INSULIN RECEPTOR THIOL REACTIVITY AND INSULIN SIGNALING

工作总结：胰岛素受体是由两个α亚基和两个β亚基通过二硫键连接在一起的同型二聚体。胰岛素与α亚基的结合触发受体β亚基胞质结构域的内在酪氨酸激酶功能。胰岛素对该受体的激活在介导多种生理过程中起重要作用，包括调节葡萄糖稳态和基因表达。早期的研究发现，胰岛素受体的功能活性可以通过细胞环境中的氧化还原调节来调节。例如，向细胞中加入抗氧化剂如N-乙酰基-L-半胱氨酸（NAC）与胰岛素受体催化功能的降低有关，而用过氧化氢处理细胞促进拟胰岛素作用。我们推测，还原型谷胱甘肽（GSH），这构成了血浆非蛋白硫醇的主要来源，和NAC可能在改变胰岛素受体的硫醇反应性，从而降低胰岛素反应性的作用。在最近发表的一项研究中，我们提供了第一个证据，即胰岛素受体α亚基含有一组选择的二硫化物，其氧化还原状态可以被还原剂GSH和NAC快速可逆地改变。虽然对胰岛素结合几乎没有影响，但GSH显著减弱胰岛素信号转导。胰岛素受体的寡聚体结构不受这两种化合物的影响。我们计划鉴定反应性受体巯基。这些知识将允许对胰岛素受体二硫化物的这一选择组进行致突变结构/功能分析。

Summary of work: The insulin receptor is a homodimer consisting of two alpha- and two beta-subunits linked together by disulfide bonds. Insulin binding to the alpha-subunit triggers the intrinsic tyrosine kinase function of the cytoplasmic domain of the receptor beta-subunit. Activation of this receptor by insulin plays an important role in mediating diverse physiological processes, including modulation of glucose homeostasis and gene expression. Earlier findings have found that the functional activity of the insulin receptor can be modulated by redox regulation in the cellular environment. For example, addition of antioxidant such as N-acetyl-L-cysteine (NAC) to cells has been associated with a reduction in insulin receptor catalytic function, whereas cell treatment with hydrogen peroxide promotes insulinomimetic effects. We postulated that reduced glutathione (GSH), which constitutes the major source of plasma nonprotein thiols, and NAC may play a role in altering thiol reactivity of the insulin receptor and thus reduce insulin responsiveness. In a recent published study, we provided the first evidence that the insulin receptor alpha-subunit contains a select group of disulfides whose redox status can be rapidly and reversibly altered by the reducing agents GSH and NAC. While having little impact on insulin binding, GSH markedly attenuated insulin signal transduction. The oligomeric structure of the insulin receptor was not affected by neither of these compounds. We plan to identify the reactive receptor thiol group(s). Such knowledge will allow mutagenic structure/function analysis of this select group of insulin receptor disulfides.