Smallwood Andrea, Estève Pierre-Olivier, Pradhan Sriharsa, Carey Michael
Department of Biological Chemistry, David Geffen School of Medicine, University of California at Los Angeles, Los Angeles, California 90095, USA.
Genes Dev. 2007 May 15;21(10):1169-78. doi: 10.1101/gad.1536807. Epub 2007 Apr 30.
Mammalian euchromatic gene silencing results from the combined repressive effects of histone and DNA methyltransferases. Little is known of the mechanism by which these enzymes cooperate to induce silencing. Here we show that mammalian HP1 family members mediate communication between histone and DNA methyltransferases. In vitro, methylation of histone 3 Lys 9 by G9a creates a binding platform for HP1alpha, beta, and gamma. DNMT1 interacts with HP1 resulting in increased DNA methylation on DNA and chromatin templates in vitro. The functional and physical interaction can be recapitulated in vivo. Binding of GAL4-HP1 to a reporter construct is sufficient to induce repression and DNA methylation in DNMT1 wild-type but not DNMT1-null cells. Additionally, silencing of the Survivin gene coincides with recruitment of G9a and HP1 in DNMT1 wild-type but not null cells. We conclude that direct interactions between HP1 and DNMT1 mediate silencing of euchromatic genes.
哺乳动物常染色质基因沉默是由组蛋白和DNA甲基转移酶的联合抑制作用导致的。对于这些酶协同诱导沉默的机制，人们了解甚少。在此我们表明，哺乳动物HP1家族成员介导组蛋白和DNA甲基转移酶之间的相互作用。在体外，G9a介导的组蛋白H3赖氨酸9位点的甲基化作用为HP1α、β和γ创建了一个结合平台。DNMT1与HP1相互作用，导致体外DNA和染色质模板上的DNA甲基化增加。这种功能和物理相互作用在体内也可以重现。GAL4-HP1与报告基因构建体的结合足以在DNMT1野生型细胞而非DNMT1缺失型细胞中诱导基因沉默和DNA甲基化。此外，Survivin基因的沉默与G9a和HP1在DNMT1野生型细胞而非缺失型细胞中的募集相一致。我们得出结论，HP1与DNMT1之间的直接相互作用介导了常染色质基因的沉默。
