpesvirus latency by virus-encoded microRNAs that target Rta and the cellular Rbl2-DNMT pathway. J Virol, 84: 2697-2706.
        doi: 10.1128/JVI.01997-09

    111. Lu F, Zhou J, Wiedmer A, Madden K, Yuan Y, Lieberman PM. 2003. Chromatin remodeling of the Kaposi's sarcoma-associated herpesvirus ORF50 promoter correlates with reactivation from latency. J Virol, 77: 11425-11435.
        doi: 10.1128/JVI.77.21.11425-11435.2003

    112. Lu J, Jha HC, Verma SC, Sun Z, Banerjee S, Dzeng R, Robertson ES. 2014. Kaposi's sarcoma-associated herpesvirus-encoded LANA contributes to viral latent replication by activating phosphorylation of survivin. J Virol, 88: 4204-4217.
        doi: 10.1128/JVI.03855-13

    113. Lu J, Verma SC, Cai Q, Saha A, Dzeng RK, Robertson ES. 2012. The RBP-Jkappa binding sites within the RTA promoter regulate KSHV latent infection and cell proliferation. PLoS Pathog, 8: e1002479.
        doi: 10.1371/journal.ppat.1002479

    114. Luna RE, Zhou F, Baghian A, Chouljenko V, Forghani B, Gao SJ, Kousoulas KG. 2004. Kaposi's sarcoma-associated herpesvirus glycoprotein K8.1 is dispensable for virus entry. J Virol, 78: 6389-6398.
        doi: 10.1128/JVI.78.12.6389-6398.2004

    115. Majerciak V, Pripuzova N, McCoy JP, Gao SJ, Zheng ZM. 2007. Targeted disruption of Kaposi's sarcoma-associated herpesvirus ORF57 in the viral genome is detrimental for the expression of ORF59, K8alpha, and K8.1 and the production of infectious virus. J Virol, 81: 1062-1071.
        doi: 10.1128/JVI.01558-06

    116. Malterer G, Dolken L, Haas J. 2011. The miRNA-targetome of KSHV and EBV in human B-cells. RNA Biol, 8: 30-34.
        doi: 10.4161/rna.8.1.13745

    117. Martinez FP, Tang Q. 2012. Leucine zipper domain is required for Kaposi sarcoma-associated herpesvirus (KSHV) K-bZIP protein to interact with histone deacetylase and is important for KSHV replication. J Biol Chem, 287: 15622-15634.
        doi: 10.1074/jbc.M111.315861

    118. Mattsson K, Kiss C, Platt GM, Simpson GR, Kashuba E, Klein G, Schulz TF, Szekely L. 2002. Latent nuclear antigen of Kaposi's sarcoma herpesvirus/human herpesvirus-8 induces and relocates RING3 to nuclear heterochromatin regions. J Gen Virol, 83:179-188.
        doi: 10.1099/0022-1317-83-1-179

    119. Mayama S, Cuevas LE, Sheldon J, Omar OH, Smith DH, Okong P, Silvel B, Hart CA, Schulz TF. 1998. Prevalence and transmission of Kaposi's sarcoma-associated herpesvirus (human herpesvirus 8) in Ugandan children and adolescents. Int J Cancer, 77: 817-820.
        doi: 10.1002/(ISSN)1097-0215

    120. Mercier A, Arias C, Madrid AS, Holdorf MM, Ganem D. 2014. Site-specific association with host and viral chromatin by Kaposi's sarcoma-associated herpesvirus LANA and its reversal during lytic reactivation. J Virol, 88: 6762-6777.
        doi: 10.1128/JVI.00268-14

    121. Merkenschlager M, Odom DT. 2013. CTCF and cohesin: linking gene regulatory elements with their targets. Cell, 152: 1285-1297.
        doi: 10.1016/j.cell.2013.02.029

    122. Mesri EA, Cesarman E, Arvanitakis L, Rafii S, Moore MA, Posnett DN, Knowles DM, Asch AS. 1996. Human herpesvirus-8/ Kaposi's sarcoma-associated herpesvirus is a new transmissible virus that infects B cells. J Exp Med, 183: 2385-2390.
        doi: 10.1084/jem.183.5.2385

    123. Mesri EA, Cesarman E, Boshoff C. 2010. Kaposi's sarcoma and its associated herpesvirus. Nat Rev Cancer, 10: 707-719.
        doi: 10.1038/nrc2888

    124. Miller G, El-Guindy A, Countryman J, Ye J, Gradoville L. 2007. Lytic cycle switches of oncogenic human gammaherpesviruses. Adv Cancer Res, 97: 81-109.
        doi: 10.1016/S0065-230X(06)97004-3

    125. Miller G, Heston L, Grogan E, Gradoville L, Rigsby M, Sun R, Shedd D, Kushnaryov VM, Grossberg S, Chang Y. 1997. Selective switch between latency and lytic replication of Kaposi's sarcoma herpesvirus and Epstein-Barr virus in dually infected body cavity lymphoma cells. J Virol, 71: 314-324.

    126. Miller G, Rigsby MO, Heston L, Grogan E, Sun R, Metroka C, Levy JA, Gao SJ, Chang Y, Moore P. 1996. Antibodies to butyrate-inducible antigens of Kaposi's sarcoma-associated herpesvirus in patients with HIV-1 infection. N Engl J Med, 334: 1292-1297.
        doi: 10.1056/NEJM199605163342003

    127. Moody R, Zhu Y, Huang Y, Cui X, Jones T, Bedolla R, Lei X, Bai Z, Gao SJ. 2013. KSHV microRNAs mediate cellular transformation and tumorigenesis by redundantly targeting cell growth and survival pathways. PLoS Pathog, 9: e1003857.
        doi: 10.1371/journal.ppat.1003857

    128. Moore PS, Chang Y. 2010. Why do viruses cause cancer? Highlights of the first century of human tumour virology. Nat Rev Cancer, 10: 878-889.

    129. Moses AV, Fish KN, Ruhl R, Smith PP, Strussenberg JG, Zhu L, Chandran B, Nelson JA. 1999. Long-term infection and transformation of dermal microvascular endothelial cells by human herpesvirus 8. J Virol, 73: 6892-6902.

    130. Myoung J, Ganem D. 2011a. Infection of lymphoblastoid cell lines by Kaposi's sarcoma-associated herpesvirus: critical role of cell-associated virus. J Virol, 85: 9767-9777.
        doi: 10.1128/JVI.05136-11

    131. Myoung J, Ganem D. 2011b. Generation of a doxycycline-inducible KSHV producer cell line of endothelial origin: Maintenance of tight latency with efficient reactivation upon induction. J Virol Methods, 174: 12-21.
        doi: 10.1016/j.jviromet.2011.03.012

    132. Myoung J, Ganem D. 2011c. Infection of primary human tonsillar lymphoid cells by KSHV reveals frequent but abortive infection of T cells. Virology, 413: 1-11.
        doi: 10.1016/j.virol.2010.12.036

    133. Nakamura H, Lu M, Gwack Y, Souvlis J, Zeichner SL, Jung JU. 2003. Global changes in Kaposi's sarcoma-associated virus gene expression patterns following expression of a tetracycline-inducible Rta transactivator. J Virol, 77: 4205-4220.
        doi: 10.1128/JVI.77.7.4205-4220.2003

    134. National Institutes of Health (NIH). 2014. Available: http://commonfund.nih.gov/4Dnucleome/index.

    135. Nevels M, Nitzsche A, Paulus C. 2011. How to control an infectious bead string: nucleosome-based regulation and targeting of herpesvirus chromatin. Rev Med Virol, 21: 154-180.
        doi: 10.1002/rmv.v21.3

    136. Niedermeier A, Talanin N, Chung EJ, Sells RE, Borris DL, Orenstein JM, Trepel JB, Blauvelt A. 2006. Histone deacetylase inhibitors induce apoptosis with minimal viral reactivation in cells infected with Kaposi's sarcoma-associated herpesvirus. J Invest Dermatol, 126: 2516-2524.
        doi: 10.1038/sj.jid.5700438

    137. Orzechowska BU, Powers MF, Sprague J, Li H, Yen B, Searles RP, Axthelm MK, Wong SW. 2008. Rhesus macaque rhadinovirus-associated non-hodgkin lymphoma: Animal model for KSHV-associated malignancies. Blood, 112: 4227-4234.
        doi: 10.1182/blood-2008-04-151498

