Sensing an Oxygen Sensor: Development and Application of Activity-Based Assays Directly Monitoring HIF Heterodimerization

• Published in: Analytical chemistry (Washington) 2021-11, Vol.93 (43), p.14462-14470
• Main Authors: Janssens, Liesl K, Stove, Christophe P
• Format: Article
• Language: English
• Subjects: Assaying; Basic Helix-Loop-Helix Transcription Factors; Bioassays; Biological Assay; Biosensors; Chemistry; Complementation; Deferoxamine; HEK293 Cells; Humans; Hydroxylase; Hypoxia; Hypoxia-Inducible Factor 1, alpha Subunit; Hypoxia-inducible factors; Monitoring; Oxygen; Oxygen probes; Procollagen-Proline Dioxygenase; Prolyl hydroxylase; Proteasome inhibitors; Proteins; Stabilization; Transcription Factors; Transfection
• ISSN: 0003-2700; 1520-6882
• DOI: 10.1021/acs.analchem.1c02923

Conventionally, hypoxia-inducible factor (HIF) activation by prolyl hydroxylase domain enzyme (PHD) inhibition is monitored by gene reporter assays. The principle relies on the monitoring of an upstream event (HIF stabilization) by the downstream transcriptional activity. Here, we developed a novel approach to directly sense HIF activation by monitoring the heterodimerization of the HIFα/HIFβ subunits, constituting the functional HIF transcription factor. Two live cell-based biosensor assay setups were designed, utilizing functional complementation of split-nanoluciferase as a tool to measure HIFα/HIFβ protein–protein interaction resulting from the stabilization of HIF1α or HIF2α. The assay setup in a 96-well format was optimized for a duration of 2 h, and a HEK293T transfection protocol was introduced for the optimal configuration of HIFα/HIFβ-fusion proteins. These new bioassays outperformed hypoxia response element-based gene reporter assay, the current state-of-the-art assay, in terms of sensitivity. Applicability was demonstrated using a panel of PHD inhibitors, including roxadustat, molidustat, daprodustat, desidustat, vadadustat, and FG-2216, for which concentration–response curves were generated, allowing for the derivation of potency (EC50) and efficacy (E max) data. The broad applicability of the biosensors was established via applying hypoxia mimetic CoCl2, iron chelator desferrioxamine, proteasome inhibitor MG-132, and 2-OG mimetic dimethyloxalylglycine on the assays, indicating concentration-dependent effects.