Zeranol Down-Regulates p53 Expression in Primary Cultured Human Breast Cancer Epithelial Cells through Epigenetic Modification

Abstract

Epidemiological studies have suggested that there are many risk factors associated with breast cancer. Silencing tumor suppressor genes through epigenetic alterations play critical roles in breast cancer initiation, promotion and progression. As a growth promoter, Zeranol (Z) has been approved by the FDA and is widely used to enhance the growth of beef cattle in the United States. However, the safety of Z use as a growth promoter is still under debate. In order to provide more evidence to clarify this critical health issue, the current study investigated the effect of Z on the proliferation of primary cultured human normal and cancerous breast epithelial cells (PCHNBECs and PCHBCECs, respectively) isolated from the same patient using MTS assay, RT-PCR and Western blot analysis. We also conducted an investigation regarding the mechanisms that might be involved. Our results show that Z is more potent to stimulate PCHBCEC growth than PCHNBEC growth. The stimulatory effects of Z on PCHBCECs and PCHBCECs may be mediated by its down-regulating expression of the tumor suppressor gene p53 at the mRNA and protein levels. Further investigation showed that the expression of DNA methylatransferase 1 mRNA and protein levels is up-regulated by treatment with Z in PCHBCECs as compared to PCHNBECs, which suggests a role of Z in epigenetic modification involved in the regulation of p53 gene expression in PCHBCECs. Our experimental results imply the potentially adverse health effect of Z in breast cancer development. Further study is continuing in our laboratory.

Hormone Use in Food Animal Production: Assessing Potential Dietary Exposures and Breast Cancer Risk

“…This report is consistent with an emerging scientific consensus on the importance of low-dose effects distinct from overt cytotoxicity at higher doses [3]. Another study found that zeranol increased the proliferation of cancerous human breast epithelial cells to a greater degree than normal cells and down-regulated expression of the tumor suppressor gene p53 [42]. Ex vivo studies of cells isolated from the tissues of rats and beef heifers implanted with zeranol have found that further exposure to zeranol in vitro increases cell proliferation, upregulates oncogenes (e.g., cyclin D1), and/or downregulates tumor suppressor genes (e.g., p53) relative to cells from tissues of untreated animals [43,44].…”

Magnetite Nanoparticles Inhibit Tumor Growth and Upregulate the Expression of P53/P16 in Ehrlich Solid Carcinoma Bearing Mice

“…They are frequently mutated and altered in most human cancers including breast cancer [15]–[17], [38], [39]. Normal breast epithelial cells induce p53-dependent apoptosis.…”

“…The possible explanation for the similar changes observed in p53 and p16 that both are tumor suppressor genes involved in many important physiological processes such as cell cycle arrest, gene transcription, DNA repair and apoptosis. They are frequently mutated and altered in most human cancers including breast cancer [15] – [17] , [38] , [39] . Normal breast epithelial cells induce p53-dependent apoptosis.…”

“…p16 contains an alternate open reading frame (ARF) that specifies a protein functions as a stabilizer of p53, as it can interact with and sequester Mouse double minute 2 homolog (MDM2) protein that cause degradation of p53 [16] . The expression level of p53 and p16 is down-regulated in different types of cancer [17] , [18] . In addition, p16 and p53 deficiency cooperate in tumorgenesis [18] .…”

State of the evidence 2017: an update on the connection between breast cancer and the environment

“…And in normal MCF-7 human ER+ cell line, addition of the growth promoter, zeranol, led to stimulatory effects on cell growth. These results were driven, at least in part, by down-regulation of the tumor suppressor gene p53, a process that was accompanied by up-regulation of DNA-methyltransferase 1 [ 84 ].…”