Erlotinib-Mediated Inhibition of EGFR Signaling Induces Metabolic Oxidative Stress through NOX4

Free Radical and Radiation Biology Program, Department of Radiation Oncology, Holden Comprehensive Cancer Center, The University of Iowa, Iowa City, Iowa 52242, USA.
Cancer Research (Impact Factor: 9.28). 06/2011; 71(11):3932-40. DOI: 10.1158/0008-5472.CAN-10-3425
Source: PubMed

ABSTRACT Redox regulation of epidermal growth factor receptor (EGFR) signaling helps protect cells against oxidative stress. In this study, we investigated whether the cytotoxicity of an EGFR tyrosine kinase inhibitor, erlotinib (ERL), was mediated by induction of oxidative stress in human head and neck cancer (HNSCC) cells. ERL elicited cytotoxicity in vitro and in vivo while increasing a panel of oxidative stress parameters which were all reversible by the antioxidant N-acetyl cysteine. Knockdown of EGFR by using siRNA similarly increased these oxidative stress parameters. Overexpression of mitochondrial targeted catalase but not superoxide dismutase reversed ERL-induced cytotoxicity. Consistent with a general role for NADPH oxidase (NOX) enzymes in ERL-induced oxidative stress, ERL-induced cytotoxicity was reversed by diphenylene iodonium, a NOX complex inhibitor. ERL reduced the expression of NOX1, NOX2, and NOX5 but induced the expression of NOX4. Knockdown of NOX4 by using siRNA protected HNSCC cells from ERL-induced cytotoxicity and oxidative stress. Our findings support the concept that ERL-induced cytotoxicity is based on a specific mechanism of oxidative stress mediated by hydrogen peroxide production through NOX4 signaling.

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    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) was able to cause malignant cell transformation. These transformed cells exhibited 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 exhibited reduced capacity of reactive oxygen species (ROS) generation along with elevated expression of antioxidant manganese superoxide dismutase 2 (SOD2). EGFR was activated in Cr(VI)-transformed BEAS-2B cells, lung tissue of animals exposed to Cr(VI) particles, and lung tumor tissue of a worker exposed to Cr(VI) for 19 years. 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. Copyright © 2014, The American Society for Biochemistry and Molecular Biology.
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