title: Disruption of polyubiquitin gene Ubc leads to attenuated resistance against arsenite-induced toxicity in mouse embryonic fibroblasts.
abstract: The polyubiquitin gene Ubc is upregulated under oxidative stress induced by arsenite [As(III)]. However, the detailed mechanism of Ubc upregulation and the exact role of ubiquitin (Ub) to protect cells against As(III)-induced toxicity remain unknown. Here, we found that Ubc-/- mouse embryonic fibroblasts (MEFs) exhibited reduced viability under As(III) exposure, although the Nrf2-Keap1 pathway was activated as a cytoprotective response. Intriguingly, due to the reduced polyubiquitination and delayed onset of degradation of Nrf2 in Ubc-/- MEFs, the basal expression levels of Nrf2 target genes were elevated. As(III)-induced accumulation of Ub conjugates occurred in an Nrf2-independent manner, probably due to cellular stress conditions, including reduced proteasomal activity. Increased cellular Ub levels were essential to polyubiquitinate misfolded proteins generated under As(III) exposure and to degrade them by the proteasome. However, when cellular Ub levels decreased, these misfolded proteins were not efficiently polyubiquitinated, but rather accumulated as large protein aggregates inside the cells, causing cytotoxicity. Furthermore, increased activity of the autophagic pathway to clear these aggregates was not observed in Ubc-/- MEFs. Therefore, reduced viability of Ubc-/- MEFs under As(III) exposure may not be due to dysregulation of the Nrf2-Keap1 pathway, but mostly to reduced efficacy to polyubiquitinate and degrade misfolded protein aggregates.
authors.affiliation: Department of Life Science, University of Seoul, Seoul 130-743, Republic of Korea.
authors.forename: Mi-Nam
authors.initials: MN
authors.lastname: Kim
authors.affiliation: Department of Life Science, University of Seoul, Seoul 130-743, Republic of Korea.
authors.forename: Juhee
authors.initials: J
authors.lastname: Choi
authors.affiliation: Department of Life Science, University of Seoul, Seoul 130-743, Republic of Korea.
authors.forename: Han-Wook
authors.initials: HW
authors.lastname: Ryu
authors.affiliation: Department of Life Science, University of Seoul, Seoul 130-743, Republic of Korea. Electronic address: kyryu@uos.ac.kr.
authors.forename: Kwon-Yul
authors.initials: KY
authors.lastname: Ryu
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000378:metabolism; D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D018053:Arsenites / Q000633:toxicity*; D002467:Cell Nucleus / Q000187:drug effects / Q000378:metabolism; D002470:Cell Survival / Q000187:drug effects; D003598:Cytoskeletal Proteins / Q000378:metabolism; D004622:Embryo, Mammalian / Q000166:cytology*; D005347:Fibroblasts / Q000187:drug effects / Q000378:metabolism*; D017353:Gene Deletion; D005786:Gene Expression Regulation / Q000187:drug effects; D000072019:Kelch-Like ECH-Associated Protein 1; D051379:Mice; D008954:Models, Biological; D051267:NF-E2-Related Factor 2 / Q000378:metabolism; D018384:Oxidative Stress / Q000187:drug effects; D025821:Polyubiquitin / Q000235:genetics* / Q000378:metabolism; D017510:Protein Folding / Q000187:drug effects; D059748:Proteolysis / Q000187:drug effects; D015398:Signal Transduction / Q000187:drug effects; D025801:Ubiquitin / Q000378:metabolism; D054875:Ubiquitination / Q000187:drug effects
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D018053:Arsenites; D003598:Cytoskeletal Proteins; C117301:Keap1 protein, mouse; D000072019:Kelch-Like ECH-Associated Protein 1; D051267:NF-E2-Related Factor 2; C527284:Ubb protein, mouse; D025801:Ubiquitin; D025821:Polyubiquitin; C015001:arsenite
keywords: Antioxidant response; Cytotoxicity; Oxidative stress; Polyubiquitination; Protein aggregate; Ubiquitin