Activated protein kinase C binds to intracellular receptors in rat hepatocytes.
The aim of this study was to identify in rat hepatocytes cellular polypeptides that bind protein kinase C (PKC) and may influence its activity and its compartmentation. At least seven proteins, with apparent M(r) values between 12,000 and 36,000, that behave like Receptors for Activated C-Kinase (RACKs) were found in the Triton-X-100-insoluble fraction of these cells; i.e. PKC bound to these polypeptides when it was in its active form. RACKS seem to be PKC substrates. Studies using isotype-specific PKC antibodies suggested some selectivity of RACKs, i.e. RACKs in the M(r) approximately 28,000-36,000 region bound PKC-alpha and PKC-beta in the presence of phosphatidylserine, diolein and Ca2+, whereas those of M(r) approximately 12,000-14,000 bound all isoforms studied, and, in contrast with the other RACKs, they did this even in the absence of Ca2+. Peptide I (KGDYEKILVALCGGN), which has a sequence suggested to be involved in the PKC-RACKs interaction [Mochly-Rosen, Khaner, Lopez and Smith (1991) J. Biol. Chem. 266, 14866-14868], inhibited PKC activity. Preincubation of RACKs with antisera directed against peptide I prevented PKC binding to them. The data suggest that peptide I blocks PKC binding to RACKs by two mechanisms: inhibition of PKC activity and competition with a putative binding site.
Robles-Flores
M
M
Departamento de Bioenergética, Facultad de Medicina, Universidad Nacional Autónoma de México, México D.F.
García-Sáinz
J A
JA
D000595:Amino Acid Sequence; D000818:Animals; D002118:Calcium / Q000494:pharmacology; D002478:Cells, Cultured; D004533:Egtazic Acid / Q000494:pharmacology; D004591:Electrophoresis, Polyacrylamide Gel; D004789:Enzyme Activation; D005260:Female; D007700:Kinetics; D008099:Liver / Q000378:metabolism*; D008969:Molecular Sequence Data; D008970:Molecular Weight; D010455:Peptides / Q000378:metabolism; D011485:Protein Binding; D011493:Protein Kinase C / Q000302:isolation & purification / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D000075370:Receptors for Activated C Kinase; D011956:Receptors, Cell Surface / Q000302:isolation & purification / Q000378:metabolism*; D013379:Substrate Specificity; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
D010455:Peptides; D000075370:Receptors for Activated C Kinase; D011956:Receptors, Cell Surface; D004533:Egtazic Acid; D011493:Protein Kinase C; D013755:Tetradecanoylphorbol Acetate; D002118:Calcium