Low Constitutive Cell Surface Expression of HLA-B Is Caused by a Posttranslational Mechanism Involving Glu180 and Arg239.
HLA class I cell surface expression is crucial for normal immune responses, and variability in HLA expression may influence the course of infections. We have previously shown that classical HLA class I expression on many human cell types is biased with greatly reduced expression of HLA-B compared with HLA-A in the absence of inflammatory signals. In the search for the mechanisms responsible for this discrepancy, we have recently reported that the regulation is mainly posttranslational and that the C-terminal part of the α2 domain and the α3 domain contain the molecular determinants that explain most of the variability of expression between common HLA-A and -B allomorphs. In this study, we present a fine mapping of the structural determinants that allow such variability by exchanging key amino acids located within the C-terminal part of the α2 domain and the α3 domain of HLA-A2 and -B8, including Glu/Asp at position 177, Gln/Glu at position 180, Gly/Arg at position 239, and Pro/Ser at position 280. We found that the HLA-A2 and -B8 expression profiles could be interconverted to a large extent by mutual exchange of Gln/Glu at position 180 or by Gly/Arg at position 239. The presence of Gln180and Gly239, as in HLA-A2, led to higher cell surface expression levels when compared with the presence of Glu180and Arg239, as in HLA-B8. This indicates that the amino acids at positions 180 and 239 determine the level of cell surface expression of common HLA-A and -B allomorphs, probably by affecting HLA processing in the Ag presentation pathway.
Department of Clinical Immunology, Odense University Hospital, 5000 Odense, Denmark.
Christoffer
C
Dellgren
Department of Clinical Immunology, Odense University Hospital, 5000 Odense, Denmark.
Vanessa A C
0000-0002-1426-9583
VA
Ekwelum
Department of Clinical Immunology, Odense University Hospital, 5000 Odense, Denmark.
Maria
M
Ormhøj
Department of Clinical Immunology, Odense University Hospital, 5000 Odense, Denmark.
Nicole
N
Pallesen
Department of Clinical Immunology, Odense University Hospital, 5000 Odense, Denmark.
Julie
0000-0001-8931-947X
J
Knudsen
Department of Clinical Immunology, Odense University Hospital, 5000 Odense, Denmark.
Jan O
0000-0001-6038-5027
JO
Nehlin
Department of Clinical Immunology, Odense University Hospital, 5000 Odense, Denmark barington@dadlnet.dk.
Torben
0000-0001-6968-148X
T
Barington
D017951:Antigen Presentation; D001120:Arginine / Q000235:genetics / Q000378:metabolism*; D002469:Cell Separation; D005434:Flow Cytometry; D018698:Glutamic Acid / Q000235:genetics / Q000378:metabolism*; D005998:Glycine / Q000235:genetics / Q000378:metabolism; D057809:HEK293 Cells; D015789:HLA-A2 Antigen / Q000235:genetics / Q000378:metabolism*; D015795:HLA-B8 Antigen / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D007239:Infections / Q000276:immunology*; D000072417:Protein Domains / Q000235:genetics; D015202:Protein Engineering; D011499:Protein Processing, Post-Translational; D017434:Protein Structure, Tertiary
D015789:HLA-A2 Antigen; D015795:HLA-B8 Antigen; D018698:Glutamic Acid; D001120:Arginine; D005998:Glycine