Low HLA-C expression at cell surfaces correlates with increased turnover of heavy chain mRNA.

• DOI: 10.1084/jem.181.6.2085
• Publication Date: 2004-06-24T07:56:10Z
• Authors: J A McCutcheon; J Gumperz; K D Smith; C T Lutz; P Parham
• Keywords: 0301 basic medicine; Base Sequence; HLA-A Antigens; Macromolecular Substances; Recombinant Fusion Proteins; Cell Membrane; Molecular Sequence Data; Gene Expression; HLA-C Antigens; Transfection; Polymerase Chain Reaction; Cell Line; Kinetics; 03 medical and health sciences; 0302 clinical medicine; HLA-B Antigens; Humans; RNA, Messenger; beta 2-Microglobulin; DNA Primers

In comparison with HLA-A and -B, the protein products of the HLA-C locus are poorly characterized, in part because of their low level of expression at the cell surface. Here, we examine how protein-protein interactions during assembly and regulation of the mRNA level affect cell surface expression of HLA-C. We find that intrinsic properties of the HLA-C heavy chain proteins do not correlate with low cell surface expression: HLA-C heavy chains associate and dissociate with beta 2-microglobulin (beta 2m) at rates comparable to those found for HLA-A and -B, and increased competition for beta 2m does not alter the surface expression of HLA-C. From studies of chimeric genes spliced from the HLA-B7 and -Cw3 genes, we find that chimeric proteins containing the B7 peptide-binding groove can have low cell surface expression, suggesting that inefficiency in binding peptides is not the cause of low cell surface expression for HLA-C. The surface levels of HLA-A, -B, or -C in cells transfected with cDNA can be similar, implicating noncoding regions of HLA-C heavy chain genes in the regulation of surface expression. We find that HLA-C mRNA is expressed at lower levels than HLA-B mRNA and that this difference results from faster degradation of the HLA-C message. Experiments examining chimeric B7/Cw3 and B7/Cw6 genes suggest that a region determining low expression of HLA-C is to be found between the 3' end of exon 3 and a site in the 3' untranslated region, approximately 600 bases downstream of the translation stop codon.