Contributions of CTCF and DNA Methyltransferases DNMT1 and DNMT3B to Epstein-Barr Virus Restricted Latency

Abstract

Establishment of persistent Epstein-Barr virus (EBV) infection requires transition from a program of full viral latency gene expression (latency III) to one that is highly restricted (latency I and 0) within memory B lymphocytes. It is well established that DNA methylation plays a critical role in EBV gene silencing, and recently the chromatin boundary protein CTCF has been implicated as a pivotal regulator of latency via its binding to several loci within the EBV genome. One notable site is upstream of the common EBNA gene promoter Cp, at which CTCF may act as an enhancer-blocking factor to initiate and maintain silencing of EBNA gene transcription. It was previously suggested that increased expression of CTCF may underlie its potential to promote restricted latency, and here we also noted elevated levels of DNA methyltransferase 1 (DNMT1) and DNMT3B associated with latency I. Within B-cell lines that maintain latency I, however, stable knockdown of CTCF, DNMT1, or DNMT3B or of DNMT1 and DNMT3B in combination did not result in activation of latency III protein expression or EBNA gene transcription, nor did knockdown of DNMTs significantly alter CpG methylation within Cp. Thus, differential expression of CTCF and DNMT1 and -3B is not critical for maintenance of restricted latency. Finally, mutant EBV lacking the Cp CTCF binding site exhibited sustained Cp activity relative to wild-type EBV in a recently developed B-cell superinfection model but ultimately was able to transition to latency I, suggesting that CTCF contributes to but is not necessarily essential for the establishment of restricted latency. E pstein-Barr virus (EBV) establishes a lifelong, largely quiescent (latent) infection within B lymphocytes of its human host.This requires the concerted actions of the viral latency-associated genes, several of which are believed to facilitate a germinal center (GC)-like reaction to promote differentiation of infected B cells into ones phenotypically defined as memory B cells and which serve as the primary reservoir of EBV within persistently infected individuals (reviewed in reference 59). During the establishment of latency in vivo, infected B cells must transition through several programs of EBV latency gene transcription, beginning with expression of the full complement of latency proteins (the latency III program), i.e., six nuclear antigens (EBNAs) and three integral plasma membrane proteins (LMPs), that is associated with a rapid EBV-induced expansion of infected cells. Thereafter, expression proceeds through a more restricted program limited to EBNA1, LMP1, and LMP2 (latency II) and ultimately to a complete restriction of EBV protein expression in the memory B cell (latency 0 [alternatively, the latency program]) (reviewed in reference 44). During subsequent periods of limited cell division, reactivation of expression of the EBV genome-maintenance protein EBNA1 alone (latency I) occurs to ensure against loss of the episomal viral genome (12).With the exception of latency 0, each of the viral latency prog...

Restricted TET2 Expression in Germinal Center Type B Cells Promotes Stringent Epstein-Barr Virus Latency

“…Methylation of the EBV genome first becomes apparent around 2 weeks after infection of B cells (30). Regulation of viral genome methylation appears to be complex, since inactivation of single DNA methyltransferases (DNMTs) or a combination of DNMT1 and DNMT3B is not sufficient to induce Cp demethylation or activation of type III latency gene expression (31). Two different EBV latency proteins, LMP1 and LMP2A, have been reported to increase expression of cellular DNA methyltransferases …”

The Open Chromatin Landscape of Kaposi's Sarcoma-Associated Herpesvirus

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B Cell Receptor Activation and Chemical Induction Trigger Caspase-Mediated Cleavage of PIAS1 to Facilitate Epstein-Barr Virus Reactivation

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