title: Allelic differences in the relationship between proteasome activity and MHC class I peptide loading.
abstract: MHC class I molecules are cell surface glycoproteins that play a pivotal role in the response to intracellular pathogens. The loading of MHC class I molecules with antigenic substrates takes place in the endoplasmic reticulum. This requires a functional TAP transporter, which translocates peptides into the endoplasmic reticulum from the cytosol. The generation of antigenic peptides from polypeptide precursors is thought to be mediated in the cytosol by the proteasome. Previously, we have demonstrated that inhibiting the proteasome with the specific covalent inhibitor lactacystin results in a direct reduction of peptide-loaded MHC class I molecules. This indicates that the proteasome is the limiting step in the MHC class I pathway. In this study we use isoelectric focusing to demonstrate that two related MHC class I alleles, HLA-A3 and HLA-A11, as well as HLA-B35 do not follow this behavior. In contrast to other class I alleles expressed by the same cells, these alleles are loaded with peptides and mature normally when proteasome activity is severely inhibited. Our observations highlight a new level of diversity in the MHC class I system and indicate that there are allele-specific differences in the linkage between proteasome activity and MHC class I peptide loading.
authors.affiliation: Division Cellular Biochemistry, Netherlands Cancer Institute, Amsterdam.
authors.forename: A M
authors.initials: AM
authors.lastname: Benham
authors.forename: M
authors.initials: M
authors.lastname: Grommé
authors.forename: J
authors.initials: J
authors.lastname: Neefjes
mesh_terms: D000483:Alleles; D002460:Cell Line; D003546:Cysteine Endopeptidases / Q000187:drug effects / Q000276:immunology / Q000378:metabolism*; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology; D015234:HLA-A Antigens / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D059870:HLA-A11 Antigen; D015791:HLA-A3 Antigen / Q000235:genetics / Q000276:immunology; D006367:HeLa Cells; D015395:Histocompatibility Antigens Class I / Q000235:genetics* / Q000276:immunology*; D006801:Humans; D007525:Isoelectric Focusing; D009097:Multienzyme Complexes / Q000187:drug effects / Q000276:immunology / Q000378:metabolism*; D010455:Peptides / Q000276:immunology / Q000378:metabolism*; D046988:Proteasome Endopeptidase Complex
chemical_list: D015853:Cysteine Proteinase Inhibitors; D015234:HLA-A Antigens; D059870:HLA-A11 Antigen; D015791:HLA-A3 Antigen; D015395:Histocompatibility Antigens Class I; D009097:Multienzyme Complexes; D010455:Peptides; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex