Arsenic-induced malignant transformation of human keratinocytes: Involvement of Nrf2

Laboratory of Comparative Carcinogenesis, NCI at NIEHS, NIH, Research Triangle Park, NC 27709, USA.
Free Radical Biology and Medicine (Impact Factor: 5.74). 07/2008; 45(5):651-8. DOI: 10.1016/j.freeradbiomed.2008.05.020
Source: PubMed


Arsenic is a well-known human skin carcinogen but the underlying mechanisms of carcinogenesis are unclear. Transcription factor Nrf2-mediated antioxidant response represents a critical cellular defense mechanism, and emerging data suggest that constitutive activation of Nrf2 contributes to malignant phenotype. In the present study when an immortalized, nontumorigenic human keratinocyte cell line (HaCaT) was continuously exposed to an environmentally relevant level of inorganic arsenite (100 nM) for 28 weeks, malignant transformation occurred as evidenced by the formation of highly aggressive squamous cell carcinoma after inoculation into nude mice. To investigate the mechanisms involved, a broad array of biomarkers for transformation were assessed in these arsenic-transformed cells (termed As-TM). In addition to increased secretion of matrix metalloproteinase-9 (MMP-9), a set of markers for squamous differentiation and skin keratinization, including keratin-1, keratin-10, involucrin, and loricrin, were significantly elevated in As-TM cells. Furthermore, As-TM cells showed increased intracellular glutathione and elevated expression of Nrf2 and its target genes, as well as generalized apoptotic resistance. In contrast to increased basal Nrf2 activity in As-TM cells, a diminished Nrf2-mediated antioxidant response induced by acute exposure to high doses of arsenite or tert-butyl hydroxyquinone occurred. The findings that multiple biomarkers for malignant transformation observed in As-TM cells, including MMP-9 and cytokeratins, are potentially regulated by Nrf2 suggest that constitutive Nrf2 activation may be involved in arsenic carcinogenesis of skin. The weakened Nrf2 activation in response to oxidative stressors observed in As-TM cells, coupled with acquired apoptotic resistance, would potentially have increased the likelihood of transmittable oxidative DNA damage and fixation of mutational/DNA damage events.

