A Conserved Family of Prolyl-4-Hydroxylases That Modify HIF

Abstract

Mammalian cells respond to changes in oxygen availability through a conserved pathway that is regulated by the hypoxia-inducible factor (HIF). The alpha subunit of HIF is targeted for degradation under normoxic conditions by a ubiquitin-ligase complex that recognizes a hydroxylated proline residue in HIF. We identified a conserved family of HIF prolyl hydoxylase (HPH) enzymes that appear to be responsible for this posttranslational modification. In cultured mammalian cells, inappropriate accumulation of HIF caused by forced expression of the HIF-1alpha subunit under normoxic conditions was attenuated by coexpression of HPH. Suppression of HPH in cultured Drosophila melanogaster cells by RNA interference resulted in elevated expression of a hypoxia-inducible gene (LDH, encoding lactate dehydrogenase) under normoxic conditions. These findings indicate that HPH is an essential component of the pathway through which cells sense oxygen.

Hypoxia-Inducible Factor Prolyl Hydroxylase Inhibition: Robust New Target or Another Big Bust for Stroke Therapeutics?

“…Hypoxia-inducible factor PHDs hydroxylate the two specific proline residues pro 402 or pro 564 (amino-acid positions designated in humans) within the oxygen degradation domain (ODD) of HIF-1a (Bruick and McKnight, 2001;Kaelin and Ratcliffe, 2008). Hydroxylation of HIF-1a allows it to bind to the VHL (Von Hippel Lindau) tumor suppressor protein that acts as a recognition component of E3 ubiquitin ligase complex.…”

“…Hypoxia-inducible factor prolyl hydroxylase domain enzymes regulate many substrates in the adaptive hypoxic response Prolyl hydroxylation is the most well-studied regulator for HIF levels and is catalyzed by nonheme iron dioxygenases known as the HIF PHDs (Bruick and McKnight, 2001). In addition to iron, HIF PHD's also require 2-oxoglutarate.…”

“…Kaelin and Ratcliffe (2008) independently used proteomic approaches to identify prolyl hydroxylation as the essential, oxygen-dependent posttranslational modification of HIF-1a that mediated its interaction with the VHL complex, and its subsequent degradation. Using genetic approaches, the HIF PHDs were soon identified by Bruick, McKnight, and Ratcliffe as dioxygenases that are dependent on iron and oxygen, thus providing a molecular link between iron sensing and oxygen sensing (Bruick and McKnight, 2001;Schofield and Ratcliffe, 2005). The findings afforded us and other members of the clinical neuroscience community several new tools to address the notion that iron chelators work in stroke via PHD inhibition.…”

Prolyl-4-hydroxylase PHD2- and hypoxia-inducible factor 2-dependent regulation of amphiregulin contributes to breast tumorigenesis

“…The HIF prolyl-4-hydroxylase domain proteins, PHD1, 2 and 3 are responsible for normoxic HIF-a proteolysis. Prolyl-4-hydroxylation is necessary for the interaction with the von Hippel-Lindau tumor suppressor protein (pVHL) that mediates HIF-a degradation (Maxwell et al, 1999;Bruick and McKnight, 2001;Epstein et al, 2001;Jaakkola et al, 2001;Ivan et al, 2002).…”

Regulation of HIF-1α Activity by Overexpression of Thioredoxin is Independent of Thioredoxin Reductase Status

“…This interaction induces the ubiquitination of HIF-α, wherein HIF-α becomes targeted for degradation by the proteasome. HIF-α proline hydroxylation is carried out by three enzymes (EGLN1, EGLN2 or EGLN3) that require oxygen, iron and 2-oxoglutarate (Bruick et al, 2001;Epstein et al, 2001) which have been proposed to function as oxygen sensors that directly regulate HIF-1α stability.…”