Rab4 is phosphorylated by the insulin-activated extracellular-signal-regulated kinase ERK1.
Rab4, a low-molecular-mass GTP-binding protein, is associated with vesicles containing Glut 4 in adipocytes. Following insulin stimulation, the translocation of Glut 4 to the plasma membrane is associated with the movement of Rab4 to the cytosol. The same modifications are induced by the phosphatase inhibitor, okadaic acid. To establish a possible role for phosphorylation in Rab4 cycling, we searched for insulin-stimulated cytosolic kinase(s) which could phosphorylate Rab4. In 3T3-L1 adipocytes, insulin induced a rapid and transient activation of cytosolic kinase(s), which phosphorylated Rab4 in vitro. At least part of the Rab4 phosphorylation can be accounted for by ERK (extracellular-signal-regulated kinases) since immunopurified ERK1 from insulin-stimulated cells phosphorylated Rab4 with a comparable time-course. Both with cytosolic extracts and immunopurified ERK1, only serine residues were phosphorylated on Rab4. The phosphorylation site was localized in the C-terminus of the molecule, and occurred very probably on Ser196. These results indicate that Rab4 is an in vitro substrate for ERK, and suggest that the insulin-induced movement of Rab4 from the Glut-4-containing vesicles to the cytosol could result from phosphorylation of Rab4 by ERK.
Cormont
M
M
INSERM U 145, Faculté de Médecine, Nice, France.
Tanti
J F
JF
Zahraoui
A
A
Van Obberghen
E
E
Le Marchand-Brustel
Y
Y
D016475:3T3 Cells; D017667:Adipocytes / Q000378:metabolism; D000595:Amino Acid Sequence; D000818:Animals; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism*; D003600:Cytosol / Q000201:enzymology; D004591:Electrophoresis, Polyacrylamide Gel; D004988:Ethers, Cyclic / Q000494:pharmacology*; D019204:GTP-Binding Proteins / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D007328:Insulin / Q000494:pharmacology*; D051379:Mice; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases; D008969:Molecular Sequence Data; D008970:Molecular Weight; D019319:Okadaic Acid; D010766:Phosphorylation; D012694:Serine / Q000378:metabolism; D020695:rab4 GTP-Binding Proteins
D004988:Ethers, Cyclic; D007328:Insulin; D019319:Okadaic Acid; D012694:Serine; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases; D019204:GTP-Binding Proteins; D020695:rab4 GTP-Binding Proteins