Global gene expression changes in human urothelial cells exposed to low-level monomethylarsonous acid

A Comprehensive Transcriptomic Analysis of Arsenic-Induced Bladder Carcinogenesis

Arsenic (sodium arsenite: NaAsO2) is a potent carcinogen and a known risk factor for the onset of bladder carcinogenesis. The molecular mechanisms that govern arsenic-induced bladder carcinogenesis remain unclear. We used a physiological concentration of NaAsO2 (250 nM: 33 µg/L) for the malignant transformation of normal bladder epithelial cells (TRT-HU1), exposed for over 12 months. The increased proliferation and colony-forming abilities of arsenic-exposed cells were seen after arsenic exposure from 4 months onwards. Differential gene expression (DEG) analysis revealed that a total of 1558 and 1943 (padj < 0.05) genes were deregulated in 6-month and 12-month arsenic-exposed TRT-HU1 cells. The gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis revealed that cell proliferation and survival pathways, such as the MAPK, PI3K/AKT, and Hippo signaling pathways, were significantly altered. Pathway analysis revealed that the enrichment of stem cell activators such as ALDH1A1, HNF1b, MAL, NR1H4, and CDH1 (p < 0.001) was significantly induced during the transformation compared to respective vehicle controls. Further, these results were validated by qPCR analysis, which corroborated the transcriptomic analysis. Overall, the results suggested that stem cell activators may play a significant role in facilitating the arsenic-exposed cells to gain a survival advantage, enabling the healthy epithelial cells to reprogram into a cancer stem cell phenotype, leading to malignant transformation.

Gene expression and DNA methylation regulation of arsenic in mouse bladder tissues and in human urothelial cells

According to a report of the International Agency for Research on Cancer, arsenic and inorganic arsenic compounds are classified into Group 1 carcinogens with regard to human health. Epidemiological studies indicate that arsenic is one of the main risk factors for the development of bladder cancer. In the present study, arsenic-altered gene expression in mouse bladder tissues and in human urothelial cells was compared. In the mouse model, sodium arsenite-induced mouse urothelial hyperplasia and intracellular inclusions were present. Following DNA array analysis, four genes with differential expression were selected for quantitative real-time PCR assay. The genes were the following: Cystathionine β-synthase (CBS), adenosine A1 receptor (ADORA1), metastasis-associated lung adenocarcinoma transcript 1 (MALAT1) and Wnt inhibitory factor 1 (Wif1). The results indicated a significant increase in the levels of Cbs and Adora1. The analysis of the DNA CpG methylation levels of the mouse Cbs and Adora1 genes revealed no significant change. In contrast to these observations, the four genes were further analyzed in the human normal urothelial cell line SV-HUC1. The data indicated that WIF1 gene expression was decreased by sodium arsenite, whereas this was not noted for CBS, MALAT1 and ADORA1. Sodium arsenite decreased mRNA and protein expression levels of the WIF1 gene. In addition, the methylation levels of the WIF1 gene were increased. Sodium arsenite inhibited cell proliferation and promoted cell migration as demonstrated in cell functional assays. The gene status was compared in 8 human urothelial cell lines, and WIF1 mRNA expression levels were determined to be higher, whereas DNA CpG methylation levels were lower in SV-HUC1 cells compared with those noted in the other 7 bladder cancer cell lines. In summary, the data indicated that sodium arsenite decreased WIF1 gene expression and promoted cell migration. The increased methylation levels of WIF1 DNA CpG could be a potential biomarker for bladder cancer.

Health effects inflicted by chronic low-level arsenic contamination in groundwater: A global public health challenge

Groundwater arsenic (As) contamination is a global public health concern. The high level of As exposure (100-1000 μg/L or even higher) through groundwater has been frequently associated with serious public health hazards, e.g., skin disorders, cardiovascular diseases, respiratory problems, complications of gastrointestinal tract, liver and splenic ailments, kidney and bladder disorders, reproductive failure, neurotoxicity and cancer. However, reviews on low-level As exposure and the imperative health effects are far less documented. The World Health Organization (WHO) and the United States Environmental Protection Agency (USEPA) has set the permissible standard of As in drinking water at 10 μg/L. Considering the WHO and USEPA guidelines, most of the developed countries have established standards at or below this guideline. Worldwide many countries including India have millions of aquifers with low-level As contamination (≤50 μg/L). The exposed population of these areas might not show any As-related skin lesions (hallmark of As toxicity particularly in a population consuming As contaminated groundwater >300 μg/L) but might be subclinically affected. This review has attempted to encompass the wide range of health effects associated with chronic low-level As exposure ≤50 μg/L and the probable mechanisms that might provide a better insight regarding the underlying cause of these clinical manifestations. Therefore, there is an urgent need to create mass awareness about the health effects of chronic low-level As exposure and planning of proper mitigation strategies.

