DNA methyltransferase 1 knockdown activates a replication stress checkpoint.
DNA methyltransferase 1 (DNMT1) is an important component of the epigenetic machinery and is responsible for copying DNA methylation patterns during cell division. Coordination of DNA methylation and DNA replication is critical for maintaining epigenetic programming. Knockdown of DNMT1 leads to inhibition of DNA replication, but the mechanism has been unclear. Here we show that depletion of DNMT1 with either antisense or small interfering RNA (siRNA) specific to DNMT1 activates a cascade of genotoxic stress checkpoint proteins, resulting in phosphorylation of checkpoint kinases 1 and 2 (Chk1 and -2), gammaH2AX focus formation, and cell division control protein 25a (CDC25a) degradation, in an ataxia telangiectasia mutated-Rad3-related (ATR)-dependent manner. siRNA knockdown of ATR blocks the response to DNMT1 depletion; DNA synthesis continues in the absence of DNMT1, resulting in global hypomethylation. Similarly, the response to DNMT1 knockdown is significantly attenuated in human mutant ATR fibroblast cells from a Seckel syndrome patient. This response is sensitive to DNMT1 depletion, independent of the catalytic domain of DNMT1, as indicated by abolition of the response with ectopic expression of either DNMT1 or DNMT1 with the catalytic domain deleted. There is no response to short-term treatment with 5-aza-deoxycytidine (5-aza-CdR), which causes demethylation by trapping DNMT1 in 5-aza-CdR-containing DNA but does not cause disappearance of DNMT1 from the nucleus. Our data are consistent with the hypothesis that removal of DNMT1 from replication forks is the trigger for this response.
Unterberger
Alexander
A
Department of Pharmacology and Therapeutics, McGill University, 3655 Sir William Osler Promenade, Montréal, Québec, Canada H3G 1Y6.
Andrews
Stephen D
SD
Weaver
Ian C G
IC
Szyf
Moshe
M
D000818:Animals; D064007:Ataxia Telangiectasia Mutated Proteins; D020134:Catalytic Domain; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism*; D002460:Cell Line; D004247:DNA / Q000235:genetics*; D000076123:DNA (Cytosine-5-)-Methyltransferase 1; D004248:DNA (Cytosine-5-)-Methyltransferases / Q000235:genetics / Q000378:metabolism*; D004261:DNA Replication / Q000235:genetics*; D015870:Gene Expression; D006657:Histones / Q000378:metabolism; D006801:Humans; D008745:Methylation; D051379:Mice; D009154:Mutation / Q000235:genetics; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism; D034622:RNA Interference
D018797:Cell Cycle Proteins; C468783:H2AX protein, human; D006657:Histones; D004247:DNA; D000076123:DNA (Cytosine-5-)-Methyltransferase 1; D004248:DNA (Cytosine-5-)-Methyltransferases; C000619380:DNMT1 protein, human; C000619381:Dnmt1 protein, mouse; C576597:ATR protein, human; D064007:Ataxia Telangiectasia Mutated Proteins; D017346:Protein Serine-Threonine Kinases