Objective NADPH oxidases have been originally implicated in the formation of reactive oxygen species (ROS) as part of innate immunity. Different NADPH oxidases mainly differing in their catalytic NOX subunits have been described in non-phagocytic cells including tumor cells. Recently, NOX proteins have been suggested to be involved in the response to hypoxia. However, the underlying mechanisms are not resolved, yet. We here investigated the response of NOX1 to hypoxia. Results: Exposure to hypoxia (1% oxygen) rapidly increased NOX1 protein levels. Upon reoxygenation, NOX1 protein levels decreased again, suggesting that hypoxia may affect NOX1 protein stability. In fact, under normoxia, but not under hypoxia, NOX1 was ubiquitinylated, and inhibition of proteasomal degradation increased NOX1 protein levels. Subsequently, hypoxic accumulation of NOX1 protein was abrogated in cells deficient in the ubiquitin E3-ligase von Hippel Lindau protein (pVHL), but was restored upon reconstitution of pVHL. Since pVHL is known to bind to hydroxylated proline residues in the oxygen-regulated HIF-alpha proteins, we tested the involvement of HIF prolyl hydroxylases (PHD) in the control of NOX1. Treatment with the PHD inhibitor DMOG or transfection of shRNA against PHD2 elevated NOX1 protein levels. In line, treatment with the PHD cofactor ascorbate was able to decrease NOX1 levels under hypoxia. Importantly, immunoprecipitation analysis revealed that not only pVHL, but also PHD2, interacted with NOX1. Mutation analysis further identified proline residues required for NOX1 ubiquitinylation. In vivo studies confirmed that NOX1 protein was primarily localized in hypoxic areas of a HepG2 xenograft. Intriguingly, NOX1 deficiency prevented tumor growth. Conclusion: We identified NOX1 as a novel target of the PHD – pVHL system controlling NOX1 abundance under hypoxic conditions and provided evidence that NOX1 may play an important role in tumor progression.