DNA2 cooperates with the WRN and BLM RecQ helicases to mediate long-range DNA-end resection in human cells

Abstract

The 5'-3' resection of DNA ends is a prerequisite for repair of DNA double-strand breaks by homologous recombination, microhomology-mediated end joining and single-strand annealing. Recent studies in yeast have shown that following an initial DNA-end processing by the Mre11-Rad50-Xrs2 complex and Sae2, extension of resection tracts is mediated either by Exonuclease 1 or by combined activities of the RecQ-family DNA helicase Sgs1 and the helicase/endonuclease Dna2. Although human DNA2 was shown to cooperate with the BLM helicase to catalyze resection of DNA ends, it remains a matter of debate whether another human RecQ helicase, namely WRN, can substitute for BLM in DNA2-catalyzed resection. Here, we present evidence that WRN and BLM act epistatically with DNA2 to promote long-range resection of DSB ends in human cells. Our biochemical experiments show that WRN and DNA2 interact physically and coordinate their enzymatic activities to mediate 5'-3' DNA-end resection in a reaction dependent on RPA. In addition, we present in vitro and in vivo data suggesting that BLM promotes DNA-end resection as part of the BLM-TOPOIIIα-RMI1-RMI2 complex. Our study provides new mechanistic insights into the process of DNA-end resection in mammalian cells.