SELECTIVE DETECTION OF INACTIVATING MUTATIONS OF THE TUMOR SUPPRESSOR GENE p53 IN BLADDER TUMORS

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Abstract
Mutations in the p53 gene are implicated in the pathogenesis of half of all human tumors. In bladder tumors they are usually detected by immunohistochemistry. The assumption underlying protein analysis is that high level p53 expression is a consequence of mutations, but numerous exceptions have been reported. We describe the detection of p53 mutations in bladder cancer using a functional assay in yeast. The prospective study consisted of 60 consecutive patients with bladder tumors (7 pT0, 2 CIS, 23 pTa, 24 pT1 and 4 pT2). High grade 3 was observed in primary carcinoma in situ, in 75% of pT1 tumors and in all pT2 tumors. The p53 mRNA extracted from endoscopic resection tissue was reverse transcribed and PCR-amplified. The transcriptional competence of the p53 cDNA was then tested in a yeast reporter strain. A simple functional assay was developed for p53 mutation in which human p53 is expressed in Saccharomyces cerevisiae which activates transcription of the ADE2 gene. Colonies containing wild type p53 are white and colonies containing mutant p53 are red. As this assay evaluates the critical biological function of p53, it can distinguish inactivating mutations from functionally silent mutations. In pTo and pTa bladder tumors, no p53 mutations were detected. In contrast, the functional assay permitted us to detect p53 mutations in 66% of patients with stage T1 tumors (72% in case of high grade 3) and in all cases with primary carcinoma in situ and in 4 cases of stage T2 tumors. This preliminary study demonstrates that this functional assay method is a simple and efficient procedure to detect p53 mutations in bladder cancers and suggests that p53 mutations seem to be associated with invasive bladder tumors.