title: Transporter (TAP)-independent processing of a multiple membrane-spanning protein, the Epstein-Barr virus latent membrane protein 2.
abstract: Antigen presentation to CD8+ cytotoxic T lymphocytes (CTL) usually involves proteolytic cleavage of antigen in the cytosol and the delivery of epitope peptides onto major histocompatibility complex class I molecules in the endoplasmic reticulum (ER) via the heterodimeric peptide transporter TAP1/TAP2. In the few exceptional cases where TAP-independent presentation of an endogenously expressed protein has been observed, the epitope-containing domain of the protein either has naturally accessed or has been directed into the ER lumen where it is thought to become susceptible to ER proteases. Here, we describe a novel example of TAP-independent processing involving the Epstein-Barr virus (EBV) latent membrane protein LMP2, a multiple membrane-spanning protein with minimal projection into the ER. Expression of LMP2 in the TAP-T2 cell line, whether from the resident EBV genome or from a recombinant vaccinia virus vector vacc-LMP2, rendered the cells sensitive to recognition by CTL clones specific for two HLA-A2.1-restricted peptide epitopes, LMP2 329-337 or 426-434. Vacc-LMP2-mediated sensitization to lysis required expression of the antigen de novo in T2 cells and was blocked by brefeldin A. In the same experiments, two other EBV-specific CTL epitopes, one derived from LMP2 but restricted through a different HLA allele (A11), the other restricted through A2.1 but derived from a different viral protein (BMLF1), did not display TAP-independent processing. The results are discussed in relation to the unusual topology of LMP2 in the membrane and the position of the epitope peptides within that structure.
authors.affiliation: CRC Institute for Cancer Studies, University of Birmingham, GB.
authors.forename: S P
authors.initials: SP
authors.lastname: Lee
authors.forename: W A
authors.initials: WA
authors.lastname: Thomas
authors.forename: N W
authors.initials: NW
authors.lastname: Blake
authors.forename: A B
authors.initials: AB
authors.lastname: Rickinson
mesh_terms: D018528:ATP-Binding Cassette Transporters / Q000235:genetics / Q000378:metabolism*; D000595:Amino Acid Sequence; D017951:Antigen Presentation; D000956:Antigens, Viral / Q000276:immunology; D002051:Burkitt Lymphoma / Q000276:immunology / Q000378:metabolism; D002461:Cell Line, Transformed; D000939:Epitopes / Q000276:immunology; D005822:Genetic Vectors / Q000276:immunology; D015789:HLA-A2 Antigen / Q000276:immunology; D004854:Herpesvirus 4, Human / Q000276:immunology* / Q000378:metabolism; D006801:Humans; D008565:Membrane Proteins / Q000276:immunology / Q000378:metabolism*; D008969:Molecular Sequence Data; D013602:T-Lymphocytes, Cytotoxic / Q000276:immunology; D014407:Tumor Cells, Cultured; D014616:Vaccinia virus / Q000235:genetics / Q000276:immunology; D014763:Viral Matrix Proteins / Q000276:immunology / Q000378:metabolism*
chemical_list: D018528:ATP-Binding Cassette Transporters; D000956:Antigens, Viral; C037662:EBV-associated membrane antigen, Epstein-Barr virus; D000939:Epitopes; D015789:HLA-A2 Antigen; D008565:Membrane Proteins; D014763:Viral Matrix Proteins