Zhang Pili, Metukuri Mallikarjurna R, Bindom Sharell M, Prochownik Edward V, O'Doherty Robert M, Scott Donald K
Department of Medicine, Division of Endocrinology and Metabolism, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15261, USA.
Mol Endocrinol. 2010 Jun;24(6):1274-86. doi: 10.1210/me.2009-0437. Epub 2010 Apr 9.
Glucose regulates programs of gene expression that orchestrate changes in cellular phenotype in several metabolically active tissues. Carbohydrate response element-binding protein (ChREBP) and its binding partner, Mlx, mediate glucose-regulated gene expression by binding to carbohydrate response elements on target genes, such as the prototypical glucose-responsive gene, liver-type pyruvate kinase (Pklr). c-Myc is also required for the glucose response of the Pklr gene, although the relationship between c-Myc and ChREBP has not been defined. Here we describe the molecular events of the glucose-mediated activation of Pklr and determine the effects of decreasing the activity or abundance of c-Myc on this process. Time-course chromatin immunoprecipitation revealed a set of transcription factors [hepatocyte nuclear factor (HNF)1alpha, HNF4alpha, and RNA polymerase II (Pol II)] constitutively resident on the Pklr promoter, with a relative enrichment of acetylated histones 3 and 4 in the same region of the gene. Glucose did not affect HNF1alpha binding or the acetylation of histones H3 or H4. By contrast, glucose promoted the recruitment of ChREBP and c-Myc and increased the occupancy of HNF4alpha and RNA Pol II, which were coincident with the glucose-mediated increase in transcription as determined by a nuclear run-on assay. Depletion of c-Myc activity using a small molecule inhibitor (10058-F4/1RH) abolished the glucose-mediated recruitment of HNF4alpha, ChREBP, and RNA Pol II, without affecting basal gene expression, histone acetylation, and HNF1alpha or basal HNF4alpha occupancy. The activation and recruitment of ChREBP to several glucose-responsive genes were blocked by 1RH, indicating a general necessity for c-Myc in this process.
葡萄糖调节基因表达程序,这些程序协调多个代谢活跃组织中细胞表型的变化。碳水化合物反应元件结合蛋白(ChREBP)及其结合伴侣Mlx通过与靶基因上的碳水化合物反应元件结合来介导葡萄糖调节的基因表达,例如典型的葡萄糖反应基因——肝型丙酮酸激酶(Pklr)。c-Myc对于Pklr基因的葡萄糖反应也是必需的,尽管c-Myc与ChREBP之间的关系尚未明确。在此,我们描述了葡萄糖介导的Pklr激活的分子事件,并确定降低c-Myc的活性或丰度对这一过程的影响。时间进程染色质免疫沉淀显示一组转录因子[肝细胞核因子(HNF)1α、HNF4α和RNA聚合酶II(Pol II)]持续存在于Pklr启动子上,在该基因的同一区域乙酰化组蛋白3和4相对富集。葡萄糖不影响HNF1α的结合或组蛋白H3或H4的乙酰化。相比之下,葡萄糖促进了ChREBP和c-Myc的募集,并增加了HNF4α和RNA Pol II的占据,这与通过细胞核连续转录分析确定的葡萄糖介导的转录增加相一致。使用小分子抑制剂(10058-F4/1RH)耗尽c-Myc活性消除了葡萄糖介导的HNF4α、ChREBP和RNA Pol II的募集,而不影响基础基因表达、组蛋白乙酰化以及HNF1α或基础HNF4α的占据。1RH阻断了ChREBP对几个葡萄糖反应基因的激活和募集,表明在此过程中c-Myc普遍是必需的。