title: gp78 functions downstream of Hrd1 to promote degradation of misfolded proteins of the endoplasmic reticulum.
abstract: Eukaryotic cells eliminate misfolded proteins from the endoplasmic reticulum (ER) via a conserved process termed ER-associated degradation (ERAD). Central regulators of the ERAD system are membrane-bound ubiquitin ligases, which are thought to channel misfolded proteins through the ER membrane during retrotranslocation. Hrd1 and gp78 are mammalian ubiquitin ligases homologous to Hrd1p, an ubiquitin ligase essential for ERAD in Saccharomyces cerevisiae. However, the functional relevance of these proteins to Hrd1p is unclear. In this paper, we characterize the gp78-containing ubiquitin ligase complex and define its functional interplay with Hrd1 using biochemical and recently developed CRISPR-based genetic tools. Our data show that transient inactivation of the gp78 complex by short hairpin RNA-mediated gene silencing causes significant stabilization of both luminal and membrane ERAD substrates, but unlike Hrd1, which plays an essential role in retrotranslocation and ubiquitination of these ERAD substrates, knockdown of gp78 does not affect either of these processes. Instead, gp78 appears to act downstream of Hrd1 to promote ERAD via cooperation with the BAG6 chaperone complex. We conclude that the Hrd1 complex forms an essential retrotranslocation module that is evolutionarily conserved, but the mammalian ERAD system uses additional ubiquitin ligases to assist Hrd1 during retrotranslocation.
authors.affiliation: Laboratory of Molecular Biology, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892.
authors.forename: Ting
authors.initials: T
authors.lastname: Zhang
authors.affiliation: Laboratory of Molecular Biology, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892.
authors.forename: Yue
authors.initials: Y
authors.lastname: Xu
authors.affiliation: Laboratory of Molecular Biology, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892.
authors.forename: Yanfen
authors.initials: Y
authors.lastname: Liu
authors.affiliation: Laboratory of Molecular Biology, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892 yihongy@mail.nih.gov.
authors.forename: Yihong
authors.initials: Y
authors.lastname: Ye
mesh_terms: D004721:Endoplasmic Reticulum / Q000378:metabolism*; D060746:Endoplasmic Reticulum-Associated Degradation; D057809:HEK293 Cells; D006801:Humans; D018832:Molecular Chaperones / Q000378:metabolism; D011485:Protein Binding; D017510:Protein Folding; D059748:Proteolysis; D060285:Receptors, Autocrine Motility Factor / Q000378:metabolism*; D025801:Ubiquitin / Q000378:metabolism; D044767:Ubiquitin-Protein Ligases / Q000378:metabolism*; D054875:Ubiquitination
chemical_list: D018832:Molecular Chaperones; D025801:Ubiquitin; C555000:AMFR protein, human; D060285:Receptors, Autocrine Motility Factor; C482345:SYVN1 protein, human; D044767:Ubiquitin-Protein Ligases