Regulation of Insulin Gene Expression in Liver Cells

描述(由申请人提供)：转录调控在决定组织特异性方面起着重要作用，每个组织都有一组特定的转录因子。在胰腺中，限制胰岛素基因表达的主要转录因子是同源结构域蛋白PDX-1。胰岛素的产生是维持血糖稳态所必需的，而葡萄糖调节的胰岛素基因转录缺陷会导致糖尿病。我们最近发现，葡萄糖通过组蛋白H4的超乙酰化来调节β细胞中胰岛素基因的表达。有趣的是，在胰岛素基因转录沉默的肝细胞中，没有显著的组蛋白乙酰化与胰岛素基因启动子相关。然而，将PDX-1导入肝细胞，以葡萄糖依赖的方式增加了正常沉默的胰岛素基因启动子上的组蛋白H4乙酰化，并刺激了胰岛素的产生。基于这些数据，我们假设，将PDX-1引入肝细胞后，通过增加组蛋白H4的乙酰化，激活了正常沉默的胰岛素基因，以响应高水平的葡萄糖。这项建议的主要目标是通过解决以下问题来了解将PDX-1导入肝细胞如何刺激正常沉默的胰岛素基因的转录： 1.将PDX-1导入肝细胞是否会引起组蛋白修饰的葡萄糖调节变化？组蛋白修饰通常是沉默的胰岛素基因。 2.PDX-1是否通过以葡萄糖依赖的方式招募胰岛素基因启动子的共激活子或共抑制子来改变肝细胞组蛋白H4乙酰化水平？ 3.将β细胞特异性转录因子Ribe3b1导入肝细胞是否如PDX-1观察到的那样引起组蛋白修饰的变化？ 了解PDX-1如何刺激正常沉默的胰岛素基因在肝细胞中的转录，将有助于发展能够以葡萄糖依赖的方式产生胰岛素的肝细胞系。这种非β细胞系的发展对于I型和II型糖尿病的治疗将是重要的。

DESCRIPTION (provided by applicant): Transcriptional regulation plays an important role in determining tissue specificity and every tissue is characterized by a set of specific transcription factors. In the pancreas, the major transcription factor that restricts insulin gene expression to the pancreatic beta cells is the homeodomain protein Pdx-1. Insulin production is essential for maintaining glucose homeostasis and defects in glucose-regulated insulin gene transcription result in diabetes. We have recently discovered that glucose regulates insulin gene expression in beta cells by hyperacetylation of histone H4. Interestingly, in liver cells where the insulin gene is transcriptionally silent, no significant histone acetylation is associated with the insulin gene promoter. However, introduction of Pdx-1 into liver cells caused increased histone H4 acetylation at the normally silent insulin gene promoter in a glucose-dependent manner and stimulated insulin production. Based on these data, we hypothesize that introduction of Pdx-1 into liver cells activates the normally silent insulin gene in response to high levels of glucose by increasing histone H4 acetylation. The major goal of this proposal is to understand how introduction of Pdx-1 into the liver cells stimulates the transcription of the normally silent insulin gene, by addressing the following questions: 1. Does introduction of Pdx-1 into liver cells cause glucose-regulated changes in histone modification, at the normally silent insulin gene locus? 2. Does Pdx-1 change histone H4 acetylation levels in liver cells by recruiting co-activators or co-repressors to the insulin gene promoter in a glucose-dependent manner? 3. Does the introduction of the beta-cell specific transcription factor Ribe3b1 into the liver cells cause changes in histone modification as observed with Pdx-1? Understanding of how Pdx-1 stimulates the transcription of the normally silent insulin gene in liver cells, will facilitate the development of liver cell lines that can produce insulin in a glucose-dependent manner. The development of such non-beta cell lines will be important for the treatment of type I and as well as type II diabetes.