Insulin plays an important role in glucose homeostasis by stimulating muscle and fat cells to take up glucose. Insulin does so by activating a signaling pathway that culminates in the recruitment of the glucose transporter GLUT4 from an intracellular compartment to the cell surface. This pathway apparently involves the activation of phosphatidylinositol 3-kinase (PI 3-kinase). However, the signaling target of PI 3-kinase remains unclear, and the effector machinery that translocates GLUT4 remains elusive. This insulin signaling pathway has significant medical implications, since its impairment may contribute to the development of obesity, diabetes mellitus, and polycystic ovarian syndrome. The long-term objective of the applicant is to understand in molecular terms how insulin works. Such knowledge may engender new treatments for the aforementioned diseases. The applicant proposes to address the following questions in cultured fat cells: 1. Does insulin-induced GLUT4 translocation involve the activation by PI 3-kinase of its proposed targets, such as protein kinase B and isoforms of protein kinase C? The role of these kineses will be investigated by activating or blocking them and observing the resultant effect on GLUT4 translocation. 2. Can insulin-induced GLUT4 translocation be explained by a putative intracellular GLUT4 chaperon? This chaperon would serve to anchor GLUT4 intracellularly in the absence of insulin. In the presence of insulin, the chaperon would release GLUT4 and allow it to follow the exocytic flow toward cell surface. To clone this putative chaperon, two strategies are proposed. 3. Does insulin-induced GLUT4 translocation involve sorting of GLUT4 into clathrin-coated vesicles by assembly proteins (APs)? APs interact with other proteins bearing similar sorting motifs as GLUT4, and sort them into clathrin-coated vesicles. These vesicles have been proposed to mediate GLUT4 translocation. The role of APs in GLUT4 trafficking will be investigated by determining if APs interact with GLUT4 and if the interaction is modulated by insulin.
| Sbodio, Juan I; Lodish, Harvey F; Chi, Nai-Wen (2002) Tankyrase-2 oligomerizes with tankyrase-1 and binds to both TRF1 (telomere-repeat-binding factor 1) and IRAP (insulin-responsive aminopeptidase). Biochem J 361:451-9 |
| Sbodio, Juan I; Chi, Nai-Wen (2002) Identification of a tankyrase-binding motif shared by IRAP, TAB182, and human TRF1 but not mouse TRF1. NuMA contains this RXXPDG motif and is a novel tankyrase partner. J Biol Chem 277:31887-92 |
| Chi, N W; Lodish, H F (2000) Tankyrase is a golgi-associated mitogen-activated protein kinase substrate that interacts with IRAP in GLUT4 vesicles. J Biol Chem 275:38437-44 |
