Insulin signals to prenyltransferases via the Shc branch of intracellular signaling.
We assessed the roles of insulin receptor substrate-1 (IRS-1) and Shc in insulin action on farnesyltransferase (FTase) and geranylgeranyltransferase I (GGTase I) using Chinese hamster ovary (CHO) cells that overexpress wild-type human insulin receptors (CHO-hIR-WT) or mutant insulin receptors lacking the NPEY domain (CHO-DeltaNPEY) or 3T3-L1 fibroblasts transfected with adenoviruses that express the PTB or SAIN domain of IRS-1 and Shc, the pleckstrin homology (PH) domain of IRS-1, or the Src homology 2 (SH2) domain of Shc. Insulin promoted phosphorylation of the alpha-subunit of FTase and GGTase I in CHO-hIR-WT cells, but was without effect in CHO-DeltaNPEY cells. Insulin increased FTase and GGTase I activities and the amounts of prenylated Ras and RhoA proteins in CHO-hIR-WT (but not CHO-DeltaNPEY) cells. Overexpression of the PTB or SAIN domain of IRS-1 (which blocked both IRS-1 and Shc signaling) prevented insulin-stimulated phosphorylation of the FTase and GGTase I alpha-subunit activation of FTase and GGTase I and subsequent increases in prenylated Ras and RhoA proteins. In contrast, overexpression of the IRS-1 PH domain, which impairs IRS-1 (but not Shc) signaling, did not alter insulin action on the prenyltransferases, but completely inhibited the insulin effect on the phosphorylation of IRS-1 and on the activation of phosphatidylinositol 3-kinase and Akt. Finally, overexpression of the Shc SH2 domain completely blocked the insulin effect on FTase and GGTase I activities without interfering with insulin signaling to MAPK. These data suggest that insulin signaling from its receptor to the prenyltransferases FTase and GGTase I is mediated by the Shc pathway, but not the IRS-1/phosphatidylinositol 3-kinase pathway. Shc-mediated insulin signaling to MAPK may be necessary (but not sufficient) for activation of prenyltransferase activity. An additional pathway involving the Shc SH2 domain may be necessary to mediate the insulin effect on FTase and GGTase I.
Veterans Affairs Medical Center Research Service and the Department of Medicine, University of Colorado Health Sciences Center, Denver, Colorado 80220, USA.
M L
ML
Goalstone
J W
JW
Leitner
P
P
Berhanu
P M
PM
Sharma
J M
JM
Olefsky
B
B
Draznin
D016475:3T3 Cells; D048868:Adaptor Proteins, Signal Transducing; D033942:Adaptor Proteins, Vesicular Transport; D000256:Adenoviridae; D019883:Alkyl and Aryl Transferases / Q000378:metabolism*; D000818:Animals; D016466:CHO Cells; D006224:Cricetinae; D051231:Farnesyltranstransferase; D051380:GRB2 Adaptor Protein; D006801:Humans; D007328:Insulin / Q000494:pharmacology*; D055504:Insulin Receptor Substrate Proteins; D007700:Kinetics; D051379:Mice; D010750:Phosphoproteins / Q000378:metabolism; D010766:Phosphorylation; D017368:Protein Prenylation; D021122:Protein Subunits; D011506:Proteins / Q000378:metabolism*; D011972:Receptor, Insulin / Q000235:genetics / Q000502:physiology*; D011994:Recombinant Proteins / Q000378:metabolism; D055765:Shc Signaling Adaptor Proteins; D000071425:Src Homology 2 Domain-Containing, Transforming Protein 1; D014162:Transfection; D018909:src Homology Domains
D048868:Adaptor Proteins, Signal Transducing; D033942:Adaptor Proteins, Vesicular Transport; D051380:GRB2 Adaptor Protein; C495948:GRB2 protein, human; C495949:Grb2 protein, mouse; C526292:IRS1 protein, human; D007328:Insulin; D055504:Insulin Receptor Substrate Proteins; C526295:Irs1 protein, mouse; D010750:Phosphoproteins; D021122:Protein Subunits; D011506:Proteins; D011994:Recombinant Proteins; C528024:SHC1 protein, human; D055765:Shc Signaling Adaptor Proteins; C528034:Shc1 protein, mouse; D000071425:Src Homology 2 Domain-Containing, Transforming Protein 1; D019883:Alkyl and Aryl Transferases; C083291:geranylgeranyltransferase type-I; D051231:Farnesyltranstransferase; D011972:Receptor, Insulin