Recruitment of normal stem cells to an oncogenic phenotype by noncontiguous carcinogen-transformed epithelia depends on the transforming carcinogen

Molecular interplay between NOX1 and autophagy in cadmium-induced prostate carcinogenesis

Chronic exposure to cadmium (Cd), a class I carcinogen, leads to malignant transformation of normal prostate epithelial cells (RWPE-1). The constant generation of Cd-induced ROS and resulting ER stress induces cellular responses that are needed for cell survival, and autophagy has an important role in this process. However, the mechanisms that regulate Cd-induced ROS and how these differ in terms of acute and chronic cadmium exposure remain unexplained. Here, we show that acute or chronic Cd exposure facilitates NOX1 assembly by activating its cytosolic regulators p47phox and p67phox in RWPE-1 cells. Upregulation of NOX1 complex proteins and generation of ROS activates unfolded protein response (UPR) via phosphorylation of protein kinase RNA-like endoplasmic reticulum kinase (PERK), eukaryotic initiation factor 2 alpha (eIF2α), and selective translation of activating transcription factor 4 (ATF4). Chronic Cd exposure constantly activates NOX1 complex and generates consistent ROS and ER stress that led to defective autophagy, wherein ATG5 expression is downregulated in contrast to acute Cd exposure. As a result, selective/defective autophagy creates depletion of autophagosome-lysosome fusion that gives a survival advantage to transforming cells, which is not available to RWPE-1 cells acutely exposed to Cd. Knockdown of key molecules in a lockstep manner directly affects the most downstream autophagy pathways in transforming cells. Overall, this study demonstrates that assembly of NOX1 complex proteins is indispensable for Cd-induced persistent ROS and controls ER stress-induced defective autophagy in mice and humans.

Bioinformatics analysis of key genes and potential mechanism in cadmium-induced breast cancer progression

Cadmium (Cd) may be associated with breast cancer progression, but the detailed molecular mechanism has not been fully elucidated. In this study, one public dataset (GSE136595) was used to identify differentially expressed genes (DEGs) in Cd-treated MCF-7 breast cancer cells. We determined a total of 2077 DEGs, and Ingenuity Pathway Analysis (IPA) software showed that 246 of them were related to tumor progression. Pathway analysis of these DEGs indicated that the HIF1α signaling and the epithelial-mesenchymal transition (EMT) pathway regulated by growth factors might be activated. Moreover, twist family bHLH transcription factor 1 (TWIST1), lysine demethylase 3A (KDM3A), Kruppel-like factor 4 (KLF4), nuclear protein 1 (NUPR1), neurogenin 3 (NEUROG3), and HNF1 homeobox B (HNF1B) might be the key transcription factors. And the result of protein-protein interaction (PPI) analysis showed that the hub genes in these 246 DEGs were tumor protein p53 (TP53), polo-like kinase 1 (PLK1), sirtuin 1 (SIRT1), protein tyrosine phosphatase non-receptor type 11 (PTPN11), caspase 8 (CASP8), cyclin-dependent kinase 6 (CDK6), calmodulin 3 (CALM3), KRAS proto-oncogene (KRAS), extra spindle pole bodies like 1 (ESPL1), and marker of proliferation Ki-67 (MKI67). Further analysis indicated that TWIST1, NUPR1, KRAS, and PTPN11 were related to the prognostic of breast cancer based on the Cancer Genome Atlas (TCGA) and they were validated to be upregulated in the Cd-treated MCF-7 cells. Our results suggested that the HIF1α signaling and the EMT pathway regulated by growth factors might be participant in the Cd-induced breast cancer progression and TWIST1, NUPR1, KRAS, and PTPN11 might be potential key genes.

Environmental Exposure to Heavy Metals Contributes to Diseases Via Deregulated Wnt Signaling Pathways

Wnt signaling plays a critical role during embryogenesis and is responsible for regulating the homeostasis of the adult stem cells and cells fate via a multitude of signaling pathways and associated transcription factors, receptors, effectors, and inhibitors. For this review, published articles were searched from PubMed Central, Embase, Medline, and Google Scholar. The search terms were Wnt, canonical, noncanonical, signaling pathway, β-catenin, environment, and heavy metals. Published articles on Wnt signaling pathways and heavy metals as contributing factors for causing diseases via influencing Wnt signaling pathways were included. Wnt canonical or noncanonical signaling pathways are the key regulators of stem cell homeostasis that control many mechanisms. There is an adequate balance between β-catenin dependent and independent Wnt signaling pathways and remain highly conserved throughout different development stages. Environmental heavy metal exposure may cause either inhibition or overexpression of any component of Wnt signaling pathways such as Wnt protein, transcription factors, receptors, ligands, or transducers to impede normal cellular function via negatively affecting Wnt signaling pathways. Environmental exposure to heavy metals potentially contributes to diseases via deregulated Wnt signaling pathways. 

