The present study was carried out with the purpose of analyzing the additive effect of c-Ha-ras oncogene on tumorigenesis in human breast epithelial cells (HBEC) treated with chemical carcinogens. A human breast epithelial cell (HBEC) line, MCF-10F, previously treated with dimethylbenz(a) anthracene (DMBA) and benzo(a)pyrene (BP) was used in these studies. The MCF-10F cells, DMBA and/or BP-transformed cells originated from the clones D3-1 and BP1 which were transfected with the plasmid pH06T1 containing the human T24 mutated c-Ha-ras oncogene and termed MCF-10F-Tras, D3-1-Tras and BP1-Tras, respectively. Whereas the c-Ha-ras transfected cells presented altered morphology, increased anchorage independent growth in agar-methocel, invasiveness and tumorigenicity, the MCF-10F cells, the clones D3 and BP1 were not tumorigenic. Importantly, whereas MCF-10F-Tras was slightly tumorigenic, the D3-1-Tras and BP1-Tras transfected cells were 100% tumorigenic in the SCID mice; and the tumors thus obtained were poorly differentiated carcinomas. DNA fingerprinting confirmed that the tumors derived originated from the cell lineage used. It was concluded that c-Ha ras induces an additive effect on the expression of tumorigenesis in human breast epithelial cell line MCF-10F treated with chemical carcinogens. Our work provide a model for analyzing the role of c-Ha-ras in human breast cancer.

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