title: Coordinated dual cleavages induced by the proteasome regulator PA28 lead to dominant MHC ligands.
abstract: The eukaryotic 20S proteasome is known to associate with the IFN gamma-inducible regulator PA28. We analyzed the kinetics of product generation by 20S proteasomes with and without PA28. In the absence of PA28, the 20S proteasome rapidly generates peptides that have been cleaved only once, while internal fragments accumulate only slowly. In the presence of PA28, products generated by two flanking cleavages appear immediately as main products while the generation of single-cleavage products is strongly reduced. Kinetic data support a PA28-induced, coordinated double-cleavage mechanism. In particular, degradation of peptides derived from mouse cytomegalovirus pp89 and JAK1 kinase in the presence of PA28 leads to strongly enhanced production of the respective major histocompatibility complex ligands and potential precursors. These results show that PA28 profoundly alters the cleavage mechanism of the proteasome and appears to optimize the generation of dominant T-cell epitopes.
authors.affiliation: Department of Tumorvirus-Immunology, German Cancer Research Center, Heidelberg, Federal Republic of Germany.
authors.forename: T P
authors.initials: TP
authors.lastname: Dick
authors.forename: T
authors.initials: T
authors.lastname: Ruppert
authors.forename: M
authors.initials: M
authors.lastname: Groettrup
authors.forename: P M
authors.initials: PM
authors.lastname: Kloetzel
authors.forename: L
authors.initials: L
authors.lastname: Kuehn
authors.forename: U H
authors.initials: UH
authors.lastname: Koszinowski
authors.forename: S
authors.initials: S
authors.lastname: Stevanović
authors.forename: H
authors.initials: H
authors.lastname: Schild
authors.forename: H G
authors.initials: HG
authors.lastname: Rammensee
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001324:Autoantigens; D002851:Chromatography, High Pressure Liquid; D000939:Epitopes / Q000378:metabolism; D005260:Female; D005347:Fibroblasts / Q000737:chemistry / Q000201:enzymology; D006649:Histocompatibility Antigens / Q000378:metabolism*; D006801:Humans; D007700:Kinetics; D008024:Ligands; D013058:Mass Spectrometry; D051379:Mice; D008969:Molecular Sequence Data; D009124:Muscle Proteins; D010455:Peptides / Q000378:metabolism; D010920:Placenta / Q000737:chemistry; D011247:Pregnancy; D046988:Proteasome Endopeptidase Complex; D011506:Proteins / Q000502:physiology*; D013379:Substrate Specificity; D013601:T-Lymphocytes / Q000201:enzymology / Q000276:immunology
chemical_list: D001324:Autoantigens; D000939:Epitopes; D006649:Histocompatibility Antigens; C099558:Ki antigen; D008024:Ligands; D009124:Muscle Proteins; C085047:PSME1 protein, human; D010455:Peptides; D011506:Proteins; D046988:Proteasome Endopeptidase Complex