Epstein-Barr virus (EBV) is a human gamma herpesvirus that infects approximately 95% of the population and remains latent in memory B cells as a chromatin-associated multicopy episome. EBV infection is causally associated with several pathologies including infectious mononucleosis, different types of lymphomas and gastric carcinoma. This heterogeneity in EBV-associated diseases may reflect the different gene expression programs that EBV adopts in different cell types and host-cell conditions. Epigenetic modifications and alternative viral chromatin conformations contribute to the establishment and maintenance of these alternative viral gene expression programs, which are referred to as latency types. Although we know that chromatin- organizing factors, such as CTCF, affect the epigenetic state of the EBV episome we know little about the mechanisms that govern EBV genome plasticity and function and how EBV manipulates the host epigenetic machinery to avoid complete epigenetic silencing of viral latent promoters. The long-term goal of this project is to understand how EBV hijacks host epigenetic machinery to establish a latent infection, regulating both viral and host gene expression. Post-translational modifications regulate several cellular processes including the host response against pathogens. Poly-ADP-ribosylation consists of the attachment of negatively charged polymers of ADP-ribose to acceptor proteins. The reaction is catalyzed by members of the Poly(ADP-ribose) polymerase (PARP) family. In previous work, we demonstrated that PARP1 regulates EBV replication by interacting with the viral genome. Our preliminary work provides new genome wide and biochemical data that reveals for the first time that LMP1 activates PARP1 and that PARP1 activity prevents EZH2 from silencing the viral genome. Thus, we hypothesize that the EBV protein LMP1 affects viral gene expression by altering chromatin structure through PARP1/EZH2 interaction. Our project aims to fill the gap in our understanding of the epigenetic regulation of the EBV genome. To achieve our goal, we aim to: 1) how PARP1 activation regulates EBV latency programs; and 2) determine if EZH2 plays a role in regulating EBV latency. Completion of this project will reveal new mechanisms by which EBV can contribute to maintain and switch between different gene expression programs observed in infected cells. It will also identify new potential therapeutic targets for EBV infection and EBV-associated malignancies.
Every year nearly 144,000 individuals die as a consequence of untreatable malignancies caused by Epstein- Barr virus (EBV) latent infections. EBV-induced malignancies have been challenging to target, in large part because EBV establishes a latent infection with complex and dynamic gene expression patterns. These gene expression patterns are referred to as ?latency types? that can adapt to diverse host cell types and immunological responses. This dynamic gene expression allows EBV to escape eradication by immune surveillance and persist as a long-term latent infection. Disrupting the natural capacity of EBV to modulate its gene expression pattern may offer a new approach for treating EBV+ cancers. The changes in viral gene expression are regulated by both viral and cellular factors, including epigenetic modulators. Altering epigenetic modulators is a promising approach as many newly developed drugs target these epigenetic modifiers. For EBV+ malignancies, however, the application of these drugs requires a more complete understanding of the epigenetic mechanisms that regulate the EBV latency. We previously discovered that an important epigenetic feature of EBV is the three-dimensional (3D) structure of the viral chromosome. Changes in 3D structure (i.e. chromatin looping) correlates with different patterns of gene expression. The primary factor that mediates the 3D genome structure in EBV is CTCF. Our preliminary work reveals for the first time that LMP1 activates PARP1 and that PARP1 activity modulates EBV 3D chromatin structure and prevents EZH2 from silencing the viral genome. Therapeutic strategies aimed at this axis may prove to be a novel, or complementary, approach to treating EBV+ cancers. Thus we hypothesize that LMP1/PARP1/EZH2 is an important regulatory axis that interconnects EBV 3D structure, chromatin modification and viral gene expression. Here we will test our hypothesis by: 1) Determine how changes in LMP1/PARP1 activity affect EBV chromatin loop formation; 2) Establish the role and mechanism of EZH2 in regulating EBV chromatin composition and structure; and 3) Establish that the latency state of EBV can be switched by pharmacological modulation of PARP1 and EZH2. The completion of this work will determine the role and pathogenic mechanisms of LMP1/PARP1/EZH2 axis in the epigenetic regulation of EBV gene expression. We anticipate providing a rationale for targeting PARP1 and/or EZH2 as a treatment for EBV+ malignancies ? as single agents or combination therapy. In the long run, this work has the potential to reveal new mechanisms of regulation of EBV infection, and potentially other viruses, and provide novel therapeutic approaches for treating EBV-induced malignancies.
| Lupey-Green, Lena N; Caruso, Lisa B; Madzo, Jozef et al. (2018) PARP1 Stabilizes CTCF Binding and Chromatin Structure To Maintain Epstein-Barr Virus Latency Type. J Virol 92: |
