Effect of Ultraviolet Radiation and Benzo[a]pyrene Co-Exposure on Skin Biology: Autophagy as a Potential Target

The skin is the outermost protective barrier of the human body. Its role is to protect against different physical, chemical, biological and environmental stressors. The vast majority of studies have focused on investigating the effects of single environmental stressors on skin homeostasis and the induction of several skin disorders, such as cancer or ageing. On the other hand, much fewer studies have explored the consequences of the co-exposure of skin cells to two or more stressors simultaneously, which is much more realistic. In the present study, we investigated, using mass-spectrometry-based proteomic analysis, the dysregulated biological functions in skin explants after their co-exposure to ultraviolet radiation (UV) and benzo[a]pyrene (BaP). We observed that several biological processes were dysregulated, among which autophagy appeared to be significantly downregulated. Furthermore, immunohistochemistry analysis was carried out to validate the downregulation of the autophagy process further. Altogether, the output of this study provides an insight into the biological responses of skin to combined exposure to UV + BaP and highlights autophagy as a potential target that might be considered in the future as a novel candidate for pharmacological intervention under such stress conditions.

METTL3 regulates PM2.5-induced cell injury by targeting OSGIN1 in human airway epithelial cells

N⁶-methyladenosine (m⁶A) is implicated in alteration of cellular biological processes caused by exogenous environmental factors. However, little is known about the role of m⁶A in airborne fine particulate matter (PM_2.5)-induced adverse effects. Thus, we investigated the role of m⁶A modification in PM_2.5-induced airway epithelial cell injury. We observed a methyltransferase-like 3 (METTL3)-dependent induction of m⁶A modification after PM_2.5 treatment in HBE and A549 cells. METTL3 knockdown attenuated PM_2.5-induced apoptosis and arrest of cell cycle. mRNA sequencing and RNA N⁶-methyladenosine binding protein immunoprecipitation (Me-RIP) assay identified m⁶A-modified oxidative stress induced growth inhibitor 1 (OSGIN1) as the target gene of METTL3. Knockdown of METTL3 resulted a shorter mRNA half-life of OSGIN1 by catalyzing its m⁶A modification. Knockdown of METTL3 or OSGIN1 attenuated cell apoptosis, arrest of cell cycle and autophagy induced by PM_2.5. In conclusion, METTL3 may mediate PM_2.5-induced cell injury by targeting OSGIN1 in human airway epithelial cells. Our work uncovered a critical role of METTL3 in PM_2.5-induced airway epithelial cell injury and provided insight into the vital role of m⁶A modification in PM_2.5-induced human hazards.

Pinocembrin attenuates benzo(a)pyrene-induced CYP1A1 expression through multiple pathways: An in vitro and in vivo study

Benzo(a)pyrene [B(a)P], which is a carcinogen, is a substance most typically known in cigarette smoke and considered as an important intermediary of lung cancer. The enzyme CYP1A1 is crucial for the metabolic conversion of B(a)P into the intermediates that induce carcinogenesis. Stimulation of the aryl hydrocarbon receptor, which is regulated by B(a)P, is thought to induce numerous signaling cascades. Interruption in the mitogen-activated protein kinase (MAPK) pathway causes changes in cellular processes and may alter the AhR pathway. The aim of this investigation is to examine the potential ability of a flavonoid pinocembrin (PCB) to alleviate B(a)P toxicity and analyze the underlying molecular mechanisms. We found that PCB inhibited DNA adduct formation by attenuating CYP1A1 expression through the suppression of the AhR/Src/ERK pathways. PCB mitigated the B(a)P-stimulated DNA damage, inhibited Src and ERK1/2 expression, decreased CYP1A1 expression, and reduced the B(a)P-induced stimulation of NF-κB and MAPK signaling in lung epithelial cells. Finally, the activity of CYP1A1 and Src in lung tissues from mice supplemented with PCB was noticeably decreased and lower than that in lung tissues from mice supplemented with B(a)P alone. Collectively, these data suggest that PCB may alleviate the toxic effects of PAHs, which are important environmental pollutants.

