The EBV-encoded viral mimic of CD40, latent membrane protein 1 (LMP1) strikingly mimics CD40 signals to B cells, but does so in an amplified and sustained manner. This dysregulated signaling is consistent with the well-documented association of LMP1 function with human B cell lymphoma, and emerging information on the potential role of LMP1 in autoimmune disease, both of which have similar underlying pathogenic mechanisms. Interestingly, CD40 and LMP1 use the same cytoplasmic adapter molecules (TNFR associated factors, TRAFs) in unexpectedly distinct ways. We recently discovered that LMP1 signaling is independent of TRAF2, a major mediator of CD40 signals, but that TRAFs 3, 5, and 6 make important contributions to LMP1 effects in B cells. When expressed as transgenes in mice lacking endogenous CD40, the cytoplasmic tail of either CD40 or LMP1 can restore T-dependent humoral immunity. However, expression of molecules with the LMP1 CY domain result in an expanded B cell compartment, B cell hyperactivity and autoreactivity, and disordered lymphoid architecture. The major goals of the proposed project period are to understand how LMP1 uses TRAFs 3, 5, and 6 in signaling to B cells, and which LMP1-induced biological effects require each of these TRAFs, alone or in interacting complexes. We also seek to understand how LMP1 makes use of TRAF6 by indirect, rather than direct association. Finally, interactions between CD40 and LMP1 on B cells, which have important implications for ultimate LMP1 biological effects and potential therapies, will be investigated. All major goals will be addressed usi complementary vitr and in vivo experimental approaches.
The focus of this project is a protein (LMP1) produced by a virus called Epstein Barr virus. This virus infects >90% of the world's adult human population, and exists in an inactive state in a type of white blood cell called the B lymphocyte for the lifetime of the individual. LMP1 is not normally expressed in latently infected people, but can be aberrantly re-expressed in people whose immune systems are seriously suppressed, as well as in disease flares of rheumatic diseases. LMP1 has been associated with exacerbating autoimmune diseases and B cell malignancies, due to its ability to abnormally mimic the activating properties of a normal cellular protein, CD40. This project seeks to examine the mechanisms by which LMP1 affects B lymphocyte function, and how it mediates effects that contribute to pathogenesis of autoimmunity and B cell cancers.
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