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.
Publication types
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Research Support, Non-U.S. Gov't
MeSH terms
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Adjuvants, Immunologic / biosynthesis*
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Adjuvants, Immunologic / genetics
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Adjuvants, Immunologic / physiology
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Amino Acid Sequence
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Animals
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Antigen Presentation / genetics
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Antigen Presentation / immunology*
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Autoantigens
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Cell Line
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Cysteine Endopeptidases / biosynthesis*
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Cysteine Endopeptidases / genetics
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Cysteine Endopeptidases / immunology
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Cytosol / immunology
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Cytosol / metabolism
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Epitopes, T-Lymphocyte / genetics
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Epitopes, T-Lymphocyte / metabolism*
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H-2 Antigens / biosynthesis
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H-2 Antigens / genetics
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Histocompatibility Antigen H-2D
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Hybridomas
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Immunodominant Epitopes / genetics
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Immunodominant Epitopes / metabolism*
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Lymphocytic choriomeningitis virus / genetics
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Lymphocytic choriomeningitis virus / immunology*
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Mice
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Mice, Inbred BALB C
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Molecular Sequence Data
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Multienzyme Complexes / biosynthesis*
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Multienzyme Complexes / genetics
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Multienzyme Complexes / immunology
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Nucleoproteins / biosynthesis
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Nucleoproteins / genetics
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Nucleoproteins / immunology
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Nucleoproteins / metabolism
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Peptide Fragments / biosynthesis
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Peptide Fragments / genetics
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Peptide Fragments / immunology
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Peptide Fragments / metabolism
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Proteasome Endopeptidase Complex
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Protein Biosynthesis*
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Protein Precursors / biosynthesis
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Protein Precursors / genetics
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Proteins / genetics
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Proteins / immunology
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Transfection
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Viral Proteins / biosynthesis
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Viral Proteins / genetics
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Viral Proteins / immunology
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Viral Proteins / metabolism
Substances
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Adjuvants, Immunologic
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Autoantigens
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Epitopes, T-Lymphocyte
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H-2 Antigens
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Histocompatibility Antigen H-2D
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Immunodominant Epitopes
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Ki antigen
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Multienzyme Complexes
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Nucleoproteins
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Peptide Fragments
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Protein Precursors
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Proteins
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Viral Proteins
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nucleoprotein peptide 118-126, lymphocytic choriomeningitis virus
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LMP-2 protein
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Cysteine Endopeptidases
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LMP7 protein
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Proteasome Endopeptidase Complex
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Psmb10 protein, mouse
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Psme1 protein, mouse