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    • "For instance, NRF2 appears to be involved in tumorigenesis and development of chemoresistance in cancer cells (Singh et al., 2006; Lau et al., 2008; Homma et al., 2009; Jiang et al., 2010; Zhang, 2010; Zhang et al., 2010; DeNicola et al., 2011; Rushworth et al., 2011). In keeping with the role of NRF2 in protection against oxidative/electrophilic stress, we previously showed that persistent activation of the NRF2-mediated antioxidant response is involved in the development of acquired apoptotic resistance and thus contributes to arsenic carcinogenesis (Pi et al., 2008). Constitutive activation of NRF2 in cancer cells may protect them against oxidative/electrophilic stress and thereby enhance proliferation with associated resistance to chemotherapy and radiotherapy (Gao et al., 2013; Kansanen et al., 2013; Tao et al., 2014; Wang et al., 2014; Wu et al., 2014). "
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    ABSTRACT: Nuclear factor erythroid 2-related factor 2 (NRF2), a master regulator of the antioxidant response element (ARE)-dependent transcription, plays a pivotal role in chemical detoxification in normal and tumor cells. Consistent with previous findings that NRF2-ARE contributes to chemotherapeutic resistance of cancer cells, we found that stable knockdown of NRF2 by lentiviral shRNA in human acute monocytic leukemia (AML) THP-1 cells enhanced the cytotoxicity of several chemotherapeutic agents, including arsenic trioxide (As2O3), etoposide and doxorubicin. Using an ARE-luciferase reporter expressed in several human and mouse cells, we identified a set of compounds, including isonicotinic acid amides, isoniazid and ethionamide, that inhibited NRF2-ARE activity. Treatment of THP-1 cells with ethionamide, for instance, significantly reduced mRNA expression of multiple ARE-driven genes under either basal or As2O3-challenged conditions. As determined by cell viability and cell cycle, suppression of NRF2-ARE by ethionamide also significantly enhanced susceptibility of THP-1 and U937 cells to As2O3-induced cytotoxicity. In THP-1 cells, the sensitizing effect of ethionamide on As2O3-induced cytotoxicity was highly dependent on NRF2. To our knowledge, the present study is the first to demonstrate that ethionamide suppresses NRF2-ARE signaling and disrupts the transcriptional network of the antioxidant response in AML cells, leading to sensitization to chemotherapeutic agents.
    Full-text · Article · Dec 2015 · Toxicology and Applied Pharmacology
    • "This long-term activation resembles the constitutive activation seen in cancer cells (see below), suggesting that it does not prevent, but rather contributes to the carcinogenic activity of arsenic. This may also be the case in the skin as suggested by the finding that HaCaT keratinocytes transformed by long-term treatment with low concentrations of arsenic showed a general apoptosis resistance as well as resistance to UV-induced apoptosis, thereby allowing survival of mutated cells [40] [41]. Therefore , it will be interesting in the future to precisely define the role of Nrf2 in acute arsenic toxicity and in arsenic-induced skin carcinogenesis. "
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    ABSTRACT: The skin is frequently exposed to environmental challenges, such as UV irradiation, toxic chemicals or mechanical wounding. These insults cause an increase in the levels of reactive oxygen species, resulting in oxidative stress and concomitant inflammation, skin aging and even cancer development. Therefore, an efficient antioxidant defense strategy is of major importance in this tissue. Since the NRF2 transcription factor regulates a battery of genes involved in the defense against reactive oxygen species and in compound metabolism, it plays a key role in skin homeostasis, repair and disease. In this review we summarize current knowledge on the expression and function of NRF2 in normal skin, its role in the acute and chronic UV response as well as in the pathogenesis of epithelial skin cancer and of different inflammatory skin diseases. Finally, we discuss the potential of NRF2-activating compounds for skin protection under stress conditions and for the treatment of major human skin disorders. Copyright © 2015. Published by Elsevier Inc.
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    • "However, other transcription factors involved in the regulation of TGIF cannot be ruled out. For example, Nrf2 is involved in arsenic-induced oxidative stress and cellular transformation (Pi et al., 2008; Zhao et al., 2012; Sumi et al., 2013). Furthermore, Nrf2 can regulate several genes that are involved in the cytoprotective response against oxidative stress (Itoh et al., 2010). "
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    ABSTRACT: Arsenic trioxide (ATO) is a multi-target drug approved by the Food and Drug Administration as the first-line chemotherapeutic agent for the treatment of acute promyelocytic leukemia. In addition, several clinical trials are being conducted with arsenic-based drugs for the treatment of other hematological malignancies and solid tumors. However, ATO's modest clinical efficacy on some cancers, and potential toxic effects on humans have been reported. Determining how best to reduce these adverse effects while increasing its therapeutic efficacy is obviously a critical issue. Previously, we demonstrated that the JNK-induced complex formation of phosphorylated c-Jun and TG-interacting factor (TGIF) antagonizes ERK-induced cyclin-dependent kinase inhibitor CDKN1A (p21(WAF1/CIP1)) expression and resultant apoptosis in response to ATO in A431 cells. Surprisingly, at low-concentrations (0.1~0.2 μM), ATO increased cellular proliferation, migration and invasion, involving TGIF expression, however, at high-concentrations (5~20 μM), ATO induced cell apoptosis. Using a promoter analysis, TGIF was transcriptionally regulated by ATO at the FOXO3A binding site (-1486 to -1479 bp) via the c-Src/EGFR/AKT pathway. Stable overexpression of TGIF promoted advancing the cell cycle into S phase, and attenuated 20 μM ATO-induced apoptosis. Furthermore, blockage of the AKT pathway enhanced ATO-induced CDKN1A expression and resultant apoptosis in cancer cells, but overexpression of AKT1 inhibited CDKN1A expression. Therefore, we suggest that TGIF is transcriptionally regulated by the c-Src/EGFR/AKT pathway, which plays a role as a negative regulator in antagonizing ATO-induced CDKN1A expression and resultant apoptosis. Suppression of these antagonistic effects might be a promising therapeutic strategy toward improving clinical efficacy of ATO. Copyright © 2015. Published by Elsevier Inc.
    Preview · Article · Mar 2015 · Toxicology and Applied Pharmacology
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