Regulation of the HIF pathway: enzymatic hydroxylation of a conserved prolyl residue inhypoxia-inducible factor alpha subunits governs capture by the pVHL E3 ubiquitin ligase complex

摘要

The hypoxia-inducible factor-1 transcriptional complex plays a key role in oxygen homeostasis, and is regulated predominantly through stability of its α-subunit. In normoxic conditions HIF-lα is targeted for proteasomal degradation through recognition of its oxygen-dependent destruction domain by the pVHL E3 ubiquitin ligase complex. We have shown that the features of iron and oxygen sensitivity demonstrated by the HIF system can be represented in the pVHL/HIF-lα interaction. Furthermore, post-translational enzymatic modification of HIF-lα by iron and oxygen is required for binding to pVHL. We have shown that modification by this enzyme, in the presence of iron and oxygen, leads to hydroxylation of Pro564, within the ODDD of HIF-lα, and that hydroxylation of Pro564 is sufficient to promote binding to pVHL, thus representing a novel signal for degradation by the ubiquitin/proteasome pathway. We have termed this activity HIF prolyl hydro-xylase, and in keeping with other prolyl hydroxylases it has an absolute requirement for 2-oxoglutarate, in addition to iron and oxygen, and can be inhibited by analogs of 2-oxoglutarate. The key position of HIF prolyl hydroxylase in the degradation of HIF-lα, its ability to explain many of the seminal observations on oxygen sensing, and its graded response to oxygen, suggest that it is acting as an enzymatic oxygen sensor.