Kinetic Investigations of the Role of Factor Inhibiting Hypoxia-inducible Factor (FIH) as an Oxygen Sensor.

Abstract

The hypoxia-inducible factor (HIF) hydroxylases regulate hypoxia sensing in animals. In humans, they comprise three prolyl hydroxylases (PHD1-3 or EGLN1-3) and factor inhibiting HIF (FIH). FIH is an asparaginyl hydroxylase catalyzing post-translational modification of HIF-α, resulting in reduction of HIF-mediated transcription. Like the PHDs, FIH is proposed to have a hypoxia-sensing role in cells, enabling responses to changes in cellular O2 availability. PHD2, the most important human PHD isoform, is proposed to be biochemically/kinetically suited as a hypoxia sensor due to its relatively high sensitivity to changes in O2 concentration and slow reaction with O2. To ascertain whether these parameters are conserved among the HIF hydroxylases, we compared the reactions of FIH and PHD2 with O2. Consistent with previous reports, we found lower Km(app)(O2) values for FIH than for PHD2 with all HIF-derived substrates. Under pre-steady-state conditions, the O2-initiated FIH reaction is significantly faster than that of PHD2. We then investigated the kinetics with respect to O2 of the FIH reaction with ankyrin repeat domain (ARD) substrates. FIH has lower Km(app)(O2) values for the tested ARDs than HIF-α substrates, and pre-steady-state O2-initiated reactions were faster with ARDs than with HIF-α substrates. The results correlate with cellular studies showing that FIH is active at lower O2 concentrations than the PHDs and suggest that competition between HIF-α and ARDs for FIH is likely to be biologically relevant, particularly in hypoxic conditions. The overall results are consistent with the proposal that the kinetic properties of individual oxygenases reflect their biological capacity to act as hypoxia sensors.

• Authors: Hanna Tarhonskaya, Adam P Hardy, Emily A Howe, Nikita D Loik, Holger B Kramer, James S O McCullagh, Christopher J Schofield, Emily Flashman
• Journal: The Journal of biological chemistry (J Biol Chem) Vol. 290 Issue 32 Pg. 19726-42 (Aug 07 2015) ISSN: 1083-351X [Electronic] United States
• PMID: 26112411 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)
• Copyright: © 2015 by The American Society for Biochemistry and Molecular Biology, Inc.

Chemical References

• Ankyrins
• HIF1A protein, human
• Hypoxia-Inducible Factor 1, alpha Subunit
• Recombinant Proteins
• Repressor Proteins
• Mixed Function Oxygenases
• HIF1AN protein, human
• EGLN1 protein, human
• Hypoxia-Inducible Factor-Proline Dioxygenases
• Oxygen

Topics

• Amino Acid Sequence
• Animals
• Ankyrins (genetics, metabolism)
• Biocatalysis
• Escherichia coli (genetics, metabolism)
• Gene Expression
• Gene Expression Regulation
• Humans
• Hypoxia (genetics, metabolism)
• Hypoxia-Inducible Factor 1, alpha Subunit (genetics, metabolism)
• Hypoxia-Inducible Factor-Proline Dioxygenases (genetics, metabolism)
• Kinetics
• Mixed Function Oxygenases (genetics, metabolism)
• Molecular Sequence Data
• Oxygen (metabolism)
• Protein Structure, Tertiary
• Recombinant Proteins (genetics, metabolism)
• Repressor Proteins (genetics, metabolism)
• Signal Transduction
• Transcription, Genetic