title: Overexpression of the proteasome subunits LMP2, LMP7, and MECL-1, but not PA28 alpha/beta, enhances the presentation of an immunodominant lymphocytic choriomeningitis virus T cell epitope.
abstract: The proteasome is a large protease complex that generates most of the peptide ligands of MHC class I molecules either in their final form or in the form of N-terminally extended precursors. Upon the stimulation of cells with IFN-gamma, three constitutively expressed subunits of the 20S proteasome are replaced by the inducible subunits LMP2 (low-molecular mass polypeptide 2), LMP7, and MECL-1 (multicatalytic endopeptidase complex-like-1) to form so-called immunoproteasomes. We show in this study that overexpression of these three subunits in triple transfectants led to a marked enhancement in the H-2Ld-restricted presentation of the immunodominant nonameric epitope NP118, which is derived from the nucleoprotein (NP) of lymphocytic choriomeningitis virus. Overexpression of the alpha and beta subunits of the IFN-gamma-inducible proteasome regulator PA28, in contrast, did not have a comparable effect. In vitro, immunoproteasomes as compared with constitutive proteasomes generated higher amounts of 11- and 12-mer fragments containing the NP118 epitope. These are likely to be cytosolic precursors of NP118, as a proline anchor residue in the second position of NP118 may interfere with TAP-mediated transport of the nonameric epitope itself. In conclusion, we provide evidence that up-regulation of the three inducible subunits, LMP2, LMP7, and MECL-1, can result in a marked improvement of Ag presentation and that, depending on the epitope, PA28 and immunoproteasomes may differentially affect Ag processing.
authors.affiliation: Research Department, Cantonal Hospital St. Gall, St. Gallen, Switzerland.
authors.forename: K
authors.initials: K
authors.lastname: Schwarz
authors.forename: M
authors.initials: M
authors.lastname: van Den Broek
authors.forename: S
authors.initials: S
authors.lastname: Kostka
authors.forename: R
authors.initials: R
authors.lastname: Kraft
authors.forename: A
authors.initials: A
authors.lastname: Soza
authors.forename: G
authors.initials: G
authors.lastname: Schmidtke
authors.forename: P M
authors.initials: PM
authors.lastname: Kloetzel
authors.forename: M
authors.initials: M
authors.lastname: Groettrup
mesh_terms: D000276:Adjuvants, Immunologic / Q000096:biosynthesis* / Q000235:genetics / Q000502:physiology; D000595:Amino Acid Sequence; D000818:Animals; D017951:Antigen Presentation / Q000235:genetics / Q000276:immunology*; D001324:Autoantigens; D002460:Cell Line; D003546:Cysteine Endopeptidases / Q000096:biosynthesis* / Q000235:genetics / Q000276:immunology; D003600:Cytosol / Q000276:immunology / Q000378:metabolism; D018984:Epitopes, T-Lymphocyte / Q000235:genetics / Q000378:metabolism*; D006183:H-2 Antigens / Q000096:biosynthesis / Q000235:genetics; D064532:Histocompatibility Antigen H-2D; D006825:Hybridomas; D016056:Immunodominant Epitopes / Q000235:genetics / Q000378:metabolism*; D008217:Lymphocytic choriomeningitis virus / Q000235:genetics / Q000276:immunology*; D051379:Mice; D008807:Mice, Inbred BALB C; D008969:Molecular Sequence Data; D009097:Multienzyme Complexes / Q000096:biosynthesis* / Q000235:genetics / Q000276:immunology; D009698:Nucleoproteins / Q000096:biosynthesis / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D010446:Peptide Fragments / Q000096:biosynthesis / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D046988:Proteasome Endopeptidase Complex; D014176:Protein Biosynthesis; D011498:Protein Precursors / Q000096:biosynthesis / Q000235:genetics; D011506:Proteins / Q000235:genetics / Q000276:immunology; D014162:Transfection; D014764:Viral Proteins / Q000096:biosynthesis / Q000235:genetics / Q000276:immunology / Q000378:metabolism
chemical_list: D000276:Adjuvants, Immunologic; D001324:Autoantigens; D018984:Epitopes, T-Lymphocyte; D006183:H-2 Antigens; D064532:Histocompatibility Antigen H-2D; D016056:Immunodominant Epitopes; C099558:Ki antigen; D009097:Multienzyme Complexes; D009698:Nucleoproteins; D010446:Peptide Fragments; D011498:Protein Precursors; D011506:Proteins; D014764:Viral Proteins; C094246:nucleoprotein peptide 118-126, lymphocytic choriomeningitis virus; C071313:LMP-2 protein; D003546:Cysteine Endopeptidases; C077436:LMP7 protein; D046988:Proteasome Endopeptidase Complex; C490920:Psmb10 protein, mouse; C486213:Psme1 protein, mouse