Head-on collisions between the replication and transcription machinery over R-loopforming sequences potently stall replication forks. Stalled fork structures can then be
converted into DNA breaks, leading to apoptosis or growth arrest of cycling cells. The
mechanisms which coordinate transcription and replication to avoid these genotoxic
collisions are therefore critical for cellular fitness, especially in the case of rapidly
dividing tumor cells. However it is unclear if coordination occurs passively through
globally encoded co-directionality between transcription units and replication forks, or
actively, through transcriptional regulatory mechanisms that function to silence head-on
transcripts during S-phase. ‘Active’ coordination would imply that transcriptional
regulators could be effectively targeted in cancer to induce collisions and subsequent
tumor cell killing. However, the ‘active’ coordination model has never been
systematically assessed. In this dissertation, we present work demonstrating that
head-on transcription over R-loop forming sequences occurs at a high frequency during
the cell cycle across tumor cell types, that this transcription is temporally downregulated
during S-phase, and that INO80 and MOT1 are leveraged in NSCLC to suppress
genotoxic TRCs and preserve tumor cell viability. These results suggest that
transcriptional regulation is imperative to genome stability, and transcriptional regulators
serve as promising targets for the treatment of NSCLC.