Akt activation is responsible for enhanced migratory and invasive behavior of arsenic-transformed human bronchial epithelial cells

Long noncoding RNA ABHD11-AS1 interacts with SART3 and regulates CD44 RNA alternative splicing to promote lung carcinogenesis

Hexavalent chromium [Cr(VI)] is a common environmental pollutant and chronic exposure to Cr(VI) causes lung cancer in humans, however, the mechanism of Cr(VI) carcinogenesis has not been well understood. Lung cancer is the leading cause of cancer-related death, although the mechanisms of how lung cancer develops and progresses have been poorly understood. While long non-coding RNAs (lncRNAs) are found abnormally expressed in cancer, how dysregulated lncRNAs contribute to carcinogenesis remains largely unknown. The goal of this study is to investigate the mechanism of Cr(VI)-induced lung carcinogenesis focusing on the role of the lncRNA ABHD11 antisense RNA 1 (tail to tail) (ABHD11-AS1). It was found that the lncRNA ABHD11-AS1 expression levels are up-regulated in chronic Cr(VI) exposure-transformed human bronchial epithelial cells, chronically Cr(VI)-exposed mouse lung tissues, and human lung cancer cells as well. Bioinformatics analysis revealed that ABHD11-AS1 levels are up-regulated in lung adenocarcinomas (LUADs) tissues and associated with worse overall survival of LUAD patients but not in lung squamous cell carcinomas. It was further determined that up-regulation of ABHD11-AS1 expression plays an important role in chronic Cr(VI) exposure-induced cell malignant transformation and tumorigenesis, and the stemness of human lung cancer cells. Mechanistically, it was found that ABHD11-AS1 directly binds SART3 (spliceosome associated factor 3, U4/U6 recycling protein). The interaction of ABHD11-AS1 with SART3 promotes USP15 (ubiquitin specific peptidase 15) nuclear localization. Nuclear localized USP15 interacts with pre-mRNA processing factor 19 (PRPF19) to increase CD44 RNA alternative splicing activating β-catenin and enhancing cancer stemness. Together, these findings indicate that lncRNA ABHD11-AS1 interacts with SART3 and regulates CD44 RNA alternative splicing to promote cell malignant transformation and lung carcinogenesis.

Epigenetic downregulation of O6-methylguanine-DNA methyltransferase contributes to chronic hexavalent chromium exposure-caused genotoxic effect and cell transformation

Hexavalent chromium [Cr(VI)] is a common environmental pollutant and chronic exposure to Cr(VI) causes lung cancer and other types of cancer in humans, although the mechanism of Cr(VI) carcinogenesis remains elusive. Cr(VI) has been considered as a genotoxic carcinogen, but accumulating evidence indicates that Cr(VI) also causes various epigenetic toxic effects that play important roles in Cr(VI) carcinogenesis. However, it is not clear how Cr(VI)-caused epigenetic dysregulations contributes to Cr(VI) carcinogenesis. This study investigates whether Cr(VI) epigenetic toxic effect has an impact on its genotoxic effect. It was found that chronic low dose of Cr(VI) exposure time-dependently down-regulates the expression of a critical DNA damage repair protein O6-methylguanine-DNA methyltransferase (MGMT), leading to the increases of the levels of the highly mutagenic and carcinogenic DNA lesion O6-methylguanine (O6-MeG) in human bronchial epithelial BEAS-2B cells. Moreover, the levels of MGMT and O6-MeG in chronic Cr(VI) exposure-caused human lung cancer tissues are also significantly lower and higher than that in the adjacent normal lung tissues, respectively. It was further determined that chronic low dose of Cr(VI) exposure-transformed BEAS-2B cells display impaired DNA damage repair capacity and a high sensitivity to the toxicity of the alkylating chemotherapeutic drug Temozolomide. In contrast, stably overexpressing MGMT in parental BEAS-2B cells reverses chronic low dose of Cr(VI) exposure-caused DNA damage repair deficiency and significantly reduces cell transformation by Cr(VI). Further mechanistical studies revealed that chronic low dose of Cr(VI) exposure down-regulates MGMT expression through epigenetic mechanisms by increasing DNA methylation and histone H3 repressive modifications. Taken together, these findings suggest that epigenetic down-regulation of a crucial DNA damage repair protein MGMT contributes significantly to the genotoxic effect and cell transformation caused by chronic low dose of Cr(VI) exposure.

N6-methyladenosine plays a dual role in arsenic carcinogenesis by temporal-specific control of core target AKT1

High-profile RNA epigenetic modification N⁶-methyladenosine (m⁶A), as a double-edged sword for cancer, can either promote or inhibit arsenic-induced skin carcinogenesis. However, the core m⁶A-target gene determining the duality of m⁶A and the regulatory mechanism of m⁶A on the core gene are still poorly understood. Based on m⁶A microarray detection, integrated multi-omics analysis, and further experiments in vitro and in vivo, we explored the molecular basis for the dual role of m⁶A in cancer induced by environmental pollutants using models in different stages of arsenic carcinogenesis, including As-treated, As-transformed, and As-tumorigenic cell models. We found that the key proliferative signaling node AKT1 is in the center of the m⁶A-regulatory network in arsenic carcinogenicity. The m⁶A level on AKT1 mRNA (3'UTR, CDS, and 5'UTR) dynamically changed in different stages of arsenic carcinogenesis. The m⁶A writer METTL3-catalyzed upregulation of m⁶A promotes AKT1 expression by elevating m⁶A reader YTHDF1-mediated AKT1 mRNA stability in As-treated and As-transformed cells, while the m⁶A eraser FTO-catalyzed downregulation of m⁶A promotes AKT1 expression mainly by inhibiting m⁶A reader YTHDF2-mediated AKT1 mRNA degradation in As-tumorigenic cells. Furthermore, upregulation of m⁶A inhibits the expression of AKT1 negative regulator PHLPP2 and promotes the expression of AKT1 positive regulator PDK1. These changes in AKT1 regulators result in AKT1 activation by upregulating AKT1 phosphorylation at S473 and T308. Interestingly, the FTO-catalyzed decrease in m⁶A prevents AKT upregulation in As-treated cells but promotes AKT upregulation in As-tumorigenic cells. Both inhibitors targeting the m⁶A writer and eraser can inhibit the AKT1-mediated proliferation of As-tumorigenic cells by breaking the balance of m⁶A regulators. Our results demonstrated that AKT1 is the core hub determining m⁶A as a double-edged sword. Changed m⁶A dynamically upregulates the expression and activity of AKT1 in different stages of arsenic carcinogenesis. This study can advance our understanding of the dual role and precise time-specific mechanism of RNA epigenetics involved in the carcinogenesis of hazardous materials.

Arsenic and cancer: Evidence and mechanisms

Arsenic is a potent carcinogen and poses a significant health concern worldwide. Exposure occurs through ingestion of drinking water and contaminated foods and through inhalation due to pollution. Epidemiological evidence shows arsenic induces cancers of the skin, lung, liver, and bladder among other tissues. While studies in animal and cell culture models support arsenic as a carcinogen, the mechanisms of arsenic carcinogenesis are not fully understood. Arsenic carcinogenesis is a complex process due its ability to be metabolized and because of the many cellular pathways it targets in the cell. Arsenic metabolism and the multiple forms of arsenic play distinct roles in its toxicity and contribute differently to carcinogenic endpoints, and thus must be considered. Arsenic generates reactive oxygen species increasing oxidative stress and damaging DNA and other macromolecules. Concurrently, arsenic inhibits DNA repair, modifies epigenetic regulation of gene expression, and targets protein function due its ability to replace zinc in select proteins. While these mechanisms contribute to arsenic carcinogenesis, there remain significant gaps in understanding the complex nature of arsenic cancers. In the future improving models available for arsenic cancer research and the use of arsenic induced human tumors will bridge some of these gaps in understanding arsenic driven cancers.

Non-malignant respiratory illness associated with exposure to arsenic compounds in the environment

Arsenic (As), a toxic metalloid, primarily originates from both natural and anthropogenic activities. Reports suggested that millions of people globally exposed to high levels of naturally occurring As compounds via inhalation and ingestion. There is evidence that As is a well-known lung carcinogen. However, there has been relatively little evidence suggesting its non-malignant lung effects. This review comprehensively summarises current experimental and clinical studies implicating the association of As exposure and the development of several non-malignant lung diseases. Experimental studies provided evidence that As exposure induces redox imbalance, apoptosis, inflammatory response, epithelial-to-mesenchymal transition (EMT), and affected normal lung development through alteration of the components of intracellular signaling cascades. In addition, we also discuss the sources and possible mechanisms of As influx and efflux in the lung. Finally, current experimental studies on treatment strategies using phytochemicals and our perspective on future research with As are also discussed.