KRAS-retroviral fusion transcripts and gene amplification in arsenic-transformed, human prostate CAsE-PE cancer cells

CAsE-PE cells are an arsenic-transformed, human prostate epithelial line containing oncogenic mutations in KRAS compared to immortalized, normal KRAS parent cells, RWPE-1. We previously reported increased copy number of mutated KRAS in CAsE-PE cells, suggesting gene amplification. Here, KRAS flanking genomic and transcriptomic regions were sequenced in CAsE-PE cells for insight into KRAS amplification. Comparison of DNA-Seq and RNA-Seq showed increased reads from background aligning to all KRAS exons in CAsE-PE cells, while a uniform DNA-Seq read distribution occurred in RWPE-1 cells with normal transcript expression. We searched for KRAS fusions in DNA and RNA sequencing data finding a portion of reads aligning to KRAS and viral sequence. After generation of cDNA from total RNA, short and long KRAS probes were generated to hybridize cDNA and KRAS enriched fragments were PacBio sequenced. More KRAS reads were captured from CAsE-PE cDNA versus RWPE-1 by each probe set. Only CAsE-PE cDNA showed KRAS viral fusion transcripts, primarily mapping to LTR and endogenous retrovirus sequences on either 5'- or 3'-ends of KRAS. Most KRAS viral fusion transcripts contained 4 to 6 exons but some PacBio sequences were in unusual orientations, suggesting viral insertions within the gene body. Additionally, conditioned media was extracted for potential retroviral particles. RNA-Seq of culture media isolates identified KRAS retroviral fusion transcripts in CAsE-PE media only. Truncated KRAS transcripts suggested multiple retroviral integration sites occurred within the KRAS gene producing KRAS retroviral fusions of various lengths. Findings suggest activation of endogenous retroviruses in arsenic carcinogenesis should be explored.

Environmental exposures, stem cells, and cancer

An estimated 70-90% of all cancers are linked to exposure to environmental risk factors. In parallel, the number of stem cells in a tissue has been shown to be a strong predictor of risk of developing cancer in that tissue. Tumors themselves are characterized by an acquisition of "stem cell" characteristics, and a growing body of evidence points to tumors themselves being sustained and propagated by a stem cell-like population. Here, we review our understanding of the interplay between environmental exposures, stem cell biology, and cancer. We provide an overview of the role of stem cells in development, tissue homeostasis, and wound repair. We discuss the pathways and mechanisms governing stem cell plasticity and regulation of the stem cell state, and describe experimental methods for assessment of stem cells. We then review the current understanding of how environmental exposures impact stem cell function relevant to carcinogenesis and cancer prevention, with a focus on environmental and occupational exposures to chemical, physical, and biological hazards. We also highlight key areas for future research in this area, including defining whether the biological basis for cancer disparities is related to effects of complex exposure mixtures on stem cell biology.

Biological and molecular modifications induced by cadmium and arsenic during breast and prostate cancer development

Breast and prostate cancer are two of the most common malignancies worldwide. Both cancers can develop into hormone -dependent or -independent subtypes and are associated to environmental exposure in the context of an inherited predisposition. As and Cd have been linked to the onset of both cancers, with the exception of As, which lacks a definitive association with breast carcinogenesis. The two elements exert an opposite effect dependent on acute versus chronic exposure. High doses of As or Cd were shown to induce cell death in acute experimental exposure, while chronic exposure triggers cell proliferation and viability, which is no longer limited by telomere shortening and apoptosis. The chronically exposed cells also increase their invasion capacity and tumorigenic potential. At molecular level, malignant transformation is evidenced mainly by up-regulation of BCL-2, MMP-2, MMP-9, VIM, Snail, Twist, MT, MLH and down-regulation of Casp-3, PTEN, E-CAD, and BAX. The signaling pathways most commonly activated are KRAS, p53, TGF-β, TNF-α, WNT, NRF2 and AKT. This knowledge could potentially raise public awareness over the health risks faced by the human population living or working in a polluted environment and smokers. Human exposure to As and Cd should be minimize as much as possible. Healthcare policies targeting people belonging to these risk categories should include analysis of: DNA damage, oxidative stress, molecular alterations, and systemic level of heavy metals and of essential minerals. In this review, we present the literature regarding cellular and molecular alterations caused by exposure to As or Cd, focusing on the malignant transformation of normal epithelial cells after long-term intoxication with these two carcinogens.

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.

