Point mutation in codons 12 and 61 of the ha‐ras gene in rat urinary bladder carcinomas induced by N‐[4‐(5‐nitro‐2‐furyl)‐2‐thiazolyl]formamide

Male F344 rats were fed N‐[4‐(5‐nitro‐2‐furyl)‐2‐thiazolyl]formamide (FANFT) for up to 4 wk, then were given the basal diets (Prolab 3200 or AIN‐76A) with or without 5% sodium saccharin for up to 100 wk. Eleven transitional cell carcinomas (TCCs), one undifferentiated carcinoma, and two sarcomas of the urinary bladder were examined for the expression of ras gene product, p21, by immunohistochemical staining and western blot analysis. Point mutation in codons 12 or 61 of the Ha‐ras genes amplified by polymerase chain reaction was examined by a slot‐blot screening procedure using allele‐specific oligonucleotide probes. Immunohistochemical staining showed enhanced immunoreactivity with the antibody to ras p21 in seven TCCs and one undifferentiated carcinoma. Western blot analysis showed faster migration of the p21 band in 6 of 11 TCCs. Oligonucleotide hybridization revealed the point mutation in codon 12 of Ha‐ras gene (GGA → GTA in 1 TCC) and in codon 61 (CAA → CGA in 5 TCCs and CAA → CTA in 1 TCC). Two mutations in codons 12 and 61 coexisted in one tumor, which were found to be present in different Ha‐ras alleles. The incidence of Ha‐ras gene mutations were similar in groups treated with (3 of 6) or without (3 of 8) sodium saccharin. These results suggest the involvement of activated Ha‐ras gene in rat urinary bladder carcinogenesis induced by FANFT.