Environmental epitranscriptomics

Chemical modifications of RNA molecules have gained increasing attention since evidence emerged for their substantive roles in a range of biological processes, such as the stability and translation of mRNA transcripts. More than 150 modifications have been identified in different organisms to date, collectively known as the 'epitranscriptome', with 6-methyladenosine (m⁶A), 5-methylcytidine (m⁵C), pseudouridine and N1-methyladenosine (m¹A) the most extensively investigated. Although we are just beginning to elucidate the roles of these modifications in cellular functions, there is already evidence for their dysregulation in diseases such as cancer and neurodevelopmental disorders. There is currently more limited knowledge regarding how environmental exposures affect the epitranscriptome and how this may mediate disease risk, but evidence is beginning to emerge. Here, we review the current evidence for the impact of environmental exposures such as benzo[a]pyrene, bisphenol A, pesticides, metals and nanoparticles upon RNA modifications and the expression of their 'writers' (methyl transferases), 'erasers' (demethylases) and 'readers'. We discuss future directions of the field and identify areas of particular promise and consider the technical challenges that are faced.

Association of Arsenic Exposure with Whole Blood DNA Methylation: An Epigenome-Wide Study of Bangladeshi Adults

BACKGROUND

Arsenic exposure affects [Formula: see text] people worldwide, including [Formula: see text] in Bangladesh. Arsenic exposure increases the risk of cancer and other chronic diseases, and one potential mechanism of arsenic toxicity is epigenetic dysregulation.

OBJECTIVE

We assessed associations between arsenic exposure and genome-wide DNA methylation measured at baseline among 396 Bangladeshi adults participating in the Health Effects of Arsenic Longitudinal Study (HEALS) who were exposed by drinking naturally contaminated well water.

METHODS

Methylation in whole blood DNA was measured at [Formula: see text] using the Illumina InfiniumMethylationEPIC (EPIC) array. To assess associations between arsenic exposure and CpG methylation, we used linear regression models adjusted for covariates and surrogate variables (SVs) (capturing unknown technical and biologic factors). We attempted replication and conducted a meta-analysis using an independent dataset of [Formula: see text] from 400 Bangladeshi individuals with arsenical skin lesions.

RESULTS

We identified 34 CpGs associated with [Formula: see text] creatinine-adjusted urinary arsenic [[Formula: see text]]. Sixteen of these CpGs annotated to the [Formula: see text] array, and 10 associations were replicated ([Formula: see text]). The top two CpGs annotated upstream of the ABR gene (cg01912040, cg10003262 ). All urinary arsenic-associated CpGs were also associated with arsenic concentration measured in drinking water ([Formula: see text]). Meta-analysis ([Formula: see text] samples) identified 221 urinary arsenic-associated CpGs ([Formula: see text]). The arsenic-associated CpGs from the meta-analysis were enriched in non-CpG islands and shores ([Formula: see text]) and depleted in promoter regions ([Formula: see text]). Among the arsenic-associated CpGs ([Formula: see text]), we observed significant enrichment of genes annotating to the reactive oxygen species pathway, inflammatory response, and tumor necrosis factor [Formula: see text] ([Formula: see text]) signaling via nuclear factor kappa-B ([Formula: see text]) hallmarks ([Formula: see text]).

CONCLUSIONS

The novel and replicable associations between arsenic exposure and DNA methylation at specific CpGs observed in this work suggest that epigenetic alterations should be further investigated as potential mediators in arsenic toxicity and as biomarkers of exposure and effect in exposed populations. https://doi.org/10.1289/EHP3849.

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

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

Genome-Wide Functional and Stress Response Profiling Reveals Toxic Mechanism and Genes Required for Tolerance to Benzo[a]pyrene in S. cerevisiae

Benzo[a]pyrene (BaP) is a ubiquitous, potent, and complete carcinogen resulting from incomplete organic combustion. BaP can form DNA adducts but other mechanisms may play a role in toxicity. We used a functional toxicology approach in S. cerevisiae to assess the genetic requirements for cellular resistance to BaP. In addition, we examined translational activities of key genes involved in various stress response pathways. We identified multiple genes and processes involved in modulating BaP toxicity in yeast which support DNA damage as a primary mechanism of toxicity, but also identify other potential toxicity pathways. Gene ontology enrichment analysis indicated that DNA damage and repair as well as redox homeostasis and oxidative stress are key processes in cellular response to BaP suggesting a similar mode of action of BaP in yeast and mammals. Interestingly, toxicant export is also implicated as a potential novel modulator of cellular susceptibility. In particular, we identified several transporters with human orthologs (solute carrier family 22) which may play a role in mammalian systems.

