Arsenic (As3+) is a carcinogen with considerable environmental and occupational relevancy. The present study shows that As3+-transformed human lung bronchial epithelial BEAS-2B cells (AsT cells) exhibit the property of apoptosis resistance. The level of basal reactive oxygen species (ROS) is very low in AsT cells in correlation with elevated expressions of both antioxidant enzymes and antiapoptotic proteins. Nuclear factor erythroid 2-related factor (Nrf2) and p62 are constitutively expressed. These two proteins up-regulate antioxidant enzymes and antiapoptotic proteins. The knockdown of Nrf2 or p62 by small interfering RNA (siRNA) enhanced both ROS levels and As3+-induced apoptosis in transformed cells. AsT cells have autophagy deficiency as evidenced by reduced formation of microtubule-associated protein 1 light chain 3 (LC3)-II, GFP-LC3 puncta, and autophagy flux. Results obtained using a soft agar assay and shRNA Nrf2-transfected cells show that Nrf2 plays an antioncogenic role before transformation, whereas this transcription factor plays an oncogenic role after transformation. In addition, depletion of Nrf2 by shRNA dramatically inhibited growth and proliferation of transformed cells. Furthermore, the Nrf2 protein levels and antiapoptotic and antioxidant enzyme levels are higher in lung adenocarcinoma than in normal tissues. Collectively, this study demonstrates that a constitutively high level of Nrf2 in AsT cells up-regulates the antioxidant proteins catalase and superoxide dismutase as well as the antiapoptotic proteins Bcl-2 and Bcl-xL. The final consequences are decreased ROS generation and increased apoptotic resistance, cell survival and proliferation, and tumorigenesis.
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This work was supported by National Institutes of Health Grants R01 ES025515, R01 ES021771, and R01 ES020870 and the Biospecimen and Tissue Procurement Shared Resource Facility and the Cytometry and Cell Sorting core facility of the University of Kentucky Markey Cancer Center (National Institutes of Health Grant P30CA177558). The authors declare that they have no conflicts of interest with the contents of this article.
Son, Young-Ok; Pratheeshkumar, Poyil; Roy, Ram Vinod; Hitron, Andrew; Wang, Lei; Divya, Sasidharan Padmaja; Xu, Mei; Luo, Jia; Chen, Gang; Zhang, Zhuo; and Shi, Xianglin, "Antioncogenic and Oncogenic Properties of Nrf2 in Arsenic-Induced Carcinogenesis" (2015). Center for Research on Environmental Disease Faculty Publications. 3.