Recent advances have revealed the critical role of IL-15 and NKG2D/MIC interactions in linking innate and adaptive immunity at the level of intraepithelial cytolytic T lymphocytes (IEL) in the human intestine. NKG2D recognizes the MHC-encoded MIC A and B molecules induced upon stress at the surface of intestinal epithelial cells (IEC) and signals through the Dap 10 adaptor to mediate direct cytolytic functions and enhance TCR-mediated effector functions and proliferation. IL-15, a cytokine produced by IEC, primes multiple steps of the NKG2D/Dap10 signaling pathway. Recent reports have established that dysregulated activation of NKG2D is involved in the pathogenesis of autoimmune and inflammatory disorders, such as celiac disease, rheumatoid arthritis and type I autoimmune diabetes, supporting the importance of this pathway in noninfectious immunopathology. This proposal extends our earlier studies of CD94/NKG2, NKG2D and IL-15 in IEL to dissect at the molecular level the mechanisms underlying NKG2D expression, trafficking and signaling in normal IEL and their coordinated regulation by IL-15.
Specific aim 1 will characterize NKG2D signaling for direct cytolysis. Using kinase specific inhibitors, dominant negative kinases, and kinase-deficient cell lines we will study the signaling pathways mediated by NKG2D that are involved in cytolysis.
Specific aim 2 will characterize NKG2D recycling and degradation, as surface NKG2D downregulation upon ligand engagement tightly controls NKG2D activation.
Specific aim 3 will dissect the molecular and biochemical basis for NKG2D regulation by IL-15 and Histone deacetylases (HDAC). Our preliminary data suggest that IL-15 upregulates HDACs and that HDACs play a role in NKG2D synthesis and degradation. Collectively, these studies will dissect the NKG2D signaling pathways in IEL and the mechanisms underlying the striking physiological effects of IL-15 on NKG2D expression and function. The results may provide the basis for novel therapeutic approaches, using for example HDAC inhibitors, for autoimmune and inflammatory diseases such as celiac disease, rheumatoid arthritis and type 1 juvenile diabetes, where dysregulated expression of NKG2D and IL-15 plays an important pathogenic role.
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