Hepatic gene expression analysis of mice exposed to raw water from Meiliang Bay, Lake Taihu, China

Lake water is a micro-polluted water system, and characterization of its toxicity remains difficult. Microarray-based determination of altered gene expression might be an alterative approach. We chose raw water from Meiliang Bay, Lake Taihu, China as the target water. Male mice were exposed to the lake water for 90 days. Total hepatic RNA was applied to interrogate the Affymetrix Mouse Genome 430A 2.0 array. Gene ontology analysis, pathway analysis and gene network analysis were used to identify biological effects of differently expressed genes. The results showed that the expressions of 170 genes were altered. Nine biological processes and nine biological pathways were significantly perturbed (P ≤ 0.01), mainly linked to the regulation of cell processes, DNA repair, chromatin modification, oxidative reduction and carbohydrate metabolism. Important genes, such as Prkca, Pik3r1, Fgfr1 and Zbtb16, were identified by gene network analysis. This study provided excellent insights into early toxicological effects related to raw Lake Taihu water, and illustrated that the toxicogenomic approach might be a useful tool to evaluate potential environmental health effects of raw lake water.

Integration of gene chip and topological network techniques to screen a candidate biomarker gene (CBG) for predication of the source water carcinogenesis risks on mouse Mus musculus

Screening of a candidate biomarker gene (CBG) to predicate the carcinogenesis risks in the Yangtze River source of drinking water in Nanjing area (YZR-SDW-NJ) on mouse (Mus musculus) was conducted in this research. The effects of YZR-SDW-NJ on the genomic transcriptional expression levels were measured by the GeneChip(®) Mouse Genome and data treated by the GO database analysis. The 298 genes discovered as the differently expressed genes (DEGs) were down-regulated and their values were ≤-1.5-fold. Of the 298 DEGs, 25 were cancer-related genes selected as the seed genes to build a topological network map with Genes2Networks software, only 7 of them occurred at the constructed map. Smad2 gene was at the constructed map center and could be identified as a candidate biomarker gene (CBG) primarily which involves the genesis and development of colorectal, leukemia, lung and prostate cancers directly. Analysis of the gene signal pathway further approved that smad2 gene had the relationships closely to other 16 cancer-related genes and could be used as a CBG to indicate the carcinogenic risks in YZR-SDW-NJ. The data suggest that integration of gene chip and network techniques may be a way effectively to screen a CBG. And the parameter values for further judgment of the CBG through signal pathway relationship analysis also will be discussed.

Gene expression of normal human epidermal keratinocytes modulated by trivalent arsenicals

Chronic exposure to inorganic arsenic (iAs) is associated with the development of benign and malignant human skin lesions including nonmelanoma skin cancers. The precise arsenical form(s) responsible for this carcinogenic effect are unknown, although trivalent inorganic arsenic (iAs(III)) and two of its toxic metabolites, monomethylarsonous acid (MMA(III)) and methylarsinous acid (DMA(III)), are attractive candidates. In an effort to better understand and compare their toxic effects in the skin, we compared the global gene expression profiles of normal human epidermal keratinocytes (NHEKs) exposed to varying noncytotoxic/slightly cytotoxic concentrations of iAs(III), MMA(III), and DMA(III) for 24 h. Exposure to each arsenical treatment group exhibited a dose effect in the number of altered genes and the magnitude of expression change in NHEKs. The most significant gene expression changes associated with iAs(III) and MMA(III) exposure were consistent with several key events believed to be important to As-driven skin carcinogenesis, namely induction of oxidative stress, increased transcript levels of keratinocyte growth factors, and modulation of MAPK and NF-κB pathways. At both comparable arsenical concentrations and comparable NHEK toxicity, greater potential carcinogenic effects were observed in MMA(III)-exposed NHEKs than those exposed to iAs(III), including involvement of more proinflammatory signals and increased transcript levels of more growth factor genes. In contrast, none of these above-mentioned transcriptional trends were among the most significantly altered functions in the DMA(III) treatment group. This study suggests the relative capacity of each of the tested arsenicals to drive suspected key events in As-mediated skin carcinogenesis is MMA(III) > iAs(III) with little contribution from DMA(III).