Arsenic Alters Exosome Quantity and Cargo to Mediate Stem Cell Recruitment Into a Cancer Stem Cell-Like Phenotype

Inorganic arsenic is a human carcinogen that can target the prostate. Accumulating evidence suggests arsenic can disrupt stem cell (SC) dynamics during the carcinogenic process. Previous work demonstrated arsenic-transformed prostate epithelial (CAsE-PE) cells can recruit prostate SCs into rapidly acquiring a cancer SC (CSC) phenotype via the secretion of soluble factors. Exosomes are small, membrane-derived vesicles that contain lipids, RNA, and proteins, and actively contribute to cancer initiation and progression when taken up by target cells. Here we hypothesized that CAsE-PE cells are recruiting SCs to a CSC-like phenotype via exosomal signaling. CAsE-PE cells secreted 700% more exosomes than parental RWPE-1 cells. CAsE-PE exosomes were enriched with oncogenic factors, including oncogenes (KRAS, NRAS, VEFGA, MYB, and EGFR), inflammation-related (cyclooxygenase-2, interleukin 1B (IL1B), IL6, transforming growth factor-β, and tumor necrosis factor-A), and apoptosis-related (CASP7, CASP9, and BCL2) transcripts, and oncogenesis-associated microRNAs. When compared with SCs cultured in exosome-depleted conditioned medium (CM), SCs cultured in CM containing CAsE-PE-derived exosomes showed increased (198%) matrix metalloproteinase activity and underwent an epithelial-to-mesenchymal transition in morphology, suggesting an exosome-mediated transformation. KRAS plays an important role in arsenic carcinogenesis. Although KRAS transcript (>24 000%) and protein (866%) levels were elevated in CAsE-PE exosomes, knock-down of KRAS in these cells only partially mitigated the CSC-like phenotype in cocultured SCs. Collectively, these results suggest arsenic impacts both exosomal quantity and cargo. Exosomal KRAS is only minimally involved in this recruitment, and additional factors (eg, cancer-associated miRNAs) likely also play a role. This work furthers our mechanistic understanding of how arsenic disrupts SC dynamics and influences the tumor microenvironment during carcinogenesis.

Preprocessing Tools Applied to Improve the Assessment of Aldrin Effects on Prostate Cancer Cells Using Raman Spectroscopy

The study of pollutant effects on living organisms provides information about the possible biological and environmental response to a contaminant. Progression of prostate cancer may be related to exposure to pesticides or other chemical substances. In this work, the effect of the pesticide aldrin on human prostate cancer cells (DU145) is studied using Raman spectroscopy and chemometric techniques. Prostate cancer cell line DU145 has been exposed acutely the pesticide aldrin. Individual Raman spectra coming from control and treated cell populations have been acquired. Partial least squares discriminant analysis (PLSDA) has been used to assess differences among treated and control samples and to identify spectral biomarkers associated with pollutant stress. Some preprocessing methodologies have been tested in order to improve the capability of discrimination between fingerprints. Partial least squares discriminant analysis results suggest that the best normalization-scaling preprocessing combination is provided by Euclidean normalization (EN)-SIMPLISMA-based scaling (SBS). SIMPLISMA-based scaling has been proposed as a scaling method focused on the classification objective, which enhances variables with high relative variation among samples. The most relevant spectral variables related to aldrin effect on DU145 seem to be mainly related to lipids, proteins, and variations in nucleic acids.

Recent views of heavy metals as possible risk factors and potential preventive and therapeutic agents in prostate cancer

Prostate cancer is the most common cancer in men in many industrialized countries. A role for androgens in prostate tumor progression is well recognized, while estrogens may cooperate with androgens in prostate carcinogenesis. The incidence of prostate cancer is highly variable in the different countries, suggesting an important role of environmental factors. Heavy metals are common environmental contaminants and some of them are confirmed or suspected human carcinogens. Some metals are endowed with estrogenic and/or androgenic activities and may play a role as cancer risk factors through this mechanism. Moreover, prostate cancer may present alterations in the intracellular balance of trace metals, such as zinc and copper, which are involved in several regulatory proteins. Herein, we review the possible role of environmental heavy metals and of metal-dyshomeostasis in prostate cancer development and promotion as well as the potential use of some metals in the prevention and therapy of prostate cancer.

Silencing KRAS Overexpression in Cadmium-Transformed Prostate Epithelial Cells Mitigates Malignant Phenotype