Low-dose arsenic trioxide enhances membrane-GLUT1 expression and glucose uptake via AKT activation to support L-02 cell aberrant proliferation

Long term low dose exposure of arsenic has been reported to lead various cells proliferation and malignant transformation. GLUT1, as the key transporter of glucose, has been reported to have association with rapid proliferation of various cells or tumor cells. In our study, we found that low dose exposure to arsenic trioxide (0.1μmol/L As₂O₃) could induce an increase in glucose uptake and promote cell viability and DNA synthesis. And, 2-DG, a non-metabolized glucose analog, significantly decreased the glucose uptake and cell proliferation of 0.1μmol/L As₂O₃ treated L-02 cells. However, 4 mmol/L 2-DG was co-utilized with equal dose glucose had no significant effect on the cell proliferation of 0.1μmol/L As₂O₃ treated L-02 cells. Further studies showed that exposure to 0.1μmol/L As₂O₃ could promote the expression of GLUT1 on plasma membrane. Inhibition of GLUT1 expression by 5μmol/L BAY-876 significantly decreased the abilities of glucose uptake and cell proliferation in As₂O₃-treated L-02 cells. Moreover, 0.1μmol/L As₂O₃ induced the AKT activation indicated by increased the phospho-AKT (Ser473 and Thr308). Knockdown AKT by shRNA or inhibited AKT activation by LY294002 was followed by significantly decreased glucose uptake, GLUT1 plasma membrane expression and cell proliferation in As₂O₃-treated L-02 cells. All in all, these results demonstrated that arsenic trioxide-induced AKT activation contributed to the cells proliferation through upregulating expression of GLUT1 on plasma membrane that enhanced glucose uptake.

Arsenic and Human Health: Genotoxicity, Epigenomic Effects, and Cancer Signaling

Arsenic is a well-known element because of its toxicity. Humans as well as plants and animals are negatively affected by its exposure. Some countries suffer from high levels of arsenic in their tap water and soils, which is considered a primary arsenic-linked risk factor for living beings. Humans generally get exposed to arsenic by contaminated drinking waters, resulting in many health problems, ranging from cancer to skin diseases. On the other hand, the FDA-certified drug arsenic trioxide provides solutions for various diseases, including several types of cancers. This issue emphasizes the importance of speciation of the metalloid elements in terms of impacts on health. When species get exposed to arsenic, it affects the cells altering their involvement. It can lead to abnormalities in inflammatory mechanisms and the immune system which contribute to the negative impacts generated on the body. The poisoning originating from arsenic gives rise to various biological signs on the body which can be useful for the diagnosis. It is important to find true biomarkers for the detection of arsenic poisoning. In view of its application in medicine and biology, studies on understanding the biological activity of arsenic have increased. In this review, we aim at summarizing the current state of knowledge of arsenic and the mechanism behind its toxicity including genotoxicity, oxidative insults, epigenomic changes, and alterations in cellular signaling.

Chronic Hexavalent Chromium Exposure Up-regulates the RNA Methyltransferase METTL3 Expression to Promote Cell Transformation, Cancer Stem Cell-like Property and Tumorigenesis

Hexavalent chromium [Cr(VI)] is a common environmental carcinogen causing lung cancer in humans. This study investigates the mechanism of Cr(VI) carcinogenesis focusing on the role of the epitranscriptomic dysregulation. The epitranscriptomic effect of Cr(VI) was determined in Cr(VI)-transformed human bronchial epithelial cells, chromate-exposed mouse and human lungs. The epitranscriptomic effect and its role in Cr(VI)-induced cell transformation, cancer stem cell (CSC)-like property and tumorigenesis were determined by microarray analysis, soft agar colony formation, suspension spheroid formation and mouse xenograft tumorigenesis assays. It was found that chronic Cr(VI) exposure causes epitranscriptomic dysregulations as evidenced by the increased levels of total RNA N6-methyladenosine (m6A) modification and the RNA m6A methyltransferase METTL3 in Cr(VI)-transformed cells and chromate exposure-caused mouse and human lung tumors. Knockdown of METTL3 expression in Cr(VI)-transformed cells significantly reduces their m6A levels and transformed phenotypes and tumorigenicity in mice. Moreover, knockdown of METTL3 expression in parental non-transformed cells significantly reduces the capability of chronic Cr(VI) exposure to induce cell transformation and CSC-like property. Together, this study reveals that chronic Cr(VI) exposure is capable of altering cellular epitranscriptome by increasing the m6A RNA modification via upregulating the RNA methyltransferase METTL3 expression, which plays an important role in Cr(VI)-induced cell transformation, CSC-like property and tumorigenesis.

CircSPAG16 suppresses cadmium-induced transformation of human bronchial epithelial cells by decoying PIP5K1α to inactivate Akt

Circular RNAs (circRNAs) have been implicated to have important regulatory functions in chemical carcinogenesis via sponging microRNAs to regulate gene expression. Our study revealed a novel mechanism of circRNA in cadmium carcinogenesis through directly binding with protein. Here, we used cadmium-transformed human bronchial epithelial BEAS-2B cells to study the involvement and mechanism of circRNA in lung carcinogenesis caused by cadmium. By high-throughput sequencing, circSPAG16 was identified to be the most significantly downregulated circRNA in cadmium-transformed cells. CircSPAG16 was downregulated at Week 8, 12, 16, and 20 during cadmium-induced cell transformation. In addition, circSPAG16 overexpression prevented cadmium-induced transformation of BEAS-2B cells. Mechanistically, circSPAG16 inhibited the function of phosphatidylinositol 4-phosphate 5-kinase type-1 α (PIP5K1α) by binding with it. We demonstrated that PIP5K1α acted as an oncogene to activate Akt and promoted cancer hallmarks including proliferation, migration, invasion, and anchorage-independent growth in cadmium-transformed cells. CircSPAG16 overexpression inactivates PIP5K1α/Akt signaling in the transformed cells. Furthermore, PIP5K1α overexpression significantly rescued the inhibitory effects of circSPAG16 overexpression on pAkt and cancer hallmarks in cadmium-transformed cells. Collectively, our results revealed that circSPAG16 could prevent cadmium-induced transformation through binding with PIP5K1α to inactivate Akt. These results provide a novel regulatory mechanism of circRNA into carcinogenesis induced by cadmium.

Arsenic-induced HER2 promotes proliferation, migration and angiogenesis of bladder epithelial cells via activation of multiple signaling pathways in vitro and in vivo

Arsenic (As) is a known human carcinogen with a hitherto unknown mechanism of action. Dimethylarsinic acid (DMA^V) is a methylated metabolite of arsenicals found in most mammals, and long-term exposure to DMA^V can lead to bladder cancer in rats. Human epidermal growth factor receptor 2 (HER2) is an oncogenic factor that is overexpressed in bladder cancer, but its role in the initiation and progression of As-induced bladder cancer has not been elucidated. We found that HER2 was up-regulated in human uroepithelial cells treated with arsenite as well as in the bladder tissues of DMA^V-exposed rats. HER2 overexpression correlated to increased cell proliferation, epithelial-to-mesenchymal transition (EMT), migration and angiogenesis in vitro. The anti-HER2 monoclonal antibody trastuzumab significantly decreased serum vascular endothelial-derived growth factor (VEGF) levels and that of proliferation-related proteins in the bladder tissues of DMA^V-exposed rats. Furthermore, inhibition of HER2, as well as that of the MAPK, AKT and STAT3 pathways, attenuated arsenite-induced proliferation, migration and angiogenesis of human uroepithelial cells, and increased apoptosis rates in vitro. These findings indicate that HER2 mediates the oncogenic effects of As on bladder epithelial cells by activating the MAPK, PI3K/AKT and Src/STAT3 signaling pathways, and is therefore a promising biomarker.

Chronic and acute arsenic exposure enhance EGFR expression via distinct molecular mechanisms

The impacts of acute arsenic exposure (i.e. vomiting, diarrhea, and renal failure) are distinct from those brought about by sustained, low level exposure from environmental sources or drinking of contaminated well water. Chronic arsenic exposure is a risk factor for the development of pulmonary diseases, including lung cancer. How arsenic exposure leads to pulmonary disease is not fully understood. Both acute versus chronic arsenic exposure increase EGFR expression, but do so via distinct molecular mechanisms. BEAS-2B cells were exposed to either acute sodium arsenite (5 μM for 24 h) or chronic sodium arsenite (100 nM for 24 weeks). Cells treated with acute arsenic exhibited a decrease in viability, changes in morphology, and increased mRNA level of BTC. In contrast, during 24 weeks of arsenic exposure, the cells had increased EGFR expression and activity, and increased mRNA and protein levels of TGFα. Further, chronic arsenic treatment caused an increase in cell migration in the absence of exogenous ligand. Elevated TGFα and EGFR expression are features of many non-small cell lung cancers. We propose that lung epithelial cells chronically exposed to low level arsenic increases EGFR signaling via TGFα production to enhance ligand-independent cell migration.

