Mutation frequencies at codon 248 of the p53 tumour suppressor gene are not increased in colon cancer cell lines with the RER+ phenotype.

The replication-error positive (RER+) phenotype characterizes tumour cells with microsatellite instability. This 'mutator phenotype' is thought to induce spread mutations throughout the genome, thus increasing the risk of tumour development. Here we analyse spontaneously arising mutations at the tetranucleotide CCGG ( Msp I recognition site), at positions 14 067-14 070 of the p53 gene sequence, in three colon cancer cell lines, two with microsatellite instability and one without this characteristic. This restriction site covers hot-spot codon 248, which is often mutated in colon carcinomas. Using the Msp I RFLP-PCR assay we found that the mean mutation frequency at this site was not different among the cell lines considered. Taking the substitutions separately, none of the mutations involving codon 248 arose with significantly higher frequency in each of the RER+ cell lines (HCT116 and DLD1) compared with the RER-one (SW480). Only the CG transversion at nt 14 067 (codon 247) occurred with a slightly higher, but biologically insignificant, frequency in one of the RER+ cell lines (HCT116). Our in vitro data support the previously reported lack of correlation between microsatellite instability and p53 mutations in RER+ tumour specimens.