LOH and mutational analysis of p53 alleles in mouse urinary bladder carcinomas induced by N-butyl-N-(4-hydroxybutyl) nitrosamine

In human urinary bladder carcinogenesis, alterations in the p53 tumor suppr essor gene are common events. We have previously reported that they are als o frequent in invasive urinary bladder carcinomas induced by N-butyl-N-(4-h ydroxybutyl)nitrosamine (BBN) in NON/Shi mice. To further investigate the s ignificance of the p53 gene status for mouse urinary bladder carcinogenesis , we examined both allele loss and mutational alterations in urinary bladde r cancers of (NON/Shi x C3H/He/Shi) F1 hybrid mice exposed to the carcinoge n for 12 weeks and then maintained for a further 9 weeks without treatment. An intragenic silent polymorphism within exon 7 of the p53 gene between NO N/Shi and C3H/He/Shi mice allows assessment of allele loss of the p53 gene and determination of the parental origin of mutated and/or lost alleles, A tissue microdissection method was employed to obtain carcinoma samples with out excessive contamination with normal tissue. Allele losses were detected in one of 14 tumors (7.1%) and nine mutations in eight of 14 (57 %) tumors were found in exons 5-8 by polymerase chain reaction-single strand conform ation polymorphism followed by DNA direct sequencing analysis. All mutation s involved one base substitution with an amino acid change, although the ty pes of base substitution were random. In conclusion, the high incidence of p53 alterations suggests a significant role in the genesis of invasive urin ary bladder tumors in BBN-treated mice.