DNA methylation-related chromatin modification in the regulation of mouse delta-opioid receptor gene.

DNA methylation plays critical roles in gene-silencing through chromatin modification. We reported previously that promoter-region CpG methylation repressed mouse delta-opioid receptor (mDOR) gene expression. In the current study, we demonstrated that the methylation of mDOR gene promoter is correlated with a repressive chromatin structure that has less HaeIII and MspI nuclear accessibility and more deacetylated histone H3 and H4 than that of unmethylated mDOR promoter. Chromatin immunoprecipitation analysis showed the association of a methyl-CpG-binding domain protein 2 (MBD2) with methylated mDOR promoter. Transient expression of MBD2 enhanced the repression of partially methylated mDOR promoter activity, and this repression was partially reversed by treatment of trichostatin A, a specific histone deacetylase inhibitor, indicating that MBD2 may mediate DNA methylation-related chromatin modification through recruiting histone deacetylases to mDOR promoter region. In addition, trichostatin A treatment increased both methylated mDOR promoter activity in a transient transfection assay and endogenous mDOR mRNA level in Neuro2A cells. Taken together, these results demonstrate that the mDOR gene expression is regulated by DNA methylation-related chromatin modification, especially histone acetylation and deacetylation.