Effect of insulin on farnesyltransferase activity in 3T3-L1 adipocytes.
Activation of p21(ras) by GTP loading is a critical step in a cascade of intracellular insulin signaling. Farnesylation of p21(ras) protein is an obligatory event that facilitates Ras migration to the plasma membrane and subsequent activation. Farnesyltransferase (FTase) is a ubiquitous enzyme that catalyzes the lipid modification of p21(ras) by the addition of farnesyl to the C-terminal "CAAX" motif. In vitro and in vivo FTase activities were studied in 3T3-L1 adipocytes in response to insulin challenge. Insulin exerted a biphasic stimulatory effect on FTase activity measured in vitro with a 31% increase at 5 min and a 130% increase at 60 min. Insulin-stimulated farnesylation of p21(ras) pools in vivo correlated with FTase activity seen in vitro by displaying an increase in farnesylated p21(ras) from 40% of total cellular Ras in control cells to 63% by 5 min and 80% by 60 min (p < 0.05) in insulin-treated cells. Insulin challenge of 3T3-L1 adipocytes increased incorporation of tritiated mevalonic acid in p21(ras) in a dose-dependent manner and stimulated a 2-fold increase in phosphorylation of the alpha-subunit of FTase at 5 min and a 4-fold increase at 60 min.
Medical Research Service and the Department of Medicine, Veterans Affairs Medical Center and the University of Colorado Health Sciences Center, Denver, Colorado 80220, USA. BDraznin@sembilan.UCHSC.edu
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D016475:3T3 Cells; D017667:Adipocytes / Q000201:enzymology*; D019883:Alkyl and Aryl Transferases; D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D002454:Cell Differentiation; D002462:Cell Membrane / Q000378:metabolism; D051231:Farnesyltranstransferase; D007328:Insulin / Q000494:pharmacology*; D007700:Kinetics; D046911:Macromolecular Substances; D008798:Mevalonic Acid / Q000378:metabolism; D051379:Mice; D010766:Phosphorylation; D017368:Protein Prenylation; D016283:Proto-Oncogene Proteins p21(ras) / Q000302:isolation & purification / Q000378:metabolism*; D013997:Time Factors; D014166:Transferases / Q000378:metabolism*
D007328:Insulin; D046911:Macromolecular Substances; D014166:Transferases; D019883:Alkyl and Aryl Transferases; D051231:Farnesyltranstransferase; D016283:Proto-Oncogene Proteins p21(ras); D008798:Mevalonic Acid