PSMA2
Available structures PDB Ortholog search: PDBe RCSB List of PDB id codes 4R3O, 4R67, 5A0Q
Identifiers
Aliases	PSMA2, HC3, MU, PMSA2, PSC2, proteasome subunit alpha 2, proteasome 20S subunit alpha 2
External IDs	OMIM: 176842 MGI: 104885 HomoloGene: 2081 GeneCards: PSMA2
Gene location (Human) Chr. Chromosome 7 (human)[1] Band 7p14.1 Start 42,916,828 bp[1] End 42,932,185 bp[1]
Gene location (Mouse) Chr. Chromosome 13 (mouse)[2] Band 13|13 A1 Start 14,787,825 bp[2] End 14,848,821 bp[2]
RNA expression pattern Bgee Human Mouse (ortholog) Top expressed in ganglionic eminence gastrocnemius muscle islet of Langerhans right adrenal gland endometrium body of pancreas right lobe of liver left adrenal gland monocyte appendix Top expressed in somite primitive streak endocardial cushion medial ganglionic eminence maxillary prominence hand facial motor nucleus abdominal wall renal corpuscle cumulus cell More reference expression data BioGPS More reference expression data
Gene ontology Molecular function endopeptidase activity peptidase activity protein binding threonine-type endopeptidase activity hydrolase activity Cellular component cytoplasm cytosol nucleoplasm proteasome complex extracellular exosome nucleus proteasome core complex extracellular region secretory granule lumen ficolin-1-rich granule lumen proteasome core complex, alpha-subunit complex P-body Biological process regulation of cellular amino acid metabolic process antigen processing and presentation of exogenous peptide antigen via MHC class I, TAP-dependent regulation of mRNA stability ubiquitin-dependent protein catabolic process positive regulation of canonical Wnt signaling pathway response to virus protein polyubiquitination stimulatory C-type lectin receptor signaling pathway tumor necrosis factor-mediated signaling pathway proteolysis MAPK cascade Fc-epsilon receptor signaling pathway NIK/NF-kappaB signaling anaphase-promoting complex-dependent catabolic process proteolysis involved in cellular protein catabolic process T cell receptor signaling pathway negative regulation of canonical Wnt signaling pathway proteasome-mediated ubiquitin-dependent protein catabolic process Wnt signaling pathway, planar cell polarity pathway negative regulation of G2/M transition of mitotic cell cycle protein deubiquitination SCF-dependent proteasomal ubiquitin-dependent protein catabolic process neutrophil degranulation transmembrane transport regulation of transcription from RNA polymerase II promoter in response to hypoxia post-translational protein modification regulation of hematopoietic stem cell differentiation proteasomal protein catabolic process proteasomal ubiquitin-independent protein catabolic process interleukin-1-mediated signaling pathway regulation of mitotic cell cycle phase transition Sources:Amigo / QuickGO
Orthologs Species Human Mouse Entrez 5683 19166 Ensembl ENSG00000106588 ENSMUSG00000015671 UniProt P25787 P49722 RefSeq (mRNA) NM_002787 NM_008944 RefSeq (protein) NP_002778 NP_032970 Location (UCSC) Chr 7: 42.92 – 42.93 Mb Chr 13: 14.79 – 14.85 Mb PubMed search [3] [4]
Wikidata
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Proteasome subunit alpha type-2 is a protein that in humans is encoded by the PSMA2 gene.^[5][6][7] This protein is one of the 17 essential subunits (alpha subunits 1–7, constitutive beta subunits 1–7, and inducible subunits including beta1i, beta2i, beta5i) that contributes to the complete assembly of 20S proteasome complex.

Structure

Function

Crystal structures of isolated 20S proteasome complex demonstrate that the two rings of beta subunits form a proteolytic chamber and maintain all their active sites of proteolysis within the chamber.^[10] Concomitantly, the rings of alpha subunits form the entrance for substrates entering the proteolytic chamber. In an inactivated 20S proteasome complex, the gate into the internal proteolytic chamber are guarded by the N-terminal tails of specific alpha-subunit.^[11][12] The proteolytic capacity of 20S core particle (CP) can be activated when CP associates with one or two regulatory particles (RP) on one or both side of alpha rings. These regulatory particles include 19S proteasome complexes, 11S proteasome complex, etc. Following the CP-RP association, the confirmation of certain alpha subunits will change and consequently cause the opening of substrate entrance gate. Besides RPs, the 20S proteasomes can also be effectively activated by other mild chemical treatments, such as exposure to low levels of sodium dodecylsulfate (SDS) or NP-14.^[12][13] The eukaryotic proteasome recognized degradable proteins, including damaged proteins for protein quality control purpose or key regulatory protein components for dynamic biological precesses. An essential function of a modified proteasome, the immunoproteasome, is the processing of class I MHC peptides.

