The proposed study is part of the Investigator's broad interest in elucidating genetic mechanisms that program salivary cell differentiation and proliferation. It has been established that isoproternol (Ipr)-mediated salivary adaptive response represents a shift of salivary cells from having a normal physiological function to ones exhibiting the hyperplastic and hypertrophic phenotypes in the rats or mice receiving chronic Ipr-administration regimen. During the current grant period, the investigators have demonstrated that chronic Ipr-administration induces the parotid Raf-1 protein kinase activity in a time-dependent manner, and the constitutive activation of Raf-1 induces the expression of a chromosomal architectural protein, HMGI-C, at the transcriptional level. The induction of HMGI-C expression also coincides with Raf-1 mediated transformation of salivary Pa-4 cells. However, the exact mechanism underlying this Raf-1-mediated HMGI-C induction is poorly defined. In this application, they will test the hypothesis that a novel salivary Raf-1 dependent regulatory element (RDRE), which differs from those known in Raf-1 immediate-early-response genes not only by the DNA sequences(s) but also by its interacting protein(s), is essential for the induction of HMGI-C expression in salivary cells by the Raf-1 kinase module activation. They will also test the hypothesis that besides regulating embryonic development, HMGI-C protein serves as an architectural protein to interact with other nuclear proteins such as transcription factors, and thereby regulating salivary adaptive response and transformation. The long-term goal of this research is to use salivary adaptive response as a paradigm to develop a mechanistic description if events in which the membrane-associated activities, such as the occupation of cell surface receptors, lead to the accumulation of intracellular second messengers that direct the genomic response of the cells to environmental stimuli. Experimentally, there are three specific aims in this application: (i) identify and characterize the transcriptional regulatory elements required for salivary basal and induced HMGI-C expression; (ii) elucidate the molecular mechanism(s) underlying the induction of HMGI-C expression by the activated Raf-1 signaling module; (iii) investigate the functional role(s) of the HMGI-C protein in salivary cells. The intent is that these results will not only provide a new dimension to the Raf-1 signaling pathways and mechanisms, but also enhance our understanding the role of this Raf-1 signaling pathways and mechanisms, but also enhance our understanding the role of this Raf-1 mediated gene regulation in salivary adaptive response to drugs, other stimuli, and genomic instability. A better knowledge of molecular basis of gene regulation is the key to successful tissue regeneration, which leads to an improved salivary function through agents that act on crucial elements of signaling pathways involved in morphological and functional maturation. Moreover, the proposed study is of great significance as the dysregulation of this Raf-1 mediated process could lead to cell transformation.
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