WRN helicase and mismatch repair complexes independently and synergistically disrupt cruciform DNA structures

Area of Science:

• Genetics
• Molecular Biology
• Cancer Research

Background:

• Microsatellite instability (MSI) leads to expanded TA repeats, forming cruciform DNA structures.
• These structures cause DNA breaks and cell death when Werner Syndrome helicase (WRN) is downregulated.
• WRN is a potential therapeutic target in MSI cancers.

Purpose of the Study:

• To investigate the role of WRN in processing cruciform DNA structures.
• To explore the interaction between WRN and DNA mismatch repair (MMR) proteins in maintaining genome stability.
• To provide a mechanistic basis for the synthetic-lethal interaction between WRN and MMR defects in MSI cancers.

Main Methods:

• Biochemical assays were used to study the interaction between WRN and cruciform DNA.
• The effect of WRN and MMR proteins (MutSα, MutSβ, MutLα) on cruciform structures was analyzed.
• In vitro cruciform processing was assessed for WRN and MutLα, both individually and in combination.

Main Results:

• WRN helicase efficiently unfolds cruciform DNA structures, preventing their cleavage by SLX1-SLX4 endonuclease.
• TA repeats are prone to cruciform formation, explaining their preferential breakage in MSI cells upon WRN downregulation.
• MMR complexes also reduce cruciform levels via a different mechanism; WRN and MutLα show synergistic effects.

Conclusions:

• WRN directly resolves cruciform DNA structures, a key mechanism in preventing genome instability in MSI cancers.
• WRN and MMR proteins cooperate in processing cruciforms, explaining genome instability in MSI cells with expanded TA repeats.
• These findings support the synthetic-lethal interaction of WRN and MMR defects, with implications for precision cancer therapy.