As a component of alpha ring, Proteasome subunit alpha type-2 contributes to the formation of heptameric alpha rings and substrate entrance gate. Importantly, alpha2 subunit plays a critical role in the assembly of 19S base and 20S. In a study using Saccharomyces cerevisiae proteasome core particle 20S and regulatory particle 19S (similar to human proteasome) base component to delineate the binding process between 19S and 20S, evidences showed that one 19S subunit, Rpt6, can insert its tail into the pocket formed by alpha2 and alpha3 subunit, facilitating the complex formation between 20S and 19S base component.^[14]

Clinical significance

The proteasome and its subunits are of clinical significance for at least two reasons: (1) a compromised complex assembly or a dysfunctional proteasome can be associated with the underlying pathophysiology of specific diseases, and (2) they can be exploited as drug targets for therapeutic interventions. More recently, more effort has been made to consider the proteasome for the development of novel diagnostic markers and strategies. An improved and comprehensive understanding of the pathophysiology of the proteasome should lead to clinical applications in the future.

The proteasomes form a pivotal component for the ubiquitin–proteasome system (UPS) ^[15] and corresponding cellular Protein Quality Control (PQC). Protein ubiquitination and subsequent proteolysis and degradation by the proteasome are important mechanisms in the regulation of the cell cycle, cell growth and differentiation, gene transcription, signal transduction and apoptosis.^[16] Subsequently, a compromised proteasome complex assembly and function lead to reduced proteolytic activities and the accumulation of damaged or misfolded protein species. Such protein accumulation may contribute to the pathogenesis and phenotypic characteristics in neurodegenerative diseases,^[17][18] cardiovascular diseases,^[19][20][21] inflammatory responses and autoimmune diseases,^[22] and systemic DNA damage responses leading to malignancies.^[23]

Several experimental and clinical studies have indicated that aberrations and deregulations of the UPS contribute to the pathogenesis of several neurodegenerative and myodegenerative disorders, including Alzheimer's disease,^[24] Parkinson's disease^[25] and Pick's disease,^[26] Amyotrophic lateral sclerosis (ALS),^[26] Huntington's disease,^[25] Creutzfeldt–Jakob disease,^[27] and motor neuron diseases, polyglutamine (PolyQ) diseases, Muscular dystrophies^[28] and several rare forms of neurodegenerative diseases associated with dementia.^[29] As part of the ubiquitin–proteasome system (UPS), the proteasome maintains cardiac protein homeostasis and thus plays a significant role in cardiac ischemic injury,^[30] ventricular hypertrophy^[31] and heart failure.^[32] Additionally, evidence is accumulating that the UPS plays an essential role in malignant transformation. UPS proteolysis plays a major role in responses of cancer cells to stimulatory signals that are critical for the development of cancer. Accordingly, gene expression by degradation of transcription factors, such as p53, c-jun, c-Fos, NF-κB, c-Myc, HIF-1α, MATα2, STAT3, sterol-regulated element-binding proteins and androgen receptors are all controlled by the UPS and thus involved in the development of various malignancies.^[33] Moreover, the UPS regulates the degradation of tumor suppressor gene products such as adenomatous polyposis coli (APC) in colorectal cancer, retinoblastoma (Rb). and von Hippel–Lindau tumor suppressor (VHL), as well as a number of proto-oncogenes (Raf, Myc, Myb, Rel, Src, Mos, Abl). The UPS is also involved in the regulation of inflammatory responses. This activity is usually attributed to the role of proteasomes in the activation of NF-κB which further regulates the expression of pro inflammatory cytokines such as TNF-α, IL-β, IL-8, adhesion molecules (ICAM-1, VCAM-1, P-selectin) and prostaglandins and nitric oxide (NO).^[22] Additionally, the UPS also plays a role in inflammatory responses as regulators of leukocyte proliferation, mainly through proteolysis of cyclines and the degradation of CDK inhibitors.^[34] Lastly, autoimmune disease patients with SLE, Sjögren syndrome and rheumatoid arthritis (RA) predominantly exhibit circulating proteasomes which can be applied as clinical biomarkers.^[35]

References

Further reading