Loss of human ribosomal gene CpG methylation enhances cryptic RNA polymerase II transcription and disrupts ribosomal RNA processing.
Epigenetic methyl-CpG silencing of the ribosomal RNA (rRNA) genes is thought to downregulate rRNA synthesis in mammals. In contrast, we now show that CpG methylation in fact positively influences rRNA synthesis and processing. Human HCT116 cells, inactivated for DNMT1 and DNMT3b or treated with aza-dC, lack CpG methylation and reactivate a large fraction of normally silent rRNA genes. Unexpectedly, these cells display reduced rRNA synthesis and processing and accumulate unprocessed 45S rRNA. Reactivation of the rRNA genes is associated with their cryptic transcription by RNA polymerase II. Ectopic expression of cryptic rRNA gene transcripts recapitulates the defects associated with loss of CpG methylation. The data demonstrate that rRNA gene silencing prevents cryptic RNA polymerase II transcription of these genes. Lack of silencing leads to the partial disruption of rRNA synthesis and rRNA processing, providing an explanation for the cytotoxic effects of loss of CpG methylation.
Gagnon-Kugler
Thérèse
T
Cancer Research Centre, CHUQ-HDQ Research Centre, Pavillon St. Patrick, 9 Rue McMahon, Québec, QC G1R 3S3, Canada.
Langlois
Frédéric
F
Stefanovsky
Victor
V
Lessard
Frédéric
F
Moss
Tom
T
D001374:Azacitidine / Q000031:analogs & derivatives / Q000494:pharmacology; D002466:Cell Nucleolus / Q000187:drug effects / Q000378:metabolism* / Q000473:pathology; D049109:Cell Proliferation; D002470:Cell Survival; D018899:CpG Islands; D000076123:DNA (Cytosine-5-)-Methyltransferase 1; D004248:DNA (Cytosine-5-)-Methyltransferases / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D019175:DNA Methylation / Q000187:drug effects; D004275:DNA, Ribosomal / Q000378:metabolism*; D000077209:Decitabine; D004791:Enzyme Inhibitors / Q000494:pharmacology; D045325:HCT116 Cells; D006801:Humans; D007700:Kinetics; D012319:RNA Polymerase II / Q000235:genetics / Q000378:metabolism*; D012323:RNA Processing, Post-Transcriptional; D020871:RNA Stability; D012335:RNA, Ribosomal / Q000378:metabolism*; D014158:Transcription, Genetic / Q000187:drug effects; D000097584:DNA Methyltransferase 3B
D001374:Azacitidine; D000076123:DNA (Cytosine-5-)-Methyltransferase 1; D004248:DNA (Cytosine-5-)-Methyltransferases; D004275:DNA, Ribosomal; D000077209:Decitabine; D004791:Enzyme Inhibitors; D012319:RNA Polymerase II; D012335:RNA, Ribosomal; D000097584:DNA Methyltransferase 3B; C088179:RNA, ribosomal, 45S; C000619380:DNMT1 protein, human