Defective intracellular transport as a common mechanism limiting expression of inappropriately paired class II major histocompatibility complex α/β chains

Lymphocyte Biology Section, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland 20892.
Journal of Experimental Medicine (Impact Factor: 12.52). 11/1991; 174(4):799-808.
Source: PubMed


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.

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Available from: Laura R Hendrix, Oct 13, 2015
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    • "This comparison is hampered because whereas the gift of Dr R.N.Germain (National Institutes of Health, Bethesda, most of αβ–IiP10 is SDS-stable at room temperature, MD). Similar reagents were generated in our laboratory as described many αβ–polypeptide complexes may be unstable and not elsewhere (Sant et al., 1991). appear as αβc in SDS–PAGE, just as most of αβ–Ii is Mice not resolved as a separate SDS-stable species. "
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    ABSTRACT: Major histocompatibility complex (MHC) class II molecules bind and present to CD4+ T cells peptides derived from endocytosed antigens. Class II molecules associate in the endoplasmic reticulum with invariant chain (Ii), which (i) mediates the delivery of the class II–Ii complexes into the endocytic compartments where the antigenic peptides are generated; and (ii) blocks the peptide-binding site of the class II molecules until they reach their destination. Once there, Ii must be removed to allow peptide binding. The bulk of Ii–class II complexes reach late endocytic compartments where Ii is eliminated in a reaction in which the cysteine protease cathepsin S and the accessory molecule H-2DM play an essential role. Here, we here show that Ii is also eliminated in early endosomal compartments without the intervention of cysteine proteases or H-2DM. The Ii-free class II molecules generated by this alternative mechanism first bind high molecular weight polypeptides and then mature into peptide-loaded complexes.
    The EMBO Journal 02/2000; 19(5):882-891. DOI:10.1093/emboj/19.5.882 · 10.43 Impact Factor
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    • "To test whether these functions may be differentially mediated by p31 and p41 isoforms in the intact animal, we next analyzed synthesis and assembly of a6 heterodimers by spleen cells exclusively expressing p31 Ii chain. To evaluate specifically the ratios of free a and 5 subunits and assembled dimers, we used M5/114 MAb (Bhattacharya et al., 1981) and conformation- independent rabbit antibodies directed against determinants located in the cytoplasmic tailsof the a and 8 chains, respectively (Sant et al., 1991). As expected, wild-type lysates showed substantial amounts of p31 and p41 Ii chain associated with a6 heterodimers. "
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    ABSTRACT: We used a "hit and run" gene targeting strategy to generate mice expressing only the p31 isoform of the conserved invariant (Ii) chain associated with major histocompatibility complex (MHC) class II molecules. Spleen cells from these mice appear indistinguishable from wild type with respect to class II subunit assembly, transport, peptide acquisition, surface expression, and the ability to present intact protein antigens. Moreover, these mutant mice have normal numbers of thymic and peripheral CD4+ T cells, and intact CD4+ T-dependent proliferative responses towards a soluble antigen. In short, MHC class II expression and function are surprisingly unaffected in mice lacking p41 invariant chain, implying that the p31 and p41 isoforms may be functionally redundant in the intact animal.
    Immunity 10/1995; 3(3):385-96. DOI:10.1016/1074-7613(95)90122-1 · 21.56 Impact Factor
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    • "Rabbit antisera specific for determinants located in the cytoplasmic tails of the a and B chains have been described (Sant et al., 1991). M5/114(Bhattacharyaetal., 1961), lO-2-16and 11-5-2(Dietal., 1976), and MKD6 (Kappler et al., 1961) were obtained from the American Type Culture Collection (Rockville, Maryland). "
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    ABSTRACT: The conserved invariant chain associates with highly polymorphic alpha and beta subunits guiding class II transport through the secretory pathway. Early associations of these three polypeptides inside antigen-presenting cells are poorly understood. The present experiments provide a detailed picture of the structure and fate of class II alpha and beta subunits in invariant chain mutants possessing different MHC haplotypes. In the absence of invariant chain, A alpha bA beta b is predominantly expressed as free A alpha b and A beta b chains by both splenocytes and activated LPS/IL-4 blasts, confirming that A alpha bA beta b assembly is strongly dependent on invariant chain coexpression. A quite different situation exists with respect to other allelic products. In the absence of invariant chain, A alpha kA beta k, E alpha kE beta k, and A alpha dA beta d molecules assemble efficiently and are conformationally similar to mature wild-type heterodimers. The contribution of invariant chain to subunit assembly thus differs for allelic variants, suggesting that sequential associations of alpha, beta, and invariant chain may be affected by polymorphic differences.
    Immunity 04/1995; 2(3):301-10. DOI:10.1016/1074-7613(95)90054-3 · 21.56 Impact Factor
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