Role of O-GlcNAc transferase in insulin gene expression

描述(由申请人提供)：尽管有几条证据表明O-GIcNAc修饰水平的增加干扰了正常的葡萄糖稳态，但这种修饰的确切功能后果仍有待确定。最近的数据表明，与共抑制基因HDAC1和mSin3A形成的复合体中的O-连锁GIcNAc转移酶(OGT1)介导了对HepG2肝细胞系基因表达的抑制。然而，靶基因和抑制物复合体在体内活跃的条件尚不清楚。 胰岛素基因在胰岛β细胞中的表达是由高血糖水平诱导的，当血糖水平较低时，胰岛素基因的表达就会减少。利用脱乙酰酶抑制剂曲古抑素A，我们最近发现，在小鼠胰岛素瘤(MIN6)细胞系中，通过将脱乙酰酶募集到胰岛素启动子上，在低浓度葡萄糖下胰岛素基因的表达受到抑制。此外，我们还发现，在MIN6β细胞中，OGT1和HDAC1/2被招募到胰岛素基因启动子上，并且只有在低糖水平下才相互作用。基于这些数据，我们假设OGT1和HDAC1/2处于复杂的状态，并且在低糖水平下抑制胰岛素基因的表达。我们将按照以下三个具体目标来检验这一假设。 1)分析OGT1在抑制MIN6β细胞胰岛素基因表达中的作用。 2)鉴定将OGT1-HDAC1/2抑制因子复合体招募到胰岛素基因启动子的转录因子(S)。 3)鉴定O-GIcNAc修饰增加后转录改变的基因。了解OGT1在调节胰岛素基因转录中的作用将为O-GIcNAc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的新战略。

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.