title: Inefficient assembly limits transport and cell surface expression of HLA-Cw4 molecules in C1R.
abstract: HLA-C antigens are expressed to the cell surface at roughly 10% the level of HLA-B or -A, and their serological definition remains persistently difficult. To characterize the factors limiting surface expression, the processes of assembly and intracellular transport of HLA-Cw4 molecules were investigated in the C1R cell line. When appropriate peptides were added to cultured cells or in cell lysates significant amounts of conformed HLA-C molecules that associate with beta 2-microglobulin (beta 2 m) are detected, but are indeed not sufficient to restore expression to the level observed for HLA-A or -B molecules. Furthermore, a precursor/product relationship exists between the free class I heavy chain and the mature conformation of HLA-Cw4 molecules. Thus, HLA-C assembly promotes the conversion of HC-10-reactive molecules (weakly-beta 2m-associated non-ligand associated free HC form) into the beta 2m-associated class I molecules recognized by W6/32. To further investigate the factors that regulate cell surface expression, intracellular transport of HLA-Cw4 was studied in pulse chase analysis. In contrast to some HLA-A and B, maturation of HLA-Cw4 heavy chains and their export to the medial and trans-Golgi compartments are quite inefficient. After 4 h of chase period, roughly half of the pulse-labeled HLA-Cw4 molecules have transited to the medial-Golgi and acquired complex oligosaccharides characteristic of mature form. In addition, treatment with gamma-interferon does not appear to improve maturation of HLA-Cw4 heavy chains, suggesting that increased supply of peptides does not influence intracellular transport. Moreover, only a small fraction in the pool of HLA-Cw4 molecules was subsequently transported through the trans-Golgi network, as indicated by their acquisition of sialic acids. Taken together these studies show that HLA-Cw4 molecules are inefficiently transported through the Golgi apparatus and presumably retained in the endoplasmic reticulum or cis-Golgi compartment.
authors.affiliation: Institut Cochin de Génétique Moléculaire, INSERM U 445, Hôpital Cochin, Paris, France.
authors.forename: J
authors.initials: J
authors.lastname: Zemmour
mesh_terms: D001692:Biological Transport; D002461:Cell Line, Transformed; D002462:Cell Membrane; D015686:Gene Products, env / Q000138:chemical synthesis / Q000494:pharmacology; D006056:Golgi Apparatus / Q000378:metabolism; D015236:HLA-C Antigens / Q000737:chemistry* / Q000276:immunology*; D006801:Humans; D007371:Interferon-gamma / Q000494:pharmacology; D008024:Ligands; D009844:Oligosaccharides / Q000737:chemistry / Q000276:immunology; D010455:Peptides / Q000494:pharmacology; D011487:Protein Conformation
chemical_list: D015686:Gene Products, env; D015236:HLA-C Antigens; C039966:HLA-C*04 antigen; D008024:Ligands; D009844:Oligosaccharides; D010455:Peptides; D007371:Interferon-gamma