GLUCAGON BIOSYNTHESIS AND METABOLISM

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Glucagon, a 29 amino acid peptide, that regulates glucose and amino acid metabolism, is a member of a large family of structurally-related peptides expressed in the gastro-intestinal and nervous systems. The goals are to gain an understanding of the biologic functions of this complex set of genes. During the past grant period we isolated and sequenced the cDNAs and genes encoding the rat pre-proglucagon, as well as two corresponding distinct angler fish cDNAs. The proglucagons are polyproteins that contain multiple glucagon-related peptides. The fish proglucagon encodes one and the rat two additional glucagon-like peptides. The processing of proglucagon differs markedly in pancreas vs. intestine resulting in the formation of three different glucagon-like peptide I's, glucagon-like peptide II, and an amidated intervening peptide. The glucagon-like peptide I(7-37) has potent insulinotropic actions and the other peptides derived from the proglucagon appear to be growth factors. We have developed clonal cell lines derived from rat islets that have different hormone-producing phenotypes and have initiated studies of the enhancer, silencer and metabolic-response elements involved in cell-specific and metabolic regulation of the gene. Cell-specific enhancer sequences and protein Kinase C-response elements appear to reside within one kilobase of the 5' flanking region of the gene. Our aims are to: (1) isolate and structurally and functionally characterize the cis-acting DNA elements and the trans-acting DNA-binding proteins that govern cell-specific expression of the glucagon gene, (2) Characterize the antisera and radioimmunoassays for the GLP's and the structures of the GLP peptides, (3) determine the biologic functions of the glucagon-like peptides and (4) characterize the new glucagon-related peptides and genes expresed in the brain. These investigations have potential relevance to an understanding of cellular differentiation and the pathogenesis of diabetes mellitus.