Human RECQ5 helicase promotes repair of DNA double-strand breaks by synthesis-dependent strand annealing

Abstract

Most mitotic homologous recombination (HR) events proceed via a synthesis-dependent strand annealing mechanism to avoid crossing over, which may give rise to chromosomal rearrangements and loss of heterozygosity. The molecular mechanisms controlling HR sub-pathway choice are poorly understood. Here, we show that human RECQ5, a DNA helicase that can disrupt RAD51 nucleoprotein filaments, promotes formation of non-crossover products during DNA double-strand break-induced HR and counteracts the inhibitory effect of RAD51 on RAD52-mediated DNA annealing in vitro and in vivo. Moreover, we demonstrate that RECQ5 deficiency is associated with an increased occupancy of RAD51 at a double-strand break site, and it also causes an elevation of sister chromatid exchanges on inactivation of the Holliday junction dissolution pathway or on induction of a high load of DNA damage in the cell. Collectively, our findings suggest that RECQ5 acts during the post-synaptic phase of synthesis-dependent strand annealing to prevent formation of aberrant RAD51 filaments on the extended invading strand, thus limiting its channeling into potentially hazardous crossover pathway of HR.

Differential and Concordant Roles for Poly(ADP-Ribose) Polymerase 1 and Poly(ADP-Ribose) in Regulating WRN and RECQL5 Activities

“…This shows that, other than PARylation, phosphorylation also regulates the recruitment of RECQL5 and WRN at sites of double-strand breaks. Previously, it was reported that RECQL5 enhances noncrossover HR-mediated DSB repair (30). Indeed, our results support this finding and furthermore show that RECQL5 and PARP1 participate in the same pathway (Fig.…”

“…It has been shown that RECQL5 interacts with RAD51 to inhibit RAD51-induced D-loop formation and sister chromatid exchange (29). Consistent with that finding, RECQL5 prevents RAD51 single-stranded DNA (ssDNA) filament formation by promoting synthesis-dependent strand annealing to mediate DSB repair (30). Our previous studies used confocal laser microscopy to study the kinetics of recruitment of RECQL5 to DSBs in real time in live cells (31).…”

“…Homologous recombination (HR) and nonhomologous end joining (NHEJ) are the two major pathways for DNA DSB repair. RECQL5 was previously shown to mediate noncrossover DSB repair by HR (30). However, it is unclear whether PARP1 plays a role in the process of repair here or whether RECQL5 has any function in regulating NHEJ-mediated repair.…”

Regulation of Recombination and Genomic Maintenance

“…Interestingly, both yeast Srs2 and mammalian RECQ5 have been implicated in antirecombination (see above) and anticrossover pathways (Aylon et al 2003;Ira et al 2003;Paliwal et al 2014). Although the mechanisms involved still need to be established, it is possible that removal of Rad51 from ssDNA is involved in both.…”

Noncanonical views of homology-directed DNA repair

“…Human BLM, along with TopIII α topoisomerase, promotes noncrossover formation by dissolution of dHJ intermediates and by preventing the exchange of flanking sequences (Wu and Hickson 2003). Recently, another member of the RecQ helicase family, RecQ5, a potential Srs2 ortholog in mammals, was shown to promote SDSA by disrupting Rad51-ssDNA filaments and counteracting the inhibitory effect of Rad51 on the strand-annealing activity of Rad52 (Paliwal et al 2014). It will be interesting to examine whether FANCM can also perform a function similar to its yeast ortholog, Mph1, in dissociating Rad51-coated D loops and promoting SDSA.…”