title: The role of BiP in endoplasmic reticulum-associated degradation of major histocompatibility complex class I heavy chain induced by cytomegalovirus proteins.
abstract: Human cytomegalovirus (HCMV1) US11 and US2 proteins cause rapid degradation of major histocompatibility complex (MHC) molecules, apparently by ligating cellular endoplasmic reticulum (ER)-associated degradation machinery. Here, we show that US11 and US2 bind the ER chaperone BiP. Four related HCMV proteins, US3, US7, US9, and US10, which do not promote degradation of MHC proteins, did not bind BiP. Silencing BiP reduced US11- and US2-mediated degradation of MHC class I heavy chain (HC) without altering the synthesis or translocation of HC into the ER or the stability of HC in the absence of US11 or US2. Induction of the unfolded protein response (UPR) did not affect US11-mediated HC degradation and could not explain the stabilization of HC when BiP was silenced. Unlike in yeast, BiP did not act by maintaining substrates in a retrotranslocation-competent form. Our studies go beyond previous observations in mammalian cells correlating BiP release with degradation, demonstrating that BiP is functionally required for US2- and US11-mediated HC degradation. Further, US2 and US11 bound BiP even when HC was absent and degradation of US2 depended on HC. These data were consistent with a model in which US2 and US11 bridge HC onto BiP promoting interactions with other ER-associated degradation proteins.
authors.affiliation: Department of Molecular Microbiology & Immunology, Oregon Health & Science University, Portland, Oregon 97239.
authors.forename: Nagendra R
authors.initials: NR
authors.lastname: Hegde
authors.affiliation: Department of Molecular Microbiology & Immunology, Oregon Health & Science University, Portland, Oregon 97239.
authors.forename: Mathieu S
authors.initials: MS
authors.lastname: Chevalier
authors.affiliation: Department of Molecular Microbiology & Immunology, Oregon Health & Science University, Portland, Oregon 97239.
authors.forename: Todd W
authors.initials: TW
authors.lastname: Wisner
authors.affiliation: Department of Molecular Microbiology & Immunology, Oregon Health & Science University, Portland, Oregon 97239.
authors.forename: Michael C
authors.initials: MC
authors.lastname: Denton
authors.affiliation: Department of Medical Genetics and Microbiology, University of Toronto, Toronto, Ontario M5S 1A8, Canada.
authors.forename: Kathy
authors.initials: K
authors.lastname: Shire
authors.affiliation: Department of Medical Genetics and Microbiology, University of Toronto, Toronto, Ontario M5S 1A8, Canada.
authors.forename: Lori
authors.initials: L
authors.lastname: Frappier
authors.affiliation: Department of Molecular Microbiology & Immunology, Oregon Health & Science University, Portland, Oregon 97239. Electronic address: johnsoda@ohsu.edu.
authors.forename: David C
authors.initials: DC
authors.lastname: Johnson
mesh_terms: D000818:Animals; D045744:Cell Line, Tumor; D002522:Chlorocebus aethiops; D003587:Cytomegalovirus / Q000235:genetics*; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D000091342:Endoplasmic Reticulum Chaperone BiP; D020868:Gene Silencing; D005805:Genes, MHC Class I; D006360:Heat-Shock Proteins / Q000378:metabolism / Q000502:physiology*; D006801:Humans; D013058:Mass Spectrometry; D018832:Molecular Chaperones / Q000378:metabolism / Q000502:physiology*; D034622:RNA Interference; D014709:Vero Cells; D014764:Viral Proteins / Q000737:chemistry*
chemical_list: D000091342:Endoplasmic Reticulum Chaperone BiP; D006360:Heat-Shock Proteins; D018832:Molecular Chaperones; D014764:Viral Proteins