The role of protein kinase C in GH secretion induced by GH-releasing factor and GH-releasing peptides in cultured ovine somatotrophs.
The involvement of protein kinase C (PKC) in the action of GH-releasing factor (GRF) and synthetic GH-releasing peptides (GHRP-2 and GHRP-6) was investigated in ovine somatotrophs in primary culture. In partially purified sheep somatotrophs, GRF and GHRP-2 caused translocation of PKC activity from the cytosol to the cell membranes and caused GH release in a dose- and time-dependent manner. GHRP-6 did not cause PKC translocation. The PKC inhibitors, calphostin C, staurosporine and chelerythrine, partially reduced GH release in response to GRF and GHRP-2 at doses which selectively inhibit PKC activity. These inhibitors totally abolished GH release caused by phorbol 12-myristate 13-acetate (PMA). Down-regulation of PKC by the treatment of cells with phorbol 12,13-dibutyrate for 16 h caused a significant (P < 0.001) reduction in total PKC activity and totally abolished PKC translocation in response to a challenge with GRF, GHRP-2 or PMA. In addition, down-regulation abolished GH release in response to GRF, GHRP-2 or GHRP-6. Treatment of cells with H89, a selective PKA inhibitor, totally blocked GH release caused by either GRF or GHRP-2 and partially reduced PMA-induced GH release. H89 had no effect on PKC translocation caused by GRF, GHRP-2 or PMA and did not affect GH release caused by GHRP-6. These data suggest that GHRP-2 and GRF activate PKC in addition to stimulating adenylyl cyclase activity. Although the cAMP-protein kinase A (PKA) pathway is the major signalling pathway employed by GRF and GHRP-2, the activation of PKC may potentiate signalling via the cAMP-PKA pathway in ovine GH secretion. Importantly, the effect of PMA in increasing the secretion of GH from ovine somatotrophs is effected, in part, by up-regulation of the cAMP-PKA pathway. We conclude that there is cross-talk between the PKC pathway and the cAMP-PKA pathway in ovine somatotrophs during the action of GRF or GHRP.
Wu
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Prince Henry's Institute of Medical Research, Victoria, Australia.
Clarke
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IJ
Chen
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C
D000470:Alkaloids; D000818:Animals; D053119:Benzophenanthridines; D002273:Carcinogens / Q000494:pharmacology; D002462:Cell Membrane / Q000201:enzymology; D002478:Cells, Cultured; D000242:Cyclic AMP / Q000378:metabolism; D017868:Cyclic AMP-Dependent Protein Kinases / Q000037:antagonists & inhibitors; D003600:Cytosol / Q000201:enzymology; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000494:pharmacology; D013006:Growth Hormone / Q000378:metabolism*; D013007:Growth Hormone-Releasing Hormone / Q000494:pharmacology*; D007546:Isoquinolines / Q000494:pharmacology; D009281:Naphthalenes / Q000494:pharmacology; D009842:Oligopeptides / Q000494:pharmacology; D010617:Phenanthridines / Q000494:pharmacology; D010902:Pituitary Gland / Q000201:enzymology / Q000378:metabolism*; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000502:physiology*; D015290:Second Messenger Systems / Q000502:physiology*; D012756:Sheep; D019311:Staurosporine / Q000494:pharmacology; D013449:Sulfonamides; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D013997:Time Factors
D000470:Alkaloids; D053119:Benzophenanthridines; D002273:Carcinogens; D004791:Enzyme Inhibitors; D007546:Isoquinolines; D009281:Naphthalenes; D009842:Oligopeptides; D010617:Phenanthridines; D013449:Sulfonamides; C041048:growth hormone releasing hexapeptide; D013006:Growth Hormone; D013007:Growth Hormone-Releasing Hormone; D000242:Cyclic AMP; C016299:chelerythrine; C091874:growth hormone-releasing peptide-2; D017868:Cyclic AMP-Dependent Protein Kinases; D011493:Protein Kinase C; D019311:Staurosporine; C058819:calphostin C; C063509:N-(2-(4-bromocinnamylamino)ethyl)-5-isoquinolinesulfonamide; D013755:Tetradecanoylphorbol Acetate