    138. Pantry SN, Medveczky PG. 2009. Epigenetic regulation of Kaposi's sarcoma-associated herpesvirus replication. Semin Cancer Biol, 19: 153-157.
        doi: 10.1016/j.semcancer.2009.02.010

    139. Panyutich EA, Said JW, Miles SA. 1998. Infection of primary dermal microvascular endothelial cells by Kaposi's sarcoma-associated herpesvirus. AIDS, 12: 467-472.
        doi: 10.1097/00002030-199805000-00007

    140. Paulus C, Nitzsche A, Nevels M. 2010. Chromatinisation of herpesvirus genomes. Rev Med Virol, 20: 34-50.
        doi: 10.1002/rmv.v20:1

    141. Peng C, Chen J, Tang W, Liu C, Chen X. 2014. Kaposi's sarcoma-associated herpesvirus ORF6 gene is essential in viral lytic replication. PLoS One, 9: e99542.
        doi: 10.1371/journal.pone.0099542

    142. Picchio GR, Sabbe RE, Gulizia RJ, McGrath M, Herndier BG, Mosier DE. 1997. The KSHV/HHV8-infected BCBL-1 lymphoma line causes tumors in scid mice but fails to transmit virus to a human peripheral blood mononuclear cell graft. Virology, 238: 22-29.
        doi: 10.1006/viro.1997.8822

    143. Plaisance-Bonstaff K, Choi HS, Beals T, Krueger BJ, Boss IW, Gay LA, Haecker I, Hu J, Renne R. 2014. KSHV miRNAs decrease expression of lytic genes in latently infected PEL and endothelial cells by targeting host transcription factors. Viruses, 6: 4005-4023.
        doi: 10.3390/v6104005

    144. Qin Z, Peruzzi F, Reiss K, Dai L. 2014. Role of host microRNAs in Kaposi's sarcoma-associated herpesvirus pathogenesis. Viruses, 6: 4571-4580.
        doi: 10.3390/v6114571

    145. Quan L, Qiu T, Liang J, Li M, Zhang Y, Tao K. 2015. Identification of Target Genes Regulated by KSHV miRNAs in KSHV-Infected Lymphoma Cells. Pathol Oncol Res. (Epub ahead of print)

    146. Raab-Traub N. 2012. Novel mechanisms of EBV-induced oncogenesis. Curr Opin Virol, 2: 453-458.
        doi: 10.1016/j.coviro.2012.07.001

    147. Ramalingam D, Kieffer-Kwon P, Ziegelbauer JM. 2012. Emerging themes from EBV and KSHV microRNA targets. Viruses, 4: 1687-1710.
        doi: 10.3390/v4091687

    148. Renne R, Blackbourn D, Whitby D, Levy J, Ganem D. 1998. Limited Transmission of Kaposi's Sarcoma-Associated Herpesvirus in Cultured Cells. J Virol, 72: 5182-5188.

    149. Renne R, Zhong W, Herndier B, McGrath M, Abbey N, Kedes D, Ganem D. 1996. Lytic growth of Kaposi's sarcoma-associated herpesvirus (human herpesvirus 8) in culture. Nat Med, 2: 342-346.
        doi: 10.1038/nm0396-342

    150. Rochford R, Mosier DE. 1995. Differential Epstein-Barr-Virus Gene-Expression in B-Cell Subsets Recovered from Lymphomas in Scid Mice after Transplantation of Human Peripheral-Blood Lymphocytes. J Virol, 69: 150-155.

    151. Rossetto CC, Pari G. 2012. KSHV PAN RNA associates with demethylases UTX and JMJD3 to activate lytic replication through a physical interaction with the virus genome. PLoS Pathog, 8: e1002680.
        doi: 10.1371/journal.ppat.1002680

    152. Rossetto CC, Pari GS. 2011. Kaposi's sarcoma-associated herpesvirus noncoding polyadenylated nuclear RNA interacts with virus-and host cell-encoded proteins and suppresses expression of genes involved in immune modulation. J Virol, 85: 13290-13297.
        doi: 10.1128/JVI.05886-11

    153. Rossetto CC, Pari GS. 2014. PAN's Labyrinth: Molecular biology of Kaposi's sarcoma-associated herpesvirus (KSHV) PAN RNA, a multifunctional long noncoding RNA. Viruses, 6: 4212-4226.
        doi: 10.3390/v6114212

    154. Rossetto CC, Tarrant-Elorza M, Verma S, Purushothaman P, Pari GS. 2013. Regulation of viral and cellular gene expression by Kaposi's sarcoma-associated herpesvirus polyadenylated nucle ar RNA. J Virol, 87: 5540-5553.
        doi: 10.1128/JVI.03111-12

    155. Sakakibara S, Ueda K, Nishimura K, Do E, Ohsaki E, Okuno T, Yamanishi K. 2004. Accumulation of heterochromatin components on the terminal repeat sequence of Kaposi's sarcoma-associated herpesvirus mediated by the latency-associated nuclear antigen. J Virol, 78: 7299-7310.
        doi: 10.1128/JVI.78.14.7299-7310.2004

    156. Samols MA, Skalsky RL, Maldonado AM, Riva A, Lopez MC, Baker HV, Renne R. 2007. Identification of cellular genes targeted by KSHV-encoded microRNAs. PLoS Pathog, 3: e65.
        doi: 10.1371/journal.ppat.0030065

    157. Sarosiek KA, Cavallin LE, Bhatt S, Toomey NL, Natkunam Y, Blasini W, Gentles AJ, Ramos JC, Mesri EA, Lossos IS. 2010. Efficacy of bortezomib in a direct xenograft model of primary effusion lymphoma. Proc Natl Acad Sci U S A, 107: 13069-13074.
        doi: 10.1073/pnas.1002985107

    158. Sathish N, Yuan Y. 2010. Functional characterization of Kaposi's sarcoma-associated herpesvirus small capsid protein by bacterial artificial chromosome-based mutagenesis. Virology, 407: 306-318.
        doi: 10.1016/j.virol.2010.08.017

    159. Sexton BS, Avey D, Druliner BR, Fincher JA, Vera DL, Grau DJ, Borowsky ML, Gupta S, Girimurugan SB, Chicken E, Zhang J, Noble WS, Zhu F, Kingston RE, Dennis JH. 2014a. The spring-loaded genome: nucleosome redistributions are widespread, transient, and DNA-directed. Genome Res, 24: 251-259.
        doi: 10.1101/gr.160150.113

    160. Sexton BS, Druliner BR, Avey D, Zhu F, Dennis JH. 2014b. Changes in nucleosome occupancy occur in a chromosome specific manner. Genom Data, 2: 114-116.
        doi: 10.1016/j.gdata.2014.06.006

    161. Sexton BS, Druliner BR, Vera DL, Avey D, Zhu F, Dennis JH. 2015. Hierarchical regulation of the genome: global changes in nucleosome organization potentiate genome response. Science Advances. (Submitted for publication).

    162. Shin HJ, DeCotiis J, Giron M, Palmeri D, Lukac DM. 2014. Histone deacetylase classes Ⅰ and Ⅱ regulate Kaposi's sarcoma-associated herpesvirus reactivation. J Virol, 88: 1281-1292.
        doi: 10.1128/JVI.02665-13

    163. Sin SH, Roy D, Wang L, Staudt MR, Fakhari FD, Patel DD, Henry D, Harrington WJ, Jr., Damania BA, Dittmer DP. 2007. Rapamycin is efficacious against primary effusion lymphoma (PEL) cell lines in vivo by inhibiting autocrine signaling. Blood, 109: 2165-2173.
        doi: 10.1182/blood-2006-06-028092

    164. Skalsky RL, Samols MA, Plaisance KB, Boss IW, Riva A, Lopez MC, Baker HV, Renne R. 2007. Kaposi's sarcoma-associated herpesvirus encodes an ortholog of miR-155. J Virol, 81: 12836-12845.
        doi: 10.1128/JVI.01804-07

    165. Soulier J, Grollet L, Oksenhendler E, Cacoub P, Cazals-Hatem D, Babinet P, d'Agay MF, Clauvel JP, Raphael M, Degos L, et al. 1995. Kaposi's sarcoma-associated herpesvirus-like DNA sequences in multicentric Castleman's disease. Blood, 86: 1276-1280.

