Roles of the TRAF2/3 binding site in differential B cell signaling by CD40 and its viral oncogenic mimic, LMP1.
The EBV protein, latent membrane protein 1 (LMP1), is a functional mimic of the cellular receptor CD40, but signals to B lymphocytes in an amplified and sustained manner compared with CD40. LMP1 contributes to the development of B cell lymphoma in immunosuppressed patients, and may exacerbate flares of certain autoimmune diseases. The cytoplasmic domain of LMP1 binds the signaling adaptor TRAF2 with lower avidity than the cytoplasmic domain of CD40, and TRAF2 is needed for 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 of CD40 vs LMP1, controls the disparate ways in which CD40 and LMP1 use TRAFs 2 and 3, and their distinct signaling characteristics. CD40 and LMP1 mutants in which the TRAF binding site sequences were swapped were examined, testing TRAF binding and degradation, and induction of B cell activation. Results revealed that TRAF binding affinity and TRAF binding site sequence dictate a distinct subset of CD40 vs LMP1 signaling properties. Examination of TRAF binding, degradation, cytokine production, IgM secretion, and the activation of c-Jun kinase and NF-kappaB revealed that some events are dictated by TRAF binding site sequences, others are partially regulated, and still others are independent of the TRAF binding site sequence.
Graham
John P
JP
Interdisciplinary Program in Immunology, Veterans Affairs Medical Center, Iowa City, Iowa 52242, USA.
Moore
Carissa R
CR
Bishop
Gail A
GA
D000818:Animals; D016175:B-Lymphocyte Subsets / Q000276:immunology* / Q000378:metabolism; D001665:Binding Sites / Q000276:immunology; D019013:CD40 Antigens / Q000737:chemistry / Q000502:physiology*; D002460:Cell Line; D002999:Clone Cells; D004854:Herpesvirus 4, Human / Q000276:immunology; D006801:Humans; D051379:Mice; D018716:Molecular Mimicry / Q000276:immunology*; D011485:Protein Binding / Q000276:immunology; D011518:Proto-Oncogene Proteins / Q000737:chemistry / Q000502:physiology*; D015398:Signal Transduction / Q000276:immunology*; D047992:TNF Receptor-Associated Factor 2 / Q000378:metabolism / Q000502:physiology*; D048008:TNF Receptor-Associated Factor 3 / Q000378:metabolism / Q000502:physiology*; D014407:Tumor Cells, Cultured; D014763:Viral Matrix Proteins / Q000737:chemistry / Q000502:physiology*
D019013:CD40 Antigens; C037662:EBV-associated membrane antigen, Epstein-Barr virus; D011518:Proto-Oncogene Proteins; D047992:TNF Receptor-Associated Factor 2; D048008:TNF Receptor-Associated Factor 3; D014763:Viral Matrix Proteins