A time-series analysis of altered histone H3 acetylation and gene expression during the course of MMAIII-induced malignant transformation of urinary bladder cells

Our previous studies have shown that chronic exposure to low doses of monomethylarsonous acid (MMAIII) causes global histone acetylation dysregulation in urothelial cells (UROtsa cells) during the course of malignant transformation. To reveal the relationship between altered histone acetylation patterns and aberrant gene expression, more specifically, the carcinogenic relevance of these alterations, we performed a time-course analysis of the binding patterns of histone 3 lysine 18 acetylation (H3K18ac) across the genome and generated global gene-expression profiles from this UROtsa cell malignant transformation model. We showed that H3K18ac, one of the most significantly upregulated histone acetylation sites following MMAIII exposure, was enriched at gene promoter-specific regions across the genome and that MMAIII-induced upregulation of H3K18ac led to an altered binding pattern in a large number of genes that was most significant during the critical window for MMAIII-induced UROtsa cells' malignant transformation. Some genes identified as having a differential binding pattern with H3K18ac, acted as upstream regulators of critical gene networks with known functions in tumor development and progression. The altered H3K18ac binding patterns not only led to changes in expression of these directly affected upstream regulators but also resulted in gene-expression changes in their regulated networks. Collectively, our data suggest that MMAIII-induced alteration of histone acetylation patterns in UROtsa cells led to a time- and malignant stage-dependent aberrant gene-expression pattern, and that some gene regulatory networks were altered in accordance with their roles in carcinogenesis, probably contributing to MMAIII-induced urothelial cell malignant transformation and carcinogenesis.

Contribution of breast milk and formula to arsenic exposure during the first year of life in a US prospective cohort

Arsenic is a carcinogen that can also affect the cardiac, respiratory, neurological and immune systems. Children have higher dietary arsenic exposure than adults owing to their more restricted diets and greater intake per unit body mass. We evaluated the potential contributions of breast milk and formula to arsenic exposure throughout the first year of life for 356 infants in the prospective New Hampshire Birth Cohort Study (NHBCS) using infant diets reported by telephone at 4, 8 and 12 months of age; measured household water arsenic concentrations; and literature data. Based on our central-tendency models, population-wide geometric mean (GM) estimated arsenic exposures in the NHBCS were relatively low, decreasing from 0.1 μg/kg/day at 4 months of age to 0.07 μg/kg/day at 12 months of age. At all three time points, exclusively formula-fed infants had GM arsenic exposures ~8 times higher than exclusively breastfed infants owing to arsenic in both tap water and formula powder. Estimated maximum exposures reached 9 μg/kg/day among exclusively formula-fed infants in households with high tap water arsenic (80 μg/l). Overall, modeled arsenic exposures via breast milk and formula were low throughout the first year of life, unless formula was prepared with arsenic-contaminated tap water.

The NIEHS Superfund Research Program: 25 Years of Translational Research for Public Health

BACKGROUND

The Superfund Research Program (SRP) is an academically based, multidisciplinary, translational research program that for 25 years has sought scientific solutions to health and environmental problems associated with hazardous waste sites. SRP is coordinated by the National Institute of Environmental Health Sciences (NIEHS). It supports multi-project grants, undergraduate and postdoctoral training programs, individual research grants, and Small Business Innovation Research (SBIR) and Technology Transfer Research (STTR) grants.

RESULTS

SRP has had many successes: discovery of arsenic's toxicity to the developing human central nervous system; documentation of benzene toxicity to hematologic progenitor cells in human bone marrow; development of novel analytic techniques such as the luciferase expression assay and laser fragmentation fluorescence spectroscopy; demonstration that PCBs can cause developmental neurotoxicity at low levels and alter the genomic characteristics of sentinel animals; elucidation of the neurodevelopmental toxicity of organophosphate insecticides; documentation of links between antimicrobial agents and alterations in hormone response; discovery of biological mechanisms through which environmental chemicals may contribute to obesity, atherosclerosis, diabetes, and cancer; tracking the health and environmental effects of the attacks on the World Trade Center and Hurricane Katrina; and development of novel biological and engineering techniques to facilitate more efficient and lower-cost remediation of hazardous waste sites.

CONCLUSION

SRP must continue to address the legacy of hazardous waste in the United States, respond to new issues caused by rapid advances in technology, and train the next generation of leaders in environmental health science while recognizing that most of the world's worst toxic hot spots are now located in low- and middle-income countries.

