DESENSITIZATION OF CALCIOTROPIC HORMONE RECEPTORS

该研究计划的长期目标是阐明 降钙素（CT）调节自身反应的机制 骨骼和肾脏等组织。 有证据表明 CT 对腺苷酸环化酶 (AC) 的刺激在激动剂期间脱敏 行动。 尽管还有其他机制可以实现脱敏 发生时，引起脱敏的主要修饰位点是 受体本身。 与其他鸟嘌呤核苷酸结合调节（G） 蛋白质偶联受体（GPCR），已发现脱敏作用 由受体-G蛋白解偶联、受体内化和 受体下调。 我们将检验以下假设 关于 CT 反应脱敏的机制。 推定的羧基末端和第三末端的氨基酸残基 CT受体的细胞内环介导受体-G蛋白 解偶联、受体内化和受体下调， 部分通过刺激受体降解而发生。 为了测试这个 假设，我们将追求以下具体目标：1）设计和 构建 CT 受体的合成基因。 这个进球当 所取得的成果将对这一领域的研究产生重大的实际影响 因为它将极大地促进对该受体的研究 分子遗传学技术。 2) 建立细胞系统 转染的 CT 受体 cDNA 表现出刺激和脱敏作用 AC 和磷酸肌醇特异性磷脂酶 C (PPlase)， 受体内化和受体下调。 3）确定 与 G 相互作用的 CT 受体的结构特征 激活 AC 和 PPLase 的蛋白质。 4）确定结构 CT受体介导受体-G蛋白解偶联的特征， 和受体内化和下调。 分子遗传学 将用于构建合成基因并突变受体 DNA。 脱敏（或快速耐受），限制了程度和 反应持续时间，限制了通过作用的药物的功效 这些受体。 因此，了解这一点的重要原因之一是 脱敏机制是能够设计非肽类药物， 不需要胃肠外或鼻内给药， 可能会规避脱敏。 这些药物可以增强疗效 通过抑制脱敏作用成为受体激动剂或成为激动剂 CT-R 本身。 这些药物可用于治疗 骨质疏松症。

The long-term objectives of this research program are to elucidate the mechanisms through which calcitonin (CT) regulates its own responses in tissues such as bone and kidney. Evidence has been presented that stimulation of adenylyl cyclase (AC) by CT desensitizes during agonist action. Although there are other mechanisms by which desensitization can occur, a major site of modification causing desensitization is the receptor itself. With other guanine nucleotide-binding regulatory (G) protein-coupled receptors (GPCRs), desensitization has been found to be caused by receptor-G protein uncoupling, receptor internalization and receptor down-regulation. We will test the following hypothesis regarding the mechanisms involved in desensitization of responses to CT. Amino acid residues in the putative carboxyl termini and third intracellular loops of the CT receptor mediate receptor-G protein uncoupling, receptor internalization and receptor down-regulation, which occurs in part by stimulating receptor degradation. To test this hypothesis, we will pursue the following Specific Aims: 1) To design and construct a synthetic gene for the CT receptor. This goal when accomplished will have a major practical impact on research in this field because it will greatly facilitate the study of this receptor by molecular genetic techniques. 2) To establish cell systems with transfected CT receptor cDNAs that show stimulation and desensitization of both AC and phosphoinoitide-specific phospholipase C (PPlase), receptor internalization and receptor down-regulation. 3) To determine the structural features of the CT receptor that interact with a G protein(s) to activate AC and PPlase. 4) To determine the structural features of the CT receptor that mediate receptor-G protein uncoupling, and receptor internalization and down-regulation. Molecular genetics will be used to construct the synthetic genes and to mutate the receptor DNAs. Desensitization (or tachyphylaxis), which limits the magnitude and duration of responses, limits the efficacy of drugs that act through these receptors. Therefore, one important reason to understand the mechanism of desensitization is to be able to design non-peptide drugs, which would not require parenteral nor intranasal administration, that may circumvent desensitization. These drugs could enhance the efficacy of receptor agonists by inhibiting desensitization or be agonists themselves of the CT-R. These agents could be used to treat osteoporosis.