    166. Staudt MR, Kanan Y, Jeong JH, Papin JF, Hines-Boykin R, Dittmer DP. 2004. The tumor microenvironment controls primary effusion lymphoma growth in vivo. Cancer Res, 64: 4790-4799.
        doi: 10.1158/0008-5472.CAN-03-3835

    167. Stedman W, Kang H, Lin S, Kissil JL, Bartolomei MS, Lieberman PM. 2008. Cohesins localize with CTCF at the KSHV latency control region and at cellular c-myc and H19/Igf2 insulators. EMBO J, 27: 654-666.
        doi: 10.1038/emboj.2008.1

    168. Strang BL, Stow ND. 2005. Circularization of the herpes simplex virus type 1 genome upon lytic infection. J Virol, 79: 12487-12494.
        doi: 10.1128/JVI.79.19.12487-12494.2005

    169. Sturzl M, Gaus D, Dirks WG, Ganem D, Jochmann R. 2013. Kaposi's sarcoma-derived cell line SLK is not of endothelial origin, but is a contaminant from a known renal carcinoma cell line. Int J Cancer, 132: 1954-1958.
        doi: 10.1002/ijc.v132.8

    170. Sunil-Chandra NP, Arno J, Fazakerley J, Nash AA. 1994. Lymphoproliferative disease in mice infected with murine gammaherpesvirus 68. Am J Pathol, 145: 818-826.

    171. Sun R, Lin S-F, Gradoville L, Yuan Y, Zhu F, Miller G. 1998. A viral gene that activates lytic cycle expression of Kaposi's sarcoma-associated herpesvirus. Proc Natl Acad Sci U S A, 95: 10866-10871.
        doi: 10.1073/pnas.95.18.10866

    172. Szekely L, Kiss C, Mattsson K, Kashuba E, Pokrovskaja K, Juhasz A, Holmvall P, Klein G. 1999. Human herpesvirus-8-encoded LNA-1 accumulates in heterochromatin-associated nuclear bodies. J Gen Virol, 80: 2889-2900.
        doi: 10.1099/0022-1317-80-11-2889

    173. Toth Z, Brulois K, Jung JU. 2013a. The chromatin landscape of Kaposi's sarcoma-associated herpesvirus. Viruses, 5: 1346-1373.
        doi: 10.3390/v5051346

    174. Toth Z, Brulois K, Lee HR, Izumiya Y, Tepper C, Kung HJ, Jung JU. 2013b. Biphasic euchromatin-to-heterochromatin transition on the KSHV genome following de novo infection. PLoS Pathog, 9: e1003813.
        doi: 10.1371/journal.ppat.1003813

    175. Toth Z, Brulois KF, Wong LY, Lee HR, Chung B, Jung JU. 2012. Negative elongation factor-mediated suppression of RNA polymerase Ⅱ elongation of Kaposi's sarcoma-associated herpesvirus lytic gene expression. J Virol, 86: 9696-9707.
        doi: 10.1128/JVI.01012-12

    176. Toth Z, Maglinte DT, Lee SH, Lee HR, Wong LY, Brulois KF, Lee S, Buckley JD, Laird PW, Marquez VE, Jung JU. 2010. Epigenetic analysis of KSHV latent and lytic genomes. PLoS Pathog, 6: e1001013.
        doi: 10.1371/journal.ppat.1001013

    177. Towata T, Komizu Y, Suzu S, Matsumoto Y, Ueoka R, Okada S. 2010. Hybrid liposomes inhibit the growth of primary effusion lymphoma in vitro and in vivo. Leuk Res, 34: 906-911.
        doi: 10.1016/j.leukres.2009.12.010

    178. Tsankov AM, Thompson DA, Socha A, Regev A, Rando OJ. 2010. The role of nucleosome positioning in the evolution of gene regulation. PLoS Biol, 8: e1000414.
        doi: 10.1371/journal.pbio.1000414

    179. Uldrick TS, Whitby D. 2011. Update on KSHV epidemiology, Kaposi Sarcoma pathogenesis, and treatment of Kaposi Sarcoma. Cancer Lett, 305: 150-162.
        doi: 10.1016/j.canlet.2011.02.006

    180. Ule J, Jensen K, Mele A, Darnell RB. 2005. CLIP: a method for identifying protein-RNA interaction sites in living cells. Methods, 37: 376-386.
        doi: 10.1016/j.ymeth.2005.07.018

    181. Ule J, Jensen KB, Ruggiu M, Mele A, Ule A, Darnell RB. 2003. CLIP identifies Nova-regulated RNA networks in the brain. Science, 302: 1212-1215.
        doi: 10.1126/science.1090095

    182. Verma SC, Robertson ES. 2003. Molecular biology and pathogenesis of Kaposi sarcoma-associated herpesvirus. FEMS Microbiol Lett, 222: 155-163.
        doi: 10.1016/S0378-1097(03)00261-1

    183. Vieira J, Huang ML, Koelle DM, Corey L. 1997. Transmissible Kaposi's sarcoma-associated herpesvirus (human herpesvirus 8) in saliva of men with a history of Kaposi's sarcoma. J Virol, 71: 7083-7087.

    184. Vieira J, O'Hearn PM. 2004. Use of the red fluorescent protein as a marker of Kaposi's sarcoma-associated herpesvirus lytic gene expression. Virology, 325: 225-240.
        doi: 10.1016/j.virol.2004.03.049

    185. Viejo-Borbolla A, Kati E, Sheldon JA, Nathan K, Mattsson K, Szekely L, Schulz TF. 2003. A Domain in the C-terminal region of latency-associated nuclear antigen 1 of Kaposi's sarcoma-associated Herpesvirus affects transcriptional activation and binding to nuclear heterochromatin. J Virol, 77: 7093-7100.
        doi: 10.1128/JVI.77.12.7093-7100.2003

    186. Walker LR, Hussein HA, Akula SM. 2014. Disintegrin-like domain of glycoprotein B regulates Kaposi's sarcoma-associated herpesvirus infection of cells. J Gen Virol, 95: 1770-1782.
        doi: 10.1099/vir.0.066829-0

    187. Wang HW, Trotter MW, Lagos D, Bourboulia D, Henderson S, Makinen T, Elliman S, Flanagan AM, Alitalo K, Boshoff C. 2004. Kaposi sarcoma herpesvirus-induced cellular reprogramming contributes to the lymphatic endothelial gene expression in Kaposi sarcoma. Nat Genet, 36: 687-693.
        doi: 10.1038/ng1384

    188. Wang LX, Kang G, Kumar P, Lu W, Li Y, Zhou Y, Li Q, Wood C. 2014. Humanized-blt mouse model of Kaposi's sarcoma-associated herpesvirus infection. Proc Natl Acad Sci U S A., 111: 3146-3151.
        doi: 10.1073/pnas.1318175111

    189. Wang SE, Wu FY, Yu Y, Hayward GS. 2003. CCAAT/en hancer-binding protein-alpha is induced during the early stages of Kaposi's sarcoma-associated herpesvirus (KSHV) lytic cycle reactivation and together with the KSHV replication and transcription activator (RTA) cooperatively stimulates the viral RTA, MTA, and PAN promoters. J Virol, 77: 9590-9612.
        doi: 10.1128/JVI.77.17.9590-9612.2003

    190. Weninger W, Partanen TA, Breiteneder-Geleff S, Mayer C, Kowalski H, Mildner M, Pammer J, Sturzl M, Kerjaschki D, Alitalo K, Tschachler E. 1999. Expression of vascular endothelial growth factor receptor-3 and podoplanin suggests a lymphatic endothelial cell origin of Kaposi's sarcoma tumor cells. Lab Invest, 79: 243-251.

    191. Woodcock CL, Ghosh RP. 2010. Chromatin higher-order structure and dynamics. Cold Spring Harb Perspect Biol, 2: a000596.

