Phorbol ester-mediated protein kinase C interaction with wild-type and COOH-terminal truncated insulin receptors.
The effects of 12-O-tetradecanoylphorbol-13-acetate (TPA) and insulin were compared in wild-type human insulin receptors (HIRc cells) and human insulin receptors lacking 43 COOH-terminal amino acid residues (HIR delta CT cells). TPA increased total phosphorylation of the wild-type insulin receptor and inhibited insulin-stimulated autophosphorylation by 32 +/- 10% in HIRc cells. TPA inhibited insulin-stimulated autophosphorylation by 46 +/- 14% in HIR delta CT cells and also caused a 65% decrease in basal phosphorylation. Insulin-stimulated tyrosine kinase activity for poly(Glu4/Tyr1) was inhibited by TPA in HIRc and HIR delta CT cells by 50 and 40%, respectively. TPA decreased insulin-stimulated glucose incorporation into glycogen by 50% in HIRc cells and to near basal levels in HIR delta CT cells; this inhibitory effect of TPA was reversed in both cell lines by staurosporine. In conclusion, 1) TPA-induced inhibition of insulin receptor tyrosine autophosphorylation was linked to concomitant inhibition of the biological effects of insulin in cells expressing either wild-type or COOH-terminal truncated insulin receptors; and 2) the inhibitory effects of TPA were not dependent upon phosphorylation of COOH-terminal residues and furthermore appeared to be independent of phosphorylation of any insulin receptor serine/threonine residues. These findings suggest a novel protein kinase C mechanism that results in altered insulin receptor function without increasing phosphorylation of the receptor.
Anderson
C M
CM
Department of Medicine, University of California San Diego School of Medicine, La Jolla 92093.
Olefsky
J M
JM
D000470:Alkaloids / Q000494:pharmacology; D000818:Animals; D002460:Cell Line; D002872:Chromosome Deletion; D005947:Glucose / Q000378:metabolism; D006003:Glycogen / Q000096:biosynthesis; D006801:Humans; D007328:Insulin / Q000378:metabolism / Q000494:pharmacology; D007700:Kinetics; D010766:Phosphorylation; D011493:Protein Kinase C / Q000378:metabolism*; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D051381:Rats; D011972:Receptor, Insulin / Q000235:genetics / Q000378:metabolism*; D016329:Sp1 Transcription Factor / Q000302:isolation & purification / Q000378:metabolism*; D019311:Staurosporine; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology*; D014162:Transfection
D000470:Alkaloids; D007328:Insulin; D016329:Sp1 Transcription Factor; D006003:Glycogen; D011505:Protein-Tyrosine Kinases; D011972:Receptor, Insulin; D011493:Protein Kinase C; D019311:Staurosporine; D005947:Glucose; D013755:Tetradecanoylphorbol Acetate