Arsenic and benzo[a]pyrene co-exposure acts synergistically in inducing cancer stem cell-like property and tumorigenesis by epigenetically down-regulating SOCS3 expression

Arsenic and benzo[a]pyrene (BaP) are among the most common environmental carcinogens causing lung cancer. Millions of people are exposed to arsenic through consuming arsenic-contaminated drinking water. High levels of BaP are found in well-done barbecued meat and other food in addition to cigarette smoke. Hence, arsenic and BaP co-exposure in humans is common. However, the combined health effect and the underlying mechanism of arsenic and BaP co-exposure have not been well-understood. In this study we investigate the combined tumorigenic effect of arsenic and BaP co-exposure and the mechanism using both cell culture and mouse models. It was found that arsenic (sodium arsenite, 1.0 µM) and BaP (2.5 µM) co-exposure for 30 weeks synergizes in inducing malignant transformation of immortalized non-tumorigenic human bronchial epithelial cells and cancer stem cell (CSC)-like property to enhance their tumorigenicity. In animal studies, A/J mice were exposed to arsenic in drinking water (sodium arsenite, 20 ppm) starting from gestation day 18. After birth, the dams continuously received arsenic water throughout lactation. At weaning (3 weeks of age), male offspring were exposed to either arsenic alone via drinking the same arsenic water or exposed to arsenic plus BaP. BaP was administered via oral gavage (3 µmol per mouse per week) once a week starting from 3 weeks of age for 8 weeks. All mice were euthanized 34-weeks after the first BaP exposure. It was found that mice in control and arsenic exposure alone group did not develop lung tumors. All mice in BaP exposure alone group developed lung adenomas. However, arsenic and BaP co-exposure synergized in increasing lung tumor multiplicity and tumor burden. Furthermore, 30% of mice in arsenic and BaP co-exposure group also developed lung adenocarcinomas. Mechanistic studies revealed that arsenic and BaP co-exposure does not produce more BPDE-DNA adducts than BaP exposure alone; but acts synergistically in activating aryl hydrocarbon receptor (AhR) to up-regulate the expression of a histone H3 lysine 9 methyltransferase SUV39H1 and increase the level of suppressive H3 lysine 9 dimethylation (H3K9me2), which down-regulates the expression of tumor suppressive SOCS3 leading to enhanced activation of Akt and Erk1/2 to promote cell transformation, CSC-like property and tumorigenesis. Together, these findings suggest that arsenic and BaP co-exposure synergizes in causing epigenetic dysregulation to enhance cell transformation, CSC-like property and tumorigenesis.

Metal carcinogen exposure induces cancer stem cell-like property through epigenetic reprograming: A novel mechanism of metal carcinogenesis

Arsenic, cadmium, nickel and hexavalent chromium are among the most common environmental pollutants and potent carcinogens. Chronic exposure to these metals causes various types of cancer in humans, representing a significant environmental health issue. Although under active investigation, the mechanisms of metal carcinogenesis have not been clearly defined. One common feature of these metal carcinogens is that they are all able to cause various epigenetic dysregulations, which are believed to play important roles in their carcinogenicity. However, how metal carcinogen-caused epigenetic dysregulation contributes to metal carcinogenesis remains largely unknown. The evolution of cancer stem cell (CSC) theory has opened exciting new avenues for studying the mechanism of metal carcinogenesis. Increasing evidence indicates that chronic metal carcinogen exposure produces CSC-like cells through dysregulated epigenetic mechanisms. This review will first provide some brief introductions about CSC, epigenetics and epigenetic regulation of CSCs; then summarize progresses in recent studies on metal carcinogen-induced CSC-like property through epigenetic reprograming as a novel mechanism of metal carcinogenesis. Some perspectives for future studies in this field are also presented.

Synthesis and biological evaluation of quercetin-zinc (II) complex for anti-cancer and anti-metastasis of human bladder cancer cells

Bladder cancer is the 13th leading cause of cancer death worldwide, and its mortality rate is highly associated with the motility of the malignant cells. Although the techniques of urothelial cancer treatment have been continuously advanced in the last decade, the invasive bladder cancer remains incurable and the mean survival time of the patients with high-grade malignancy after cancer relapse is still < 6 months, indicating a new strategy which can reduce bladder cancer cell motility and/or progression is urgently needed. Quercetin is a polyphenolic flavonoid with approved anti-tumor effect. However, the drawbacks of quercetin, including low absorption, extensive metabolism, and rapid elimination, severely hamper its availability in the clinic. In this study, we aim to synthesize the quercetin-zinc complex (Q-ZnCPX) and explore its anti-cancer and anti-metastasis efficacies on human bladder cancer cells in vitro. Based on the results of cell movement and protein expressions in BFTC-905 cells, we found that both cell migratability and invasiveness were markedly reduced by the Q-ZnCPX with concentration of ≥ 12.5 μM through p-AKT and MT1-MMP regulations compared to the cells without treatment (P < 0.05). Moreover, the synthesized Q-ZnCPX with ≥ 75 μM can even provide > 50% of mortality rate (P < 0.05) to the cancer cell after 24-h treatment. These results demonstrated that the synthetic Q-ZnCPX may serve as feasible tool for both anti-cancer and anti-metastasis on human bladder cancer cells dependent on the dosage.

A review of arsenic exposure and lung cancer

As a well-established human carcinogen, arsenic has increased the risk of lung cancer over the past decades. Wide exposure to arsenic in the environment has attracted the attention of scientists. Its carcinogenicity at early life stages has been observed in certain animal studies already, yet current evidence is insufficient to extrapolate this to humans. Although the mechanisms of lung cancer induced by arsenic remain unclear, most of them are related to the biotransformation of arsenic, which would further provide target sites for precaution and therapy. This review comprehensively summarizes current studies associated to arsenic exposure and lung cancer and the mechanism of its carcinogenesis in lung cancer in three sections, namely, epidemiological studies, experimental studies, and mechanistic studies. In addition, prevention and treatment strategies as well as directions for future studies are discussed.

Chronic low dose arsenic exposure preferentially perturbs mitotic phase of the cell cycle

Environmental pollution is a big challenge for human survival. Arsenic compounds are well-known biohazard, the exposure of which is closely linked to onsets of various human diseases, particularly cancers. Upon chronically exposing to arsenic compounds, genomic integrity is often disrupted, leading to tumor development. However, the underlying mechanisms by which chronic, low dose arsenic exposure targets genetic stability to initiate carcinogenesis still remain not fully understood. In this study, human lung epithelial BEAS-2B cells and keratinocytes were treated with 0.5 μM of sodium arsenite for one month (designated as BEAS-2B-SA cells or keratinocytes-SA), and its effect on cell cycle responses was analyzed. After being arrested in mitotic phase of the cell cycle by nocodazole treatment, BEAS-2B-SA cells or keratinocytes-SA were delayed to enter next cytokinesis. The lagging exit of the cells from mitosis was accompanied by a sustained Plk1 phosphorylation, which led to a persistent activation of the mitotic regulators BubR1 and Cdc27. As the result, cyclin B1 (clnB1) degradation was attenuated. BEAS-2B-SA cells or keratinocytes-SA also expressed a constitutively active Akt. The cytogenetic analysis showed an increased numbers of aneuploidy in these cells. The suppression of Akt reversed the aberrant expressions of the mitotic regulators, delay of mitotic exit as well as chromosomal aberrations. Our findings suggest that a long-term exposure to low dose sodium arsenite aberrantly retains the catenation of mitosis, which facilitates establishing genetic instability and predisposes the cells to tumorigenesis.

A review on arsenic carcinogenesis: Epidemiology, metabolism, genotoxicity and epigenetic changes

Long-term exposure to arsenic (inorganic arsenic) is a world-wide environmental health concern. Arsenic is classified as the Group 1 human carcinogen by the International Agency for Research on Cancer (IARC). Epidemiological studies have established a strong association between inorganic arsenic (iAs) exposure in drinking water and an increased incidence of cancer including bladder, liver, lung, prostate, and skin cancer. iAs also increases the risk of other diseases such as cardiovascular disease, hypertension and diabetes. The molecular mechanisms of carcinogenesis of iAs remain poorly defined, several mechanisms have been proposed, including genotoxicity, altered cell proliferation, oxidative stress, changes to the epigenome, disturbances of signal transduction pathways, cytotoxicity and regenerative proliferation. In this article, we will summarize current knowledge on the mechanisms of arsenic carcinogenesis and focus on integrating all these issues to garner a broader perspective.

