P53 MUTATIONS AND DNA-PLOIDY IN COLORECTAL ADENOCARCINOMAS

The p53 tumour suppressor gene has an important role in the the mainte nance of genome stability and its mutational inactivation may be at th e origin of aneuploidy in cancer cells. The aim of this study was to d etermine whether p53 mutations were associated to DNA aneuploidy, as a ssessed by flow cytometry, in colorectal adenocarcinomas. Analysis of p53 mutations spectrum of the sorted nuclei was done by Denaturing Gra dient Gel Electrophoresis (DGGE) and DNA sequencing Overall, we studie d 20 adenocarcinomas, the corresponding control mucosa, and 7 lymph no de metastases. Five tumours (25%) were DNA diploid, while 15 tumours ( 75%) were composed of DNA aneuploid and diploid subpopulations. DNA di ploid control mucosa and adenocarcinomas showed no p53 mutations, whil e 60% of the tumours with DNA aneuploidy had p53 mutations. Therefore, p53 mutations occurred significantly more often in DNA aneuploid than in DNA diploid tumours (p < 0.04, Fisher's exact test). Incidences of DNA aneuploidy and p53 mutations in lymph node metastases were 60 and 86%, respectively. In all tumours showing a p53 mutation, the wild-ty pe allele was not or only bearly visible in DNA aneuploid cells sugges ting that, in such cells, aneuploidy is accompanied by complete p53 fu nctional inactivation. The present observations suggest that p53 mutat ions may have a role in the origin of aneuploidy at late stages of col orectal carcinogenesis.