Enhanced induction of mutation by X-irradiation in Werner syndrome cells

Abstract

Werner syndrome (WS) is a rare premature aging syndrome. Because the WS gene, WRN, is a member of the RecQ helicase family, it is assumed to be a caretaker of genomic integrity. In the present study, we examined the X-ray-induced mutation frequency at the hypoxiantin guanine phosphoribosyl transferase (HPRT) locus in a WS cell line (WS780), and analyzed the different types of mutations by using multiplex PCR. The results indicated that the mutation frequency induced by X-irradiation was higher in the WS cells than in the control cells. It is notable that the majority of mutations observed in the WS cells consist of deletion mutations. We then examined in vitro assays for the end-joining ability of the DNA double-strand breaks (DBSs) in the nuclear extracts prepared from the WS cells, and the control cells. Sequencing analysis revealed that the deletions possibly caused by illegitimate recombination between two short homologies, occurred more frequently in the WS cells than in the control cells. These results suggest that a defect in the WRN gene function promotes the illegitimate recombination, and that this recombination might lead to the induction of large deletion mutations in WS cells.