title: tert-Butylhydroquinone mobilizes intracellular-bound zinc to stabilize Nrf2 through inhibiting phosphatase activity.
abstract: The nuclear factor erythroid 2-related factor 2 (Nrf2) is required to combat increases in oxidative stress. The chemical compound tert-butylhydroquinone (tBHQ) can downregulate Kelch-like ECH-associated protein 1 (Keap1), a repressor of Nrf2, thus maintaining the stability of Nrf2. tBHQ can also increase intracellular "free" zinc in human bronchial epithelial (16HBE) cells. We aim to investigate whether the intracellular free zinc change plays a role in Nrf2 activation. tBHQ exposure dose-dependently increases intracellular free zinc concentrations within 30 min in 16HBE cells by mobilizing intracellular zinc pools. Active Nrf2 and the antioxidant enzyme heme oxygenase-1 (HO-1) increase at 3 h after tBHQ treatment. Chelating intracellular free zinc with tetrakis-(2-pyridylmethyl)ethylenediamine (TPEN) during tBHQ exposure partially abrogates the tBHQ-induced activation of Nrf2 and HO-1 expression, while Keap1 is further decreased. These results indicate that tBHQ-induced stability of Nrf2 is associated with the intracellular free zinc level. Because the activated Nrf2 is phosphorylated, the serine/threonine protein phosphatase activity, which is known to be inhibited by zinc, is assayed. The results showed that tBHQ treatment can suppress cellular protein phosphatase-2A (PP2A) and protein phosphatase-2C (PP2C) activity, which can be abrogated by adding TPEN. This finding is verified in a cell-free protein extract experiment by supplying zinc or by chelating zinc with TPEN. These results provide a novel mechanistic insight into Nrf2 activation in antioxidant enzyme induction involving zinc signaling. The increase of intracellular free zinc may be one mechanism for Nrf2 activation. The inhibition of PP2A and PP2C activity may be involved in Nrf2 phosphorylation modulation.
authors.affiliation: Experiment Medical Research Center, Guangzhou Medical University, Guangzhou, China;
authors.forename: Yunfang
authors.initials: Y
authors.lastname: Chen
authors.affiliation: National key Laboratory of Respiratory Diseases, Guangzhou Medical University, Guangzhou, China.
authors.forename: Sheng
authors.initials: S
authors.lastname: Wang
authors.affiliation: Experiment Medical Research Center, Guangzhou Medical University, Guangzhou, China;
authors.forename: Xin
authors.initials: X
authors.lastname: Fu
authors.affiliation: Experiment Medical Research Center, Guangzhou Medical University, Guangzhou, China;
authors.forename: Wenqu
authors.initials: W
authors.lastname: Zhou
authors.affiliation: Experiment Medical Research Center, Guangzhou Medical University, Guangzhou, China;
authors.forename: Wei
authors.initials: W
authors.lastname: Hong
authors.affiliation: Experiment Medical Research Center, Guangzhou Medical University, Guangzhou, China;
authors.forename: Dongting
authors.initials: D
authors.lastname: Zou
authors.affiliation: Experiment Medical Research Center, Guangzhou Medical University, Guangzhou, China;
authors.forename: Xichong
authors.initials: X
authors.lastname: Li
authors.affiliation: Department of Pathophysiology, Guangzhou Medical University, Guangzhou, China; and.
authors.forename: Jinbao
authors.initials: J
authors.lastname: Liu
authors.affiliation: National key Laboratory of Respiratory Diseases, Guangzhou Medical University, Guangzhou, China.
authors.forename: Pixin
authors.initials: P
authors.lastname: Ran
authors.affiliation: Experiment Medical Research Center, Guangzhou Medical University, Guangzhou, China; libing@gzhmu.edu.cn.
authors.forename: Bing
authors.initials: B
authors.lastname: Li
mesh_terms: D002460:Cell Line; D004791:Enzyme Inhibitors / Q000378:metabolism / Q000494:pharmacology; D004847:Epithelial Cells / Q000187:drug effects / Q000378:metabolism; D006801:Humans; D006873:Hydroquinones / Q000378:metabolism* / Q000494:pharmacology; D007425:Intracellular Membranes / Q000187:drug effects / Q000378:metabolism*; D051267:NF-E2-Related Factor 2 / Q000378:metabolism*; D010749:Phosphoprotein Phosphatases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D054648:Protein Phosphatase 2 / Q000037:antagonists & inhibitors / Q000378:metabolism*; D000071636:Protein Phosphatase 2C; D015032:Zinc / Q000378:metabolism*
chemical_list: D004791:Enzyme Inhibitors; D006873:Hydroquinones; D051267:NF-E2-Related Factor 2; C495635:NFE2L2 protein, human; C018855:2-tert-butylhydroquinone; C000607456:PPM1A protein, human; C000607457:PPM1B protein, human; C000607460:PPM1G protein, human; D010749:Phosphoprotein Phosphatases; D054648:Protein Phosphatase 2; D000071636:Protein Phosphatase 2C; D015032:Zinc
keywords: heme oxygenase-1; nuclear factor erythroid 2-related factor 2