    192. Xu Y, Rodriguez-Huete A, Pari GS. 2006. Evaluation of the lytic origins of replication of Kaposi's sarcoma-associated virus/ human herpesvirus 8 in the context of the viral genome. J Virol, 80: 9905-9909.
        doi: 10.1128/JVI.01004-06

    193. Yakushko Y, Hackmann C, Gunther T, Ruckert J, Henke M, Koste L, Alkharsah K, Bohne J, Grundhoff A, Schulz TF, Henke-Gendo C. 2011. Kaposi's sarcoma-associated herpesvirus bacterial artificial chromosome contains a duplication of a long unique-region fragment within the terminal repeat region. J Virol, 85: 4612-4617.
        doi: 10.1128/JVI.02068-10

    194. Yang Y, Boss IW, McIntyre LM, Renne R. 2014. A systems biology approach identified different regulatory networks targeted by KSHV miR-K12-11 in B cells and endothelial cells. BMC Genomics, 15: 668.
        doi: 10.1186/1471-2164-15-668

    195. Ye FC, Zhou FC, Yoo SM, Xie JP, Browning PJ, Gao SJ. 2004. Disruption of Kaposi's sarcoma-associated herpesvirus latent nuclear antigen leads to abortive episome persistence. J Virol, 78: 11121-11129.
        doi: 10.1128/JVI.78.20.11121-11129.2004

    196. Ye J, Gradoville L, Daigle D, Miller G. 2007. De novo protein synthesis is required for lytic cycle reactivation of Epstein-Barr virus, but not Kaposi's sarcoma-associated herpesvirus, in response to histone deacetylase inhibitors and protein kinase C agonists. J Virol, 81: 9279-9291.
        doi: 10.1128/JVI.00982-07

    197. Yoo SM, Ahn AK, Seo T, Hong HB, Chung MA, Jung SD, Cho H, Lee MS. 2008. Centrifugal enhancement of Kaposi's sarcoma-associated virus infection of human endothelial cells in vitro. J Virol Methods, 154: 160-166.
        doi: 10.1016/j.jviromet.2008.07.026

    198. Young LS, Murray PG. 2003. Epstein-Barr virus and oncogenesis: from latent genes to tumours. Oncogene, 22: 5108-5121.
        doi: 10.1038/sj.onc.1206556

    199. Yu X, Shahir AM, Sha J, Feng Z, Eapen B, Nithianantham S, Das B, Karn J, Weinberg A, Bissada NF, Ye F. 2014. Short-chain fatty acids from periodontal pathogens suppress histone deacetylases, EZH2, and SUV39H1 to promote Kaposi's sarcoma-associated herpesvirus replication. J Virol, 88: 4466-4479.
        doi: 10.1128/JVI.03326-13

    200. Zhou FC, Zhang YJ, Deng JH, Wang XP, Pan HY, Hettler E, Gao SJ. 2002. Efficient infection by a recombinant Kaposi's sarcoma-associated herpesvirus cloned in a bacterial artificial chromosome: Application for genetic analysis. J Virol, 76: 6185-6196.
        doi: 10.1128/JVI.76.12.6185-6196.2002

    201. Zhu FX, Li X, Zhou F, Gao SJ, Yuan Y. 2006. Functional characterization of Kaposi's sarcoma-associated herpesvirus ORF45 by bacterial artificial chromosome-based mutagenesis. J Virol, 80: 12187-12196.
        doi: 10.1128/JVI.01275-06

    202. Zhu Y, Haecker I, Yang Y, Gao SJ, Renne R. 2013. gamma-Herpesvirus-encoded miRNAs and their roles in viral biology and pathogenesis. Curr Opin Virol, 3: 266-275.
        doi: 10.1016/j.coviro.2013.05.013

    203. Ziegelbauer JM. 2011. Functions of Kaposi's sarcoma-associated herpesvirus microRNAs. Biochim Biophys Acta, 1809: 623-630.
        doi: 10.1016/j.bbagrm.2011.05.003

  • 加载中

Figures(2) / Tables(1)

Article Metrics

Article views(8977) PDF downloads(28) Cited by()

Related
Proportional views

    Recent advances in the study of Kaposi's sarcoma-associated herpesvirus replication and pathogenesis

      Corresponding author: Fanxiu Zhu, fzhu@bio.fsu.edu
    • Department of Biological Science, Florida State University, Tallahassee 32306, USA

    Abstract: It has now been over twenty years since a novel herpesviral genome was identified in Kaposi’s sarcoma biopsies. Since then, the cumulative research effort by molecular biologists, virologists, clinicians, and epidemiologists alike has led to the extensive characterization of this tumor virus, Kaposi’s sarcoma-associated herpesvirus (KSHV; also known as human herpesvirus 8 (HHV- 8)), and its associated diseases. Here we review the current knowledge of KSHV biology and pathogenesis, with a particular emphasis on new and exciting advances in the field of epigenetics. We also discuss the development and practicality of various cell culture and animal model systems to study KSHV replication and pathogenesis.

    • The original description of a unique skin lesion by Moritz Kaposi in 1872 predates the foundation of viral oncology (Kaposi, 1872). Over 100 years later, an epidemic of this disease, Kaposi's sarcoma(KS), was the first indicator of the devastating HIV/AIDS epidemic to follow (CDC, 1981; Gottlieb et al., 1981). The discovery of the causative agent of KS, Kaposi's sarcoma-associated herpesvirus(KSHV), is one of the great successes of modern biomedical research (Chang et al., 1994; Ganem, 2010; Moore and Chang, 2010; Chang and Moore, 2014). KSHV is also etiologically linked to two lymphoproliferative disorders, primary effusion lymphoma(PEL) and multicentric Castleman's disease(MCD) (Soulier et al., 1995; Cesarman et al., 1996). In the past 20 years, molecular, clinical, and epidemiological studies have generated vast amounts of data, and facilitated our current understanding of KSHV and its associated diseases. A comprehensive description of the pathobiology and epidemiology of KS is beyond the scope of this review, and has been elegantly summarized by several review articles (Ganem, 1997; Verma and Robertson, 2003; Ganem, 2006; Cesarman and Mesri, 2007; Dittmer and Damania, 2007; Ganem, 2007; Ganem, 2010; Mesri et al., 2010; Uldrick and Whitby, 2011; Dittmer and Damania, 2013; Gramolelli and Schulz, 2015). Instead, we will briefly introduce the biology of KSHV pertinent to the following sections on the KSHV epigenome and model systems to study KSHV.

      KSHV is a large(~165 kb), double-stranded DNA(dsDNA) virus of the subfamily gammaherpesvirinae (Figure 1). Its closest relatives, herpesvirus saimiri(HVS), Rhesus monkey rhadinovirus(RRV), and murid herpesvirus 68(MHV-68), are important model systems for the study of gammaherpesviruses. The closely related gammaherpesvirus, Epstein-Barr virus(EBV), is also intensively studied, since it is a ubiquitous and potentially oncogenic human pathogen (Young and Murray, 2003; Raab-Traub, 2012). Herpesviral particles are composed of a linear dsDNA genome enclosed by an icosahedral protein capsid, which is enveloped by a glycoprotein-studded lipid bilayer. An intermediate layer between the capsid and envelope is referred to as the tegument. KSHV can infect a variety of cell types, and enters cells either through fusion or receptor-mediated endocytosis (Chandran, 2010; Chakraborty et al., 2012; Veettil et al., 2014). Once the genome is delivered into the host nucleus, KSHV, like all herpesviruses, is capable of entering into one of two alternative life cycles: latency or lytic replication.

      Figure 1.  The KSHV episome. Kaposi's sarcoma-associated herpesvirus (KSHV) encodes 87 open reading frames (ORFs) and at least 17 microRNAs (purple boxes), 14 of which are co-expressed as a cluster. A striking feature of KSHV is the number of ORFs (at least 14) that encode cellular orthologues (yellow boxes). Putative latent transcripts are indicated in green. KSHV exists as an episome (double-stranded circular DNA) within the host nucleus. Reactivation can occur when the promoter of ORF50 is activated, resulting in the expression of replication and transcription activator (RTA), the main regulator for the viral lytic replication programme. Early lytic genes include those encoding viral proteins required for DNA replication or viral gene expression, whereas late lytic genes are those encoding viral structural proteins, such as envelope and capsid proteins, that are required for assembly of viral particles (virions). Polyadenylated nuclear (PAN) RNA is transcribed from a locus residing between K6 and ORF16. The terminal repeat (TR) sequences account for ~20–30 kb. Adapted by permission from Macmillan Publishers Ltd: Nature Reviews Cancer (Mesri et al., 2010) © 2010.

      In the context of oncogenesis, both serve critical roles. Latency, during which only a few key genes are substantially expressed, is required for maintenance of the viral genome(episome) within cells and thus, persistent infection. Lytic replication, in which the entire complement of genes is expressed in a temporally regulated cascade leading to production of progeny virions, is also crucial, because (ⅰ) lytically infected cells serve as a reservoir of new infectious viral particles; and (ⅱ) paracrine signals induced by lytic gene products contribute to inflammation and angiogenesis (Ganem, 2010). Elucidating the factors that influence the gene expression program employed by KSHV upon either primary infection or the latent-lytic switch are of major interest to KSHV researchers and paramount relevance to KSHV pathobiology. Accumulating evidence suggests that epigenetic regulation plays a crucial role in dictating the outcome of KSHV infection.

