Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:1.14.11.2 (prolyl hydroxylase)
 1,814 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Sensing of ambient dioxygen levels and appropriate feedback mechanisms are essential processes for all multicellular organisms. In animals, moderate hypoxia causes an increase in the transcription levels of specific genes, including those encoding vascular endothelial growth factor and erythropoietin. The hypoxic response is mediated by hypoxia-inducible factor (HIF), an alphabeta heterodimeric transcription factor in which both the HIF subunits are members of the basic helix-loop-helix PAS (PER-ARNT-SIM) domain family. Under hypoxic conditions, levels of HIFalpha rise, allowing dimerization with HIFbeta and initiating transcriptional activation. Two types of dioxygen-dependent modification to HIFalpha have been identified, both of which inhibit the transcriptional response. Firstly, HIFalpha undergoes trans -4-hydroxylation at two conserved proline residues that enable its recognition by the von Hippel-Lindau tumour-suppressor protein. Subsequent ubiquitinylation, mediated by an ubiquitin ligase complex, targets HIFalpha for degradation. Secondly, hydroxylation of an asparagine residue in the C-terminal transactivation domain of HIFalpha directly prevents its interaction with the co-activator p300. Hydroxylation of HIFalpha is catalysed by enzymes of the iron(II)- and 2-oxoglutarate-dependent dioxygenase family. In humans, three prolyl hydroxylase isoenzymes (PHD1-3) and an asparagine hydroxylase [factor inhibiting HIF (FIH)] have been identified. The role of 2-oxoglutarate oxygenases in the hypoxic and other signalling pathways is discussed.
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PMID:The role of iron and 2-oxoglutarate oxygenases in signalling. 1277 46

A complex bioregulatory network could be more easily comprehended if its essential function could be described by a small "core" subsystem, and if its response characteristics were switch-like. We tested this proposition by simulation studies of the hypoxia response control network. We hypothesized that a small subsystem governs the basics of the cellular response to hypoxia and that this response has a sharp oxygen-dependent transition. A molecular interaction map of the network was prepared, and an evolutionarily conserved core subsystem was extracted that could control the activity of hypoxia response promoter elements on the basis of oxygen concentration. The core subsystem included the hypoxia-inducible transcription factor (HIFalpha:ARNT heterodimer), proline hydroxylase, and the von Hippel-Lindau protein. Simulation studies showed that the same core subsystem can exhibit switch-like responses both to oxygen level and to HIFalpha synthesis rate, thus suggesting a mechanism for hypoxia response promoter element-dependent responses common to both hypoxia and growth factor signaling. The studies disclosed the mechanism responsible for the sharp transitions. We show how parameter sets giving switch-like behavior can be found and how this type of behavior provides a foundation for quantitative studies in cells.
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PMID:Properties of switch-like bioregulatory networks studied by simulation of the hypoxia response control system. 1510 65

The fruit fly Drosophila melanogaster, a widely utilized genetic model, is highly resistant to oxygen starvation and is beginning to be used for studying physiological, developmental, and cellular adaptations to hypoxia. The Drosophila respiratory (tracheal) system has features in common with the mammalian circulatory system so that an angiogenesis-like response occurs upon exposure of Drosophila larvae to hypoxia. A hypoxia-responsive system homologous to mammalian hypoxia-inducible factor (HIF) has been described in the fruit fly, where Fatiga is a Drosophila oxygen-dependent HIF prolyl hydroxylase, and the basic helix-loop-helix Per/ARNT/Sim (bHLH-PAS) proteins Sima and Tango are, respectively, the Drosophila homologues of mammalian HIF-alpha (alpha) and HIF-beta (beta). Tango is constitutively expressed regardless of oxygen tension and, like in mammalian cells, Sima is controlled at the level of protein degradation and subcellular localization. Sima is critically required for development in hypoxia, but, unlike mammalian model systems, it is dispensable for development in normoxia. In contrast, fatiga mutant alleles are all lethal; however, strikingly, viability to adulthood is restored in fatiga sima double mutants, although these double mutants are not entirely normal, suggesting that Fatiga has Sima-independent functions in fly development. Studies in cell culture and in vivo have revealed that Sima is activated by the insulin receptor (InR) and target-of-rapamycin (TOR) pathways. Paradoxically, Sima is a negative regulator of growth. This suggests that Sima is engaged in a negative feedback loop that limits growth upon stimulation of InR/TOR pathways.
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PMID:Cellular and developmental adaptations to hypoxia: a Drosophila perspective. 1799 52

Hypoxia-inducible factor-1 alpha (HIF-1 alpha) and the aryl hydrocarbon receptor (AhR) work as environmental sensors in human tissues. These proteins are members of the helix-loop-helix/Per-ARNT-SIM transcription factor family and form heterodimers with the aryl hydrocarbon receptor nuclear translocator. HIF-1 alpha can be activated by low oxygen concentrations and hypoxia-inducing agents. The AhR is activated by xenobiotica such as dioxins. Here, we analyze the interference between the AhR signaling, activated by 10 nM 2,3,7,8-tetrachlorodibenzo- p-dioxin (TCDD), and the HIF-1 alpha pathway, induced by hypoxia (5% O2), in two human cell lines, the breast carcinoma cell line MCF-7 and the hepatocyte cell line HepG2. In both cell lines, treatment with TCDD and hypoxia clearly reduced the stabilization of HIF-1 alpha and HRE-mediated promoter activity when compared to the induction under hypoxia alone. Because these effects were not observed after alpha-naphthoflavone treatment and HIF-1 alpha mRNA was not down-regulated, HIF-1 alpha stabilization was revealed to be the target by TCDD in an AhR-depended mechanism. Under exposure to TCDD or hypoxia, the main regulator of HIF-1 alpha stability, the prolyl hydroxylase domain containing protein 2 (PHD2) showed an increase in promoter activity, transcript numbers, and protein amount. Therefore, PHD2 expression is regulated in an AhR-dependent manner under normoxia. The AhR-dependent regulation of PHD2 under normoxia, however, is overwritten by the TCDD-mediated destabilization of HIF-1 alpha. The destabilization of HIF-1 alpha is the dominant effect causing the reduced PHD2 expression after simultaneous exposure to TCDD and hypoxia. We conclude that PHD2 does not mediate the TCDD-mediated HIF-1 alpha destabilization and does not control the interference of AhR and HIF-1 alpha pathways.
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PMID:Significance of prolyl hydroxylase 2 in the interference of aryl hydrocarbon receptor and hypoxia-inducible factor-1 alpha signaling. 1807 50