GLUCOSE METABOLISM RESPONSIVE GENES IN PANCREATIC ISLETS

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The objective of this project is to begin to identify and catalog non-insulin genes in the pancreatic islet that are induced by metabolizable insulin secretagogues - especially by glucose, the most potent insulin secretagogue. A unique feature of insulin secretion by the beta cell of the pancreatic islet is that it is regulated by metabolism of secretagogues rather than by the interaction of an agonist with a receptor. Although secretagogue metabolism and insulin secretion in the islet are well studied areas, little is known about the regulation of these factors at the level of gene expression. Insulin and other hormone genes have been well-characterized and they will not be studied. The genes involved in the regulation of secretagogue metabolism and insulin secretion have not been studied much, if at all, and it is these genes that we propose to isolate and characterize. The intent is to test the hypothesis that some control over glucose-induced insulin secretion in the pancreatic beta cell is achieved at the level of gene expression - to a first approximation by gene transcription. We will begin by identifying specific messenger RNAs whose abundance increases in pancreatic islets that have been cultured in the presence of insulinotropic glucose. cDNA libraries will be constructed from rat and human pancreatic islets and will be screened by differential land subtraction hybridization. RNA thus identified will be characterized in respect to tissue distribution, time course of expression, response to different insulin secretagogues, and nucleotide and deduced amino acid sequences. The genes that encode these RNAs will then be isolated and their regulatory regions mapped. Studies will be initiated to obtain clues as to how glucose-responsive genes are regulated. The long term goal of this project is to understand how metabolism of glucose and other secretagogues regulate the transcription of the genes involved in secretagogue metabolism and insulin release in pancreatic islets. Such information may prove to be important in the use of gene therapy in the treatment of insulin dependent diabetes mellitus, since it will be necessary to treat patients with not only the insulin gene, but also with genes that regulate insulin secretion. Insulin secretion must be stimulated only when the blood glucose concentration is increasing and suppressed when the blood glucose concentration is low so that hyperglycemia and hypoglycemia do not occur.