Overexpression of hsa-miR-186 induces chromosomal instability in arsenic-exposed human keratinocytes

The role of exosome-shuttled miRNAs in heavy metal-induced peripheral tissues and neuroinflammation in Alzheimer's disease

Heavy metal-induced neuroinflammation is a significant pathophysiologic mechanism in Alzheimer's disease (AD). Microglia-mediated neuroinflammation plays a crucial role in the pathogenesis of AD. Multiple miRNAs are differentially expressed in peripheral tissues after heavy metal exposure, and increasing evidence suggests that they are involved in AD progression by regulating microglial homeostasis. Exosomes, which are capable of loading miRNAs and crossing the bloodbrain barrier, serve as mediators of communication between peripheral tissues and the brain. In this review, we summarize the current evidence on the link between miRNAs in peripheral tissues and neuroinflammation in AD after heavy metal exposure and propose a role for miRNAs in the microglial neurodegenerative phenotype (MGnD) of AD. This study will help to elucidate the link between peripheral tissue damage and MGnD-mediated neuroinflammation in AD after heavy metal exposure. Additionally, we summarize the regulatory effects of natural compounds on peripheral tissue-derived miRNAs, which could be potential therapeutic targets for natural compounds to regulate peripheral tissue-derived exosomal miRNAs to ameliorate heavy metal-induced MGnD-mediated neuroinflammation in patients with AD after heavy metal exposure.

Association between miR-202, miR-211, and miR-1238 gene polymorphisms and risk of vitiligo

Vitiligo, as a common pigment defect in the skin, hair, and mucous membranes, results from the destruction of melanocytes. Recent investigations have shown that miRNA dysregulation contributes in the pathogenesis of vitiligo. Therefore, in this research, our aim is to explore the relationship between miR-202 rs12355840, miR-211 rs8039189, and miR-1238 rs12973308 polymorphisms and susceptibility to vitiligo. A total number of 136 vitiligo patients and 129 healthy individuals as a control group were included in this research. The salting out approach was implemented to extraction genomic DNA. The genetic polymorphisms of miR-202 rs12355840, miR-211 rs8039189, and miR-1238 rs12973308 were determined using PCR-RFLP approach. The findings revealed that miR-202 rs12355840 polymorphism under codominant (CT and TT genotypes), dominant, recessive, overdominant, and also allelic models is correlated with increased risk of vitiligo. In addition, codominant, dominant, overdominant, as well as allelic models of miR-211 rs8039189 polymorphism decrease risk of vitiligo. No significant relationship was observed between the miR-1238 rs12973308 polymorphism and susceptibility to vitiligo. The miR-211 rs8039189 polymorphism may serve a protective effect on vitiligo development and miR-202 rs12355840 polymorphism may act as a risk factor for vitiligo susceptibility.

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

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

Clonal variability in chromosomal instability as a potential driver in the acquisition of tumorigenic phenotype in chronic arsenic-exposed and hsa-miR-186 overexpressing human keratinocytes

Chronic arsenic exposure through drinking water is a global health issue, affecting >200 million people. Arsenic is a group I human carcinogen and causes chromosomal instability (CIN). Arsenic exposure is the second most common cause of skin cancer after UV radiation. hsa-miR-186 is overexpressed in arsenic-induced squamous cell carcinoma relative to premalignant hyperkeratosis. Among predicted targets of hsa-miR-186 are cell cycle regulators including regulators of mitotic progression. Disruption of mitotic progression can contribute to CIN. Thus, we hypothesized that hsa-miR-186 overexpression contributes to malignant transformation of arsenic exposed HaCaT cells by induction of CIN. Stable clones of HaCaT cells transfected with pEP-hsa-miR-186 expression vector or empty vector were maintained under puromycin selection and exposed to 0 or 100 nM NaAsO2 and cultured for 29 weeks. HaCaT clones overexpressing hsa-miR-186 and exposed to NaAsO2 showed increased CIN and anchorage independent growth at 29 weeks in a stochastic manner, in contrast to unexposed empty vector transfected clones. These results suggest that clonal variability mediates arsenic-induced carcinogenesis in hsa-miR-186 overexpressing human keratinocytes.

