Párrizas M, Maestro M A, Boj S F, Paniagua A, Casamitjana R, Gomis R, Rivera F, Ferrer J
Endocrinology and Hormonal Biochemistry units, Hospital Clínic, Institut d'Investigacions Biomèdiques August Pi i Sunyer, Barcelona, Spain 08036.
Mol Cell Biol. 2001 May;21(9):3234-43. doi: 10.1128/MCB.21.9.3234-3243.2001.
Mutations in the gene encoding hepatic nuclear factor 1-alpha (HNF1-alpha) cause a subtype of human diabetes resulting from selective pancreatic beta-cell dysfunction. We have analyzed mice lacking HNF1-alpha to study how this protein controls beta-cell-specific transcription in vivo. We show that HNF1-alpha is essential for the expression of glut2 glucose transporter and L-type pyruvate kinase (pklr) genes in pancreatic insulin-producing cells, whereas in liver, kidney, or duodenum tissue, glut2 and pklr expression is maintained in the absence of HNF1-alpha. HNF1-alpha nevertheless occupies the endogenous glut2 and pklr promoters in both pancreatic islet and liver cells. However, it is indispensable for hyperacetylation of histones in glut2 and pklr promoter nucleosomes in pancreatic islets but not in liver cells, where glut2 and pklr chromatin remains hyperacetylated in the absence of HNF1-alpha. In contrast, the phenylalanine hydroxylase promoter requires HNF1-alpha for transcriptional activity and localized histone hyperacetylation only in liver tissue. Thus, different HNF1-alpha target genes have distinct requirements for HNF1-alpha in either pancreatic beta-cells or liver cells. The results indicate that HNF1-alpha occupies target gene promoters in diverse tissues but plays an obligate role in transcriptional activation only in cellular- and promoter-specific contexts in which it is required to recruit histone acetylase activity. These findings provide genetic evidence based on a live mammalian system to establish that a single activator can be essential to direct nucleosomal hyperacetylation to transcriptional targets.
编码肝细胞核因子1α（HNF1α）的基因突变会导致一种人类糖尿病亚型，其病因是胰腺β细胞选择性功能障碍。我们分析了缺乏HNF1α的小鼠，以研究这种蛋白质在体内如何控制β细胞特异性转录。我们发现，HNF1α对于胰腺胰岛素生成细胞中葡萄糖转运蛋白2（glut2）和L型丙酮酸激酶（pklr）基因的表达至关重要，而在肝脏、肾脏或十二指肠组织中，即使没有HNF1α，glut2和pklr的表达仍能维持。然而，HNF1α在胰岛细胞和肝细胞中均占据内源性glut2和pklr启动子。但是，它对于胰岛中glut2和pklr启动子核小体上组蛋白的高度乙酰化是不可或缺的，而在肝细胞中并非如此，在肝细胞中即使没有HNF1α，glut2和pklr染色质仍保持高度乙酰化。相反，苯丙氨酸羟化酶启动子仅在肝脏组织中需要HNF1α来实现转录活性和局部组蛋白高度乙酰化。因此，不同的HNF1α靶基因在胰腺β细胞或肝细胞中对HNF1α有不同的需求。结果表明，HNF1α在多种组织中占据靶基因启动子，但仅在需要募集组蛋白乙酰化酶活性的细胞和启动子特异性环境中，才在转录激活中发挥必要作用。这些发现基于一个活的哺乳动物系统提供了遗传学证据，以证实单一激活剂对于将核小体高度乙酰化导向转录靶点可能是必不可少的。