Genomic expression profiles in liver of mice exposed to purified terephthalic acid manufacturing wastewater

DNA micorarray was used to analyze hepatic transcriptional profile of male mice (Mus musculus) after 35-d intragastric perfusion treatment with purified terephthalic acid (PTA) manufacturing wastewater. Haematological analysis demonstrated that the levels of glutamyl transferase and lactate dehydrogenase in serum were significantly decreased, and DNA microarray showed that a total of 306 genes were differentially expressed in PTA wastewater-treated mice. According to Kyoto encyclopedia of genes and genomes pathway database, the differentially expressed genes were mainly grouped to metabolic pathways (58 genes) and biological processes (101 genes). PTA wastewater had significant impacts upon metabolisms of lipid, carbohydrate, amino acid, vitamin and nucleotide. Several signal transduction pathways are most susceptible to PTA wastewater, including mitogen-activated protein kinases, Janus kinase/signal transducers and activators of transcription and calcium signaling pathways. Potential public health problems may arise from the discharge of PTA wastewater into the environment.

Genomics and proteomics approaches to the study of cancer-stroma interactions

Background

The development and progression of cancer depend on its genetic characteristics as well as on the interactions with its microenvironment. Understanding these interactions may contribute to diagnostic and prognostic evaluations and to the development of new cancer therapies. Aiming to investigate potential mechanisms by which the tumor microenvironment might contribute to a cancer phenotype, we evaluated soluble paracrine factors produced by stromal and neoplastic cells which may influence proliferation and gene and protein expression.

Methods

The study was carried out on the epithelial cancer cell line (Hep-2) and fibroblasts isolated from a primary oral cancer. We combined a conditioned-medium technique with subtraction hybridization approach, quantitative PCR and proteomics, in order to evaluate gene and protein expression influenced by soluble paracrine factors produced by stromal and neoplastic cells.

Results

We observed that conditioned medium from fibroblast cultures (FCM) inhibited proliferation and induced apoptosis in Hep-2 cells. In neoplastic cells, 41 genes and 5 proteins exhibited changes in expression levels in response to FCM and, in fibroblasts, 17 genes and 2 proteins showed down-regulation in response to conditioned medium from Hep-2 cells (HCM). Nine genes were selected and the expression results of 6 down-regulated genes (ARID4A, CALR, GNB2L1, RNF10, SQSTM1, USP9X) were validated by real time PCR.

Conclusions

A significant and common denominator in the results was the potential induction of signaling changes associated with immune or inflammatory response in the absence of a specific protein.

Oncofetal H19-derived miR-675 regulates tumor suppressor RB in human colorectal cancer

H19 is an imprinted oncofetal non-coding RNA recently shown to be the precursor of miR-675. The pathophysiological roles of H19 and its mature product miR-675 to carcinogenesis have, however, not been defined. By quantitative reverse transcription-polymerase chain reaction, both H19 and miR-675 were found to be upregulated in human colon cancer cell lines and primary human colorectal cancer (CRC) tissues compared with adjacent non-cancerous tissues. Subsequently, the tumor suppressor retinoblastoma (RB) was confirmed to be a direct target of miR-675 as the microRNA suppressed the activity of the luciferase reporter carrying the 3'-untranslated region of RB messenger RNA that contains the miR-675-binding site. Suppression of miR-675 by transfection with anti-miR-675 increased RB expression and at the same time, decreased cell growth and soft agar colony formation in human colon cancer cells. Reciprocally, enhanced miR-675 expression by transfection with miR-675 precursor decreased RB expression, increased tumor cell growth and soft agar colony formation. Moreover, the inverse relationship between the expressions of RB and H19/miR-675 was also revealed in human CRC tissues and colon cancer cell lines. Our findings demonstrate that H19-derived miR-675, through downregulation of its target RB, regulates the CRC development and thus may serve as a potential target for CRC therapy.

