title: Allele-selective effect of PA28 in MHC class I antigen processing.
abstract: PA28 is an IFN-gamma-inducible proteasome activator and its genetic ablation causes complete loss of processing of certain Ags, but not all of them. The reason why this occurs and how PA28 influences the formation of peptide repertoires for MHC class I molecules remains unknown. In this study, we show the allele-specific role of PA28 in Ag processing. Retrovirus-transduced overexpression of PA28alpha decreased expression of K(d) (D(d)) while it increased K(b) and L(d) on the cell surface. By contrast, overexpression of PA28alphaDeltaC5, a mutant carrying a deletion of its five C-terminal residues and capable of attenuating the activity of endogenous PA28, produced the opposite effect on expression of those MHC class I molecules. Moreover, knockdown of both PA28alpha and beta by small-interfering RNA profoundly augmented expression of K(d) and D(d), but not of L(d), on the cell surface. Finally, we found that PA28-associated proteasome preferentially digested within epitopic sequences of K(d), although correct C-terminal flankings were removed, which in turn hampered production of K(d) ligands. Our results indicate that whereas PA28 negatively influences processing of K(d) (D(d)) ligands, thereby, down-regulating Ag presentation by those MHC class I molecules, it also efficiently produces K(b) (L(d)) epitopes, leading to up-regulation of the MHC molecules.
authors.affiliation: Laboratory for Immunochaperones, Research Center for Allergy and Immunology, RIKEN Yokohama Institute, Tsurumi, Yokohama, Japan.
authors.forename: Taketoshi
authors.initials: T
authors.lastname: Yamano
authors.forename: Hidetoshi
authors.initials: H
authors.lastname: Sugahara
authors.forename: Shusaku
authors.initials: S
authors.lastname: Mizukami
authors.forename: Shigeo
authors.initials: S
authors.lastname: Murata
authors.forename: Tomoki
authors.initials: T
authors.lastname: Chiba
authors.forename: Keiji
authors.initials: K
authors.lastname: Tanaka
authors.forename: Katsuyuki
authors.initials: K
authors.lastname: Yui
authors.forename: Heiichiro
authors.initials: H
authors.lastname: Udono
mesh_terms: D000483:Alleles; D000818:Animals; D017951:Antigen Presentation / Q000276:immunology*; D002462:Cell Membrane / Q000276:immunology / Q000378:metabolism; D002478:Cells, Cultured; D000939:Epitopes / Q000276:immunology; D017353:Gene Deletion; D005786:Gene Expression Regulation; D015395:Histocompatibility Antigens Class I / Q000235:genetics / Q000276:immunology*; D019746:Intramolecular Oxidoreductases / Q000235:genetics / Q000378:metabolism; D008024:Ligands; D051379:Mice; D018345:Mice, Knockout; D009154:Mutation / Q000235:genetics; D010047:Ovalbumin / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D010446:Peptide Fragments / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D011485:Protein Binding; D011506:Proteins / Q000235:genetics / Q000276:immunology* / Q000378:metabolism*
chemical_list: D000939:Epitopes; D015395:Histocompatibility Antigens Class I; D008024:Ligands; C110366:OVA-8; D010446:Peptide Fragments; D011506:Proteins; D010047:Ovalbumin; D046988:Proteasome Endopeptidase Complex; C486213:Psme1 protein, mouse; C486214:Psme2 protein, mouse; D019746:Intramolecular Oxidoreductases