DNA Sequencing of p53 Gene Mutation in Colorectal Carcinomas

ABSTRACT

Mutations in the p53 gene occur during the development of colorectal carcinomas, and play an important role in the conversion of adenoma into carcinoma. To detect the p53 gene mutation and its pattern of expression in colorectal carcinomas, polymerase chain reaction for exons 5, 6, 7, and 8, recombinant gene cloning, and automated DNA sequencing were performed with 30 fresh colorectal carcinomas. Each tissue was also analyzed by immunohistochemical staining for p53 protein. p53 protein was detected in 25 of 30 (83.3%) colorectal carcinomas by immunohistochemical study. p53 mutation was detected in 4 of 30 (13.3%) colorectal carcinomas. The distribution of these mutations among these exons investigated was as follows Three mutations in exon 5 (66.7%) and 1 mutation in exon 7 (33.3%). One case with mutation in exon 5 had mutations at three different codons. Mutations in exon 5 were found at codon 153 (GGG to AGG Gly to Arg), 170 (TGC to GGC Cys to Gly), 186 (CTA to TTA silent mutation), 158 (GCG to ACG Ala to Thr), and 176 (ACG to ATG Thr to Met). Mutation in exon 7 was found at codon 248 (AGG to AGA silent mutation). Four of them were missense mutations. Two of 6 mutations were silent mutations. Five transition mutations and 1 transversion mutation were also detected. All cases with mutations by automated DNA sequencing showed positive p53 protein immunohistochemical stainining. In conclusion, p53 gene mutation was detected in 4 of 30 (13.3%) colorectal carcinomas, located in codon 153, 158, 170, 176, and 186 of exon 5 and codon 248 of exon 7. Further studies are needed to evaluate the significance of the codon 153 mutation which was not recognized in other studies on colorectal carcinomas.