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Chromatin insulators are boundary elements between distinctly regulated, neighboring chromosomal domains, and they function by blocking the effects of nearby enhancers in a position-dependent manner. Here, we show that the SNF2-like chromodomain helicase protein CHD8 interacts with the insulator binding protein CTCF. Chromatin immunoprecipitation analysis revealed that CHD8 was present at known CTCF target sites, such as the differentially methylated region (DMR) of H19 , the locus control region of beta-globin , and the promoter region of BRCA1 and c-myc genes. RNA interference-mediated knockdown of CHD8 significantly abolished theH19 DMR insulator activity that depends highly on CTCF, leading to reactivation of imprinted IGF2 from chromosome of maternal origin. Further, the lack of CHD8 affected CpG methylation and histone acetylation around the CTCF binding sites, adjacent to heterochromatin, of BRCA1 and c-mycgenes. These findings provide insight into the role of CTCF-CHD8 complex in insulation and epigenetic regulation at active insulator sites.

 

Figure：The CTCF-CHD8 complex binds to the DMR insulator and blocks the interaction between the enhancers and the IGF2 gene. The knockdown of CHD8 caused reactivation of the IGF2 gene on the maternal chromosome. The binding sites of the CTCF-CHD8 complex in the c-myc and BRCA1 genes lie adjacent to heterochromatin. Loss of CHD8 induced both DNA hypermethylation and histone hypoacethylation at the sites.