The Role of microRNAs in Arsenic-Induced Human Diseases: A Review

MicroRNAs (miRNAs) are noncoding RNAs with 20-22 nucleotides, which are encoded by endogenous genes and are capable of targeting the majority of human mRNAs. Arsenic is regarded as a human carcinogen, which can lead to many adverse health effects including diabetes, skin lesions, kidney disease, neurological impairment, male reproductive injury, and cardiovascular disease (CVD) such as cardiac arrhythmias, ischemic heart failure, and endothelial dysfunction. miRNAs can act as tumor suppressors and oncogenes via directly targeting oncogenes or tumor suppressors. Recently, miRNA dysregulation was considered to be an important mechanism of arsenic-induced human diseases and a potential biomarker to predict the diseases caused by arsenic exposure. Endogenic miRNAs such as miR-21, the miR-200 family, miR-155, and the let-7 family are involved in arsenic-induced human disease by inducing translational repression or RNA degradation and influencing multiple pathways, including mTOR/Arg 1, HIF-1α/VEGF, AKT, c-Myc, MAPK, Wnt, and PI3K pathways. Additionally, exogenous miRNAs derived from plants, such as miR-34a, miR-159, miR-2911, miR-159a, miR-156c, miR-168, etc., among others, can be transported from blood to specific tissue/organ systems in vivo. These exogenous miRNAs might be critical players in the treatment of human diseases by regulating host gene expression. This review summarizes the regulatory mechanisms of miRNAs in arsenic-induced human diseases, including cancers, CVD, and other human diseases. These special miRNAs could serve as potential biomarkers in the management and treatment of human diseases linked to arsenic exposure. Finally, the protective action of exogenous miRNAs, including antitumor, anti-inflammatory, anti-CVD, antioxidant stress, and antivirus are described.

Mechanisms of genotoxicity and proteotoxicity induced by the metalloids arsenic and antimony

Arsenic and antimony are metalloids with profound effects on biological systems and human health. Both elements are toxic to cells and organisms, and exposure is associated with several pathological conditions including cancer and neurodegenerative disorders. At the same time, arsenic- and antimony-containing compounds are used in the treatment of multiple diseases. Although these metalloids can both cause and cure disease, their modes of molecular action are incompletely understood. The past decades have seen major advances in our understanding of arsenic and antimony toxicity, emphasizing genotoxicity and proteotoxicity as key contributors to pathogenesis. In this review, we highlight mechanisms by which arsenic and antimony cause toxicity, focusing on their genotoxic and proteotoxic effects. The mechanisms used by cells to maintain proteostasis during metalloid exposure are also described. Furthermore, we address how metalloid-induced proteotoxicity may promote neurodegenerative disease and how genotoxicity and proteotoxicity may be interrelated and together contribute to proteinopathies. A deeper understanding of cellular toxicity and response mechanisms and their links to pathogenesis may promote the development of strategies for both disease prevention and treatment.

miR-186 induces tetraploidy in arsenic exposed human keratinocytes

Chronic inorganic arsenic (iAs) exposure in drinking water is a global issue affecting >225 million people. Skin is a major target organ for iAs. miRNA dysregulation and chromosomal instability (CIN) are proposed mechanisms of iAs-induced carcinogenesis. CIN is a cancer hallmark and tetraploid cells can better tolerate increase in chromosome number and aberration, contributing to the evolution of CIN. miR-186 is overexpressed in iAs-induced squamous cell carcinoma relative to iAs-induced hyperkeratosis. Bioinformatic analysis indicated that miR-186 targets mRNAs of important cell cycle regulators including mitotic checkpoint serine/threonine kinase B (BUB1) and cell division cycle 27 (CDC27). We hypothesized that miR-186 overexpression contributes to iAs-induced transformation of keratinocytes by targeting mitotic regulators leading to induction of CIN. Ker-CT cells, a near diploid human keratinocyte cell line, were transduced with miR-186 overexpressing or scrambled control lentivirus. Stable clones were isolated after puromycin selection. Clones transduced with lentivirus expressing either a scrambled control miRNA or miR-186 were maintained with 0 or 100 nM iAs for 4 weeks. Unexposed scrambled control clones were considered as passage matched controls. Chronic iAs exposure increased miR-186 expression in miR-186 clones. miR-186 overexpression significantly reduced CDC27 levels irrespective of iAs exposure. The percentage of tetraploid or aneuploid cells was increased in iAs exposed miR-186 clones. Aneuploidy can arise from a tetraploid intermediate. Suppression of CDC27 by miR-186 may lead to impairment of mitotic checkpoint complex formation and its ability to maintain cell cycle arrest leading to chromosome misalignment. As a result, cells overexpressing miR-186 and chronically exposed to iAs may have incorrect chromosome segregation and CIN. These data suggest that dysregulation of miRNA by iAs mediates tetraploidy, aneuploidy and chromosomal instability contributing to iAs-induced carcinogenesis.

