Primary sites of actions of staurosporine and H-7 in the cascade of insulin action to glucose transport in rat adipocytes

Section: Resultsmentioning

confidence: 99%

Direct Interaction of Rab4 with Syntaxin 4

Lü

Omata

Kojima

et al. 2001

“…Several studies have suggested that the regulation of glucose transport in cells is a multistep process (22)(23)(24)(25)(26)(27). The best studied of these steps is the translocation of Glut4 glucose transporters from an intracellular pool or low density membranes to the plasma membrane.…”

Section: Fig 4 Glucose Transporter Translocation and Rad Localizationmentioning

confidence: 99%

Overexpression of Rad Inhibits Glucose Uptake in Cultured Muscle and Fat Cells

Moyers

Bilan

Reynet

et al. 1996

117

Rad is a Ras-like GTPase that was isolated by subtraction cloning of human muscle and shown to have increased expression in some individuals with Type II diabetes. To ascertain the potential role of Rad in insulin-mediated signaling, we have overexpressed Rad in myocyte and adipocyte cell lines. Expression of Rad resulted in a 50-90% reduction in insulin-stimulated 2-deoxyglucose glucose uptake in C2C12 murine myotubes, L6 rat myotubes, and 3T3-L1 adipocytes and a 25% reduction in 3-O-methylglucose uptake in 3T3-L1 adipocytes. This occurred despite unaltered levels of glucose transporter expression, with no detectable change in Glut4 translocation and with no alteration in insulin receptor or substrate phosphorylation or phosphatidylinositol 3-kinase activity. These data indicate that Rad is a negative regulator of glucose uptake and that this effect may be due to a decrease in the intrinsic activity of the transporter molecules, rather than an effect on the translocation of Glut4.

“…Although the precise mechanism(s) of insulin-induced GLUT4 redistribution is still unclear, several lines of evidence indicate that GTP-binding protein(s) is involved in the insulin action. Thus, nonhydrolyzable GTP analogues induce GLUT4 translocation (4,5) and stimulate glucose transport (6,7) in permeabilized adipocytes. Furthermore, by dissecting the recycling pathway of GLUT4 into exocytosis and endocytosis, we have demonstrated recently that GTP␥S 1 stimulates exocytotic fusion of GLUT4-containing vesicles, whereas the nucleotide inhibits endocytosis of the glucose transporter (8).…”

mentioning

confidence: 99%

A Synthetic Peptide Corresponding to the Rab4 Hypervariable Carboxyl-terminal Domain Inhibits Insulin Action on Glucose Transport in Rat Adipocytes

Shibata

Omata

Suzuki

et al. 1996

The present study was conducted to examine the involvement of Rab4, a low molecular weight GTP-binding protein, in the action of insulin on glucose transport. A synthetic peptide corresponding to the Rab4 hypervariable carboxyl-terminal domain, Rab4-(191-210), was successfully transferred into rat adipocytes by electroporation and inhibited insulin-stimulated glucose transport by about 50% without affecting the basal transport activity. In contrast, synthetic peptides corresponding to the Rab3C and Rab3D carboxyl-terminal hypervariable domain had little effect on insulin action on glucose transport. The Rab4-(191-210) peptide also reduced insulin-induced GLUT4 translocation from the intracellular pool to the plasma membrane. Furthermore, the Rab4-(191-210) peptide reduced both insulin-induced glucose transport and GLUT4 translocation in the presence of a major histocompatibility complex class I antigen-derived peptide, D k -(62-85), which is a potent inhibitor of GLUT4 internalization, suggesting that the peptide inhibited exocytotic recruitment of GLUT4-containing vesicles. The Rab4-(191-210) peptide also inhibited GTP␥S-stimulated glucose transport. In addition, insulin-stimulated glucose transport was inhibited by the addition of anti-Rab4 antibody. These results suggest that Rab4 protein plays a crucial role in insulin action on GLUT4 translocation, especially in exocytotic recruitment by the hormone of the glucose transporter to the plasma membrane from the intracellular retention pool.Insulin stimulates glucose uptake in skeletal/cardiac muscles and adipocytes by promotion of translocation of glucose transporter isoform, GLUT4, from the intracellular pool to the plasma membrane (1-3). Although the precise mechanism(s) of insulin-induced GLUT4 redistribution is still unclear, several lines of evidence indicate that GTP-binding protein(s) is involved in the insulin action. Thus, nonhydrolyzable GTP analogues induce GLUT4 translocation (4, 5) and stimulate glucose transport (6, 7) in permeabilized adipocytes. Furthermore, by dissecting the recycling pathway of GLUT4 into exocytosis and endocytosis, we have demonstrated recently that GTP␥S 1 stimulates exocytotic fusion of GLUT4-containing vesicles, whereas the nucleotide inhibits endocytosis of the glucose transporter (8). Our previous study also indicated that the number of GLUT4 molecules in recycling pool is not large in the basal state and the rate-limiting step of insulin-induced redistribution of GLUT4 is the exocytotic recruitment from the intracellular retention pool to the plasma membrane (8).The Rab family proteins of Ras-related small GTP-binding proteins have been implicated in regulation of intracellular vesicular traffic (9). Given that exocytotic movement of vesicles is regulated by the Rab family protein(s), GTP␥S may promote exocytosis of GLUT4-containing vesicles by stimulation of the Rab protein(s) associated with the vesicles, although other candidates (e.g. trimeric GTP-binding proteins) cannot be ruled out. In this regard, Baldini et al....