The long term objective of the research outlined in this proposal is to understand the molecular mechanism(s) governing salivary gland gene expression and to elucidate the developmental program(s) modulating the proliferation and differentiation of salivary cells. An understanding of the molecular mechanisms and hierarchies of salivary-specific gene expression and differentiation program(s) is not only of fundamental biological interest, but also of practical importance in implementing possible therapy for Xerostomia and other salivary dysfunctions.
Specific aims of this proposal include: 1) To characterize the newly identified salivary specific cAMP-response element (SCRE) of the rat proline-rich protein gene (PRP), RP4, and its putative transfactors, SCBPs and SCREB, 2) to dissect the functional motif(s) modulating the nonproliferation/terminal differentiation-specific S1 expression in salivary cells, and initiate in vitro analysis of its regulatory mechanism(s), and 3) to develop an in vivo transgenic mouse model to elucidate mechanism(s) governing PRP expression during salivary gland development, and to investigate the influence of pharmacological manipulation and nutritional factors, especially isoproterenol and tannins, of PRP expression. The unique appearance of proline rich proteins in human and other higher primates' saliva at high levels (>70% of total soluble protein of saliva) suggests a functional role(s) for PRPs in the oral cavity or elsewhere. In particular, saliva might play a major role in the oral defense against HIV-1; the expression of these unusual proteins may also protect both rodents and higher primates from the negative nutritional and weight loss effects of tannins or other polyphenols. Our proposed model for isoproterenol-regulated gene expression in salivary cells has four premises: i)the catalytic subunit of cAMP-dependent protein kinase A (PKA) plays an important role in terms of modulating PRP and S1 gene expression, ii) the post-translation phosphorylation of SCBPs or SCREB and putative protein-protein interactions may be critical for the induction of PRP gene expression, (iii) a putative protein factor(s) is responsible for the repression of S1 gene expression, and (iv) the induction of particular immediate early genes may modulate PRP and S1 expression by a direct or indirect mechanism(s). The overall goal of this proposed study is to identify and characterize the """"""""master switch"""""""" of salivary cell determination and differentiation. A combination of in vitro genetic and biochemical (transfection, EMSA, footprinting, DNA protein blotting, etc.) and in vitro transgenic techniques will be employed to address specific questions related to this overall goal. We predict that our findings will have important implications for the study of salivary cell differentiation and salivary-specific gene expression. Such knowledge may finally lead to clinical treatment for patients who are orally compromised because of various salivary dysfunctions.
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