International Immunology Advance Access originally published online on December 16, 2005
International Immunology 2006 18(1):173-182; doi:10.1093/intimm/dxh362
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Subtle sequence variation among MHC class I locus products greatly influences sensitivity to HCMV US2- and US11-mediated degradation
1 Department of Medical Microbiology, Leiden University Medical Center, PO Box 9600, 2300 RC Leiden, The Netherlands
2 INSERM U563, CPTP, Bat A, Hôpital Purpan, BP 3028, 31024 Toulouse cedex 3, France
3 Present address: INSERM U 589, Institut L. Bugnard, Hôpital Rangueil, BP 84225, 31 432 Toulouse cedex 4, France
Correspondence to: F. Lenfant; E-mail: lenfant{at}toulouse.inserm.fr
Human cytomegalovirus (HCMV) interferes with cellular immune responses by modulating surface expression of MHC class I molecules. Here, we focused on HCMV-encoded unique short (US) 2 and US11, which bind newly synthesized MHC class I heavy chains (HCs) and support their dislocation into the cytosol for subsequent degradation by proteasomes. Not all MHC class I locus products are equally sensitive to this down-modulation. The aim of this study was to identify which domains, and ultimately which residues, are responsible for the resistance or sensitivity of MHC class I molecules to US2- and US11-mediated down-regulation. We show that, besides endoplasmic reticulumlumenal regions, the C-terminus of class I molecules represents an important determinant for allele specificity in US11-mediated degradation. HLA-E becomes sensitive to US11-mediated down-regulation when its cytoplasmic tail is extended. Interestingly, this only requires two additional residues, lysine and valine, at its C-terminus. For US2, the MHC class I allele specificity is largely determined by a small region at the junction of the
2/
3 domain of the HC. It is quite remarkable that minor changes, in only four residues, can completely revert the sensitivity of naturally US2-resistant HLA-E molecules. With this study we provide better insights into the features underlying the selectivity in MHC class I down-regulation by US2 and US11.
Keywords: cytomegalovirus, HLA-E, immune evasion, US