Activation of mitogen-activated protein kinases (MAPKs) by aromatic hydrocarbons: role in the regulation of aryl hydrocarbon receptor (AHR) function

Potential AhR-independent mechanisms of 2,3,7,8-Tetrachlorodibenzo-p-dioxin inhibition of human glioblastoma A172 cells migration

The toxicity of 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is generally believed to be mediated by aryl hydrocarbon receptor (AhR), but some evidence suggests that the effects of TCDD can also be produced through AhR-independent mechanisms. In previous experiments, we found that mainly AhR-dependent mechanism was involved in the migration inhibition of glioblastoma U87 cells by TCDD. Due to the heterogeneity of glioblastomas, not all tumor cells have significant AhR expression. The effects and mechanisms of TCDD on the migration of glioblastomas with low AhR expression are still unclear. We employed a glioblastoma cell line A172 with low AhR expression as a model, using wound healing and Transwell® assay to detect the effect of TCDD on cell migration. We found that TCDD can inhibit the migration of A172 cells without activating AhR signaling pathway. Further, after being pre-treated with AhR antagonist CH223191, the inhibition of TCDD on A172 cells migration was not changed, indicating that the effect of TCDD on A172 cells is not dependent on AhR activation. By transcriptome sequencing analysis, we propose dysregulation of the expression of certain migration-related genes, such as IL6, IL1B, CXCL8, FOS, SYK, and PTGS2 involved in cytokines, MAPK, NF-κB, and IL-17 signaling pathways, as potential AhR-independent mechanisms that mediate the inhibition of TCDD migration in A172 cells.

The β-Blocker Carvedilol Prevents Benzo(a)pyrene-Induced Lung Toxicity, Inflammation and Carcinogenesis

The current study evaluated the effects of the β-blocker carvedilol on benzo(a)pyrene (B(a)P) and its active metabolite benzo(a)pyrene diol epoxide (BPDE)-induced lung toxicity, inflammation and carcinogenesis and explored the potential mechanisms. Carvedilol blocked the BPDE-induced malignant transformation of human bronchial epithelial cells BEAS-2B. In BEAS-2B cells, B(a)P strongly activated ELK-1, a transcription factor regulating serum response element (SRE) signaling, which was attenuated by carvedilol. Carvedilol also inhibited the B(a)P-induced AhR/xenobiotic responsive element (XRE) and mRNA expression of CYP1A1 and attenuated B(a)P-induced NF-κB activation. In a B(a)P-induced acute lung toxicity model in CD-1/IGS mice, pretreatment with carvedilol for 7 days before B(a)P exposure effectively inhibited the B(a)P-induced plasma levels of lactate dehydrogenase and malondialdehyde, inflammatory cell infiltration and histopathologic abnormalities in the lung, and upregulated the expression of GADD45α, caspase-3 and COX-2 in the lung. In a B(a)P-induced lung carcinogenesis model in A/J mice, carvedilol treatment for 20 weeks did not affect body weight but significantly attenuated tumor multiplicity and volume. These data reveal a previously unexplored role of carvedilol in preventing B(a)P-induced lung inflammation and carcinogenesis by inhibiting the cross-talk of the oncogenic transcription factors ELK-1, AhR and NF-κB.

The tryptophan-metabolizing enzyme indoleamine 2,3-dioxygenase 1 regulates polycystic kidney disease progression

Autosomal dominant polycystic kidney disease (ADPKD), the most common monogenic nephropathy, is characterized by phenotypic variability that exceeds genic effects. Dysregulated metabolism and immune cell function are key disease modifiers. The tryptophan metabolites, kynurenines, produced through indoleamine 2,3-dioxygenase 1 (IDO1), are known immunomodulators. Here, we study the role of tryptophan metabolism in PKD using an orthologous disease model (C57BL/6J Pkd1RC/RC). We found elevated kynurenine and IDO1 levels in Pkd1RC/RC kidneys versus wild type. Further, IDO1 levels were increased in ADPKD cell lines. Genetic Ido1 loss in Pkd1RC/RC animals resulted in reduced PKD severity, as measured by cystic index and percentage kidney weight normalized to body weight. Consistent with an immunomodulatory role of kynurenines, Pkd1RC/RC;Ido1-/- mice presented with significant changes in the cystic immune microenvironment (CME) versus controls. Kidney macrophage numbers decreased and CD8+ T cell numbers increased, both known PKD modulators. Also, pharmacological IDO1 inhibition in Pkd1RC/RC mice and kidney-specific Pkd2-knockout mice with rapidly progressive PKD resulted in less severe PKD versus controls, with changes in the CME similar to those in the genetic model. Our data suggest that tryptophan metabolism is dysregulated in ADPKD and that its inhibition results in changes to the CME and slows disease progression, making IDO1 a therapeutic target for ADPKD.

