A novel pro-apoptotic function for Epstein-Barr virus LMP2A: increasing B cell sensitivity to Fas-mediated apoptosis via Lyn and Syk kinases (VIR1P.1136)

Abstract

Abstract Latent Membrane Protein 2A (LMP2A) of Epstein-Barr virus (EBV) protects B cells from many pro-apoptotic signals. LMP2A is expressed in EBV-infected B cells in the germinal center, which is a site of significant Fas-mediated apoptosis. Given that B cell receptor (BCR) stimulation protects B cells from Fas-mediated apoptosis and since LMP2A acts as a BCR mimic, we hypothesized that LMP2A would protect B cells from Fas-induced apoptosis. To test this hypothesis, LMP2A-negative and -positive B cell lines were exposed to a Fas-specific monoclonal antibody and apoptosis was assessed by Annexin V staining and PARP cleavage. Surprisingly, LMP2A-expressing B cell lines demonstrate an increased sensitivity to Fas-mediated apoptosis, due to a LMP2A-dependent enhancement in Fas expression. B cell lines harboring LMP2A mutations in either the Lyn or Syk binding site do not show an LMP2A-dependent increase in Fas levels and/or Fas-mediated apoptosis, indicating that LMP2A requires these two kinases to mediate these pro-apoptotic effects. Furthermore, experiments demonstrate that LMP2A enhances Fas-mediated apoptosis in human B cell lines in the presence of additional EBV latency proteins, indicating that LMP2A promotes Fas-dependent apoptosis in the natural context of the virus. These findings are the first to demonstrate a pro-apoptotic function of LMP2A and have implications for both EBV latency and EBV-associated malignancies.