PSMD3

PSMD3 (Rpn3) is an essential non-ATPase subunit of the 19S regulatory particle of the 26S proteasome required for ubiquitin-dependent proteolysis of specific substrates (PMID:10490625). It is integral to proteasome assembly and integrity: PSMD3 directly binds the deubiquitinating subunit Rpn11, stabilizes it, and is needed for its incorporation into mature proteasomes, so that loss of PSMD3 impairs 19S–20S association, reduces proteasome engagement of the shuttle factor Rad23, and causes accumulation of multiubiquitin-protein conjugates and stabilization of proteolytic substrates (PMID:21619884). Through this control over substrate turnover, PSMD3 selectively governs the proteolysis of cell cycle regulators (SCF and APC/C substrates) (PMID:10490625) and stabilizes a set of oncogenic clients—HER2 (PMID:31013812), NF-κB (PMID:33712704), and ILF3 (PMID:37337223)—by limiting their ubiquitin-dependent degradation, with knockdown redirecting HER2 toward lysosomal degradation and reducing NF-κB nuclear activity and cancer-cell survival (PMID:31013812, PMID:33712704, PMID:37337223). PSMD3 is also a binding target of the metabolite OAA, which destabilizes the m6A-reader YTHDF2 to derepress Rxrb and promote intestinal lipid absorption (PMID:41844893). Loss-of-function PSMD3 point mutations reduce its expression, trigger apoptosis of retinal pigment epithelial cells, and increase ocular axial length in knock-in mice, linking PSMD3 to pathological myopia (PMID:36948574).

1. 1999 High

   Established that a specific 19S subunit is not a generic proteolysis factor but is selectively required for degradation of defined substrates, distinguishing substrate-specific from substrate-general roles within the regulatory particle.

   Evidence Temperature-sensitive rpn3 alleles in budding yeast with cell-cycle analysis and pulse-chase substrate half-life measurements

   PMID:10490625

   Open questions at the time

   • Does not define the structural basis by which Rpn3 confers substrate selectivity
   • Mechanism distinguishing Sic1-independent from Cln2/Clb-dependent processing unresolved
   • Human PSMD3 not directly tested in this study
2. 2011 High

   Answered how Rpn3 contributes to proteasome function mechanistically, showing it acts as an assembly determinant that recruits and stabilizes the deubiquitinase Rpn11 into intact 26S particles.

   Evidence Reciprocal Co-IP, native gel/glycerol-gradient fractionation, protein stability and Rad23-binding assays in yeast

   PMID:21619884

   Open questions at the time

   • Atomic interface between Rpn3 and Rpn11 not resolved
   • Whether human PSMD3 stabilizes the human Rpn11 ortholog not tested here
3. 2019 Medium

   Extended PSMD3 function to client-protein stabilization in cancer, showing PSMD3 physically protects HER2 from ubiquitin-mediated and lysosomal degradation.

   Evidence Reciprocal Co-IP, siRNA knockdown, ubiquitination assay, and LAMP-1 localization in HER2+ breast cancer cells

   PMID:31013812

   Open questions at the time

   • Whether stabilization is direct or via general proteasome assembly defect not separated
   • Single lab; no in vivo confirmation of HER2 stabilization
4. 2021 Medium

   Showed PSMD3 sustains NF-κB protein levels and nuclear activity, linking proteasome subunit function to a survival-signaling output in leukemia cells.

   Evidence shRNA/siRNA knockdown, NF-κB luciferase reporter, nucleocytoplasmic fractionation and apoptosis assays in CML cells

   PMID:33712704

   Open questions at the time

   • Direct physical interaction between PSMD3 and NF-κB not demonstrated
   • Mechanism of NF-κB stabilization versus general proteostasis effect unresolved
5. 2023 Medium

   Identified ILF3 as a PSMD3-stabilized client, with PSMD3 promoting ILF3 deubiquitination to support tumor cell proliferation and invasion.

   Evidence Co-IP/MS, CHX-chase stability and ubiquitination assays, immunofluorescence co-localization, knockdown and xenograft model in lung cancer

   PMID:37337223

   Open questions at the time

   • Whether ILF3 deubiquitination is mediated through the Rpn11-PSMD3 axis not established
   • Single lab
6. 2023 Medium

   Connected PSMD3 loss-of-function to a defined disease phenotype, showing point mutations reduce PSMD3 expression, cause retinal cell apoptosis, and increase ocular axial length.

   Evidence Exome/Sanger sequencing, RT-qPCR, apoptosis flow cytometry, and CRISPR knock-in mouse with ocular biometry

   PMID:36948574

   Open questions at the time

   • Molecular link between reduced PSMD3 and axial elongation not mechanistically traced
   • Single family/lab
7. 2026 Medium

   Revealed a non-canonical regulatory input, showing the metabolite OAA directly binds PSMD3 to destabilize YTHDF2 and reprogram intestinal lipid absorption.

   Evidence Biotin-OAA pull-down with proteomics plus in vitro and in vivo YTHDF2 loss-of-function validation in intestinal cells

   PMID:41844893

   Open questions at the time

   • Structural binding site of OAA on PSMD3 not mapped
   • How OAA binding mechanistically alters YTHDF2 stability unresolved
   • Single lab

• How PSMD3 achieves substrate-selective stabilization versus degradation, and whether its cancer clients and OAA-dependent regulation operate through the same Rpn11-coupled assembly mechanism, remains unresolved.
• No structural model of human PSMD3 within the 19S particle in the corpus
• Unclear whether client stabilization is direct binding or indirect via proteasome integrity
• Mechanistic unification of metabolic, oncogenic, and ocular roles not established