Glucose is a primary and essential energy source for humans. It is broken down from complex carbohydrates in the diet and absorbed across the gut epithelium into the blood stream. Glucose homeostasis is important as hyperglycermia causes damage of pancreatic and peripheral cells. In response to a meal glucose is principally taken up by fat and muscle tissues and this response is activated by insulin release from pancreatic beta cells. Insulin stimulates the translocation of GLUT4 from the intracellular storage vesicles to the plasma membrane in fat and muscle cells. Although many proteins have been implicated in this process, the key insulin-regulated substrate has not been determined yet. In the present study, the phosphoserine/threonine binding protein 14-3-3 was used as a tool to affinity-purify insulin-stimulated phosphoproteins from 3T3-L1 adipocytes. By using mass spectrometry 38 proteins were identified, reflecting the important role of 14-3-3 in mediating many insulin-regulated processes. Among the potential phosphoproteins was Myosin 1C (Myo1c), an actin-associated molecular motor, which has previously been implicated in insulin-stimulated GLUT4 trafficking in adipocytes. I showed that insulin stimulates the activation of CaMKII which phosphorylates Myo1c at S701 in a Ca2+/PI3K-dependent manner. Myo1c phosphorylation induced its interaction with 14-3-3-proteins, reduced calmodulin-binding and stimulated its in vitro ATPase activity. Insulin-dependent stimulation of Myo1c phosphorylation and its ATPase activity were both required for GLUT4 translocation. By using yeast two-hybrid techniques, I identified a candidate ligand of the Myo1c tail, Armcx5, and demonstrated the in vivo interaction in 3T3-L1 adipocytes. The siRNA-mediated knockdown of Armcx5 inhibited insulin-stimulated glucose uptake and GLUT4 translocation. These results suggest that the regulation of Myo1c and its ligand Armcx5 are essential in insulin-regulated GLUT4 trafficking, possibly playing a key role in vesicle fusion.
| Identifer | oai:union.ndltd.org:ADTP/258517 |
| Date | January 2009 |
| Creators | Yip, Ming Fai Freddy, Biotechnology & Biomolecular Sciences, Faculty of Science, UNSW |
| Publisher | Publisher:University of New South Wales. Biotechnology & Biomolecular Sciences |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | http://unsworks.unsw.edu.au/copyright, http://unsworks.unsw.edu.au/copyright |
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