Arsenic responsive microRNAs in vivo and their potential involvement in arsenic-induced oxidative stress

Arsenic exposure is postulated to modify microRNA (miRNA) expression, leading to changes of gene expression and toxicities, but studies relating the responses of miRNAs to arsenic exposure are lacking, especially with respect to in vivo studies. We utilized high-throughput sequencing technology and generated miRNA expression profiles of liver tissues from Sprague Dawley (SD) rats exposed to various concentrations of sodium arsenite (0, 0.1, 1, 10 and 100mg/L) for 60days. Unsupervised hierarchical clustering analysis of the miRNA expression profiles clustered the SD rats into different groups based on the arsenic exposure status, indicating a highly significant association between arsenic exposure and cluster membership (p-value of 0.0012). Multiple miRNA expressions were altered by arsenic in an exposure concentration-dependent manner. Among the identified arsenic-responsive miRNAs, several are predicted to target Nfe2l2-regulated antioxidant genes, including glutamate-cysteine ligase (GCL) catalytic subunit (GCLC) and modifier subunit (GCLM) which are involved in glutathione (GSH) synthesis. Exposure to low concentrations of arsenic increased mRNA expression for Gclc and Gclm, while high concentrations significantly reduced their expression, which were correlated to changes in hepatic GCL activity and GSH level. Moreover, our data suggested that other mechanisms, e.g., miRNAs, rather than Nfe2l2-signaling pathway, could be involved in the regulation of mRNA expression of Gclc and Gclm post-arsenic exposure in vivo. Together, our findings show that arsenic exposure disrupts the genome-wide expression of miRNAs in vivo, which could lead to the biological consequence, such as an altered balance of antioxidant defense and oxidative stress.

Arsenic induces polyadenylation of canonical histone mRNA by down-regulating stem-loop-binding protein gene expression

The replication-dependent histone genes are the only metazoan genes whose messenger RNA (mRNA) does not terminate with a poly(A) tail at the 3'-end. Instead, the histone mRNAs display a stem-loop structure at their 3'-end. Stem-loop-binding protein (SLBP) binds the stem-loop and regulates canonical histone mRNA metabolism. Here we report that exposure to arsenic, a carcinogenic metal, decreased cellular levels of SLBP by inducing its proteasomal degradation and inhibiting SLBP transcription via epigenetic mechanisms. Notably, arsenic exposure dramatically increased polyadenylation of canonical histone H3.1 mRNA possibly through down-regulation of SLBP expression. The polyadenylated H3.1 mRNA induced by arsenic was not susceptible to normal degradation that occurs at the end of S phase, resulting in continued presence into mitosis, increased total H3.1 mRNA, and increased H3 protein levels. Excess expression of canonical histones have been shown to increase sensitivity to DNA damage as well as increase the frequency of missing chromosomes and induce genomic instability. Thus, polyadenylation of canonical histone mRNA following arsenic exposure may contribute to arsenic-induced carcinogenesis.

Cardiac epithelial-mesenchymal transition is blocked by monomethylarsonous acid (III)

Arsenic exposure during embryonic development can cause ischemic heart pathologies later in adulthood which may originate from impairment in proper blood vessel formation. The arsenic-associated detrimental effects are mediated by arsenite (iAs(III)) and its most toxic metabolite, monomethylarsonous acid [MMA (III)]. The impact of MMA (III) on coronary artery development has not yet been studied. The key cellular process that regulates coronary vessel development is the epithelial-mesenchymal transition (EMT). During cardiac EMT, activated epicardial progenitor cells transform to mesenchymal cells to form the cellular components of coronary vessels. Smad2/3 mediated TGFβ2 signaling, the key regulator of cardiac EMT, is disrupted by arsenite exposure. In this study, we compared the cardiac toxicity of MMA (III) with arsenite. Epicardial progenitor cells are 15 times more sensitive to MMA (III) cytotoxicity when compared with arsenite. MMA (III) caused a significant blockage in epicardial cellular transformation and invasion at doses 10 times lower than arsenite. Key EMT genes including TGFβ ligands, TβRIII, Has2, CD44, Snail1, TBX18, and MMP2 were down regulated by MMA (III) exposure. MMA (III) disrupted Smad2/3 activation at a dose 20 times lower than arsenite. Both arsenite and MMA (III) significantly inhibited Erk1/2 and Erk5 phosphorylation. Nuclear translocation of Smad2/3 and Erk5 was also blocked by arsenical exposure. However, p38 activation, as well as smooth muscle differentiation, was refractory to the inhibition by the arsenicals. Collectively, these findings revealed that MMA (III) is a selective disruptor of cardiac EMT and as such may predispose to arsenic-associated cardiovascular disorders.

