title: Inadequate fine-tuning of protein synthesis and failure of amino acid homeostasis following inhibition of the ATPase VCP/p97.
abstract: The cellular mechanisms that control protein degradation may constitute a non-oncogenic cancer cell vulnerability and, therefore, a therapeutic target. Although this proposition is supported by the clinical success of proteasome inhibitors in some malignancies, most cancers are resistant to proteasome inhibition. The ATPase valosin-containing protein (VCP; p97) is an essential regulator of protein degradation in multiple pathways and has emerged as a target for cancer therapy. We found that pharmacological depletion of VCP enzymatic activity with mechanistically different inhibitors robustly induced proteotoxic stress in solid cancer and multiple myeloma cells, including cells that were insensitive, adapted, or clinically resistant to proteasome inhibition. VCP inhibition had an impact on two key regulators of protein synthesis, eukaryotic initiation factor 2α (eIF2α) and mechanistic target of rapamycin complex 1 (mTORC1), and attenuated global protein synthesis. However, a block on protein translation that was itself cytotoxic alleviated stress signaling and reduced cell death triggered by VCP inhibition. Some of the proteotoxic effects of VCP depletion depended on the eIF2α phosphatase, protein phosphatase 1 regulatory subunit 15A (PPP1R15A)/PP1c, but not on mTORC1, although there appeared to be cross-talk between them. Thus, cancer cell death following VCP inhibition was linked to inadequate fine-tuning of protein synthesis and activity of PPP1R15A/PP1c. VCP inhibitors also perturbed intracellular amino acid levels, activated eukaryotic translation initiation factor 2α kinase 4 (EIF2AK4), and enhanced cellular dependence on amino acid supplies, consistent with a failure of amino acid homeostasis. Many of the observed effects of VCP inhibition differed from the effects triggered by proteasome inhibition or by protein misfolding. Thus, depletion of VCP enzymatic activity triggers cancer cell death in part through inadequate regulation of protein synthesis and amino acid metabolism. The data provide novel insights into the maintenance of intracellular proteostasis by VCP and may have implications for the development of anti-cancer therapies.
authors.affiliation: Department of Medicine, Centre for Haematology, Imperial College London, London W12 0NN, UK.
authors.forename: K
authors.initials: K
authors.lastname: Parzych
authors.affiliation: Department of Medicine, Centre for Haematology, Imperial College London, London W12 0NN, UK.|Craniofacial Development and Stem Cell Biology, King's College London, London SE1 9RT, UK.
authors.forename: T M
authors.initials: TM
authors.lastname: Chinn
authors.affiliation: Department of Medicine, Centre for Haematology, Imperial College London, London W12 0NN, UK.
authors.forename: Z
authors.initials: Z
authors.lastname: Chen
authors.affiliation: Department of Medicine, Centre for Haematology, Imperial College London, London W12 0NN, UK.
authors.forename: S
authors.initials: S
authors.lastname: Loaiza
authors.affiliation: Department of Medicine, Centre for Haematology, Imperial College London, London W12 0NN, UK.
authors.forename: F
authors.initials: F
authors.lastname: Porsch
authors.affiliation: Faculty of Medicine, Department of Surgery and Cancer, Imperial College London, London W12 0NN, UK.
authors.forename: G N
authors.initials: GN
authors.lastname: Valbuena
authors.affiliation: Department of Medicine, Centre for Haematology, Imperial College London, London W12 0NN, UK.
authors.forename: M F
authors.initials: MF
authors.lastname: Kleijnen
authors.affiliation: Department of Medicine, Centre for Haematology, Imperial College London, London W12 0NN, UK.
authors.forename: A
authors.initials: A
authors.lastname: Karadimitris
authors.affiliation: Craniofacial Development and Stem Cell Biology, King's College London, London SE1 9RT, UK.
authors.forename: E
authors.identifier: http://orcid.org/0000-0003-0447-5137
authors.initials: E
authors.lastname: Gentleman
authors.affiliation: Faculty of Medicine, Department of Surgery and Cancer, Imperial College London, London W12 0NN, UK.
authors.forename: H C
authors.initials: HC
authors.lastname: Keun
authors.affiliation: Department of Medicine, Centre for Haematology, Imperial College London, London W12 0NN, UK.
authors.forename: H W
authors.initials: HW
authors.lastname: Auner
mesh_terms: D000251:Adenosine Triphosphatases / Q000037:antagonists & inhibitors* / Q000378:metabolism; D000596:Amino Acids / Q000378:metabolism*; D017209:Apoptosis / Q000187:drug effects; D045744:Cell Line, Tumor; D004791:Enzyme Inhibitors / Q000494:pharmacology; D015852:Eukaryotic Initiation Factor-2 / Q000378:metabolism; D006706:Homeostasis / Q000187:drug effects; D006801:Humans; D000076222:Mechanistic Target of Rapamycin Complex 1; D008954:Models, Biological; D046912:Multiprotein Complexes / Q000378:metabolism; D009687:Nuclear Proteins / Q000037:antagonists & inhibitors* / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D061988:Proteasome Inhibitors / Q000494:pharmacology; D014176:Protein Biosynthesis / Q000187:drug effects; D054645:Protein Phosphatase 1 / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D058570:TOR Serine-Threonine Kinases / Q000378:metabolism; D015854:Up-Regulation / Q000187:drug effects
chemical_list: D000596:Amino Acids; D004791:Enzyme Inhibitors; D015852:Eukaryotic Initiation Factor-2; D046912:Multiprotein Complexes; D009687:Nuclear Proteins; D061988:Proteasome Inhibitors; D000076222:Mechanistic Target of Rapamycin Complex 1; D058570:TOR Serine-Threonine Kinases; C087519:PPP1R15A protein, human; D054645:Protein Phosphatase 1; D000251:Adenosine Triphosphatases; C404942:p97 ATPase