MOLECULAR MECHANISM REGUALTING PROGIP PROCESSING

胃抑制肽(GIP)是从猪体内首次分离得到的 肠，最初因其抑酸能力而得名 分泌物。随后对其生理特性的分析 证明GIP是一种有效的内源性胰岛素释放刺激剂 它在维持血糖和血脂方面起着重要作用 动态平衡。II型糖尿病患者的最新研究 已经证明，尽管营养刺激的GIP释放似乎 正常情况下，外源性GIP的胰岛素样作用大 减弱，表明GIP可能在功能上不活跃。多数 胃肠调节多肽进行翻译后加工 在变得具有生物活性之前。尽管GIP最初被认为是 作为一种42个氨基酸的多肽，最近在本实验室进行的研究 表明较小的α-酰胺化形式的GIP(1-30)具有类似的 对GIP的促胰岛素作用(1-42)。此外，一种甘氨酸延伸 前激素和二碱性Lys-Lys残基已在 GIP基因的cDNA序列。因此，proGIP很可能会经历 翻译后C-末端的α-酰胺化修饰 生物活性的。此外，也有可能出现异常 ProGIP的翻译后加工可能在 2型糖尿病的发病机制。然而，到目前为止，没有 关于GIP C-末端的翻译后处理的信息 是可用的。确定翻译后处理的重要性 本项目将：(1)确定具有生物活性的部分 通过检测不同的ProGIP多肽片段的作用 刺激大鼠胰岛素瘤细胞株(RIN-5AH)释放胰岛素； (2)考察ProGIP的C-末端在翻译后的加工 大鼠十二指肠和唾液腺，已知表达GIP基因的器官， 在基础状态和刺激(葡萄糖喂养)状态下，使用区域- 针对ProGIP不同肽段的特异性抗体；(3) 确定调控翻译后加工的分子机制 内分泌和小肠导入对原糖蛋白C末端的影响 野生型和突变型(定点突变)GIP细胞系 DNA总的来说，从这项提案中获得的信息将增加一个 我们对分子机制的理解有了新的意义 参与ProGIP的翻译后加工。此外，由于 GIP与其他GI的密切结构和功能关系 多肽，这样的研究将促进我们对 涉及与营养相关的激素处理的分子机制。 最后，这些研究应该加强我们对生物的了解。 GIP以及GIP在慢性粒细胞白血病发病中的作用 以胃酸分泌异常为特征的疾病和 葡萄糖动态平衡。

Gastric inhibitory peptide (GIP) was first isolated from porcine small intestine and was originally named for its ability to inhibit acid secretion. Subsequent analysis of its physiological properties has demonstrated that GIP is a potent stimulator of endogenous insulin release and that it plays an important role in maintaining glucose and lipid homeostasis. Recent studies in patients with type II diabetes mellitus have demonstrated that although nutrient-stimulated GIP release appears to be normal, the insulinotropic effect of exogenous GIP is greatly diminished, suggesting that GIP may not be functionally active. Most gastrointestinal regulatory peptides undergo posttranslational processing prior to becoming biologically active. Although GIP was first recognized as a 42 amino acid polypeptide, recent studies performed in this laboratory indicated that a smaller alpha-amidated form of GIP(1-30) possesses similar insulinotropic effects to GIP(1-42). Furthermore, a glycine-extended prohormone followed by a dibasic Lys-Lys residue has been identified in the GIP cDNA sequence. It is thus likely that proGIP undergoes posttranslational C-terminal alpha-amidation modification before becoming biologically active. Moreover, it is also possible that abnormal posttranslational processing of proGIP could play a role in the pathogenesis of type II diabetes mellitus. To date, however, no information regarding posttranslational processing of the C-terminus of GIP is available. To determine the importance of posttranslational processing of proGIP, this project will: (1) define the biologically active portions of proGIP by examining the effects of different peptide fragments of proGIP in stimulating insulin release from a rat insulinoma cell line (RIN-5AH); (2) examine the postranslational processing of the C-terminus of proGIP in the rat duodenum and salivary glands, organs known to express the GIP gene, during both basal and stimulated (glucose fed) states, using region- specific antibodies against different peptide fragments of proGIP; (3) determine the molecular mechanisms regulating posttranslational processing of the C-terminus of proGP by transfecting endocrine and small intestinal cell lines with wild type and mutant (by site-directed mutagenesis) GIP DNA. Collectively, the information gained from this proposal will add a significant new dimension to our understanding of the molecular mechanisms involved in posttranslational processing of proGIP. Moreover, because of the close structural and functional relationship of GIP to other GI peptides, such studies will advance our general understanding of the molecular mechanisms involved in nutrient-related hormone processing. Finally, these studies should enhance our understanding of the biology of GIP and of the possibility of GIP contributing to the pathogenesis of diseases characterized by abnormalities in gastric acid secretion and glucose homeostasis.