Regulation of SREBP-1c Processing by Insulin and Cyclic-AMP

胰岛素和环磷酸腺苷对 SREBP-1c 加工的调节

• 批准号: 7630411
• 负责人: MARSHALL B ELAM
• 金额: $ 26.47万
• 依托单位: UNIVERSITY OF TENNESSEE HEALTH SCI CTR
• 依托单位国家: 美国
• 财政年份: 2007
• 资助国家: 美国
• 起止时间: 2007-07-01 至 2011-06-30
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/7630411
• 关键词: 1-Phosphatidylinositol 3-Kinase; ADD-1 protein; Abbreviations; Acyl Coenzyme A; Acyltransferase; Address; Animals; Bucladesine; COPII-Coated Vesicles; Cell Nucleus; Cell membrane; Ceramides; Cholesterol; Chronic; Complex; Cyclic AMP; Cyclic AMP-Dependent Protein Kinases; Dyslipidemias; Elements; Enzymes; Equilibrium; Fatty acid glycerol esters; Fatty-acid synthase; Figs - dietary; Functional disorder; Genes; Genetic Transcription; Genetic Translation; Glucagon; Glycogen; Glycogen Synthase Kinase 3; Goals; Golgi Apparatus; Hepatic; Hepatocyte; Hour; Hyperinsulinism; Hyperlipidemia; In Vitro; Insulin; Integral Membrane Protein; Length; Lipids; Lipoproteins; Liver; MAP Kinase Gene; MEKs; Marshal; Mediating; Membrane; Membrane Proteins; Metabolic; Metabolic syndrome; Mitogen-Activated Protein Kinase 3; Mitogen-Activated Protein Kinases; Modification; Molecular Chaperones; Myocardial Infarction; N-terminal; Non-Insulin-Dependent Diabetes Mellitus; Nuclear; Obesity; Pathogenesis; Pathway interactions; Phosphatidylinositide 3-Kinase Inhibitor; Phosphatidylinositols; Phosphorylation; Phosphotransferases; Plasma; Polyunsaturated Fatty Acids; Post-Translational Regulation; Process; Protein Isoforms; Protein Kinase C; Proteins; Proteolytic Processing; Rattus; Regulation; Research; Research Personnel; Risk; Role; SCAP protein; SRE-2 binding protein; SREBP-1a; Signal Pathway; Site; Sphingolipids; Sphingomyelinase; Sterol O-Acyltransferase; Sterols; Stroke; Testing; Triglycerides; Up-Regulation; Very low density lipoprotein; Vesicle; base; efficacy testing; genetic regulatory protein; in vivo; in vivo Model; inhibitor/antagonist; inorganic phosphate; lipid biosynthesis; new therapeutic target; novel; particle; prevent; programs; promoter; protein kinase A kinase; response; sterol esterase; transcription factor

DESCRIPTION (provided by applicant): The chronic hyperinsulinemia that accompanies obesity, metabolic syndrome, and type II diabetes mellitus sustains increased hepatic lipogenesis via transcriptional upregulation of lipogenic enzymes. This results in overproduction of VLDL by the liver with resulting accumulation of atherogenic triglyceride-rich lipoproteins in the plasma. Induction of lipogenesis by insulin is mediated by sterol regulatory element binding protein-1c (SREBP-1c) via transcriptional upregulation. SREBP-1c is synthesized as an integral membrane protein localized in the ER where it is associated with its chaperone (SCAP) and regulatory proteins (Insig2, Sec24). We have found that, in addition to promoting transcription of nascent SREBP-1c, insulin also stimulates transport of the SREBP-SCAP complex to the golgi where it undergoes proteolytic cleavage to release the transcriptionally active N-terminal fragment of SREBP-1c (SREBP-1c processing), thereby amplifying the transcriptional effects of insulin. Conversely, cAMP (a surrogate for glucagon) prevents processing of SREBP-1c. Thus, processing of SREBP-1c is a novel and potentially important additional level by which insulin and other factors regulate this pivotal transcription factor. Although the mechanisms by which processing of the cholesterol regulating isoform, SREBP-2, by sterol balance have been extensively studied, little is known about regulation of SREBP-1c processing by insulin and cAMP. We have also found that nascent SREBP-1c is phosphorylated in the presence of insulin via MAPK and PI-3K dependent pathways. Inhibitors of these pathways prevent both phosphorylation of SREBP-1c and insulin induced processing indicating that phosphorylation of SREBP-1c (and possibly of other participating proteins) may mediate the effect of insulin on processing. We therefore propose to delineate the mechanism(s) by which insulin and cAMP regulate proteolytic processing of SREBP-1c by identifying (1) the sites on SREBP-1c that are phosphorylated by insulin, (2) the signaling pathways that mediate the effect of insulin to stimulate and cAMP to inhibit processing, and (3) the functional significance of phosphorylation for regulation of SREBP-1c processing. We will also determine the additional roles of regulation of ER membrane cholesterol content and Insig2 expression by insulin in SREBP-1c processing. These studies will be carried out both in vitro in primary rat hepatocytes and in an in vivo model of hyperinsulinemia, the corpulent JCR:LA-cp rat. Relevance: in obesity, metabolic syndrome, and adult-onset diabetes mellitus, high insulin levels promote formation of fat (triglyceride) by the liver. The resulting elevated levels of triglyceride in the plasma increase the risk of heart attack and stroke. This research examines the role of an important regulatory protein, SREBP-1c in the response of the liver to high insulin levels. The goal of this research is to identify new treatments for hyperlipidemia by understanding the mechanisms by which insulin regulates this protein.

