The protective role of Nrf2 against arsenic-induced toxicity and carcinogenicity

University Of Arizona, Tucson AZ

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Abstract

DESCRIPTION (provided by applicant): The transcription factor, Nrf2, has emerged as the master regulator of a cellular protective mechanism by upregulating antioxidant response element (ARE)- bearing genes encoding antioxidant enzymes, detoxifying enzymes, xenobiotic transporters, and stress response proteins. Very recently, mounting evidence points to the dual function of Nrf2 in cancer. (i) In normal cells when the Nrf2- Keap1 axis is intact and basal level of Nrf2 are low, transient activation of Nrf2 by chemopreventive compounds confers protection against environmental toxins and carcinogens. (ii) In certain cancer cell lines, constitutive activation of Nrf2 creates an environment conducive for cancer cell survival. Moreover, Nrf2 contributes to chemoresistance and inhibition of the Nrf2 pathway enhances the efficacy of cancer treatments. Arsenic (As) is a human carcinogen, which causes tumors in the skin, lung and bladder. Large populations around the world are exposed to arsenic through contaminated drinking water, which imposes a major challenge to human health. However, a sufficient rodent model to study arsenic-carcinogenicity is still lacking. This competing renewal of NIH ES015010 takes advantage of a previously unrecognized role of arsenic in autophagy leading to prolonged activation of Nrf2, which was uncovered during the last funding period. We hypothesize that arsenic-mediated carcinogenicity is associated with its ability to deregulate the autophagic pathway. We believe that canonical Nrf2 inducers can alleviate this effect and thus, can be used as chemopreventive agents to counteract the damaging effects of arsenic. The following three aims are proposed: Aim 1 (in vitro): Elucidate a novel mechanism of Nrf2 induction by arsenic through deregulation of autophagy (prolonged activation of Nrf2). Aim 2 (ex vivo): Determine the role of Nrf2 in arsenic-mediated autophagosome formation and carcinogenicity using a transplantable syngeneic mouse lung cancer model. Aim 3 (in vivo): Validate the biological and pharmacological relevancy of this work. From this proposal we will (i) gain novel mechanistic insight of how arsenic deregulates autophagy, (ii) confirm the association between deregulation of autophagy and tumorigenicity of arsenic, (iii) provide new biomarkers and a sensitive animal model for arsenic carcinogenicity studies and (iv) demonstrate the potential translational impact of targeting the Nrf2 pathway using canonical Nrf2 activators to combat arsenic-induced toxicity and carcinogenicity. In addition, the syngeneic mouse lung cancer model developed will be invaluable for scientific communities studying other carcinogens.