The Role of Non-Coding RNAs in Chromosomal Instability in Cancer

Chromosomal instability (CIN) is characterized by an increased frequency of changes in chromosome structure or number and is regarded as a hallmark of cancer. CIN plays a prevalent role in tumorigenesis and cancer progression by assisting the cancer cells' phenotypic adaptation to stress, which have been tightly linked to therapy resistance and metastasis. Both CIN-inducing and CIN-repressing agents are being clinically tested for the treatment of cancer to increase CIN levels to unsustainable levels leading to cell death or to decrease CIN levels to limit the development of drug resistance, respectively. Non-coding RNAs (ncRNAs) including microRNAs and long ncRNAs (lncRNAs) have been fundamentally implicated in CIN. The miR-22, miR-26a, miR-28, and miR-186 target important checkpoint proteins involved in mediating chromosomal stability and their expression modulation has been directly related to CIN occurrence. lncRNAs derived from telomeric, centrosomal, and enhancer regions play an important role in mediating genome stability, while specific lncRNA transcripts including genomic instability inducing RNA called Ginir, P53-responsive lncRNA termed as GUARDIN, colon cancer-associated transcript 2, PCAT2, and ncRNA activated by DNA damage called NORAD have been shown to act within CIN-associated pathways. In this review, we discuss how these ncRNAs either maintain or disrupt the stability of chromosomes and how these mechanisms could be exploited for novel therapeutic approaches targeting CIN in cancer patients. SIGNIFICANCE STATEMENT: Chromosomal instability increases tumor heterogeneity and thereby assists the phenotypic adaptation of cancer cells, causing therapy resistance and metastasis. Several microRNAs and long non-coding RNAs that have been causally linked to chromosomal instability could represent novel therapeutic targets. Understanding the role of non-coding RNAs in regulating different genes involved in driving chromosomal instability will give insights into how non-coding RNAs can be utilized toward modifying chemotherapeutic regimens in different cancers.

CircP50 functions through the phosphorylation- and acetylation-activated p53 pathway to mediate inorganic arsenic-induced apoptosis in A549 cells

As a class I carcinogen, arsenic has been reported to cause diseases accompanied by circRNAs regulating proliferation and apoptosis at the molecular level, but whether circP50 (circBase ID: hsa_circ_0008012) does the same has not been demonstrated. The aim of this study is to provide the basis for anti-lung cancer mechanism research, by studying the expression of circP50 under arsenic-induced conditions, and the effect and mechanism on the proliferation and apoptosis of A549 cells based on the circP50 knockdown models. To explore whether the circP50 is responsive to arsenic exposure, the qRT-PCR was applied to discover that the relative expression of circP50 in A549 cells increased only with increasing NaAsO₂ dose and independent of its metabolites. We further determined the mechanism of circP50 by establishing circP50 knockdown models. The results of cell viability and EdU assays indicated the proliferation of A549 cells. According to the western blotting, phosphorylation of p53 at Ser15, Ser376, and Ser392 and acetylation of p53 at Lys370 and Lys382 were inhibited, resulting in the deficiency of p53 expression. Subsequently, the expression of genes downstream of p53 was reduced, including p21, PUMA, Caspase3, and Bcl-xS. Furthermore, the expressions of IKB-α, p65, and p50 decreased, but C-myc expression did not change significantly, referring to the NF-κB pathway was not dominant. The results suggest that circP50 mainly functions through the p53 pathway to mediate apoptosis in response to arsenic exposure.

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.

Implication of microRNAs in Carcinogenesis with Emphasis on Hematological Malignancies and Clinical Translation

MicroRNAs (miRNAs) are evolutionarily conserved small non-coding RNAs, that are involved in the multistep process of carcinogenesis, contributing to all established hallmarks of cancer. In this review, implications of miRNAs in hematological malignancies and their clinical utilization fields are discussed. As components of the complex regulatory network of gene expression, influenced by the tissue microenvironment and epigenetic modifiers, miRNAs are “micromanagers” of all physiological processes including the regulation of hematopoiesis and metabolic pathways. Dysregulated miRNA expression levels contribute to both the initiation and progression of acute leukemias, the metabolic reprogramming of malignantly transformed hematopoietic precursors, and to the development of chemoresistance. Since they are highly stable and can be easily quantified in body fluids and tissue specimens, miRNAs are promising biomarkers for the early detection of hematological malignancies. Besides novel opportunities for differential diagnosis, miRNAs can contribute to advanced chemoresistance prediction and prognostic stratification of acute leukemias. Synthetic oligonucleotides and delivery vehicles aim the therapeutic modulation of miRNA expression levels. However, major challenges such as efficient delivery to specific locations, differences of miRNA expression patterns between pediatric and adult hematological malignancies, and potential side effects of miRNA-based therapies should be considered.

