Emerging roles of microRNAs in the molecular responses to hypoxia

Recent studies have established that the regulation of microRNAs (miRs) is a feature of the hypoxic response. In this review, we discuss the role of hypoxia-regulated miRs, with an emphasis on miR-210 and miR-373, and anticipate directions for clinical applications. The induction of miR-210 and miR-373 is dependent upon hypoxia inducible factor (HIF), and their up-regulation has been detected in a variety of solid tumors. Both miRs have been associated with adverse prognosis and metastatic potential. The increased expression of miR-210 is linked to an in vivo hypoxic signature. MiR-210 also participates in endothelial and neuronal cells' response to oxygen deprivation and may possess a role in the regulation of angiogenesis. A variety of miR-210 and miR-373 targets that may be relevant to hypoxia have been validated or proposed. Very recently, targets of these miRs that are implicated in DNA repair have been identified, thus establishing an additional link between the hypoxic tumor microenvironment and DNA damage. Extending beyond cancer biology, some of miR-210 targets are likely involved in the regulation of angiogenesis, and neuronal cell survival. Inactivation of miRs affected by hypoxia presents a promising therapeutic strategy in the case of difficult-to-treat cancers, as well as in other non-cancer-related diseases.