Regulation of microRNA expression: the hypoxic component.

microRNAs are involved in a wide variety of normal and pathological cellular processes, including tumorigenic transformation. Despite significant progress made towards understanding their mechanisms of action, much less is known about the regulation of expression of specific microRNAs. Recent reports have established a link between hypoxia, a key feature of the tumor microenvironment, and a group of microRNAs. Select members of this group seem to affect apoptotic signaling in a hypoxic environment and are also predicted to target genes of critical importance for tumor biology. Interestingly, most hypoxia-induced microRNAs are also overexpressed in human cancers, suggesting a role in tumorigenesis. We hereby discuss the known and predicted regulators of microRNA expression and approaches for expanding this fledgling research area.