title: Human MHC class I antigens are associated with a 90-kDa cell surface protein.
abstract: Human MHC class I proteins are expressed on almost all nucleated cells as a heavy chain (about 45 kDa) non-covalently associated with beta 2-microglobulin (12 kDa). In this report we show that MHC class I (MHC-I) proteins can also be associated with a 90-kDa protein in the cell membrane. Surface-radiolabelled cells were treated with dithiobis succinimidyl propionate (DSP) in order to preserve multimer protein complexes during cell lysis. The lysates were immunoprecipitated and analysed by SDS-PAGE and autoradiography. Immunoprecipitation of human MHC-I proteins co-precipitated another protein of about 90 kDa in molecular weight-p90. p90 was coprecipitated from all the MHC-I expressing cells tested: U937, Raji, Molt-4 and IFN-gamma treated K562, but not from untreated, MHC-I negative K562. A 90-kDa protein was also co-precipitated with MHC-I from fresh peripheral blood mononuclear cells (PBMC). Furthermore, p90 was coprecipitated by different MoAbs to the MHC-I heavy chain or beta 2-microglobulin, but not by control antibodies. Two additional co-precipitating proteins at 34 kDa and 28 kDa were seen in MHC-I precipitates from Raji cells. Our results suggest that MHC-I proteins and the 90-kDa protein are associated in the cell membrane, probably by a close but weak, non-covalent interaction. Two additional cell surface proteins at 34 kDa and 28 kDa seem to be MHC-I associated on Raji Burkitt's lymphoma cells.
authors.affiliation: Department of Immunology, Karolinska Institutet, Stockholm, Sweden.
authors.forename: M T
authors.initials: MT
authors.lastname: Ferm
authors.forename: A
authors.initials: A
authors.lastname: Grönberg
mesh_terms: D000911:Antibodies, Monoclonal / Q000276:immunology; D003432:Cross-Linking Reagents; D015395:Histocompatibility Antigens Class I / Q000276:immunology / Q000378:metabolism*; D006801:Humans; D046911:Macromolecular Substances; D008565:Membrane Proteins / Q000737:chemistry / Q000378:metabolism*; D008970:Molecular Weight; D011233:Precipitin Tests; D014407:Tumor Cells, Cultured
chemical_list: D000911:Antibodies, Monoclonal; D003432:Cross-Linking Reagents; D015395:Histocompatibility Antigens Class I; D046911:Macromolecular Substances; D008565:Membrane Proteins