XPF mediates 3' flap processing for FEN1-independent Okazaki fragment maturation

Area of Science:

• Molecular Biology
• Genetics
• Cancer Research

Background:

• Okazaki fragment maturation (OFM) removes RNA-DNA primers during DNA replication, a process prone to stress and mutations.
• The canonical OFM pathway involves 5' flaps, processed by FEN1 and LIG1.
• A 3' flap-based OFM pathway has been observed in yeast under stress, but its role in human cells is unclear.

Purpose of the Study:

• To investigate the occurrence and significance of 3' flap-based OFM in human cancer cells.
• To identify nucleases involved in 3' flap processing in human cells.
• To evaluate the therapeutic potential of targeting this pathway in cancer.

Main Methods:

• Analysis of 3' flap formation in various human cancer cell lines.
• Assessment of FEN1 deficiency effects on flap levels and replication fork integrity.
• Investigation of XPF recruitment and function in FEN1-deficient cells.
• Evaluation of synergistic effects of XPF and FEN1 inhibitors on cancer cell viability.

Main Results:

• 3' flaps are frequently detected in human cancer cells, with levels increasing upon FEN1 deficiency.
• XPF is recruited to replication forks in FEN1-compromised cells and is essential for 3' flap degradation.
• XPF deficiency leads to 3' flap accumulation, DNA strand breaks, and distinct mutation signatures.
• Combined inhibition of XPF and FEN1 exhibits synergistic cytotoxicity against human cancer cells.

Conclusions:

• 3' flap-based OFM is a significant alternative pathway to 5' flap-based OFM in mammalian cells.
• XPF is a critical nuclease for 3' flap processing and cellular survival under replication stress.
• Targeting the XPF-mediated 3' flap pathway presents a promising therapeutic strategy for cancer treatment, particularly under replication stress conditions.