title: Differences in phorbol ester-induced decrease of the activity of protein kinase C isozymes in rat hepatocytes.
abstract: Two main forms of protein kinase C (PKC) activity were found in rat hepatocytes using DEAE-cellulose chromatography: PKC 1 and PKC 2. Treatment of cells with 1 microM 12-O-tetradecanoylphorbol 13-acetate (TPA) for 15 min caused a marked loss of PKC 1 activity and only a small loss of PKC 2 activity. Hydroxyapatite column chromatography resolved PKC 1 into three distinct peaks 1a, 1b and 1c, and PKC 2 into four peaks 2a, 2b, 2c and 2d. Immunoblot analysis with isozyme-specific monoclonal antibodies identified peak 1a as PKC-beta and peak 1b as PKC-alpha; the other peaks of activity were not identified. Treatment with TPA provoked a loss of activity of peaks 1b (PKC-alpha) and 1c, whereas peak 1a (PKC-beta) activity was not affected. The peaks of activity corresponding to PCK 2 did not show any major change due to TPA treatment except peak 2d that decreased. The apparent disappearance of PKC histone-kinase activity induced by TPA was also observed using other substrates (protamine or vinculin). The TPA-induced decrease in activity occurs in a time-dependent and dose-dependent fashion. However, the time-courses, the extent of depletion and the potency order of phorbol esters in induction of an activity decrease in the two groups of isoforms exhibited substantial differences.
authors.affiliation: Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, D.F.
authors.forename: M
authors.initials: M
authors.lastname: Robles-Flores
authors.forename: R
authors.initials: R
authors.lastname: Alcántara-Hernández
authors.forename: J A
authors.initials: JA
authors.lastname: García-Sáinz
mesh_terms: D000818:Animals; D002848:Chromatography, DEAE-Cellulose; D017886:Durapatite; D004789:Enzyme Activation / Q000187:drug effects; D005260:Female; D006882:Hydroxyapatites; D007527:Isoenzymes / Q000037:antagonists & inhibitors*; D008099:Liver / Q000166:cytology / Q000201:enzymology*; D011493:Protein Kinase C / Q000037:antagonists & inhibitors*; D051381:Rats; D011919:Rats, Inbred Strains; D013379:Substrate Specificity; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology*
chemical_list: D006882:Hydroxyapatites; D007527:Isoenzymes; D017886:Durapatite; D011493:Protein Kinase C; D013755:Tetradecanoylphorbol Acetate