Mechanism Of Arsenic-induced Carcinogenesis Research Articles

Geological Sources of Arsenic and Cancer Risk Associated with The Metalloid- An Overview

Arsenic, a widely prevalent metalloid in the environment, poses significant health risks due to chronic exposure through contaminated water, food, and various human activities. This comprehensive overview highlights the prevalence of arsenic poisoning, particularly in regions like India and Bangladesh, stemming from arsenic-contaminated drinking water. The toxicological impact of chronic arsenic exposure on human health is multifaceted, leading to dermatological, neurological, and organ-related complications. Notably, arsenic exposure has been linked to the development of malignancies such as lung, bladder, liver, kidney, gastrointestinal, and brain cancers. Mechanisms of arsenic-induced carcinogenesis, DNA damage, and associated health conditions are elucidated. Understanding the sources, prevalence, and health impacts of arsenic contamination is crucial for implementing effective mitigation strategies.

Epigenetic regulations in alternative telomere lengthening: Understanding the mechanistic insight in arsenic-induced skin cancer patients

Telomere integrity is considered to be one of the primary mechanisms during malignant transformation. Arsenic, a group 1 carcinogenic metalloid, has been reported to cause telomere lengthening in a telomerase-independent manner. Recent studies suggest a significant role for epigenetic modifications in regulating telomeric length and integrity. Here, we have explored the role of epigenetic deregulation in alternative lengthening of telomeres (ALT) in arsenic-exposed skin cancer tissues and corresponding non-tumor tissues. The relative telomere length (RTL) was analyzed by qRT-PCR using 2−ΔΔCt method. The subtelomeric methylation pattern of the four chromosomes (7q, 18p, 21q and XpYp) were analysed by Methylation Specific PCR (MSP) in 40 pairs of arsenic exposed skin cancer tissues and its corresponding control. The role of constitutive heterochromatin histone marks in the regulation of telomere length (TL) was analyzed by targeted ELISA. A 2-fold increase of relative telomere length in 85% of the arsenic-induced skin cancer tissues was observed. Among the four chromosomes, subtelomere of XpYp was found to be hypermethylated (p < 0.001) whereas 18p was hypomethylated (p < 0.01). Additionally, the level of H4K20me3, a heterochromatic mark was found to be significantly down-regulated (p < 0.0003), and inversely correlated with telomere length indicating loss of heterochromatinization of telomeric DNA. These observations highlight the novel role of epigenetic regulation in the maintenance of constitutive heterochromatin structure at telomere. Alteration in subtelomeric DNA methylation patterns and depletion of H4K20me3 might lead to loss of heterochromatinization resulting in arsenic-induced telomeric elongation. We provide novel data indicating possible alternative determinants of telomere elongation through epigenetic modifications during arsenic-induced skin carcinogenesis which could be used as early ‘epimarkers’ in the near future. The findings provide new insights about the mechanism of arsenic-induced carcinogenesis.

Abstract 356: Polyadenyaltion of canonical histone mRNA: A potential mechanism of arsenic-induced carcinogenesis

Abstract Naturally occurring inorganic arsenic has been identified as a prominent causal agent in lung, bladder, liver, and prostate cancers. Although arsenic (As) has long been known to induce carcinogenicity via epigenetic mechanisms, alteration in histone gene expression has not been explored. The replication-dependent histone genes (also known as canonical histone genes) are the only genes found in multicellular organisms whose messenger RNA (mRNA) does not terminate with a poly(A) tail at the 3' end. Instead, they contain a conserved 26-nucleotide sequence that forms a stem-loop structure, and serves as the binding site for the Stem-loop binding protein (SLBP). SLBP is critical for canonical histone pre-mRNA processing and histone mRNA translation. Our previous studies demonstrated that arsenic exposure increases polyadenylation of histone H3.1 mRNA (a canonical histone H3) and its presence outside of S phase of the cell cycle due to the loss of SLBP protein and mRNA. Here we report that ectopic expression of polyadenylated H3.1 mRNA induces cell transformation and that the transformed cells are able to form tumors in athymic nude mice. These carcinogenic effects are dependent on the level of polyadenylation of canonical H3.1 mRNA. Notably, transfection of H3.1 cDNA with a stem-loop sequence in the front of the poly(A) signal generates less polyadenylated H3.1 mRNA and thereby attenuates cell transformation. Furthermore, the increase in polyadenylated H3.1 mRNA is able to antagonize histone H3.3 (a non-canonical variant of H3) in the promoter of active genes and perturb expression of cancer-related genes. In addition transfection of H3.1 with a poly(A) tail causes mitotic block in the cell cycle as well as chromosome instability. Furthermore, acute arsenic exposure by inhalation in mice results in the loss of SLBP and gain of polyadenylated H3.1 mRNA in lung tissues. These results suggest that the polyadenylation of canonical histone mRNAs induce by Arsenic is very disruptive to cellular genomic integrity and contributes to development of human cancers. Citation Format: Qiao Yi Chen, Danqi Chen, Thomas Kluz, Feng Wu, Yusha Zhu, Thomas Des Marais, Jinquan Li, Xiaoru Zhang, Ashley Jordan, Hong Sun, Chunyuan Jin, Max Costa. Polyadenyaltion of canonical histone mRNA: A potential mechanism of arsenic-induced carcinogenesis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 356.

Arsenite downregulates H3K4 trimethylation and H3K9 dimethylation during transformation of human bronchial epithelial cells.

