The Copper Metabolism MURR1 Domain containing 1 protein COMMD1 has been associated with copper homeostasis, NF-kappaB signaling, and sodium transport. Recently, we identified COMMD1 as a novel protein in HIF-1 signaling. Mouse embryos deficient for Commd1 have increased expression of hypoxia/HIF-regulated genes i.e. VEGF, PGK and Bnip3. Hypoxia-inducible factors (HIFs) are master regulators of oxygen homeostasis, which control angiogenesis, erythropoiesis, glycolysis and cell survival/proliferation under normal and pathologic conditions. Although HIF activity is mainly controlled by ubiquitination and protein degradation by the von Hippel Lindau (pVHL) tumor suppressor gene other mechanisms have recently been identified that regulate HIF signaling independently of pVHL.Here we characterized the mechanism by which COMMD1 regulates HIF-1alpha protein degradation. We show that COMMD1 competes with the chaperone heat shock protein HSP90beta for binding to the NH(2)-terminal DNA-binding and heterodimerization domain of HIF-1alpha to regulate HIF-1alpha stability together with HSP70. Inhibition of HSP90 activity with 17-Allylamino-17-demethoxygeldanamycin (17-AAG) increased COMMD1-mediated HIF-1alpha degradation independent of ubiquitin and pVHL.These data reveal a novel role for COMMD1 in conjunction with HSP90beta/HSP70 in the ubiquitin and O(2)-independent regulation of HIF-1alpha.