Transcriptional repression and heterochromatin formation by MBD1 and MCAF/AM family proteins.
DNA methylation cooperates with methylation at lysine 9 of histone H3 (H3-K9), a modified histone molecule that is targeted by heterochromatin protein 1, to form a transcriptionally silent chromatin. Methyl CpG-binding protein MBD1 recognizes methylated CpG dinucleotide and recruits H3-K9 methyltransferases such as SETDB1 to genomic regions. Here we show that MBD1-containing chromatin-associated factor (MCAF) 1, also known as the human homologue of murine ATFa-associated modulator (AM), is required for transcriptional repression and heterochromatin formation by MBD1, together with the involvement of SETDB1. Moreover, the amino acid sequence of MCAF1 shows similarity to a number of sequences of the MCAF/AM-related proteins, resulting in the identification of a new member of the protein family, termed MCAF2. Immunoprecipitation and in vitro binding analyses reveal that both MCAF proteins interact with MBD1, SETDB1, and Sp1 via two evolutionarily conserved distinct domains. Furthermore, MCAF1 enhances transcriptional repression by MBD1 together with SETDB1, and exogenous expression of MCAF2 partly compensates for the repressive activity in MCAF1 knockdown HeLa cells. The expression of MBD1 mutant, which lacks interaction with MCAF proteins, perturbs heterochromatin protein 1-enriched heterochromatin formation at the MBD1-containing chromosomal loci. These data suggest that MBD1.MCAF1.SETDB1 complex facilitates the formation of heterochromatic domains, emphasizing the role of MCAF/AM family proteins in epigenetic control.