PSMD1

PSMD1 (p112) is the largest non-ATPase subunit of the 19S regulatory particle of the 26S proteasome, established by cDNA cloning and functional complementation of the yeast SEN3 disruptant, where it supports ubiquitin-pathway proteolysis, N-end rule degradation, stress response, and nuclear protein transport (PMID:8816993). Within the regulatory particle it provides a docking platform for the ubiquitinated-substrate recruitment subunit Adrm1, and this interaction is controlled by PIASy-mediated SUMOylation of PSMD1 at a lysine adjacent to the Adrm1-binding domain; the deconjugating enzyme xSENP1 reverses this modification, coupling proteasome composition to timely mitotic exit (PMID:24910440). Through its proteasomal function PSMD1 governs turnover of regulatory substrates—its depletion stabilizes p53 and induces p21 and SFN with cell-cycle arrest (PMID:28992264)—and in cancer cells it stabilizes pro-survival factors, promoting NF-κB protein expression in CML cells (PMID:33712704) and suppressing PINK1 ubiquitination to enhance PINK1 stability and lung adenocarcinoma viability (PMID:35192838). PSMD1 also regulates expression of de novo lipid synthesis genes through p38-JNK and AKT signaling, supporting lipid droplet formation and proliferation (PMID:31703613), and is itself subject to autophagic clearance via direct interaction with ATG16 and delivery to lysosomes (PMID:30269947).

1. 1988 Medium

   Before its proteasomal role was known, PSMD1 was first detected as a tissue-enriched cell-surface antigen, raising the question of what this 112 kDa lung endothelial protein was.

   Evidence monoclonal antibody, immunogold EM, and in vivo radiolabeled antibody biodistribution in lung endothelium

   PMID:2460698

   Open questions at the time

   • molecular identity and function not established at this stage
   • surface localization not reconciled with later proteasomal assignment
   • no link to ubiquitin-proteasome system
2. 1996 High

   Cloning and cross-species complementation established p112 as a bona fide largest regulatory subunit of the 26S proteasome with conserved roles in ubiquitin-dependent proteolysis.

   Evidence cDNA cloning and yeast SEN3-disruptant complementation with phenotypic analysis of proteolysis, N-end rule, stress, and nuclear transport defects

   PMID:8816993

   Open questions at the time

   • substrate-specific contributions not dissected
   • structural position within 19S particle not resolved
   • regulation of subunit incorporation unknown
3. 2014 High

   SUMOylation was shown to be a regulatory switch governing how PSMD1 recruits the substrate receptor Adrm1, linking a post-translational modification to proteasome composition and cell-cycle timing.

   Evidence Co-IP, SUMOylation site mapping by mutagenesis, PIASy E3 identification, Adrm1-binding and xSENP1 mitotic-exit assays

   PMID:24910440

   Open questions at the time

   • fraction of proteasomes modified in vivo unquantified
   • consequences for global substrate degradation not measured
   • human SENP/PIAS specificity not addressed
4. 2018 Medium

   PSMD1 was placed in the pathway controlling p53 stability, explaining how its loss imposes a cell-cycle checkpoint.

   Evidence siRNA knockdown in breast cancer cells with p53/p21/SFN immunoblot and cell-cycle analysis

   PMID:28992264

   Open questions at the time

   • single primary method and single lab
   • direct role in p53 ubiquitin transfer versus general proteasome capacity not separated
   • no in vivo validation
5. 2018 Medium

   Discovery of a direct PSMD1-ATG16 interaction revealed that proteasome subunits are themselves turned over by autophagy, identifying a cross-regulatory link between the two degradation systems.

   Evidence reciprocal Co-IP, ATG16 deletion mapping, autophagosome/lysosome co-localization imaging, and atg16-/atg9- knockouts in Dictyostelium

   PMID:30269947

   Open questions at the time

   • demonstrated in Dictyostelium, not human cells
   • physiological trigger for autophagic clearance unknown
   • effect on assembled 26S proteasome levels not quantified
6. 2019 Medium

   PSMD1 was connected to lipid metabolism, showing its proteasomal activity feeds into signaling that drives de novo lipid synthesis gene expression.

   Evidence siRNA knockdown in HepG2 with lipid droplet quantification, signaling immunoblots (p38/JNK/AKT), and gene expression analysis

   PMID:31703613

   Open questions at the time

   • mechanism linking proteasome to p38-JNK/AKT not defined
   • direct versus indirect effect on lipogenic genes unresolved
   • single lab, single cell line
7. 2021 Medium

   PSMD1 was shown to sustain NF-κB in leukemic cells with a selectivity for malignant over normal progenitors, nominating it as a context-dependent survival dependency.

   Evidence shRNA knockdown, luciferase reporter, nucleocytoplasmic fractionation, immunoblot, and apoptosis flow cytometry in CML cells

   PMID:33712704

   Open questions at the time

   • molecular basis of NF-κB regulation not defined
   • selectivity for CML cells mechanistically unexplained
   • no in vivo confirmation in this study
8. 2022 Medium

   PSMD1 was found to stabilize PINK1 by limiting its ubiquitination, providing a substrate-level mechanism for its pro-tumorigenic role in lung adenocarcinoma.

   Evidence Co-IP, ubiquitination assay, shRNA knockdown/overexpression, and xenograft mouse model

   PMID:35192838

   Open questions at the time

   • how a proteasome subunit inhibits substrate ubiquitination not mechanistically resolved
   • directness of PSMD1-PINK1 interaction not validated reciprocally
   • generality across tumor types untested

• How PSMD1's SUMOylation-controlled Adrm1 docking, autophagic turnover, and apparent substrate-selective stabilization of factors like PINK1 and NF-κB are mechanistically integrated within the assembled 26S proteasome remains unresolved.
• no structural model connecting modification state to substrate selectivity
• human-cell confirmation of autophagic clearance lacking
• whether substrate-specific effects reflect direct binding or general proteasome capacity unclear