Topoisomerase I suppresses genomic instability by preventing interference between replication and transcription.
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.
Institute of Human Genetics CNRS UPR1142, F-34396 Montpellier, France.
Sandie
S
Tuduri
Laure
L
Crabbé
Chiara
C
Conti
Hélène
H
Tourrière
Heidi
H
Holtgreve-Grez
Anna
A
Jauch
Véronique
V
Pantesco
John
J
De Vos
Aubin
A
Thomas
Charles
C
Theillet
Yves
Y
Pommier
Jamal
J
Tazi
Arnaud
A
Coquelle
Philippe
P
Pasero
D000818:Animals; D047369:Chromatin Immunoprecipitation; D004261:DNA Replication / Q000502:physiology*; D004264:DNA Topoisomerases, Type I / Q000502:physiology*; D042822:Genomic Instability / Q000502:physiology*; D016196:S Phase; D014158:Transcription, Genetic
D004264:DNA Topoisomerases, Type I