The role of protein kinase C in GH secretion induced by GH-releasing factor and GH-releasing peptides in cultured ovine somatotrophs

D. Wu, I. J. Clarke, C. Chen

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Abstract

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 urine 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 l2,13-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 urine 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 urine somatotrophs during the action of GRF or GHRP.

Original languageEnglish
Pages (from-to)219-230
Number of pages12
JournalJournal of Endocrinology
Volume154
Issue number2
DOIs
Publication statusPublished - 1 Jan 1997
Externally publishedYes

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