Effects of diet and diabetes on gene expression in the liver

描述（由申请人提供）：提议的项目将测试假设，即高血糖和糖尿病，单独或联合作用，通过己糖胺生物合成途径引起葡萄糖通量增加，从而导致o - glcn酰化增加，泛素化减少，并减少肝脏中4E-BP1的蛋白体介导降解。反过来，4E-BP1的上调表达产生了从帽依赖到帽不依赖的mRNA翻译的转变。哺乳动物eIF4E结合蛋白（4E- bp）通过与帽结合蛋白eIF4E结合并阻止其与eIF4G的关联来抑制帽依赖性翻译。eIF4E结合5'-cap通常被认为是翻译起始的限速步骤，因此，4E-BP1的可逆磷酸化是调控mRNA结合的最佳表征机制之一。一种未被探索的机制也可能有助于调控mRNA帽结合，即改变一种或多种4e - bp的表达。4E-BP1的表达上调可能导致与代谢失调相关的病理，这是由于从帽依赖翻译转变为帽独立翻译导致肝脏蛋白表达改变的结果。在拟建的研究中，我们将使用糖尿病大鼠和培养的HepG2细胞来评估高血糖导致肝脏中4E-BP1表达上调的机制。

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.