title: Exogenous peptide ligand influences the expression and half-life of free HLA class I heavy chains ubiquitously detected at the cell surface.
abstract: A pool of free HLA class I chains has been detected at the plasma membrane of all cells concomitantly expressing folded and assembled class I molecules. To determine the origin of these free HLA heavy chains, we have examined the biosynthesis of a single HLA class I molecule, HLA-B27, expressed by a murine cell line (L-B27). In L-B27 cells, as previously shown in Epstein-Barr virus-transformed lymphoblastoid cell lines, a precursor/product relationship exists, early in biosynthesis, between free (HC10-reactive) and beta-2-microglobulin (beta 2m)-associated (W6/32-reactive) class I heavy chains as demonstrated by pulse/chase experiments. At later stages in class I biosynthesis, both HC10- and W6/32-reactive heavy chains display complex oligosaccharides and accumulate at the cell surface. HC10- and W6/32-reactive molecules are both very stable at the cell surface, with half-lifes (t1/2) of > 7 h and approximately 4 h, respectively. Interestingly, cell surface expression and turnover of HC10- and W6/32-reactive molecules were affected by the addition of peptide ligands to the culture media. Culturing cells in the presence of HLA-B27 ligands resulted in the increased expression of W6/32-reactive molecules and the decreased expression of HC10-reactive molecules. Moreover, addition of exogenous peptide extended the t1/2 of W6/32-reactive molecules to > 7 h and reduced that of HC10-reactive molecules to 4 h. These results indicate that surface HC10-reactive molecules result largely from W6/32-reactive molecules following peptide and beta 2m dissociation. Therefore, HC10-reactive species are not only the precursors but also the end products in class I biosynthesis.
authors.affiliation: Department of Genetics, Washington University School of Medicine, St. Louis, MO 63110.
authors.forename: B M
authors.initials: BM
authors.lastname: Carreno
authors.forename: T H
authors.initials: TH
authors.lastname: Hansen
mesh_terms: D000328:Adult; D000818:Animals; D000911:Antibodies, Monoclonal; D002461:Cell Line, Transformed; D005434:Flow Cytometry; D015796:HLA-B27 Antigen / Q000096:biosynthesis / Q000737:chemistry / Q000378:metabolism*; D006207:Half-Life; D006801:Humans; D008024:Ligands; D008565:Membrane Proteins / Q000096:biosynthesis / Q000737:chemistry / Q000378:metabolism*; D051379:Mice; D008807:Mice, Inbred BALB C; D008822:Mice, Transgenic; D010455:Peptides / Q000276:immunology*; D011233:Precipitin Tests; D017510:Protein Folding; D001613:beta 2-Microglobulin
chemical_list: D000911:Antibodies, Monoclonal; D015796:HLA-B27 Antigen; D008024:Ligands; D008565:Membrane Proteins; D010455:Peptides; D001613:beta 2-Microglobulin