title: Thymoproteasome: role in thymic selection and clinical significance as a diagnostic marker for thymic epithelial tumors.
abstract: The thymoproteasome is a specialized type of proteasomes expressed exclusively in the thymic cortex. It has a unique catalytic subunit β5t with unusual enzymatic activity. The thymoproteasome exhibits lower chymotrypsin-like activity than other forms of proteasomes such as constitutive proteasomes and immunoproteasomes. Its cleavage specificity appears uniquely suited for the production of peptides that mediate positive selection of CD8⁺ T cells. Similar to major histocompatibility complex molecules and T/B-cell receptors, the thymoproteasome occurs only in jawed vertebrates, suggesting that it evolved concomitant with the cardinal elements of adaptive immunity. β5t can be used as a marker in the differential diagnosis of thymic tumors. It is expressed in most type B and some type AB thymomas, but not in type A thymoma, thymic carcinoma, or tumors of non-thymic epithelial origin.
authors: Department of Pathology, Hokkaido University Graduate School of Medicine, Sapporo, Japan, tomaruu@med.hokudai.ac.jp.
authors: Utano
authors: U
authors: Tomaru
authors: Masanori
authors: M
authors: Kasahara
mesh_terms: D000818:Animals; D014408:Biomarkers, Tumor / Q000378:metabolism; D018414:CD8-Positive T-Lymphocytes / Q000276:immunology; D060966:Clonal Selection, Antigen-Mediated; D003937:Diagnosis, Differential; D006801:Humans; D009928:Organ Specificity; D010446:Peptide Fragments / Q000378:metabolism; D046988:Proteasome Endopeptidase Complex / Q000276:immunology* / Q000378:metabolism; D011948:Receptors, Antigen, T-Cell / Q000378:metabolism; D013379:Substrate Specificity; D013950:Thymus Gland / Q000276:immunology*; D013953:Thymus Neoplasms / Q000175:diagnosis / Q000276:immunology*
chemical_list: D014408:Biomarkers, Tumor; D010446:Peptide Fragments; D011948:Receptors, Antigen, T-Cell; C520308:PSMB11 protein, human; D046988:Proteasome Endopeptidase Complex