Lei T, Adams E F, Buchfelder M, Fahlbusch R
Department of Neurosurgery, University of Erlangen-Nürnberg, Germany.
Neurosurgery. 1996 Sep;39(3):569-75; discussion 575-6. doi: 10.1097/00006123-199609000-00027.
To determine the potential role of protein kinase C (PKC) and its relationship to adenylyl cyclase activity in controlling growth hormone (GH) secretion by human pituitary somatotrophinomas.
Twenty-eight somatotrophinomas were placed into cell culture, and the in vitro effects of the PKC activator 12-O-tetradecanoylphorbol 13-acetate (TPA) and the PKC inhibitor staurosporine on basal and GH-releasing hormone (GHRH)-stimulated GH secretion were examined. In addition, the influence of chronic exposure of cultured somatotrophinoma cells to TPA on the rate of inositol 1,4,5-trisphosphate production was determined. Each tumor was assessed for the presence of gsp oncogenes, and thus constitutive adenylyl cyclase activity, by direct sequence analysis of polymerase chain reaction-generated deoxyribonucleic acid. GH secretory responses of tumors with and without these oncogenes were compared.
TPA consistently stimulated GH secretion by cultured somatotrophinoma cells. There was no difference in response between somatotrophinomas with and without gsp oncogenes, and the effects did not correlate with the variable stimulation exerted by GHRH. Tumors in which GHRH had no significant effect nevertheless responded to TPA. In combination, TPA and GHRH exerted additive stimulation. TPA treatment of cultured somatotrophinoma cells eventually resulted in suppression of inositol 1,4,5-trisphosphate production, probably reflecting down-regulation of membrane phosphatidylinositol hydrolysis, a second messenger system that also generates the endogenous PKC activator diacylglycerol. GHRH had no effect on phosphatidylinositol hydrolysis. In contrast to the effects of TPA, the PKC inhibitor staurosporine tended to reduce GH secretion, although this effect was not observed in all tumors examined. As with TPA, the effects of staurosporine did not correlate with presence or absence of gsp oncogenes. Furthermore, staurosporine did not reduce the stimulatory effects exerted by GHRH on GH secretion.
These results demonstrate a role for the phosphatidylinositol-PKC second messenger cascade in controlling GH secretion by human pituitary somatotrophinomas. The results also show that the system operates relatively independent of intracellular adenylyl cyclase and, thus, protein kinase A.
确定蛋白激酶C（PKC）在控制人垂体生长激素瘤分泌生长激素（GH）中的潜在作用及其与腺苷酸环化酶活性的关系。
将28个生长激素瘤进行细胞培养，检测PKC激活剂12 - O - 十四烷酰佛波醇13 - 乙酸酯（TPA）和PKC抑制剂星形孢菌素对基础及生长激素释放激素（GHRH）刺激的GH分泌的体外作用。此外，还测定了培养的生长激素瘤细胞长期暴露于TPA对肌醇1,4,5 - 三磷酸生成速率的影响。通过对聚合酶链反应产生的脱氧核糖核酸进行直接序列分析，评估每个肿瘤中gsp癌基因的存在情况，从而确定组成型腺苷酸环化酶活性。比较有无这些癌基因的肿瘤的GH分泌反应。
TPA持续刺激培养的生长激素瘤细胞分泌GH。有无gsp癌基因的生长激素瘤之间的反应无差异，且这些作用与GHRH施加的可变刺激无关。GHRH无显著作用的肿瘤对TPA仍有反应。TPA和GHRH联合使用具有相加刺激作用。用TPA处理培养的生长激素瘤细胞最终导致肌醇1,4,5 - 三磷酸生成受到抑制，这可能反映了膜磷脂酰肌醇水解的下调，膜磷脂酰肌醇水解是一种第二信使系统，也产生内源性PKC激活剂二酰甘油。GHRH对磷脂酰肌醇水解无影响。与TPA的作用相反，PKC抑制剂星形孢菌素倾向于降低GH分泌，尽管在所有检测的肿瘤中未观察到这种作用。与TPA一样，星形孢菌素的作用与gsp癌基因的有无无关。此外，星形孢菌素并未降低GHRH对GH分泌的刺激作用。
这些结果证明磷脂酰肌醇 - PKC第二信使级联在控制人垂体生长激素瘤分泌GH中起作用。结果还表明该系统的运作相对独立于细胞内腺苷酸环化酶，因而也独立于蛋白激酶A。
