title: ROS inhibitor N-acetyl-L-cysteine antagonizes the activity of proteasome inhibitors.
abstract: NAC (N-acetyl-L-cysteine) is commonly used to identify and test ROS (reactive oxygen species) inducers, and to inhibit ROS. In the present study, we identified inhibition of proteasome inhibitors as a novel activity of NAC. Both NAC and catalase, another known scavenger of ROS, similarly inhibited ROS levels and apoptosis associated with H₂O₂. However, only NAC, and not catalase or another ROS scavenger Trolox, was able to prevent effects linked to proteasome inhibition, such as protein stabilization, apoptosis and accumulation of ubiquitin conjugates. These observations suggest that NAC has a dual activity as an inhibitor of ROS and proteasome inhibitors. Recently, NAC was used as a ROS inhibitor to functionally characterize a novel anticancer compound, piperlongumine, leading to its description as a ROS inducer. In contrast, our own experiments showed that this compound depicts features of proteasome inhibitors including suppression of FOXM1 (Forkhead box protein M1), stabilization of cellular proteins, induction of ROS-independent apoptosis and enhanced accumulation of ubiquitin conjugates. In addition, NAC, but not catalase or Trolox, interfered with the activity of piperlongumine, further supporting that piperlongumine is a proteasome inhibitor. Most importantly, we showed that NAC, but not other ROS scavengers, directly binds to proteasome inhibitors. To our knowledge, NAC is the first known compound that directly interacts with and antagonizes the activity of proteasome inhibitors. Taken together, the findings of the present study suggest that, as a result of the dual nature of NAC, data interpretation might not be straightforward when NAC is utilized as an antioxidant to demonstrate ROS involvement in drug-induced apoptosis.
authors.affiliation: Department of Medicine, University of Illinois at Chicago, 60612, USA.
authors.forename: Marianna
authors.initials: M
authors.lastname: Halasi
authors.forename: Ming
authors.initials: M
authors.lastname: Wang
authors.forename: Tanmay S
authors.initials: TS
authors.lastname: Chavan
authors.forename: Vadim
authors.initials: V
authors.lastname: Gaponenko
authors.forename: Nissim
authors.initials: N
authors.lastname: Hay
authors.forename: Andrei L
authors.initials: AL
authors.lastname: Gartel
mesh_terms: D000111:Acetylcysteine / Q000378:metabolism / Q000494:pharmacology*; D000972:Antineoplastic Agents, Phytogenic / Q000037:antagonists & inhibitors / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects; D002374:Catalase / Q000235:genetics / Q000378:metabolism; D045744:Cell Line, Tumor; D002839:Chromans / Q000037:antagonists & inhibitors / Q000378:metabolism / Q000494:pharmacology; D003587:Cytomegalovirus / Q000201:enzymology; D004148:Dioxolanes / Q000037:antagonists & inhibitors / Q000494:pharmacology; D000072278:Forkhead Box Protein M1; D051858:Forkhead Transcription Factors / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D016166:Free Radical Scavengers / Q000378:metabolism / Q000494:pharmacology*; D006801:Humans; D006861:Hydrogen Peroxide / Q000037:antagonists & inhibitors / Q000494:pharmacology; D016877:Oxidants / Q000037:antagonists & inhibitors / Q000494:pharmacology; D046988:Proteasome Endopeptidase Complex / Q000187:drug effects* / Q000378:metabolism; D061988:Proteasome Inhibitors / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology*; D055550:Protein Stability / Q000187:drug effects; D017382:Reactive Oxygen Species / Q000037:antagonists & inhibitors* / Q000378:metabolism; D011994:Recombinant Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism; D057149:Ubiquitinated Proteins / Q000378:metabolism; D014764:Viral Proteins / Q000235:genetics / Q000378:metabolism; D010881:Piperidones
chemical_list: D000111:Acetylcysteine; D000972:Antineoplastic Agents, Phytogenic; D002374:Catalase; D002839:Chromans; D004148:Dioxolanes; D000072278:Forkhead Box Protein M1; D051858:Forkhead Transcription Factors; D016166:Free Radical Scavengers; D006861:Hydrogen Peroxide; D016877:Oxidants; D046988:Proteasome Endopeptidase Complex; D061988:Proteasome Inhibitors; D017382:Reactive Oxygen Species; D011994:Recombinant Proteins; D057149:Ubiquitinated Proteins; D014764:Viral Proteins; C107585:FOXM1 protein, human; C498077:piperlongumine; D010881:Piperidones; C010643:6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid