Molecular Basis of Antidiabetogenic Hormone Action

描述(申请人提供)：实验治疗学中的一个新兴主题涉及使用胰升糖素样肽-1-(7-36)-酰胺(GLP-1)及其合成肽类似物(“胰岛素模拟物”)来降低2型糖尿病受试者的血糖水平。GLP-1的这种作用至少部分是由于它能够刺激位于朗格汉斯胰岛的胰岛β细胞分泌胰岛素。鉴于GLP-1在糖尿病治疗中的重要性，我们的实验室有兴趣确定β细胞GLP-1受体(GLP-1-R)的信号转导特性。为此，我们重点研究了一种新发现的信号机制，该机制使用第二信使cAMP激活cAMP调节的鸟嘌呤核苷酸交换因子，命名为Epac1和Epac2(由环AMP直接激活的交换蛋白)。我们的研究使我们假设GLP-1，一种cAMP升高的激素，刺激依赖于钙的胰岛素的分泌，并且这种胰岛素调节作用不仅通过蛋白激酶A(PKA)，而且还通过EPAC。为了验证我们关于EPAC在GLP-1-R介导的信号转导中可能扮演的角色的假说，本项目的具体目的是：1)确定GLP-1是否利用Epac1和/或Epac2通过起源于内质网(ER)的钙诱导钙释放(CICR)过程来动员细胞内钙；2)评估Rap家族GTP酶在ER钙动员过程中的作用，特别是Rap1作为EPAC激活与磷脂酶C-epsilon刺激的中间环节的潜在作用。3)确定一种新的信号机制的性质，通过这种新的信号机制，β细胞生长因子和受体酪氨酸激酶利用RAS GTP酶将Epac2募集到质膜上，在质膜上Epac2与其可能的效应分子磺酰脲受体-1(SUR1)发生相互作用。这条调查路线的相关性是完全显而易见的。我们希望建立一种新型降糖剂的“抗糖尿病”特性的分子基础，这种降糖剂可以激活GLP-1-R并刺激胰腺胰岛素的分泌。

DESCRIPTION (provided by applicant): An emerging theme in experimental therapeutics concerns the use of glucagon-like peptide-1-(7-36)-amide (GLP-1) and its synthetic peptide analogs (the "incretin mimetics") to lower levels of blood glucose in Type 2 diabetic subjects. This action of GLP-1 results, at least in part, from its ability to stimulate the secretion of insulin from pancreatic beta cells located in the islets of Langerhans. Given the established importance of GLP-1 for the treatment of diabetes, our laboratory is interested in defining the signal transduction properties of the beta cell GLP-1 receptor (GLP-1-R). To this end, we have focused on a newly-discovered signaling mechanism that uses the second messenger cAMP to activate cAMP-regulated guanine nucleotide exchange factors designated as Epac1 and Epac2 (the Exchange Proteins directly Activated by Cyclic AMP). Our studies lead us to Hypothesize that GLP-1, a cAMP-elevating hormone, stimulates Ca2+-dependent insulin secretion, and that this insulinotropic action is mediated not simply by protein kinase A (PKA), but also by Epac. To test our Hypothesis concerning the putative role of Epac in GLP-1-R-mediated signal transduction, the Specific Aims of this project are to: 1) determine if GLP-1 uses Epac1 and/or Epac2 to mobilize intracellular Ca2+ via a process of Ca2+-induced Ca2+ release (CICR) that originates at the endoplasmic reticulum (ER) and which may involve IP3 receptors or ryanodine receptors, 2) assess what role Rap family GTPases play in the process of ER Ca2+ mobilization, with special emphasis on the potential role of Rap1 as an intermediary linking activation of Epac to the stimulation of phospholipase C-epsilon, and 3) determine the nature of a novel signaling mechanism by which beta cell growth factors and receptor tyrosine kinases utilize the Ras GTPases to recruit Epac2 to the plasma membrane where an interaction of Epac2 with its putative effector molecule the sulfonylurea receptor-1 (SUR1) occurs. The Relevance of this line of investigation is fully apparent. We wish to establish the molecular basis for "antidiabetogenic" properties of a new class of blood glucose-lowering agents that activate the GLP-1-R and which stimulate pancreatic insulin secretion.