title: The structure-specific endonuclease Ercc1-Xpf is required to resolve DNA interstrand cross-link-induced double-strand breaks.
abstract: Interstrand cross-links (ICLs) are an extremely toxic class of DNA damage incurred during normal metabolism or cancer chemotherapy. ICLs covalently tether both strands of duplex DNA, preventing the strand unwinding that is essential for polymerase access. The mechanism of ICL repair in mammalian cells is poorly understood. However, genetic data implicate the Ercc1-Xpf endonuclease and proteins required for homologous recombination-mediated double-strand break (DSB) repair. To examine the role of Ercc1-Xpf in ICL repair, we monitored the phosphorylation of histone variant H2AX (gamma-H2AX). The phosphoprotein accumulates at DSBs, forming foci that can be detected by immunostaining. Treatment of wild-type cells with mitomycin C (MMC) induced gamma-H2AX foci and increased the amount of DSBs detected by pulsed-field gel electrophoresis. Surprisingly, gamma-H2AX foci were also induced in Ercc1(-/-) cells by MMC treatment. Thus, DSBs occur after cross-link damage via an Ercc1-independent mechanism. Instead, ICL-induced DSB formation required cell cycle progression into S phase, suggesting that DSBs are an intermediate of ICL repair that form during DNA replication. In Ercc1(-/-) cells, MMC-induced gamma-H2AX foci persisted at least 48 h longer than in wild-type cells, demonstrating that Ercc1 is required for the resolution of cross-link-induced DSBs. MMC triggered sister chromatid exchanges in wild-type cells but chromatid fusions in Ercc1(-/-) and Xpf mutant cells, indicating that in their absence, repair of DSBs is prevented. Collectively, these data support a role for Ercc1-Xpf in processing ICL-induced DSBs so that these cytotoxic intermediates can be repaired by homologous recombination.
authors.affiliation: Department of Cell Biology and Genetics, Erasmus Medical Center, Rotterdam, The Netherlands. niedernhoferl@upmc.edu
authors.forename: Laura J
authors.initials: LJ
authors.lastname: Niedernhofer
authors.forename: Hanny
authors.initials: H
authors.lastname: Odijk
authors.forename: Magda
authors.initials: M
authors.lastname: Budzowska
authors.forename: Ellen
authors.initials: E
authors.lastname: van Drunen
authors.forename: Alex
authors.initials: A
authors.lastname: Maas
authors.forename: Arjan F
authors.initials: AF
authors.lastname: Theil
authors.forename: Jan
authors.initials: J
authors.lastname: de Wit
authors.forename: N G J
authors.initials: NG
authors.lastname: Jaspers
authors.forename: H Berna
authors.initials: HB
authors.lastname: Beverloo
authors.forename: Jan H J
authors.initials: JH
authors.lastname: Hoeijmakers
authors.forename: Roland
authors.initials: R
authors.lastname: Kanaar
mesh_terms: D000818:Animals; D002453:Cell Cycle; D002460:Cell Line; D002869:Chromosome Aberrations; D004247:DNA / Q000737:chemistry / Q000378:metabolism; D004249:DNA Damage / Q000187:drug effects / Q000528:radiation effects; D004260:DNA Repair; D004268:DNA-Binding Proteins / Q000172:deficiency / Q000235:genetics* / Q000502:physiology; D004720:Endonucleases / Q000172:deficiency / Q000235:genetics* / Q000502:physiology; D005720:Gamma Rays; D006657:Histones / Q000032:analysis; D007150:Immunohistochemistry; D051379:Mice; D018345:Mice, Knockout; D016685:Mitomycin / Q000494:pharmacology; D009690:Nucleic Acid Conformation; D014466:Ultraviolet Rays
chemical_list: D004247:DNA; D004268:DNA-Binding Proteins; D004720:Endonucleases; D006657:Histones; D016685:Mitomycin; C095888:xeroderma pigmentosum group F protein; C499360:Ercc1 protein, mouse; C475961:gamma-H2AX protein, mouse