title: The cytoplasmic domain of rhesus cytomegalovirus Rh178 interrupts translation of major histocompatibility class I leader peptide-containing proteins prior to translocation.
abstract: Cytomegalovirus (CMV) efficiently evades many host immune defenses and encodes a number of proteins that prevent antigen presentation by major histocompatibility complex class I (MHC-I) molecules in order to evade recognition and killing of infected cells by cytotoxic CD8(+) T cells. We recently showed that rhesus CMV-specific Rh178 intercepts MHC-I protein translation before interference of MHC-I maturation by homologues of the human CMV US6 family. Here, we demonstrate that Rh178 localizes to the membrane of the endoplasmic reticulum, displaying a short luminal and large cytosolic domain, and that the membrane-proximal cytosolic portion is essential for inhibition of MHC-I expression. We further observed that Rh178 does not require synthesis of full-length MHC-I heavy chains but is capable of inhibiting the translation of short, unstable amino-terminal fragments of MHC-I. Moreover, the transfer of amino-terminal fragments containing the MHC-I signal peptide renders recipient proteins susceptible to targeting by Rh178. The cytosolic orientation of Rh178 and its ability to target protein fragments carrying the MHC-I signal peptide are consistent with Rh178 intercepting partially translated MHC-I heavy chains after signal recognition particle-dependent transfer to the endoplasmic reticulum membrane. However, interference with MHC-I translation by Rh178 seems to occur prior to SEC61-dependent protein translocation, since inhibition of MHC-I translocation by eeyarestatin 1 resulted in a full-length degradation intermediate that can be stabilized by proteasome inhibitors. These data are consistent with Rh178 blocking protein translation of MHC-I heavy chains at a step prior to the start of translocation, thereby downregulating MHC-I at a very early stage of translation.
authors.affiliation: Department of Molecular Microbiology and Immunology, Oregon Health and Science University, Portland, Oregon 97205, USA.
authors.forename: Rebecca
authors.initials: R
authors.lastname: Richards
authors.forename: Isabel
authors.initials: I
authors.lastname: Scholz
authors.forename: Colin
authors.initials: C
authors.lastname: Powers
authors.forename: William R
authors.initials: WR
authors.lastname: Skach
authors.forename: Klaus
authors.initials: K
authors.lastname: Früh
mesh_terms: D000818:Animals; D002460:Cell Line; D003587:Cytomegalovirus / Q000472:pathogenicity*; D004721:Endoplasmic Reticulum / Q000737:chemistry; D015395:Histocompatibility Antigens Class I / Q000096:biosynthesis*; D054884:Host-Pathogen Interactions; D006801:Humans; D008253:Macaca mulatta; D014176:Protein Biosynthesis; D021382:Protein Sorting Signals; D014764:Viral Proteins / Q000378:metabolism*
chemical_list: D015395:Histocompatibility Antigens Class I; D021382:Protein Sorting Signals; D014764:Viral Proteins