Selective involvement of proteasomes and cysteine proteases in MHC class I antigen presentation.
CTL recognize peptides derived from protein Ags bound to MHC-class I molecules. Proteasomes probably participate in the generation of these peptide epitopes. We investigated the role of proteasomes in the presentation of endogenously synthesized short viral proteins. To this end, we employed proteasome and cysteine protease inhibitors and two closely related recombinant vaccinia viruses that code for 17- and 19-amino acid-long products encompassing murine CMV 9pp89 epitope. Presentation of both minigene products required processing to shorter peptides and was independent of ubiquitination. Proteasomes were necessary for processing the 17-mer product, and cysteine proteases were not required. In contrast, the 19-mer product could be processed in parallel either by proteasomes or by cysteine proteases independently. These results highlight the diversity of alternative processing pathways even for short peptidic Ags, provide evidence for the involvement of cysteine proteases in MHC class I presentation, and show that cleavage by cysteine proteases is governed by sequences flanking the epitope.
López
D
D
Centro Nacional de Biología Fundamental, Instituto de Salud Carlos III, Madrid, Spain.
Del Val
M
M
D000111:Acetylcysteine / Q000031:analogs & derivatives / Q000494:pharmacology; D000595:Amino Acid Sequence; D000818:Animals; D017951:Antigen Presentation / Q000187:drug effects / Q000235:genetics; D002460:Cell Line; D003546:Cysteine Endopeptidases / Q000276:immunology*; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology; D003587:Cytomegalovirus / Q000235:genetics; D006513:Hepatitis B e Antigens / Q000235:genetics; D015395:Histocompatibility Antigens Class I / Q000378:metabolism*; D017874:Immediate-Early Proteins / Q000235:genetics; D016056:Immunodominant Epitopes / Q000235:genetics; D051379:Mice; D008807:Mice, Inbred BALB C; D008969:Molecular Sequence Data; D009097:Multienzyme Complexes / Q000276:immunology*; D016254:Mutagenesis, Insertional; D046988:Proteasome Endopeptidase Complex; D013602:T-Lymphocytes, Cytotoxic / Q000201:enzymology / Q000276:immunology; D014616:Vaccinia virus / Q000235:genetics / Q000276:immunology
D015853:Cysteine Proteinase Inhibitors; D006513:Hepatitis B e Antigens; D015395:Histocompatibility Antigens Class I; D017874:Immediate-Early Proteins; D016056:Immunodominant Epitopes; D009097:Multienzyme Complexes; C052612:cytomegalovirus immediate early phosphoprotein pp89; C067713:lactacystin; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex; D000111:Acetylcysteine