TRANSCRIPTIONAL CONTROL OF CARBOHYDRATE RESPONSIVE GENES

碳水化合物响应基因的转录控制

• 批准号: 6381215
• 负责人: DAVID B RHOADS
• 金额: $ 25.57万
• 依托单位: MASSACHUSETTS GENERAL HOSPITAL
• 依托单位国家: 美国
• 财政年份: 1999
• 资助国家: 美国
• 起止时间: 1999-06-01 至 2003-05-31
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/6381215
• 关键词: binding proteins; carbohydrate metabolism; gastrointestinal epithelium; gene expression; gene mutation; genetic enhancer element; genetic mapping; genetic promoter element; genetic regulation; genetic transcription; genetically modified animals; glucose metabolism; glucose transporter; homeostasis; laboratory mouse; laboratory rat; pyruvate kinase; sodium; tissue /cell culture; transcription factor

The general goal of this project is to increase our understanding of the transcriptional mechanisms regulating carbohydrate- responsive genes. Glucose homeostasis depends on the strict control of numerous enzymatic and absorptive pathways. As a model, we have been studying the small intestinal high-affinity Na+/glucose cotransporter (SGLT1), the activity of which shows diurnal periodicity and induction by carbohydrate. We have shown that SGLT1 expression exhibits diurnal periodicity in both mRNA abundance and transcription. The rat SGLT1 promoter contains an HNF-1 (hepatocyte nuclear factor 1) element that forms complexes with intestinal epithelial cell nuclear extracts differing in the presence of the HNF-1beta isoform depending on the time of day nuclei were isolated. The presence of homologous HNF-1 sites in the carbohydrate-response elements in the promoters of two other carbohydrate-responsive genes--liver pyruvate kinase and sucrase- isomaltase, which we have also shown to exhibit diurnal periodicity--indicates that HNF-1 may mediate both the diurnal transcription program as well as induction by dietary carbohydrate. Periodicity in the intestinal SGLT1 mRNA levels in rhesus monkeys suggests that a similar mechanism is also present in humans. It is proposed that rhythmic SGLT1 transcription is controlled by the diurnal activation (or synthesis) of transcription factors interacting with the SGLT1 promoter. Identifying the factors responsible and defining their functions are important steps toward delineating these homeostatic mechanisms. To these ends, two hypotheses will be tested: (1) "Circadian" elements in the SGLT1 promoter drive its diurnal transcription; and (2) Carbohydrate induces SGLT1 and other carbohydrate-responsive genes by modulating their diurnal expression program. Because a wide range of proteins involved in carbohydrate metabolism--digestive enzymes, transporters, glycolytic enzymes, and gluconeogenic enzymes--are carbohydrate- responsive, knowledge of the shared and distinctive pathways regulating the expression of members of this class will lead to a better understanding of changes in carbohydrate tolerance. Underscoring the importance of elucidating this regulation, mutations have recently been identified in both HNF-1alpha and beta dimerization partners that are etiologic in one or more forms of diabetes in humans. Finally, it is anticipated that elucidation of the mechanisms regulating SGLT1 may reveal targets amenable to pharmaceutical control of carbohydrate absorption in conditions such as obesity and diabetes mellitus.

该项目的总体目标是增加我们对调节碳水化合物反应基因的转录机制的理解。 葡萄糖稳态取决于对众多酶促和吸收途径的严格控制。 作为模型，我们一直在研究小肠高亲和力 Na+/葡萄糖协同转运蛋白 (SGLT1)，其活性显示出昼夜周期性和碳水化合物的诱导作用。 我们已经证明 SGLT1 表达在 mRNA 丰度和转录方面都表现出昼夜周期性。 大鼠 SGLT1 启动子含有 HNF-1（肝细胞核因子 1）元件，可与肠上皮细胞核提取物形成复合物，根据一天中分离细胞核的时间，HNF-1β 亚型的存在情况有所不同。 在另外两个碳水化合物反应基因（肝脏丙酮酸激酶和蔗糖酶异麦芽糖酶）的启动子中碳水化合物反应元件中存在同源 HNF-1 位点，我们也证明它们表现出昼夜周期性，表明 HNF-1 可能介导昼夜转录程序以及饮食碳水化合物的诱导。 恒河猴肠道 SGLT1 mRNA 水平的周期性表明人类也存在类似的机制。 据推测，有节奏的 SGLT1 转录是由与 SGLT1 启动子相互作用的转录因子的昼夜激活（或合成）控制的。确定相关因素并定义其功能是描述这些稳态机制的重要步骤。 为此，将测试两个假设：（1）SGLT1启动子中的“昼夜节律”元件驱动其昼夜转录； (2) 碳水化合物通过调节其昼夜表达程序来诱导 SGLT1 和其他碳水化合物反应基因。 由于参与碳水化合物代谢的多种蛋白质（消化酶、转运蛋白、糖酵解酶和糖异生酶）均具有碳水化合物反应性，因此了解调节此类成员表达的共享和独特途径将有助于更好地理解碳水化合物耐受性的变化。最近在 HNF-1α 和 β 二聚化伙伴中发现了突变，这些突变是人类一种或多种糖尿病的病因，这强调了阐明这种调节的重要性。 最后，预计对 SGLT1 调节机制的阐明可能会揭示在肥胖和糖尿病等疾病中药物控制碳水化合物吸收的靶点。