Differential genomic destabilisation in human cells with pathogenic MSH2 mutations introduced by genome editing

Area of Science:

• Genetics
• Molecular Biology
• Cancer Research

Background:

• Microsatellite instability (MSI) is linked to human diseases, particularly cancer.
• MSI is often considered a direct indicator of DNA mismatch repair (MMR) deficiency.
• However, discrepancies exist, including varying MSI phenotypes (MSI-H, MSI-L) and distinct alteration modes (Type A, Type B).

Purpose of the Study:

• To investigate the molecular mechanisms underlying repeat destabilization in human cells.
• To clarify the relationship between MMR deficiency and MSI phenotypes, specifically Type A and Type B.
• To model Lynch syndrome-associated MSH2 mutations in a cellular context.

Main Methods:

• Utilized CRISPR/Cas9 gene editing to introduce MSH2 mutations into HeLa cells.
• Assessed MMR-defective phenotypes, including alkylating agent tolerance and mutation frequency.
• Analyzed microsatellite alterations, classifying them as Type A or Type B.

Main Results:

• MSH2-mutated HeLa cells exhibited MMR deficiency, increased mutation rates, and tolerance to alkylating agents.
• Despite MMR deficiency, microsatellites were not significantly destabilized, unlike in MSI-H tumors.
• All observed microsatellite alterations were consistently of the Type A mode.

Conclusions:

• MMR deficiency does not always lead to the drastic microsatellite destabilization (Type B) seen in MSI-H cancers.
• The findings suggest a more complex molecular basis for repeat destabilization than previously assumed.
• Cellular models confirm that specific MMR defects can result in subtle, Type A microsatellite alterations.