Oct4-mediated inhibition of Lsd1 activity promotes the active and primed state of pluripotency enhancers [ChIP-seq]

Enhancer reactivation and pluripotency gene (PpG) expression could induce stemness and enhance tumorigenicity in cancer stem cells. Silencing of PpG enhancers (PpGe) during embryonic stem cell differentiation involves Lsd1–mediated H3K4me1 demethylation followed by DNA methylation. Here, we observed a widespread retention of H3K4me1 and DNA hypomethylation at PpGe associated with a partial repression of PpGs in F9 embryonal carcinoma cells (ECCs) post-differentiation. The absence of H3K4me1 demethylation could not be rescued by Lsd1 overexpression. Based on the observation that H3K4me1 demethylation is accompanied by strong Oct4 repression in P19 ECCs, we tested if Lsd1-Oct4 interaction affects Lsd1 catalytic activity. Our data show a dose-dependent inhibition of Lsd1 by Oct4 in vitro and retention of H3K4me1 at PpGe post-differentiation in Oct4 overexpressing P19 ECCs. These data suggest that Lsd1-Oct4 interaction in cancer stem cells may establish a primed enhancer state that is susceptible to reactivation leading to aberrant PpG expression.

增强子激活与多能性基因（pluripotency gene, PpG）的表达，可诱导癌症干细胞获得干性并增强其致瘤性。胚胎干细胞分化过程中，多能性基因增强子（pluripotency gene enhancer, PpGe）的沉默依赖于赖氨酸特异性去甲基化酶1（Lsd1）介导的组蛋白H3赖氨酸4单甲基化（H3K4me1）去甲基化，随后伴随DNA甲基化事件。本研究观察到，在分化后的F9胚胎癌细胞（embryonal carcinoma cells, ECCs）中，多能性基因增强子区域普遍保留了H3K4me1修饰且呈现DNA低甲基化状态，同时伴随多能性基因的部分表达抑制。单纯过表达Lsd1无法挽救该H3K4me1去甲基化缺陷。基于在P19胚胎癌细胞中观察到H3K4me1去甲基化伴随八聚体结合转录因子4（Oct4）的显著抑制这一现象，我们探究了Lsd1与Oct4的相互作用是否会影响Lsd1的催化活性。实验数据显示，Oct4在体外可剂量依赖性地抑制Lsd1的活性，且在过表达Oct4的P19胚胎癌细胞中，分化后多能性基因增强子区域的H3K4me1修饰得以保留。上述结果表明，癌症干细胞中Lsd1与Oct4的相互作用可能会建立一种致敏增强子状态，该状态易被重新激活，进而导致多能性基因的异常表达。