Abstract
Elevated levels of reactive oxygen species (ROS) reduce replication fork velocity by causing dissociation of the TIMELESS-TIPIN complex from the replisome. Here, we show that ROS generated by exposure of human cells to the ribonucleotide reductase inhibitor hydroxyurea (HU) promote replication fork reversal in a manner dependent on active transcription and formation of co-transcriptional RNA:DNA hybrids (R-loops).
The frequency of R-loop-dependent fork stalling events is also increased after TIMELESS depletion or a partial inhibition of replicative DNA polymerases by aphidicolin, suggesting that this phenomenon is due to a global replication slowdown. In contrast, replication arrest caused by HU-induced depletion of deoxynucleotides does not induce fork reversal but, if allowed to persist, leads to extensive R-loop-independent DNA breakage during S-phase.
Our work reveals a link between oxidative stress and transcription-replication interference that causes genomic alterations recurrently found in human cancer. Excessive oxidative stress is widely perceived as a key factor in cancer progression.
Here, the authors reveal that oxidative stress induces transcription-dependent replication fork stalling that appears to be a major source of chromosomal rearrangements found in human cancers.