Department of Medicine, University of Minnesota Medical School, Minneapolis, Minnesota, USA.
Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, Texas, USA.
J Biol Chem. 2020 Dec 18;295(51):17560-17572. doi: 10.1074/jbc.RA120.015592.
Hepatocyte nuclear factor-1β (HNF-1β) is a tissue-specific transcription factor that is required for normal kidney development and renal epithelial differentiation. Mutations of HNF-1β produce congenital kidney abnormalities and inherited renal tubulopathies. Here, we show that ablation of HNF-1β in mIMCD3 renal epithelial cells results in activation of β-catenin and increased expression of lymphoid enhancer-binding factor 1 (LEF1), a downstream effector in the canonical Wnt signaling pathway. Increased expression and nuclear localization of LEF1 are also observed in cystic kidneys from Hnf1b mutant mice. Expression of dominant-negative mutant HNF-1β in mIMCD3 cells produces hyperresponsiveness to exogenous Wnt ligands, which is inhibited by siRNA-mediated knockdown of Lef1. WT HNF-1β binds to two evolutionarily conserved sites located 94 and 30 kb from the mouse Lef1 promoter. Ablation of HNF-1β decreases H3K27 trimethylation repressive marks and increases β-catenin occupancy at a site 4 kb upstream to Lef1. Mechanistically, WT HNF-1β recruits the polycomb-repressive complex 2 that catalyzes H3K27 trimethylation. Deletion of the β-catenin-binding domain of LEF1 in HNF-1β-deficient cells abolishes the increase in Lef1 transcription and decreases the expression of downstream Wnt target genes. The canonical Wnt target gene, Axin2, is also a direct transcriptional target of HNF-1β through binding to negative regulatory elements in the gene promoter. These findings demonstrate that HNF-1β regulates canonical Wnt target genes through long-range effects on histone methylation at Wnt enhancers and reveal a new mode of active transcriptional repression by HNF-1β.
肝细胞核因子-1β(HNF-1β)是一种组织特异性转录因子,对于正常肾脏发育和肾上皮细胞分化是必需的。HNF-1β 的突变会导致先天性肾脏异常和遗传性肾小管病变。在这里,我们表明,在 mIMCD3 肾上皮细胞中敲除 HNF-1β 会导致β-连环蛋白的激活和淋巴增强结合因子 1(LEF1)的表达增加,LEF1 是经典 Wnt 信号通路的下游效应物。在 Hnf1b 突变小鼠的囊性肾脏中也观察到 LEF1 的表达增加和核定位。在 mIMCD3 细胞中表达显性负突变的 HNF-1β 会导致对外源性 Wnt 配体的超反应性,而 Lef1 的 siRNA 介导的敲低可以抑制这种超反应性。WT HNF-1β 结合到位于 Lef1 启动子 94 和 30 kb 处的两个进化上保守的位点。敲除 HNF-1β 会降低 H3K27 三甲基化抑制标记,并增加 Lef1 上游 4 kb 处的 β-连环蛋白占有率。在机制上,WT HNF-1β 募集多梳抑制复合物 2,该复合物可催化 H3K27 三甲基化。在 HNF-1β 缺陷细胞中缺失 LEF1 的 β-连环蛋白结合域会消除 Lef1 转录的增加,并降低下游 Wnt 靶基因的表达。经典 Wnt 靶基因 Axin2 也是 HNF-1β 的直接转录靶标,通过结合基因启动子中的负调控元件。这些发现表明,HNF-1β 通过对 Wnt 增强子的组蛋白甲基化进行长程调控来调节经典 Wnt 靶基因,并揭示了 HNF-1β 进行主动转录抑制的一种新方式。
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