Von Hippel-Lindau (VHL) disease is characterised by frequent mutation of VHL protein, a tumour suppressor which functions as the substrate recognition subunit of a Cullin2 E3 ligase complex (CRL2VHL). CRL2VHL plays important roles in oxygen sensing by targeting Hypoxia Inducible Factor-alpha (HIF-α) subunits for ubiquitination and degradation. VHL is also commonly hijacked by bifunctional molecules such as proteolysis-targeting chimeras (PROTACs) to induce degradation of target molecules. We previously reported the design and characterisation of VHL inhibitors VH032 and VH298 that block the VHL:HIF-α interaction, activate the HIF transcription factor and induce a hypoxic response, which can be beneficial to treat anemia and mitochondrial diseases. How these compounds affect the global cellular proteome remained unknown. Here, we use unbiased quantitative mass spectrometry to identify the proteomic changes elicited by the VHL inhibitor compared to hypoxia or the broad-spectrum prolyl-hydroxylase domain (PHD) enzyme inhibitor IOX2. Our results demonstrate that VHL inhibitors selectively activate the HIF response similar to the changes induced in hypoxia and IOX2 treatment. Interestingly, VHL inhibitors were found to specifically upregulate VHL itself. Our analysis revealed that this occurs via protein stabilisation of VHL isoforms and not via changes in transcript levels. Increased VHL levels upon VH298 treatment resulted in turn in reduced levels of HIF-1α protein. This work demonstrates the specificity of VHL inhibitors and reveal different antagonistic effects upon their acute versus prolonged treatment in cells. These findings suggest that therapeutic use of VHL inhibitors may not produce overt side effects from HIF stabilisation as previously thought.
- E3 ubiquitin ligase
- small molecule
- hypoxia-inducible factor (HIF)
- von Hippel-Lindau (VHL)
- chemical probe