Monomethylarsonous acid inhibited endogenous cholesterol biosynthesis in human skin fibroblasts

Human exposure to arsenic in drinking water is a widespread public health concern, and such exposure is known to be associated with many human diseases. The detailed molecular mechanisms about how arsenic species contribute to the adverse human health effects, however, remain incompletely understood. Monomethylarsonous acid [MMA(III)] is a highly toxic and stable metabolite of inorganic arsenic. To exploit the mechanisms through which MMA(III) exerts its cytotoxic effect, we adopted a quantitative proteomic approach, by coupling stable isotope labeling by amino acids in cell culture (SILAC) with LC-MS/MS analysis, to examine the variation in the entire proteome of GM00637 human skin fibroblasts following acute MMA(III) exposure. Among the ~6500 unique proteins quantified, ~300 displayed significant changes in expression after exposure with 2 μM MMA(III) for 24 h. Subsequent analysis revealed the perturbation of de novo cholesterol biosynthesis, selenoprotein synthesis and Nrf2 pathways evoked by MMA(III) exposure. Particularly, MMA(III) treatment resulted in considerable down-regulation of several enzymes involved in cholesterol biosynthesis. In addition, real-time PCR analysis showed reduced mRNA levels of select genes in this pathway. Furthermore, MMA(III) exposure contributed to a distinct decline in cellular cholesterol content and significant growth inhibition of multiple cell lines, both of which could be restored by supplementation of cholesterol to the culture media. Collectively, the present study demonstrated that the cytotoxicity of MMA(III) may arise, at least in part, from the down-regulation of cholesterol biosynthesis enzymes and the resultant decrease of cellular cholesterol content.

Genomic characterization of three urinary bladder cancer cell lines: understanding genomic types of urinary bladder cancer

Several genomic regions are frequently altered and associated with the type, stage and progression of urinary bladder cancer (UBC). We present the characterization of 5637, T24 and HT1376 UBC cell lines by karyotyping, fluorescence in situ hybridization (FISH), array comparative genomic hybridization (aCGH) and multiplex ligation-dependent probe amplification (MLPA) analysis. Some cytogenetic anomalies present in UBC were found in the three cell lines, such as chromosome 20 aneuploidy and the loss of 9p21. Some gene loci losses (e.g. CDKN2A) and gains (e.g. HRAS, BCL2L1 and PTPN1) were coincident across all cell lines. Although some significant heterogeneity and complexity were detected between them, their genomic profiles exhibited a similar pattern to UBC. We suggest that 5637 and HT1376 represent the E2F3/RB1 pathway due to amplification of 6p22.3, concomitant with loss of one copy of RB1 and mutation of the remaining copy. The HT1376 presented a 10q deletion involving PTEN region and no alteration of PIK3CA region which, in combination with the inactivation of TP53, bears more invasive and metastatic properties than 5637. The T24 belongs to the alternative pathway of FGFR3/CCND1 by presenting mutated HRAS and over-represented CCND1. These cell lines cover the more frequent subtypes of UBC and are reliable models that can be used, as a group, in preclinical studies.

Prediction of the number of activated genes in multiple independent Cd(+2)- and As(+3)-induced malignant transformations of human urothelial cells (UROtsa)

BACKGROUND

Many toxic environmental agents such as cadmium and arsenic are found to be epidemiologically linked to increasing rates of cancers. In vitro studies show that these toxic agents induced malignant transformation in human cells. It is not clear whether such malignant transformation induced by a single toxic agent is driven by a common set of genes. Although the advancement of high-throughput technology has facilitated the profiling of global gene expression, it remains a question whether the sample size is sufficient to identify this common driver gene set.

RESULTS

We have developed a statistical method, SOFLR, to predict the number of common activated genes using a limited number of microarray samples. We conducted two case studies, cadmium and arsenic transformed human urothelial cells. Our method is able to precisely predict the number of stably induced and repressed genes and the number of samples to identify the common activated genes. The number of independent transformed isolates required for identifying the common activated genes is also estimated. The simulation study further validated our method and identified the important parameters in this analysis.

CONCLUSIONS

Our method predicts the degree of similarity and diversity during cell malignant transformation by a single toxic agent. The results of our case studies imply the existence of common driver and passenger gene sets in toxin-induced transformation. Using a pilot study with small sample size, this method also helps microarray experimental design by determining the number of samples required to identify the common activated gene set.

