Role of a novel CREB regulator in hepatic gluconeogenesis

描述（由申请人提供）：在早期禁食期间，循环胰高血糖素的增加部分通过pka介导的磷酸化和转录因子CREB的激活来刺激糖异生程序。CREB共激活子CRTC2在CREB诱导的转录激活中起着重要的相互作用伙伴的作用。然而，CRTC2选择性激活CREB靶基因的分子机制尚不清楚。在CREB相关蛋白的无偏分析中，蛋白精氨酸甲基转移酶5 （PRMT5）被确定为CREB的推定相互作用蛋白。初步结果表明，PRMT5过表达可增加CREB活性，而CRTC2共表达可进一步增加CREB活性，提示PRMT5作为共激活因子发挥作用。该研究旨在确定PRMT5是否通过肝细胞中CREB或其共激活因子的精氨酸甲基化来调节CREB介导的糖异生基因激活。在具体目标1中，将探讨PRMT5在CREB甲基化和调节CREB与CRTC2或CBP之间相互作用中的作用。经过甲基化的CREB精氨酸残基将被识别。在特定目标2中，PRMT5在介导胰高血糖素对creb调节的糖异生程序的作用将通过肝细胞中PRMT5的过表达或缺失来确定。PRMT5在胰高血糖素作用下对creb结合的糖异生启动子的招募将被揭示。将探讨精氨酸甲基化在creb介导的转录中的重要性。在特定目标3中，将评估PRMT5在调节空腹葡萄糖生成中的作用。PRMT5促进高血糖的潜在作用将在胰岛素抵抗条件下进行测试。总的来说，拟议的研究将提供在禁食期间如何调节肝脏糖异生的见解。空腹高血糖在胰岛素抵抗患者中很常见，部分原因是肝脏糖异生上调。因此，该结果可能为开发新的2型糖尿病治疗方法提供新的分子靶点。

DESCRIPTION (provided by applicant): During early fasting, increases in circulating pancreatic glucagon stimulate the gluconeogenic program in part via PKA-mediated phosphorylation and activation of the transcription factor CREB. The CREB coactivator, CRTC2, has been shown to function as an essential interacting partner in CREB-induced transcription activation. However, the molecular mechanisms by which CRTC2 selectively activates CREB target genes remain unclear. In an unbiased analysis of CREB- associated proteins, the protein arginine methyltransferase 5 (PRMT5) was identified as a putative interacting protein of CREB. Preliminary results indicate that overexpression of PRMT5 increases CREB activity and co-expression of CRTC2 further increases these effects, suggesting that PRMT5 functions as a coactivator. The proposed research is to determine whether PRMT5 modulates CREB-mediated gluconeogenic gene activation through arginine methylation of CREB or its coactivators in hepatic cells. In specific aim 1, the role of PRMT5 in methylating CREB and modulating the interaction between CREB and CRTC2 or CBP will be explored. CREB arginine residues that undergo methylation will be identified. In specific aim 2, the role of PRMT5 in mediating glucagon effects on the CREB-regulated gluconeogenic program will be determined by overexpression or depletion of PRMT5 in hepatocytes. The recruitment of PRMT5 to CREB-bound gluconeogenic promoters in response to glucagon will be revealed. The importance of arginine methylation in CREB-mediated transcription will be explored. In specific aim 3, the role of PRMT5 in regulating fasting glucose production will be evaluated. The potential effects of PRMT5 in promoting hyperglycemia will be tested under insulin resistance conditions. Collectively, the proposed studies will provide insight of how hepatic gluconeogenesis is regulated during fasting. Fasting hyperglycemia is common in insulin resistance patients in part due to up-regulation of hepatic gluconeogenesis. Thus, the results may lead to new molecular targets for the development of new therapeutic treatment of type II diabetes. PUBLIC HEALTH RELEVANCE: Type II diabetic patients exhibit insulin resistance, a condition characterized by increased blood glucose production in the liver and reduced glucose uptake by muscle. Fasting blood glucose levels are increased in insulin resistant patients in part due to up-regulation of hepatic gluconeogenesis. Understanding the molecular mechanism by which gluconeogenesis is regulated may lead to new targets for therapeutic intervention in type II diabetes.