title: Induction of tumor cell apoptosis by a proteasome deubiquitinase inhibitor is associated with oxidative stress.
abstract: OBJECTIVE
  b-AP15 is a recently described inhibitor of the USP14/UCHL5 deubiquitinases (DUBs) of the 19S proteasome. Exposure to b-AP15 results in blocking of proteasome function and accumulation of polyubiquitinated protein substrates in cells. This novel mechanism of proteasome inhibition may potentially be exploited for cancer therapy, in particular for treatment of malignancies resistant to currently used proteasome inhibitors. The aim of the present study was to characterize the cellular response to b-AP15-mediated proteasome DUB inhibition.
  
  
  RESULTS
  We report that b-AP15 elicits a similar, but yet distinct, cellular response as the clinically used proteasome inhibitor bortezomib. b-AP15 induces a rapid apoptotic response, associated with enhanced induction of oxidative stress and rapid activation of Jun-N-terminal kinase 1/2 (JNK)/activating protein-1 signaling. Scavenging of reactive oxygen species and pharmacological inhibition of JNK reduced b-AP15-induced apoptosis. We further report that endoplasmic reticulum (ER) stress is induced by b-AP15 and is involved in apoptosis induction. In contrast to bortezomib, ER stress is associated with induction of α-subunit of eukaryotic initiation factor 2 phosphorylation.
  
  
  METHODS
  The findings establish that different modes of proteasome inhibition result in distinct cellular responses, a finding of potential therapeutic importance.
  
  
  CONCLUSIONS
  Our data show that enhanced oxidative stress and ER stress are major determinants of the strong apoptotic response elicited by the 19S DUB inhibitor b-AP15.
authors.affiliation: 1 Department of Oncology and Pathology, Cancer Center Karolinska, Karolinska Institute , Stockholm, Sweden .
authors.forename: Slavica
authors.initials: S
authors.lastname: Brnjic
authors.forename: Magdalena
authors.initials: M
authors.lastname: Mazurkiewicz
authors.forename: Mårten
authors.initials: M
authors.lastname: Fryknäs
authors.forename: Chao
authors.initials: C
authors.lastname: Sun
authors.forename: Xiaonan
authors.initials: X
authors.lastname: Zhang
authors.forename: Rolf
authors.initials: R
authors.lastname: Larsson
authors.forename: Pádraig
authors.initials: P
authors.lastname: D'Arcy
authors.forename: Stig
authors.initials: S
authors.lastname: Linder
mesh_terms: D017209:Apoptosis; D015153:Blotting, Western; D001897:Boronic Acids / Q000494:pharmacology; D000069286:Bortezomib; D045744:Cell Line, Tumor; D020869:Gene Expression Profiling; D006801:Humans; D018384:Oxidative Stress; D010881:Piperidones / Q000494:pharmacology; D016133:Polymerase Chain Reaction; D011480:Protease Inhibitors / Q000494:pharmacology*; D046988:Proteasome Endopeptidase Complex / Q000187:drug effects*; D011719:Pyrazines / Q000494:pharmacology; D017382:Reactive Oxygen Species / Q000378:metabolism; D014158:Transcription, Genetic; D064570:Ubiquitin-Specific Proteases / Q000037:antagonists & inhibitors*
chemical_list: C569633:3,5-bis((4-nitrophenyl)methylidene)-1-prop-2-enoylpiperidin-4-one; D001897:Boronic Acids; D010881:Piperidones; D011480:Protease Inhibitors; D011719:Pyrazines; D017382:Reactive Oxygen Species; D000069286:Bortezomib; D064570:Ubiquitin-Specific Proteases; D046988:Proteasome Endopeptidase Complex