REGULATION OF CELLULAR GENE EXPRESSION AND METABOLISM BY EPSTEIN-BARR VIRUS LATENT MEMBRANE PROTEIN 1

Abstract

Epstein-Barr virus (EBV) is one of the most ubiquitous human viruses, with over 95% of the adult population harboring lifelong latent EBV infection in a small fraction of their B- lymphocytes. EBV is known to cause lymphoproliferative disorders and is associated with Hodgkin’s lymphoma, Burkitt’s lymphoma and Nasopharyngeal carcinoma. However, in most cases, the approach to EBV-positive lymphomas does not differ from EBV-negative lymphomas of the same histology. Latent membrane protein 1 (LMP1) is the major transforming protein of EBV and is critical for EBV-induced B-cell transformation in vitro. LMP1 activates several epigenetic regulators to modify host gene expression, including the chromatin-modifying enzyme Poly(ADP- ribose) polymerase 1, or PARP1. We have determined that LMP1 can activate PARP1 to increase hypoxia-inducible factor 1-alpha (HIF-1α)-dependent gene expression, leading to a change in host cell metabolism indicative of a ‘Warburg effect’ (aerobic glycolysis). This subsequently provides a proliferative advantage to LMP1-expressing cells. The LMP1-induced increase in HIF-1α-dependent gene expression, alteration of cellular metabolism, and accelerated cellular proliferation can be offset with the PARP inhibitor olaparib. We further determined that LMP1 can induce metabolic changes in the form of fatty acid synthesis. Ectopic expression of LMP1 and EBV-mediated B-cell growth transformation induced fatty acid synthase (FASN) and increased lipid droplet formation. FASN is a crucial lipogenic enzyme responsible for de novo biogenesis of fatty acids in transformed cells. FASN can be stabilized at the protein level through interaction with USP2a, a ubiquitin-specific protease that de-ubiquitinates FASN leading to its overexpression. We have evidence to suggest that following ectopic expression of LMP1 and EBV-mediated B-cell growth transformation, USP2a is increased, leading to stabilization of FASN at the post-translational level. Furthermore, following dosing with C75, an inhibitor of lipogenesis, we observed preferential killing of LMP1-expressing B cells. Our findings demonstrate that EBV-mediated B-cell growth transformation, partly through LMP1, leads to induction of FASN, fatty acids and lipid droplet formation, possibly pointing to a reliance on lipogenesis. In summary, targeting PARP1 activity and lipogenesis programs may be an effective strategy in the treatment of LMP1+ EBV-associated malignancies.