Epstein-Barr Virus Oncoprotein LMP1 Mediates Epigenetic Changes in Host Gene Expression through PARP1

Abstract

The latent infection of Epstein-Barr virus (EBV) is associated with 1% of human cancer incidence. Poly(ADP-ribosyl)ation (PARylation) is a posttranslational modification catalyzed by poly(ADP-ribose) polymerases (PARPs) that mediate EBV replication during latency. In this study, we detail the mechanisms that drive cellular PARylation during latent EBV infection and the effects of PARylation on host gene expression and cellular function. EBV-infected B cells had higher PAR levels than EBV-negative B cells. Moreover, cellular PAR levels were up to 2-fold greater in type III than type I latently infected EBV B cells. We identified a positive association between expression of the EBV genome-encoded latency membrane protein 1 (LMP1) and PAR levels that was dependent upon PARP1. PARP1 regulates gene expression by numerous mechanisms, including modifying chromatin structure and altering the function of chromatin-modifying enzymes. Since LMP1 is essential in establishing EBV latency and promoting tumorigenesis, we explored the model that disruption in cellular PARylation, driven by LMP1 expression, subsequently promotes epigenetic alterations to elicit changes in host gene expression. PARP1 inhibition resulted in the accumulation of the repressive histone mark H3K27me3 at a subset of LMP1-regulated genes. Inhibition of PARP1, or abrogation of PARP1 expression, also suppressed the expression of LMP1-activated genes and LMP1-mediated cellular transformation, demonstrating an essential role for PARP1 activity in LMP1-induced gene expression and cellular transformation associated with LMP1. In summary, we identified a novel mechanism by which LMP1 drives expression of host tumor-promoting genes by blocking generation of the inhibitory histone modification H3K27me3 through PARP1 activation. IMPORTANCEEBV is causally linked to several malignancies and is responsible for 1% of cancer incidence worldwide. The EBV-encoded protein LMP1 is essential for promoting viral tumorigenesis by aberrant activation of several well-known intracellular signaling pathways. We have identified and defined an additional novel molecular mechanism by which LMP1 regulates the expression of tumor-promoting host genes. We found that LMP1 activates the cellular protein PARP1, leading to a decrease in a repressive histone modification, accompanied by induction in expression of multiple cancer-related genes. PARP1 inhibition or depletion led to a decrease in LMP1-induced cellular transformation. Therefore, targeting PARP1 activity may be an effective treatment for EBV-associated malignancies. The Epstein-Barr virus (EBV) is a human gammaherpesvirus that latently infects approximately 95% of the population worldwide (1). Latent EBV infection contributes to 1% of human cancers, including Burkitt's lymphoma and nasopharyngeal carcinoma (2, 3). To establish a latent infection in a naive B cell, EBV first adopts a type III latent gene expression program in which all latency genes are expressed to provide intracellular signals to the infected B cell th...

PARP1 restricts Epstein Barr Virus lytic reactivation by binding the BZLF1 promoter

“…In addition, the lymphomas in the mice exhibited abortive lytic infection, in which expression of the early lytic protein BMRF1 was mutually exclusive with that of LMP1 in cells. Previously, we identified a positive association between the latency protein LMP1 and PAR levels, in which LMP1 activates PARylation through PARP1 (Martin et al, 2016). Although LMP1 is upregulated during lytic reactivation, paradoxically, LMP1 suppresses lytic induction and progression through a number of unique mechanisms (Chang et al, 2004; Adler et al, 2002; Prince et al, 2003).…”

“…Chromatin immunoprecipitation (ChIP) assays were performed according to the Upstate Biotechnology Inc. protocol as described previously, with minor modifications (Martin et al, 2016). Briefly, cells were fixed in 1% formaldehyde for 15 min, and DNA was sonicated using a sonic dismembrator (Fisher Scientific) to generate 200–500-bp fragments.…”

Epstein–Barr virus: a master epigenetic manipulator

“…In germinal center B cells, LMP1 expression induced a single DNMT (DNMT3A) and the H3K27 demethylase, KDM6B, [49,50]. In addition, reduced global levels of the repressive H3K27me3 mark were observed in LMP1-expressing B cells, where LMP1 activation of PARP1 was shown to inhibit EZH2, blocking the accumulation of H3K27me3 [51,52]. …”

Disrupting the Code: Epigenetic Dysregulation of Lymphocyte Function during Infectious Disease and Lymphoma Development

“…Viruses such as EBV and HIV prevent recognition by host immunosurveillance by remaining latent inside host cells through epigenetic modification of their genome to mimic their host genome (99,100). The latency membrane protein 1 establishes EBV latency and induces tumorigenesis by promoting epigenetic alterations of histones and resulting in the chromatin accessibility of two established latency membrane protein 1-target protooncogenes, c-Fos and EGR1 (101). The overexpression of these oncogenes eventually results in the development of tumors associated with EBV infection such as Burkitt lymphoma, nasopharyngeal carcinoma, and some gastric cancer (102)(103)(104).…”