VBP1

VBP1 functions as a scaffold protein that coordinates ubiquitin-dependent degradation of multiple substrates, primarily through its interaction with the tumor suppressor pVHL and additional E3 ubiquitin ligase complexes. VBP1 directly binds the C-terminal domain of pVHL and enhances pVHL stability and its ubiquitin ligase activity toward HIF-1α, thereby suppressing HIF-1α-driven epithelial-mesenchymal transition and metastasis; it similarly promotes pVHL-mediated proteasomal degradation of all four TCF/LEF transcription factors, attenuating Wnt/β-catenin signaling (PMID:8674032, PMID:29121446, PMID:32989053). VBP1 also mediates pVHL-independent HIF-1α degradation by recruiting the CHIP/HSP70 ubiquitin ligase complex, and it cooperates with the AAA+ ATPase p97 to target hMSH4 for proteasomal and autophagic degradation (PMID:37201586, PMID:23964080). The C. elegans ortholog is essential for embryonic morphogenesis, indicating a conserved role in development (PMID:12579260).

1. 1996 High

   Identifying VBP1 as a direct pVHL-binding protein established the first molecular link between VBP1 and the VHL tumor suppressor pathway, and revealed that VHL controls VBP1 nucleocytoplasmic localization.

   Evidence Yeast two-hybrid screen and reciprocal co-immunoprecipitation with epitope-tagged localization studies in mammalian cells

   PMID:8674032

   Open questions at the time

   • Functional consequence of VBP1–pVHL interaction on pVHL activity was unknown
   • Endogenous VBP1 substrates or downstream targets not identified
   • Structural basis of the C-terminal pVHL–VBP1 interface not resolved
2. 2003 Medium

   Demonstrating that the C. elegans VBP-1 ortholog is required for embryonic morphogenesis established an essential developmental role, moving VBP1 beyond a mere binding partner.

   Evidence RNAi knockdown in C. elegans causing morula-stage arrest

   PMID:12579260

   Open questions at the time

   • Mechanism by which VBP-1 loss causes morphogenesis arrest was not defined
   • Whether developmental role depends on VHL interaction was untested
   • Single-organism RNAi study; not confirmed in other metazoan models at that time
3. 2008 Medium

   Showing that VBP1 interacts with hepatitis B virus HBx protein and facilitates NF-κB activation expanded VBP1's functional scope to viral pathogenesis and inflammatory signaling.

   Evidence Yeast two-hybrid, in vitro/in vivo co-immunoprecipitation, and NF-κB reporter assays in cultured cells

   PMID:18315953

   Open questions at the time

   • Mechanism linking VBP1–HBx interaction to NF-κB activation was not delineated
   • Whether this involves pVHL or ubiquitination was not tested
   • Single-lab finding without independent replication
4. 2013 High

   Revealing that VBP1 recruits p97 and promotes polyubiquitination and dual proteasomal/autophagic degradation of hMSH4 established VBP1 as an active scaffold for substrate-directed protein turnover beyond the canonical pVHL–HIF axis.

   Evidence Co-immunoprecipitation, ubiquitination assays, proteasome and autophagy inhibitor experiments in HEK293T cells

   PMID:23964080

   Open questions at the time

   • Identity of the E3 ligase responsible for hMSH4 ubiquitination in this complex was not definitively assigned
   • Physiological consequence of hMSH4 degradation (e.g., meiotic recombination effects) was not tested
   • Whether p97 interaction is direct or bridged by VHL was unclear
5. 2017 High

   Demonstrating that VBP1 stabilizes pVHL and enhances pVHL-mediated HIF-1α ubiquitination and degradation connected VBP1 to the hypoxia response and showed it suppresses epithelial-mesenchymal transition and metastasis in vivo.

   Evidence Co-immunoprecipitation, ubiquitination and stability assays, in vitro EMT assays, and in vivo tumor metastasis models

   PMID:29121446

   Open questions at the time

   • Mechanism by which VBP1 stabilizes pVHL protein was not resolved
   • Whether VBP1 regulates HIF-2α through pVHL was not addressed
   • Structural determinants of VBP1-enhanced ubiquitination were unknown
6. 2020 High

   Showing that VBP1 directly binds all four TCF/LEF transcription factors and bridges them to pVHL for proteasomal degradation revealed VBP1 as a negative regulator of Wnt/β-catenin signaling.

   Evidence Co-immunoprecipitation, Wnt reporter assays, proteasome inhibitor experiments, zebrafish developmental model, and knockdown/overexpression in cultured cells

   PMID:32989053

   Open questions at the time

   • Paradoxical effect where both overexpression and knockdown enhance TCF/LEF–pVHL association was mechanistically unexplained
   • Whether VBP1's role in Wnt suppression is relevant to tumorigenesis in vivo was not tested
   • Stoichiometric versus catalytic role of VBP1 in bridging TCF/LEF to pVHL was unclear
7. 2023 High

   Identifying the CHIP/HSP70 complex as a pVHL-independent route by which VBP1 targets HIF-1α (but not HIF-2α) for degradation demonstrated functional specificity among HIF isoforms and expanded VBP1's E3 ligase partnerships.

   Evidence Reciprocal co-immunoprecipitation, protein degradation assays, zebrafish vbp1 knockout with Hif target gene analysis

   PMID:37201586

   Open questions at the time

   • Structural basis for HIF-1α selectivity over HIF-2α in the CHIP/HSP70 pathway was not determined
   • Relative contribution of VHL-dependent versus CHIP-dependent HIF-1α degradation under physiological conditions is unknown
   • Whether VBP1 functions as a co-chaperone or adaptor within the CHIP/HSP70 complex was not resolved

• The structural basis of VBP1's multi-partner scaffolding, its potential enzymatic activities, and its roles in human disease beyond cancer remain undefined.
• No crystal or cryo-EM structure of VBP1 or its complexes is available
• Whether VBP1 has intrinsic catalytic activity or functions purely as a scaffold is unresolved
• Genetic association of VBP1 mutations with human disease has not been established