Human cytomegalovirus protein US6 inhibits the transporter associated with antigen processing (TAP), which transports peptides into the endoplasmic reticulum (ER) for binding to major histocompatibility complex (MHC) class I molecules. We demonstrate that, in TAP-deficient cells, US6 is retained in the ER and binds to calnexin, but does not inhibit cell-surface expression of HLA-A201, an MHC class I allele that binds to peptides whose import into the ER is TAP-independent. Furthermore, in TAP-positive cells, US6 reduces the cell-surface expression of HLA-B2705, an MHC class I allele that is dependent on TAP for peptide binding, to a greater extent than that of HLA-A201. These data demonstrate that US6 has differential effects on the cell-surface expression of MHC class I alleles and are consistent with TAP being the sole inhibitory target of US6 in the MHC class I antigen-presentation pathway.
Abele, R. & Tampe, R.(2004). The ABCs of immunology: structure and function of TAP, the transporter associated with antigen processing. Physiology (Bethesda)19, 216–224.[CrossRef][Google Scholar]
Ahn, K., Gruhler, A., Galocha, B., Jones, T. R., Wiertz, E. J., Ploegh, H. L., Peterson, P. A., Yang, Y. & Fruh, K.(1997). The ER-luminal domain of the HCMV glycoprotein US6 inhibits peptide translocation by TAP. Immunity6, 613–621.[CrossRef][Google Scholar]
Antoniou, A. N., Powis, S. J. & Elliott, T.(2003). Assembly and export of MHC class I peptide ligands. Curr Opin Immunol15, 75–81.[CrossRef][Google Scholar]
Daniel, S., Brusic, V., Caillat-Zucman, S., Petrovsky, N., Harrison, L., Riganelli, D., Sinigaglia, F., Gallazzi, F., Hammer, J. & van Endert, P. M.(1998). Relationship between peptide selectivities of human transporters associated with antigen processing and HLA class I molecules. J Immunol161, 617–624.
[Google Scholar]
Dugan, G. E. & Hewitt, E. W.(2008). Structural and functional dissection of the human cytomegalovirus immune evasion protein US6. J Virol82, 3271–3282.[CrossRef][Google Scholar]
Ellis, S. A., Taylor, C. & McMichael, A.(1982). Recognition of HLA-B27 and related antigen by a monoclonal antibody. Hum Immunol5, 49–59.[CrossRef][Google Scholar]
Gewurz, B. E., Gaudet, R., Tortorella, D., Wang, E. W., Ploegh, H. L. & Wiley, D. C.(2001). Antigen presentation subverted: structure of the human cytomegalovirus protein US2 bound to the class I molecule HLA-A2. Proc Natl Acad Sci U S A98, 6794–6799.[CrossRef][Google Scholar]
Henderson, R. A., Michel, H., Sakaguchi, K., Shabanowitz, J., Appella, E., Hunt, D. F. & Engelhard, V. H.(1992). HLA-A2.1-associated peptides from a mutant cell line: a second pathway of antigen presentation. Science255, 1264–1266.[CrossRef][Google Scholar]
Hengel, H., Koopmann, J. O., Flohr, T., Muranyi, W., Goulmy, E., Hammerling, G. J., Koszinowski, U. H. & Momburg, F.(1997). A viral ER-resident glycoprotein inactivates the MHC-encoded peptide transporter. Immunity6, 623–632.[CrossRef][Google Scholar]
Hewitt, E. W.(2003). The MHC class I antigen presentation pathway: strategies for viral immune evasion. Immunology110, 163–169.[CrossRef][Google Scholar]
Hewitt, E. W. & Dugan, G. E.(2004). Virus subversion of protective immunity. Curr Allergy Asthma Rep4, 365–370.[CrossRef][Google Scholar]
Hewitt, E. W., Gupta, S. S. & Lehner, P. J.(2001). The human cytomegalovirus gene product US6 inhibits ATP binding by TAP. EMBO J20, 387–396.[CrossRef][Google Scholar]
Hewitt, E. W., Duncan, L., Mufti, D., Baker, J., Stevenson, P. G. & Lehner, P. J.(2002). Ubiquitylation of MHC class I by the K3 viral protein signals internalization and TSG101-dependent degradation. EMBO J21, 2418–2429.[CrossRef][Google Scholar]
Jackson, M. R., Cohen-Doyle, M. F., Peterson, P. A. & Williams, D. B.(1994). Regulation of MHC class I transport by the molecular chaperone, calnexin (p88, IP90). Science263, 384–387.[CrossRef][Google Scholar]
Kyritsis, C., Gorbulev, S., Hutschenreiter, S., Pawlitschko, K., Abele, R. & Tampe, R.(2001). Molecular mechanism and structural aspects of transporter associated with antigen processing inhibition by the cytomegalovirus protein US6. J Biol Chem276, 48031–48039.
