Epstein-Barr virus Latent Membrane Protein 2A (LMP2A) is expressed in EBV-infected B cells in the germinal center, a site of significant apoptosis induced by engagement of Fas on activated B cells. Signals from the B cell receptor (BCR) protect germinal center B cells from Fas-mediated apoptosis, and since LMP2A is a BCR mimic, we hypothesized that LMP2A would also protect B cells from Fas-mediated apoptosis. Surprisingly, latently-infected human and murine B cell lines expressing LMP2A were more sensitive to Fas-mediated apoptosis, as determined by increases in Annexin-V staining, and cleavage of caspase-8, −3 and PARP. Additional studies show that LMP2A-expressing B cell lines demonstrate a Lyn- and Syk-dependent increase in sensitivity to Fas-mediated apoptosis, due to an LMP2A-dependent enhancement in Fas expression. These findings demonstrate the ability for LMP2A to directly increase a pro-apoptotic molecule and have implications for EBV latency as well as the treatment of EBV-associated malignancies.

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.