Topoisomerase I (Top1) is a key enzyme in functioning at the interface between DNA replication, transcription and mRNA maturation. Here, we show that Top1 suppresses genomic instability in mammalian cells by preventing a conflict between transcription and DNA replication. Using DNA combing and ChIP (chromatin immunoprecipitation)-on-chip, we found that Top1-deficient cells accumulate stalled replication forks and chromosome breaks in S phase, and that breaks occur preferentially at gene-rich regions of the genome. Notably, these phenotypes were suppressed by preventing the formation of RNA-DNA hybrids (R-loops) during transcription. Moreover, these defects could be mimicked by depletion of the splicing factor ASF/SF2 (alternative splicing factor/splicing factor 2), which interacts functionally with Top1. Taken together, these data indicate that Top1 prevents replication fork collapse by suppressing the formation of R-loops in an ASF/SF2-dependent manner. We propose that interference between replication and transcription represents a major source of spontaneous replication stress, which could drive genomic instability during the early stages of tumorigenesis.
Topoisomerase I suppresses genomic instability by preventing interference between replication and transcription
Tuduri, S.; Crabbe, L.; Conti, C.; Tourriere, H.; Holtgreve-Grez, H.; Jauch, A.; Pantesco, V.; De Vos, J.; Thomas, A.; Theillet, C.; Pommier, Y.; Tazi, J.; Coquelle, A.; Pasero, P.
Nat Cell Biol
2009-11 / vol 11 / pages 1315-24
ncb1984 [pii] 10.1038/ncb1984
1476-4679 (Electronic) 1465-7392 (Linking)
Animals; *Transcription, Genetic; Chromatin Immunoprecipitation; DNA Replication/*physiology; S Phase; DNA Topoisomerases, Type I/*physiology; Genomic Instability/*physiology