Expression of microRNA-122 in human breast cancer tissue and the influence on tamoxifen resistance of human breast cancer cells cultured in vitro

Wang Peng; Li Kaimin; Feng Ruigang

doi:10.3760/j.issn.1673-4777.2020.01.016

Abstract：Objective To investigate the expression ofmicroRNA-122(miR-122) in human breast cancer tissue and its effect on tamoxifen(Tam) resistance of human breast cancer cells cultured in vitro.Methods Tumor tissue and adjacent normal tissue were separated from 56 patients with Luminal breast cancer who had mastectomy in the Second Central Hospital of Baoding City,Hebei Province from January to June 2015.Real-time fluorescence quantitative polymerase chain reaction(qPCR) was used to detect miR-122 expression.All patients took Tam for 3 years;Tam-resistance was determined according to the Response Evaluation Criteria in Solid Tumors.Breast cancer cell line MCF-7 was cultured in vitro and Tam-resistance was initiated by stepwise revulsion with Tam.Tam-resistance cell line MCF-7TamR was transfected by miR-122 inhibitor(inhibitor group).Cell proliferation was detected by methyl thiazolyl tetrazolium(MTT) assay.Estrogen receptor-α(ER-α),human epithelial growth factor receptor-2(HER-2),mitogen-activated protein kinase 3 (MAPK3) mRNA expressions were detected by qPCR.ER-α,HER-2,extracellular signal-regulated kinase/mitogen-activated protein kinase(ERK/MAPK) and phosphoERK/MARK (p-ERK/MAPK) expressions were detected by western blotting.Results Expression level of miR-122 in tumor tissue was higher than that in normal tissue [(0.70 ± 0.38) vs (0.24 ± 0.10)];expression level of miR-122 in 11 patients with Tam-resistance was higher than that in 45 patients with Tam-sensitivity [(0.89 ± 0.13) vs (0.67 ± 0.15)] (both P ＜ 0.001).Proliferation inhibition rates induced by 0.1,0.5,2.5,12.5,62.5 and 312.5 μmol/L Tam of MCF-7TamR cells were significantly lower than those of MCF-7 cells(all P ＜ 0.05);Tam-resistance index was 4.97.Expression level of miR-122 in MCF-7TamR cells in inhibitor group was (0.14 ± 0.04),which was significantly lower than that in blank control group[CTL group:(0.67 ± 0.09)] and null transfection group [NC group:(0.65 ± 0.08)] (both P ＜ 0.05).Proliferation inhibition rates induced by different concentrations of Tam of MCF-7TamR cells in inhibitor group were significantly higher than those in CTL group and NC group(all P ＜ 0.001).qPCR showed that ER-α mRNA expression in inhibitor group(1.02 ± 0.17) was higher and HER-2 and MAPK3 mRNA expressions [(0.37 ± 0.09),(0.25 ± 0.07)] were lower than those in CTL group and NC group (all P ＜ 0.05).Western blotting showed that ER-α expression (0.91 ± 0.18) was higher and HER-2 and p-ERK/MAPK expressions [(0.24 ± 0.09),(1.15 ± 0.26)] were lower than those in CTL group and NC group (all P ＜ 0.05).Conclusions Expression of miR-122 increases in breast cancer tissue.Down-regulation of miR-122 can reverse the resistance of breast cancer cells MCF-7TamR to tamoxifen and inhibit cell proliferation,which may be related to blocking ERK/MAPK signaling pathway and increasing ER sensitivity.