Oxidative stress increases frameshift mutations in human colorectal cancercells

Chronic inflammation in the gastrointestinal tract increases the risk for d evelopment of cancer by an incompletely understood pathway, which may invol ve microsatellite instability (MSI). Low frequency of MSI referred to as "M SI-L" occurs frequently in chronically inflamed nonneoplastic tissue. In th is work, we have tested the hypothesis that oxidative stress may induce the accumulation of frameshift mutations in human microsatellite DNA. Mismatch repair (MMR)-proficient HCT116+chr3 and MMR-deficient HCT116 cells were tr ansfected with pCMV-(CA)(13)-EGFP, a plasmid that contains a (CA)(13) dinuc leotide repeat, which disrupts the reading frame of the downstream enhanced green fluorescent protein gene. A dose-dependent increase in frameshift mu tations restoring the enhanced green fluorescent protein reading frame was detected in HCT116 by flow cytometry. At 1 mm H2O2, the mutant fraction was 9-fold higher than that in mock-treated control cells. Although demonstrat ing stability at lower H2O2 concentrations, MMR-proficient HCT116+chr3 cell s accumulated mutations at the 1 mm H2O2 level (4.1-fold above mock-treated control). No significant mutations were detected when HCT116 cells were tr ansfected with the pCMV-(N)(26)-EGFP construct that contains 26 nucleotides in a random sequence. These data indicate that oxidative stress is a poten tial mutagen leading to accumulation of frameshift mutations and may contri bute to MSI in the setting of chronic inflammation.