    • In the past decade, our understanding of epigenetic phenomena has expanded tremendously. This is due, in large part, to the development and application of tools and techniques to study patterns of DNA methylation, protein-DNA interactions, post-translational modifications, gene expression, and higher-order chromatin structure, as well as unprecedented advances in sequencing technology. With regard to KSHV, the wealth of information that has emerged provides insights into the roles of chromatin organization throughout the viral life cycle. Together, these data indicate that epigenetic regulation is intimately linked to the fate of KSHV and its human host.

    • Herpesviral genomes are thought to exist in one of three general states of primary chromatin structure:(ⅰ) as naked DNA within capsids; (ⅱ) regularly chromatinized(packaged with cellular histone proteins to form nucleosomes, the fundamental repeating units of chromatin) during latency; or (ⅲ) in an intermediate 'lytic state' characterized by dynamic alterations in chromatin architecture (Paulus et al., 2010; Nevels et al., 2011). Upon infecting cells, herpesviruses must transport their genome to the nucleus, where it is circularized and chromatinized, resulting in the formation of stable, non-integrated episomes with similar structure to the host genome (Lieberman, 2013). Genome circularization is critical for viral episome maintenance, DNA replication, and evasion of the host DNA damage response (Ballestas et al., 1999; Strang and Stow, 2005; Deng et al., 2012). Chromatinization after primary infection is also a major determinant of the fate of KSHV. This is intuitive, since the precise nature of nucleosome positions and epigenetic modifications potentiates replication, recombination, repair, and transcription of the underlying DNA (Bannister and Kouzarides, 2011). Early findings that KSHV stable episome maintenance is not very efficient indicated a role of epigenetic factors in persistent infection (Grundhoff and Ganem, 2004). It is likely that inefficient circularization or chromatinization accounts for the high failure rate in the establishment of stable infections by gammaherpesviruses(KSHV and EBV) (Hurley and Thorley-Lawson, 1988; Darst et al., 2013).

      Several recent studies have characterized the epigenetic landscape of KSHV, both during latency and lytic replication. This has led to the identification and characterization of many viral and host factors responsible for modulating the viral epigenome. The high-resolution study of epigenomic marks, including DNA methylation, histone post-translational modifications, nucleosome position, and 3D chromatin organization, has been facilitated by the development of powerful sequencing-based methods, including Chromatin Immunoprecipitation(ChIP), a versatile and efficient technique used to investigate protein-DNA interactions. ChIP has been combined with DNA microarrays(ChIP-on-Chip) or sequencing(ChIP-seq) to offer high-throughput, genome-wide characterization of the extent of histone modifications and/or histone-modifying enzymes at specific genomic loci, or with chromatin conformation capture(3C) assays to investigate higher-order chromatin structure. Recently, next-generation sequencing following Formaldehyde-Assisted Isolation of Regulatory Elements(FAIRE-seq) has also served as a viable alternative to ChIP-seq assays. The following sections will discuss the novel and salient findings regarding epigenetic regulation in the context of KSHV replication.

    • DNA methylation, typically occurring at CpG sites in mammalian cells, are associated with gene silencing (Jin et al., 2011; Jones, 2012). Unsurprisingly, the level increases over time following KSHV de novo infection, presumably contributing to repressed viral gene expression (Gunther et al., 2014). A study coupling immunoprecipitation of methylated DNA(MeDIP) to a KSHV tiling microarray characterized the DNA methylation pattern of the KSHV genome in latently-infected cells (Gunther and Grundhoff, 2010). In general, the data suggested an inverse correlation between DNA methylation and KSHV gene expression(i.e., reduced DNA methylation at transcriptionally active sites, such as the latency locus, while most lytic gene loci were methylated). Interestingly, DNA methylation appears to play a role in the control of latency, since a DNA methyltransferase inhibitor, 5-azacytidine(5-AzaC) triggers lytic reactivation (Pantry and Medveczky, 2009). Consistent with this role, a KSHV-encoded microRNA, miRNAK12-5, has been shown to increase global levels of viral/cellular DNA methylation, thereby preventing lytic gene expression (Lu et al., 2010). A more recent study employing MAPit(Methylation Accessibility Probing for individual templates) single-molecule footprinting found that the status of DNA methylation is incredibly diverse at specific loci across a population of KSHV episomal genomes (Darst et al., 2013).

    • Nucleosome position and post-translational modifications of histone tails are widely recognized predictors of gene expression, since they affect the local chromatin architecture and accessibility of transcription factors (Kornberg and Lorch, 1999; Karlic et al., 2010; Tsankov et al., 2010). The putative effect(s) on transcriptional regulation depends on the histone residue modified, and the specific modification(i.e., methylation, acetylation, phosphorylation, ubiquitylation, sumoylation, etc.). The first clues that histone modifications possess functional roles in the KSHV life cycle came from the findings that the histone deacetylase(HDAC) inhibitor sodium butyrate(NaB) and the histone acetyltransferase(HAT) inducer, tetradecanoylphorbol acetate(TPA) potently stimulate KSHV lytic reactivation (Renne et al., 1996; Wang et al., 2003; Miller et al., 2007). In 2010, two independent studies used ChIP-on-Chip to reveal the epigenetic landscape of KSHV episomes in infected cells. The first of these analyzed DNA methylation(discussed above) and histone modifications in PEL-and KS-derived cell lines during latency (Gunther and Grundhoff, 2010). Interestingly, the widespread distribution across latent genomes of the bivalent mark, H3K27me3, which is capable of transcriptional repression despite the presence of activating marks(i.e., H3K9/K14ac and H3K4me3), suggested a poised state of repression, allowing for rapid and robust induction of transcription upon lytic reactivation. Indeed, Toth et al. analyzed the same activating and repressive histone modifications during latency and lytic reactivation, and observed this bivalent chromatin structure at several viral genomic loci(especially regions encoding immediate-early and early genes), as well as a rapid change involving increasing H3ac and H3K4me3 marks and decreasing H3K27me3 upon reactivation (Toth et al., 2010). These results were later supported by the finding that RNA polymerase Ⅱ-mediated transcription of many lytic genes is paused at the elongation step during latency, but can be promptly reactivated by external stimuli (Toth et al., 2012). This bivalent control of gene expression is reminiscent of that observed in embryonic stem cells (Bernstein et al., 2006). Further experiments implicated EZH2, the H3K27me3 histone methyltransferase of the Polycomb group proteins(PcG), as a key regulator of this modification. The current view is that this epigenetic regulator contributes to the maintenance of latency (Toth et al., 2010), and promotes cancer angiogenesis (He et al., 2012).

      The level of H3K9 methylation associated with viral episomes also appears to be tightly regulated. It has long been known that the terminal repeat(TR) region of KSHV episomes accumulates heterochromatin components, and that this is mediated by the latency-associated nuclear antigen(LANA) (Szekely et al., 1999; Mattsson et al., 2002; Lim et al., 2003; Viejo-Borbolla et al., 2003; Sakakibara et al., 2004). The genome-wide studies previously mentioned characterized the pattern of H3K9me3 across viral episomes during latency and lytic reactivation (Gunther and Grundhoff, 2010; Toth et al., 2010). The H3K9me3 demethylase, JMJD2A, was later shown to play a critical role in regulating this modification and, thus, the latent-lytic switch (Chang et al., 2011). The H3K9me1/2 histone demethylase, KDM3A/JMJD1A, has also been implicated in the control of latency, a function that likely depends on its association with LANA (Kim et al., 2013). Another mechanism by which LANA may contribute to epigenetic modifications of KSHV episomes is through interacting with Set1, the H3K4 methyltransferase (Hu et al., 2014). Intriguingly, K-bzip, an immediate-early gene product essential for viral lytic replication (Ellison et al., 2009; Lefort and Flam, 2009), was shown to inhibit JMJD2A demethylase activity (Chang et al., 2011). K-bzip has also been shown to modulate histone acetylation by interacting with and inhibiting histone deacetylases(HDACs) (Martinez and Tang, 2012). Several studies have documented the effect(s) of chemical HDAC inhibitors on gammaherpesvirus reactivation (Miller et al., 1997; Gwack et al., 2001; Lu et al., 2003; Ye et al., 2007; Gorres et al., 2014; Li et al., 2014; Lu et al., 2014; Shin et al., 2014; Yu et al., 2014), and some HDAC inhibitors have been explored as potential therapies to treat KSHV-related malignancies (Niedermeier et al., 2006; Bhatt et al., 2013).

