title: Modulation of class I major histocompatibility complex antigen cell-surface stability by transmembrane domain length variation.
abstract: Cell surface localization of major histocompatibility complex (MHC) class I proteins is conferred to a large extent by their transmembrane domains (TMs) which exhibit allelic, inter-locus and inter-species variation in both amino acid composition and length. Here, the consequences of TM length variation on trafficking and cell-surface stability were examined using the human MHC class I protein HLA-A2. Transformed B lymphocytes (CIR cells) transfected with an HLA-A2 gene encoding an additional 12 hydrophobic amino acids in the TM exhibited a marked decrease in steady-state cell-surface levels of the HLA-A2 protein relative to cells transfected with the wild-type HLA-A2 gene. Diminished surface expression was observed regardless of the presence or absence of the cytoplasmic domain and could not be accounted for by altered association with beta2-microglobulin. While intracellular trafficking rates were affected by TM length enlargement and/or the absence of cytoplasmic domains, this, as well, could not completely explain the TM length-dependent differential cell-surface levels. Studies using brefeldin A to block transport of HLA-A2 proteins to the cell surface suggested that the diminished cell-surface levels of TM enlarged HLA-A2 proteins was a result of decreased cell-surface stability. A significant negative correlation between cell-surface stability and TM length was observed in a comparison of four HLA-A2 proteins differing only in TM length. Similar studies employing an HLA-A2 protein with the TM of HLA-B27 (which is the same length as the HLA-A2 TM but is only 72% identical) suggested that MHC class I TM length variation, independent of amino acid composition and the cytoplasmic domain, may appreciably affect cell-surface stability.
authors.affiliation: Department of Biochemistry and Molecular Biology, University of Arkansas for Medical Sciences, Little Rock 72205, USA.
authors.forename: C K
authors.initials: CK
authors.lastname: Osborn
authors.forename: V
authors.initials: V
authors.lastname: Grigoriev
authors.forename: M D
authors.initials: MD
authors.lastname: Crew
mesh_terms: D000595:Amino Acid Sequence; D000954:Antigens, Surface / Q000235:genetics / Q000378:metabolism; D020126:Brefeldin A; D002478:Cells, Cultured; D003517:Cyclopentanes / Q000494:pharmacology; D005434:Flow Cytometry; D005805:Genes, MHC Class I / Q000235:genetics*; D015789:HLA-A2 Antigen / Q000378:metabolism*; D006801:Humans; D008969:Molecular Sequence Data; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D011863:Radioimmunoassay; D013997:Time Factors; D014162:Transfection
chemical_list: D000954:Antigens, Surface; D003517:Cyclopentanes; D015789:HLA-A2 Antigen; D011500:Protein Synthesis Inhibitors; D020126:Brefeldin A