p53 Mutations in bladder carcinoma cell lines

Point mutations and deletions in the p53 tumor suppressor gene occur frequently in advanced stage bladder tumors. To extend these observations to an in vitro model of bladder tumorigenicity, we have evaluated the presence of p53 mutations in a panel of bladder carcinoma cell lines. 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 overexpressed p53 protein on western blot analysis. Except for the HT-1197 cell line, these point mutations occurred in evolutionarily conserved domains, which are characteristic hot spots for mutations. HT-1197 encodes an unusual C-terminal point mutation in codon 365, within the basic motif tetramerization domain, suggesting a linkage between induction of a mutant p53 confirmation and alterations in protein oligomerization. Six of 11 cell lines had wild-type 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 only in cell lines derived from either a low-grade, papillary tumor (RT4) or fetal bladder (FHs 738BI). The T24 cell line was found to contain 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 low levels, comparable to cell lines containing wild-type p53 alleles. Our 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.