Conformation and surface expression of free HLA-CW1 heavy chains in the absence of beta 2-microglobulin.
A beta 2-microglobulin (beta 2m)-deficient kidney carcinoma cell line and three monoclonal antibodies to the alpha 1 (L31), alpha 2 (W6/32), and alpha 3 (Q1/28) domain of class I HLA molecules were selected to assess the role of beta 2m in regulating the conformation and surface expression of HLA-C molecules. HLA-A2, -B27, and -CW1 molecules synthesized by beta 2m-deficient cells were compared to heavy chains synthesized in transfectants expressing a large excess of beta 2m. As assessed by differential binding with monoclonal antibodies and partitioning studies in the detergent TX-114, no HLA-A2, -B27, or -CW1 molecules can be expressed, in a correct conformation, by beta 2m-deficient cells. These cells, however, do express low but significant amounts of free HLA-CW1 heavy chains at the cell surface. Transfection with beta 2m causes a coordinate change in the antibody reactivity of the three domains of HLA-CW1 molecules, thereby providing the first experimental demonstration that assembly with beta 2m affects the folding of not only the alpha 1 and alpha 2, but also of the alpha 3 domain. HLA-CW1 heavy chains, when free of beta 2m, are less soluble in the detergent TX-114 than free HLA-B27 heavy chains, and when associated with beta 2m share an alpha 3 domain epitope with free HLA-A2 and -B27 heavy chains. Moreover, their assembly with beta 2m is largely incomplete. Those data additionally demonstrate an impaired ability of HLA-CW1 to properly fold and establish a close similarity of HLA-CW1 to murine Db and Ld molecules. Although the functional role, if any, of free HLA-CW1 heavy chains remains to be determined, the present study demonstrates that the absence of beta 2m does not completely ablate class I expression in neoplastic cells of human origin.
Martayan
A
A
Immunology Laboratory, Regina Elena Institute CRS, Rome, Italy.
Fiscella
M
M
Setini
A
A
Ciccarelli
G
G
Gambari
R
R
Feriotto
G
G
Beretta
A
A
Siccardi
A G
AG
Appella
E
E
Giacomini
P
P
D002292:Carcinoma, Renal Cell; D002469:Cell Separation; D003902:Detergents; D005838:Genotype; D015234:HLA-A Antigens / Q000235:genetics; D015235:HLA-B Antigens / Q000235:genetics; D015236:HLA-C Antigens / Q000096:biosynthesis* / Q000737:chemistry* / Q000235:genetics; D006801:Humans; D007525:Isoelectric Focusing; D007680:Kidney Neoplasms; D017830:Octoxynol; D011092:Polyethylene Glycols; D011487:Protein Conformation; D014162:Transfection; D014407:Tumor Cells, Cultured; D001613:beta 2-Microglobulin / Q000172:deficiency* / Q000235:genetics
D003902:Detergents; D015234:HLA-A Antigens; D015235:HLA-B Antigens; D015236:HLA-C Antigens; C047431:HLA-Cw1 antigen; D001613:beta 2-Microglobulin; D011092:Polyethylene Glycols; D017830:Octoxynol; C010615:Nonidet P-40