Detection of p53 protein overexpression and DNA ploidy analysis in colon cancer

This study was designed to demonstrate the accumulation of the mutant p53 protein in human neoplasms. The correlation of flow cytometric DNA ploidy pattern with p53 expression using the immunoblotting technique was also investigated.

In this study, the occurrence of p53 overexpression was analyzed in 34 cases of adenocarcinoma of the colon by western immunoblotting technique, using an anti-human p53 monoclonal antibody (Do-7). The nuclear protein extract from human colon tumor specimens was immunoblotted relative to protein standards of known molecular weight. Flow cytometric analysis was used to study the DNA ploidy pattern of the tumor cells.

Monoclonal antibody p53-Do 7 detected a single band of 53 KDa in 70.5% (24 of 34) of the tumor specimens examined. Whereas, no bands were detected in the normal colon mucosa. The relation between p53 overexpression and the clinicopathological variable (Dukes' staging) was studied and no significant difference in p53 overexpression between Dukes' stages B and C was found. Flow cytometric analysis revealed a higher incidence of DNA aneuploidy in 75% (15 of 20) of p53 positive cases compared with 64.3% (9 of 14) in the diploid tumors.

The immunoblotting technique can successfully detect the mutant p53 and is therefore expected to provide valuable information on the role of p53 in the process of carcinogenesis.