Myant Kevin, Stancheva Irina
Wellcome Trust Centre for Cell Biology, University of Edinburgh, Michael Swann Building, Mayfield Road, Edinburgh EH9 3JR, United Kingdom.
Mol Cell Biol. 2008 Jan;28(1):215-26. doi: 10.1128/MCB.01073-07. Epub 2007 Oct 29.
LSH, a protein related to the SNF2 family of chromatin-remodeling ATPases, is required for efficient DNA methylation in mammals. How LSH functions to support DNA methylation and whether it associates with a large protein complex containing DNA methyltransferase (DNMT) enzymes is currently unclear. Here we show that, unlike many other chromatin-remodeling ATPases, native LSH is present mostly as a monomeric protein in nuclear extracts of mammalian cells and cannot be detected in a large multisubunit complex. However, when targeted to a promoter of a reporter gene, LSH acts as an efficient transcriptional repressor. Using this as an assay to identify proteins that are required for LSH-mediated repression we found that LSH cooperates with the DNMTs DNMT1 and DNMT3B and with the histone deacetylases (HDACs) HDAC1 and HDAC2 to silence transcription. We show that transcriptional repression by LSH and interactions with HDACs are lost in DNMT1 and DNMT3B knockout cells but that the enzymatic activities of DNMTs are not required for LSH-mediated silencing. Our data suggest that LSH serves as a recruiting factor for DNMTs and HDACs to establish transcriptionally repressive chromatin which is perhaps further stabilized by DNA methylation at targeted loci.
LSH是一种与染色质重塑ATP酶的SNF2家族相关的蛋白质,是哺乳动物有效DNA甲基化所必需的。目前尚不清楚LSH如何发挥作用以支持DNA甲基化,以及它是否与包含DNA甲基转移酶(DNMT)的大型蛋白质复合物相关联。在这里,我们表明,与许多其他染色质重塑ATP酶不同,天然LSH在哺乳动物细胞核提取物中大多以单体蛋白形式存在,并且在大型多亚基复合物中无法检测到。然而,当靶向报告基因的启动子时,LSH作为一种有效的转录抑制因子发挥作用。利用这一检测方法来鉴定LSH介导的抑制作用所需的蛋白质,我们发现LSH与DNMT1和DNMT3B以及组蛋白脱乙酰酶(HDAC)HDAC1和HDAC2协同作用以沉默转录。我们表明,在DNMT1和DNMT3B基因敲除细胞中,LSH的转录抑制作用以及与HDAC的相互作用丧失,但DNMT的酶活性对于LSH介导的沉默作用不是必需的。我们的数据表明,LSH作为DNMT和HDAC的募集因子,以建立转录抑制性染色质,这可能通过靶向位点的DNA甲基化进一步稳定。