PI3K/Akt/mTOR Signaling Pathway and the Biphasic Effect of Arsenic in Carcinogenesis

Arsenic is a naturally occurring, ubiquitous metalloid found in the Earth’s crust. In its inorganic form, arsenic is highly toxic and carcinogenic and is widely found across the globe and throughout the environment. As an International Agency for Research on Cancer–defined class 1 human carcinogen, arsenic can cause multiple human cancers, including liver, lung, urinary bladder, skin, kidney, and prostate. Mechanisms of arsenic-induced carcinogenesis remain elusive, and this review focuses specifically on the role of the PI3K/AKT/mTOR pathway in promoting cancer development. In addition to exerting potent carcinogenic responses, arsenic is also known for its therapeutic effects against acute promyelocytic leukemia. Current literature suggests that arsenic can achieve both therapeutic as well as carcinogenic effects, and this review serves to examine the paradoxical effects of arsenic, specifically through the PI3K/AKT/mTOR pathway. Furthermore, a comprehensive review of current literature reveals an imperative need for future studies to establish and pinpoint the exact conditions for which arsenic can, and through what mechanisms it is able to, differentially regulate the PI3K/AKT/mTOR pathway to maximize the therapeutic and minimize the carcinogenic properties of arsenic.

Laminar shear stress inhibits high glucose-induced migration and invasion in human bladder cancer cells

High glucose has been known to play a pathogenic role in the development and progression of bladder cancer in diabetics, whereas the leading cause of death in such patients is mainly attributed to hyperglycemia-enhanced metastasis. In addition to the impact of glucose, cancer cells may be affected by laminar shear stress (LSS) generated from interstitial, blood, and/or lymphatic fluid flows during metastasis. Although the effect of flow-induced mechanical force on cancer pathophysiology has been extensively investigated, very little is understood regarding the cells that are simultaneously stimulated by LSS and hyperglycemia. To address this issue, the influence of LSS on bladder cancer cell motility in a hyperglycemic environment was examined. Based on the results of cell movement and protein expression analyses, we found that both cell migration and invasion were up- and downregulated by 25 mM glucose and 12 dynes/cm² LSS, respectively. Furthermore, the motility of the cells with simultaneous hyperglycemic and LSS stimulations was significantly reduced compared with that of the cells stimulated by high glucose alone (P < 0.05), demonstrating that the LSS rather than hyperglycemia played the dominant role in regulation of cell motility. These results implied that LSS with an intensity ≥ 12 dynes/cm² may serve as a feasible tool to reduce bladder cancer motility in diabetics.

Alterations of miRNAs and Their Potential Roles in Arsenite-Induced Transformation of Human Bronchial Epithelial Cells

The alterations of micro RNAs (miRNAs) and their potential roles in arsenite-induced tumorigenesis are still poorly understood. In this study, miRNA Array was used to detect the expression level of miRNAs in human bronchial epithelial (HBE) cells that were transformed by 2.5 μM arsenite for 13 weeks. These cells exhibited a neoplastic phenotype manifested by increased levels of cellular proliferation and migration and clone formation. Subsequently, 191 dysregulated miRNAs were identified to be associated with arsenite-induced transformation by miRNA Array. Among them, six miRNAs were validated by their expression levels with quantitative real-time polymerase chain reaction (qPCR), and 17 miRNAs were further explored via their target genes as well as regulatory network. Three databases, TargetMiner, miRDB, and TarBase, were used to predict the target genes of the 17 miRNAs, and a total of 954 common genes were sorted. Results of Gene Ontology (GO) analyses showed that the 954 genes were involved in diverse terms of GO categories, such as positive regulation of macroautophagy, epithelial cell maturation, and synaptic vesicle clustering. Moreover, results of Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analyses demonstrated that most of these target genes were enriched in various cancer-related pathways, including non-small cell lung cancer, Wnt signaling pathway, cell cycle, and p53 signaling pathway. The miRNA-gene regulatory network, which was constructed by cytoscape software with miRNAs and their target genes, showed that miR-15b-5p, miR-106b-5p, and miR-320d were the core hubs. Collectively, our results provide new insights into miRNA-mediated mechanisms underlying arsenite-induced transformation, although more experimental verification is still needed to prove these predictions.

MicroRNA-155 regulates arsenite-induced malignant transformation by targeting Nrf2-mediated oxidative damage in human bronchial epithelial cells

Arsenite is a well-documented human lung carcinogen but the detailed mechanisms of carcinogenesis remain unclear. In this study, human bronchial epithelial (16-HBE) cells were continuously exposed to 2.5μM arsenite for about 13 weeks to induce the phenotypes of malignant transformation. Our results showed that Nrf2 expression was gradually decreased whereas no significant change was observed on NF-κB activation with increased time of arsenite exposure. To test the roles of Nrf2-meidtaed oxidative damage in the arsenite-induced malignant transformation, we compared the levels of cGMP, PKG and oxidative damage-related indicators between arsenic-transformed cells and control cells. Our data demonstrated there were no significantly differences on the contents of cGMP, PKG, MDA and the production of ROS, but the levels of GSH and NO, the activities of SOD, tNOS and iNOS were significantly enhanced in the arsenic-transformed cells. Importantly, Nrf2 inactivation could be modulated by miR-155, and inhibition of miR-155 remarkably attenuated the malignant phenotypes and promoted apoptotic cell death in the arsenic-transformed cells. Together, our findings provide the novel mechanism that miR-155 may regulate arsenite-induced cell malignant transformation by targeting Nrf2-mediated oxidative damage, indicating that inhibition of miR-155 may be a potential strategy against lung carcinogenesis of arsenite.

ARHGAP18 Downregulation by miR-200b Suppresses Metastasis of Triple-Negative Breast Cancer by Enhancing Activation of RhoA

Rho GTPases activated in cancer cells drive proliferation, migration, and metastasis. Thus, RhoGAP proteins, which negatively regulate Rho GTPases, are generally thought to function as tumor suppressors. Here this expectation was challenged by characterization of ARHGAP18, a RhoGAP family member that is selectively overexpressed in highly migratory triple-negative breast cancer (TNBC) cells. In human breast tumors, higher ARHGAP18 levels associated with worse overall survival, recurrence-free survival, and metastasis-free survival. In TNBC cells, ARHGAP18 deletion increased RhoA activation but reduced growth, migration, and metastatic capacity. Mechanistic investigations revealed that ARHGAP18 levels were controlled by miR-200b, the enforced expression of which was sufficient to activate RhoA, enhanced formation of focal adhesions and actin stress fibers, and reduced migration and metastasis. Enforced elevation of ARHGAP18 where miR-200b was stably expressed reduced RhoA activity but increased cell migration. Pharmacologic inhibition of the Rho effector kinase ROCK blocked RhoA signaling and reversed the inhibitory effect of miR-200b on cell migration. Finally, ARHGAP18 overexpression or ROCK inhibition was sufficient to overcome metastatic blockade by miR-200b. Taken together, these results define opposing roles for oncogenic ARHGAP18 and tumor suppressive miR-200b in determining TNBC cell migration and metastatic prowess. Cancer Res; 77(15); 4051-64. ©2017 AACR.

Gestational Exposure to Sidestream (Secondhand) Cigarette Smoke Promotes Transgenerational Epigenetic Transmission of Exacerbated Allergic Asthma and Bronchopulmonary Dysplasia

Embryonic development is highly sensitive to xenobiotic toxicity and in utero exposure to environmental toxins affects physiological responses of the progeny. In the United States, the prevalence of allergic asthma (AA) is inexplicably rising and in utero exposure to cigarette smoke increases the risk of AA and bronchopulmonary dysplasia (BPD) in children and animal models. We reported that gestational exposure to sidestream cigarette smoke (SS), or secondhand smoke, promoted nicotinic acetylcholine receptor-dependent exacerbation of AA and BPD in mice. Recently, perinatal nicotine injections in rats were reported to induce peroxisome proliferator-activated receptor γ-dependent transgenerational transmission of asthma. Herein, we show that first generation and second generation progeny from gestationally SS-exposed mice exhibit exacerbated AA and BPD that is not dependent on the decrease in peroxisome proliferator-activated receptor γ levels. Lungs from these mice show strong eosinophilic infiltration, excessive Th2 polarization, marked airway hyperresponsiveness, alveolar simplification, decreased lung compliance, and decreased lung angiogenesis. At the molecular level, these changes are associated with increased RUNX3 expression, alveolar cell apoptosis, and the antiangiogenic factor GAX, and decreased expression of HIF-1α and proangiogenic factors NF-κB and VEGFR2 in the 7-d first generation and second generation lungs. Moreover, the lungs from these mice exhibit lower levels of microRNA (miR)-130a and increased levels of miR-16 and miR-221. These miRs regulate HIF-1α-regulated apoptotic, angiogenic, and immune pathways. Thus the intergenerational effects of gestational SS involve epigenetic regulation of HIF-1α through specific miRs contributing to increased incidence of AA and BPD in the progenies.

