Hypoxia-regulated microRNAs in human cancer

Hypoxia plays an important role in the tumor microenvironment by allowing the development and maintenance of cancer cells, but the regulatory mechanisms by which tumor cells adapt to hypoxic conditions are not yet well understood. MicroRNAs are recognized as a new class of master regulators that control gene expression and are responsible for many normal and pathological cellular processes. Studies have shown that hypoxia inducible factor 1 (HIF1) regulates a panel of microRNAs, whereas some of microRNAs target HIF1. The interaction between microRNAs and HIF1 can account for many vital events relevant to tumorigenesis, such as angiogenesis, metabolism, apoptosis, cell cycle regulation, proliferation, metastasis, and resistance to anticancer therapy. This review will summarize recent findings on the roles of hypoxia and microRNAs in human cancer and illustrate the machinery by which microRNAs interact with hypoxia in tumor cells. It is expected to update our knowledge about the regulatory roles of microRNAs in regulating tumor microenvironments and thus benefit the development of new anticancer drugs.