Wille Coral K, Li Yangguang, Rui Lixin, Johannsen Eric C, Kenney Shannon C
Department of Medical Microbiology and Immunology, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin, USA.
Department of Medicine, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin, USA.
J Virol. 2017 Feb 14;91(5). doi: 10.1128/JVI.01987-16. Print 2017 Mar 1.
Epstein-Barr virus (EBV) latently infects normal B cells and contributes to the development of certain human lymphomas. Newly infected B cells support a highly transforming form (type III) of viral latency; however, long-term EBV infection in immunocompetent hosts is limited to B cells with a more restricted form of latency (type I) in which most viral gene expression is silenced by promoter DNA methylation. How EBV converts latency type is unclear, although it is known that type I latency is associated with a germinal center (GC) B cell phenotype, and type III latency with an activated B cell (ABC) phenotype. In this study, we have examined whether expression of TET2, a cellular enzyme that initiates DNA demethylation by converting 5-methylcytosine (5mC) into 5-hydroxymethylcytosine (5hmC), regulates EBV latency type in B cells. We found that TET2 expression is inhibited in normal GC cells and GC type lymphomas. In contrast, TET2 is expressed in normal naive B cells and ABC type lymphomas. We also demonstrate that GC type cell lines have increased 5mC levels and reduced 5hmC levels in comparison to those of ABC type lines. Finally, we show that TET2 promotes the ability of the EBV transcription factor EBNA2 to convert EBV-infected cells from type I to type III latency. These findings demonstrate that TET2 expression is repressed in GC cells independent of EBV infection and suggest that TET2 promotes type III EBV latency in B cells with an ABC or naive phenotype by enhancing EBNA2 activation of methylated EBV promoters. EBV establishes several different types of viral latency in B cells. However, cellular factors that determine whether EBV enters the highly transforming type III latency, versus the more restricted type I latency, have not been well characterized. Here we show that TET2, a cellular enzyme that initiates DNA demethylation by converting 5-methylcytosine (5mC) into 5-hydroxymethylcytosine (5hmC), regulates EBV latency type in B cells by enhancing the ability of the viral transcription factor EBNA2 to activate methylated viral promoters that are expressed in type III (but not type I) latency. Furthermore, we demonstrate that (independent of EBV) TET2 is turned off in normal and malignant germinal center (GC) B cells but expressed in other B cell types. Thus, restricted TET2 expression in GC cells may promote type I EBV latency.
爱泼斯坦-巴尔病毒（EBV）可潜伏感染正常B细胞，并促使某些人类淋巴瘤的发生发展。新感染的B细胞支持病毒潜伏期的一种高度转化形式（III型）；然而，在免疫功能正常的宿主中，EBV的长期感染仅限于潜伏期形式更为受限的B细胞（I型），其中大多数病毒基因表达因启动子DNA甲基化而沉默。尽管已知I型潜伏期与生发中心（GC）B细胞表型相关，III型潜伏期与活化B细胞（ABC）表型相关，但EBV如何转换潜伏期类型尚不清楚。在本研究中，我们检测了TET2（一种通过将5-甲基胞嘧啶（5mC）转化为5-羟甲基胞嘧啶（5hmC）来启动DNA去甲基化的细胞酶）的表达是否调节B细胞中的EBV潜伏期类型。我们发现，TET2在正常GC细胞和GC型淋巴瘤中表达受到抑制。相反，TET2在正常幼稚B细胞和ABC型淋巴瘤中表达。我们还证明，与ABC型细胞系相比，GC型细胞系的5mC水平升高，5hmC水平降低。最后，我们表明，TET2促进EBV转录因子EBNA2将EBV感染细胞从I型潜伏期转换为III型潜伏期的能力。这些发现表明，TET2在GC细胞中的表达受抑制，与EBV感染无关，并提示TET2通过增强EBNA2对甲基化EBV启动子的激活作用，促进具有ABC或幼稚表型的B细胞中EBV的III型潜伏期。EBV在B细胞中建立了几种不同类型的病毒潜伏期。然而，决定EBV是进入高度转化的III型潜伏期还是更受限的I型潜伏期的细胞因子尚未得到充分表征。在这里，我们表明，TET2（一种通过将5-甲基胞嘧啶（5mC）转化为5-羟甲基胞嘧啶（5hmC）来启动DNA去甲基化的细胞酶）通过增强病毒转录因子EBNA2激活在III型（而非I型）潜伏期表达的甲基化病毒启动子的能力，来调节B细胞中的EBV潜伏期类型。此外，我们证明（与EBV无关）TET2在正常和恶性生发中心（GC）B细胞中关闭，但在其他B细胞类型中表达。因此，GC细胞中TET2表达受限可能促进EBV的I型潜伏期。
