title: Regulated folding of tyrosinase in the endoplasmic reticulum demonstrates that misfolded full-length proteins are efficient substrates for class I processing and presentation.
abstract: Short-lived protein translation products have been proposed to be the principal substrates that enter the class I MHC processing and presentation pathway. However, the biochemical nature of these substrates is poorly defined. Whether the major processing substrates are misfolded full-length proteins, or alternatively, aberrantly initiated or truncated polypeptides still remains to be addressed. To examine this, we used melanoma in which one-third of wild-type tyrosinase molecules were correctly folded and localized beyond the Golgi, while the remainder were present in the endoplasmic reticulum in an unfolded/misfolded state. Increasing the efficiency of tyrosinase folding using chemical chaperones led to a reduction in the level of substrate available to the proteasome and decreased the expression of a tyrosinase-derived epitope. Conversely, in transfectants expressing tyrosinase mutants that are completely misfolded, both proteasome substrate and epitope presentation were significantly enhanced. Proteasome substrate availability was a consequence of misfolding and not simply due to retention in the endoplasmic reticulum. Thus, the extent of folding/misfolding of a full-length protein is an important determinant of the level of epitope presentation.
authors.affiliation: Carter Immunology Center and Department of Microbiology, University of Virginia, Charlottesville, VA 22908, USA.
authors.forename: Marina
authors.initials: M
authors.lastname: Ostankovitch
authors.forename: Valentina
authors.initials: V
authors.lastname: Robila
authors.forename: Victor H
authors.initials: VH
authors.lastname: Engelhard
mesh_terms: D000409:Alanine / Q000235:genetics; D019943:Amino Acid Substitution / Q000235:genetics; D000818:Animals; D017951:Antigen Presentation / Q000235:genetics; D001120:Arginine / Q000235:genetics; D002460:Cell Line; D045744:Cell Line, Tumor; D004721:Endoplasmic Reticulum / Q000201:enzymology*; D000939:Epitopes / Q000235:genetics; D005973:Glutamine / Q000235:genetics; D015395:Histocompatibility Antigens Class I / Q000276:immunology* / Q000378:metabolism*; D007424:Intracellular Fluid / Q000201:enzymology; D008545:Melanoma / Q000201:enzymology / Q000235:genetics / Q000276:immunology; D051379:Mice; D008810:Mice, Inbred C57BL; D014442:Monophenol Monooxygenase / Q000737:chemistry / Q000235:genetics / Q000276:immunology* / Q000378:metabolism*; D010446:Peptide Fragments / Q000276:immunology / Q000378:metabolism; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D017510:Protein Folding; D011499:Protein Processing, Post-Translational; D021381:Protein Transport / Q000235:genetics; D013379:Substrate Specificity / Q000235:genetics; D013912:Threonine / Q000235:genetics; D014162:Transfection; D014443:Tyrosine / Q000235:genetics
chemical_list: D000939:Epitopes; D015395:Histocompatibility Antigens Class I; D010446:Peptide Fragments; D005973:Glutamine; D013912:Threonine; D014443:Tyrosine; D001120:Arginine; D014442:Monophenol Monooxygenase; D046988:Proteasome Endopeptidase Complex; D000409:Alanine