Laboratory of Biosignaling and Therapeutics, Department of Molecular Cell Biology, Faculty of Medicine, KULeuven, B-3000 Leuven, Belgium.
Nucleic Acids Res. 2010 Nov;38(21):7500-12. doi: 10.1093/nar/gkq643. Epub 2010 Jul 29.
Polycomb group (PcG) proteins are key regulators of stem-cell and cancer biology. They mainly act as repressors of differentiation and tumor-suppressor genes. One key silencing step involves the trimethylation of histone H3 on Lys27 (H3K27) by EZH2, a core component of the Polycomb Repressive Complex 2 (PRC2). The mechanism underlying the initial recruitment of mammalian PRC2 complexes is not well understood. Here, we show that NIPP1, a regulator of protein Ser/Thr phosphatase-1 (PP1), forms a complex with PP1 and PRC2 components on chromatin. The knockdown of NIPP1 or PP1 reduced the association of EZH2 with a subset of its target genes, whereas the overexpression of NIPP1 resulted in a retargeting of EZH2 from fully repressed to partially active PcG targets. However, the expression of a PP1-binding mutant of NIPP1 (NIPP1m) did not cause a redistribution of EZH2. Moreover, mapping of the chromatin binding sites with the DamID technique revealed that NIPP1 was associated with multiple PcG target genes, including the Homeobox A cluster, whereas NIPP1m showed a deficient binding at these loci. We propose that NIPP1 associates with a subset of PcG targets in a PP1-dependent manner and thereby contributes to the recruitment of the PRC2 complex.
多梳抑制复合物(PcG)蛋白是干细胞和癌症生物学的关键调节因子。它们主要作为分化和肿瘤抑制基因的抑制剂发挥作用。关键的沉默步骤之一涉及 EZH2 对组蛋白 H3 赖氨酸 27(H3K27)的三甲基化,EZH2 是多梳抑制复合物 2(PRC2)的核心组成部分。哺乳动物 PRC2 复合物初始募集的机制尚未得到很好的理解。在这里,我们表明,蛋白丝氨酸/苏氨酸磷酸酶-1(PP1)的调节剂 NIPP1 在染色质上与 PP1 和 PRC2 成分形成复合物。NIPP1 或 PP1 的敲低会减少 EZH2 与其部分靶基因的结合,而 NIPP1 的过表达会导致 EZH2 从完全沉默的 PcG 靶标重新靶向到部分激活的靶标。然而,NIPP1(NIPP1m)的 PP1 结合突变体的表达不会导致 EZH2 的重新分布。此外,利用 DamID 技术对染色质结合位点进行映射表明,NIPP1 与多个 PcG 靶基因相关,包括同源盒 A 簇,而 NIPP1m 在这些基因座上的结合能力较弱。我们提出,NIPP1 以依赖于 PP1 的方式与 PcG 靶标子集相关联,从而有助于 PRC2 复合物的募集。