P53 MUTATIONS IN BLADDER-CARCINOMA CELL-LINES

Point mutations and deletions in the p53 tumor suppressor gene occur f requently in advanced stage bladder tumors. To extend these observatio ns to an in vitro model of bladder tumorigenicity, we have evaluated t he presence of p53 mutations in a panel of bladder carcinoma cell line s. p53 alleles were cloned using the reverse transcriptase-polymerase chain reaction method, and exons 2-11 were sequenced. Of 11 cell lines examined, 5 cell lines had missense point mutations, and each overexp ressed p53 protein on western blot analysis. Except for the HT-1197 ce ll line, these point mutations occurred in evolutionarily conserved do mains, which are characteristic hot spots for mutations. HT-1197 encod es an unusual C-terminal point mutation in codon 365, within the basic motif tetramerization domain, suggesting a linkage between induction of a mutant p53 conformation and alterations in protein oligomerizatio n. Six of 11 cell lines had wildtype levels of p53 expression, with 4 producing p53 proteins having either internal deletions or truncations , and 2 producing wild-type p53. Presence of wild-type p53 was found o nly in cell lines derived from either a low-grade, papillary tumor (RT 4) or fetal bladder (FHs 738Bl). The T24 cell line was found to contai n a novel p53 mutant having an in-frame deletion of tyrosine 126. This p53 mutant does not bind SV40 large T antigen, yet is expressed at lo w levels, comparable to cell lines containing wild-type p53 alleles. O ur findings characterize p53 mutations in a panel of bladder carcinoma cell lines, and provide a model for testing the role of wild-type or mutant p53 cDNA to suppress or induce tumorigenic properties.