Activity of hypoxia-inducible factor 2α is regulated by association with the NF-κB essential modulator

Abstract

The hypoxia-inducible factors 1α (HIF-1α) and 2α (HIF-2α) are key regulators of the transcriptional response to low oxygen and are closely related in domain architecture, DNA binding, and activation mechanisms. Despite these similarities, targeted disruption of the HIF-α genes in mice results in distinctly different phenotypes demonstrating nonredundancy of function, although the underlying mechanisms remain unclear. Here we report on the novel and specific interaction of HIF-2α, but not HIF-1α, with the NF-κB essential modulator (NEMO) using immunoprecipitation, mammalian two-hybrid, and in vitro protein interaction assays. Reporter gene assays demonstrate that this interaction specifically enhances normoxic HIF-2α transcriptional activity, independently of the HIF-2α transactivation domain, consistent with a model by which NEMO aids CBP/p300 recruitment to HIF-2α. In contrast, HIF-2α overexpression does not alter NF-κB signaling, suggesting that the functional consequence of the HIF-2α/NEMO interaction is limited to the HIF pathway. The specificity of NEMO for HIF-2α represents one of the few known differential protein-protein interactions between the HIF-α proteins, which has important implications for the activity of HIF-2α and is also the first postulated NF-κB-independent role for NEMO. © 2005 by The American Society for Biochemistry and Molecular Biology, Inc.