Abstract
Tumors and virus-related antigens induced by 3-methyl-cholanthrene (MCA) were observed in 16 genotypically different strains of mice having differing natural expressions of C-type RNA tumor virus genomes. The MCA-induced tumors, which were nearly all subcutaneous sarcomas of mesenchymal origin, contained complement-fixing antigens reactive with rat antisera selected for high-titered reactions to the group-specific (gs) antigens of the C-type RNA tumor virus. Since normal mesenchymal tissues (muscle and subcutaneous) did not reveal gs antigenm the concurrent activation, or derepression of phenotypic expression of viral or viral-related antigens in many of the tumors, suggests that oncogenes of C-type RNA virus genomes have served as specific determinants of the induced cancers. Because other studies showed that the virogenes and oncogenes of the C-type RNA viral genome are vertically transmitted as repressed genomes, probably as a part of natural gene inheritance, we hypothesize that the carcinogenic action of MCA is achieved by directly or indirectly derepressing the endogenous RNA tumor virus oncogenes that must be in all mouse cells. Since endogenous C-type RNA viruses were also demonstrated in hamsters, rats, cats, and chickens, we suggest our hypothesis should apply to induced carcinogenesis in other vertebrates as well.
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