Cadmium (Cd) is a potential human prostate carcinogen. Chronic Cd exposure malignantly transforms RWPE-1 human prostate epithelial cells into CTPE cells by an unclear mechanism. Previous studies show that RWPE-1 can also be malignantly transformed by arsenic, and KRAS activation is key to causation and maintenance of this phenotype. Although Cd and arsenic can both transform prostate epithelial cells, it is uncertain whether their mechanisms are similar. Thus, here we determined whether KRAS activation is critical in causing and maintaining Cd-induced malignant transformation in CTPE cells. Expression of KRAS, miRNAs, and other genes of interest was analyzed by Western blot and RT-PCR. Following stable KRAS knockdown (KD) by RNA interference using shRNAmir, the malignant phenotype was assessed by various physical and genetic parameters. CTPE cells greatly overexpressed KRAS by 20-fold, indicating a likely role in Cd transformation. Thus, we attempted to reverse the malignant phenotype via KRAS KD. Two weeks after shRNAmir transduction, KRAS protein was undetectable in CTPE KD cells, confirming stable KD. KRAS KD reduced stimulated RAS/ERK and PI3K/AKT signaling pathways and markedly mitigated multiple physical and molecular malignant cell characteristics including: hypersecretion of MMP-2, colony formation, cell survival, and expression of cancer-relevant genes (reduced proliferation and cell cycle-related genes; activated tumor suppressor PTEN). However, KRAS KD did not reverse miRNA expression originally down-regulated by Cd transformation. These data strongly suggest KRAS is a key gene in development and maintenance of the Cd-induced malignant phenotype, at least in the prostate. It is not, however, the only genetic factor sustaining this phenotype.

EDC-2: The Endocrine Society's Second Scientific Statement on Endocrine-Disrupting Chemicals

The Endocrine Society's first Scientific Statement in 2009 provided a wake-up call to the scientific community about how environmental endocrine-disrupting chemicals (EDCs) affect health and disease. Five years later, a substantially larger body of literature has solidified our understanding of plausible mechanisms underlying EDC actions and how exposures in animals and humans-especially during development-may lay the foundations for disease later in life. At this point in history, we have much stronger knowledge about how EDCs alter gene-environment interactions via physiological, cellular, molecular, and epigenetic changes, thereby producing effects in exposed individuals as well as their descendants. Causal links between exposure and manifestation of disease are substantiated by experimental animal models and are consistent with correlative epidemiological data in humans. There are several caveats because differences in how experimental animal work is conducted can lead to difficulties in drawing broad conclusions, and we must continue to be cautious about inferring causality in humans. In this second Scientific Statement, we reviewed the literature on a subset of topics for which the translational evidence is strongest: 1) obesity and diabetes; 2) female reproduction; 3) male reproduction; 4) hormone-sensitive cancers in females; 5) prostate; 6) thyroid; and 7) neurodevelopment and neuroendocrine systems. Our inclusion criteria for studies were those conducted predominantly in the past 5 years deemed to be of high quality based on appropriate negative and positive control groups or populations, adequate sample size and experimental design, and mammalian animal studies with exposure levels in a range that was relevant to humans. We also focused on studies using the developmental origins of health and disease model. No report was excluded based on a positive or negative effect of the EDC exposure. The bulk of the results across the board strengthen the evidence for endocrine health-related actions of EDCs. Based on this much more complete understanding of the endocrine principles by which EDCs act, including nonmonotonic dose-responses, low-dose effects, and developmental vulnerability, these findings can be much better translated to human health. Armed with this information, researchers, physicians, and other healthcare providers can guide regulators and policymakers as they make responsible decisions.

Inorganic Arsenic-induced cellular transformation is coupled with genome wide changes in chromatin structure, transcriptome and splicing patterns

Background

Arsenic (As) exposure is a significant worldwide environmental health concern. Low dose, chronic arsenic exposure has been associated with a higher than normal risk of skin, lung, and bladder cancer, as well as cardiovascular disease and diabetes. While arsenic-induced biological changes play a role in disease pathology, little is known about the dynamic cellular changes resulting from arsenic exposure and withdrawal.

Results

In these studies, we sought to understand the molecular mechanisms behind the biological changes induced by arsenic exposure. A comprehensive global approach was employed to determine genome-wide changes to chromatin structure, transcriptome patterns and splicing patterns in response to chronic low dose arsenic and its subsequent withdrawal. Our results show that cells exposed to chronic low doses of sodium arsenite have distinct temporal and coordinated chromatin, gene expression, and miRNA changes consistent with differentiation and activation of multiple biochemical pathways. Most of these temporal patterns in gene expression are reversed when arsenic is withdrawn. However, some gene expression patterns remained altered, plausibly as a result of an adaptive response by cells. Additionally, the correlation of changes to gene expression and chromatin structure solidify the role of chromatin structure in gene regulatory changes due to arsenite exposure. Lastly, we show that arsenite exposure influences gene regulation both at the initiation of transcription as well as at the level of splicing.

Conclusions

Our results show that adaptation of cells to iAs-mediated EMT is coupled to changes in chromatin structure effecting differential transcriptional and splicing patterns of genes. These studies provide new insights into the mechanism of iAs-mediated pathology, which includes epigenetic chromatin changes coupled with changes to the transcriptome and splicing patterns of key genes.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-015-1295-9) contains supplementary material, which is available to authorized users.