The role of serine phosphorylation of IRS-2 in hepatic insulin resistance

项目摘要 本修订提案(DK081513)重点研究IRS-2的丝氨酸/苏氨酸磷酸化。 ERK、mTOR和p70S6K在介导初始肝胰岛素抵抗中的作用胰岛素在肝脏中的作用 在维持血糖动态平衡方面起着重要作用。肝脏胰岛素信号的缺陷导致系统性 胰岛素抵抗与2型糖尿病的慢性高血糖。在肝脏中，IRS-2是主要的 胰岛素受体酪氨酸激酶的生理底物；因此，IRS-2的足够功能是 对于正常的肝脏胰岛素信号来说是必不可少的。IRS-2含有许多潜在的丝氨酸/苏氨酸磷酸化 潜在地被不同的丝氨酸/苏氨酸激酶作为靶点的位置。IRS-1丝氨酸磷酸化 已被证明可以减弱胰岛素信号；然而，对IRS-2知之甚少。我们的初步研究已经 确认了许多丝氨酸/苏氨酸激酶的激活以及多个 胰岛素抵抗动物肝脏IRS-2中丝/苏氨酸残留量。在被测试的少数人中，已知 IRS-1、ERK和mTOR/p70S6K是唯一与肝脏胰岛素抵抗相关的激酶， 提示这些丝氨酸激酶在耐药肝中被选择性地激活。在这项提案中，我们 假设ERK、mTOR和/或p70S6K使IRS-2丝氨酸/苏氨酸磷酸化形成 肝脏中的初始胰岛素抵抗信号并导致肝脏胰岛素抵抗，导致外周胰岛素 抵抗。这一应用是为了在肝脏和分离的原代肝细胞中测试这一假说。 IRS-2上这些激酶的激活及其磷酸化的动态变化 将监测胰岛素抵抗的发展情况。关键的丝氨酸/苏氨酸激酶将被确定，其 将使用腺病毒研究与胰岛素信号通路的相互作用，特别是IRS-2。 和/或siRNA技术。还将应用独特的策略来识别未知的丝氨酸/苏氨酸 IRS-2和IRS-2激酶的磷酸化位点。这项建议的目的是定义初始胰岛素 肝脏中的抗性信号(激酶激活和IRS-2的磷酸化)。这次调查的结果 应提供对胰岛素敏感性的分子决定因素的更清晰、更完整的理解 肝脏和整个生物体。

Project Summary This revised proposal (DK081513) focuses on the investigation of serine/threonine phosphorylation of IRS-2 by ERK, mTOR and p70S6K in mediating initial hepatic insulin resistance. Insulin action in the liver plays an important role in maintaining glucose homeostasis. Defects in hepatic insulin signaling contribute to systematic insulin resistance and the chronic hyperglycemia of type 2 diabetes. In the liver, IRS-2 is the primary physiological substrate for the insulin receptor tyrosine kinase; as such, sufficient functionality of IRS-2 is essential for proper hepatic insulin signaling. IRS-2 contains many potential serine/threonine phosphorylation sites which are potentially targeted by diverse serine/threonine kinases. Serine phosphorylation of IRS-1 has been shown to attenuate insulin signaling; however, little is known about IRS-2. Our preliminary studies have confirmed activation of numerous serine/threonine kinases as well as phosphorylation of multiple serine/threonine residues in IRS-2 from the liver of insulin-resistant animals. Among tested handful known kinases for IRS-1, ERK and mTOR/p70S6K were the only kinases that correlated with hepatic insulin resistance, suggesting that these serine kinases are selectively activated in resistant liver. In this proposal, we hypothesize that serine/threonine phosphorylation of IRS-2 by ERK, mTOR and/or p70S6K forms an initial insulin resistant signal in liver and cause hepatic insulin resistance, leading to peripheral insulin resistance. This application is designed to test this hypothesis in liver and in isolated primary hepatocytes. Dynamic changes in the activation of these kinases and their phosphorylation on IRS-2 during the development of insulin resistance will be monitored. Key serine/threonine kinase will be identified and its interactions with the insulin signaling pathway -and IRS-2 in particular- will be investigated using adenoviral and/or siRNA techniques. Unique strategies will also be applied to identify unknown serine/threonine phosphorylation sites in IRS-2 and IRS-2 kinases. The objective of this proposal is to define the initial insulin resistant signal (activation of kinase and phosphorylation of IRS-2) in liver. The results from this investigation should provide a clearer, integrative understanding of the molecular determinants of insulin sensitivity in the liver as well as the whole organism.