Effects of diet and diabetes on gene expression in the liver

描述（由申请人提供）：拟定项目将检验以下假设：高血糖症和糖尿病单独或联合作用，导致通过氨基己糖生物合成途径的葡萄糖流量增加，从而导致O-GlcNAc酰化增加、泛素化减少和肝脏中4 E-BP 1蛋白酶体介导的降解减少。4 E-BP 1的上调表达反过来又产生从帽依赖性到帽非依赖性mRNA翻译的转变。哺乳动物eIF 4 E结合蛋白（4 E-BP）通过结合帽结合蛋白eIF 4 E并阻止其与eIF 4G结合来抑制帽依赖性翻译。通过eIF 4 E的5 '-帽结合通常被认为是翻译起始中的限速步骤，因此4 E-BP 1的可逆磷酸化是调节mRNA结合的最佳表征机制之一。一个未探索的机制，也可能有助于调节mRNA帽结合是改变表达的一个或多个4 E-BP。4 E-BP 1的上调表达可能导致与适应不良的代谢相关的病理学，这是由于从帽依赖性翻译转变为帽非依赖性翻译导致的肝蛋白表达改变的结果。在本研究中，我们将使用糖尿病大鼠和培养的HepG 2细胞来评估高血糖导致肝脏中4 E-BP 1表达上调的机制。 公共卫生相关性：该项目将探索高血糖和/或糖尿病状态诱导肝脏中4 E-BP 1表达上调的机制。尽管4 E-BP 1可逆磷酸化对翻译起始的调控已被广泛表征，但翻译阻遏物表达的变化在很大程度上未被探索。由于营养过剩和糖尿病状态导致的肝脏中4 E-BP 1表达增加可能导致与代谢功能障碍相关的病理学，因此是公共卫生方面探索的关键领域。

DESCRIPTION (provided by applicant): The proposed project will test the hypothesis that hyperglycemia and diabetes, acting alone or in combination, cause increased flux of glucose through the hexosamine biosynthetic pathway which results in increased O-GlcNAcylation, decreased ubiquitination, and decreased proteosomal-mediated degradation of the 4E-BP1 in the liver. The upregulated expression of 4E-BP1, in turn, produces a shift from cap-dependent to cap-independent mRNA translation. Mammalian eIF4E binding proteins (4E- BPs) inhibit cap-dependent translation by binding to the cap-binding protein eIF4E and preventing its association with eIF4G. 5'-cap binding by eIF4E is typically thought of as the rate-limiting step in translation initiation, and as such the reversible phosphorylation of 4E-BP1 is one of the best characterized mechanisms for regulating mRNA binding. An unexplored mechanism that also likely contributes to the regulation of mRNA cap-binding is altered expression of one or more of the 4E-BPs. Upregulated expression of 4E-BP1 likely contributes to pathologies associated with maladapted metabolism, as a result of altered hepatic protein expression due to the shift from cap-dependent to cap-independent translation. In the proposed studies, we will use diabetic rats and HepG2 cells in culture to evaluate the mechanism through which hyperglycemia leads to upregulated expression of 4E-BP1 in the liver. PUBLIC HEALTH RELEVANCE: The proposed project will explore the mechanism(s) through which hyperglycemia and/or the diabetic state induce upregulated expression of 4E-BP1 in the liver. Although the regulation of translation initiation by the reversible phosphorylation of 4E-BP1 has been extensively characterized, changes in the expression of the translational repressor are largely unexplored. Increased expression of the 4E-BP1 in the liver due to excess nutrients and the diabetic state likely contributes to pathologies associated with metabolic dysfunction and as a result is a critical area for exploration in regards to public health.