Rate of antigen degradation by the ubiquitin-proteasome pathway influences MHC class I presentation.
The effect on MHC class I Ag presentation of enhancing a protein's rate of degradation by the ubiquitin-proteasome pathway was investigated. In extracts of mouse B-lymphoblasts and reticulocytes, as in rabbit reticulocytes, proteins with acidic or basic N-termini are conjugated to ubiquitin and degraded by the 26S proteasome very rapidly. We found that the rate of MHC class I presentation of microinjected beta-galactosidase was enhanced when this antigenic protein was modified with such a destabilizing amino-terminal residue. This enhanced presentation was inhibited by blocking potential ubiquitination sites on the protein through methylation of amino groups and by peptide aldehyde inhibitors of the proteasome. Furthermore, in B lymphoblast cell extracts, the rapid degradation of these beta-galactosidase constructs required ATP and ubiquitin and was blocked by inhibitors of proteasomes. Their rates of degradation in extracts correlated with their rates of class I Ag presentation in vivo. These results indicate that ubiquitin conjugation is a key rate-limiting step in Ag presentation and provide further evidence for a critical role of ubiquitin and the 26S proteasome in generating MHC class I-presented peptides.
Grant
E P
EP
Department of Pathology, Harvard Medical School, Boston, MA 02115, USA.
Michalek
M T
MT
Goldberg
A L
AL
Rock
K L
KL
D000595:Amino Acid Sequence; D000818:Animals; D017951:Antigen Presentation / Q000187:drug effects / Q000276:immunology*; D002460:Cell Line; D004791:Enzyme Inhibitors / Q000494:pharmacology; D015395:Histocompatibility Antigens Class I / Q000276:immunology*; D008247:Lysosomes / Q000187:drug effects / Q000201:enzymology; D008745:Methylation; D051379:Mice; D010447:Peptide Hydrolases / Q000187:drug effects / Q000502:physiology*; D046988:Proteasome Endopeptidase Complex; D013347:Subcellular Fractions / Q000201:enzymology / Q000276:immunology; D013379:Substrate Specificity; D014452:Ubiquitins / Q000187:drug effects / Q000502:physiology*; D001616:beta-Galactosidase / Q000502:physiology
D004791:Enzyme Inhibitors; D015395:Histocompatibility Antigens Class I; D014452:Ubiquitins; D001616:beta-Galactosidase; D010447:Peptide Hydrolases; D046988:Proteasome Endopeptidase Complex; C061553:ATP dependent 26S protease