Expression Of Selected Pathway-Marker Genes In Human Urothelial Cells Exposed Chronically To A Non-Cytotoxic Concentration Of Monomethylarsonous Acid

Bladder cancer has been associated with chronic arsenic exposure. Monomethylarsonous acid [MMA(III)] is a metabolite of inorganic arsenic and has been shown to transform an immortalized urothelial cell line (UROtsa) at concentrations 20-fold less than arsenite. MMA(III) was used as a model arsenical to examine the mechanisms of arsenical-induced transformation of urothelium. A previous microarray analysis revealed only minor changes in gene expression at one and two months of chronic exposure to MMA(III), contrasting with substantial changes observed at three months of exposure. To address the lack of information between two and three months of exposure (the critical period of transformation), the expression of select pathway marker genes was measured by PCR array analysis on a weekly basis. Cell proliferation rate, anchorage-independent growth, and tumorigenicity in SCID mice were also assessed to determine the early, persistent phenotypic changes and their association with the changes in expression of these selected marker genes. A very similar pattern of alterations in these genes was observed when compared to the microarray results, and suggested that early perturbations in cell signaling cascades, immunological pathways, cytokine expression, and MAPK pathway are particularly important in driving malignant transformation. These results showed a strong association between the acquired phenotypic changes that occurred as early as one to two months of chronic MMA(III) exposure, and the observed gene expression pattern that is indicative of the earliest stages in carcinogenesis.

Cytotoxicity and gene expression changes induced by inorganic and organic trivalent arsenicals in human cells

Inorganic arsenic (iAs) is a human urinary bladder, skin and lung carcinogen. iAs is metabolized to methylated arsenicals, with trivalent arsenicals more cytotoxic than pentavalent forms in vitro. In this study, cytotoxicity and gene expression changes for arsenite (iAs(III)), monomethylarsonous acid (MMA(III)) and dimethylarsinous acid (DMA(III)) were evaluated in three human cell types, urothelial (1T1), keratinocyte (HEK001) and bronchial epithelial (HBE) cells, corresponding to target organs for iAs-induced cancer. Cells were exposed to arsenicals to determine cytotoxicity and to study gene expression changes. Affymetrix chips were used to determine differentially expressed genes (DEGs) by statistical analysis. Lethal concentrations (LC50) for trivalent arsenicals in all cells ranged from 1.6 to 10μM. MMA(III) and DMA(III) had 4-12-fold greater potency compared to iAs. Increasing concentrations of iAs(III) induced more genes and additional signaling pathways in HBE cells. At equivalent cytotoxic concentrations, greater numbers of DEGs were induced in 1T1 cells compared to the other cells. Each arsenical altered slightly different signaling pathways within and between cell types, but when altered pathways from all three arsenicals were combined, they were similar between cell types. The major signaling pathways altered included NRF2-mediated stress response, interferon, p53, cell cycle regulation and lipid peroxidation. These results show a similar process qualitatively and quantitatively for all three cell types, and support a mode of action involving cytotoxicity and regenerative proliferation.

Cross-contamination of a UROtsa stock with T24 cells--molecular comparison of different cell lines and stocks

BACKGROUND

UROtsa is an authentic, immortalized human urothelial cell line that is used to study the effects of metals and other toxic substances, mostly in the context of bladder cancer carcinogenesis. Unusual properties on the molecular level of a provided UROtsa cell line stock prompted us to verify its identity.

METHODS

UROtsa cell line stocks from different sources were tested on several molecular levels and compared with other cell lines. MicroRNA and mRNA expression was determined by Real-Time PCR. Chromosome numbers were checked and PCR of different regions of the large T-antigen was performed. DNA methylation of RARB, PGR, RASSF1, CDH1, FHIT, ESR1, C1QTNF6, PTGS2, SOCS3, MGMT, and LINE1 was analyzed by pyrosequencing and compared with results from the cell lines RT4, T24, HeLa, BEAS-2B, and HepG2. Finally, short tandem repeat (STR) profiling was applied.

RESULTS

All tested UROtsa cell line stocks lacked large T-antigen. STR analysis unequivocally identified our main UROtsa stock as the bladder cancer cell line T24, which was different from two authentic UROtsa stocks that served as controls. Analysis of DNA methylation patterns and RNA expression confirmed their differences. Methylation pattern and mRNA expression of the contaminating T24 cell line showed moderate changes even after long-term culture of up to 56 weeks, whereas miRNAs and chromosome numbers varied markedly.

CONCLUSIONS

It is important to check the identity of cell lines, especially those that are not distributed by major cell banks. However, for some cell lines STR profiles are not available. Therefore, new cell lines should either be submitted to cell banks or at least their STR profile determined and published as part of their initial characterization. Our results should help to improve the identification of UROtsa and other cells on different molecular levels and provide information on the use of urothelial cells for long-term experiments.