Insulin stimulates mitogen-activated protein kinase by a Ras-independent pathway in 3T3-L1 adipocytes.
To characterize tissue-specific differences in insulin signaling, we compared the mechanisms of mitogen-activated protein (MAP) kinase activation by insulin in the mitogenically active 3T3-L1 fibroblasts with the metabolically active 3T3-L1 adipocytes. In both cell lines, insulin significantly increased p21(ras).GTP loading (1.5-2-fold) and MAP kinase activity (5-8-fold). Inhibition of Ras farnesylation with lovastatin blocked activation of p21(ras) and Raf-1 kinase in both 3T3-L1 fibroblasts and 3T3-L1 adipocytes. In 3T3-L1 fibroblasts, this was accompanied by an inhibition of the stimulatory effect of insulin on MAP kinase. In contrast, in 3T3-L1 adipocytes, despite an inhibition of activation of p21(ras) and Raf-1 by lovastatin, insulin continued to stimulate MAP kinase activity. Fractionation of the cell lysates on the FPLC Mono-Q column revealed that lovastatin inhibited insulin stimulation of ERK2 (and, to a lesser extent, ERK1) in 3T3-L1 fibroblasts and had no effect on the insulin-stimulated ERK2 in 3T3-L1 adipocytes. These results demonstrate an important distinction between the mechanism of insulin signaling in the metabolically and mitogenically active cells. Insulin activates MAP kinase by the Ras-dependent pathway in the 3T3-L1 fibroblasts and by the Ras-independent pathway in the 3T3-L1 adipocytes.
Carel
K
K
Medical Research Service, Veterans Affairs Medical Center, Denver, Colorado 80220, USA.
Kummer
J L
JL
Schubert
C
C
Leitner
W
W
Heidenreich
K A
KA
Draznin
B
B
D017667:Adipocytes / Q000201:enzymology*; D019883:Alkyl and Aryl Transferases; D000818:Animals; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism*; D004789:Enzyme Activation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005204:Farnesol / Q000031:analogs & derivatives / Q000494:pharmacology; D051231:Farnesyltranstransferase; D006160:Guanosine Triphosphate / Q000378:metabolism; D019161:Hydroxymethylglutaryl-CoA Reductase Inhibitors; D007328:Insulin / Q000494:pharmacology*; D008148:Lovastatin / Q000494:pharmacology; D051379:Mice; D063065:Organophosphonates; D009943:Organophosphorus Compounds / Q000494:pharmacology; D011493:Protein Kinase C / Q000502:physiology; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D019908:Proto-Oncogene Proteins c-raf; D016283:Proto-Oncogene Proteins p21(ras) / Q000502:physiology; D051381:Rats; D015398:Signal Transduction; D014166:Transferases / Q000037:antagonists & inhibitors
C080570:(alpha-hydroxyfarnesyl)phosphonic acid; D004791:Enzyme Inhibitors; D019161:Hydroxymethylglutaryl-CoA Reductase Inhibitors; D007328:Insulin; D063065:Organophosphonates; D009943:Organophosphorus Compounds; D011518:Proto-Oncogene Proteins; D005204:Farnesol; D006160:Guanosine Triphosphate; D008148:Lovastatin; D014166:Transferases; D019883:Alkyl and Aryl Transferases; D051231:Farnesyltranstransferase; D017346:Protein Serine-Threonine Kinases; D019908:Proto-Oncogene Proteins c-raf; D011493:Protein Kinase C; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D016283:Proto-Oncogene Proteins p21(ras)