PSMA5

PSMA5 is the α5 subunit of the outer alpha-ring of the 20S core proteasome, contributing to proteasomal protein degradation; in solution the refolded recombinant protein assembles predominantly as a tetramer, consistent with its structural role in the alpha-ring (PMID:15135414), and endogenous PSMA5 resides in a native protein complex accessible to co-immunoprecipitation (PMID:22894781). Beyond its core structural role, PSMA5 functions as a pro-tumorigenic driver: in lung adenocarcinoma it acts upstream of JAK/STAT signaling, where its overexpression suppresses apoptosis and its knockdown inhibits proliferation, invasion, and metastasis while sensitizing cells to cisplatin (PMID:35605971), and in prostate cancer its loss similarly induces apoptosis, restricts migration and invasion, and restores bortezomib sensitivity (PMID:30807553). In hepatocellular carcinoma, PSMA5 is packaged into tumor-derived exosomes that are internalized by macrophages, where it activates JAK2/STAT3 signaling to drive M2 polarization and promote tumor progression (PMID:38415977). Upstream, IRF9 positively regulates PSMA5 expression to control macrophage polarization (PMID:39170377).

1. 2004 Medium

   Established the biochemical and oligomeric behavior of human PSMA5 in isolation, defining it as the α5 subunit that self-associates as a tetramer consistent with outer alpha-ring assembly.

   Evidence Recombinant expression, refolding, size-exclusion chromatography and dynamic light scattering of purified PSMA5

   PMID:15135414

   Open questions at the time

   • Does not demonstrate function within the assembled 20S proteasome
   • No mutagenesis defining subunit interfaces
   • In vitro reconstitution only, no cellular validation
2. 2012 Low

   Confirmed that PSMA5 exists in a native, co-immunoprecipitable protein complex in human cells, validating reagents for capturing endogenous PSMA5.

   Evidence Immunoprecipitation of endogenous and FLAG-tagged PSMA5 with anti-PSMA5 antibodies in human cell lines

   PMID:22894781

   Open questions at the time

   • Single method without identification of complex partners
   • No functional follow-up
   • Does not define stoichiometry or proteasome incorporation
3. 2019 Medium

   Linked PSMA5 to cancer cell survival and proteasome-inhibitor resistance, showing its loss reverses bortezomib resistance in prostate cancer.

   Evidence siRNA knockdown with viability, apoptosis, migration/invasion, and bortezomib resistance assays in prostate cancer cells

   PMID:30807553

   Open questions at the time

   • Mechanism connecting PSMA5 to bortezomib resistance not resolved
   • No in vivo validation
   • Single lineage, single lab
4. 2022 Medium

   Placed PSMA5 upstream of JAK/STAT signaling as an anti-apoptotic, pro-metastatic driver in lung adenocarcinoma and a determinant of cisplatin sensitivity.

   Evidence siRNA knockdown and overexpression with apoptosis/invasion assays, xenograft model, and JAK/STAT pathway Western blots

   PMID:35605971

   Open questions at the time

   • Direct molecular link between PSMA5 and JAK/STAT activation not defined
   • Whether the effect depends on proteasomal activity unknown
   • Single lab
5. 2024 Medium

   Extended PSMA5 function to intercellular signaling, showing tumor exosomal PSMA5 reprograms macrophages toward M2 polarization via JAK2/STAT3 to promote HCC progression.

   Evidence Exosome internalization assays, macrophage co-culture, siRNA knockdown, JAK2/STAT3 Western blots, and xenograft model in HCC

   PMID:38415977

   Open questions at the time

   • Mechanism of PSMA5 sorting into exosomes unknown
   • How exosomal PSMA5 engages JAK2/STAT3 in recipient cells not resolved
   • Single lab
6. 2024 Low

   Positioned IRF9 upstream of PSMA5 in controlling macrophage polarization and inflammatory cytokine output.

   Evidence Bioinformatics correlation, IRF9 knockdown in RAW264.7 macrophages, cytokine measurement, and a CIA mouse model

   PMID:39170377

   Open questions at the time

   • No direct promoter or binding assay confirming transcriptional regulation of PSMA5 by IRF9
   • Correlative pathway placement
   • Single lab

• It remains unresolved whether the cancer- and macrophage-related JAK/STAT phenotypes depend on PSMA5's canonical proteasome function or a moonlighting activity, and how exosomal PSMA5 is sorted and acts in recipient cells.
• No mechanism linking proteasomal degradation activity to JAK/STAT signaling
• No structural or biochemical account of exosomal packaging
• Direct PSMA5 interactors in signaling contexts not identified