Abstract 5364: Zeranol Down-regulates p53 Expression in Primary Cultured Human Breast Cancer Epithelial Cells through Epigenetic Modification

Despite great improvements in diagnosis, treatment advances, and healthier life-styles, breast cancer remains the most common cancer among women in the United States. It is estimated that 192,370 new cases arise and 40,170 women will die from breast cancer in 2009. Epidemiological studies have suggested that there are many risk factors associated with breast cancer such as dietary fat and environmental estrogenic endocrine disruptors. Zeranol (Z), as one of the six growth promoters approved by FDA, has been widely used to enhance the growth of beef cattle. Researchers are still in disagreement whether the growth promoters pose any adverse health risk from consuming beef products produced from Z-implanted beef cattle. Our previous results showed that pre-adipocytes isolated from the cattle 60 days post Z-implantation (72 mg/pellet/animal) grow about 12 fold faster than the pre-adipocytes isolated from the control cattle. Treatment with 0.2, 1 and 5% sera (Z-Sera) harvested from the cattle 30 days post implantation in culture medium significantly stimulated MCF-10A, a human normal breast epithelial cells, and MCF-7 cell growth. Proliferation might be caused by Z-Sera down-regulating the expression of a tumor suppressor gene, protein tyrosine phosphatase γ (PTP γ). The current study investigated the effects of Z on primary cultured human normal and cancerous breast epithelial cell growth (PCHNBECs, PCHBCECs), and the regulation of p53 expression, as well as the potential mechanism. Using non-radioactive cell proliferation assay, real time PCR and western blot analysis, we demonstrated that PCHBCECs are more sensitive in response to treatment with Z than PCHNBECs. Treatment with 7.5, 15 and 30 nM Z increased the growth of PCHNBECs at 27, 45, 50%, respectively, as compared to the control group. The same concentrations enhanced the proliferation of PCHBCECs at 25, 84 and 91%. The expression of p53 protein in PCHNBECs did not decrease by the treatment of Z. However, in PCHBCECs, treatment with 7.5, 15 and 30 nM Z significantly down-regulated the expression of p53 protein by 10, 20 and 40%, respectively. Further investigation suggests that the effect of Z on decreasing the expression of p53 in PCHBCECs might be mediated through its epigenetic modification. Our results showed that Z treatment up-regulates the expression of DNMT1 mRNA by 36, 58 and 160%, and protein by 14, 25 and 42% in PCHBCECs after 24 hour exposure. Our data suggest that the stimulatory effect of Z on PCHBCECs growth might be via down-regulation of p53 expression as a result of epigenetic modification mediated through Z enhancing the expression of DNMT1 mRNA and protein levels. These results imply the potential adverse health risks of the consumption of beef products with Z or its bio-active metabolites. Further investigation on this critical issue is in-progress in our laboratory (Supported by NIH grant R01 ES015212-01). Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 5364.