title: Expression of the proteasome activator PA28 rescues the presentation of a cytotoxic T lymphocyte epitope on melanoma cells.
abstract: The proteasome system represents a major source of HLA class I- presented peptides exposed to CTLs. Stimulation of cells with IFN-gamma instantly induces the expression of the proteasome immunosubunits as well as the proteasome activator PA28. These proteins have been shown to optimize class I antigen presentation of several viral CTL epitopes; however, their contribution to tumor antigen processing remains poorly understood. Here, we analyzed the generation of an HLA-A*0201-presented epitope derived from the melanoma antigen tyrosinase-related protein 2 (TRP2). Melanoma cells that lacked the IFN-gamma-inducible proteasome activator PA28 and immunoproteasomes did not display the TRP2(360-368) epitope to specific CTLs. Our experiments demonstrate that epitope presentation correlated with the presence of PA28 and could be completely rescued by restoration of PA28 expression. In vitro digestion of TRP2 polypeptides with 20S proteasomes confirmed that PA28 is essential for epitope liberation. Thus, our experiments indicate that PA28 provides the threshold for CTL recognition of this epitope. Importantly, processing of a second TRP2-derived epitope, TRP2(288-296), was diminished in IFN-gamma-treated cells, even in the absence of immunoproteasome up-regulation. Therefore, the reported IFN-gamma-induced self-regulation of epitopes may not necessarily be a consequence of immunoproteasomes as suggested previously.
authors.affiliation: Skin Cancer Unit of German Cancer Research Center, University of Heidelberg, Theodor Kutzer Ufer 1, 68135 Mannheim, Germany.
authors.forename: Yuansheng
authors.initials: Y
authors.lastname: Sun
authors.forename: Alice J A M
authors.initials: AJ
authors.lastname: Sijts
authors.forename: Mingxia
authors.initials: M
authors.lastname: Song
authors.forename: Katharina
authors.initials: K
authors.lastname: Janek
authors.forename: Alexander K
authors.initials: AK
authors.lastname: Nussbaum
authors.forename: Sylvie
authors.initials: S
authors.lastname: Kral
authors.forename: Markus
authors.initials: M
authors.lastname: Schirle
authors.forename: Stefan
authors.initials: S
authors.lastname: Stevanovic
authors.forename: Annette
authors.initials: A
authors.lastname: Paschen
authors.forename: Hansjörg
authors.initials: H
authors.lastname: Schild
authors.forename: Peter-M
authors.initials: PM
authors.lastname: Kloetzel
authors.forename: Dirk
authors.initials: D
authors.lastname: Schadendorf
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D017951:Antigen Presentation / Q000276:immunology*; D019556:COS Cells; D018984:Epitopes, T-Lymphocyte / Q000276:immunology*; D015234:HLA-A Antigens / Q000276:immunology; D015789:HLA-A2 Antigen; D006801:Humans; D007371:Interferon-gamma / Q000276:immunology / Q000378:metabolism; D019746:Intramolecular Oxidoreductases / Q000096:biosynthesis / Q000235:genetics / Q000276:immunology*; D020014:K562 Cells; D008545:Melanoma / Q000276:immunology*; D008969:Molecular Sequence Data; D009124:Muscle Proteins; D010446:Peptide Fragments / Q000096:biosynthesis / Q000276:immunology; D046988:Proteasome Endopeptidase Complex; D014176:Protein Biosynthesis; D011506:Proteins / Q000235:genetics / Q000276:immunology*; D013602:T-Lymphocytes, Cytotoxic / Q000276:immunology*; D014162:Transfection; D014407:Tumor Cells, Cultured
chemical_list: D018984:Epitopes, T-Lymphocyte; D015234:HLA-A Antigens; C435939:HLA-A*02:01 antigen; D015789:HLA-A2 Antigen; D009124:Muscle Proteins; C085047:PSME1 protein, human; D010446:Peptide Fragments; D011506:Proteins; D007371:Interferon-gamma; D046988:Proteasome Endopeptidase Complex; D019746:Intramolecular Oxidoreductases; C042501:dopachrome isomerase