MUS81 nuclease activity is essential for replication stress tolerance and chromosome segregation in BRCA2-deficient cells

Abstract

Failure to restart replication forks stalled at genomic regions that are difficult to replicate or contain endogenous DNA lesions is a hallmark of BRCA2 deficiency. The nucleolytic activity of MUS81 endonuclease is required for replication fork restart under replication stress elicited by exogenous treatments. Here we investigate whether MUS81 could similarly facilitate DNA replication in the context of BRCA2 abrogation. Our results demonstrate that replication fork progression in BRCA2-deficient cells requires MUS81. Failure to complete genome replication and defective checkpoint surveillance enables BRCA2-deficient cells to progress through mitosis with under-replicated DNA, which elicits severe chromosome interlinking in anaphase. MUS81 nucleolytic activity is required to activate compensatory DNA synthesis during mitosis and to resolve mitotic interlinks, thus facilitating chromosome segregation. We propose that MUS81 provides a mechanism of replication stress tolerance, which sustains survival of BRCA2-deficient cells and can be exploited therapeutically through development of specific inhibitors of MUS81 nuclease activity.

Brca2 abrogation engages with the alternative lengthening of telomeres via break‐induced replication

“…6E), indicating that Brca2 deficiency indeed resulted in the break then subsequent BIR. While we were working on this question, a couple of papers showed that genic replication stress induced by the absence of Brca2 led to MiDAS [47,48], in agreement with our results. Approximately 2% of the whole genome, depending on how they are calculated, are transcribed.…”

“…7). We do not rule out the possibility that MUS81 nuclease might play a role in this pathway, as MUS81 is required for compensatory DNA synthesis during mitosis when Brca2 is absent [48]. Unexpectedly, the depletion of Rad51, and its paralogs as well, did not result in ALT features, unlike abrogation of Brca2 (Figs 4 and 5).…”

“…). We do not rule out the possibility that MUS81 nuclease might play a role in this pathway, as MUS81 is required for compensatory DNA synthesis during mitosis when Brca2 is absent .…”

Multifaceted Impact of MicroRNA 493-5p on Genome-Stabilizing Pathways Induces Platinum and PARP Inhibitor Resistance in BRCA2-Mutated Carcinomas

“…Identifying the mechanism of platinum and PARPi resistance in BRCA2 -mutated carcinomas has been a challenge as HRR is not restored in cells expressing mutant BRCA2 . However, few recent studies have revealed that BRCA2 mutant carcinomas might still develop platinum and PARPi resistance without restoration of HRR proficiency via a complex mechanism where stalled DNA replication fork is protected from degradation by nucleases by downregulation of proteins such as PTIP , CHD4 , or EZH2 (Guillemette et al, 2015; Lai et al, 2017; Patch et al, 2015; Ray Chaudhuri et al, 2016; Rondinelli et al, 2017). Importantly, it is not clear how these factors would be downregulated in BRCA2 mutant cancers.…”

BRCA2 abrogation triggers innate immune responses potentiated by treatment with PARP inhibitors

“…ionizing radiation, DNA cross linking agents), the role of BRCA2 in replication is intrinsic to cell physiology. In the absence of external challenges, loss of BRCA2 triggers a significant decrease in replication fork progression and a high frequency of stalled forks 3,4 . A subset of these forks collapse and are converted to DSBs which, due to compromised HR repair, accumulate in BRCA2-deficient cells.…”