The identification of genes involved in breast cancer is of critical importance in understanding the pathogenesis of the disease. Expression of the nuclear proto-oncogenes, c-myc, c-jun and c-fos, are indicative of early response events during cellular proliferation. Among them, the c-myc oncogene has been found frequently over-expressed in breast cancer. In vitro systems allow us to test the sensitivity of human breast epithelial cells to different carcinogens, including ionizing radiation. The aim of this work was to define whether these oncogenes play a functional role in radiation-induced transformation of human breast epithelial cells. We examined: a) the spontaneously immortalized MCF-10F cell line, b) clones derived from these cells treated with the carcinogen benzo(a)pyrene (BP) and then transfected with c-Ha-ras-oncogene, followed, c) by a single 3 Gy dose of γ-rays. Protein expressions were analysed by Western immunoblot assays. Results indicated that 3 Gy dose of γ-ray decreased the expression of these oncoproteins in the MCF-10F cells (ranging from 23 to 80%). In BP1, non-tumorigenic MCF-10F cells, radiation induced an even sharper decrease in the oncoprotein levels (ranging from 50 to 100%) relative to their non-irradiated controls. In contrast, in BP1-E tumorigenic cell line radiation increased the expression in 68-80% of c-myc, c-jun and c-fos protein expression relative to non-irradiated control. Furthermore, radiation increased c-my, c-jun and c-fos protein expression in the c-Ha-ras-3 Gy cell line relative to non-irradiated control cell line (ranging from 45 and 120%). Interesting, among the tumorigenic MCF-10F cells previously exposed to both BP and c-Ha-ras (BP1-Tras-3 Gy cell line), radiation increased the c-myc, c-jun, c-fos protein expression by more than 120% relative to the non-irradiated controls. In can be concluded that the MCF-10F model of breast carcinogenesis allows us to examine various aspects of regulations in gene expression and can provide us the basis for understanding the process of breast cancer.

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