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: 5.71). 07/2008; 45(5):651-8. DOI: 10.1016/j.freeradbiomed.2008.05.020
Source: PubMed

ABSTRACT 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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Available from: Jie Liu, Aug 17, 2015
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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 · 3.63 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 · 2.55 Impact Factor
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    • "Very recently it was shown that long isoforms of NRF1 are involved in arsenic-induced apoptosis in human keratinocytes (Zhao et al., 2011), which are the major target tissues of arsenic toxicity as the classical symptoms induced by arsenic exposure are all dermatological in nature. Long term exposure to arsenic at a dose comparable to in vivo exposure, to an immortalized, nontumorigenic human keratinocyte cell line (HaCaT) was found to greatly increase the stability of nuclear protein kinase B (PKB), an antiapoptotic molecule (Pi et al., 2005) and also to activate transcription factor Nrf2 constitutively, which in turn led to marked apoptotic resistance and thus enhancing the possibility of arsenic involvement in skin carcinogenesis (Pi et al., 2008). In fact, it has been demonstrated using an interaction analysis algorithm that several of the top 25 arsenic-interacting genes belong to the cell cycle, cell proliferation and apoptotic pathway (including BCL2, CCND1, CDKN2A, VEGFA, CDNK1A, GADD45A, BAX) and many of them interact with several arsenic compounds (Davis et al., 2008). "
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    ABSTRACT: Exposure to chronic arsenic toxicity is associated with cancer. Although unstable genome is a characteristic feature of cancer cells, the mechanisms leading to genomic instability in arsenic-induced carcinogenesis are poorly understood. While there are excellent reviews relating to genomic instability in general, there is no comprehensive review presenting the mechanisms involved in arsenic-induced genomic instability. This review was undertaken to present the current state of research in this area and to highlight the major mechanisms that may involved in arsenic-induced genomic instability leading to cancer. Genomic instability is broadly classified into chromosomal instability (CIN), primarily associated with mitotic errors; and microsatellite instability (MIN), associated with DNA level instability. Arsenic-induced genomic instability is essentially multi-factorial in nature and involves molecular cross-talk across several cellular pathways, and is modulated by a number of endogenous and exogenous factors. Arsenic and its metabolites generate oxidative stress, which in turn induces genomic instability through DNA damage, irreversible DNA repair, telomere dysfunction, mitotic arrest and apoptosis. In addition to genetic alteration; epigenetic regulation through promoter methylation and miRNA expression alters gene expression profiling leading to genome more vulnerable and unstable towards cancer risk. Moreover, mutations or silencing of pro-apoptotic genes can lead to genomic instability by allowing survival of damaged cells that would otherwise die. Although a large body of information is now generated regarding arsenic-induced carcinogenesis; further studies exploring genome-wide association, role of environment and diet are needed for a better understanding of the arsenic-induced genomic instability.
    Environment international 01/2013; 53C:29-40. DOI:10.1016/j.envint.2012.12.004 · 5.66 Impact Factor
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