title: Species-specific differences in proteasomal processing and tapasin-mediated loading influence peptide presentation by HLA-B27 in murine cells.
abstract: Expression of HLA-B27 in murine cells has been used to establish animal models for human spondyloarthritis and for antigen presentation studies, but the effects of xenogeneic HLA-B27 expression on peptide presentation are little known. The issue was addressed in this study. HLA-B27-bound peptide repertoires from human and murine cells overlapped by 75-85%, indicating that many endogenous HLA-B27 ligands are generated and presented in both species. Of 20 differentially presented peptides that were sequenced, only 40% arose from obvious inter-species protein polymorphism, suggesting that differences in antigen processing-loading accounted for many species-specific ligands. Digestion of synthetic substrates with human and murine 20 S proteasomes revealed cleavage differences that accounted for or correlated with differential expression of particular peptides. One HLA-B27 ligand found only in human cells was similarly generated in vitro by human and murine proteasomes. Differential presentation correlated with significantly decreased amounts of this ligand in human tapasin-deficient cells reconstituted with murine tapasin, indicating that species-specific interactions between HLA-B27, tapasin, and/or other proteins in the peptide-loading complex influenced presentation of this peptide. Our results indicate that differences in proteasomal specificity and in interactions involving tapasin determine differential processing and presentation of a significant number of HLA-B27 ligands in human and murine cells.
authors.affiliation: Centro de Biología Molecular Severo Ochoa (Consejo Superior de Investigaciones Científicas and Universidad Autónoma de Madrid), Facultad de Ciencias, Universidad Autónoma, 28049 Madrid, Spain.
authors.forename: Laura
authors.initials: L
authors.lastname: Sesma
authors.forename: Iñaki
authors.initials: I
authors.lastname: Alvarez
authors.forename: Miguel
authors.initials: M
authors.lastname: Marcilla
authors.forename: Alberto
authors.initials: A
authors.lastname: Paradela
authors.forename: José A
authors.initials: JA
authors.lastname: López de Castro
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D017951:Antigen Presentation; D017920:Antiporters / Q000276:immunology*; D002460:Cell Line; D003546:Cysteine Endopeptidases / Q000378:metabolism*; D015796:HLA-B27 Antigen / Q000276:immunology*; D006801:Humans; D007136:Immunoglobulins / Q000276:immunology*; D008024:Ligands; D026901:Membrane Transport Proteins; D051379:Mice; D009097:Multienzyme Complexes / Q000378:metabolism*; D010455:Peptides / Q000276:immunology* / Q000378:metabolism; D046988:Proteasome Endopeptidase Complex; D017385:Sequence Homology; D013045:Species Specificity; D014162:Transfection
chemical_list: D017920:Antiporters; D015796:HLA-B27 Antigen; D007136:Immunoglobulins; D008024:Ligands; D026901:Membrane Transport Proteins; D009097:Multienzyme Complexes; D010455:Peptides; C107762:tapasin; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex