title: Induction of glutathione synthesis in human hepatocytes by acute and chronic arsenic exposure: differential roles of mitogen-activated protein kinases.
abstract: Glutathione (GSH) is a vital component of antioxidant defense which protects cells from toxic insults. Previously we found intracellular GSH was involved in cell resistance against arsenic-induced cytotoxicity. However, molecular mechanisms of GSH homeostasis during arsenic exposure are largely undefined. Here, we investigated roles of mitogen-activated protein kinases (MAPKs) in GSH synthesis pathway with two arsenic exposure strategies by using Chang human hepatocytes. In one strategy, acute arsenic exposure (20 μM, 24 h) was applied, as MAPK signaling is generally considered to be transient. In the other one, chronic arsenic exposure (500 nM, 20 weeks) was applied, which mimicked the general human exposure to arsenic. We found that acute arsenic exposure activated extracellular signal-regulated 1/2 kinases (ERK1/2) and c-Jun N-terminal kinase (JNK) in parallel with increased transcription and nuclear translocation of factor-erythroid 2-related factor 2 (NRF2) and enhanced expression of γ-glutamyl cysteine ligase catalytic subunit (GCLC), resulting in elevated intracellular GSH levels. Specific ERK inhibitor abolished arsenic-induced NRF2 nuclear translocation and GSH synthesis. During chronic arsenic exposure which induced a malignant cellular phenotype, continuous p38 activation and NRF2 nuclear translocation were observed with enhanced GSH synthesis. Specific p38 inhibitor attenuated arsenic-enhanced GSH synthesis without changing NRF2 nuclear translocation. Taken together, our results indicate MAPK pathways play an important role in cellular GSH homeostasis in response to arsenic. However, the specific activation of certain MAPK is different between acute and chronic arsenic exposure. Furthermore, it appears that during chronic arsenic exposure, GSH synthesis is regulated by p38 at least in part independent of NRF2.
authors.affiliation: Environmental Toxicology Program, School of Public Health, China Medical University, No. 92 North 2nd Road, Shenyang, Liaoning 110001, PR China. Electronic address: yyhou@mail.cmu.edu.cn.
authors.forename: Yongyong
authors.initials: Y
authors.lastname: Hou
authors.affiliation: Environmental Toxicology Program, School of Public Health, China Medical University, No. 92 North 2nd Road, Shenyang, Liaoning 110001, PR China. Electronic address: wangyi@mail.cmu.edu.cn.
authors.forename: Yi
authors.initials: Y
authors.lastname: Wang
authors.affiliation: Environmental Toxicology Program, School of Public Health, China Medical University, No. 92 North 2nd Road, Shenyang, Liaoning 110001, PR China.
authors.forename: Huihui
authors.initials: H
authors.lastname: Wang
authors.affiliation: Environmental Toxicology Program, School of Public Health, China Medical University, No. 92 North 2nd Road, Shenyang, Liaoning 110001, PR China. Electronic address: yyxu@mail.cmu.edu.cn.
authors.forename: Yuanyuan
authors.initials: Y
authors.lastname: Xu
mesh_terms: D018053:Arsenites / Q000633:toxicity*; D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D004351:Drug Resistance; D004789:Enzyme Activation; D005978:Glutathione / Q000096:biosynthesis*; D022781:Hepatocytes / Q000187:drug effects* / Q000201:enzymology; D006801:Humans; D020935:MAP Kinase Signaling System / Q000187:drug effects; D020928:Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D051267:NF-E2-Related Factor 2 / Q000378:metabolism; D018384:Oxidative Stress / Q000187:drug effects; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D017670:Sodium Compounds / Q000633:toxicity*; D013997:Time Factors
chemical_list: D018053:Arsenites; D051267:NF-E2-Related Factor 2; C495635:NFE2L2 protein, human; D047428:Protein Kinase Inhibitors; D017670:Sodium Compounds; C017947:sodium arsenite; D020928:Mitogen-Activated Protein Kinases; D005978:Glutathione
keywords: Arsenic; Glutathione; Hepatocytes; MAPKs; NRF2; Oxidative stress