Non-insulin dependent diabetes is characterized by impaired glucose utilization in muscle and fat. Glucose transport, which is rate limiting for glucose transport in these tissues primarily by translocating glucose transporters from an intracellular domain to the cell surface. Recently, new insight into the mechanism of insulin-stimulated glucose transport was provided by the cloning of an insulin-regulated glucose transporter (IRGT) present only in insulin-sensitive tissues. IRGT appears to be the major glucose transporter species in insulin-sensitive tissues of the rat. One of the most interesting and possible important features of IRGT is that in the absence of insulin it is located almost exclusively inside the cell. The primary goal of the present proposal is to understand mechanisms by which IRGT moves to and from the cell surface in response to insulin. To elucidate the mechanism it will first be important to determine the intracellular localization of IRGT and to characterize the vesicles that usher IRGT molecules to the surface. This will be achieved by attempting to co-localize the glucose transporter vesicles with markers specific for endosomes and the trans Golgi reticulum. Secondly, it will be important to ascertain how the IRGT is targeted to the intracellular vesicles because this mechanism presumably constitutes the evolution of the translocation mechanism. The selective sorting of 3 very homologous glucose transporters (the insulin-regulatable, the HepG2 transporter and the liver transporter) will be examined following their expression in either an insulin-sensitive or a non-insulin sensitive cell type. Based upon the outcome of these experiments we shall attempt to identify specific sequence domains that may encode for the specific targeting of the IRGT. These studies may provide further understanding of the factors involved in hormone-regulated exocytosis of membrane proteins and thus contribute to the expanding body of knowledge concerning the communication between the interior and exterior of the cell.
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