Interactions of protein kinase C with insulin signaling. Influence on GAP and Sos activities.
In this study, we investigated the influence of the protein kinase C (PKC)-dependent system upon the ability of insulin to stimulate p21(ras).GTP loading in 3T3-L1 adipocytes. Activation of PKC by 12-0-tetradecanoylphorbol-13-acetate (TPA) did not affect the basal amount of p21(ras).GTP but significantly reduced insulin-induced increases in p21(ras).GTP. This reduction was due to inhibition of the insulin's ability to stimulate guanine nucleotide exchange activity of Sos in cells incubated with 100 nM TPA for either 30 min or 3 h. TPA had no effect on basal activity of Sos. Depletion of PKC by an 18-h incubation with TPA or inhibition by bisindolylmaleimide resulted in profound inhibition of the insulin-induced p21(ras).GTP loading. In contrast to PKC activation, removal of PKC did not influence Sos activity but resulted in a 2-fold stimulation of GTPase activating protein (GAP). This effect of PKC depletion is unique to 3T3-L1 adipocytes and was not observed in either 3T3-L1 fibroblasts or Rat-1 fibroblasts. Thus, it appears that in 3T3-L1 adipocytes, PKC has a constitutive inhibitory effect on GAP that permits insulin to activate Sos and p21(ras). Removal of this inhibitory influence activates GAP and reduces insulin-stimulated p21(ras).GTP loading.
Schubert
C
C
Medical Research Service, Veterans Affairs Medical Center and the University of Colorado Health Sciences Center, Denver, Colorado 80220, USA.
Carel
K
K
DePaolo
D
D
Leitner
W
W
Draznin
B
B
D016475:3T3 Cells; D000818:Animals; D002478:Cells, Cultured; D020690:GTPase-Activating Proteins; D006160:Guanosine Triphosphate / Q000378:metabolism; D008565:Membrane Proteins / Q000502:physiology*; D051379:Mice; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000502:physiology*; D011506:Proteins / Q000378:metabolism; D016283:Proto-Oncogene Proteins p21(ras) / Q000502:physiology; D051381:Rats; D011972:Receptor, Insulin / Q000502:physiology*; D011994:Recombinant Proteins; D015290:Second Messenger Systems; D015398:Signal Transduction; D020664:Son of Sevenless Proteins; D020703:ras GTPase-Activating Proteins
D020690:GTPase-Activating Proteins; D008565:Membrane Proteins; D011506:Proteins; D011994:Recombinant Proteins; D020664:Son of Sevenless Proteins; D020703:ras GTPase-Activating Proteins; D006160:Guanosine Triphosphate; D011972:Receptor, Insulin; D011493:Protein Kinase C; D016283:Proto-Oncogene Proteins p21(ras)