POLQ seals post-replicative ssDNA gaps to maintain genome stability in BRCA-deficient cancer cells

Area of Science:

• Genetics
• Molecular Biology
• Cancer Research

Background:

• DNA double-strand break (DSB) repair is crucial for maintaining genomic stability.
• POLQ (polymerase theta) is a key enzyme in microhomology-mediated end-joining (MMEJ) and is overexpressed in various cancers.
• POLQ inhibitors show synthetic lethality in homologous recombination (HR) and Shieldin-deficient cancers, suggesting a dependence on MMEJ.

Purpose of the Study:

• To investigate the functions of POLQ beyond its established role in MMEJ.
• To explore POLQ's involvement in repairing post-replicative single-stranded DNA (ssDNA) gaps.
• To understand the implications of POLQ's activities in cancer genome evolution and therapeutic strategies.

Main Methods:

• Cellular assays examining DNA repair pathways in POLQ-deficient cells.
• Biochemical analyses of POLQ's helicase and polymerase activities.
• Investigation of POLQ's role in microhomology-mediated gap skipping (MMGS).

Main Results:

• POLQ-deficient cells accumulate post-replicative ssDNA gaps when HR is compromised (e.g., BRCA1/2 loss) or PARP inhibitors are used.
• Biochemical studies demonstrate POLQ's ability to displace RPA and fill ssDNA gaps.
• POLQ mediates MMGS, generating deletions similar to those found in POLQ-overexpressing cancers.

Conclusions:

• POLQ plays a significant role in mutagenic post-replicative gap sealing, independent of MMEJ.
• This activity of POLQ can contribute to genome evolution in cancer.
• Loss of POLQ function creates a dependency on HR for cellular viability, offering a potential therapeutic vulnerability.