TRANSCRIPTIONAL CONTROL OF CARBOHYDRATE RESPONSIVE GENES

碳水化合物响应基因的转录控制

• 批准号: 2853032
• 负责人: DAVID B RHOADS
• 金额: $ 22.4万
• 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/2853032
• 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.

这个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。 葡萄糖稳态依赖于对许多酶和吸收途径的严格控制。 作为一个模型，我们一直在研究小肠高亲和力Na+/葡萄糖协同转运蛋白（SGLT 1），其活性显示昼夜周期性和诱导碳水化合物。 我们已经证明，SGLT 1表达在mRNA丰度和转录方面都表现出昼夜周期性。 大鼠SGLT 1启动子含有HNF-1（肝细胞核因子1）元件，该元件与肠上皮细胞核提取物形成复合物，不同之处在于HNF-1 β亚型的存在，这取决于分离细胞核的时间。 在另外两个碳水化合物响应基因--肝丙酮酸激酶和蔗糖酶-异麦芽糖酶的启动子中的碳水化合物响应元件中存在同源HNF-1位点，我们已经证明它们也表现出昼夜周期性--表明HNF-1可以介导昼夜转录程序以及膳食碳水化合物的诱导。 恒河猴肠道SGLT 1 mRNA水平的周期性表明，人类也存在类似的机制。 有人提出，有节奏的SGLT 1转录控制的昼夜激活（或合成）的转录因子与SGLT 1启动子相互作用。确定负责的因素和定义其功能是描绘这些稳态机制的重要步骤。 为此，将检验两个假设：（1）SGLT 1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诱导SGLT 1和其他碳水化合物应答基因。 由于参与碳水化合物代谢的蛋白质-消化酶、转运蛋白、糖酵解酶和促碳水化合物生成酶-都是碳水化合物反应性的，因此了解调节这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。为了强调阐明这种调节的重要性，最近已经在HNF-1 α和β二聚化伴侣中鉴定出突变，这些突变是人类一种或多种糖尿病的病因。 最后，预计阐明SGLT 1的调节机制可能会揭示肥胖和糖尿病等疾病中碳水化合物吸收的药物控制靶点。