Tang K, Wu H, Mahata S K, Mahata M, Gill B M, Parmer R J, O'Connor D T
Department of Medicine and Center for Molecular Genetics, University of California, San Diego, California 92161, USA.
J Clin Invest. 1997 Sep 1;100(5):1180-92. doi: 10.1172/JCI119630.
How do chromaffin cell secretory stimuli program resynthesis of secreted peptides and amines? We previously showed that the physiologic nicotinic cholinergic signal for secretion also activates the biosynthesis of chromogranin A, the major protein released with catecholamines. Here, we examine signal transduction pathways whereby secretory stimuli influence exocytotic secretion versus chromogranin A transcription. Both secretion and transcription depended on initial nicotinic-triggered sodium entry into the cytosol, followed by calcium entry through -type voltage-gated channels. When calcium entered through -type channels, activation of secretion paralleled activation of transcription (r = 0.897, P = 0.002). Calcium entry from intracellular stores or through calcium ionophore channels activated secretion, though not transcription. Nicotinic-stimulated transcription depended upon protein kinase C activation; nicotine caused translocation of protein kinase C to the cell membrane fraction, and inhibition of protein kinase C blocked activation of transcription, while activation of protein kinase C mimicked nicotine effects. Transcriptional responses to both nicotine and protein kinase C mapped principally onto the chromogranin A promoter's cAMP response element (TGACGTAA; CRE box). KCREB, a dominant negative mutant of the CRE-binding protein CREB, blunted activation of chromogranin A transcription by nicotine, phorbol ester, or membrane depolarization. We conclude that activation of chromogranin A transcription by secretory stimulation in chromaffin cells is highly dependent upon precise route of calcium entry into the cytosol; transcription occurred after entry of calcium through -type channels on the cell surface, and was mediated by protein kinase C activation. The trans-acting factor CREB ultimately relays the secretory signal to the chromogranin A promoter's CRE box in cis.
嗜铬细胞的分泌刺激是如何调控分泌肽和胺的重新合成的？我们之前发现，用于分泌的生理性烟碱型胆碱能信号也会激活嗜铬粒蛋白A的生物合成，嗜铬粒蛋白A是与儿茶酚胺一同释放的主要蛋白质。在此，我们研究了分泌刺激影响胞吐分泌与嗜铬粒蛋白A转录的信号转导途径。分泌和转录均依赖于最初烟碱触发的钠离子进入胞质溶胶，随后钙离子通过L型电压门控通道进入。当钙离子通过L型通道进入时，分泌的激活与转录的激活平行（r = 0.897，P = 0.002）。从细胞内储存库进入或通过钙离子载体通道进入的钙离子激活了分泌，但未激活转录。烟碱刺激的转录依赖于蛋白激酶C的激活；尼古丁导致蛋白激酶C转位至细胞膜部分，抑制蛋白激酶C可阻断转录的激活，而激活蛋白激酶C则模拟尼古丁的作用。对尼古丁和蛋白激酶C的转录反应主要映射到嗜铬粒蛋白A启动子的cAMP反应元件（TGACGTAA；CRE框）上。KCREB是CRE结合蛋白CREB的显性负突变体，可减弱尼古丁、佛波酯或膜去极化对嗜铬粒蛋白A转录的激活。我们得出结论，嗜铬细胞中分泌刺激对嗜铬粒蛋白A转录的激活高度依赖于钙离子进入胞质溶胶的精确途径；转录发生在钙离子通过细胞表面的L型通道进入之后，并由蛋白激酶C的激活介导。反式作用因子CREB最终将分泌信号顺式传递至嗜铬粒蛋白A启动子的CRE框。
