Genetic alterations of the c-myc, c-neu and int-2 oncogenes have been reported in human breast cancer. In order to determine if these oncogenes are activated at different stages of breast cancer progression, we are using an in vitro system in which human breast epithelial cells (MCF-10F) have been transformed with benzo(a)pyrene(BP) or dimethylbenz(a)anthracene (DMBA). DMBA-treated cells gave rise to clones D3 and D3-1, BP-treated cells gave rise to clones BP1 and BP1-E. BP1-E cell line, derived from BP1 cell line, was tumorigenic in SCID mice. Southern blot analysis detected gene amplification and rearrangement of the int-2 oncogene in BP1 and BP1-E cells, but no changes were detected in D3 and D3-1 cells. Amplification of c-neu gene was only observed in BP1 and BP1-E cell lines. Neither amplification nor rearrangement was detected for the c-myc gene. At the transcriptional level, Northern blot analysis showed that int-2 mRNA was increased 1.5, 1.8, 1.3 and 2.0-fold in the BP1, BP1-E, D3 and D3-1 cell lines respectively. c-neu mRNA was increased 8.0-fold in BP1 and BP-1E cells and c-myc mRNA was increased 1.5-fold in D3 cells, but no changes were detected in the other cell lines. The data indicate that BP treatment induces changes both at the genomic and transcriptional level. However, none of the differences explain the tumorigenic properties of the BP1-E cell line. DMBA treatment induces changes that are only reflected at transcriptional level for the two oncogenes studied. Whereas none of these oncogenes can be considered the driving force in the expression of the tumorigenic phenotype, the interaction among them or with other oncogenes in the expression of the transformation phenotype cannot be ruled out.

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