Overexpression of a constitutively active form of phosphatidylinositol 3-kinase is sufficient to promote Glut 4 translocation in adipocytes.
Insulin stimulates glucose transport in its target cells by recruiting the glucose transporter Glut 4 from an intracellular compartment to the cell surface. Previous studies have indicated that phosphatidylinositol 3-kinase (PI 3-kinase) is a necessary step in this insulin action. We have investigated whether PI 3-kinase activation is sufficient to promote Glut 4 translocation in transiently transfected adipocytes. Rat adipose cells were cotransfected with expression vectors that allowed transient expression of epitope-tagged Glut 4 and a constitutively active form of PI 3-kinase (p110*). The expression of p110* induced the appearance of epitope-tagged Glut 4 at the cell surface at a level similar to that obtained after insulin treatment, whereas a kinase-dead version of p110* had no effect. The p110* effect was observed over a wide range of the transfected cDNA. When subcellular fractionation of adipocytes was performed, p110* was found, similar to the endogenous PI 3-kinase, enriched in the low density microsomal compartment, which also contains the Glut 4 vesicles. This could suggest that a specific localization of PI 3-kinase in this compartment is required for the action on Glut 4. The observations made with PI 3-kinase are in contrast with those seen with the MAP kinase cascade. Indeed, a constitutively active form of MAP kinase kinase had no effect on Glut 4 translocation in basal conditions. At the highest degree of expression, the constitutively active form of MAP kinase kinase slightly inhibited the insulin stimulation of Glut 4 translocation. Taken together, our results indicate that Glut 4 translocation can be efficiently promoted by an active form of PI 3-kinase but not by the activation of the MAP kinase pathway.
Tanti
J F
JF
INSERM U 145, Faculté de Médecine, Avenue de Valombrose 06107, Nice Cedex 02, France.
Grémeaux
T
T
Grillo
S
S
Calleja
V
V
Klippel
A
A
Williams
L T
LT
Van Obberghen
E
E
Le Marchand-Brustel
Y
Y
D017667:Adipocytes / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism; D002478:Cells, Cultured; D004822:Epididymis; D017930:Genes, Reporter; D051275:Glucose Transporter Type 4; D007328:Insulin / Q000494:pharmacology; D008156:Luciferases / Q000096:biosynthesis; D008297:Male; D008861:Microsomes / Q000378:metabolism; D020929:Mitogen-Activated Protein Kinase Kinases; D008969:Molecular Sequence Data; D009004:Monosaccharide Transport Proteins / Q000096:biosynthesis / Q000378:metabolism*; D009124:Muscle Proteins; D019869:Phosphatidylinositol 3-Kinases; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000096:biosynthesis / Q000378:metabolism*; D011494:Protein Kinases / Q000378:metabolism; D011499:Protein Processing, Post-Translational / Q000187:drug effects; D051381:Rats; D017208:Rats, Wistar; D011993:Recombinant Fusion Proteins / Q000096:biosynthesis / Q000378:metabolism; D016324:Sequence Tagged Sites; D013347:Subcellular Fractions / Q000378:metabolism; D014162:Transfection
D051275:Glucose Transporter Type 4; D007328:Insulin; D009004:Monosaccharide Transport Proteins; D009124:Muscle Proteins; D011993:Recombinant Fusion Proteins; C495694:Slc2a4 protein, rat; D008156:Luciferases; D011494:Protein Kinases; D019869:Phosphatidylinositol 3-Kinases; D017853:Phosphotransferases (Alcohol Group Acceptor); D017871:Calcium-Calmodulin-Dependent Protein Kinases; D020929:Mitogen-Activated Protein Kinase Kinases