Persistent Exposure to Porphyromonas gingivalis Promotes Proliferative and Invasion Capabilities, and Tumorigenic Properties of Human Immortalized Oral Epithelial Cells

Recent epidemiological studies revealed a significant association between oral squamous cell carcinoma (OSCC) and Porphyromonas gingivalis, a major pathogen of periodontal disease. As a keystone pathogen of periodontitis, P. gingivalis is known not only to damage local periodontal tissues, but also to evade the host immune system and eventually affect systemic health. However, its role in OSCC has yet to be defined. To explore the underlying effect of chronic P. gingivalis infection on OSCC and to identify relevant biomarkers as promising targets for therapy and prevention, we established a novel model by exposing human immortalized oral epithelial cells (HIOECs) to P. gingivalis at a low multiplicity of infection (MOI) for 5–23 weeks. The P. gingivalis infected HIOECs were monitored for tumor biological alteration by proliferation, wound healing, transwell invasion, and gelatin zymography assays. Microarray and proteomic analyses were performed on HIOECs infected with P. gingivalis for 15 weeks, and some selected data were validated by quantitative real-time PCR and (or) western blot on cells infected for 15 and 23 weeks. Persistent exposure to P. gingivalis caused cell morphological changes, increased proliferation ability with higher S phase fraction in the cell cycle, and promoted cell migratory and invasive properties. In combining results of bioinformatics analyses and validation assays, tumor-related genes such as NNMT, FLI1, GAS6, lncRNA CCAT1, PDCD1LG2, and CD274 may be considered as the key regulators in tumor-like transformation in response to long-time exposure of P. gingivalis. In addition, some useful clinical biomarkers and novel proteins were also presented. In conclusion, P. gingivalis could promote tumorigenic properties of HIOECs, indicating that chronic P. gingivalis infection may be considered as a potential risk factor for oral cancer. The key regulators detected from the present model might be used in monitoring the development of OSCC with chronic periodontal infection.

The role of microRNAs in metal carcinogen-induced cell malignant transformation and tumorigenesis

MicroRNAs (miRNAs), an important component of epigenetic mechanisms of carcinogenesis, have been shown to play crucial roles in cancer initiation, metastasis, prognosis and responses to drug treatment and may serve as biomarkers for early diagnosis of cancer and tools for cancer therapy. Metal carcinogens, such as arsenic, cadmium, hexavalent chromium and nickel, are well-established human carcinogens causing various cancers upon long term exposure. However, the mechanism of metal carcinogenesis has not been well understood, which limits our capability to effectively diagnose and treat human cancers resulting from chronic metal carcinogen exposure. Over recent years, the role of miRNAs in metal carcinogenesis has been actively explored and a growing body of evidence indicates the critical involvement of miRNAs in metal carcinogenesis. This review aims to discuss recent studies showing that miRNAs play important roles in metal carcinogen-induced cell malignant transformation and tumorigenesis. Some thoughts for future further studies in this field are also presented.

17β-Estradiol Inhibites Tumor Necrosis Factor-α Induced Apoptosis of Human Nucleus Pulposus Cells via the PI3K/Akt Pathway

Background

Tumor necrosis factor-α (TNF-α) has been widely known to induce degeneration of nucleus pulposus cells (NPCs). 17β-estradiol (17β-E2) has been broadly proven for its function of suppressing cell apoptosis. The aim of this study is to explore whether 17β-E2 protects apoptosis of human NPCs induced by TNF-α via the PI3K/AKT pathway.

Material/Methods

NPCs were divided into four groups: control, TNF-α (100 ng/mL), TNF-α (100 ng/mL) with pretreated 17β-E2 (10 um/L), TNF-α (100 ng/mL) with pretreated 17β-E2 (10 um/L) and MK2206 (10 um/L, inhibitor of the PI3K/AKT pathway). Flow cytometry was used to measure the apoptotic incidence. Inverted phase-contrast microscopy was used to accomplish the morphological observation for apoptosis of treated cells. Additionally, Cell Counting Kit 8 (CCK-8) assay was used to detected cell proliferation. Western blot and quantitative real-time PCR (qRT-PCR) were applied to explore the expression of pro-caspase-3, caspase-3/p17, cleaved PARP, PARP, Akt, and phospho-Akt (p-Akt).

Results

First, inverted phase-contrast microscopy, CCK-8, and flow cytometry showed that TNF-α induced marked apoptosis, which was abolished by 17β-E2. Furthermore, Western blot and qRT-PCR showed that 17β-E2 protects TNF-α which can induced apoptosis by upregulating p-Akt, whereas Akt was essentially constant. Our data revealed that p-Akt expression peaked at 24 hours in a time-dependent manner (0–48 hours) after treating with TNF-α; and the p-Akt expression generally increased in a time-dependent manner (0–48 hours) after treating with TNF-α and 17β-E2.

Conclusions

17β-E2 is shown to protect NPCs against TNF-α induced apoptosis by upregulating p-Akt in the PI3K/AKT pathway. 17β-E2 generally increases expression of p-Akt.

The microRNA-200 family: small molecules with novel roles in cancer development, progression and therapy

MicroRNAs (miRNAs) are a large family of small non-coding RNAs that negatively regulate protein-coding gene expression post-transcriptionally via base pairing between the 5′ seed region of a miRNA and the 3′ untranslated region (3′UTR) of a messenger RNA (mRNA). Recent evidence has supported the critical role that miRNAs play in many diseases including cancer. The miR-200 family consisting of 5 members (miR-200a, -200b, -200c, -141, -429) is an emerging miRNA family that has been shown to play crucial roles in cancer initiation and metastasis, and potentially be important for the diagnosis and treatment of cancer. While miR-200s were found to be critically involved in the metastatic colonization to the lungs in mouse mammary xenograft tumor models, a large number of studies demonstrated their strong suppressive effects on cell transformation, cancer cell proliferation, migration, invasion, tumor growth and metastasis. This review aims to discuss research findings about the role of the miR-200 family in cancer initiation, each step of cancer metastatic cascade, cancer diagnosis and treatment. A comprehensive summary of currently validated miR-200 targets is also presented. It is concluded that miR-200 family may serve as novel targets for the therapy of multiple types of cancer.

Functional role of inorganic trace elements in angiogenesis part III: (Ti, Li, Ce, As, Hg, Va, Nb and Pb)

Many essential elements exist in nature with significant influence on human health. Angiogenesis is vital in developmental, repair, and regenerative processes, and its aberrant regulation contributes to pathogenesis of many diseases including cancer. Thus, it is of great importance to explore the role of these elements in such a vital process. This is third in a series of reviews that serve as an overview of the role of inorganic elements in regulation of angiogenesis and vascular function. Here we will review the roles of titanium, lithium, cerium, arsenic, mercury, vanadium, niobium, and lead in these processes. The roles of other inorganic elements in angiogenesis were discussed in part I (N, Fe, Se, P, Au, and Ca) and part II (Cr, Si, Zn, Cu, and S) of these series. The methods of exposure, structure, mechanisms, and potential activities of these elements are briefly discussed. An electronic search was performed on the role of these elements in angiogenesis from January 2005 to April 2014. These elements can promote and/or inhibit angiogenesis through different mechanisms. The anti-angiogenic effect of titanium dioxide nanoparticles comes from the inhibition of angiogenic processes, and not from its toxicity. Lithium affects vasculogenesis but not angiogenesis. Nanoceria treatment inhibited tumor growth by inhibiting angiogenesis. Vanadium treatment inhibited cell proliferation and induced cytotoxic effects through interactions with DNA. The negative impact of mercury on endothelial cell migration and tube formation activities was dose and time dependent. Lead induced IL-8 production, which is known to promote tumor angiogenesis. Thus, understanding the impact of these elements on angiogenesis will help in development of new modalities to modulate angiogenesis under various conditions.

Chronic inorganic arsenic exposure in vitro induces a cancer cell phenotype in human peripheral lung epithelial cells

Inorganic arsenic is a human lung carcinogen. We studied the ability of chronic inorganic arsenic (2 μM; as sodium arsenite) exposure to induce a cancer phenotype in the immortalized, non-tumorigenic human lung peripheral epithelial cell line, HPL-1D. After 38 weeks of continuous arsenic exposure, secreted matrix metalloproteinase-2 (MMP2) activity increased to over 200% of control, levels linked to arsenic-induced cancer phenotypes in other cell lines. The invasive capacity of these chronic arsenic-treated lung epithelial (CATLE) cells increased to 320% of control and colony formation increased to 280% of control. CATLE cells showed enhanced proliferation in serum-free media indicative of autonomous growth. Compared to control cells, CATLE cells showed reduced protein expression of the tumor suppressor gene PTEN (decreased to 26% of control) and the putative tumor suppressor gene SLC38A3 (14% of control). Morphological evidence of epithelial-to-mesenchymal transition (EMT) occurred in CATLE cells together with appropriate changes in expression of the EMT markers vimentin (VIM; increased to 300% of control) and e-cadherin (CDH1; decreased to 16% of control). EMT is common in carcinogenic transformation of epithelial cells. CATLE cells showed increased KRAS (291%), ERK1/2 (274%), phosphorylated ERK (p-ERK; 152%), and phosphorylated AKT1 (p-AKT1; 170%) protein expression. Increased transcript expression of metallothioneins, MT1A and MT2A and the stress response genes HMOX1 (690%) and HIF1A (247%) occurred in CATLE cells possibly in adaptation to chronic arsenic exposure. Thus, arsenic induced multiple cancer cell characteristics in human peripheral lung epithelial cells. This model may be useful to assess mechanisms of arsenic-induced lung cancer.

