title: Thymoproteasome: probable role in generating positively selecting peptides.
abstract: The proteasome is the protein destroying machinery conserved in all eukaryotes and plays essential roles in various cellular processes. Apart from the conserved 'standard' proteasome, a special type of proteasome called 'immunoproteasome' exists in vertebrates for better presentation of antigenic peptides on MHC class I molecules. Recently, another vertebrate-specific proteasome was discovered in the thymus. This 'thymoproteasome' has a novel catalytic subunit 'beta5t' with unusual enzymatic activity and is expressed exclusively in cortical thymic epithelial cells (cTECs), which catalyze positive selection of developing thymocytes. beta5t-deficient mice exhibit severe impairment in CD8(+) T cell development. These findings suggest that cTECs are quite unique cells capable of presenting a unique set of self-peptides that are not seen in other cells and are required for positive selection of CD8(+) T cells.
authors.affiliation: Laboratory of Protein Metabolism, Graduate School of Pharmaceutical Sciences, The University of Tokyo, Tokyo 113-0033, Japan. smurata@mol.f.u-tokyo.ac.jp
authors.forename: Shigeo
authors.initials: S
authors.lastname: Murata
authors.forename: Yousuke
authors.initials: Y
authors.lastname: Takahama
authors.forename: Keiji
authors.initials: K
authors.lastname: Tanaka
mesh_terms: D000818:Animals; D017951:Antigen Presentation; D018414:CD8-Positive T-Lymphocytes / Q000201:enzymology / Q000276:immunology; D004847:Epithelial Cells / Q000201:enzymology; D015395:Histocompatibility Antigens Class I / Q000378:metabolism; D006801:Humans; D051379:Mice; D010455:Peptides / Q000276:immunology* / Q000378:metabolism; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism*; D013950:Thymus Gland / Q000201:enzymology / Q000276:immunology*
chemical_list: D015395:Histocompatibility Antigens Class I; D010455:Peptides; D046988:Proteasome Endopeptidase Complex