title: Caffeine delays replication fork progression and enhances UV-induced homologous recombination in Chinese hamster cell lines.
abstract: The ability to bypass DNA lesions encountered during replication is important in order to maintain cell viability and avoid genomic instability. Exposure of mammalian cells to UV-irradiation induces the formation of DNA lesions that stall replication forks. In order to restore replication, different bypass mechanisms are operating, previously named post-replication repair. Translesion DNA synthesis is performed by low-fidelity polymerases, which can replicate across damaged sites. The nature of lesions and of polymerases involved influences the resulting frequency of mutations. Homologous recombination represents an alternative pathway for the rescue of stalled replication forks. Caffeine has long been recognized to influence post-replication repair, although the mechanism is not identified. Here, we found that caffeine delays the progress of replication forks in UV-irradiated Chinese hamster cells. The length of this enhanced delay was similar in wild-type cells and in cell deficient in either homologous recombination or nucleotide excision repair. Furthermore, caffeine attenuated the frequency of UV-induced mutations in the hprt gene, whereas the frequency of recombination, monitored in this same gene, was enhanced. These observations indicate that in cells exposed to UV-light, caffeine inhibits the rescue of stalled replication forks by translesion DNA synthesis, thereby causing a switch to bypass via homologous recombination. The biological consequence of the former pathway is mutations, while the latter results in chromosomal aberrations.
authors.affiliation: Department of Genetics, Microbiology and Toxicology, Arrhenius Laboratories for the Natural Sciences, Stockholm University, S-106 91 Stockholm, Sweden.
authors.forename: Fredrik
authors.initials: F
authors.lastname: Johansson
authors.forename: Anne
authors.initials: A
authors.lastname: Lagerqvist
authors.forename: Silvia
authors.initials: S
authors.lastname: Filippi
authors.forename: Fabrizio
authors.initials: F
authors.lastname: Palitti
authors.forename: Klaus
authors.initials: K
authors.lastname: Erixon
authors.forename: Thomas
authors.initials: T
authors.lastname: Helleday
authors.forename: Dag
authors.initials: D
authors.lastname: Jenssen
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D016466:CHO Cells; D002110:Caffeine / Q000494:pharmacology*; D002869:Chromosome Aberrations / Q000187:drug effects; D006224:Cricetinae; D004260:DNA Repair / Q000187:drug effects; D004261:DNA Replication / Q000187:drug effects*; D005091:Exons; D007041:Hypoxanthine Phosphoribosyltransferase / Q000235:genetics; D007700:Kinetics; D011995:Recombination, Genetic / Q000187:drug effects*; D014466:Ultraviolet Rays
chemical_list: D002110:Caffeine; D007041:Hypoxanthine Phosphoribosyltransferase