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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    • "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.
    Free Radical Biology and Medicine 04/2015; DOI:10.1016/j.freeradbiomed.2015.04.018 · 5.74 Impact Factor
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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.
    Toxicology and Applied Pharmacology 03/2015; 319(1). DOI:10.1016/j.taap.2015.03.007 · 3.71 Impact Factor
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    • "Involvement of NRF2 in the arsenic-induced malignant transformation of keratinocytes has also been suggested [Pi et al., 2008]. In contrast to NF-jB, however, the activation of the NRF2 pathway provides protection against the effects of arsenic trioxide induced oxidative stress in keratinocytes [Pi et al., 2008] and immortalized human bladder urothelial cells [Wang et al., 2007a]. "
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    ABSTRACT: Gene expression changes in primary human uroepithelial cells exposed to arsenite and its methylated metabolites were evaluated to identify cell signaling pathway perturbations potentially associated with bladder carcinogenicity. Cells were treated with mixtures of inorganic arsenic and its pentavalent or trivalent metabolites for 24 hr at total arsenic concentrations ranging from 0.06 μM to 18 μM. One series (five samples) was conducted with arsenite and pentavalent metabolites and a second (10 samples) with arsenite and trivalent metabolites. Similar gene expression responses were obtained for pentavalent or trivalent metabolites. A suite of eight gene changes was consistently identified across individuals that reflect effects on key signaling pathways: oxidative stress, protein folding, growth regulation, metallothionine regulation, DNA damage sensing, thioredoxin regulation, and immune response. No statistical significance of trend (NOSTASOT) analysis of these common genes identified lowest observed effect levels (LOELs) from 0.6 to 6.0 μM total arsenic and no observed effect levels (NOELs) from 0.18 to 1.8 μM total arsenic. For the trivalent arsenical mixture, benchmark doses (BMDs) ranged from 0.13 to 0.92 μM total arsenic; benchmark dose lower 95% confidence limits (BMDLs) ranged from 0.09 to 0.58 μM total arsenic. BMDs ranged from 0.53 to 2.7 μM and BMDLs from 0.35 to 1.7 μM, for the pentavalent arsenical mixture. Both endpoints varied by a factor of 3 across individuals. Thisstudy is the first to examine gene expression response in primary uroepithelial cells frommultiple individuals and to identify no effect levels for arsenical-induced cell signaling perturbations in normal human cells exposed to a biologically plausible concentration range. © Environ. Mol. Mutagen., 2012. © 2012 Wiley Periodicals, Inc.
    Environmental and Molecular Mutagenesis 03/2013; 54(2):82-98. DOI:10.1002/em.21749 · 2.63 Impact Factor
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