Effects Of Selenium And Cadmium On The Estrogen Receptor And Epigenetics Of Breast Cancer Cells

ObjectiveCadmium（Cd）is an important productive toxicant,which was listed at IARC（International Agency for Research on Cancer）as Type 1carcinogen in 1993.In recent years,research has shown that Cd was now thought to increase breast cancer risk.However,its mechanism has not meant to explain.Selenium（Se）is an indispensable trace element in the human body,which has the function of anticancer.Moreover,selenium has antagonistic or inhibitory effect on the cytotoxicity of cadmium.In this present study,technology of flow cytometry,western blot,immunofluorescence and qRT-PCR were utilized to explore roles of selenium in the estrogen receptor and epigenetics of breast cancer induced by cadmium in vitro.AIM To provide the experimental evidences for explaining the mechanism of Cd-induced breast cancer and the anticancer effect of selenium.MethodSection one:MCF-7 cells（estrogen receptor positive）and MCF-10A cells（estrogen receptor negative）were cultured in vitro.MCF-7 cells were treated with different concentrations of cadmium chloride（CdCl₂）at the doses of 2.5,5.0,10.0μmol/L for 24h;ICI（Fulvestrant）pretreatment groups:1.0μmol/L ICI pretreatment for 12h,then treated with different concentrations of CdCl₂（2.5,5.0,10.0μmol/L）for 24h;and the control group treated with nothing but cell supernatant.MCF-10A cells had the same treatment as MCF-7 cells except no ICI pretreatment groups.Section two:MCF-7 cells and MCF-10A cells were cultured in vitro.Sodium selenite（Na₂SeO₃）pretreatment groups:0.1μmol/L sodium selenite pretreatment for 12h,then treated with different concentrations of CdCl₂（2.5,5.0,10.0μmol/L）for 24h;The cell proliferation activity were measured by MTT assay,the flow cytometry was used to measured apoptosis,the western blot was applied to measure the relative translation level of estrogen receptor protein（ERαand ERβ）,the DNA methylation levels were qualitatively detected by5-methylcytosine immunofluorescence.And the expression levels of miRNA-155 and miRNA-200c were detected by real-time fluorescence quantitative PCR.Results（1）The cell proliferation activity of MCF-7 cells and MCF-10A was decreased after the treatment of cadmium（P<0.05）,and the apoptosis rate of MCF-7 cells and MCF-10A was increased after the treatment of cadmium（P<0.05）,The cell cycle was disrupted at a certain dose（P<0.05）.And sodium selenite could be antagonistic to the cell proliferation inhibition and apoptosis induced by cadmium（P<0.05）.（2）The expression of estrogen receptor protein（ERαand ERβ）was significantly increased after the treatment of cadmium（P<0.05）.And the expression of estrogen receptor protein（ERαand ERβ）of the sodium selenite pretreatment groups was significantly decreased compared with the CdCl₂ groups in the same dose（P<0.05）.（3）There was no significant change in the level of DNA methylation in MCF-7 cells,but the level of DNA methylation in MCF-10A cells was significantly decreased after the treatment of cadmium（P<0.05）.after pretreated with sodium selenite,the level of DNA methylation in MCF-7cells were significantly decreased compared with the CdCl₂ groups in the same dose（P<0.05）,and significantly increased in MCF-10A cells compared with the CdCl₂ groups in the same dose（P<0.05）.（4）The expression of miRNA-155 and miRNA-200c of cadmium groups of MCF-7cells were significantly increased compared with the control group（P<0.05）;after pretreated with sodium selenite,the expression of miRNA-155 and miRNA-200c were significantly decreased compared with the CdCl₂ groups in the same dose（P<0.05）.Cadmium could induce upregulation of miRNA-155 and downregulation of miRNA-200c of MCF-10A cells;after pretreated with sodium selenite,the expression of miRNA-155 and miRNA-200c were significantly decreased compared with the CdCl₂ groups in the same dose（P<0.05）.Conclusions（1）Cadmium could inhibit cell proliferation,infuce apoptosis and interfere with cell cycle progression.Selenium could be antagonistic to the above toxicological effects induced by cadmium,and has inhibitory effect on the cytotoxicity of cadmium.（2）Cadmium has the estrogen-like effect,which significantly increased the expression of ERαand ERβ,and selenium has certain antagonistic effect to the estrogenic effect of cadmium.（3）Cadmium can affect the level of DNA methylation of mammary gland cells,which is very important to the stability of DNA,and the high expression of miRNA-155 and down-regulation of miRNA-200c induced by cadmium is vital to the development of breast cancer.Selenium can antagonize the abnormal cell methylation and miRNA expression.Which implied that selenium can be antagonistic to the carcinogenic effect induced by cadmium through epigenetic mechanism.