Activated phosphatidylinositol 3-kinase is sufficient to mediate actin rearrangement and GLUT4 translocation in 3T3-L1 adipocytes.
Insulin stimulation of 3T3-L1 adipocytes causes rapid translocation of actin and the GLUT4 glucose transporter to the plasma membrane. Both processes depend on the activity of phosphatidylinositol 3-kinase. Using single cell microinjection, we have transiently expressed a constitutively activated mutant of phosphatidylinositol 3-kinase, p110*, in 3T3-L1 adipocytes. Fluorescent detection of GLUT4 protein and actin within these cells demonstrates that expression of p110* is sufficient to cause translocation of GLUT4 to the plasma membrane and the formation of actin membrane ruffles. These effects are inhibited by wortmannin in the p110*-expressing cells, indicating that the phosphatidylinositol 3-kinase activity of the protein is required. Overexpression of an identical protein containing a point mutation in the kinase domain, p110*Deltakin, was incapable of mediating either action, confirming that neither the microinjection process nor a nonspecific effect of the protein was responsible for the observed effects. These data suggest that although insulin is capable of inducing numerous signaling pathways, the isolated activation of phosphatidylinositol 3-kinase can initiate the signaling cascade leading to both actin rearrangement and GLUT4 translocation in the absence of insulin stimulation.
Martin
S S
SS
Department of Medicine, Veterans Administration Medical Center, University of California, San Diego, La Jolla, California 92093, USA.
Haruta
T
T
Morris
A J
AJ
Klippel
A
A
Williams
L T
LT
Olefsky
J M
JM
D016475:3T3 Cells; D000199:Actins / Q000378:metabolism*; D017667:Adipocytes / Q000378:metabolism*; D000818:Animals; D001692:Biological Transport; D002451:Cell Compartmentation; D002462:Cell Membrane / Q000378:metabolism / Q000648:ultrastructure; D004789:Enzyme Activation; D005822:Genetic Vectors; D051275:Glucose Transporter Type 4; D051379:Mice; D008845:Microinjections; D008856:Microscopy, Fluorescence; D009004:Monosaccharide Transport Proteins / Q000378:metabolism*; D009124:Muscle Proteins; D019869:Phosphatidylinositol 3-Kinases; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000235:genetics / Q000378:metabolism*; D011994:Recombinant Proteins / Q000378:metabolism
D000199:Actins; D051275:Glucose Transporter Type 4; D009004:Monosaccharide Transport Proteins; D009124:Muscle Proteins; D011994:Recombinant Proteins; C495693:Slc2a4 protein, mouse; D019869:Phosphatidylinositol 3-Kinases; D017853:Phosphotransferases (Alcohol Group Acceptor)