title: COPII machinery cooperates with ER-localized Hsp40 to sequester misfolded membrane proteins into ER-associated compartments.
abstract: Proteins that fail to fold in the endoplasmic reticulum (ER) are subjected to ER-associated degradation (ERAD). Certain transmembrane ERAD substrates are segregated into specialized ER subdomains, termed ER-associated compartments (ERACs), before targeting to ubiquitin-proteasome degradation. The traffic-independent function of several proteins involved in COPII-mediated ER-to-Golgi transport have been implicated in the segregation of exogenously expressed human cystic fibrosis transmembrane conductance regulator (CFTR) into ERACs in Saccharomyces cerevisiae. Here we focus on the properties of COPII components in the sequestration of enhanced green fluorescent protein (EGFP)-CFTR into ERACs. It has been demonstrated that the temperature-sensitive growth defects in many COPII mutants can be suppressed by overexpressing other genes involved in COPII vesicle formation. However, we show that these suppression abilities are not always correlated with the ability to rescue the ERAC formation defect, suggesting that COPII-mediated EGFP-CFTR entry into ERACs is independent of its ER-to-Golgi trafficking function. In addition to COPII machinery, we find that ER-associated Hsp40s are also involved in the sequestration process by directly interacting with EGFP-CFTR. COPII components and ER-associated Hsp40, Hlj1p, act in the same pathway to sequester EGFP-CFTR into ERACs. Our findings point to an as-yet-undefined role of COPII proteins in the formation of ERACs.
authors.affiliation: Department of Life Sciences, Graduate School of Arts and Sciences, University of Tokyo, Komaba, Meguro-ku, Tokyo 153-8902, Japan.
authors.forename: Shogo
authors.initials: S
authors.lastname: Kakoi
authors.forename: Tomohiro
authors.initials: T
authors.lastname: Yorimitsu
authors.forename: Ken
authors.initials: K
authors.lastname: Sato
mesh_terms: D022181:COP-Coated Vesicles / Q000378:metabolism / Q000648:ultrastructure; D019005:Cystic Fibrosis Transmembrane Conductance Regulator / Q000378:metabolism*; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D006056:Golgi Apparatus / Q000378:metabolism*; D049452:Green Fluorescent Proteins; D050956:HSP40 Heat-Shock Proteins / Q000378:metabolism*; D006801:Humans; D008565:Membrane Proteins / Q000378:metabolism; D009154:Mutation; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D017510:Protein Folding; D021381:Protein Transport / Q000235:genetics; D059748:Proteolysis; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism; D025801:Ubiquitin / Q000235:genetics / Q000378:metabolism
chemical_list: C505032:CFTR protein, human; D050956:HSP40 Heat-Shock Proteins; D008565:Membrane Proteins; D025801:Ubiquitin; C485184:enhanced green fluorescent protein; D019005:Cystic Fibrosis Transmembrane Conductance Regulator; D049452:Green Fluorescent Proteins; D046988:Proteasome Endopeptidase Complex