The mechanistic basis of arsenicosis: pathogenesis of skin cancer

Significant amounts of arsenic have been found in the groundwater of many countries including Argentina, Bangladesh, Chile, China, India, Mexico, and the United States with an estimated 200 million people at risk of toxic exposure. Although chronic arsenic poisoning damages many organ systems, it usually first presents in the skin with manifestations including hyperpigmentation, hyperkeratoses, Bowen's disease, squamous cell carcinoma, and basal cell carcinoma. Arsenic promotes oxidative stress by upregulating nicotinamide adenine dinucleotide phosphate oxidase, uncoupling nitric oxide synthase, and by depleting natural antioxidants such as nitric oxide and glutathione in addition to targeting other proteins responsible for the maintenance of redox homeostasis. It causes immune dysfunction and tissue inflammatory responses, which may involve activation of the unfolded protein response signaling pathway. In addition, the dysregulation of other molecular targets such as nuclear factor kappa B, Hippo signaling protein Yap, and the mineral dust-induced proto-oncogene may orchestrate the pathogenesis of arsenic-mediated health effects. The metalloid decreases expression of tumor suppressor molecules and increases expression of pro-inflammatory mitogen-activated protein kinase pathways leading to a tumor-promoting tissue microenvironment. Cooperation of upregulated signal transduction molecules with DNA damage may abrogate apoptosis, promote proliferation, and enhance cell survival. Genomic instability via direct DNA damage and weakening of several cellular DNA repair mechanisms could also be important cancer development mechanisms in arsenic-exposed populations. Thus, arsenic mediates its toxicity by generating oxidative stress, causing immune dysfunction, promoting genotoxicity, hampering DNA repair, and disrupting signal transduction, which may explain the complex disease manifestations seen in arsenicosis.

MicroRNA-200b targets protein kinase Cα and suppresses triple-negative breast cancer metastasis

Triple-negative breast cancer (TNBC) is an aggressive subtype of breast cancer with poor prognosis and lacks effective targeted therapies. The microRNA-200 (miR-200) family is found to inhibit or promote breast cancer metastasis; however, the underlying mechanism is not well understood. This study was performed to investigate the effect and mechanism of miR-200b on TNBC metastasis and identify targets for developing more efficient treatment for TNBC. We found that miR-200 family expression levels are significantly lower in highly migratory TNBC cells and metastatic TNBC tumors than other types of breast cancer cells and tumors. Ectopically expressing a single member (miR-200b) of the miR-200 family drastically reduces TNBC cell migration and inhibits tumor metastasis in an orthotopic mouse mammary xenograft tumor model. We identified protein kinase Cα (PKCα) as a new direct target of miR-200b and found that PKCα protein levels are inversely correlated with miR-200b levels in 12 kinds of breast cancer cells. Inhibiting PKCα activity or knocking down PKCα levels significantly reduces TNBC cell migration. In contrast, forced expression of PKCα impairs the inhibitory effect of miR-200b on cell migration and tumor metastasis. Further mechanistic studies revealed that PKCα downregulation by miR-200b results in a significant decrease of Rac1 activation in TNBC cells. These results show that loss of miR-200b expression plays a crucial role in TNBC aggressiveness and that miR-200b suppresses TNBC cell migration and tumor metastasis by targeting PKCα. Our findings suggest that miR-200b and PKCα may serve as promising therapeutic targets for metastatic TNBC.

MicroRNA-200b targets protein kinase Cα and suppresses triple-negative breast cancer metastasis

Triple-negative breast cancer (TNBC) is an aggressive subtype of breast cancer with poor prognosis and lacks effective targeted therapies. The microRNA-200 (miR-200) family is found to inhibit or promote breast cancer metastasis; however, the underlying mechanism is not well understood. This study was performed to investigate the effect and mechanism of miR-200b on TNBC metastasis and identify targets for developing more efficient treatment for TNBC. We found that miR-200 family expression levels are significantly lower in highly migratory TNBC cells and metastatic TNBC tumors than other types of breast cancer cells and tumors. Ectopically expressing a single member (miR-200b) of the miR-200 family drastically reduces TNBC cell migration and inhibits tumor metastasis in an orthotopic mouse mammary xenograft tumor model. We identified protein kinase Cα (PKCα) as a new direct target of miR-200b and found that PKCα protein levels are inversely correlated with miR-200b levels in 12 kinds of breast cancer cells. Inhibiting PKCα activity or knocking down PKCα levels significantly reduces TNBC cell migration. In contrast, forced expression of PKCα impairs the inhibitory effect of miR-200b on cell migration and tumor metastasis. Further mechanistic studies revealed that PKCα downregulation by miR-200b results in a significant decrease of Rac1 activation in TNBC cells. These results show that loss of miR-200b expression plays a crucial role in TNBC aggressiveness and that miR-200b suppresses TNBC cell migration and tumor metastasis by targeting PKCα. Our findings suggest that miR-200b and PKCα may serve as promising therapeutic targets for metastatic TNBC.

MicroRNA-200b suppresses arsenic-transformed cell migration by targeting protein kinase Cα and Wnt5b-protein kinase Cα positive feedback loop and inhibiting Rac1 activation

MicroRNA-200b (miR-200b) is a member of miR-200 family that has been found to inhibit cell migration and cancer metastasis; however, the underlying mechanism is not well understood. We previously reported that miR-200 expression is depleted in arsenic-transformed human bronchial epithelial cells with highly migratory and invasive characteristics, whereas stably re-expressing miR-200b strongly suppresses arsenic-transformed cell migration. This study was performed to investigate how miR-200b inhibits arsenic-transformed cell migration. We found that protein kinase Cα (PKCα) is significantly up-regulated in arsenic-transformed cells. Combining bioinformatics analysis with PKCα 3'-untranslated region vector luciferase reporter assays, we showed that PKCα is a direct target of miR-200b. Inhibiting PKCα activity or knocking down PKCα expression drastically reduced cell migration, phenocoping the inhibitory effect of overexpressing miR-200b. In contrast, forced expression of PKCα in miR-200b overexpressing cells impaired the inhibitory effect of miR-200b on cell migration. In addition, we also found a positive feedback loop between Wnt5b and PKCα in arsenic-transformed cells. Knocking down Wnt5b expression reduced phospho-PKC levels and cell migration; and knocking down PKCα expression decreased Wnt5b level and cell migration. Moreover, forced expression of PKCα increased Wnt5b and phospho-PKC levels and cell migration. Further mechanistic studies revealed that Rac1 is highly activated in arsenic-transformed cells and stably expressing miR-200b abolishes Rac1 activation changing actin cytoskeleton organization. Manipulating PKCα or Wnt5b expression levels significantly altered the level of active Rac1. Together, these findings indicate that miR-200b suppresses arsenic-transformed cell migration by targeting PKCα and Wnt5b-PKCα positive feedback loop and subsequently inhibiting Rac1 activation.

Carcinogenic metalloid arsenic induces expression of mdig oncogene through JNK and STAT3 activation

Environmental or occupational exposure to arsenic, a chemical element classified as metalloid, has been associated with cancer of the lung, skin, bladder, liver, etc. Mdig (mineral dust-induced gene) is a newly identified oncogene linked to occupational lung diseases and lung cancer. It is unclear whether mdig is also involved in arsenic-induced malignant transformation of the lung cells. By using human bronchial epithelial cells and human lung cancer cell lines, we showed that arsenic was able to induce expression of mdig. We further demonstrated that this mdig induction by arsenic was partially dependent on the JNK and STAT3 signaling pathways. Disruption of the JNK or STAT3 by either chemical inhibitors or siRNAs diminished arsenic-induced accumulation of mdig mRNA and protein. Furthermore, we also showed that microRNA-21 (miR-21) and Akt were down-stream effectors of the JNK and STAT3 signaling pathways in arsenic-induced mdig expression. Transfection of the cells with anti-miR-21 or pre-treatment of the cells with Akt inhibitor blunted mdig induction by arsenic. Clinically, the levels of mdig can be applied to predict the disease progression, the first progression (FP), in non-small cell lung cancer (NSCLC) patients. Taken together, our data suggest that mdig may play important roles on the pathogenesis of arsenic-induced lung cancer and that JNK and STAT3 signaling pathways are essential in mediating arsenic-induced mdig expression.

