Nuclear PI3P produced by the Beclin-1/Vps34 complex regulates DNA mismatch repair

Area of Science:

• Cell Biology
• Molecular Biology
• Genetics

Background:

• Genome integrity is maintained by DNA mismatch repair (MMR) to correct replication errors.
• The role of non-protein cofactors in regulating MMR remains largely unexplored.
• Nuclear phosphoinositide signaling is critical for various cellular processes.

Purpose of the Study:

• To investigate the potential role of nuclear lipids as regulators of the DNA mismatch repair (MMR) pathway.
• To identify specific lipids involved in MMR complex assembly and function.
• To elucidate the mechanism by which nuclear lipids influence MMR activity and genome stability.

Main Methods:

• Utilized biosensors, lipid pulldown assays, and proximity ligation assays to detect and characterize nuclear PI3P.
• Employed pharmacological and genetic approaches to deplete the class III PI3-kinase Vps34.
• Assessed MMR component assembly, DNA substrate association, and microsatellite instability.
• Investigated the role of the Beclin-1/Vps34 complex in nuclear PI3P production.
• Evaluated MMR-dependent DNA damage signaling and drug resistance in cellular and in vivo models.

Main Results:

• Identified nuclear phosphatidylinositol-3-phosphate (PI3P) as a key regulator of MMR.
• Demonstrated that PI3P localizes near MutSα (MSH2:MSH6) and MutSβ (MSH2:MSH3) complexes.
• Showed that Vps34 depletion impairs MMR complex assembly and DNA association, leading to increased microsatellite instability.
• Exogenous PI3P restored MMR function in PI3P-deficient extracts.
• Revealed an autophagy-independent nuclear function for the Beclin-1/Vps34 complex in producing PI3P for MMR.
• Loss of nuclear PI3P impaired DNA damage signaling and conferred drug resistance.

Conclusions:

• Nuclear PI3P acts as a critical lipid mediator that promotes the assembly and DNA association of MMR recognition complexes.
• The Beclin-1/Vps34 complex generates nuclear PI3P through an autophagy-independent mechanism, contributing to genome maintenance.
• This study expands the known functions of nuclear phosphoinositide signaling and identifies a novel regulatory mechanism for MMR crucial for genome stability.