Somatostatin is a neuropeptide which is produced in neuroendocrine cells of the brain, thyroid, pancreas, and GI tract. Within these tissues somatostatin appears to act in a paracrine fashion to inhibit the release of various hormones including growth hormone, calcitonin, insulin, glucagon, and gastrin. Somatostatin biosynthesis and secretion are regulated by agents which stimulate adenyl cyclase activity. The overall objectives of this study are to elucidate the mechanisms underlying the cAMP-regulated and tissue-specific expression of the rat somatostatin gene. Experiments on cAMP-responsiveness will focus on two specific aims: (1) To determine, by Exonuclease III protection experiments, whether the cAMP-responsive element in the rat somatostatin gene binds to non-histone proteins in chromatin and nuclear extracts of cAMP-treated cells; (2) To determine whether cAMP-stimulated somatostation secretion and gene transcription are regulated by different cAMP-dependent protein kinases. These experiments will be performed by comparing secretion and transcription in transfected neuroendocrine (PC12) cell lines which are deficient in either cAMP-dependent protein kinase type 1 or type 2. The mechanisms by which cAMP-regulates peptide hormones like somatostatin may be particularly useful in obtaining an understanding of the pathophysiology of such endocrine-metabolic diseases as diabetes mellitus. Experiments on tissue-specific expression of the somatostatin gene are designed to meet the following specific aims: (3) To characterize the sequences required for cell-specific expression of the somatostatin gene in a medullary thyroid carinoma cell line by transfection of a promoter deletion series of somatostatin fusion genes containing the bacterial reporter gene chloramphenicol acetyl transferase (CAT). (4) To characterize sequences within the somatostatin gene which bind non-histone proteins in chomatin and nuclear extracts of somatostatin-producing medullary thyroid carcinoma cells.
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