Human cytomegalovirus-encoded US2 differentially affects surface expression of MHC class I locus products and targets membrane-bound, but not soluble HLA-G1 for degradation.
Human CMV (HCMV) can elude CTL as well as NK cells by modulating surface expression of MHC class I molecules. This strategy would be most efficient if the virus would selectively down-regulate viral Ag-presenting alleles, while at the same time preserving other alleles to act as inhibitors of NK cell activation. We focused on the HCMV unique short (US) region encoded protein US2, which binds to newly synthesized MHC class I H chains and supports their dislocation to the cytosol for subsequent degradation by proteasomes. We studied the effect of US2 on surface expression of individual class I locus products using flow cytometry. Our results were combined with crystal structure data of complexed US2/HLA-A2/beta(2)-microglobulin and alignments of 948 HLA class I database sequences of the endoplasmic reticulum lumenal region inplicated in US2 binding. This study suggests that surface expression of all HLA-A and -G and most HLA-B alleles will be affected by US2. Several HLA-B alleles and all HLA-C and -E alleles are likely to be insensitive to US2-mediated degradation. We also found that the MHC class I endoplasmic reticulum-lumenal domain alone is not sufficient for degradation by US2, as illustrated by the stability of soluble HLA-G1 in the presence of US2. Furthermore, we showed that the membrane-bound HLA-G1 isoform, but also tailless HLA-A2, are targeted for degradation. This indicates that the cytoplasmic tail of the MHC class I H chain is not required for its dislocation to the cytosol by US2.
Barel
Martine T
MT
Department of Medical Microbiology, Leiden University Medical Center, Leiden, The Netherlands.
Ressing
Maaike
M
Pizzato
Nathalie
N
van Leeuwen
Daphne
D
Le Bouteiller
Philippe
P
Lenfant
Francoise
F
Wiertz
Emmanuel J H J
EJ
D000483:Alleles; D000595:Amino Acid Sequence; D000818:Animals; D002460:Cell Line; D045744:Cell Line, Tumor; D002462:Cell Membrane / Q000276:immunology / Q000378:metabolism / Q000821:virology; D003587:Cytomegalovirus / Q000235:genetics / Q000276:immunology*; D003593:Cytoplasm / Q000737:chemistry / Q000235:genetics / Q000276:immunology; D015536:Down-Regulation / Q000235:genetics / Q000276:immunology; D005786:Gene Expression Regulation / Q000276:immunology; D005819:Genetic Markers / Q000276:immunology; D006680:HLA Antigens / Q000096:biosynthesis* / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D015789:HLA-A2 Antigen / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D059951:HLA-G Antigens; D015395:Histocompatibility Antigens Class I / Q000096:biosynthesis* / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D007113:Immunity, Innate / Q000235:genetics; D008562:Membrane Glycoproteins / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D051379:Mice; D008969:Molecular Sequence Data; D011485:Protein Binding / Q000235:genetics / Q000276:immunology; D020033:Protein Isoforms / Q000096:biosynthesis / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D017434:Protein Structure, Tertiary / Q000235:genetics; D016601:RNA-Binding Proteins / Q000737:chemistry / Q000235:genetics / Q000502:physiology; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D017384:Sequence Deletion; D012995:Solubility; D014162:Transfection; D014759:Viral Envelope Proteins; D014764:Viral Proteins / Q000737:chemistry / Q000235:genetics / Q000502:physiology*
D005819:Genetic Markers; D006680:HLA Antigens; D015789:HLA-A2 Antigen; D059951:HLA-G Antigens; D015395:Histocompatibility Antigens Class I; D008562:Membrane Glycoproteins; D020033:Protein Isoforms; D016601:RNA-Binding Proteins; D011993:Recombinant Fusion Proteins; C074546:US11 protein, herpesvirus; C118670:US2 protein, Varicellovirus; D014759:Viral Envelope Proteins; D014764:Viral Proteins