Arsenic is an established human carcinogen but with weak mutagenic activity. The mechanisms of arsenic-induced carcinogenesis are not well understood. In the present study, we investigated the role of histone methylation in transformation of human bronchial epithelial (BEAS-2B) cells. After 16weeks' exposure, cells were transformed by 0.1, 0.5 and 1μm arsenite. Global trimethylated H3K4 (H3K4me3) was decreased by 0.1μm arsenite at 12weeks, and 0.5 and 1μm arsenite at 8, 12 and 16weeks, which could be attributed to reduced histone methyltransferase activities, increased histone demethylase (HDM) activities as well as increased protein levels of H3K4 demethylase KDM5A. Global dimethylated H3K9 (H3K9me2) was also decreased after exposure to 0.5μm arsenite for 4, 8, 12 and 16weeks and 1.0μm arsenite for 8 and 12weeks, which was associated with an increase of HDM activities. Our findings indicated that arsenite decreased global H3K4me3 and H3K9me2 levels during cell transformation by modulating the enzymatic activities of histone methyltransferases and/or HDMs, and by upregulation of KDM5A protein levels for H3K4me3.

SILAC-based quantitative proteomic analysis reveals widespread molecular alterations in human skin keratinocytes upon chronic arsenic exposure.

Chronic exposure to arsenic is associated with dermatological and nondermatological disorders. Consumption of arsenic-contaminated drinking water results in accumulation of arsenic in liver, spleen, kidneys, lungs, and gastrointestinal tract. Although arsenic is cleared from these sites, a substantial amount of residual arsenic is left in keratin-rich tissues including skin. Epidemiological studies suggest the association of skin cancer upon arsenic exposure, however, the mechanism of arsenic-induced carcinogenesis is not completely understood. We developed a cell line based model to understand the molecular mechanisms involved in arsenic-mediated toxicity and carcinogenicity. Human skin keratinocyte cell line, HaCaT, was chronically exposed to 100 nM sodium arsenite over a period of 6 months. We observed an increase in basal ROS levels in arsenic-exposed cells. SILAC-based quantitative proteomics approach resulted in identification of 2111 proteins of which 42 proteins were found to be overexpressed and 54 downregulated (twofold) upon chronic arsenic exposure. Our analysis revealed arsenic-induced overexpression of aldo-keto reductase family 1 member C2 (AKR1C2), aldo-keto reductase family 1 member C3 (AKR1C3), glutamate-cysteine ligase catalytic subunit (GCLC), and NAD(P)H dehydrogenase [quinone] 1 (NQO1) among others. We observed downregulation of several members of the plakin family including periplakin (PPL), envoplakin (EVPL), and involucrin (IVL) that are essential for terminal differentiation of keratinocytes. MRM and Western blot analysis confirmed differential expression of several candidate proteins. Our study provides insights into molecular alterations upon chronic arsenic exposure on skin.

Oxidative stress, epigenetics, and cancer stem cells in arsenic carcinogenesis and prevention.

The carcinogenic role of arsenic has been extensively studied for more than half century. How arsenic causes human cancer, however, remains to be fully elucidated. In this brief review, we focus our attentions on the most recent discoveries by us and others on the capabilities of arsenic in inducing generation of reactive oxygen species (ROS), expression of microRNAs (miRNAs) and the generation of the cancer stem cells. We believe that these new understandings on the mechanisms of arsenic-induced carcinogenesis will shed light on the prevention and treatment of human cancers resulted from environmental or occupational arsenic exposure. Furthermore, these latest findings on arsenic-induced cellular responses will also have an important impact on the investigation of the carcinogenic effects of other environmental or occupational carcinogens or hazards.

Effects of DNMT and MEK inhibitors on the expression of RECK, MMP-9, -2, uPA and VEGF in response to arsenite stimulation in human uroepithelial cells

It has been shown that the ingestion of arsenic-contaminated drinking water is closely correlated with risk of several cancers. The mechanism of arsenic-induced carcinogenesis is still unclear. The RECK, MMP-9, -2, uPA and VEGF are the most common dysregulation in human tumors and cancer cell lines. However, the effect of arsenite on these markers expression and the molecular mechanism are still unclear. The purpose of the study was to investigate the relationship between the expression of RECK, MMP-9, -2, uPA and VEGF in arsenite-treated human and rat uroepithelial cells. In addition, we also observed and compared the expression of these markers in urothelial carcinoma (UC) from Blackfoot disease (BFD) areas and non-Blackfoot disease (non-BFD) areas. We analyzed the arsenite causing cell proliferation, RECK, MMP-9, -2, uPA and VEGF expression by Western blotting, immunocytochemistry (ICC), RT-PCR, and gelatin zymography. We demonstrated the effect of arsenite on methylation status of RECK promoter as determined by using methylation-specific PCR (MSP). Our results show that arsenite downregulation of RECK is caused by epigenetic inactivation via promoter hypermethylation, and that levels of MMP-9, -2, uPA and VEGF were increased in human uroepithelial cells (SV-HUC-1). However, when the cells were pretreated with inhibitors (5-aza-CdR or U0126) for 24 h, the effects of arsenite on RECK, MMP-9, -2, uPA and VEGF expression were suppressed. Indeed, we also found significant differences between the expression of RECK, MMP-9, -2, uPA and VEGF in UC from the BFD areas and non-BFD areas ( p = 0.006, 0.007, 0.003, <0.001 and 0.001 respectively), as detected by immunohistochemistry (IHC). In in vivo study, our results showed the RECK protein expression was reduced and the expression of MMP-9, -2, uPA and VEGF increased in arsenite treatment groups. In conclusion, our results support the notion that arsenite might cause the histologic changes, RECK, MMP-9, -2, uPA and VEGF dysregulation through epigenetic inactivation and ERK1/2 activation in SV-HUC-1 cells. These findings may provide a better understanding of the urothelial carcinogenesis of arsenite.