Effects of microRNA-18a on hypoxia-inducible factor 1α expression and hypoxia response in MDA-MB-436 cells. (A) Ectopic microRNA-18a (miR-18a) expression decreased hypoxia-inducible factor 1α (HIF1A) protein levels in cells cultured under normoxia or hypoxia (2% O2 for 16 hours). HIF1A protein levels were measured using a cell-based enzyme-linked immunosorbent assay and normalized to cytochrome c. The data are presented as mean ± SD (n = 4). *P < 0.05 by Student’s t-test. GFP, Green fluorescent protein. (B) miR-18a attenuated hypoxic gene expression. Cells were exposed to hypoxia (2% O2 for 16 hours), and mRNA levels were measured by quantitative PCR and normalized to ACTB. Data are presented as mean ± SD (n = 3). (C) Ectopic miR-18a expression reduced viable cell numbers in cells exposed to hypoxia (2% O2 for 72 hours). *P < 0.05 by Student’s t-test. (D) Ectopic miR-18a expression inhibited cell invasion under normoxia and abolished hypoxia-induced cell invasion. The results are presented as mean ± SD (n = 6). *P < 0.05 by Student’s t-test. n, the number of experimental repeats.