RÉSUMÉ
<p><b>OBJECTIVE</b>To investigate the expression of ER alpha in chemically induced, ER alpha-negative human breast cancer MDA-MB-435 cells and its restoration of the responsiveness to endocrine therapy.</p><p><b>METHODS</b>MDA-MB-435 cells were treated with HDAC inhibitor trichostatin A(TSA)and DNMT1 inhibitor 5-AZA-CdR (AZA). The mRNA level of ER alpha, PR and PS2 in treated MDA-MB-435 cells was detected by RT-PCR. The WST-8 (water-soluble tetrazolium salt-8) method was used to analyze the proliferation rate of the cells. Xenograft in female nude mice was used to further explore the change of proliferation rate of treated MDA-MB-435 cells in vivo.</p><p><b>RESULTS</b>After treatment with AZA and TSA, mRNA expression of ER alpha, PR and pS2 was up-regulated in MDA-MB-435 cells. The mRNA level of ER alpha was the hightest when MDA-MB-435 cells were treated with 2.5 micromol/L AZA and 100 ng/ml TSA. The treated MDA-MB-435 cells showed different proliferation rate in various media containing different concentration of estrodial. The MDA-MB-435 cells showed down-regulated proliferation rate after treatment with the combination of 2.5 micromol/L AZA and 100 ng/ml TSA, and 4-OH tamoxifen could suppress the growth rate of the induced MD-MBA-435 cells but not the untreated cells. The treated MDA-MB-435 cells showed slower proliferation rate than that of untreated cells in vivo (P <0. 01), and the proliferation rate of the treated MDA-MB-435 cells became lower when the nude mice were deprived of estrogen by castration (P <0. 01).</p><p><b>CONCLUSION</b>After treatment with TSA and AZA, ER alpha-negative MDA-MB-435 cells can express functional ER alpha and regain responsiveness to estrogen both in vitro and in vivo. HDAC inhibitor and DNMT1 inhibitor may play an important role in restoration of sensitivity of ER alpha-negative breast cancers to endocrine therapy.</p>