[Google Scholar]
Lehner, P. J., Karttunen, J. T., Wilkinson, G. W. & Cresswell, P.(1997). The human cytomegalovirus US6 glycoprotein inhibits transporter associated with antigen processing-dependent peptide translocation. Proc Natl Acad Sci U S A94, 6904–6909.[CrossRef][Google Scholar]
Oosten, L. E., Koppers-Lalic, D., Blokland, E., Mulder, A., Ressing, M. E., Mutis, T., van Halteren, A. G., Wiertz, E. J. & Goulmy, E.(2007). TAP-inhibiting proteins US6, ICP47 and UL49.5 differentially affect minor and major histocompatibility antigen-specific recognition by cytotoxic T lymphocytes. Int Immunol19, 1115–1122.[CrossRef][Google Scholar]
Ortmann, B., Androlewicz, M. J. & Cresswell, P.(1994). MHC class I/β2-microglobulin complexes associate with TAP transporters before peptide binding. Nature368, 864–867.[CrossRef][Google Scholar]
Peaper, D. R. & Cresswell, P.(2008). Regulation of MHC class I assembly and peptide binding. Annu Rev Cell Dev Biol24, 343–368.[CrossRef][Google Scholar]
Reits, E. A., Vos, J. C., Gromme, M. & Neefjes, J.(2000). The major substrates for TAP in vivo are derived from newly synthesized proteins. Nature404, 774–778.[CrossRef][Google Scholar]
Rock, K. L. & Goldberg, A. L.(1999). Degradation of cell proteins and the generation of MHC class I-presented peptides. Annu Rev Immunol17, 739–779.[CrossRef][Google Scholar]
Sadasivan, B., Lehner, P. J., Ortmann, B., Spies, T. & Cresswell, P.(1996). Roles for calreticulin and a novel glycoprotein, tapasin, in the interaction of MHC class I molecules with TAP. Immunity5, 103–114.[CrossRef][Google Scholar]
Schust, D. J., Tortorella, D., Seebach, J., Phan, C. & Ploegh, H. L.(1998). Trophoblast class I major histocompatibility complex (MHC) products are resistant to rapid degradation imposed by the human cytomegalovirus (HCMV) gene products US2 and US11. J Exp Med188, 497–503.[CrossRef][Google Scholar]
Smith, K. D. & Lutz, C. T.(1996). Peptide-dependent expression of HLA-B7 on antigen processing-deficient T2 cells. J Immunol156, 3755–3764.
[Google Scholar]
Stam, N. J., Spits, H. & Ploegh, H. L.(1986). Monoclonal antibodies raised against denatured HLA-B locus heavy chains permit biochemical characterization of certain HLA-C locus products. J Immunol137, 2299–2306.
[Google Scholar]
van Endert, P. M., Saveanu, L., Hewitt, E. W. & Lehner, P.(2002). Powering the peptide pump: TAP crosstalk with energetic nucleotides. Trends Biochem Sci27, 454–461.[CrossRef][Google Scholar]
Wei, M. L. & Cresswell, P.(1992). HLA-A2 molecules in an antigen-processing mutant cell contain signal sequence-derived peptides. Nature356, 443–446.[CrossRef][Google Scholar]