FAN1-MLH1 interaction affects repair of DNA interstrand cross-links and slipped-CAG/CTG repeats

Area of Science:

• Molecular Biology
• Genetics
• DNA Repair Mechanisms

Background:

• FAN1 (Fluorescent-Activated Nucleases 1) is a DNA nuclease involved in DNA repair.
• FAN1 interacts with MLH1, a key protein in DNA mismatch repair.
• FAN1 variants influence Huntington's disease (HD) progression, linked to CAG repeat expansions.

Purpose of the Study:

• To elucidate the mechanism of the FAN1-MLH1 interaction.
• To determine the role of the FAN1-MLH1 complex in DNA interstrand crosslink (ICL) repair and repeat stability.
• To investigate the regulation of the FAN1-MLH1 interaction.

Main Methods:

• Site-directed mutagenesis to identify critical amino acid residues for MLH1 binding.
• Cellular assays measuring hypersensitivity to ICL damage.
• Analysis of CAG/CTG slip-out repair.
• Phosphorylation studies of FAN1-S126 and its cell cycle regulation.

Main Results:

• Specific amino acid residues in FAN1 were identified as critical for MLH1 binding.
• Disruption of the FAN1-MLH1 interaction led to hypersensitivity to ICLs and defective repair of repeat expansions.
• FAN1-S126 phosphorylation, regulated by cyclin-dependent kinases, inhibits FAN1-MLH1 association and is reduced upon ICL induction.

Conclusions:

• The FAN1-MLH1 complex is a critical regulator of the cellular response to ICLs and maintains genome stability by preventing repeat expansions.
• Phosphorylation of FAN1-S126 dynamically controls the FAN1-MLH1 interaction.
• This complex represents a novel therapeutic target for neurodegenerative diseases and cancer.