From the College of Life Sciences, Beijing Normal University, Beijing 100875.
the National Institute of Biological Sciences, Beijing 102206.
J Biol Chem. 2019 May 31;294(22):8907-8917. doi: 10.1074/jbc.RA119.008008. Epub 2019 Apr 24.
is a maternal gene required for oogenesis and early embryogenesis. Stella overexpression in somatic cells causes global demethylation. As we have recently shown, Stella sequesters nuclear ubiquitin-like with PHD and RING finger domains 1 (UHRF1), a RING finger-type E3 ubiquitin ligase essential for DNA methylation mediated by DNA methyltransferase 1 and triggers global demethylation. Here, we report an overexpressed mutant Stella protein without nuclear export activity surprisingly retained its ability to cause global demethylation. By combining biochemical interaction assays, isothermal titration calorimetry, immunostaining, and live-cell imaging with fluorescence recovery after photobleaching, we found that Stella disrupts UHRF1's association with chromatin by directly binding to the plant homeodomain of UHRF1 and competing for the interaction between UHRF1 and the histone H3 tail. Consistently, overexpression of Stella mutants that do not directly interact with UHRF1 fails to cause genome-wide demethylation. In the presence of nuclear Stella, UHRF1 could not bind to chromatin and exhibited increased dynamics in the nucleus. Our results indicate that Stella employs a multilayered mechanism to achieve robust UHRF1 inhibition, which involves the dissociation from chromatin and cytoplasmic sequestration of UHRF1.
是卵母细胞发生和早期胚胎发生所必需的母体基因。Stella 在体细胞中的过表达导致全局去甲基化。正如我们最近所表明的那样,Stella 会将核泛素样与 PHD 和 RING 指结构域 1(UHRF1)隔离,UHRF1 是一种 RING 指型 E3 泛素连接酶,对于 DNA 甲基转移酶 1 介导的 DNA 甲基化至关重要,并引发全局去甲基化。在这里,我们报告了一种过表达的突变体 Stella 蛋白,尽管没有核输出活性,但令人惊讶的是,它仍然保留了引起全局去甲基化的能力。通过结合生化相互作用测定、等温滴定量热法、免疫染色和荧光恢复后光漂白的活细胞成像,我们发现 Stella 通过直接结合 UHRF1 的植物同源域并与 UHRF1 和组蛋白 H3 尾部之间的相互作用竞争,破坏了 UHRF1 与染色质的结合。一致地,不能与 UHRF1 直接相互作用的 Stella 突变体的过表达不能导致全基因组去甲基化。在核内 Stella 的存在下,UHRF1 不能与染色质结合,并且在核内表现出增加的动力学。我们的结果表明,Stella 采用多层次的机制来实现对 UHRF1 的强烈抑制,这涉及到与染色质的解离和 UHRF1 的细胞质隔离。