Department of Human Genetics, Leiden University Medical Center, Leiden, The Netherlands.
Human Biology Division, Fred Hutchinson Cancer Research Center, Seattle, USA.
Sci Rep. 2021 Dec 8;11(1):23642. doi: 10.1038/s41598-021-03030-3.
Structural Maintenance of Chromosomes Hinge Domain Containing 1 (SMCHD1) is a chromatin repressor, which is mutated in > 95% of Facioscapulohumeral dystrophy (FSHD) type 2 cases. In FSHD2, SMCHD1 mutations ultimately result in the presence of the cleavage stage transcription factor DUX4 in muscle cells due to a failure in epigenetic repression of the D4Z4 macrosatellite repeat on chromosome 4q, which contains the DUX4 locus. While binding of SMCHD1 to D4Z4 and its necessity to maintain a repressive D4Z4 chromatin structure in somatic cells are well documented, it is unclear how SMCHD1 is recruited to D4Z4, and how it exerts its repressive properties on chromatin. Here, we employ a quantitative proteomics approach to identify and characterize novel SMCHD1 interacting proteins, and assess their functionality in D4Z4 repression. We identify 28 robust SMCHD1 nuclear interactors, of which 12 are present in D4Z4 chromatin of myocytes. We demonstrate that loss of one of these SMCHD1 interacting proteins, RuvB-like 1 (RUVBL1), further derepresses DUX4 in FSHD myocytes. We also confirm the interaction of SMCHD1 with EZH inhibitory protein (EZHIP), a protein which prevents global H3K27me3 deposition by the Polycomb repressive complex PRC2, providing novel insights into the potential function of SMCHD1 in the repression of DUX4 in the early stages of embryogenesis. The SMCHD1 interactome outlined herein can thus provide further direction into research on the potential function of SMCHD1 at genomic loci where SMCHD1 is known to act, such as D4Z4 repeats, the inactive X chromosome, autosomal gene clusters, imprinted loci and telomeres.
结构维持染色体铰链域包含 1 型（SMCHD1）是一种染色质抑制剂，在> 95%的面肩肱型肌营养不良症（FSHD）2 型病例中发生突变。在 FSHD2 中，SMCHD1 突变最终导致肌肉细胞中存在切割阶段转录因子 DUX4，因为 4q 染色体上的 D4Z4 宏卫星重复的表观遗传抑制失败，该重复包含 DUX4 基因座。虽然 SMCHD1 与 D4Z4 的结合及其在体细胞中维持抑制性 D4Z4 染色质结构的必要性已有充分的文献记载，但尚不清楚 SMCHD1 如何被招募到 D4Z4，以及它如何对染色质发挥其抑制作用。在这里，我们采用定量蛋白质组学方法来鉴定和表征新型 SMCHD1 相互作用蛋白，并评估它们在 D4Z4 抑制中的功能。我们鉴定了 28 个稳健的 SMCHD1 核相互作用蛋白，其中 12 个存在于肌细胞的 D4Z4 染色质中。我们证明，其中一种 SMCHD1 相互作用蛋白 RuvB 样 1（RUVBL1）的缺失会进一步解除 FSHD 肌细胞中 DUX4 的抑制。我们还证实了 SMCHD1 与 EZH 抑制蛋白（EZHIP）的相互作用，EZHIP 蛋白可防止多梳抑制复合物 PRC2 对 H3K27me3 的全局沉积，为 SMCHD1 在胚胎早期抑制 DUX4 中的潜在功能提供了新的见解。因此，本文所述的 SMCHD1 相互作用组可以为研究 SMCHD1 在已知作用的基因组位点（如 D4Z4 重复序列、失活 X 染色体、常染色体基因簇、印迹基因座和端粒）上的潜在功能提供进一步的方向。
