Different roles for nonhomologous end joining and homologous recombination following replication arrest in mammalian cells.
Homologous recombination (HR) and nonhomologous end joining (NHEJ) play overlapping roles in repair of DNA double-strand breaks (DSBs) generated during the S phase of the cell cycle. Here, we characterized the involvement of HR and NHEJ in the rescue of DNA replication forks arrested or slowed by treatment of hamster cells with hydroxyurea or thymidine. We show that the arrest of replication with hydroxyurea generates DNA fragmentation as a consequence of the formation of DSBs at newly replicated DNA. Both HR and NHEJ protected cells from the lethal effects of hydroxyurea, and this agent also increased the frequency of recombination mediated by both homologous and nonhomologous exchanges. Thymidine induced a less stringent arrest of replication and did not generate detectable DSBs. HR alone rescued cells from the lethal effects of thymidine. Furthermore, thymidine increased the frequency of DNA exchange mediated solely by HR in the absence of detectable DSBs. Our data suggest that both NHEJ and HR are involved in repair of arrested replication forks that include a DSB, while HR alone is required for the repair of slowed replication forks in the absence of detectable DSBs.
Department of Genetic and Cellular Toxicology, Stockholm University, S-106 91 Stockholm, Sweden.
Cecilia
C
Lundin
Klaus
K
Erixon
Catherine
C
Arnaudeau
Niklas
N
Schultz
Dag
D
Jenssen
Mark
M
Meuth
Thomas
T
Helleday
D000818:Animals; D017209:Apoptosis / Q000502:physiology; D002460:Cell Line; D006224:Cricetinae; D004247:DNA / Q000235:genetics / Q000378:metabolism*; D004249:DNA Damage; D004254:DNA Nucleotidyltransferases / Q000378:metabolism; D004261:DNA Replication; D004268:DNA-Binding Proteins / Q000378:metabolism; D005434:Flow Cytometry; D005786:Gene Expression Regulation; D006801:Humans; D006918:Hydroxyurea / Q000494:pharmacology; D009690:Nucleic Acid Conformation; D019384:Nucleic Acid Synthesis Inhibitors / Q000494:pharmacology; D051135:Rad51 Recombinase; D011995:Recombination, Genetic; D016196:S Phase / Q000235:genetics*; D013936:Thymidine / Q000494:pharmacology
D004268:DNA-Binding Proteins; D019384:Nucleic Acid Synthesis Inhibitors; D004247:DNA; D004254:DNA Nucleotidyltransferases; C495153:RAD51 protein, human; D051135:Rad51 Recombinase; D013936:Thymidine; D006918:Hydroxyurea