Activation of ras oncogenes and expression of tumor‐specific transplantation antigens in methylcholanthrene‐induced murine fibrosarcomas

The DNA of 22 fibrosarcomas, newly induced in BALB/c mice by subcutaneous doses of 3‐methylcholanthrene (3‐MCA), was tested in NIH 3T3 transformation assay. Activation of K‐ras and N‐ras was found in 7 and 3 cases respectively. No H‐ras activation was detected. Polymerase chain reaction and oligonucleotide hybridization performed on the DNA of the 22 sarcomas revealed 5 cases of K‐ras mutation at codon 12, 3 at codon 13 and I at both codons. One case of K13 mutation was not detectable by transfection. Three cases of mutation at codon 61 of N‐ras were also found, one of which was simultaneous with a K12 mutation. Tumor‐specific transplantation antigens (TSTA) were assessed in the 22 original tumors. Altogether 16 sarcomas were immunogenic, with the highest frequency of TSTA tumors (10/11 and 5/6) in the groups given 1.0 and 0.1 mg of 3‐MCA respectively, the lowest (1/5) in that with 0.01 mg of carcinogen; ras mutations occurred in the DNAs of 11 out of the 16 TSTA+ sarcomas, but none of the DNAs of the 6 TSTA‐ tumors showed ras mutation. The results suggest that 3‐MCA‐induced transformation of subcutaneous fibroblasts can involve mutations in codons 12, 13 or 61 of K‐ and N‐ but not H‐ras gene and that such mutation is accompanied by the expression of TSTA.