Wu D, Clarke I J, Chen C
Prince Henry's Institute of Medical Research, Victoria, Australia.
J Endocrinol. 1997 Aug;154(2):219-30. doi: 10.1677/joe.0.1540219.
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.
在原代培养的绵羊生长激素分泌细胞中，研究了蛋白激酶C（PKC）在生长激素释放因子（GRF）和合成生长激素释放肽（GHRP - 2和GHRP - 6）作用中的参与情况。在部分纯化的绵羊生长激素分泌细胞中，GRF和GHRP - 2导致PKC活性从胞质溶胶转位至细胞膜，并以剂量和时间依赖性方式引起生长激素释放。GHRP - 6未引起PKC转位。PKC抑制剂calphostin C、星形孢菌素和白屈菜红碱，在选择性抑制PKC活性的剂量下，部分降低了对GRF和GHRP - 2的生长激素释放反应。这些抑制剂完全消除了佛波醇12 - 肉豆蔻酸酯13 - 乙酸酯（PMA）引起的生长激素释放。用佛波醇12,13 - 二丁酸酯处理细胞16小时使PKC下调，导致总PKC活性显著降低（P < 0.001），并完全消除了对GRF、GHRP - 2或PMA刺激的PKC转位。此外，下调消除了对GRF、GHRP - 2或GHRP - 6的生长激素释放反应。用选择性PKA抑制剂H89处理细胞，完全阻断了GRF或GHRP - 2引起的生长激素释放，并部分降低了PMA诱导的生长激素释放。H89对GRF、GHRP - 2或PMA引起的PKC转位无影响，且不影响GHRP - 6引起的生长激素释放。这些数据表明，GHRP - 2和GRF除了刺激腺苷酸环化酶活性外，还激活PKC。尽管环磷酸腺苷 - 蛋白激酶A（PKA）途径是GRF和GHRP - 2采用的主要信号通路，但PKC的激活可能增强绵羊生长激素分泌中环磷酸腺苷 - PKA途径的信号传导。重要的是，PMA增加绵羊生长激素分泌细胞生长激素分泌的作用部分是通过环磷酸腺苷 - PKA途径的上调实现的。我们得出结论，在GRF或GHRP作用期间，绵羊生长激素分泌细胞中PKC途径和环磷酸腺苷 - PKA途径之间存在相互作用。
