PSMA1

PSMA1 encodes an alpha-type core subunit of the 20S proteasome that participates in targeted degradation of ubiquitinated substrates (PMID:36527092). In myeloid malignancies, PSMA1 expression is regulated downstream of TRAF6, and its level sets proteasome activity and sensitivity to the proteasome inhibitor bortezomib: reducing PSMA1 resensitizes bortezomib-resistant MDS/AML cells to bortezomib-induced cytotoxicity (PMID:22685174). PSMA1 can also be recruited as a scaffold-binding partner by the lncRNA MDHDH, which directly bridges PSMA1 to MDH2 and promotes binding of ubiquitinated MDH2 to the proteasome to accelerate its degradation, thereby lowering mitochondrial membrane potential and shifting the NAD+/NADH ratio to impede glycolysis in glioma cells (PMID:36527092). Beyond these two contexts, no further mechanistic detail of PSMA1 has been characterized in the available corpus.

1. 2012 Medium

   Established that PSMA1 is not merely a static proteasome subunit but a regulated node whose expression, controlled downstream of TRAF6, determines proteasome activity and drug sensitivity in myeloid cancer.

   Evidence RNAi knockdown of TRAF6 with gene-expression profiling and bortezomib cytotoxicity assays in MDS/AML cell lines

   PMID:22685174

   Open questions at the time

   • Mechanism linking TRAF6 to PSMA1 transcription/expression not defined
   • Effect of PSMA1 on assembled 20S/26S proteasome structure or catalytic rate not measured directly
   • Not validated in primary patient samples or in vivo
2. 2022 Medium

   Showed that PSMA1 can be recruited by a lncRNA scaffold to direct a specific substrate to the proteasome, linking proteasomal degradation to mitochondrial/metabolic control.

   Evidence RNA pulldown, mass spectrometry, RIP, reciprocal co-IP, JC-1 membrane potential and energy assays, and xenografts in glioma cells

   PMID:36527092

   Open questions at the time

   • Direct RNA-binding interface on PSMA1 not mapped
   • Whether scaffold recruitment generalizes to other substrates is unknown
   • Structural basis of MDHDH–PSMA1 association not resolved

• How PSMA1 incorporation, abundance, or RNA-mediated recruitment is integrated into normal proteasome assembly and substrate selection remains unresolved.
• No structural model of PSMA1 within the 20S core in the corpus
• No catalytic or assembly mechanism characterized
• Generality of PSMA1-mediated substrate targeting beyond MDH2 and bortezomib contexts untested