Role of O-GlcNAc transferase in insulin gene expression

描述（由申请方提供）：尽管多条证据表明O-GlcNAc修饰水平的增加会干扰正常葡萄糖稳态，但该修饰的确切功能结果仍有待确定。最近的数据表明，O-连接的GlcNAc转移酶（OGT 1）在一个复合物与共阻遏物Hdac 1和mSin 3A介导的基因表达的抑制HepG 2肝细胞系。然而，靶基因和条件下，这种阻遏物复合物在体内是活跃的是未知的。 胰腺β细胞中的胰岛素基因表达由高血糖水平诱导，并且当血糖水平低时降低。使用去乙酰化酶抑制剂阿司他丁A，我们最近发现，胰岛素基因的表达被抑制在低浓度的葡萄糖的小鼠胰岛素瘤（MIN 6）细胞系中的胰岛素启动子的去乙酰化酶的招聘。此外，我们发现OGT 1和Hdac 1/2被募集到胰岛素基因启动子，并且仅在MIN 6 β细胞中的低水平葡萄糖下相互作用。基于这些数据，我们假设OGT 1和Hdac 1/2是在一个复杂的和抑制胰岛素基因的表达在低水平的葡萄糖。我们将按照以下三个具体目标来检验这一假设。 1)分析OGT 1对MIN 6 β细胞胰岛素基因表达的抑制作用。 2)鉴定将OGT 1-Hdac 1/2阻遏物复合物募集至胰岛素基因启动子的转录因子。 3)鉴定响应O-GlcNAc修饰增加而转录改变的基因。了解OGT 1在调节胰岛素基因转录中的作用将为O-GlcNAc修饰缺陷导致糖尿病相关症状的机制提供新的见解。此外，所获得的数据将有助于设计新的策略，用于治疗和预防I型和II型糖尿病以及与糖尿病相关的继发性并发症。

DESCRIPTION (provided by applicant): Although several lines of evidence suggest that increased levels of O-GIcNAc modification interferes with normal glucose homeostasis, the exact functional consequences of this modification remain to determined. Recent data indicate that O-linked GIcNAc transferase (OGT1) in a complex with the co-repressors Hdac1 and mSin3A mediates repression of gene expression in the HepG2 liver cell line. However, the target genes and the conditions under which this repressor complex is active in vivo are not known. Insulin gene expression in the pancreatic beta cells is induced by high blood glucose levels and is decreased when blood glucose levels are low. Using the deacetylase inhibitor trichostatin A, we have recently discovered that insulin gene expression is inhibited at low concentrations of glucose by the recruitment of deacetylases to the insulin promoter in the mouse insulinoma (MIN6) cell line. Furthermore, we found that OGT1 and Hdac1/2 are recruited to the insulin gene promoter and interact with each other only at low levels of glucose in the MIN6 beta cells. Based on these data, we hypothesize that OGT1 and Hdac1/2 are in a complex and repress insulin gene expression at low levels of glucose. We will test this hypothesis as described in the following three specific aims. 1) To analyze the role of OGT1 in repression of insulin gene expression in MIN6 beta cells. 2) To identify the transcription factor(s) that recruits the OGT1-Hdac1/2 repressor complex to the insulin gene promoter. 3) To identify genes with altered transcription in response to increased O-GIcNAc modification. Understanding the role of OGT1 in regulating insulin gene transcription will provide new insights into the mechanisms by which defects in O-GIcNAc modification lead to symptoms associated with diabetes. In addition, the obtained data will be instrumental in the design of novel strategies for the treatment and prevention of type I and type II diabetes and the secondary complications associated with diabetes.