MBD2 is a transcriptional repressor belonging to the MeCP1 histone deacetylase complex

Abstract

Mammalian DNA is methylated at many CpG dinucleotides. The biological consequences of methylation are mediated by a family of methyl-CpG binding proteins. The best characterized family member is MeCP2, a transcriptional repressor that recruits histone deacetylases. Our report concerns MBD2, which can bind methylated DNA in vivo and in vitro and has been reported to actively demethylate DNA (ref. 8). As DNA methylation causes gene silencing, the MBD2 demethylase is a candidate transcriptional activator. Using specific antibodies, however, we find here that MBD2 in HeLa cells is associated with histone deacetylase (HDAC) in the MeCP1 repressor complex. An affinity-purified HDAC1 corepressor complex also contains MBD2, suggesting that MeCP1 corresponds to a fraction of this complex. Exogenous MBD2 represses transcription in a transient assay, and repression can be relieved by the deacetylase inhibitor trichostatin A (TSA; ref. 12). In our hands, MBD2 does not demethylate DNA. Our data suggest that HeLa cells, which lack the known methylation-dependent repressor MeCP2, use an alternative pathway involving MBD2 to silence methylated genes.

Fractionated Low-Dose Radiation Exposure Leads to Accumulation of DNA Damage and Profound Alterations in DNA and Histone Methylation in the Murine Thymus

“…The methyl-binding domain of MeCP2 recognizes symmetrically methylated CpG dinucleotides through contact with the major groove of the double helix in the nucleosome and, under certain circumstances, can even displace histone H1 from chromatin (14,42). Its transcription repression domain interacts with corepressor complexes containing histone deacetylases (43,44). The properties of MeCP2 are central to understanding the mechanisms of methylation-mediated gene silencing and chromatin remodeling.…”

Methyl-CpG Binding Domain Proteins and Their Involvement in the Regulation of the MAGE-A1, MAGE-A2, MAGE-A3, and MAGE-A12 Gene Promoters

“…For EMSA, we used nuclear extracts derived from three breast cancer cells (MCF-7, T47D, and MDA-MB-231) as well as the epithelioid cervical carcinoma cell line HeLa. Nuclear extracts from HeLa cells were used because methyl-CpG binding proteins were recently found to be components of HeLa cells and served as control for the binding analyses (30,34). When the unmethylated, HpaII-and SssI-methylated probes were incubated with various nuclear extracts, prominent complexes were formed as detected by EMSA.…”

“…The shorter form, MBD2b, starting at the second methionine therefore lacks the NH 2 -terminal sequence of MBD2a (28). Recent reports described MBD2a as both an activator and a repressor of transcription (29)(30)(31). Mbd1-and Mbd2-deficient mice are viable and fertile.…”

Dynamic and reversibility of heterochromatic gene silencing in human disease

“…MBD1 was first identified as a methyl binding protein and it has been recently shown as able to bind CpG sequences independently of the methylation status [55]. MBD2 is part of the MeCP1 protein complex [56]. MBD3 binds methylated probes in vitro but this interaction is not competed by an excess of methylated cold competitor making its ability to interact specifically with methylated sequences questionable [57].…”

“…The methyl CpG binding proteins exert their function as transcriptional repressors via chromatin remodeling. These proteins are often part of larger repressor complexes as NuRD, NoRC, mSin3A and SWI-SNF, that recruit HDACs [56,[62][63][64][65][66][67] and histone methyltransefrases (HMTs) [68] on methylated targeted sequences. Acetylation of the α amino groups of evolutionary conserved lysine residues present on nucleosomal histone H3 and H4 is catalyzed by the histone acetyl transferases (HAT).…”