Ectopic microRNA-18a expression diminished hypoxia induced tumorigenic activity of MCF7 cells. (A) MicroRNA-18a (miR-18a) expression in MCF7 cells reduced hypoxia-inducible factor 1α (HIF1A) protein expression as measured using a cell-based enzyme-linked immunosorbent assay. GFP, Green fluorescent protein. *P < 0.05 by Student’s t-test. (B) miR-18a expression dampened hypoxia-induced gene expression in MCF7 cells. Gene mRNA levels were determined by quantitative PCR and normalized to ACTB. (C) Exposure to hypoxia (2% O2 for 4 weeks) prior to inoculation increased tumorigenic activity of MCF7 cells. The hypoxia-induced tumorigenic activity was abolished by ectopic miR-18a expression.