Coordinate actions of calcium and protein kinase-C in the expression of primary response genes in pituitary gonadotrophs.
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.
Cesnjaj
M
M
Endocrinology and Reproduction Research Branch, National Institute of Child Health and Human Development, National Institutes of health, Bethesda, Maryland 20892.
Catt
K J
KJ
Stojilkovic
S S
SS
D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester / Q000494:pharmacology; D001769:Blood; D002118:Calcium / Q000494:pharmacology*; D002460:Cell Line; D015870:Gene Expression / Q000187:drug effects*; D016762:Genes, fos; D016758:Genes, jun; D007987:Gonadotropin-Releasing Hormone / Q000494:pharmacology; D007031:Hypothalamus / Q000378:metabolism; D010902:Pituitary Gland / Q000187:drug effects / Q000378:metabolism*; D011188:Potassium / Q000494:pharmacology; D011493:Protein Kinase C / Q000378:metabolism / Q000494:pharmacology*; D011966:Receptors, LHRH / Q000235:genetics* / Q000502:physiology; D015398:Signal Transduction; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
D011966:Receptors, LHRH; D007987:Gonadotropin-Releasing Hormone; D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester; D011493:Protein Kinase C; D013755:Tetradecanoylphorbol Acetate; D011188:Potassium; D002118:Calcium