title: Exclusive expression of proteasome subunit {beta}5t in the human thymic cortex.
abstract: The ubiquitin-proteasome pathway, which degrades intracellular proteins, is involved in numerous cellular processes, including the supply of immunocompetent peptides to the antigen presenting machinery. Proteolysis by proteasomes is conducted by three beta subunits, beta1, beta2, and beta5, of the 20S proteasome. Recently, a novel beta subunit expressed exclusively in cortical thymic epithelial cells was discovered in mice. This subunit, designated beta5t, is a component of the thymoproteasome, a specialized type of proteasomes implicated in thymic positive selection. In this study, we show that, like its mouse counterpart, human beta5t is expressed exclusively in the thymic cortex. Human beta5t was expressed in approximately 80% of cortical thymic epithelial cells and some cortical dendritic cells. Human beta5t was incorporated into proteasomes with two other catalytically active beta subunits beta1i and beta2i, forming 20S proteasomes with subunit compositions characteristic of thymoproteasomes. The present study demonstrates, for the first time, the existence of thymoproteasomes in the human thymic cortex, indicating that thymoproteasome function is likely conserved between humans and mice.
authors.affiliation: Department of Pathology, Hokkaido University Graduate School of Medicine, Sapporo, Japan. tomaruu@med.hokudai.ac.jp
authors.forename: Utano
authors.initials: U
authors.lastname: Tomaru
authors.forename: Akihiro
authors.initials: A
authors.lastname: Ishizu
authors.forename: Shigeo
authors.initials: S
authors.lastname: Murata
authors.forename: Yukiko
authors.initials: Y
authors.lastname: Miyatake
authors.forename: Sayuri
authors.initials: S
authors.lastname: Suzuki
authors.forename: Satomi
authors.initials: S
authors.lastname: Takahashi
authors.forename: Taku
authors.initials: T
authors.lastname: Kazamaki
authors.forename: Jiro
authors.initials: J
authors.lastname: Ohara
authors.forename: Tomohisa
authors.initials: T
authors.lastname: Baba
authors.forename: Sari
authors.initials: S
authors.lastname: Iwasaki
authors.forename: Kazunori
authors.initials: K
authors.lastname: Fugo
authors.forename: Noriyuki
authors.initials: N
authors.lastname: Otsuka
authors.forename: Keiji
authors.initials: K
authors.lastname: Tanaka
authors.forename: Masanori
authors.initials: M
authors.lastname: Kasahara
mesh_terms: D003713:Dendritic Cells / Q000201:enzymology; D004847:Epithelial Cells / Q000201:enzymology; D006801:Humans; D009928:Organ Specificity; D046988:Proteasome Endopeptidase Complex / Q000032:analysis*; D013950:Thymus Gland / Q000201:enzymology*; D014018:Tissue Distribution
chemical_list: C520308:PSMB11 protein, human; D046988:Proteasome Endopeptidase Complex