Chronic arsenic exposure suppresses ATM pathway activation in human keratinocytes

Chronic arsenic exposure suppresses proteasomal and autophagic protein degradation

Ubiquitin Proteasomal System (UPS) and autophagy dysregulation initiate cancer. These pathways are regulated by zinc finger proteins. Trivalent inorganic arsenic (iAs) displaces zinc from zinc finger proteins disrupting functions of important cellular proteins. The effect of chronic environmental iAs exposure (100 nM) on UPS has not been studied. We tested the hypothesis that environmental iAs exposure suppresses UPS, activating autophagy as a compensatory mechanism. We exposed skin (HaCaT and Ker-CT; independent quadruplicates) and lung (BEAS-2B; independent triplicates) cell cultures to 0 or 100 nM iAs for 7 or 8 weeks. We quantified ER stress (XBP1 splicing employing Reverse Transcriptase -Polymerase Chain Reaction), proteasomal degradation (immunoblots), and initiation and completion of autophagy (immunoblots). We demonstrate that chronic iAs exposure suppresses UPS, initiates autophagy, but suppresses autophagic protein degradation in skin and lung cell lines. Our data suggest that chronic iAs exposure inhibits autophagy which subsequently suppresses UPS.

Chronic arsenic exposure induces malignant transformation of human HaCaT cells through both deterministic and stochastic changes in transcriptome expression

Biological processes are inherently stochastic, i.e., are partially driven by hard to predict random probabilistic processes. Carcinogenesis is driven both by stochastic and deterministic (predictable non-random) changes. However, very few studies systematically examine the contribution of stochastic events leading to cancer development. In differential gene expression studies, the established data analysis paradigms incentivize expression changes that are uniformly different across the experimental versus control groups, introducing preferential inclusion of deterministic changes at the expense of stochastic processes that might also play a crucial role in the process of carcinogenesis. In this study, we applied simple computational techniques to quantify: (i) The impact of chronic arsenic (iAs) exposure as well as passaging time on stochastic gene expression and (ii) Which genes were expressed deterministically and which were expressed stochastically at each of the three stages of cancer development. Using biological coefficient of variation as an empirical measure of stochasticity we demonstrate that chronic iAs exposure consistently suppressed passaging related stochastic gene expression at multiple time points tested, selecting for a homogenous cell population that undergo transformation. Employing multiple balanced removal of outlier data, we show that chronic iAs exposure induced deterministic and stochastic changes in the expression of unique set of genes, that populate largely unique biological pathways. Together, our data unequivocally demonstrate that both deterministic and stochastic changes in transcriptome-wide expression are critical in driving biological processes, pathways and networks towards clonal selection, carcinogenesis, and tumor heterogeneity.

Unveiling the metal mutation nexus: Exploring the genomic impacts of heavy metal exposure in lung adenocarcinoma and colorectal cancer

Mutations that activate oncogenes and deactivate tumor suppressor genes are widely recognized as significant contributors to cancer development. We investigated relationships between heavy metal exposure and the frequencies and types of gene mutations in patients with lung adenocarcinoma (LUAD) and colorectal cancer (CRC). Plasma concentrations of arsenic (As), cadmium (Cd), chromium (Cr), mercury (Hg), and lead (Pb) were measured using inductively coupled plasma mass spectrometry (ICPMS), and next-generation sequencing (NGS) of 1123 cancer-related genes was performed using the tumor tissues. Through Bayesian kernel machine regression (BKMR) analysis, we found associations between the integrated concentrations of the heavy metals and the number of gene mutations, especially insertions/deletions (indels), and Pb, As, and Cd were found to be the most significant contributors to the increased mutation rates. We extracted previously established mutational signatures and observed that they exhibit significant correlations with metal exposure. Moreover, we detected substantial shifts in the mutational landscape when comparing groups with high and low metal exposures. Several frequently mutated genes displayed positive correlations with metal exposure, whereas EGFR indels showed a negative association with Cd exposure. These findings suggest that heavy metal exposure can impact genomic stability in cancer-related genes, underscoring the importance of heavy metal exposure in cancer development.

MiR-96-5p Suppresses Progression of Arsenite-Induced Human Keratinocyte Proliferation and Malignant Transformation by Targeting Denticleless E3 Ubiquitin Protein Ligase Homolog