VEGF-PKD1-HDAC7 signaling promotes endothelial progenitor cell migration and tube formation

Histone acetylation/deacetylation is a key mechanism for regulating transcription, which plays an important role in the control of gene expression, tissue growth, and development. In particular, histone deacetylase 7 (HDAC7), a member of class IIa HDACs, is crucial in maintaining vascular integrity. Endothelial progenitor cells (EPCs) play an important role in angiogenesis. However, whether HDAC7 plays a role in the processes of EPCs angiogenesis remains unclear. Migration and tube formation were the two major components of EPC angiogenesis. In this study, we show for the first time that HDAC7 silencing weakened the migration and tube formation abilities of EPCs. VEGF-A induced an increase of phospho-HDAC7 and its nuclear export in a time-dependent manner, which could be partly inhibited by protein kinase D1 (PKD1) inhibitor, but not by the PI3K inhibitor or the MEK inhibitor. Our results showed that EPCs involved in the angiogenesis might be controlled by VEGF-PKD1-HDAC7 axis, which regulates the EPCs angiogenesis by PKD1, but not the ERK and PI3K pathway.

Sodium arsenite and arsenic trioxide differently affect the oxidative stress, genotoxicity and apoptosis in A549 cells: an implication for the paradoxical mechanism

Although arsenic toxicity greatly depends on its chemical forms, few studies have taken into account the paradoxical phenomenon which is manifested by that sodium arsenite (NaAsO₂) acts as a potent carcinogen but arsenic trioxide (As₂O₃) serves as an effective therapeutic agent. In this study, we compared the in vitro effects of NaAsO₂ and As₂O₃ on cell viability, colony formation, cell cycle progression, apoptosis, genotoxicity and oxidative stress in human lung adenocarcinoma A549 cells. Our results demonstrated that both NaAsO₂ and As₂O₃ caused oxidative stress, genotoxicity, cytotoxicity, cell cycle arrest as well as apoptosis, while As₂O₃ induced higher production of reactive oxygen species (ROS) with a more remarkable decrease in superoxide dismutase (SOD) activities and intracellular levels of glutathione (GSH) than NaAsO₂. Moreover, the degree of DNA damage, chromosomal breakage, cell cycle arrest and apoptosis in As₂O₃-treated cells were more severe than those in NaAsO₂-treated cells. These findings suggest that differential effects and mechanisms of NaAsO₂ and As₂O₃ may responsible for the paradoxical effects of arsenic on the carcinogenesis and anticancer function.

Regulation of the microRNA 200b (miRNA-200b) by transcriptional regulators PEA3 and ELK-1 protein affects expression of Pin1 protein to control anoikis

MicroRNA (miRNA) 200s regulate E-cadherin by directly targeting ZEB1/ZEB2, which are transcriptional repressors of E-cadherin. Decreased expression of E-cadherin results in cancer cells losing interaction with the extracellular matrix and detaching from the primary tumor. Normally, cells will undergo anoikis after losing interaction with the extracellular matrix. Cancer cells must, therefore, possess the ability to resist anoikis during the process of metastasis. Here we show that miRNA-200b regulates anoikis by directly targeting the 3' UTR of Pin1 mRNA and regulating Pin1 expression at the translational level. We found that down-regulation of miRNA-200b promotes cancer cells survival during metastasis, and the homeless state of these cells resulted in decreased expression of miRNA-200b in the MCF-7 cell line. We also found that expression of miRNA-200b is down-regulated in human breast cancer during lymph node metastasis, which has a significant negative correlation with Pin1 expression. Two members of the ETS (E-26) family (PEA3 and ELK-1) regulate the expression of miRNA-200b. PEA3 promotes the expression of miRNA-200b, and ELK-1 is a transcriptional repressor of miRNA-200b. In addition, miRNA-200b regulates the activity of PEA3 and ELK-1 via the Pin1-pERK pathway and forms self-regulated feedback loops. This study characterizes the role of miRNA-200b in the regulation of anoikis and demonstrates the regulation of its own expression in the process of metastasis.

Antitumor effects of Endostar on non-Hodgkin's lymphoma by regulating endothelial progenitor cells through protein kinase B-dependent pathway

Endothelial progenitor cells (EPCs) play an important role in non-Hodgkin's lymphoma (NHL) development. Endostar is an anti-angiogenic drug designed to stop cancer by nullifying a tumor's ability to obtain oxygen and nutrients. In this study, we examined the anti-angiogenic activities of Endostar on NHL cell lines and murine xenograft model of NHL in vitro and in vivo, respectively, and explored the underlying antiangiogenic mechanism of Endostar. Results showed that Endostar may inhibit the EPC proliferation by reducing the expression of p-protein kinase B, but not p-ERK expression. Our finding could lead to a better understanding of the effects of Endostar on NHL.

Epithelial to mesenchymal transition in arsenic-transformed cells promotes angiogenesis through activating β-catenin-vascular endothelial growth factor pathway

Arsenic exposure represents a major health concern increasing cancer risks, yet the mechanism of arsenic carcinogenesis has not been elucidated. We and others recently reported that cell malignant transformation by arsenic is accompanied by epithelial to mesenchymal transition (EMT). However, the role of EMT in arsenic carcinogenesis is not well understood. Although previous studies showed that short term exposure of endothelial cells to arsenic stimulated angiogenesis, it remains to be determined whether cells that were malignantly transformed by long term arsenic exposure have a pro-angiogenic effect. The objective of this study was to investigate the effect of arsenic-transformed human bronchial epithelial cells that underwent EMT on angiogenesis and the underlying mechanism. It was found that the conditioned medium from arsenic-transformed cells strongly stimulated tube formation by human umbilical vein endothelial cells (HUVECs). Moreover, enhanced angiogenesis was detected in mouse xenograft tumor tissues resulting from inoculation of arsenic-transformed cells. Mechanistic studies revealed that β-catenin was activated in arsenic-transformed cells up-regulating its target gene expression including angiogenic-stimulating vascular endothelial growth factor (VEGF). Stably expressing microRNA-200b in arsenic-transformed cells that reversed EMT inhibited β-catenin activation, decreased VEGF expression and reduced tube formation by HUVECs. SiRNA knockdown β-catenin decreased VEGF expression. Adding a VEGF neutralizing antibody into the conditioned medium from arsenic-transformed cells impaired tube formation by HUVECs. Reverse transcriptase-PCR analysis revealed that the mRNA levels of canonical Wnt ligands were not increased in arsenic-transformed cells. These findings suggest that EMT in arsenic-transformed cells promotes angiogenesis through activating β-catenin-VEGF pathway.

Molecular features in arsenic-induced lung tumors

Arsenic is a well-known human carcinogen, which potentially affects ~160 million people worldwide via exposure to unsafe levels in drinking water. Lungs are one of the main target organs for arsenic-related carcinogenesis. These tumors exhibit particular features, such as squamous cell-type specificity and high incidence among never smokers. Arsenic-induced malignant transformation is mainly related to the biotransformation process intended for the metabolic clearing of the carcinogen, which results in specific genetic and epigenetic alterations that ultimately affect key pathways in lung carcinogenesis. Based on this, lung tumors induced by arsenic exposure could be considered an additional subtype of lung cancer, especially in the case of never-smokers, where arsenic is a known etiological agent. In this article, we review the current knowledge on the various mechanisms of arsenic carcinogenicity and the specific roles of this metalloid in signaling pathways leading to lung cancer.

P38/NF-κB/snail pathway is involved in caffeic acid-induced inhibition of cancer stem cells-like properties and migratory capacity in malignant human keratinocyte

Background

Skin cancer is the most common cancer throughout the world. The epithelial-mesenchymal transition (EMT) and the acquisition of cancer stem cells (CSCs)-like properties emerge as critical steps in the metastasis of human skin cancers. Caffeic acid (CaA) exerts anticarcinogenic effects. However, the effects of CaA on the migratory capability and on the CSCs-like properties of skin cancer cells, and the molecular mechanisms underlying it are not fully understood.

Methods

Malignant HaCaT cells were treated by CaA. Transwell assay was performed to determine that CaA attenuated the migratory capability; Spheroid formation assay was performed to confirm that CaA decreased the CSCs-like phenotype; Treated malignant HaCaT cells were molecularly characterized by RT-PCR, Western blots, Southwestern blot, and immunoprecipitation.

Results

In CaA-treated malignant human keratinocyte (malignant HaCaT cells), inhibition of the migratory capability and CSCs-like phenotype were observed. CaA up-regulated the phosphorylation of p38, and down-regulated the activation of nuclear factor κB (NF-κB)/snail signal pathway. Indeed, p38 decreased the DNA-binding activity of NF-κB to the promoter of snail gene, which resulted in the transcriptional inactivation of snail. Blockage of p38 attenuated the CaA-induced inhibition of migratory capability and CSCs-like phenotype in malignant HaCaT cells.

Conclusions

CaA attenuates the migratory capability and CSCs-like Properties of malignant human keratinocyte, in which, p38-mediated down-regulation of NF-κB/snail signal pathway is involved.