      Several recent studies investigated histone modifications following de novo infection of KSHV. The first, by Dr. Jae Jung's group, described a biphasic euchromatin-to-heterochromatin transition following infection (Toth et al., 2013b). Upon KSHV infection of endothelial cells, they found high levels of activating histone marks(H3K4me3 and H3K27ac) deposited on viral genomes at early times post-infection, which decreased at later times(24–72 h) concomitant with increasing repressive marks(H3K27me3 and H2AK119ub). Importantly, these epigenetic modifications were accompanied by corresponding changes in KSHV gene expression. In contrast, KSHV-infected epithelial cells adopt a transcriptionally active euchromatin state, resulting in expression of lytic genes (Toth et al., 2013b). Another study also profiled epigenetic modifications in endothelial cells following KSHV infection, and went on to characterize the role of nuclear domain 10(ND10) components during the establishment of latency (Gunther et al., 2014). A third group characterized the pattern of epigenetic modifications following KSHV infection of human peripheral blood mononuclear cells(PBMCs), which were correlated to the KSHV gene expression program (Jha et al., 2014). Taken together, these findings corroborate the views that (ⅰ) histone modifications of the KSHV genome correlate predictably with latent/lytic gene expression; and (ⅱ) cell type-specific epigenetic factors are a key determinant in deciding the fate of KSHV replication.

    • In the past decade, our understanding of the nuclear organization has broadened significantly, aided by advances in microscopy techniques and the development of chromosome confor-mation capture(3C) and its ChIP-based modifications (Gavrilov et al., 2009; Woodcock and Ghosh, 2010; de Witandde Laat, 2012). The National Institutes of Health have realized the importance of this field, and recently started the 4D Nucleome program, the aim of which is to underst and the spatial and temporal organization of the nucleus and how it relates to cellular processes during development or disease progression (NIH, 2014). A recent collaboration by our group and the lab of Dr. Jonathan Dennis assessed nucleosome redistribution at a subset of human genomic loci(genes involved in innate immunity) during a time course of lytic reactivation. Intriguingly, it was found that changes in nucleosome distribution in response to KSHV reactivation were widespread, transient, and directed by the underlying DNA sequence (Sexton et al., 2014a; Sexton et al., 2014b). A follow-up study using the same model system of KSHV reactivation analyzed nucleosome architecture at the transcription start sites of all human genes, and further demonstrated that changes in nucleosome distribution potentiated regulatory factor binding (Sexton et al., 2015).

      KSHV episomes are tethered to the cellular chromatin by the major latent protein LANA through its interactions with histones and other cellular chromatin components. This raises an interesting question: is tethering to the host chromosome random, or could it be influenced by higher-order chromatin structure? Architectural proteins, including cellular chromatin boundary factor(CTCF) and cohesin, are crucial for sister chromatid cohesion and chromosome segregation (Merkenschlager and Odom, 2013). Work by Dr. Paul Lieberman's group and others has offered insights into the roles of these proteins during KSHV replication(reviewed in (Chen et al., 2013; Lieberman, 2013)). These studies suggest that CTCFcohesin facilitates stable episome maintenance (Stedman et al., 2008; Kang and Lieberman, 2011; Kang et al., 2011a), and is also involved in the regulation of transcription elongation and nucleosome position (Kang and Lieberman, 2011; Kang et al., 2013). 3C methods were used to show that CTCF-cohesin mediate the formation of a DNA loop between regulatory regions of latent and lytic genes (Kang et al., 2011a). It has been postulated that CTCF-cohesin association with CTCF-binding sites present at the boundaries of lytic gene promoters may serve the additional function of protecting their bivalent chromatin organization (Chen et al., 2012; Lieberman, 2013). Future investigation of higher-order chromatin structure with regard to KSHV will likely reveal new regulatory mechanisms affecting chromatin-dependent processes.

    • Non-coding RNAs(ncRNAs) have received increasing attention over the past decade, owing to their ubiquitous nature and fundamental roles in the regulation of DNA methylation, histone modifications, chromatin remodeling, and post-transcriptional regulation of gene expression. KSHV possesses a 1.1 kb long non-coding RNA(lncRNA) referred to as polyadenylated nuclear RNA(PAN RNA). Several groups contributed to the early characterization of PAN RNA, but only recently have its roles in KSHV gene expression and immune modulation been elucidated (Borah et al., 2011; Rossetto and Pari, 2011; Rossetto and Pari, 2012; Rossetto et al., 2013). These studies support the notion that, like cellular lncRNAs, PAN RNA may play a role in epigenetic regulation (Figure 2; reviewed in (Campbell et al., 2014; Rossetto and Pari, 2014)).

      Figure 2.  The KSHV Epigenome. Epigenetic regulation by KSHV affects both the viral and host genome, and can be classified into one of four major categories. (1) The state of DNA methylation affects nucleosomal structures. Regions with increased DNA methylation are often associated with transcriptional silencing. (2) Post-translational modifications (PTMs) of histone tails affect local chromatin structure and accessibility of transcription factors. Many different PTMs, including acetylation, methylation, phosphorylation, ubiquitination, and sumoylation, have been implicated in KSHV gene expression and the latent-lytic switch. (3) Nucleosome position and higher-order chromatin structure are intimately related to host chromatin-dependent processes, as well as KSHV episomal maintenance, transcriptional regulation, and control of latency. (4) Finally, non-coding RNAs, including viral/host miRNAs and KSHV PAN RNA, play critical roles in post-transcriptional epigenetic regulation. Importantly, these processes are inter-related, and all contribute to the regulation of transcription and subsequent RNA-dependent processes (denoted by red arrows). Acronyms: DNMTs – DNA methyltransferases; MeCBPs – methyl CpG binding proteins; HATs – histone acetyltransferases; HDACs – histone deacetylases; HMTs – histone methyltransferases; HDMTs – histone demethyltransferases; SUMO – small ubiquitin-like modifier; PcGs – Polycomb group proteins; ATP-DRs – ATP-dependent remodelers; CTCF – CCCTC-binding factor; PolII – RNA Polymerase Ⅱ. PAN RNA minimum free energy structure was generated using RNAfold software (Gruber et al., 2008). The KSHV capsid structure was adapted from (Xinghong Dai, 2015). This figure was adapted by permission from Macmillan Publishers Ltd on behalf of Cancer Research UK: British Journal of Cancer (Flanagan, 2007), © 2007

      In addition, KSHV encodes at least 17 microRNAs(miRNAs) (Cai et al., 2005). Several recent studies have attempted to identify the viral and cellular targets of these miRNAs (Samols et al., 2007; Skalsky et al., 2007; Abend et al., 2010; Lu et al., 2010; Gottwein et al., 2011; Liang et al., 2011b; Lin and Ganem, 2011; Lin et al., 2011; Malterer et al., 2011; Bai et al., 2014; Feldman et al., 2014; Plaisance-Bonstaff et al., 2014; Yang et al., 2014; Forte et al., 2015; Quan et al., 2015), and in doing so have discovered their diverse roles in immune evasion, transformation, and control of latency. Many excellent reviews summarize the known roles of miRNAs in KSHV replication and pathogenesis (Ganem and Ziegelbauer, 2008; Lei et al., 2010; Liang et al., 2011a; Lin and Flemington, 2011; Ziegelbauer, 2011; Ramalingam et al., 2012; Toth et al., 2013a; Zhu et al., 2013; Haecker and Renne, 2014; Qin et al., 2014). Notably, the application of a technique that combines UV cross-linking with immunoprecipitation(CLIP) has allowed for the investigation of RNA-protein interactions (Ule et al., 2003; Ule et al., 2005; Jensen and Darnell, 2008; Darnell, 2010). Variations of this method have recently been used to determine the targetomes of viral and host miRNAs in KSHV-infected cells (Gottwein et al., 2011; Kang et al., 2011b; Haecker et al., 2012; Quan et al., 2015; Haecker and Renne, 2014). Continued improvement of CLIPbased methods and/or development of novel techniques should revolutionize our understanding of ncRNA-mediated epigenetic regulation.

