HIF-2α regulates CD44 to promote cancer stem cell activation in triple-negative breast cancer via PI3K/AKT/mTOR signaling

Figure 1 Expression of hypoxia-inducible factor-2α and CD44 in carcinoma tissues of triple-negative breast cancer and non-triple-negative breast cancer patients (×200). TNBC: Triple-negative breast cancer; HIF-2α: Hypoxia-inducible factor-2α.

Figure 2 Expression of hypoxia-inducible factor-2α and CD44 in MCF-7 and MDA-MB-231 cells (×200). The expression of HIF-2α and CD44 in MDA-MB-231 cells was significantly higher than that in MCF-7 cells. HIF-2α: Hypoxia-inducible factor-2α; DAPI : 4',6-diamidino-2-phenylindole.

Figure 3 Expression of HIF-2α and CD44 mRNAs in human breast cancer cells after transfection. ^aP < 0.05 vs normoxia; ^bP < 0.05 vs hypoxia + NC. HIF-2α: Hypoxia-inducible factor-2α; NC: Negative-sequence control.

Figure 4 HIF-2α silencing reduces the CD44⁺/CD24⁻ population in MDA-MB-231 cells. Flow cytometry of the stem cell-associated cell surface markers CD44 and CD24 in hypoxia and HIF-2α-siRNA treated cells. HIF-2α: Hypoxia-inducible factor-2α.

Figure 5 TUNEL assay of hypoxia-induced MDA-MB-231 cells after transfection (×200). Light green cells are TUNEL-positive staining cells. ^aP < 0.05 vs normoxia; ^bP < 0.01 vs hypoxia + NC. DAPI: 4',6-diamidino-2-phenylindole; NC: Negative-sequence control.

Figure 6 Quantification of mammosphere formation assay of MDA-MB-231 cells before and after transfection. Cells were cultured for 7-21 d under mammosphere culture conditions. ^bP < 0.01 vs hypoxia + NC. NC: Negative-sequence control.

Figure 7 Effect of HIF-2α on the PI3K/AKT signaling pathway. In MDA-MB-231 cells induced by hypoxia, HIF-2α knockdown reduced the AKT and mTOR phosphorylation levels; ^aP < 0.05 vs normoxia; ^bP < 0.05 vs hypoxia + NC. PI3K: Phosphoinosmde-3-kinase; AKT: Protein-serine-threonine kinase; mTOR: Mammalian target of rapamycin; p-AKT: Phosphorylated AKT; p-mTOR: Phosphorylated mTOR; NC: Negative-sequence control.