title: Quiescent fibroblasts are protected from proteasome inhibition-mediated toxicity.
abstract: Proteasome inhibition is used as a treatment strategy for multiple types of cancers. Although proteasome inhibition can induce apoptotic cell death in actively proliferating cells, it is less effective in quiescent cells. In this study, we used primary human fibroblasts as a model system to explore the link between the proliferative state of a cell and proteasome inhibition-mediated cell death. We found that proliferating and quiescent fibroblasts have strikingly different responses to MG132, a proteasome inhibitor; proliferating cells rapidly apoptosed, whereas quiescent cells maintained viability. Moreover, MG132 treatment of proliferating fibroblasts led to increased superoxide anion levels, juxtanuclear accumulation of ubiquitin- and p62/SQSTM1-positive protein aggregates, and apoptotic cell death, whereas MG132-treated quiescent cells displayed fewer juxtanuclear protein aggregates, less apoptosis, and higher levels of mitochondrial superoxide dismutase. In both cell states, reducing reactive oxygen species with N-acetylcysteine lessened protein aggregation and decreased apoptosis, suggesting that protein aggregation promotes apoptosis. In contrast, increasing cellular superoxide levels with 2-methoxyestradiol treatment or inhibition of autophagy/lysosomal pathways with bafilomycin A1 sensitized serum-starved quiescent cells to MG132-induced apoptosis. Thus, antioxidant defenses and the autophagy/lysosomal pathway protect serum-starved quiescent fibroblasts from proteasome inhibition-induced cytotoxicity.
authors.affiliation: Department of Molecular Biology, Princeton University, Princeton, NJ 08544, USA.
authors.forename: Aster
authors.initials: A
authors.lastname: Legesse-Miller
authors.forename: Irene
authors.initials: I
authors.lastname: Raitman
authors.forename: Erin M
authors.initials: EM
authors.lastname: Haley
authors.forename: Albert
authors.initials: A
authors.lastname: Liao
authors.forename: Lova L
authors.initials: LL
authors.lastname: Sun
authors.forename: David J
authors.initials: DJ
authors.lastname: Wang
authors.forename: Nithya
authors.initials: N
authors.lastname: Krishnan
authors.forename: Johanna M S
authors.initials: JM
authors.lastname: Lemons
authors.forename: Eric J
authors.initials: EJ
authors.lastname: Suh
authors.forename: Elizabeth L
authors.initials: EL
authors.lastname: Johnson
authors.forename: Benjamin A
authors.initials: BA
authors.lastname: Lund
authors.forename: Hilary A
authors.initials: HA
authors.lastname: Coller
mesh_terms: D000077584:2-Methoxyestradiol; D048868:Adaptor Proteins, Signal Transducing / Q000235:genetics / Q000378:metabolism; D017209:Apoptosis / Q000187:drug effects; D001343:Autophagy / Q000187:drug effects; D002453:Cell Cycle / Q000187:drug effects; D049109:Cell Proliferation / Q000187:drug effects; D002470:Cell Survival / Q000187:drug effects; D002478:Cells, Cultured; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology; D004958:Estradiol / Q000031:analogs & derivatives / Q000494:pharmacology; D005347:Fibroblasts / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism*; D005434:Flow Cytometry; D052816:Foreskin / Q000166:cytology; D006801:Humans; D015151:Immunoblotting; D007976:Leupeptins / Q000494:pharmacology*; D018942:Macrolides / Q000494:pharmacology; D008297:Male; D024101:Mitochondrial Proteins / Q000235:genetics / Q000378:metabolism; D020411:Oligonucleotide Array Sequence Analysis; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism*; D000071456:Sequestosome-1 Protein; D013482:Superoxide Dismutase / Q000235:genetics / Q000378:metabolism; D013481:Superoxides / Q000378:metabolism; D059467:Transcriptome / Q000187:drug effects / Q000235:genetics; D025801:Ubiquitin / Q000235:genetics / Q000378:metabolism
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D015853:Cysteine Proteinase Inhibitors; D007976:Leupeptins; D018942:Macrolides; D024101:Mitochondrial Proteins; C099718:SQSTM1 protein, human; D000071456:Sequestosome-1 Protein; D025801:Ubiquitin; D013481:Superoxides; D004958:Estradiol; D000077584:2-Methoxyestradiol; C040929:bafilomycin A1; D013482:Superoxide Dismutase; D046988:Proteasome Endopeptidase Complex; C072553:benzyloxycarbonylleucyl-leucyl-leucine aldehyde