    • Oncogenic viruses, such as KSHV, provide a unique system to study and manipulate cell plasticity (Iacovides et al., 2013). In vitro experiments have shown that KSHV is capable of transcriptionally reprogramming its host, consequently altering the infected cell's phenotype (Carroll et al., 2004; Hong et al., 2004; Wang et al., 2004; Cheng et al., 2011). Multiple studies have characterized KSHV gene expression in relation to epigenetic modifications, at various stages of the KSHV life cycle and in different cell lines(discussed above). A recent study described a unique program of KSHV gene expression in primary human lymphatic endothelial cells(LECs), which did not correspond to canonical latent or lytic replication (Chang and Ganem, 2013). These results further strengthen the supposition that there do exist cell type-dependent mechanisms which regulate KSHV gene expression.

      Next-generation sequencing of RNAs(RNA-seq) can be used to identify and characterize mechanisms of transcriptional regulation. Recently, RNA-seq, in combination with sequencing the ribosome-protected RNAs(ribosome profiling or RIBO-seq), uncovered new genomic features and novel regulatory mechanisms at the level of transcription, RNA processing, and translation (Arias et al., 2014). The resulting annotation of the KSHV genome, termed KSHV 2.0, offers a comprehensive view of KSHV gene regulation during lytic reactivation. The application of RNA-seq to host transcriptional profiling of cells infected by KSHV is limited. Two studies have characterized the host transcriptome in cells exogenously expressing KSHV gene products: SOX (Clyde and Glaunsinger, 2011) or PAN RNA (Rossetto et al., 2013). There is currently only one published report, by Mercier et al., describing RNAseq analysis of host gene expression in KSHV-infected cells. They made the unexpected finding that LANA association does not lead to global host transcriptional remodeling (Mercier et al., 2014). While host transcriptome analysis of KSHV-infected cells is still in its infancy, it will likely have increasing applications in the study of KSHV in the coming years.

    • The discovery of KSHV as the etiological agent of KS necessitated the development of model systems to study this virus in the context of its associated diseases. B cell lines from patients with PEL served as the first in vitro systems. These allowed for analysis of the viral genome and all aspects of the life cycle(latency, lytic reactivation, and infection). Furthermore, the ability to induce the production of viral proteins/particles facilitated the production of assays to detect KSHV seroprevalence in naturally infected populations. Endothelial cells also provided important in vitro models, because of their clear relevance to KS pathogenesis. In vivo, endothelial cells harbor KSHV genomes and are presumed to be the precursors of the spindle cells characteristic of KS lesions. Within the past decade, new and improved systems have served to enhance the efficiency of lytic reactivation and allow for manipulation of the viral genome, making in-depth functional studies possible. Animal models of KSHV-associated diseases have obvious benefits for studying KSHV pathobiology, but each also has its unique drawbacks. The following subsections will summarize the model systems that have been developed to study KSHV, and how they have contributed to our current knowledge of KSHV replication and pathogenesis. Many of the in vitro systems that have been used to study KSHV are compiled in Table 1.

      Table 1.  in Vitro Models to Study KSHV Replicatuib and Pathogenesis

    • Two cell lines derived from HIV/AIDS patients with body cavity-based lymphomas(AIDS-BCBLs) were established shortly following the discovery of KSHV (Cesarman et al., 1995). These cell lines, BC-1 and BC-2, were used to begin investigating the genetics of this newly described tumor virus (Cesarman et al., 1995). This was followed by the establishment of the BC-3 cell line, derived from primary effusion BCBLs, to address the problem of concomitant EBV infection in other cell lines (Arvanitakis et al., 1996). The first lytic reactivation system of KSHV in culture was achieved in 1996 by Renne et al., using BCBL-1 cells induced by TPA (Renne et al., 1996). Shortly thereafter, it was shown that HDAC inhibitors are also capable of inducing KSHV lytic reactivation (Miller et al., 1997). These early systems were vital to the characterization of KSHV latent/lytic replication, and provided viral antigens for serological assays (Gao et al., 1996; Kedes et al., 1996; Miller et al., 1996; Miller et al., 1997). A few years later, Cannon et al. established a new PEL cell line, JSC-1, which yielded two orders of magnitude more infectious virions compared to other PEL cells, but are also co-infected by EBV (Cannon et al., 2000).

    • Although PEL cell culture systems have served as vital systems for characterizing and propagating KSHV, it is also necessary to study KSHV infection in endothelial cells, as KS spindle cells are thought to be of endothelial origin (Weninger et al., 1999). KS cells express both lymphatic endothelial cell(LEC) and blood endothelial cell(BEC) markers (Wang et al., 2004). Both LECs and BECs are susceptible to KSHV infection, after which transcriptional reprogramming will result in BECs resembling LECs and vice versa (Carroll et al., 2004; Hong et al., 2004; Wang et al., 2004). When bone-marrow microvascular endothelial cells(BMECs) and human umbilical vascular endothelial cells(HUVECs) are infected with KSHV, both develop spindle cell-like morphology, as well as long-term proliferation and cell survival (Flore et al., 1998). Dermal microvascular endothelial cells(DMVECs) can support long-term latent KSHV infection with a small occurrence of cells spontaneously entering the lytic cycle, which is reminiscent of KS tumors (Panyutich et al., 1998; Moses et al., 1999). KSHVinfected DMVECs develop spindle shapes resembling KS and display transformed characteristics, including loss of contact inhibition and acquisition of anchorage-independent growth (Moses et al., 1999). However, a low percentage of cells are infected upon primary infection, and the infection does not spread throughout the culture, which may be due to the limited life span of DMVEC cultures.

      DMVEC have been immortalized with hTERT to develop telomerase-immortalized microvascular endothelial(TIME) cells, a cell line that is susceptible to infection via cell-free KSHV (Lagunoff et al., 2002). TIME cells latently infected with KSHV can be reactivated with TPA, and resulting virions can successfully infect uninfected TIME cultures (Lagunoff et al., 2002). However, TIME cells cannot support long-term episomal maintenance (Lagunoff et al., 2002). Telomerase-immortalized human umbilical vein endothelial(TIVE) cells are also susceptible to KSHV infection and can be reactivated by RTA expression (An et al., 2006). TIVE cells were transformed by selecting cells that maintained KSHV episomes, resulting in TIVE long-term culture(LTC) (An et al., 2006). Unlike TIME cells, TIVE LTC cells support stable KSHV infection without selection and form tumors in nude mice (An et al., 2006). The tumor formations express the KS markers vascular endothelial growth factor(VEGF), basic fibroblast growth factor, and IL-6 (An et al., 2006).

      In vivo, circulating KSHV has been found to primarily infect B cells (Ambroziak et al., 1995; Mesri et al., 1996). However, in vitro infection of B cells with soluble KSHV is often inefficient and abortive (Renne et al., 1998; Blackbourn et al., 2000; Bechtel et al., 2003). Myoung and Ganem were able to overcome this by co-culturing reactivated iSLK.219 cells with lymphoid cells. They successfully infected BJAB, Ramos, BCBL-1, JSC1, Jurkat, and SupT1 cells and found BJAB B cells and SupT1 T cells to be the most efficiently infected (Myoung and Ganem, 2011a). In a separate study, Myoung and Ganem also showed that KSHV is capable of infecting primary human tonsillar T cells, but could not maintain persistent infection or immortalize these cells (Myoung and Ganem, 2011c). Kati et al. developed a novel method of reactivating KSHV in latently infected B cells by exposing IgM-expressing BrK.219 cells, a BJAB cell line latently infected with rKSHV.219, to anti-IgM (Kati et al., 2013). Another more recent study analyzed KSHV/EBV-negative B cell lines for their permissiveness to KSHV infection (Dollery et al., 2014). They identified MC116, a B cell line expressing IgMλ, as susceptible to KSHV infection, and were able to induce virion production with butryate or anti-IgM (Dollery et al., 2014). This result is not surprising, as a previous study found that KSHV almost exclusively infects a subset of B cells expressing IgMλ, which comprises about 20% of human tonsils (Hassman et al., 2011).

    • The discovery of KSHV RTA as the master lytic switch protein(its ectopic expression is sufficient to induce lytic reactivation Sun et al., 1998) presented the possibility to engineer systems capable of robust and efficient induction of the lytic cycle. Nakamura et al. developed a Flp-In-mediated recombination and tetracycline-inducible expression system in KSHV-infected PEL cells(TREx BCBL1-Rta), which can be utilized to study individual KSHV genes and was more efficient than previous methods of induction (Nakamura et al., 2003). In the time since, several studies have utilized this system to study KSHV lytic replication.

      Despite the development of numerous useful cell culture systems, a major caveat that remained was the high rates of spontaneous lytic replication, which made it difficult to accurately study latent viral gene expression (Myoung and Ganem, 2011b). To address this issue, Myoung et al. developed iSLK.219 cells, in which KSHV latency is tightly controlled, but lytic reactivation is efficiently inducible by doxycycline (Myoung and Ganem, 2011b). It is important to note that iSLK and iSLK.219 cell lines were developed from SLK cells, which were initially described as being of endothelial origin (Herndier et al., 1994), but were recently reported to have been contaminated with Caki-1 cells of renal carcinoma origin (Sturzl et al., 2013). This finding calls into question the use of SLK cells as a model for KS.

    • A major leap forward in the development of KSHV cell culture models was the use of bacterial artificial chromosomes(BACs) containing the KSHV genome isolated from BCBL-1 cells (Zhou et al., 2002). The construction of BAC36 was integral to the study of KSHV, as it provided an efficient method of primary infection in cultured cells (Zhou et al., 2002). This system also allowed for more efficient primary infection and precise studies of viral genes, since BAC recombineering could be performed to mutate theoretically any gene of interest. Within the decade after its description, several studies utilized BAC36 to study KSHV infection and replication, as well as the functions of specific viral products (Gao et al., 2003; Luna et al., 2004; Ye et al., 2004; Xu et al., 2006; Zhu et al., 2006; Brinkmann et al., 2007; Majerciak et al., 2007; Yoo et al., 2008; Li and Zhu, 2009; Lu et al., 2010; Sathish and Yuan, 2010; Budt et al., 2011; Lin et al., 2011; Yakushko et al., 2011; Cho and Kang, 2012; Hyosun Cho, 2012; Lu et al., 2012; Martinez and Tang, 2012; Rossetto and Pari, 2012; Peng et al., 2014; Walker et al., 2014). Importantly, it was reported that a region of the KSHV genome(including part of ORF19 and all of ORFs 18, 17, 16, K7, K6, and K5) was duplicated in BAC36 (Yakushko et al., 2011). Recently, a new KSHV BAC was developed, named BAC16 (Brulois et al., 2012). BAC16 was derived from rKSHV.219, which was isolated from KSHV and EBV co-infected JSC-1 cells(Vieira and O′Hearn, 2004). Therefore, BAC16 expresses red fluorescent protein(RFP) as a marker of lytic infection, in addition to GFP, which is expressed in both BAC36 and BAC16 latently-infected cells (Zhou et al., 2002; Brulois et al., 2012). Furthermore, induction of lytic reactivation in BAC16 stably transfected iSLK cells(iSLK.BAC16) yields higher titers of infectious virions than previous systems.

    • As the evidence of KSHV's causative role in KS grew, it became necessary to develop an animal model to allow for systemic studies. One of the major obstacles in developing an animal model has been the low incidence of KS/PEL-like disease symptoms despite high susceptibility to KSHV infection. One of the first animal models utilized was severe combined immunodeficient(SCID) mice that had been injected with KSHV-infected BCBL-1 cells, similar to what had been done with EBV and SCID mice (Rochford and Mosier, 1995; Picchio et al., 1997). Tumors were able to form upon injection of KSHV infected BCBL-1 cells, however researchers were unable transmit virus to PBMC grafts (Picchio et al., 1997). This was followed by the observation of persistent infection with PEL-derived KSHV and viral replication in SCID-hu THY/LIV mice (Dittmer et al., 1999). CD19+ lymphocytes were permissive to infection, although there was no morphological change of the implant(no cytopathic effects) (Dittmer et al., 1999). Since then, KSHV models have been attempted with Rhesus macaques, marmosets, and mice. The MHV-68 model can result in lymphoproliferative disease, but not KSlike symptoms(Sunil-Chandra et al., 1994). In Rhesus macaques, co-infection with RRV and SIV results in the development of lymphoma at a similar rate(20–30%) as that seen in AIDS-KS patients (Orzechowska et al., 2008). The marmoset model developed by Chang et al. develops an antibody response that lasted up to 1.5 years following intravenous infection with rKSHV.219 (Chang et al., 2009). However, viral recovery from the PBMCs of the infected marmosets was not successful, and the anti-KSHV response to oral infection was not as robust (Chang et al., 2009).

      Multiple mouse models have been developed and studied within the last year. Wang et al. have attempted to infect the humanized-bone marrow, liver, thymus(huBLT) model with rKSHV.219 via natural routes, such as oral mucosa, since transmission of KSHV has been found to occur primarily via saliva and to reside in the tonsils (Vieira et al., 1997; Mayama et al., 1998; Chagas et al., 2006). This model may represent a useful system for investigating transmission routes (Wang et al., 2014). They found that the mice were successfully infected, resulting in latent/lytic replication in B cells and macrophages of the spleen and latent infection of macrophages in the skin (Wang et al., 2014). However, an immune response was absent when tested three months post-infection (Wang et al., 2014). Ashlock et al. developed a mouse model by transfecting murine bone marrow-derived endothelial lineage cells with BAC36(mECK36 cells) and injecting them into immunodeficient mice, which induced the formation of KS-like tumors. However, these mice were not able to produce progeny virions (Ashlock et al., 2014). When they replaced BAC36 with rKSHV.219, KS-like tumors were accompanied by the production of herpesvirus-like particles, as observed by electron microscopy (Ashlock et al., 2014). Additionally, treatment of mice with an HDAC inhibitor induced lytic reactivation in vivo, indicating this could be a useful system to test antiviral treatments (Ashlock et al., 2014). A xenograft mouse model of KSHV-associated PEL has been previously used to study the effects of host environment on tumor growth, and to test the efficacy of PEL therapies (Staudt et al., 2004; Sin et al., 2007; Bhatt et al., 2010; Sarosiek et al., 2010; Towata et al., 2010; Bhatt et al., 2013). However, the degree to which these tumor formations were related to natural occurring PEL had not previously been investigated. In a recent study, Dai et al. injected BCBL-1 cells into non-obsess diabetic/severe combined immunodeficient mice(NOD/SCID) (Dai et al., 2014). This resulted in rapid tumor growth, massive ascites, and splenic enlargement within 3–4 weeks post-infection. However, a multitude of tumor and symptomatic characteristics differed from what is observed in PEL patients (Dai et al., 2014). Recent reports that KSHV can efficiently infect and transform primary rat embryonic metanephric mesenchymal precursor(MM) cells suggests that this system could be useful in study mechanisms of KSHV-induced growth deregulation and oncogenesis (Jones et al., 2012; Moody et al., 2013; Liang et al., 2014). However, it was recently shown that the GFP marker expressed from recombinant herpesviral genomes may not be a reliable marker for infection in this system (Ellison and Kedes, 2014). This highlights the notion that when evaluating new model systems for the study of KSHV pathogenesis, thorough analyses must be performed to avoid misinterpretation of data.

    • Our current understanding of the KSHV epigenome can be attributed, in large part, to innovations in molecular biology tools and sequencing technology. Moreover, the development and applications of cell culture and animal model systems have made it possible to study every facet of KSHV pathobiology. These systems have facilitated the detailed investigation of the two alternative life cycles of KSHV and how they contribute to pathogenesis, and unveiled the critical roles of epigenetic phenomena. With each result, we add pieces to a puzzle that is becoming simultaneously clearer and exceedingly complex. In our attempts to better underst and KSHV, we have shed light on the molecular mechanisms that govern fundamental cellular processes. Future studies aiming to elucidate the relationships between epigenomic marks(DNA methylation, histone modifications, nucleosome position, and higher-order chromatin structure) and chromatin-dependent processes(replication, recombination, repair, and transcription) should yield exciting insights into the biology of KSHV and its human host.

    • We would like to apologize to the authors of many important studies that have not been cited due to space limitations. This work was supported by National Institutes of Health grant R01DE016680 to Fanxiu Zhu and F31CA183250 to Denis Avey. We thank Sarah Tepper for critical reading of the manuscript and helpful edits.

    • The authors declare that they have no conflict of interest. This article does not contain any studies with human or animal subjects performed by any of the authors.

    Figure (2)  Table (1) Reference (203) Relative (20)

    目录

    /

    DownLoad:  Full-Size Img  PowerPoint
    Return
    Return