Efficient screening of p53 mutations by denaturing gradient gel electrophoresis in colorectal tumors

Alterations in exons 5-8 of the p53 gene have been found in the vast majority of human tumors. Although some specific codons have been revealed as preferential mutational sites in defined tumor types, mutations are generally so scattered within this region that various screening methods for their detection have been widely used. However, the capacity of these techniques to detect exhaustively all mutations has not been evaluated. In this report, conditions for analysing exons 5-8 of the p53 gene by denaturing gradient gel electrophoresis (DGGE) have been elaborated using the Melt87 and SQHTX computer programs. The procedure requires five different amplifications. The screening of 90 colorectal tumors revealed 56 amplification products demonstrating abnormal DGGE behavior. Direct sequencing of these amplification products after asymmetric polymerase chain reaction (PCR) showed, besides polymorphism, 49 somatically mutated DNA samples (54.4%) corresponding to 38 different p53 variants. Moreover, 25 additional p53 variants identified in other tumor types were also detectable with our conditions. Thus, altogether the procedure has been successfully used in the detection of 63 different p53 variants. The experimental differences in migration between the wild-type homoduplex DNA molecule and the heteroduplex(es) containing one mismatch were systematically compared with those calculated by the SQHTX program. The computer program was found to be reliably predictive. This DGGE procedure appears thus to be effective and reliable for detecting mutations in exons 5-8 of the p53 gene.