Explosive mutation accumulation triggered by heterozygous human Pol ε proofreading-deficiency is driven by...

Area of Science:

• Genetics
• Molecular Biology
• Cancer Research

Background:

• Tumors with defective DNA polymerase (Pol) ε proofreading exhibit the highest tumor mutation burdens.
• It remains unclear if Pol ε proofreading deficiency alone drives this extensive mutagenesis or requires additional factors.

Purpose of the Study:

• To investigate whether impaired Pol ε proofreading activity is sufficient to cause significant mutagenesis.
• To determine the role of mismatch repair in conjunction with Pol ε proofreading defects in driving tumor mutation burden.

Main Methods:

• Utilized next-generation sequencing and in vitro biochemistry on engineered human cell lines.
• Created cell lines with specific defects in Pol ε proofreading and mismatch repair pathways.

Main Results:

• Monoallelic Pol ε proofreading deficiency rapidly induced a distinct mutation signature when mismatch repair was absent.
• This unique mutation signature resembled that found in tumors with biallelic mismatch repair deficiency and heterozygous Pol ε mutations.
• Reinstating mismatch repair effectively suppressed the rapid accumulation of mutations.

Conclusions:

• Concomitant suppression of mismatch repair is a critical factor driving the explosive mutagenesis observed in tumors with exonuclease-deficient Pol ε.
• This finding highlights the importance of mismatch repair in preventing high tumor mutation burdens, particularly in cancers like colorectal cancer.