MicroRNA-138 inhibits hypoxia-inducible factor 1α expression in breast cancer cells

Hypoxia, a critical feature during cancer development, leads to the stabilization and activation of the hypoxia-inducible factor 1-alpha (HIF-1α) to drive the expression of many target genes which in turn can promote many aspects of breast cancer biology, mainly metastasis and resistance to therapy. MicroRNAs are known to modulate the expression of many genes involved in breast cancer tumorigenesis. In this study, we examined the regulatory effect of miRNAs on HIF1α expression. MCF-7 and MDA-MB-231 were cultivated under normoxia or hypoxia conditions. TaqMan-Low Density Array (TLDA) was used to characterize the miRNA signatures. Wild-Type (WT) or mutated fragments of HIF-1α 3’UTR containing the miR-138 potential target site were cloned downstream of the Renilla luciferase gene in the psiCHECK-1 plasmid. Luciferase assays were then carried out. A lentiviral vector containing copGFP as a reporter gene was prepared and transduced into MCF-7 and MDA-MB-231 cells to assess the effect of identified deregulated miRNAs on HIF-1α expression. Under hypoxic conditions, MCF-7 cells showed deregulated expression for 12 miRNAs. In the case of MDA-MB-231 cells, 16 miRNAs were deregulated in response to hypoxia. Interestingly, miR-138 that was downregulated in both MCF-7 and MDA-MB-231 cells cultivated under hypoxic conditions appeared to have a binding site in 3’UTR of HIF-1α. Moreover, our results indicated that miR-138 could down regulate HIF-1α expression, upon binding directly to its 3’UTR. Interestingly, our data highlights miR-138 as a potential therapeutic target to reduce HIF-1α expression and subsequently restrain breast cancer invasion and metastasis.