Rapid and transient recruitment of DNMT1 to DNA double-strand breaks is mediated by its interaction with multiple components of the DNA damage response machinery

Abstract

DNA methylation is an epigenetic mark critical for regulating transcription, chromatin structure and genome stability. Although many studies have shed light on how methylation impacts transcription and interfaces with the histone code, far less is known about how it regulates genome stability. We and others have shown that DNA methyltransferase 1 (DNMT1), the maintenance methyltransferase, contributes to the cellular response to DNA damage, yet DNMT1's exact role in this process remains unclear. DNA damage, particularly in the form of double-strand breaks (DSBs), poses a major threat to genome integrity. Cells therefore possess a potent system to respond to and repair DSBs, or to initiate cell death. In the current study, we used a near-infrared laser microirradiation system to directly study the link between DNMT1 and DSBs. Our results demonstrate that DNMT1 is rapidly but transiently recruited to DSBs. DNMT1 recruitment is dependent on its ability to interact with both PCNA and the ATR effector kinase CHK1, but is independent of its catalytic activity. In addition, we show for the first time that DNMT1 interacts with the 9-1-1 PCNA-like sliding clamp and that this interaction also contributes to DNMT1 localization to DNA DSBs. Finally, we demonstrate that DNMT1 modulates the rate of DSB repair and is essential for suppressing abnormal activation of the DNA damage response in the absence of exogenous damage. Taken together, our studies provide compelling additional evidence for DNMT1 acting as a regulator of genome integrity and as an early responder to DNA DSBs.

DNA methyltransferase 1 and DNA methylation patterning contribute to germinal center B-cell differentiation

“…It is logical to assume that at least part of the reason DNMT1 is up-regulated in GC B cells is to support methylation during rapid cell turnover. However, numerous studies demonstrate that DNMT1 also plays a role in supporting DNA replication and repair (eg, Unterberger et al, 39 Ha et al 40 ). The fact that phospho-H2AX staining was increased in the nuclei of residual GC cells in Dnmt1 hypomorphic mice is consistent with previously published data, including a report by Unterberger et al revealing that DNMT1 knockdown induces DNA damage responses and H2AX phosphorylation.…”

“…Ha et al reported that DNMT1 is involved in dsDNA breaks repair by interacting with PCNA and 9-1-1 complex, 40 and is recruited to sites of DNA damage. Because DNMT1 is abundant within GC B cells, which are undergoing genetic recombination we considered that DNMT1 might be required for DNA damage repair in these cells.…”

ATRX contributes to epigenetic asymmetry and silencing of major satellite transcripts in the maternal genome of the mouse embryo

“…For example, the yeast cohesin acetyl transferase ECO1 is loaded around centromeres and chromosome arms, and is overexpressed in response to unresolved DSBs to activate cohesion in broken centromeres and to prevent large-scale chromosome rearrangements (Unal et al, 2007;Watrin and Peters, 2009). Consistent with this notion, overexpression of Dnmt1 and Dzip3 transcripts in ATRX-deficient zygotes may be part of a cellular response to DNA damage, as DNMT1 has been recently implicated in the recruitment of DNA damage repair factors independently of its methyltransferase activity, and both DNMT1 and DZIP3 are essential for mounting an early response to DNA damage (Zhou et al, 2009;Ha et al, 2011). The striking accumulation of aurora kinase B protein at centromeric domains might be part of a global response to improper chromosomemicrotubule interactions.…”

DNA Methylation in Mammalian and Non-Mammalian Organisms

“…A recent report has validated this model in human cells by demonstrating that DNMT1 is rapidly but transiently recruited to double stranded breaks (DSBs) (Ha et al, 2011), dependent on its ability to interact with both PCNA and CHK1, but independent of its catalytic activity. What is the potential importance of the Dnmt1 signalling mechanism?…”