Modulation in the expression of murine mammary tumor virus, ras proto-oncogene, and of alveolar hyperplasia by fatty acids in mouse mammary explant cultures.

Hyperplastic alveolar nodule, present in the young adult non-lactating but mammary tumor virus harbouring mice (RIII), are biologically active precursor lesions which form mammary tumors at certain age. Using mammary explant cultures from these mice as a model for preneoplastic hyperplasia, we have examined the effects of various fatty acids on the changes in the cellular and molecular markers in vitro. We find that exposure of cultures to omega-6 fatty acids results in -13 fold increase on RT activity, -3 fold increase in expression of c-ras Hp21, and 2 fold increase in the frequency of lactogenic hormone-independent mammary alveolar lesions, MAL. In contrast, exposure of the cultures to eicosapentanoic or stearic acid results in no increase in RT activity, 3-fold decrease in expression of C-ras Hp21, and about 2-fold decrease in MAL frequency. These results suggest that tumor modulating effects of dietary fatty acids may be operative during the initiational and promotional events of viral carcinogenesis, well before the emergence of mammary tumors.