VBP1

VBP1 is a cytoplasmic protein that functions as an adaptor coupling its binding partners to the ubiquitin-proteasome system, thereby controlling the stability of multiple regulatory proteins (PMID:8674032, PMID:29121446, PMID:37201586). It was first identified as a direct pVHL-binding protein, with the interaction requiring the C-terminal end of pVHL; pVHL co-expression drives VBP1 from the cytoplasm into the nucleus, indicating that pVHL controls VBP1 localization (PMID:8674032). Through its pVHL association, VBP1 enhances pVHL stability and facilitates pVHL-mediated ubiquitination and degradation of HIF-1α, suppressing HIF-1α-driven epithelial-mesenchymal transition and tumor metastasis (PMID:29121446). VBP1 also drives HIF-1α degradation independently of pVHL by interacting with the ubiquitin ligase CHIP and the co-chaperone HSP70, regulating CHIP stability and promoting CHIP-mediated HIF-1α ubiquitination; loss of vbp1 in zebrafish causes Hif-1α accumulation, Hif target-gene upregulation, and enhanced hematopoietic stem cell induction under hypoxia (PMID:37201586). Beyond hypoxia signaling, VBP1 broadens this degradation-adaptor role: it bridges all four TCF/LEF transcription factors to pVHL to promote their proteasomal degradation, dampening Wnt/β-catenin signaling (PMID:32989053), and recruits the AAA+ ATPase p97 together with pVHL to target the meiotic DNA repair protein hMSH4 for polyubiquitination and degradation (PMID:23964080). VBP1 additionally interacts with hepatitis B virus X protein to facilitate HBx-induced NF-κB activation and cell proliferation (PMID:18315953), and is required for early embryonic morphogenesis in C. elegans, where vbp-1 knockdown arrests embryos at the morula stage (PMID:12579260).

1. 1996 Medium

   Established VBP1 as a direct physical partner of the VHL tumor suppressor and showed that pVHL governs VBP1's nucleocytoplasmic distribution, placing VBP1 in the VHL functional orbit.

   Evidence Yeast two-hybrid, reciprocal co-IP, and deletion mapping of the pVHL C-terminus with localization assay upon VHL co-expression

   PMID:8674032

   Open questions at the time

   • Did not define the catalytic/functional consequence of the VBP1-pVHL complex
   • Mechanism of pVHL-driven nuclear translocation of VBP1 unresolved
2. 2003 Medium

   Demonstrated that VBP1 has an essential organismal function beyond protein binding, being required for early embryonic development.

   Evidence RNAi knockdown of vbp-1 in C. elegans scored for embryonic arrest at the morula stage

   PMID:12579260

   Open questions at the time

   • Molecular pathway underlying the morphogenesis defect not identified
   • Single method in an ortholog model without molecular mechanism
3. 2008 Medium

   Connected VBP1 to viral signaling, showing it interacts with HBx and contributes to NF-κB-driven proliferation.

   Evidence Yeast two-hybrid, co-IP in vitro and in vivo, NF-κB reporter and proliferation assays

   PMID:18315953

   Open questions at the time

   • Whether VBP1 acts via its degradation-adaptor activity in this context is unknown
   • Single lab; no in vivo infection model
4. 2013 Medium

   Defined VBP1 as a degradation adaptor that, with pVHL and the AAA+ ATPase p97, targets a specific substrate (hMSH4) for polyubiquitination and turnover.

   Evidence Reciprocal co-IP, ubiquitination assay, proteasome/autophagy inhibitor and knockdown experiments in HEK293T cells

   PMID:23964080

   Open questions at the time

   • The responsible E3 ligase was not identified
   • Physiological relevance of hMSH4 turnover in meiosis not tested in vivo
5. 2017 Medium

   Showed VBP1 stabilizes pVHL and promotes pVHL-mediated HIF-1α degradation, linking it to suppression of EMT and metastasis.

   Evidence Co-IP, ubiquitination and protein stability assays, in vitro EMT assays, and an in vivo metastasis model

   PMID:29121446

   Open questions at the time

   • Mechanism by which VBP1 stabilizes pVHL not defined
   • Did not distinguish HIF-1α versus HIF-2α selectivity
6. 2020 Medium

   Extended the bridging-for-degradation model to Wnt signaling, with VBP1 coupling TCF/LEF factors to pVHL for proteasomal degradation.

   Evidence Co-IP, proteasome inhibitor stability assays, Wnt reporter assays, and zebrafish embryo overexpression/knockdown

   PMID:32989053

   Open questions at the time

   • Identity of the E3 ligase in TCF/LEF turnover unresolved
   • Why both overexpression and knockdown increase the TCF/LEF-pVHL association is unexplained
7. 2023 High

   Resolved a pVHL-independent route for HIF-1α control, showing VBP1 engages CHIP and HSP70 to degrade HIF-1α specifically, with organismal consequences for hypoxia-driven hematopoiesis.

   Evidence Co-IP mapping VBP1-CHIP and VBP1-HSP70, ubiquitination assays, in vitro HIF-1α degradation, and zebrafish vbp1 knockout with target-gene and HSC readouts

   PMID:37201586

   Open questions at the time

   • Structural basis for VBP1's choice between pVHL- and CHIP-dependent routes not defined
   • How VBP1 selectively regulates HIF-1α but not HIF-2α is unknown

• It remains unknown what unifies VBP1's role as a degradation adaptor across diverse substrates and how its activity is regulated to select among pVHL-dependent and pVHL-independent pathways.
• No structural model of VBP1 in any of its complexes
• Determinants of substrate and E3-ligase selectivity uncharacterized
• Endogenous regulation of VBP1 expression/activity unknown