Mechanisms of TRAF3 regulation of TLR signaling in B lymphocytes

Abstract

Abstract TRAF3 is an adaptor protein that binds to a variety of receptor types on immune cells and exerts multiple regulatory functions in signaling pathways. TRAF3 functions are cell type and context dependent. B cell-TRAF3 inhibits homeostatic NFκB2 activation and other pro-survival signaling pathways; restraint of survival is a B cell-unique TRAF3 function. Loss of B cell-TRAF3 in vivo contributes to early autoimmunity and later lymphomagenesis. TRAF3 inhibits B cell TLR functions, including cytokine production (IL-6, IL-10, IL-12p40 and TNFα), Ig isotype switching, and antibody production in response to ligands for TLRs 3, 4, 7/8 and 9. A key knowledge gap is identifying the molecular mechanisms by which TRAF3 mediates this regulation. Our working hypothesis is that B cell-TRAF3 regulates the activity, recruitment, and/or post-translational modification of specific TLR signaling proteins. Our recent data show that B cell-TRAF3 forms a heterocomplex with TRAF6, associating with the tyrosine kinase Syk and inhibiting early TLR signals, such as pIRAK1 degradation. In the absence of TRAF3, TRAF6 shows a greater association with several TLR signaling proteins. These results suggest that TRAF3 may inhibit TRAF6 access to the TLR signaling complex, and thus early TLR signaling. Further studies aimed at providing new insights into the molecular mechanisms contributing to the regulation of B cell-TRAF3 in TLR signaling can inform selection and development of more targeted therapies for B cell malignancies and autoimmunity. Supported by VA Merit Review IO1 BX001702 NIH RO1 AI62656 NIH P50 CA97274 NIH T32 Training Grant AI07485