The uptake of glucose into most eucaryotic cells is accomplished by sterio-specific facilitated transport. A major effect of insulin on the disposal of blood sugar in humans involves activation of transport in insulin-responsive target tissues. This is mediated, at least in part, by the recruitment of latent hexose carriers to the cell surface. Glucose flux is also modulated by dietary factors, obesity and oncogenic transformation. There is increasing evidence that the peripheral insulin resistance observed in most forms of diabetes mellitus is caused by disturbances in hormone-stimulated glucose transport that are a result of abnormal levels of circulating insulin and/or glucose. It is therefore of significant scientific and clinical intewrest to understand the precise biochemical mechanisms by which insulin and glucose starvation induce accelerated glucose transport. With the availability if a cDNA encoding the rat brain glucose transporter, it is now possible to introduce specific changes into the coding region of the protein, transfer it into heterologous cells, and study how those alterations affect the response to insulin and hexose starvation. Oligonucleotides encoding peptides for which high titer antisera are available will be inserted into the transporter at various locations which are likely to reside on the extracellular or cytoplasmic surface of the plasma membrane. This should allow the transporter to be recognized immunologically after transfection into fibroblast or adipocyte cell lines. Then, deletions will be systematically introduced into the coding region of the transporter prior to DNA mediated gene transfer, and the transfectants evaluated for preservation of sensitivity of the foreign protein to regulation by insulin and glucose starvation. In this way, it should be possible to test the hypothesis that there are discrete, identifiable regions which confer on the transporter the regulated phenotype. Any sequences which appear to contain information for modulated expression will be tested for their ability to transfer regulation to another integral membrane protein.
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