title: Allele-Independent Turnover of Human Leukocyte Antigen (HLA) Class Ia Molecules.
abstract: Major histocompatibility complex class I (MHCI) glycoproteins present cytosolic peptides to CD8+ T cells and regulate NK cell activity. Their heavy chains (HC) are expressed from up to three MHC gene loci (human leukocyte antigen [HLA]-A, -B, and -C in humans), whose extensive polymorphism maps predominantly to the antigen-binding groove, diversifying the bound peptide repertoire. Codominant expression of MHCI alleles is thus functionally critical, but how it is regulated is not fully understood. Here, we have examined the effect of polymorphism on the turnover rates of MHCI molecules in cell lines with functional MHCI peptide loading pathways and in monocyte-derived dendritic cells (MoDCs). Proteins were labeled biosynthetically with heavy water (2H2O), folded MHCI molecules immunoprecipitated, and tryptic digests analysed by mass spectrometry. MHCI-derived peptides were assigned to specific alleles and isotypes, and turnover rates quantified by 2H incorporation, after correcting for cell growth. MHCI turnover half-lives ranged from undetectable to a few hours, depending on cell type, activation state, donor, and MHCI isotype. However, in all settings, the turnover half-lives of alleles of the same isotype were similar. Thus, MHCI protein turnover rates appear to be allele-independent in normal human cells. We propose that this is an important feature enabling the normal function and codominant expression of MHCI alleles.
authors.affiliation: Department of Medicine, University of Cambridge, Cambridge, United Kingdom.
authors.forename: Claudia
authors.initials: C
authors.lastname: Prevosto
authors.affiliation: Department of Medicine, University of Cambridge, Cambridge, United Kingdom.
authors.forename: M Farooq
authors.initials: MF
authors.lastname: Usmani
authors.affiliation: Department of Medicine, University of Cambridge, Cambridge, United Kingdom.
authors.forename: Sarah
authors.initials: S
authors.lastname: McDonald
authors.affiliation: Department of Medicine, University of Cambridge, Cambridge, United Kingdom.
authors.forename: Aleksandra M
authors.initials: AM
authors.lastname: Gumienny
authors.affiliation: Tissue Typing Laboratory, Addenbrooke's Hospital, Cambridge, United Kingdom.
authors.forename: Tim
authors.initials: T
authors.lastname: Key
authors.affiliation: Tissue Typing Laboratory, Addenbrooke's Hospital, Cambridge, United Kingdom.
authors.forename: Reyna S
authors.initials: RS
authors.lastname: Goodman
authors.affiliation: Department of Medicine, University of Cambridge, Cambridge, United Kingdom.
authors.forename: J S Hill
authors.initials: JS
authors.lastname: Gaston
authors.affiliation: Cambridge Centre for Proteomics, University of Cambridge, Cambridge, United Kingdom.
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Deery
authors.affiliation: Department of Medicine, University of Cambridge, Cambridge, United Kingdom.|Department of Life Sciences, University of Roehampton, London, United Kingdom.
authors.forename: Robert
authors.initials: R
authors.lastname: Busch
mesh_terms: D000483:Alleles; D045744:Cell Line, Tumor; D017666:Deuterium Oxide / Q000737:chemistry; D006680:HLA Antigens / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D006801:Humans; D007553:Isotope Labeling
chemical_list: D006680:HLA Antigens; D017666:Deuterium Oxide