title: Dominant contribution of the proteasome and metalloproteinases to TAP-independent MHC-I peptide repertoire.
abstract: Tumors frequently display defects in the MHC-I antigen processing machinery, such as deficiency of the peptide transporter TAP. Interestingly, the residual peptide repertoire contains neo-antigens which are not presented by processing-proficient cells. We termed these immunogenic peptides TEIPP ('T-cell epitopes associated with impaired peptide processing') and were interested to unravel their TAP-independent processing pathways. With an array of chemical inhibitors we assessed the participation of numerous proteases to TAP-independent peptides and found that the previously described catalytic enzymes signal peptidase and furin contributed in a cell-type and MHC-I allele-specific way. In addition, a dominant role for the proteasome and metallopeptidases was observed. These findings raised the question how these proteasome products get access to MHC-I molecules. A novel TEIPP peptide-epitope that represented this intracellular route revealed that the lysosomal peptide transporter ABCB9 ('TAP-like') was dispensable for its presentation. Interestingly, prevention of endolysosomal vesicle acidification by bafilomycin enhanced the surface display of this TEIPP peptide, suggesting that this proteasome-dependent pathway intersects endolysosomes and that these antigens are merely destroyed there. In conclusion, the proteasome has a surprisingly dominant role in shaping the TAP-independent MHC-I peptide repertoire and some of these antigens might be targeted to the endocytic vesicular pathway.
authors.affiliation: Department of Clinical Oncology and Blood Transfusion, Leiden University Medical Center, 2333 ZA Leiden, The Netherlands; Graduate Program in Areas of Basic and Applied Biology, Porto, Portugal.
authors.forename: Cláudia C
authors.initials: CC
authors.lastname: Oliveira
authors.affiliation: Department of Clinical Oncology and Blood Transfusion, Leiden University Medical Center, 2333 ZA Leiden, The Netherlands.
authors.forename: Marjolein
authors.initials: M
authors.lastname: Sluijter
authors.affiliation: Department of Clinical Oncology and Blood Transfusion, Leiden University Medical Center, 2333 ZA Leiden, The Netherlands.
authors.forename: Bianca
authors.initials: B
authors.lastname: Querido
authors.affiliation: Department of Immunohematology and Blood Transfusion, Leiden University Medical Center, 2333 ZA Leiden, The Netherlands.
authors.forename: Ferry
authors.initials: F
authors.lastname: Ossendorp
authors.affiliation: Department of Clinical Oncology and Blood Transfusion, Leiden University Medical Center, 2333 ZA Leiden, The Netherlands.
authors.forename: Sjoerd H
authors.initials: SH
authors.lastname: van der Burg
authors.affiliation: Department of Clinical Oncology and Blood Transfusion, Leiden University Medical Center, 2333 ZA Leiden, The Netherlands. Electronic address: T.van_Hall@lumc.nl.
authors.forename: Thorbald
authors.initials: T
authors.lastname: van Hall
mesh_terms: D018528:ATP-Binding Cassette Transporters / Q000502:physiology; D000818:Animals; D017951:Antigen Presentation; D045744:Cell Line, Tumor; D000939:Epitopes / Q000737:chemistry / Q000276:immunology; D057809:HEK293 Cells; D015395:Histocompatibility Antigens Class I / Q000737:chemistry / Q000276:immunology*; D006801:Humans; D045726:Metalloproteases / Q000502:physiology*; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D046988:Proteasome Endopeptidase Complex / Q000502:physiology*
chemical_list: D018528:ATP-Binding Cassette Transporters; D000939:Epitopes; D015395:Histocompatibility Antigens Class I; C477327:transporter associated with antigen processing (TAP); D045726:Metalloproteases; D046988:Proteasome Endopeptidase Complex
keywords: Antigen processing; Endolysosomal vesicles; MHC-I; Proteasome; TAP-L; Transporter associated with peptide processing