Topoisomerase 1-dependent R-loop deficiency drives accelerated replication and genomic instability

Area of Science:

• Molecular Biology
• Genetics
• Cancer Research

Background:

• DNA replication ensures genome duplication, but stress can cause damage and instability.
• Replication stress often involves slow or stalled forks, but accelerated replication is a newly recognized form.
• The molecular mechanisms driving accelerated replication remain largely unknown.

Purpose of the Study:

• To investigate the molecular basis of oncogene-induced accelerated DNA replication.
• To elucidate the role of topoisomerase 1 (TOP1) in replication fork dynamics and DNA damage.
• To understand how R-loop homeostasis is maintained during DNA replication.

Main Methods:

• Analysis of cells with mutated HRAS activation.
• Measurement of topoisomerase 1 (TOP1) expression levels.
• Assessment of replication fork speed and DNA damage markers.
• Investigating the impact of TOP1 and RNaseH1 modulation on replication and R-loops.

Main Results:

• Mutated HRAS activation increases TOP1 expression, leading to aberrant replication fork acceleration.
• Increased TOP1 reduces RNA-DNA hybrids (R-loops), causing DNA damage.
• Restoring TOP1 levels or mild replication inhibition rescues replication and reduces DNA damage.
• Overexpression of TOP1 or RNaseH1 induces accelerated replication and DNA damage.

Conclusions:

• Aberrant replication fork acceleration is a mechanism of oncogene-induced DNA damage.
• TOP1 plays a critical role in maintaining R-loop homeostasis for genome integrity.
• TOP1 equilibrium is essential for faithful DNA replication and preventing genomic instability.