Expression of a prenylation-deficient Rab4 interferes with propagation of insulin signaling through insulin receptor substrate-1.
Rab proteins are small GTP-binding proteins of the Ras superfamily that function in the regulation of vesicle transport processes. The Rab4 isoform has been implicated in insulin action. For instance, overexpression of a prenylation-deficient form of Rab4 has been shown to inhibit insulin-dependent GLUT4 translocation. Other steps affected by Rab4 in the cascade of events resulting from insulin receptor activation have not been elucidated. In the present studies, we measured effects on insulin-signaling proteins in 3T3-L1 adipocytes transiently expressing cytoplasmic forms of Rab4 and Rab5. Expression of a mutant Rab4 lacking a prenylation site resulted in reduced insulin-dependent phosphorylation ofcytoplasmic and internal membrane-associated insulin receptor substrate-1, leading to decreased insulin receptor substrate-1-associated phosphatidylinositol 3'-OH kinase activation and decreased Akt activation. These effects were not observed upon introduction of a similar mutant form of Rab5. These data indicate that Rab4 or a Rab4-associated protein is involved at one or more steps in propagating the insulin signal, in addition to any role it may play in the regulation of GLUT4 vesicle translocation. Our results support models of insulin signaling in which regulation of internal membrane trafficking plays a role in transduction of the insulin signal.
Knight
J B
JB
Department of Biochemistry and Molecular Biology, University of Oklahoma Health Sciences Center, Oklahoma City 73190, USA.
Cao
K T
KT
Gibson
G V
GV
Olson
A L
AL
D016475:3T3 Cells; D017667:Adipocytes / Q000378:metabolism; D000818:Animals; D015153:Blotting, Western; D002462:Cell Membrane / Q000502:physiology; D004591:Electrophoresis, Polyacrylamide Gel; D051275:Glucose Transporter Type 4; D007328:Insulin / Q000502:physiology*; D055504:Insulin Receptor Substrate Proteins; D051379:Mice; D009004:Monosaccharide Transport Proteins / Q000378:metabolism; D009124:Muscle Proteins; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010750:Phosphoproteins / Q000235:genetics / Q000502:physiology*; D011233:Precipitin Tests; D017368:Protein Prenylation / Q000235:genetics*; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D011972:Receptor, Insulin / Q000235:genetics / Q000502:physiology*; D015398:Signal Transduction / Q000235:genetics / Q000502:physiology*; D013347:Subcellular Fractions / Q000201:enzymology; D014616:Vaccinia virus / Q000235:genetics; D020695:rab4 GTP-Binding Proteins / Q000096:biosynthesis* / Q000235:genetics
D051275:Glucose Transporter Type 4; D007328:Insulin; D055504:Insulin Receptor Substrate Proteins; D009004:Monosaccharide Transport Proteins; D009124:Muscle Proteins; D019869:Phosphatidylinositol 3-Kinases; D010750:Phosphoproteins; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D011972:Receptor, Insulin; D020695:rab4 GTP-Binding Proteins; C526295:Irs1 protein, mouse; C495693:Slc2a4 protein, mouse