(taken from the application) Diabetes is a major health problem affecting millions of Americans. In most cases, it is due to the impaired ability of insulin to stimulate glucose uptake. Understanding the pathogenesis of diabetes is essential to its prevention and management. Therefore, the goal of the original K08 project (DK02540) is to characterize the molecular mechanism of how insulin stimulates glucose uptake. The stimulated uptake is predominantly mediated by the glucose transporter GLUT4. In the absence of insulin, GLUT4 is sequestered intracellular in """"""""GLUT4 vesicles."""""""" These vesicles also sequester a transmembrane protein insulin-responsive aminopeptidase (IRAP). Upon insulin stimulation, both GLUT4 and IRAP are recruited to the plasma membrane, where GLUT4 can import extracellular glucose. The similarity in the targeting of GLUT4 and IRAP suggests that the same machinery that responds to insulin signaling regulates their translocation. To uncover candidate components of the targeting machinery for IRAP/GLUT4, the applicant has identified a novel family of proteins that specifically bind to IRAP and, by inference, interact with GLUT4 indirectly. Interestingly, both IRAP-binding proteins are phosphorylated stoichiometrically upon insulin stimulation. To understand the physiological role of these IRAP-binding proteins, the applicant proposes to disrupt their interaction with IRAP in vivo. If this affects insulin regulated GLUT4/IRAP targeting, then the role of the IRAP-binding proteins can be inferred. The applicant has shown that both IRAP-binding proteins have an intrinsic poly(ADP-ribose) polymerase activity. Whether this activity is regulated by insulin-stimulated phosphorylation will be examined. The proposed experiments may help uncover poly(ADP-ribosyl)ation as a novel mechanism of signal transduction. More importantly, they may help define the molecular mechanism of IRAP/GLUT4 trafficking and the pathogenesis of insulin resistance.