Long-term exposure to arsenic has been linked to a variety of cancers, among which skin cancer is the most prevalent form. However, the mechanism underlying arsenic carcinogenesis is unclear, and there is still limited information on the role of miRNAs in arsenic-induced skin cancer. This study aims to explore the role of miR-96-5p in the arsenite-induced proliferation and malignant transformation of human HaCaT keratinocytes. The GEO database (accession numbers GSE97303, GSE97305, and GSE97306) was used to extract mRNA and miRNA expression profiles of HaCaT cells treated with or without 0.1 μmol/L sodium arsenite for 3 and 7 weeks. In this paper, according to the CCK8 assay result, HaCaT cells exposed to 0.1 μmol/L sodium arsenite for 48 h were finalized. CCK8, MTT, EdU incorporation, and colony formation assays were used to determine the viability and proliferation of HaCaT cells and transformed HaCaT (T-HaCaT) cells. The subcellular localization and relative expression levels of DTL, as well as miR-96-5p in HaCaT cells induced by arsenite, were determined via immunofluorescence, RT-qPCR, and Western blot. Dual-luciferase reporter assay was performed to identify miR-96-5p bound directly to DTL. Transfection of miR-96-5p mimics or DTL siRNA was conducted to verify the arsenite-induced viability of HaCaT cells and T-HaCaT cells. T-HaCaT cells and nude mice were used to construct arsenite-induced malignant transformation and an in vivo xenograft model to demonstrate the over-expressed effect of miR-96-5p. The results showed that DTL was the target gene of miR-96-5p. Meanwhile, we also found that 0.1 μmol/L sodium arsenite upregulated DTL by decreasing the miR-96-5p level, leading to the proliferation and malignant transformation of HaCaT cells. MiR-96-5p agomir treatment slowed the growth of transplanted HaCaT cells transformed by arsenite in a manner associated with DTL downregulation in the nude mice xenograft model. Taken together, we confirmed that miR-96-5p, as a potent regulator of DTL, suppressed arsenite-induced HaCaT cell proliferation and malignant transformation, which might provide a novel therapeutic target for the treatment of arsenic-induced skin cancer.

Gene expression analyses reveal potential mechanism of inorganic arsenic-induced apoptosis in zebrafish

Our previous study showed that sodium arsenite (200 mg/L) affected the nervous system and induced motor neuron development via the Sonic hedgehog pathway in zebrafish larvae. To gain more insight into the effects of arsenite on other signaling pathways, including apoptosis, we have performed quantitative polymerase chain reaction array-based gene expression analyses. The 96-well array plates contained primers for 84 genes representing 10 signaling pathways that regulate several biological functions, including apoptosis. We exposed eggs at 5 h postfertilization until the 72 h postfertilization larval stage to 200 mg/L sodium arsenite. In the Janus kinase/signal transducers and activators of transcription, nuclear factor κ-light-chain-enhancer of activated B cells, and Wingless/Int-1 signaling pathways, the expression of only one gene in each pathway was significantly altered. The expression of multiple genes was altered in the p53 and oxidative stress pathways. Sodium arsenite induced excessive apoptosis in the larvae. This compelled us to analyze specific genes in the p53 pathway, including cdkn1a, gadd45aa, and gadd45ba. Our data suggest that the p53 pathway is likely responsible for sodium arsenite-induced apoptosis. In addition, sodium arsenite significantly reduced global DNA methylation in the zebrafish larvae, which may indicate that epigenetic factors could be dysregulated after arsenic exposure. Together, these data elucidate potential mechanisms of arsenic toxicity that could improve understanding of arsenic's effects on human health.

miRNAs and arsenic-induced carcinogenesis

Arsenic-induced carcinogenesis is a worldwide health problem. Identifying the molecular mechanisms responsible for the induction of arsenic-induced cancers is important for developing treatment strategies. MicroRNA (miRNA) dysregulation is known to affect development and progression of human cancer. Several studies have identified an association between altered miRNA expression in cancers from individuals chronically exposed to arsenic and in cell models for arsenic-induced carcinogenesis. This chapter provides a comprehensive review for miRNA dysregulation in arsenic-induced cancer.

Zinc supplementation prevents mitotic accumulation in human keratinocyte cell lines upon environmentally relevant arsenic exposure

Disrupted cell cycle progression underlies the molecular pathogenesis of multiple diseases. Chronic exposure to inorganic arsenic (iAs) is a global health issue leading to multi-organ cancerous and non-cancerous diseases. Exposure to supratherapeutic concentrations of iAs causes cellular accumulation in G2 or M phase of the cell cycle in multiple cell lines by inducing cyclin B1 expression. It is not clear if iAs exposure at doses corresponding to serum levels of chronically exposed populations (∼100 nM) has any effect on cell cycle distribution. In the present study we investigated if environmentally relevant iAs exposure induced cell cycle disruption and mechanisms thereof employing two human keratinocyte cell lines (HaCaT and Ker-CT), flow cytometry, immunoblots and quantitative real-time PCR (qRT-PCR). iAs exposure (100 nM; 24 h) led to mitotic accumulation of cells in both cell lines, along with the stabilization of ANAPC11 ubiquitination targets cyclin B1 and securin, without affecting their steady state mRNA levels. This result suggested that induction of cyclin B1 and securin is modulated at the level of protein degradation. Moreover, zinc supplementation successfully prevented iAs-induced mitotic accumulation and stabilization of cyclin B1 and securin without affecting their mRNA levels. Together, these data suggest that environmentally relevant iAs exposure leads to mitotic accumulation possibly by displacing zinc from the RING finger subunit of anaphase promoting complex/cyclosome (ANAPC11), the cell cycle regulating E3 ubiquitin ligase. This early cell cycle disruptive effect of environmentally relevant iAs concentration could underpin the molecular pathogenesis of multiple diseases associated with chronic iAs exposure.