title: Constitutive activation of epidermal growth factor receptor promotes tumorigenesis of Cr(VI)-transformed cells through decreased reactive oxygen species and apoptosis resistance development.
abstract: Hexavalent chromium (Cr(VI)) compounds are well-established lung carcinogens. Epidermal growth factor receptor (EGFR) is a tyrosine kinase transmembrane receptor that regulates cell survival, tumor invasion, and angiogenesis. Our results show that chronic exposure of human bronchial epithelial (BEAS-2B) cells to Cr(VI) is able to cause malignant cell transformation. These transformed cells exhibit apoptosis resistance with reduced poly ADP-ribose polymerase cleavage (C-PARP) and Bax expression and enhanced expressions of Bcl-2 and Bcl-xL. These transformed cells also exhibit reduced capacity of reactive oxygen species (ROS) generation along with elevated expression of antioxidant manganese superoxide dismutase 2 (SOD2). The expression of this antioxidant was also elevated in lung tumor tissue from a worker exposed to Cr(VI) for 19 years. EGFR was activated in Cr(VI)-transformed BEAS-2B cells, lung tissue from animals exposed to Cr(VI) particles, and human lung tumor tissue. Further study indicates that constitutive activation of EGFR in Cr(VI)-transformed cells was due to increased binding to its ligand amphiregulin (AREG). Inhibition of EGFR or AREG increased Bax expression and reduced Bcl-2 expression, resulting in reduced apoptosis resistance. Furthermore, inhibition of AREG or EGFR restored capacity of ROS generation and decreased SOD2 expression. PI3K/AKT was activated, which depended on EGFR in Cr(VI)-transformed BEAS-2B cells. Inhibition of PI3K/AKT increased ROS generation and reduced SOD2 expression, resulting in reduced apoptosis resistance with commitment increase in Bax expression and reduction of Bcl-2 expression. Xenograft mouse tumor study further demonstrates the essential role of EGFR in tumorigenesis of Cr(VI)-transformed cells. In summary, the present study suggests that ligand-dependent constitutive activation of EGFR causes reduced ROS generation and increased antioxidant expression, leading to development of apoptosis resistance, contributing to Cr(VI)-induced tumorigenesis.
authors.affiliation: From the Graduate Center for Toxicology and.
authors.forename: Donghern
authors.initials: D
authors.lastname: Kim
authors.affiliation: From the Graduate Center for Toxicology and.
authors.forename: Jin
authors.initials: J
authors.lastname: Dai
authors.affiliation: From the Graduate Center for Toxicology and.
authors.forename: Leonard Yenwong
authors.initials: LY
authors.lastname: Fai
authors.affiliation: Department of Stomatology, First Affiliated Hospital, Zhejiang University, Hangzhou, Zhejiang 310003, China, and.
authors.forename: Hua
authors.initials: H
authors.lastname: Yao
authors.affiliation: Center for Research on Environmental Disease, University of Kentucky, Lexington, Kentucky 40536.
authors.forename: Young-Ok
authors.initials: YO
authors.lastname: Son
authors.affiliation: Center for Research on Environmental Disease, University of Kentucky, Lexington, Kentucky 40536.
authors.forename: Lei
authors.initials: L
authors.lastname: Wang
authors.affiliation: Center for Research on Environmental Disease, University of Kentucky, Lexington, Kentucky 40536.
authors.forename: Poyil
authors.initials: P
authors.lastname: Pratheeshkumar
authors.affiliation: Department of Oncological Medical Services, Institute of Health Biosciences, The University of Tokushima Graduate School, Tokushima 770-8509, Japan.
authors.forename: Kazuya
authors.initials: K
authors.lastname: Kondo
authors.affiliation: Center for Research on Environmental Disease, University of Kentucky, Lexington, Kentucky 40536.
authors.forename: Xianglin
authors.initials: X
authors.lastname: Shi
authors.affiliation: From the Graduate Center for Toxicology and zhuo.zhang@uky.edu.
authors.forename: Zhuo
authors.initials: Z
authors.lastname: Zhang
mesh_terms: D066258:Amphiregulin / Q000737:chemistry; D000818:Animals; D000975:Antioxidants / Q000737:chemistry; D017209:Apoptosis; D001151:Arsenic / Q000737:chemistry; D001483:Base Sequence; D045744:Cell Line, Tumor; D002857:Chromium / Q000737:chemistry*; D066246:ErbB Receptors / Q000378:metabolism*; D005260:Female; D015972:Gene Expression Regulation, Neoplastic; D020868:Gene Silencing; D006801:Humans; D008024:Ligands; D051379:Mice; D008807:Mice, Inbred BALB C; D008819:Mice, Nude; D008856:Microscopy, Fluorescence; D008969:Molecular Sequence Data; D009368:Neoplasm Transplantation; D009532:Nickel / Q000737:chemistry; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism; D017382:Reactive Oxygen Species / Q000378:metabolism*; D012689:Sequence Homology, Nucleic Acid; D051028:bcl-2-Associated X Protein / Q000378:metabolism
chemical_list: D066258:Amphiregulin; D000975:Antioxidants; C494826:BAX protein, human; D008024:Ligands; D019253:Proto-Oncogene Proteins c-bcl-2; D017382:Reactive Oxygen Species; D051028:bcl-2-Associated X Protein; D002857:Chromium; C074702:chromium hexavalent ion; D009532:Nickel; C512478:EGFR protein, human; C541485:EGFR protein, mouse; D066246:ErbB Receptors; D001151:Arsenic
keywords: Antioxidant; Apoptosis; Carcinogenesis; Cr(VI); Epidermal Growth Factor Receptor (EGFR); Reactive Oxygen Species (ROS)