Epigenetic programming of the rRNA promoter by MBD3.
Within the human genome there are hundreds of copies of the rRNA gene, but only a fraction of these genes are active. Silencing through epigenetics has been extensively studied; however, it is essential to understand how active rRNA genes are maintained. Here, we propose a role for the methyl-CpG binding domain protein MBD3 in epigenetically maintaining active rRNA promoters. We show that MBD3 is localized to the nucleolus, colocalizes with upstream binding factor, and binds to unmethylated rRNA promoters. Knockdown of MBD3 by small interfering RNA results in increased methylation of the rRNA promoter coupled with a decrease in RNA polymerase I binding and pre-rRNA transcription. Conversely, overexpression of MBD3 results in decreased methylation of the rRNA promoter. Additionally, overexpression of MBD3 induces demethylation of nonreplicating plasmids containing the rRNA promoter. We demonstrate that this demethylation occurs following the overexpression of MBD3 and its increased interaction with the methylated rRNA promoter. This is the first demonstration that MBD3 is involved in inducing and maintaining the demethylated state of a specific promoter.
Brown
Shelley E
SE
Department of Pharmacology and Therapeutics, McGill University, 3655 Sir William Osler Promenade, Montréal, Québec H3G 1Y6, Canada.
Szyf
Moshe
M
D002466:Cell Nucleolus / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000172:deficiency / Q000378:metabolism*; D044127:Epigenesis, Genetic; D006367:HeLa Cells; D006801:Humans; D008156:Luciferases / Q000378:metabolism; D008745:Methylation; D035463:Pol1 Transcription Initiation Complex Proteins / Q000378:metabolism; D011401:Promoter Regions, Genetic / Q000235:genetics*; D011485:Protein Binding; D021381:Protein Transport; D012318:RNA Polymerase I / Q000378:metabolism; D012322:RNA Precursors / Q000235:genetics; D034741:RNA, Small Interfering / Q000378:metabolism; D014158:Transcription, Genetic
D004268:DNA-Binding Proteins; C115369:MBD3 protein, human; D035463:Pol1 Transcription Initiation Complex Proteins; D012322:RNA Precursors; D034741:RNA, Small Interfering; C063844:transcription factor UBF; D008156:Luciferases; D012318:RNA Polymerase I