Histone Acetylation and Insulin Gene Expression

描述（由申请人提供）：葡萄糖对胰岛素基因转录的正常调节对于维持葡萄糖稳态至关重要，并且需要β细胞特异性转录因子Pdx-1、MafA和NeuroD 1。然而，葡萄糖通过调节这些转录因子的功能来增加胰岛素基因表达的确切机制仍然未知。我们发现葡萄糖调节Pdx-1的DNA结合活性，并且Pdx-1被乙酰化修饰。此外，我们发现葡萄糖通过Pdx-1募集组蛋白乙酰化酶p300，在胰岛素启动子处引起组蛋白H4的超乙酰化，从而刺激胰岛素基因转录。通过乙酰化修饰核心组蛋白已被证明可以改变基因表达，但指导组蛋白乙酰化到特定基因启动子的机制还不清楚。基于我们的初步数据，我们假设高血糖水平通过调节β细胞特异性转录因子Pdx-1介导的组蛋白H4乙酰化来刺激胰岛素基因转录。将通过解决以下问题进一步研究该假设：1）葡萄糖调节的Pdx-1乙酰化对Pdx-1活性和/或DNA结合重要吗？2)组蛋白乙酰转移酶p300/CBP和GCN 5/PCAF在葡萄糖调节胰岛素基因表达中起什么作用？3)β细胞特异性转录因子MafA和NeuroD 1是否通过募集组蛋白乙酰转移酶来调节胰岛素基因的转录？ 虽然大多数实验将使用小鼠胰岛素瘤MIN 6细胞系进行，但关键发现将使用原代大鼠胰岛进行确认。最近的数据表明，组蛋白乙酰化缺陷与糖尿病的发病机制有关。MODY基因HNF-1 α和HNF-4 α中的几种导致糖尿病的突变干扰了它们与组蛋白乙酰化酶的相互作用。亨廷顿舞蹈病患者由于组蛋白乙酰化酶降解导致胰岛素基因表达降低，易患II型糖尿病。关于高血糖水平如何调节胰腺中β细胞特异性基因表达的信息将有助于理解这一过程中的缺陷如何导致糖尿病。此外，所获得的数据将有助于我们了解Pdx-1，MafA和NeuroD 1在胰腺发育和葡萄糖刺激的胰岛素基因转录调控中的功能。

DESCRIPTION (provided by applicant): Normal regulation of insulin gene transcription by glucose is essential for the maintenance of glucose homeostasis, and requires the beta-cell specific transcription factors Pdx-1, MafA and NeuroD1. However the exact mechanism(s) by which glucose increases insulin gene expression by modulating the function of these transcription factors remains unknown. We found that glucose regulates the DNA binding activity of Pdx-1 and that Pdx-1 is modified by acetylation. Furthermore, we discovered that glucose stimulates insulin gene transcription by causing hyperacetylation of histone H4 at the insulin promoter via the recruitment of the histone acetylase p300 by Pdx-1. Modification of core histones by acetylation has been shown to alter gene expression, but the mechanisms that direct histone acetylation to specific gene promoters are not well understood. Based on our preliminary data, we hypothesize that high blood glucose levels stimulate insulin gene transcription via modulation of histone H4 acetylation mediated by the beta-cell specific transcription factor Pdx-l. This hypothesis will be further investigated by addressing the following questions: 1) Is the glucose-regulated acetylation of Pdx-1 important for Pdx-1 activity and/or DNA binding? 2) What role do the histone acetyltransferases p300/CBP and GCN5/PCAF play in glucose regulation of insulin gene expression? 3) Do the beta-cell specific transcription factors MafA and NeuroD1 regulate insulin gene transcription by recruiting histone acetyltransferases? Although, most of the experiments will be carried out using the mouse insulinoma MIN6 cell line, the key findings will be confirmed using primary rat islets. Recent data indicate that defects in histone acetylation are associated with the pathogenesis of diabetes. Several of the diabetes-causing mutations in the MODY genes HNF-1alpha and HNF-4alpha interfere with their interaction with histone acetylases. Patients with Huntington's disease are prone to type II diabetes due to decreased insulin gene expression caused by degradation of histone acetylases. Information on how high blood glucose levels regulate beta-cell specific gene expression in the pancreas will help to understand how defects in this process result in diabetes. In addition, the data obtained will contribute to our understanding of Pdx-1, MafA and NeuroD1 function in the regulation of pancreas development and glucose-stimulated insulin gene transcription.