MEK inhibitors impair insulin-stimulated glucose uptake in 3T3-L1 adipocytes.
In 3T3-L1 adipocytes, insulin activates three major signaling cascades, the phosphoinositide 3-kinase (PI3K) pathway, the Cbl pathway, and the mitogen-activated protein kinase (MAPK) pathway. Although PI3K and Cbl mediate insulin-stimulated glucose uptake by promoting the translocation of the insulin-responsive glucose transporter (GLUT4) to the plasma membrane, the MAPK pathway does not have an established role in insulin-stimulated glucose uptake. We demonstrate in this report that PI3K inhibitors also inhibit the MAPK pathway. To investigate the role of the MAPK pathway separately from that of the PI3K pathway in insulin-stimulated glucose uptake, we used two specific inhibitors of MAPK kinase (MEK) activity, PD-98059 and U-0126, which reduced insulin-stimulated glucose uptake by approximately 33 and 50%, respectively. Neither MEK inhibitor affected the activation of Akt or PKCzeta/lambda, downstream signaling molecules in the PI3K pathway. Inhibition of MEK with U-0126 did not prevent GLUT4 from translocating to the plasma membrane, nor did it inhibit the subsequent docking and fusion of GLUT4-myc with the plasma membrane. MEK inhibitors affected glucose transport mediated by GLUT4 but not GLUT1. Importantly, the presence of MEK inhibitors only at the time of the transport assay markedly impaired both insulin-stimulated glucose uptake and MAPK signaling. Conversely, removal of MEK inhibitors before the transport assay restored glucose uptake and MAPK signaling. Collectively, our studies suggest a possible role for MEK in the activation of GLUT4.
Harmon
Anne W
AW
Department of Nutrition, University of North Carolina School of Public Health, Chapel Hill 27599, USA.
Paul
David S
DS
Patel
Yashomati M
YM
D016475:3T3 Cells; D017667:Adipocytes / Q000187:drug effects / Q000378:metabolism*; D000818:Animals; D015153:Blotting, Western; D002462:Cell Membrane / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D005455:Fluorescent Antibody Technique; D016259:Genes, myc / Q000235:genetics; D005947:Glucose / Q000378:metabolism*; D051275:Glucose Transporter Type 4; D007004:Hypoglycemic Agents / Q000494:pharmacology*; D007202:Indicators and Reagents; D007328:Insulin / Q000494:pharmacology*; D051379:Mice; D020929:Mitogen-Activated Protein Kinase Kinases / Q000037:antagonists & inhibitors*; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D009004:Monosaccharide Transport Proteins / Q000378:metabolism; D009124:Muscle Proteins / Q000378:metabolism; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010766:Phosphorylation; D015398:Signal Transduction / Q000187:drug effects; D048051:p38 Mitogen-Activated Protein Kinases
D004791:Enzyme Inhibitors; D051275:Glucose Transporter Type 4; D007004:Hypoglycemic Agents; D007202:Indicators and Reagents; D007328:Insulin; D009004:Monosaccharide Transport Proteins; D009124:Muscle Proteins; D000081082:Phosphoinositide-3 Kinase Inhibitors; C495693:Slc2a4 protein, mouse; D020928:Mitogen-Activated Protein Kinases; D048051:p38 Mitogen-Activated Protein Kinases; D020929:Mitogen-Activated Protein Kinase Kinases; D005947:Glucose