title: Different MHC class I heavy chains compete with each other for folding independently of beta 2-microglobulin and peptide.
abstract: We reported previously that different MHC class I molecules can compete with each other for cell surface expression in F(1) hybrid and MHC class I transgenic mice. In this study, we show that the competition also occurs in transfected cell lines, and investigate the mechanism. Cell surface expression of an endogenous class I molecule in Chinese hamster ovary (CHO) cells was strongly down-regulated when the mouse K(d) class I H chain was introduced by transfection. The competition occurred only after K(d) protein translation, not at the level of RNA, and localization studies of a CHO class I-GFP fusion showed that the presence of K(d) caused retention of the hamster class I molecule in the endoplasmic reticulum. The competition was not for beta(2)-microglobulin, because a single chain version of K(d) that included mouse beta(2)-microglobulin also had a similar effect. The competition was not for association with TAP and loading with peptide, because a mutant form of the K(d) class I H chain, not able to associate with TAP, caused the same down-regulation of hamster class I expression. Moreover, K(d) expression led to a similar level of competition in TAP2-negative CHO cells. Competition for cell surface expression was also found between different mouse class I H chains in transfected mouse cells, and this competition prevented association of the H chain with beta(2)-microglobulin. These unexpected new findings show that different class I H chains compete with each other at an early stage of the intracellular assembly pathway, independently of beta(2)-microglobulin and peptide.
authors.affiliation: Department of Immunology, Wright-Fleming Institute, Imperial College London, London, United Kingdom.
authors.forename: Sophie
authors.initials: S
authors.lastname: Tourdot
authors.forename: Mohamed
authors.initials: M
authors.lastname: Nejmeddine
authors.forename: Simon J
authors.initials: SJ
authors.lastname: Powis
authors.forename: Keith G
authors.initials: KG
authors.lastname: Gould
mesh_terms: D000071181:ATP Binding Cassette Transporter, Subfamily B, Member 2; D000071450:ATP Binding Cassette Transporter, Subfamily B, Member 3; D018528:ATP-Binding Cassette Transporters / Q000378:metabolism; D000818:Animals; D017951:Antigen Presentation / Q000235:genetics; D016466:CHO Cells; D002460:Cell Line; D045744:Cell Line, Tumor; D002462:Cell Membrane / Q000276:immunology / Q000378:metabolism; D006224:Cricetinae; D015536:Down-Regulation / Q000276:immunology; D004721:Endoplasmic Reticulum / Q000235:genetics / Q000378:metabolism; D006183:H-2 Antigens / Q000096:biosynthesis* / Q000235:genetics; D051379:Mice; D008822:Mice, Transgenic; D010455:Peptides / Q000737:chemistry*; D011485:Protein Binding / Q000235:genetics / Q000276:immunology; D017510:Protein Folding; D011499:Protein Processing, Post-Translational / Q000235:genetics / Q000276:immunology; D021122:Protein Subunits / Q000096:biosynthesis* / Q000235:genetics; D021381:Protein Transport / Q000235:genetics / Q000276:immunology; D014162:Transfection; D001613:beta 2-Microglobulin / Q000378:metabolism*
chemical_list: D000071181:ATP Binding Cassette Transporter, Subfamily B, Member 2; D000071450:ATP Binding Cassette Transporter, Subfamily B, Member 3; D018528:ATP-Binding Cassette Transporters; D006183:H-2 Antigens; C024755:H-2K(K) antigen; D010455:Peptides; D021122:Protein Subunits; C486171:Tap1 protein, mouse; C489516:Tap2 protein, mouse; D001613:beta 2-Microglobulin