The proposed study intends to elucidate the nuclear events and their subsequent downstream molecular hierarchies that integrate multiple extracellular signaling cascades governing salivary epithelial cell differentiation and proliferation. Our current studies on the characterization of salivary alpha-ENaC expression have led to the identification of a novel cross-talk between Ras/ERK and GR/STAT3 signaling pathways. We demonstrated that the induction of HMGI-C is required to effectively repress GR/Dex-stimulated transcription of alpha-ENaC and to potentiate anchorage-independent cell growth by the Ras/ERK pathway in salivary Pa-4 cells. This Ras/ERK-mediated HMGI-C induction also leads to the formation of an HMGI-C/PIAS3 complex which functions as an """"""""off-switch"""""""" for attenuating both GR/Dex- and STAT3-mediated transcriptional activation. In this application, we will test the central hypothesis that the spatially and temporally regulated HMGI-C expression plays an essential role in fine-tuning alpha-ENaC expression by antagonizing GR/Dex-mediated trans-activation via formation of the HMGI-C/PIAS3 complex. We will also test the hypothesis that HMGI-C functions as a global gene modulatory factor in vivo by participating in the enhanceosome/repressosome formation, leading to the subsequent phenotypic manifestations in salivary epithelium. The proposed study is of great significance as the perturbation of multiple stimulatory and inhibitory signals and its net outcome are associated with the development of many human systematic or organ-specific diseases, such as Sjogren's syndrome and cancer. Experimentally, there are three Specific Aims in this application: i) to examine functional interactions between HMGI-C and other components of the GR-mediated trans-activation pathway that regulates alpha-ENaC expression in epithelial cells; ii) to perform a comprehensive analysis of alpha-ENaC expression and ENaC function in salivary glands derived from AQP5-HA-HMGI-C transgenic mice; and iii) to determine the potential involvement of HMGI-C in salivary homeostatic regulation. A comprehensive cell biological, molecular biological, biochemical and pharmacological studies are proposed to explore the (patho) physiological consequences of HMGI-C expression in vivo and in vitro. These results will provide us with a blueprint for the """"""""plasticity"""""""" of salivary epithelial cell differentiation and proliferation. A better understanding of the functional role for HMGI-C expression could lead to the development of novel therapies that act on critical elements of the signaling pathways governing salivary homeostatic regulation.
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