Antithetic effects of MBD2a on gene regulation

DNA methylation is essential for epigenetic gene regulation during development. The cyclic AMP (cAMP)responsive element (CRE) is found in the promoter of many cAMP-regulated genes and plays important roles in their gene expression. Methylation occurs on the CRE site and results in transcriptional repression via a direct mechanism, that is, prevention by the methyl group of binding of the cAMP-responsive factor CREB to this site. A recent study indicated that the nucleosome is also important in repressing transcription. In this study, we investigated the regulation of transcriptional repression on methylated CRE. We focused on methyl-CpG binding domain protein 2 (MBD2). MBD2 consists of two forms, MBD2a and MBD2b, the latter lacking the N-terminal extension of MBD2a. Unexpectedly, we found that MBD2a, but not MBD2b, promoted activation of the unmethylated cAMP-responsive genes. An in vivo binding assay revealed that MBD2a selectively interacted with RNA helicase A (RHA), a component of CREB transcriptional coactivator complexes. MBD2a and RHA cooperatively enhanced CREB-dependent gene expression. Interestingly, coimmunoprecipitation assays demonstrated that MBD2a binding to RHA was not associated with histone deacetylase 1. Our results indicate a novel role for MBD2a in gene regulation.