Cesnjaj M, Catt K J, Stojilkovic S S
Endocrinology and Reproduction Research Branch, National Institute of Child Health and Human Development, National Institutes of health, Bethesda, Maryland 20892.
Endocrinology. 1994 Aug;135(2):692-701. doi: 10.1210/endo.135.2.7518388.
Activation of GnRH receptors in cultured pituitary cells and alpha T3-1 gonadotrophs caused prominent, but transient, increases in messenger RNAs for primary response genes (PRGs) including c-fos, c-jun, and junB. GnRH-induced stimulation peaked at 30 min and was dose related, with similar EC50 values (approximately 1 nM) for all three PRGs and higher maximum responses for junB than for c-jun and c-fos. The agonist-induced expression of PRGs was mimicked by activation of protein kinase-C with the phorbol ester phorbol 12-myristate 13-acetate (PMA), which acted additively with GnRH at low concentrations of both stimuli. Depletion of cellular protein kinase-C by prior treatment with PMA reduced GnRH- and PMA-induced expression of PRGs. The protein kinase-C inhibitor staurosporine also attenuated agonist- and phorbol ester-induced PRG expression. Activation of Ca2+ entry by the calcium channel agonist BayK 8644 or high K(+)-induced depolarization caused a concentration-dependent rise in intracellular Ca2+ ([Ca2+]i) and a concentration-dependent and transient expression of PRGs, albeit of smaller amplitudes than those elicited by GnRH and PMA. Ca(2+)-dependent PRG expression was abolished by the calmodulin inhibitor W-7. Parallel measurements of [Ca2+]i and steady-state levels of PRG messenger RNAs indicated that intracellular Ca2+ exerted both additive and suppressive actions over its physiological concentration range on GnRH- and PMA-induced PRG expression. At lower intracellular calcium concentrations, calcium acted additively with low concentrations of GnRH and PMA. However, high calcium concentrations suppressed high agonist- and phorbol ester-induced PRG expression. In contrast, omission of Ca2+ from the extracellular medium significantly enhanced induction of PRGs. These findings indicate that GnRH-induced PRG expression in gonadotrophs is mediated by protein kinase-C and calcium, and that protein kinase-C-dependent induction of PRGs is modulated both positively and negatively by physiological changes in [Ca2+]i. Such coordinate actions of the two signaling molecules provide a mechanism for the control of PRG expression by preferential integration of low strength, and attenuation of high strength, extracellular signals.
培养的垂体细胞和αT3-1促性腺激素细胞中促性腺激素释放激素（GnRH）受体的激活导致包括c-fos、c-jun和junB在内的初级反应基因（PRGs）的信使核糖核酸显著但短暂增加。GnRH诱导的刺激在30分钟时达到峰值，且与剂量相关，所有三种PRGs的半数有效浓度（EC50）值相似（约1 nM），junB的最大反应高于c-jun和c-fos。佛波酯佛波醇12-肉豆蔻酸酯13-乙酸酯（PMA）激活蛋白激酶-C可模拟激动剂诱导的PRGs表达，在两种刺激的低浓度下，PMA与GnRH起相加作用。用PMA预先处理使细胞蛋白激酶-C耗竭，可降低GnRH和PMA诱导的PRGs表达。蛋白激酶-C抑制剂星形孢菌素也减弱了激动剂和佛波酯诱导的PRG表达。钙通道激动剂BayK 8644激活Ca2+内流或高钾诱导的去极化导致细胞内Ca2+（[Ca2+]i）浓度依赖性升高以及PRGs浓度依赖性和短暂性表达，尽管其幅度小于GnRH和PMA诱导的幅度。钙调蛋白抑制剂W-7消除了Ca2+依赖性PRG表达。对[Ca2+]i和PRG信使核糖核酸稳态水平的平行测量表明，细胞内Ca2+在其生理浓度范围内对GnRH和PMA诱导的PRG表达发挥相加和抑制作用。在较低的细胞内钙浓度下，钙与低浓度的GnRH和PMA起相加作用。然而，高钙浓度抑制高浓度激动剂和佛波酯诱导的PRG表达。相反，从细胞外培养基中去除Ca2+可显著增强PRGs的诱导。这些发现表明，GnRH诱导的促性腺激素细胞中PRG表达由蛋白激酶-C和钙介导，并且蛋白激酶-C依赖性的PRGs诱导受到[Ca2+]i生理变化的正向和负向调节。这两种信号分子的这种协同作用为通过优先整合低强度细胞外信号和减弱高强度细胞外信号来控制PRG表达提供了一种机制。
