CHROMOGRANIN A--NICOTINIC SIGNALING AND DESENSITIZATION

嗜铬粒素A：烟碱信号和脱敏。尼古丁是一种 烟草的一种成分，尽管有害，但仍会刺激人们继续滥用 效果。儿茶酚胺能细胞的儿茶酚胺释放被触发 通过烟碱能胆碱能刺激，促使胞吐共释放 储存囊成分：儿茶酚胺、神经肽和酸性物质 嗜铬颗粒蛋白，主要成分为嗜铬颗粒蛋白A(CGA)。CGA 被切割成生物活性多肽，例如一个新的片段 (CgA344-364，我们发现并命名为儿茶素) 反馈-抑制儿茶酚胺的释放。我们发现，刺激 神经元尼古丁受体引起儿茶酚胺的分泌和 CGA，转录上调CGA和CGA的生物合成 儿茶酚胺，并进一步脱敏(产生耐受性) 尼古丁反应，包括分泌和转录。在预赛中 研究发现，儿茶素能拮抗所有这些胆碱能 回应。因此，CgA(及其片段儿茶素)似乎扮演着一个 在神经元型烟碱能胆碱能信号中的中心作用 对尼古丁呈阳性反应(在分泌和转录方面)，以及 在阻断所有已知的刺激(分泌或转录)或 尼古丁的脱敏作用。CGA的这些特点和 儿茶素的反应和作用表明体内平衡是负面的 反馈作用。在这里，我们将探索CGA的这些功能和 儿茶素，使用培养的嗜铬细胞。以下是两个主要领域 特色化的。I.烟碱能胆碱能刺激引起的效应 (儿茶酚胺和CGA)分泌，CGA生物合成，以及 对进一步分泌或转录的脱敏(耐受性) 对尼古丁的反应。我们已经描述了CGA启动子的特征 调节尼古丁反应的结构域(在顺式中)，并具有 开始建立信号转导通路，参与 转录及其脱敏。儿茶素的拮抗作用 烟碱反应(分泌、转录和脱敏 其一)。我们鉴定了儿茶素对分泌的抑制作用， 特别是作为非竞争性烟碱胆碱能拮抗剂，以及 确定了它对尼古丁信号转导的影响，以及 防止先前的烟碱脱敏。这些研究可能 建立一种新的动态平衡(负反馈)机制 一种内源性多肽拮抗烟碱刺激 儿茶酚胺释放、CGA基因转录和脱敏 包括分泌和转录。这种保护措施不会对 脱敏对机体来说可能是有利的 长期紧张的情况，也许是为了防范 提早终止分泌和转录反应 生理烟碱刺激。

Chromogranin A: nicotinic signaling and desensitization. Nicotine is a component of tobacco that motivates continued abuse despite harmful effects. Catecholamine release from catecholaminergic cells is triggered by nicotinic cholinergic stimulation, prompting exocytotic co-release of storage vesicle constituents: catecholamines, neuropeptides, and acidic chromogranins, the major component being chromogranin A (CgA). CgA is cleaved to biologically active peptides, such as a novel fragment (CgA344-364, which we discovered and named "catestatin") that feedback-inhibits catecholamine release. We found that stimulation of neuronal nicotinic receptors causes secretion of catecholamines and CgA, transcriptionally upregulates the biosynthesis of CgA and catecholamines, and desensitizes (creates tolerance to) further nicotinic responses, both secretory and transcriptional. In preliminary studies, we found that catestatin antagonized all of these cholinergic responses. Thus, CgA (and its fragment catestatin) seem to play a central role in neuronal nicotinic cholinergic signaling, both in responding positively to nicotine (in secretion and transcription), and in blocking all known stimulatory (secretory or transcriptional) or desensitizing action of nicotine. These features of CgA's and catestatin's responses and action suggest a homeostatic, negative feedback role. Here we will explore these functions of CgA and catestatin, using cultured chromaffin cells. Two general areas will be characterized. I. Effects of nicotinic cholinergic stimulation to cause secretion (of catecholamines and CgA), CgA biosynthesis, and desensitization of (tolerance to) further secretion or transcriptional responses to nicotine. We have already characterized CgA promoter domains (in cis) which mediate the response to nicotine, and have begun to establish signal transduction pathways involved in transcription and its desensitization. II. Catestatin's antagonism of nicotinic responses (secretion, transcription, and desensitization thereof). We characterized catestatin's inhibitory effects on secretion, specifically as a non-competitive nicotinic cholinergic antagonist, and established its effect on nicotinic signal transduction, as well as protection against prior nicotinic desensitization. These studies may establish a novel homeostatic (negative feedback) mechanism by which an endogenous peptide antagonizes nicotinic stimulation of catecholamine release, CgA gene transcription, and desensitization of both secretion and transcription. Such protection against desensitization may be advantageous to an organism during circumstances of prolonged stress, perhaps guarding against premature termination of secretory and transcriptional responses to physiological nicotinic stimulation.