The role of the TRAF2/3 binding site in LMP1 and CD40 signaling (44.6)

Abstract

Abstract The Epstein-Barr virus protein, LMP1, is a mimic of the cellular receptor CD40. However, LMP1 signals to B lymphocytes in an amplified and sustained manner compared to CD40. LMP1 contributes to the development of B lymphoma in HIV patients or in immunosuppressed transplant recipients. LMP1 binds the signaling adaptor TRAF2 with lower affinity than CD40, and TRAF2 is needed for inducing CD40-mediated degradation of TRAFs 2 and 3. LMP1 doesn't induce TRAF degradation, and employs TRAF3 as a positive mediator of cell signaling, whereas CD40 signals are inhibited by TRAF3. We thus tested the hypothesis that relative affinity for TRAF2 and/or, distinct sequence differences in the TRAF2/3 binding sites (TBS) of CD40 vs. LMP1, controls the disparate ways in which CD40 and LMP1 use TRAFs 2 and 3, and their distinct signaling characteristics. We examined CD40 and LMP1 mutants in which the TBS sequences were swapped, testing TRAF binding and degradation, and induction of B cell activation. Results revealed that TRAF binding affinity and TBS sequence dictate some, but not all CD40 vs. LMP1 signaling properties. Examination of TRAF binding, degradation, cytokine production, IgM secretion, and the activation of c-Jun kinase and NF-kB revealed that some events are dictated by TBS sequences, others partially regulated, and still others appear independent of the TBS sequence. NIH grant CA099997