Toxicogenomic approaches for understanding molecular mechanisms of heavy metal mutagenicity and carcinogenicity

Heavy metals that are harmful to humans include arsenic, cadmium, chromium, lead, mercury, and nickel. Some metals or their related compounds may even cause cancer. However, the mechanism underlying heavy metal-induced cancer remains unclear. Increasing data show a link between heavy metal exposure and aberrant changes in both genetic and epigenetic factors via non-targeted multiple toxicogenomic technologies of the transcriptome, proteome, metabolome, and epigenome. These modifications due to heavy metal exposure might provide a better understanding of environmental disorders. Such informative changes following heavy metal exposure might also be useful for screening of biomarker-monitored exposure to environmental pollutants and/or predicting the risk of disease. We summarize advances in high-throughput toxicogenomic-based technologies and studies related to exposure to individual heavy metal and/or mixtures and propose the underlying mechanism of action and toxicant signatures. Integrative multi-level expression analysis of the toxicity of heavy metals via system toxicology-based methodologies combined with statistical and computational tools might clarify the biological pathways involved in carcinogenic processes. Although standard in vitro and in vivo endpoint testing of mutagenicity and carcinogenicity are considered a complementary approach linked to disease, we also suggest that further evaluation of prominent biomarkers reflecting effects, responses, and disease susceptibility might be diagnostic. Furthermore, we discuss challenges in toxicogenomic applications for toxicological studies of metal mixtures and epidemiological research. Taken together, this review presents toxicogenomic data that will be useful for improvement of the knowledge of carcinogenesis and the development of better strategies for health risk assessment.

Feedback regulations of miR-21 and MAPKs via Pdcd4 and Spry1 are involved in arsenite-induced cell malignant transformation

OBJECTIVE

To establish the functions of miR-21 and the roles of two feedback regulation loops, miR-21-Spry1-ERK/NF-κB and miR-21-Pdcd4-JNK/c-Jun, in arsenite-transformed human embryo lung fibroblast (HELF) cells.

METHODS

For arsenite-transformed HELF cells, apoptosis, clonogenicity, and capacity for migration were determined by Hoechst staining, assessment of their capacity for anchorage-independent growth, and wound-healing, respectively, after blockage, with inhibitors or with siRNAs, of signal pathways for JNK/c-Jun or ERK/NF-κB. Decreases of miR-21 levels were determined with anti-miR-21, and the up-regulation of Pdcd4 and Spry1 was assessed in transfected cells; these cells were molecularly characterized by RT-PCR, qRT-PCR, Western blots, and immunofluorescence assays.

RESULTS

MiR-21 was highly expressed in arsenite-transformed HELF cells and normal HELF cells acutely treated with arsenite, an effect that was concomitant with activation of JNK/c-Jun and ERK/NF-κB and down-regulation of Pdcd4 and Spry1 protein levels. However, there were no significant changes in mRNA levels for Pdcd4 and Spry1, which suggested that miR-21 regulates the expressions of Pdcd4 and Spry1 through translational repression. In arsenite-transformed HELF cells, blockages of JNK/c-Jun or ERK/NF-κB with inhibitors or with siRNAs prevented the increases of miR-21and the decreases of the protein levels but not the mRNA levels of Pdcd4 and Spry1. Down-regulation of miR-21 and up-regulations of Pdcd44 or Spry1 blocked the arsenite-induced activations of JNK/c-Jun or ERK/NF-κB, indicating that knockdown of miR-21 inhibits feedback of ERK activation and JNK activation via increases of Pdcd4 and Spry1 protein levels, respectively. Moreover, in arsenite-transformed HELF cells, inhibition of miR-21 promoted cell apoptosis, inhibited clonogenicity, and reduced migration.

CONCLUSION

The results indicate that miR-21 is both a target and a regulator of ERK/NF-κB and JNK/c-Jun and the feedback regulations of miR-21 and MAPKs via Pdcd4 and Spry1, respectively, are involved in arsenite-induced malignant transformation of HELF cells.

Inhibition of AKT enhances mitotic cell apoptosis induced by arsenic trioxide

Accumulated evidence has revealed a tight link between arsenic trioxide (ATO)-induced apoptosis and mitotic arrest in cancer cells. AKT, a serine/threonine kinase frequently over-activated in diverse tumors, plays critical roles in stimulating cell cycle progression, abrogating cell cycle checkpoints, suppressing apoptosis, and regulating mitotic spindle assembly. Inhibition of AKT may therefore enhance ATO cytotoxicity and thus its clinical utility. We show that AKT was activated by ATO in HeLa-S3 cells. Inhibition of AKT by inhibitors of the phosphatidyl inositol 3-kinase/AKT pathway significantly enhanced cell sensitivity to ATO by elevating mitotic cell apoptosis. Ectopic expression of the constitutively active AKT1 had no effect on ATO-induced spindle abnormalities but reduced kinetochore localization of BUBR1 and MAD2 and accelerated mitosis exit, prevented mitotic cell apoptosis, and enhanced the formation of micro- or multi-nuclei in ATO-treated cells. These results indicate that AKT1 activation may prevent apoptosis of ATO-arrested mitotic cells by attenuating the function of the spindle checkpoint and therefore allowing the formation of micro- or multi-nuclei in surviving daughter cells. In addition, AKT1 activation upregulated the expression of aurora kinase B (AURKB) and survivin, and depletion of AURKB or survivin reversed the resistance of AKT1-activated cells to ATO-induced apoptosis. Thus, AKT1 activation suppresses ATO-induced mitotic cell apoptosis, despite the presence of numerous spindle abnormalities, probably by upregulating AURKB and survivin and attenuating spindle checkpoint function. Inhibition of AKT therefore effectively sensitizes cancer cells to ATO by enhancing mitotic cell apoptosis.

JNK and STAT3 signaling pathways converge on Akt-mediated phosphorylation of EZH2 in bronchial epithelial cells induced by arsenic

The molecular mechanisms by which arsenic (As ( 3+) ) causes human cancers remain to be fully elucidated. Enhancer of zeste homolog 2 (EZH2) is the catalytic subunit of polycomb-repressive complexes 2 (PRC2) that promotes trimethylation of lysine 27 of histone H3, leading to altered expression of tumor suppressors or oncogenes. In the present study, we determined the effect of As ( 3+) on EZH2 phosphorylation and the signaling pathways important for As ( 3+) -induced EZH2 phosphorylation in human bronchial epithelial cell line BEAS-2B. The involvement of kinases in As ( 3+) -induced EZH2 phosphorylation was validated by siRNA-based gene silencing. The data showed that As ( 3+) can induce phosphorylation of EZH2 at serine 21 in human bronchial epithelial cells and that the phosphorylation of EZH2 requires an As ( 3+) -activated signaling cascade from JNK and STAT3 to Akt. Transfection of the cells with siRNA specific for JNK1 revealed that JNK silencing reduced serine727 phosphorylation of STAT3, Akt activation and EZH2 phosphorylation, suggesting that JNK is the upstream kinase involved in As ( 3+) -induced EZH2 phosphorylation. Because As ( 3+) is capable of inducing miRNA-21 (miR-21), a STAT3-regulated miRNA that represses protein translation of PTEN or Spry2, we also tested the role of STAT3 and miR-21 in As ( 3+) -induced EZH2 phosphorylation. Ectopic overexpression of miR-21 promoted Akt activation and phosphorylation of EZH2, whereas inhibiting miR-21 by transfecting the cells with anti-miR-21 inhibited Akt activation and EZH2 phosphorylation. Taken together, these results demonstrate a contribution of the JNK, STAT3 and Akt signaling axis to As ( 3+) -induced EZH2 phosphorylation. Importantly, these findings may reveal new molecular mechanisms underlying As ( 3+) -induced carcinogenesis.

Chronic arsenic exposure in nanomolar concentrations compromises wound response and intercellular signaling in airway epithelial cells

Paracrine ATP signaling in the lung epithelium participates in a variety of innate immune functions, including mucociliary clearance, bactericide production, and as an initiating signal in wound repair. We evaluated the effects of chronic low-dose arsenic relevant to U.S. drinking water standards (i.e., 10 ppb [130nM]) on airway epithelial cells. Immortalized human bronchial epithelial cells (16HBE14o-) were exposed to 0, 130, or 330nM arsenic (as Na-arsenite) for 4-5 weeks and examined for wound repair efficiency and ATP-mediated Ca(2+) signaling. We found that chronic arsenic exposure at these low doses slows wound repair and reduces ATP-mediated Ca(2+) signaling. We further show that arsenic compromises ATP-mediated Ca(2+) signaling by altering both Ca(2+) release from intracellular stores (via metabotropic P2Y receptors) and Ca(2+) influx mechanisms (via ionotropic P2X receptors). To better model the effects of arsenic on ATP-mediated Ca(2+) signaling under conditions of natural exposure, we cultured tracheal epithelial cells obtained from mice exposed to control or 50 ppb Na-arsenite supplemented drinking water for 4 weeks. Tracheal epithelial cells from arsenic-exposed mice displayed reduced ATP-mediated Ca(2+) signaling dynamics similar to our in vitro chronic exposure. Our findings demonstrate that chronic arsenic exposure at levels that are commonly found in drinking water (i.e., 10-50 ppb) alters cellular mechanisms critical to airway innate immunity.