DESENSITIZATION OF CALCIOTROPIC HORMONE RECEPTORS

这项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， 例如骨骼和肾脏。 有证据表明， CT对腺苷酸环化酶（AC）刺激在激动剂期间脱敏 行动上 尽管还有其他机制可以使脱敏作用 发生时，引起脱敏的主要修饰部位是 受体本身。 与其他鸟嘌呤核苷酸结合调节（G） 蛋白偶联受体（GPCR），脱敏已被发现是 由受体-G蛋白解偶联、受体内化和 受体下调。 我们将测试以下假设 关于CT反应脱敏的机制。 假定羧基末端和第三末端的氨基酸残基 CT受体介导的受体-G蛋白的细胞内环 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。 为了验证这一 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。 这个目标，当 这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这种受体的研究， 分子遗传学技术2)建立细胞系统， 显示刺激和脱敏的转染的CT受体cDNA AC和磷脂酰肌醇特异性磷脂酶C（PPlase）， 受体内化和受体下调。3)以确定 与G蛋白相互作用的CT受体的结构特征 蛋白质以激活AC和PPlase。4)为了确定结构 介导受体-G蛋白解偶联的CT受体的特征， 以及受体内化和下调。 分子遗传学 将用于构建合成基因并使受体突变 DNA 脱敏（或快速耐受），这限制了 反应的持续时间，限制了药物的疗效， 这些受体。 因此，了解 脱敏的机制是能够设计非肽类药物， 其不需要肠胃外或鼻内给药， 可以避免脱敏。 这些药物可以提高疗效 受体激动剂通过抑制脱敏或be激动剂 自己的CT-R。 这些药物可以用来治疗 骨质疏松

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.