RED CELLS MBD2 is a critical component of a methyl cytosine–binding protein complex isolated from primary erythroid cells

The chicken embryonic -type globin gene, , is a member of a small group of vertebrate genes whose developmentally regulated expression is mediated by DNA methylation. Previously, we have shown that a methyl cytosine–binding complex binds to the methylated -globin gene in vitro. We have now chromatographically purified and characterized this complex from adult chicken primary erythroid cells. Four components of the MeCP1 transcriptional repression complex were identified: MBD2, RBAP48, HDAC2, and MTA1. These 4 proteins, as well as the zincfinger protein p66 and the chromatin remodeling factor Mi2, were found to coelute by gel-filtration analysis and pulldown assays. We conclude that these 6 proteins are components of the MeCPC. In adult erythrocytes, significant enrichment for MBD2 is seen at the inactive -globin gene by chromatin immunoprecipitation assay, whereas no enrichment is observed at the active A-globin gene, demonstrating MBD2 binds to the methylated and transcriptionally silent -globin gene in vivo. Knock-down of MBD2 resulted in up-regulation of a methylated -gene construct in mouse erythroleukemic (MEL)– cells. These results represent the first purification of a MeCP1-like complex from a primary cell source and provide support for a role for MBD2 in developmental gene regulation. (Blood. 2006;108:2836-2845)