Objective   This work aims to explore the effect of silencing hypoxia-inducible factor(HIF)-2α expression on the enrichment of breast cancer stem cell(BCSC) microspheres under hypoxia.

  Methods   A lentiviral vector of the RNA interference(RNAi) of human HIF-2 α gene was constructed and transfected into Michigan Cancer Foundation(MCF)-7 cells.The mRNAand protein expressions of HIF-2α were determined using real time-polymerase chain reaction(RT-PCR) and Western blot, respectively.The proliferation activity of the MCF-7 cells under different oxygen concentrations was measured using the methyl thiazolyl tetrazolium assay.The formation of the BCSC microspheres under hypoxia was observed by a fluorescence microscope.The monoclonal formation ability of the microsphere cells was detected by limiting dilution assay.The mRNA expressions of the BCSC markers, ABCG, CD44, and OCT-4, were tested by RT-PCR.

  Results   The siRNA expression vector targeting the HIF-2α gene was successfully constructed.Both the HIF-2a mRNA and protein levels noticeably decreased in the MCF-7 cells transfected with the RNAi expression vector(P < 0.05).Compared with the groups with empty vectors or those that were not transfected, the proliferation activity of MCF-7 cells and the monoclonal formation ability of BCSCs in the RNAi group were markedly inhibited after silencing the HIF-2α gene(P < 0.05).RT-PCR results showed that the mRNA expressions of BCSC markers ABCG2, CD44, and OCT-4 in cells from the RNAi group decreased significantly under hypoxia(P < 0.05).

  Conclusion   Hypoxia induced and enhanced cancer stem cell-like characteristics in MCF-7 cells.HIF-2α silencing leads to the decreased enrichment of BCSC microspheres under hypoxia.HIF-2 α may be a new candidate gene for BCSC-targeting therapy.