Defective intracellular transport as a common mechanism limiting expression of inappropriately paired class II major histocompatibility complex alpha/beta chains.

Lymphocyte Biology Section, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland 20892.
Journal of Experimental Medicine (Impact Factor: 13.21). 11/1991; 174(4):799-808. DOI: 10.1084/jem.174.4.799
Source: PubMed

ABSTRACT Distinct combinations of class II major histocompatibility complex (MHC) alpha and beta chains show widely varying efficiencies of cell surface expression in transfected cells. Previous studies have analyzed the regions of the class II chains that are critically involved in this phenomenon of variable expression and have shown a predominant effect of the NH2-terminal domains comprising the peptide-binding site. The present experiments attempt to identify the post-translational defects responsible for this variation in surface class II molecule expression for both interisotypic alpha/beta combinations failing to give rise to any detectable cell membrane molecules (e.g., E alpha A beta k) and intraisotypic pairs with inefficient surface expression (e.g., A alpha d A beta k). The results of metabolic labeling and immunoprecipitation experiments using L cell transfectants demonstrate that in both of these cases, the alpha and beta chains form substantial amounts of stable intracellular dimers. However, the isotype- and allele-mismatched combinations do not show the typical post-translational increases in molecular weight that accompany maturation of the N-linked glycans of class II MHC molecules. Studies with endoglycosidase H reveal that no or little progression to endoglycosidase H resistance occurs for these mismatched dimers. These data are consistent with active or passive retention of relatively stable and long-lived mismatched dimers in a pre-medial-Golgi compartment, possibly in the endoplasmic reticulum itself. This retention accounts for the absent or poor surface expression of these alpha/beta combinations, and suggests that conformational effects of the mismatching in the NH2-terminal domain results in a failure of class II molecules to undergo efficient intracellular transport.

  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: HLA class II α and β chains form receptors for antigen presentation to CD4+ T cells. Numerous pairings of class II α and β subunits from the wide range of haplotypes and isotypes may form, but most of these combinations, in particular those produced by isotype mixing, yielded mismatched dimers. It is unclear how selection of functional receptors is achieved. At the atomic level, it is not known which interactions of class II residues regulate selection of matched αβ heterodimers and the evolutionary origin of matched isotype mixed dimer formation. In this study, we investigated assembly of isotype-mixed HLA class II α and βheterodimers. Assembly and carbohydrate maturation of various HLA-class II isotype-mixed α and β subunits was dependent on the groove-binding section of the invariant chain (Ii). By mutation of polymorphic DPβ sequences, we identified two motifs, K69 and GGPM84-87, which are engaged in Ii-dependent assembly of DPβ with DRα. We identified five members of a family of DPβ chains containing K69 and GGPM 84-87, which assemble with DRα. The K/GGPM motif is present in the DPβ sequence of the Neandertal genome and this ancient sequence is related to the human allele DPB1*0401. By site- directed mutagenesis we inspected Neandertal amino acid residues which differ from the DPB1*0401 allele and whether matched heterodimers are formed by assembly of DPβ mutants with DRα. Since the *0401 allele is rare in the Sub-Saharan population but frequent in the European population it may have arisen in modern humans by admixture with Neandertals in Europe.
    Journal of Biological Chemistry 11/2013; · 4.65 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: DM catalyses class II-associated invariant chain peptide (CLIP) release, edits the repertoire of peptides bound to major histocompatibility complex (MHC) class II molecules, affects class II structure, and thereby modulates binding of conformation-sensitive anti-class II antibodies. Here, we investigate the ability of DM to enhance the cell surface binding of monomorphic antibodies. We show that this enhancement reflects increases in cell surface class II expression and total cellular abundance, but notably these effects are selective for particular alleles. Evidence from analysis of cellular class II levels after cycloheximide treatment and from pulse-chase experiments indicates that DM increases the half-life of affected alleles. Unexpectedly, the pulse-chase experiments also revealed an early effect of DM on assembly of these alleles. The allelically variant feature that correlates with susceptibility to these DM effects is low affinity for CLIP; DM-dependent changes in abundance are reduced by invariant chain (CLIP) mutants that enhance CLIP binding to class II. We found evidence that DM mediates rescue of peptide-receptive DR0404 molecules from inactive forms in vitro and evidence suggesting that a similar process occurs in cells. Thus, multiple mechanisms, operating along the biosynthetic pathway of class II molecules, contribute to DM-mediated increases in the abundance of low-CLIP-affinity alleles.
    Immunology 09/2010; 131(1):18-32. · 3.71 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Mammalian class II major histocompatibility (MHCII) proteins bind peptide antigens in endosomal compartments of antigen-presenting cells. The nonclassical MHCII protein HLA-DM chaperones peptide-free MHCII, protecting it against inactivation, and catalyzes peptide exchange on loaded MHCII. Another nonclassical MHCII protein, HLA-DO, binds HLA-DM and influences the repertoire of peptides presented by MHCII proteins. However, the mechanism by which HLA-DO functions is unclear. Here we have used X-ray crystallography, enzyme kinetics and mutagenesis approaches to investigate human HLA-DO structure and function. In complex with HLA-DM, HLA-DO adopts a classical MHCII structure, with alterations near the α subunit's 3(10) helix. HLA-DO binds to HLA-DM at the same sites implicated in MHCII interaction, and kinetic analysis showed that HLA-DO acts as a competitive inhibitor. These results show that HLA-DO inhibits HLA-DM function by acting as a substrate mimic, and the findings also limit the possible functional roles for HLA-DO in antigen presentation.
    Nature Structural & Molecular Biology 12/2012; · 11.90 Impact Factor

Full-text (4 Sources)

Available from
Jun 1, 2014