POLθ processes ssDNA gaps and promotes replication fork progression in BRCA1-deficient cells

Area of Science:

• Molecular Biology
• Cancer Genetics
• DNA Repair Mechanisms

Background:

• Polymerase theta (POLθ) is an error-prone DNA polymerase.
• Its inhibition is synthetically lethal in cancer cells with BRCA1/2 mutations.

Purpose of the Study:

• Investigate the genetic interaction between POLθ and BRCA1.
• Elucidate the molecular mechanisms underlying POLθ's role in BRCA1-deficient cells.

Main Methods:

• Utilized a small-molecule inhibitor targeting POLθ.
• Performed a genome-scale CRISPR-Cas9 knockout screen.
• Analyzed the roles of NBN and CDK6 in the synthetic lethality.

Main Results:

• POLθ processes single-stranded DNA (ssDNA) gaps in BRCA1-deficient cells, ensuring replication fork progression.
• NBN (MRN complex) and CDK6 were identified as suppressors of the POLθ-BRCA1 interaction.
• MRN complex nucleolytically processes ssDNA gaps, while CDK6 exacerbates replication stress.

Conclusions:

• ssDNA gap formation, influenced by cell-cycle regulators and MRN complex activity, drives synthetic lethality between POLθ and BRCA1.
• This provides critical insights for clinical trials targeting POLθ inhibitors in BRCA1/2-mutant cancers.