Roles of miRNA dysregulation in the pathogenesis of multiple myeloma

Multiple myeloma (MM) is a malignant disease of plasma cells with complex pathology, causing significant morbidity due to its end-organ destruction. The outcomes of patients with myeloma have significantly improved in the past couple of decades with the introduction of novel agents, such as proteasome inhibitors, immunomodulators, and monoclonal antibodies. However, MM remains incurable and presents considerable individual heterogeneity. MicroRNAs (miRNAs) are short, endogenous noncoding RNAs of 19-22 nucleotides that regulate gene expression at the posttranscriptional level. Numerous studies have shown that miRNA deregulation is closely related to MM pathology, including tumor initiation, progression, metastasis, prognosis, and drug response, which make the complicated miRNA network an attractive and marvelous area of investigation for novel anti-MM therapeutic approaches. Herein, we mainly summarized the current knowledge on the roles of miRNAs, which are of great significance in regulating pathological factors involved in MM progressions, such as bone marrow microenvironment, methylation, immune regulation, genomic instability, and drug resistance. Meanwhile, their potential as novel prognostic biomarkers and therapeutic targets was also discussed.

miRNA dysregulation is an emerging modulator of genomic instability

Genomic instability consists of a range of genetic alterations within the genome that contributes to tumor heterogeneity and drug resistance. It is a well-established characteristic of most cancer cells. Genome instability induction results from defects in DNA damage surveillance mechanisms, mitotic checkpoints and DNA repair machinery. Accumulation of genetic alterations ultimately sets cells towards malignant transformation. Recent studies suggest that miRNAs are key players in mediating genome instability. miRNAs are a class of small RNAs expressed in most somatic tissues and are part of the epigenome. Importantly, in many cancers, miRNA expression is dysregulated. Consequently, this review examines the role of miRNA dysregulation as a causal step for induction of genome instability and subsequent carcinogenesis. We focus specifically on mechanistic studies assessing miRNA(s) and specific subtypes of genome instability or known modes of genome instability. In addition, we provide insight on the existing knowledge gaps within the field and possible ways to address them.

Dysregulation of microRNAs in metal-induced angiogenesis and carcinogenesis

MicroRNAs (miRNAs) are small endogenous non-coding RNAs that regulate cancer initiation, development, angiogenesis, and therapeutic resistance. Metal exposure widely occurs through air, water, soil, food, and industrial contaminants. Hundreds of millions of people may have metal exposure associated with toxicity, serious health problems, and cancer occurrence. Metal exposure is found to induce oxidative stress, DNA damage and repair, and activation of multiple signaling pathways. However, molecular mechanisms of metal-induced carcinogenesis remain to be elucidated. Recent studies demonstrated that the exposure of metals such as arsenic, hexavalent chromium, cadmium, and nickel caused dysregulation of microRNAs that are implicated to play an important role in cell transformation, tumor growth and angiogenesis. This review focuses on the recent studies that show metal-induced miRNA dysregulation and underlined mechanisms in cell malignant transformation, angiogenesis and tumor growth.

Arsenic-Induced Carcinogenesis and Immune Dysregulation

Arsenic, a metal ubiquitously distributed in the environment, remains an important global health threat. Drinking arsenic-contaminated water is the major route of human exposure. Exposure to arsenic contributes to several malignancies, in the integumentary, respiratory, hepatobiliary, and urinary systems. Cutaneous lesions are important manifestations after long-term arsenic exposure. Arsenical skin cancers usually herald the development of other internal cancers, making the arsenic-induced skin carcinogenesis a good model to investigate the progression of chemical carcinogenesis. In fact, only a portion of arsenic-exposed humans eventually develop malignancies, likely attributed to the arsenic-impaired immunity in susceptible individuals. Currently, the exact pathophysiology of arsenic-induced carcinogenesis remains elusive, although increased reactive oxidative species, aberrant immune regulations, and chromosome abnormalities with uncontrolled cell growth might be involved. This review discusses how arsenic induces carcinogenesis, and how the dysregulated innate and adaptive immunities in systemic circulation and in the target organs contribute to arsenic carcinogenesis. These findings offer evidence for illustrating the mechanism of arsenic-related immune dysregulation in the progression of carcinogenesis, and this may help explain the nature of multiple and recurrent clinical lesions in arsenic-induced skin cancers.