title: VAMP-associated Proteins (VAP) as Receptors That Couple Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) Proteostasis with Lipid Homeostasis.
abstract: Unesterified cholesterol accumulates in late endosomes in cells expressing the misfolded cystic fibrosis transmembrane conductance regulator (CFTR). CFTR misfolding in the endoplasmic reticulum (ER) or general activation of ER stress led to dynein-mediated clustering of cholesterol-loaded late endosomes at the Golgi region, a process regulated by ER-localized VAMP-associated proteins (VAPs). We hypothesized that VAPs serve as intracellular receptors that couple lipid homeostasis through interactions with two phenylalanines in an acidic track (FFAT) binding signals (found in lipid sorting and sensing proteins, LSS) with proteostasis regulation. VAPB inhibited the degradation of ΔF508-CFTR. The activity was mapped to the ligand-binding major sperm protein (MSP) domain, which was sufficient in regulating CFTR biogenesis. We identified mutations in an unstructured loop within the MSP that uncoupled VAPB-regulated CFTR biogenesis from basic interactions with FFAT. Using this information, we defined functional and physical interactions between VAPB and proteostasis regulators (ligands), including the unfolded protein response sensor ATF6 and the ER degradation cluster that included FAF1, VCP, BAP31, and Derlin-1. VAPB inhibited the degradation of ΔF508-CFTR in the ER through interactions with the RMA1-Derlin-BAP31-VCP pathway. Analysis of pseudoligands containing tandem FFAT signals supports a competitive model for VAP interactions that direct CFTR biogenesis. The results suggest a model in which VAP-ligand binding couples proteostasis and lipid homeostasis leading to observed phenotypes of lipid abnormalities in protein folding diseases.
authors.affiliation: From the Department of Cell Biology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15261.
authors.forename: Wayne L
authors.initials: WL
authors.lastname: Ernst
authors.affiliation: From the Department of Cell Biology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15261.
authors.forename: Kuntala
authors.initials: K
authors.lastname: Shome
authors.affiliation: From the Department of Cell Biology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15261.
authors.forename: Christine C
authors.initials: CC
authors.lastname: Wu
authors.affiliation: From the Department of Cell Biology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15261.
authors.forename: Xiaoyan
authors.initials: X
authors.lastname: Gong
authors.affiliation: From the Department of Cell Biology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15261.
authors.forename: Raymond A
authors.identifier: http://orcid.org/0000-0003-0167-4421
authors.initials: RA
authors.lastname: Frizzell
authors.affiliation: From the Department of Cell Biology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15261 aridor@pitt.edu.
authors.forename: Meir
authors.initials: M
authors.lastname: Aridor
mesh_terms: D048868:Adaptor Proteins, Signal Transducing; D000251:Adenosine Triphosphatases; D051017:Apoptosis Regulatory Proteins; D001665:Binding Sites; D018797:Cell Cycle Proteins; D002784:Cholesterol / Q000378:metabolism*; D019005:Cystic Fibrosis Transmembrane Conductance Regulator / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000378:metabolism; D057809:HEK293 Cells; D006367:HeLa Cells; D006706:Homeostasis; D006801:Humans; D008565:Membrane Proteins / Q000378:metabolism; D011485:Protein Binding; D055550:Protein Stability; D059748:Proteolysis; D044767:Ubiquitin-Protein Ligases / Q000378:metabolism; D000074405:Valosin Containing Protein; D033921:Vesicular Transport Proteins / Q000378:metabolism*
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D051017:Apoptosis Regulatory Proteins; C091247:BCAP31 protein, human; D018797:Cell Cycle Proteins; C487709:DERL1 protein, human; D004268:DNA-Binding Proteins; C490780:FAF1 protein, human; D008565:Membrane Proteins; C496748:VAPB protein, human; D033921:Vesicular Transport Proteins; C093349:cystic fibrosis transmembrane conductance regulator delta F508; D019005:Cystic Fibrosis Transmembrane Conductance Regulator; D002784:Cholesterol; C111501:RNF5 protein, human; D044767:Ubiquitin-Protein Ligases; D000251:Adenosine Triphosphatases; C000614178:VCP protein, human; D000074405:Valosin Containing Protein
keywords: ER-associated degradation; amyotrophic lateral sclerosis (ALS) (Lou Gehrig disease); cholesterol regulation; cystic fibrosis transmembrane conductance regulator (CFTR); proteostasis