title: PA28 and the proteasome immunosubunits play a central and independent role in the production of MHC class I-binding peptides in vivo.
abstract: Proteasomes play a fundamental role in the processing of intracellular antigens into peptides that bind to MHC class I molecules for the presentation of CD8(+) T cells. Three IFN-γ-inducible catalytic proteasome (immuno)subunits as well as the IFN-γ-inducible proteasome activator PA28 dramatically accelerate the generation of a subset of MHC class I-presented antigenic peptides. To determine whether these IFN-γ-inducible proteasome components play a compounded role in antigen processing, we generated mice lacking both PA28 and immunosubunits β5i/LMP7 and β2i/MECL-1. Analyses of MHC class I cell-surface levels ex vivo demonstrated that PA28 deficiency reduced the production of MHC class I-binding peptides both in cells with and without immunosubunits, in the latter cells further decreasing an already diminished production of MHC ligands in the absence of immunoproteasomes. In contrast, the immunosubunits but not PA28 appeared to be of critical importance for the induction of CD8(+) T-cell responses to multiple dominant Influenza and Listeria-derived epitopes. Taken together, our data demonstrate that PA28 and the proteasome immunosubunits use fundamentally different mechanisms to enhance the supply of MHC class I-binding peptides; however, only the immunosubunit-imposed effects on proteolytic epitope processing appear to have substantial influence on the specificity of pathogen-specific CD8(+) T-cell responses.
authors.affiliation: Department of Infectious Diseases and Immunology, Faculty of Veterinary Medicine, University of Utrecht, Utrecht, The Netherlands.
authors.forename: Natascha
authors.initials: N
authors.lastname: de Graaf
authors.forename: Mary J G
authors.initials: MJ
authors.lastname: van Helden
authors.forename: Kathrin
authors.initials: K
authors.lastname: Textoris-Taube
authors.forename: Tomoki
authors.initials: T
authors.lastname: Chiba
authors.forename: David J
authors.initials: DJ
authors.lastname: Topham
authors.forename: Peter-Michael
authors.initials: PM
authors.lastname: Kloetzel
authors.forename: Dietmar M W
authors.initials: DM
authors.lastname: Zaiss
authors.forename: Alice J A M
authors.initials: AJ
authors.lastname: Sijts
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D015496:CD4-Positive T-Lymphocytes / Q000276:immunology; D018414:CD8-Positive T-Lymphocytes / Q000276:immunology; D002460:Cell Line; D015395:Histocompatibility Antigens Class I / Q000276:immunology*; D008024:Ligands; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D008969:Molecular Sequence Data; D010455:Peptides / Q000737:chemistry / Q000276:immunology*; D046988:Proteasome Endopeptidase Complex / Q000172:deficiency / Q000276:immunology*
chemical_list: D015395:Histocompatibility Antigens Class I; D008024:Ligands; D010455:Peptides; D046988:Proteasome Endopeptidase Complex; C486213:Psme1 protein, mouse; C486214:Psme2 protein, mouse