title: Protein kinase C activation and positive and negative agonist regulation of 3',5'-cyclic adenosine monophosphate levels in cultured rat Sertoli cells.
abstract: The present study examines the effects of 12-O-tetradecanoylphorbol-13-acetate (TPA) on agonist-regulated 3',5'-cyclic adenosine monophosphate (cAMP) formation and cAMP-mediated effects in cultured Sertoli cells from immature rats. Concentration-dependent stimulation of cAMP levels by follicle-stimulating hormone (FSH) was inhibited dramatically by the coaddition of 100 nmol/l TPA, which exerted a similar inhibition of glucagon- and isoproterenol-stimulated cAMP production. These results show that protein kinase C (PKC) activation by TPA attenuates Gs-protein-mediated agonist activation of cAMP production. (-)-N6(R)-Phenylisopropyladenosine (L-PIA), an A1-adenosine receptor agonist, inhibited cAMP stimulation by FSH in a concentration-dependent manner. When L-PIA was added in increasing concentrations simultaneously with 100 nmol/l TPA, the L-PIA still inhibited FSH-stimulated cAMP production in a concentration-dependent manner. In the presence of TPA, the half-inhibitory concentration (IC50) for L-PIA inhibition of cAMP formation was reduced by more than one order of magnitude, indicating that PKC activation by TPA increases the sensitivity of Sertoli cells to Gi-protein-mediated agonist inhibition of cAMP production. The inhibitory effects of TPA on FSH-stimulated cAMP production were still observed when cAMP phosphodiesterase activity was inhibited by 1 mmol/l methylisobutylxanthine or when the activity of G alpha i-protein was eliminated by pretreatment with 100 micrograms/l pertussis toxin. Taken together, the results indicate that PKC activation inhibits agonist-dependent stimulation of cAMP production by phosphorylation of components common to all the activating agonists used, and not via stimulation of G(i)-protein activity or degradation of cAMP by cAMP phosphodiesterase activity.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Institute of Medical Biochemistry, University of Oslo, Blindern, Norway.
authors.forename: L
authors.initials: L
authors.lastname: Eikvar
authors.forename: K A
authors.initials: KA
authors.lastname: Taskén
authors.forename: W
authors.initials: W
authors.lastname: Eskild
authors.forename: V
authors.initials: V
authors.lastname: Hansson
mesh_terms: D015056:1-Methyl-3-isobutylxanthine / Q000494:pharmacology; D015105:3',5'-Cyclic-AMP Phosphodiesterases / Q000096:biosynthesis; D000818:Animals; D002478:Cells, Cultured; D000242:Cyclic AMP / Q000096:biosynthesis*; D004305:Dose-Response Relationship, Drug; D004789:Enzyme Activation; D005640:Follicle Stimulating Hormone / Q000494:pharmacology; D005934:Glucagon / Q000494:pharmacology; D007545:Isoproterenol / Q000494:pharmacology; D008297:Male; D010660:Phenylisopropyladenosine / Q000494:pharmacology; D011493:Protein Kinase C / Q000096:biosynthesis / Q000187:drug effects / Q000378:metabolism*; D051381:Rats; D012708:Sertoli Cells / Q000378:metabolism*; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology*
chemical_list: D010660:Phenylisopropyladenosine; D005640:Follicle Stimulating Hormone; D005934:Glucagon; D000242:Cyclic AMP; D011493:Protein Kinase C; D015105:3',5'-Cyclic-AMP Phosphodiesterases; D007545:Isoproterenol; D013755:Tetradecanoylphorbol Acetate; D015056:1-Methyl-3-isobutylxanthine