Human DNA topoisomerase I poisoning causes R loop-mediated genome instability attenuated by transcription factor IIS

Area of Science:

• Molecular Biology
• Genetics
• Cancer Research

Background:

• DNA topoisomerase I (Top1cc) activity is crucial for DNA replication and transcription.
• Top1cc intermediates can lead to genomic instability, including DNA double-strand breaks (DSBs), DNA-RNA hybrids, and micronuclei formation.
• The precise mechanisms by which Top1cc induces these genomic alterations are not fully understood.

Purpose of the Study:

• To elucidate the mechanisms underlying Top1cc-induced DNA-RNA hybrids and DSBs.
• To investigate the role of RNA polymerase II (RNAPII) accumulation and transcription-replication conflicts in Top1cc-mediated genomic instability.
• To determine the cell cycle dependency of Top1cc-induced micronuclei formation.

Main Methods:

• Integration of genomic data analyzing Top1cc-triggered hybrids and DSBs.
• Utilized a transcription factor IIS mutant to study the impact on RNAPII accumulation and transcription elongation.
• Assessed micronuclei formation across different cell cycle phases.

Main Results:

• Top1ccs induce DNA-RNA hybrids via distinct mechanisms.
• DSBs occur at highly transcribed genes in early replicating zones, overlapping with hybrids downstream of accumulated RNAPII at gene 5'-ends.
• Impaired transcription elongation leads to increased RNAPII accumulation and Top1cc-induced DSBs and micronuclei, particularly when Top1ccs occur during specific cell cycle phases (late G1, early/mid S).

Conclusions:

• RNAPII accumulation and subsequent transcription-replication conflicts play a significant role in Top1cc-induced DSBs and micronuclei.
• Transcription factor IIS activity can mitigate Top1cc-induced genomic instability.
• These findings highlight the complex interplay between Top1cc, transcription, replication, and genome integrity in cancer cells.