Abstract
RecQ family DNA helicases function in the maintenance of genome stability. Mice deficient in RecQL5, one of five RecQ helicases, show a cancer predisposition phenotype, suggesting that RecQL5 plays a tumor suppressor role. RecQL5 interacts with Rad51, a key factor in homologous recombination (HR), and displaces Rad51 from Rad51-single stranded DNA (ssDNA) filaments in vitro. However, the precise roles of RecQL5 in the cell remain elusive. Here, we present evidence suggesting that RecQL5 is involved in DNA interstrand crosslink (ICL) repair. Chicken DT40 RECQL5 gene knockout (KO) cells showed sensitivity to ICL-inducing agents such as cisplatin (CDDP) and mitomycin C (MMC) and a higher number of chromosome aberrations in the presence of MMC than wild-type cells. The phenotypes of RECQL5 KO cells resembled those of Fanconi anemia gene KO cells. Genetic analysis using corresponding gene knockout cells showed that RecQL5 is involved in the FANCD1 (BRCA2)-dependent ICL repair pathway in which Rad51-ssDNA filament formation is promoted by BRCA2. The disappearance but not appearance of Rad51-foci was delayed in RECQL5 KO cells after MMC treatment. Deletion of Rad54, which processes the Rad51-ssDNA filament in HR, in RECQL5 KO cells increased sensitivity to CDDP and further delayed the disappearance of Rad51-foci, suggesting that RecQL5 and Rad54 have different effects on the Rad51-ssDNA filament. Furthermore, the frequency and variation of CDDP-induced gene conversion at the immunoglobulin locus were increased in RECQL5 KO cells. These results suggest that RecQL5 plays a role in regulating the incidence and quality of ICL-induced recombination.