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The hypoxia-inducible factor (HIF) pathway is essential for cell survival under low oxygen and plays an important role in tumor cell homeostasis. We investigated the function of miR-210, the most prominent microRNA upregulated by hypoxia and a direct transcriptional target of HIFs. miR-210 expression was elevated in multiple cancer types and correlated with metastasis of breast and melanoma tumors. miR-210 overexpression in cancer cell lines bypassed hypoxia-induced cell cycle arrest and partially reversed the hypoxic gene expression signature. We identified MNT, a known MYC antagonist, as a miR-210 target. MNT mRNA contains multiple miR-210 binding sites in the 3' UTR and its knockdown phenocopied miR-210 overexpression. Furthermore, loss of MYC abolished miR-210-mediated override of hypoxia-induced cell cycle arrest. Comparison of miR-210 and MYC overexpression with MNT knockdown signatures also indicated that miR-210 triggered a "MYC-like" transcriptional response. Thus, miR-210 influences the hypoxia response in tumor cells through targeting a key transcriptional repressor of the MYC-MAX network.

Clear cell carcinoma of the kidney is a major cause of mortality in patients with von Hippel-Lindau (VHL) disease, which is caused by germ line mutations that inactivate the VHL tumor suppressor gene. Biallelic VHL inactivation, due to mutations or hypermethylation, is also common in sporadic clear cell renal carcinomas. The VHL gene product, pVHL, is part of a ubiquitin ligase complex that targets the alpha subunits of the heterodimeric transcription factor hypoxia-inducible factor (HIF) for destruction under well-oxygenated conditions. All VHL mutations linked to classical VHL disease compromise this pVHL function although some missense mutations result in a low risk of kidney cancer (type 2A VHL disease) while others result in a high risk (type 2B VHL disease). We found that type 2A mutants were less defective than type 2B mutants when reintroduced into VHL / renal carcinoma cells with respect to HIF regulation. A stabilized version of HIF2 promoted tumor growth by VHL / cells engineered to produce type 2A mutants, while knock-down of HIF2 in cells producing type 2B mutants had the opposite effect. Therefore, quantitative differences with respect to HIF deregulation are sufficient to account for the differential risks of kidney cancer linked to VHL mutations. von Hippel-Lindau (VHL) disease is an autosomal dominant hereditary cancer syndrome caused by germ line mutations of the VHL tumor suppressor gene and is characterized by an increased risk of tumor development in multiple organs, such as hemangioblastoma of the central nervous system, pheochromocytoma of the adrenal glands, and clear cell carcinoma of the kidneys (36). Tumor development occurs when the remaining wild-type allele is inactivated. Kidney cancer develops in 75% of VHL patients by age 60 and is a leading cause of death in this population (70). In keeping with the Knudson two-hit model, somatic VHL mutations leading to VHL inactivation are also common in sporadic clear cell renal cell carcinomas (RCC) and restoration of VHL function in VHL / RCC is sufficient to suppress tumor formation in vivo (21, 30).