title: TAP-independent delivery of antigenic peptides to the endoplasmic reticulum: therapeutic potential and insights into TAP-dependent antigen processing.
abstract: We have taken several approaches to investigate the capacity of the secretory pathway to liberate major histocompatibility complex (MHC) class I-restricted antigenic peptides from precursor polypeptides. Cells lacking the peptide transporter (TAP) are unable to deliver peptides from cytosolic antigens to class I molecules. TAP can be bypassed by targeting peptides directly to the endoplasmic reticulum (ER) using NH2-terminal signal sequences. This results in the generation of enormous numbers of MHC class I complexes (50,000 peptides/cell), and recombinant vaccinia viruses expressing such peptides are highly immunogenic. In contrast to signal sequence-targeted peptides, peptides are liberated very inefficiently from internal locations in ER-targeted full-length proteins, indicating that the secretory pathway has a limited capacity for generating antigenic peptides from most polypeptide contexts. We have, however, identified a location in proteins from which peptides can be liberated in numerous contexts in the secretory pathway. Placing a number of different peptides at the COOH termini of a secreted protein and two proteins with type II membrane anchors resulted in their TAP-independent presentation. These findings demonstrate that the secretory compartment possesses proteases able to liberate COOH-terminal antigenic peptides from virtually any context, entirely consistent with a role for these proteases in the processing of TAP-transported antigenic peptide precursors.
authors.affiliation: Laboratory of Viral Diseases, National Institute of Allergy and Infectious Diseases, NIH, Bethesda, MD 20892-0440, USA.
authors.forename: J W
authors.initials: JW
authors.lastname: Yewdell
authors.forename: H L
authors.initials: HL
authors.lastname: Snyder
authors.forename: I
authors.initials: I
authors.lastname: Bacik
authors.forename: L C
authors.initials: LC
authors.lastname: Antón
authors.forename: Y
authors.initials: Y
authors.lastname: Deng
authors.forename: T W
authors.initials: TW
authors.lastname: Behrens
authors.forename: T
authors.initials: T
authors.lastname: Bachi
authors.forename: J R
authors.initials: JR
authors.lastname: Bennink
mesh_terms: D000071181:ATP Binding Cassette Transporter, Subfamily B, Member 2; D018528:ATP-Binding Cassette Transporters / Q000276:immunology* / Q000378:metabolism*; D000818:Animals; D017951:Antigen Presentation / Q000276:immunology*; D004721:Endoplasmic Reticulum / Q000276:immunology* / Q000378:metabolism*; D006801:Humans; D010455:Peptides / Q000276:immunology* / Q000378:metabolism*
chemical_list: D000071181:ATP Binding Cassette Transporter, Subfamily B, Member 2; D018528:ATP-Binding Cassette Transporters; D010455:Peptides; C073119:TAP1 protein, human