Comparative functional genomic analysis identifies distinct and overlapping sets of genes required for resistance to monomethylarsonous acid (MMAIII) and arsenite (AsIII) in yeast

Arsenic is a human toxin and carcinogen commonly found as a contaminant in drinking water. Arsenite (As(III)) is the most toxic inorganic form, but recent evidence indicates that the metabolite monomethylarsonous acid (MMA(III)) is even more toxic. We have used a chemical genomics approach to identify the genes that modulate the cellular toxicity of MMA(III) and As(III) in the yeast Saccharomyces cerevisiae. Functional profiling using homozygous deletion mutants provided evidence of the requirement of highly conserved biological processes in the response against both arsenicals including tubulin folding, DNA double-strand break repair, and chromatin modification. At the equitoxic doses of 150 microM MMA(III) and 300 microM As(III), genes related to glutathione metabolism were essential only for resistance to the former, suggesting a higher potency of MMA(III) to disrupt glutathione metabolism than As(III). Treatments with MMA(III) induced a significant increase in glutathione levels in the wild-type strain, which correlated to the requirement of genes from the sulfur and methionine metabolic pathways and was consistent with the induction of oxidative stress. Based on the relative sensitivity of deletion strains deficient in GSH metabolism and tubulin folding processes, oxidative stress appeared to be the primary mechanism of MMA(III) toxicity whereas secondary to tubulin disruption in the case of As(III). Many of the identified yeast genes have orthologs in humans that could potentially modulate arsenic toxicity in a similar manner as their yeast counterparts.

Chronic exposure to low concentration of arsenic is immunotoxic to fish: role of head kidney macrophages as biomarkers of arsenic toxicity to Clarias batrachus

The present study was aimed at elucidating the effect of chronic low-level arsenic exposure on the head kidney (HK) of Clarias batrachus and at determining the changes in head kidney macrophage (HKM) activity in response to arsenic exposure. Chronic exposure (30 days) to arsenic (As(2)O(3), 0.50 microM) led to significant increase in arsenic content in the HK accompanied by reduction in both HKM number and head kidney somatic index (HKSI). Arsenic induced HK hypertrophy, reduction in melano-macrophage population and increased hemosiderin accumulation. Transmission electron microscopy of 30 days exposed HKM revealed prominent endoplasmic reticulum, chromatin condensation and loss in structural integrity of nuclear membrane. Head kidney macrophages from exposed fish demonstrated significant levels of superoxide anions but on infection with Aeromonas hydrophila were unable to clear the intracellular bacteria and died. Exposure-challenge experiments with A. hydrophila revealed that chronic exposure to micromolar concentration of arsenic interfered with the phagocytic potential of HKM, helped in intracellular survival of the ingested bacteria inside the HKM inducing significant HKM cytotoxicity. The immunosuppressive effect of arsenic was further evident from the ability of A. hydrophila to colonize and disseminate efficiently in exposed fish. Enzyme linked immunosorbent assay indicated that chronic exposure to arsenic suppressed the production of pro-inflammatory 'IL-1beta like' factors from HKM. It is concluded that arsenic even at very low concentration is immunotoxic to fish and the changes observed in HKM may provide a useful early biomarker of low-level xenobiotic exposure.

Allele-specific induction of IL1B -31T/C promoter polymorphism by lung carcinogens

Environmental and occupational toxicants may induce pulmonary inflammation. Chronic inflammation has been linked to several human diseases and also to initiation and promotion of cancer. Generation of reactive oxygen/nitrogen species (ROS/RNS), secretion of cytokines, chemokines and pro-angiogenic factors are believed to play a role. Interleukin IL-1beta, encoded by the IL1B gene, is a key cytokine produced and secreted by many cell types after activation by biological or chemical agents. Several polymorphisms in the IL1B gene have been identified, and some are associated with increased risk for lung cancer. Especially, the IL1B -31T/C polymorphism has received attention. We have investigated the effect of the lung carcinogens cigarette-smoke condensate (CSC) and benzo[a]pyrene (B[a]P) on the promoters of the IL1B gene varying only at the site of the -31T/C polymorphism. The promoter fragments containing either C or T were cloned in luciferase reporter vectors and transfected into human lung epithelial NCI-H2009 cells. The results show that treatment of the transfected cells with CSC or B[a]P induced the promoter significantly above the control level. Interestingly, the promoter with the wild-type allele T in position -31 showed the stronger induction when compared with the promoter with variant allele C in this position. Bioinformatics and DNA-protein analysis indicated the presence of a novel transcription-factor binding site and the formation of protein complexes at the C promoter.