Please read the following article abstract and answer the question that follows. THE JOURNAL OF BIOLOGICAL CHEMISTRY VOL. 289, NO. 32, pp. 22413-22426, August 8, 2014 2014 by The American Society for Biochemistry and Molecular Biology, Inc. Published in the USA. Heavy Metal-induced Metallothionein Expression Is Regulated by Specific Protein Phosphatase 2A Complexes* Received for publication, January 7, 2014, and in revised form, June 20, 2014 Published, JBC Papers in Press, June 24, 2014, DOI 10.1074/jbc.M114.548677 Liping Chen, Lu Ma, Qing Bai, Xiaonian Zhu, Jinmiao Zhang, Qing Wel', Daochuan Li, Chen Gao, Jie Li', Zhengbao Zhang, Caixia Liu, Zhini He*, Xiaowen Zeng, Aihua Zhang, Weidong Qu, Zhixiong Zhuang, Wen Chen, and Yongmei Xiao From the *Department of Toxicology, School of Public Health, Sun Yat-sen University, Guangzhou 510080, China, "Department of Toxicology, School of Public Health, Guiyang Medical University, Guiyang 550004, China, "Department of Environmental Health, School of Public Health, Fudan University, Shanghai 200032, China, and Department of Toxicology, Shenzhen Center for Disease Control and Prevention, Shenzhen 518001, China Background: The molecular mechanism and key signaling pathways underlying MT expression in response to metal stress remains elusive. Results: Upon metal stress, PP2A PR110 complexes bind to and dephosphorylate MTF-1 at Thr-254, leading to the transacti- vation of MTs. Conclusion: Specific PP2A complexes regulate metal-induced MTs expression. Significance: Delineate a novel pathway regulating metal-induced cytotoxicity and clarify the role of PP2A in cellular stress response. Induction of metallothionein (MT) expression is involved in metal homeostasis and detoxification. To identify the key path- ways that regulate metal-induced cytotoxicity, we investigate how phosphorylated metal-responsive transcription factor-1 (MTF-1) contributed to induction of MT expression. Immortal human embryonic kidney cells (HEK cells) were treated with seven kinds of metals including cadmium chloride (CdCl2), zinc sulfate (ZnSO4), copper sulfate (CuSO4), lead acetate (PbAc), nickel sulfate (NiSO4), sodium arsenite (NaAsO₂), and potas- sium bichromate (K2Cr2O7). The MT expression was induced in a dose-response and time-dependent manner upon various metal treatments. A cycle of phosphorylation and dephosphor- ylation was required for translocation of MTF-1 from cytoplasm to nucleus, leading to the up-regulation of MTs expression. Pro- tein phosphatase 2A (PP2A) participated in regulating MT expression through dephosphorylation of MTF-1. A loss-of- function screen revealed that the specific PP2A complexes con- taining PR110 were involved in metal-induced MT expression. Suppression of PP2A PR110 in HEK cells resulted in the persis- tent MTF-1 phosphorylation and the disturbance of MTF-1 nuclear translocation, which was concomitant with a significant decrease of MT expression and enhanced cytotoxicity in HEK cells. Notably, MTF-1 was found in complex with specific PP2A complexes containing the PR110 subunit upon metal exposure. Furthermore, we identify that the dephosphorylation of MTF-1 at residue Thr-254 is directly regulated by PP2A PR110 com- plexes and responsible for MTF-1 activation. Taken together, these findings delineate a novel pathway that determines cyto- toxicity in response to metal treatments and provide new insight into the role of PP2A in cellular stress response. Toxic heavy metals such as arsenic, cadmium, lead, and mer- cury are ubiquitous, have no essential role in maintaining cel- lular homeostasis, and are known to exert multiple organ tox- icities and contribute to a variety of chronic diseases (1-3). To date, environmental heavy metal contamination becomes an increasingly serious threat to human health. Currently, high level exposure to heavy metals in some regions of China remains a serious issue. For example, the Dabaoshan mine in the southeast of Guangdong Province is at high risk of multi- matal nollutant discharge into a local river Hanachiha and the