title: Nrf2/p62 signaling in apoptosis resistance and its role in cadmium-induced carcinogenesis.
abstract: The cadmium-transformed human lung bronchial epithelial BEAS-2B cells exhibit a property of apoptosis resistance as compared with normal non-transformed BEAS-2B cells. The level of basal reactive oxygen species (ROS) is extremely low in transformed cells in correlation with elevated expressions of both antioxidant enzymes (catalase, SOD1, and SOD2) and antiapoptotic proteins (Bcl-2/Bcl-xL). Moreover, Nrf2 and p62 are highly expressed in these transformed cells. The knockdown of Nrf2 or p62 by siRNA enhances ROS levels and cadmium-induced apoptosis. The binding activities of Nrf2 on the antioxidant response element promoter regions of p62/Bcl-2/Bcl-xL were dramatically increased in the cadmium-exposed transformed cells. Cadmium exposure increased the formation of LC3-II and the frequency of GFP-LC3 punctal cells in non-transformed BEAS-2B cells, whereas these increases are not shown in transformed cells, an indication of autophagy deficiency of transformed cells. Furthermore, the expression levels of Nrf2 and p62 are dramatically increased during chronic long term exposure to cadmium in the BEAS-2B cells as well as antiapoptotic proteins and antioxidant enzymes. These proteins are overexpressed in the tumor tissues derived from xenograft mouse models. Moreover, the colony growth is significantly attenuated in the transformed cells by siRNA transfection specific for Nrf2 or p62. Taken together, this study demonstrates that cadmium-transformed cells have acquired autophagy deficiency, leading to constitutive p62 and Nrf2 overexpression. These overexpressions up-regulate the antioxidant proteins catalase and SOD and the antiapoptotic proteins Bcl-2 and Bcl-xL. The final consequences are decrease in ROS generation, apoptotic resistance, and increased cell survival, proliferation, and tumorigenesis.
authors.affiliation: From the Center for Research on Environmental Disease and the Graduate Center for Toxicology, College of Medicine, University of Kentucky, Lexington, Kentucky 40536-0305.
authors.forename: Young-Ok
authors.initials: YO
authors.lastname: Son
authors.affiliation: From the Center for Research on Environmental Disease and the Graduate Center for Toxicology, College of Medicine, University of Kentucky, Lexington, Kentucky 40536-0305.
authors.forename: Poyil
authors.initials: P
authors.lastname: Pratheeshkumar
authors.affiliation: From the Center for Research on Environmental Disease and the Graduate Center for Toxicology, College of Medicine, University of Kentucky, Lexington, Kentucky 40536-0305.
authors.forename: Ram Vinod
authors.initials: RV
authors.lastname: Roy
authors.affiliation: the Graduate Center for Toxicology, College of Medicine, University of Kentucky, Lexington, Kentucky 40536-0305.
authors.forename: John Andrew
authors.initials: JA
authors.lastname: Hitron
authors.affiliation: From the Center for Research on Environmental Disease and the Graduate Center for Toxicology, College of Medicine, University of Kentucky, Lexington, Kentucky 40536-0305.
authors.forename: Lei
authors.initials: L
authors.lastname: Wang
authors.affiliation: the Graduate Center for Toxicology, College of Medicine, University of Kentucky, Lexington, Kentucky 40536-0305.
authors.forename: Zhuo
authors.initials: Z
authors.lastname: Zhang
authors.affiliation: From the Center for Research on Environmental Disease and the Graduate Center for Toxicology, College of Medicine, University of Kentucky, Lexington, Kentucky 40536-0305 xshi5@email.uky.edu.
authors.forename: Xianglin
authors.initials: X
authors.lastname: Shi
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000235:genetics; D001343:Autophagy / Q000235:genetics; D001980:Bronchi / Q000187:drug effects / Q000378:metabolism / Q000473:pathology; D002104:Cadmium / Q000633:toxicity*; D002374:Catalase / Q000235:genetics / Q000378:metabolism; D002460:Cell Line; D002471:Cell Transformation, Neoplastic / Q000139:chemically induced / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D004847:Epithelial Cells / Q000187:drug effects* / Q000378:metabolism / Q000473:pathology; D015972:Gene Expression Regulation, Neoplastic; D017930:Genes, Reporter; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism; D006801:Humans; D008175:Lung Neoplasms / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D008297:Male; D051379:Mice; D008819:Mice, Nude; D008869:Microtubule-Associated Proteins / Q000235:genetics / Q000378:metabolism; D051267:NF-E2-Related Factor 2 / Q000037:antagonists & inhibitors / Q000235:genetics* / Q000378:metabolism; D009368:Neoplasm Transplantation; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000235:genetics / Q000378:metabolism; D034741:RNA, Small Interfering / Q000235:genetics / Q000378:metabolism; D016601:RNA-Binding Proteins / Q000037:antagonists & inhibitors / Q000235:genetics* / Q000378:metabolism; D017382:Reactive Oxygen Species / Q000378:metabolism; D015398:Signal Transduction; D013482:Superoxide Dismutase / Q000235:genetics / Q000378:metabolism; D051020:bcl-X Protein / Q000235:genetics / Q000378:metabolism
chemical_list: C494811:BCL2L1 protein, human; C477012:MAP1LC3A protein, human; D008869:Microtubule-Associated Proteins; D051267:NF-E2-Related Factor 2; C495635:NFE2L2 protein, human; C118585:P62 protein, human; D019253:Proto-Oncogene Proteins c-bcl-2; D034741:RNA, Small Interfering; D016601:RNA-Binding Proteins; D017382:Reactive Oxygen Species; D051020:bcl-X Protein; D002104:Cadmium; D049452:Green Fluorescent Proteins; D002374:Catalase; D013482:Superoxide Dismutase
keywords: Apoptosis; Autophagy; Cadmium; Carcinogenesis; Nuclear Factor 2 (Erythroid-derived 2-like Factor) (NFE2L2) (Nrf2); Reactive Oxygen Species (ROS); p62