描述（由申请人提供）：伴随肥胖、代谢综合征和II型糖尿病的慢性高胰岛素血症通过脂肪生成酶的转录上调维持肝脂肪生成增加。这导致肝脏过量产生极低密度脂蛋白（VLDL），从而导致血浆中富含致动脉粥样硬化的甘油三酯的脂蛋白积累。胰岛素诱导脂肪生成是由甾醇调节元件结合蛋白-1c (SREBP-1c) 通过转录上调介导的。 SREBP-1c 被合成为位于 ER 中的整合膜蛋白，与其分子伴侣 (SCAP) 和调节蛋白（Insig2、Sec24）相关。我们发现，除了促进新生SREBP-1c的转录外，胰岛素还刺激SREBP-SCAP复合物转运至高尔基体，在高尔基体中进行蛋白水解，释放SREBP-1c的转录活性N端片段（SREBP-1c加工），从而放大胰岛素的转录效应。相反，cAMP（胰高血糖素的替代物）会阻止 SREBP-1c 的加工。因此，SREBP-1c 的加工是一种新颖且潜在重要的附加水平，胰岛素和其他因子通过它来调节这一关键转录因子。尽管通过甾醇平衡调节胆固醇同工型 SREBP-2 的加工机制已被广泛研究，但对胰岛素和 cAMP 对 SREBP-1c 加工的调节知之甚少。我们还发现，新生的 SREBP-1c 在胰岛素存在下通过 MAPK 和 PI-3K 依赖性途径被磷酸化。这些途径的抑制剂可阻止 SREBP-1c 的磷酸化和胰岛素诱导的加工，表明 SREBP-1c（以及可能的其他参与蛋白）的磷酸化可能介导胰岛素对加工的影响。因此，我们建议通过确定（1）SREBP-1c上被胰岛素磷酸化的位点，（2）介导胰岛素刺激作用和cAMP抑制加工作用的信号通路，以及（3）磷酸化对调节SREBP-1c蛋白水解加工的功能意义来描述胰岛素和cAMP调节SREBP-1c蛋白水解加工的机制。 SREBP-1c 处理。我们还将确定胰岛素在 SREBP-1c 加工中调节 ER 膜胆固醇含量和 Insig2 表达的额外作用。这些研究将在体外原代大鼠肝细胞和体内高胰岛素血症模型（肥胖的 JCR:LA-cp 大鼠）中进行。相关性：在肥胖、代谢综合征和成人糖尿病中，高胰岛素水平会促进肝脏形成脂肪（甘油三酯）。由此产生的血浆中甘油三酯水平升高会增加心脏病发作和中风的风险。这项研究探讨了一种重要的调节蛋白 SREBP-1c 在肝脏对高胰岛素水平的反应中的作用。这项研究的目的是通过了解胰岛素调节这种蛋白质的机制来确定高脂血症的新疗法。