Ribosomal protein L22-like1 (RPL22L1) mediates sorafenib sensitivity via ERK in hepatocellular carcinoma

Precision medicine in hepatocellular carcinoma (HCC) relies on validated biomarkers that help subgroup patients for targeted treatment. Here, we identified a novel candidate oncogene, ribosomal protein L22-like1 (RPL22L1), which was markedly elevated in HCC, contributed to HCC malignancy and adverse patient survival. Functional studies indicated RPL22L1 overexpression accelerated cell proliferation, migration, invasion and sorafenib resistance. Mechanism studies revealed that RPL22L1 activated ERK to induce atypical epithelial-to-mesenchymal transition (EMT) progress. Importantly, the ERK inhibitor (ERKi) could potentiate sorafenib efficiency in RPL22L1-high HCC cells. In summary, these data uncover RPL22L1 is a potential marker to guide precision therapy for utilizing ERKi to enhance the sorafenib efficacy in RPL22L1-high HCC patients.

Polycyclic aromatic hydrocarbons in bone homeostasis

Prolonged exposure to polycyclic aromatic hydrocarbons (PAHs) may result in autoimmune diseases, such as rheumatoid arthritis (RA) and osteoporosis (OP), which are based on an imbalance in bone homeostasis. These diseases are characterized by bone erosion and even a disruption in homeostasis, including in osteoblasts and osteoclasts. Current evidence indicates that multiple factors affect the progression of bone homeostasis, such as genetic susceptibility and epigenetic modifications. However, environmental factors, especially PAHs from various sources, have been shown to play an increasingly prominent role in the progression of bone homeostasis. Hence, it is essential to investigate the effects and pathogenesis of PAHs in bone homeostasis. In this review, recent progress is summarized concerning the effects and mechanisms of PAHs and their ligands and receptors in bone homeostasis. Moreover, strategies based on the effects and mechanisms of PAHs in the regulation of the bone balance and alleviation of bone destruction are also reviewed. We further discuss the future challenges and perspectives regarding the roles of PAHs in autoimmune diseases based on bone homeostasis.

Aromatic hydrocarbon receptors in mitochondrial biogenesis and function

Mitochondria are ubiquitous membrane-bound organelles that not only play a key role in maintaining cellular energy homeostasis and metabolism but also in signaling and apoptosis. Aryl hydrocarbons receptors (AhRs) are ligand-activated transcription factors that recognize a wide variety of xenobiotics, including polyaromatic hydrocarbons and dioxins, and activate diverse detoxification pathways. These receptors are also activated by natural dietary compounds and endogenous metabolites. In addition, AhRs can modulate the expression of a diverse array of genes related to mitochondrial biogenesis and function. The aim of the present review is to analyze scientific data available on the AhR signaling pathway and its interaction with the intracellular signaling pathways involved in mitochondrial functions, especially those related to cell cycle progression and apoptosis. Various evidence have reported the crosstalk between the AhR signaling pathway and the nuclear factor κB (NF-κB), tyrosine kinase receptor signaling and mitogen-activated protein kinases (MAPKs). The AhR signaling pathway seems to promote cell cycle progression in the absence of exogenous ligands, whereas the presence of exogenous ligands induces cell cycle arrest. However, its effects on apoptosis are controversial since activation or overexpression of AhR has been observed to induce or inhibit apoptosis depending on the cell type. Regarding the mitochondria, although activation by endogenous ligands is related to mitochondrial dysfunction, the effects of endogenous ligands are not well understood but point towards antiapoptotic effects and inducers of mitochondrial biogenesis.

Identification of molecular toxicity pathways across early life-stages of zebrafish exposed to PCB126 using a whole transcriptomics approach

Although withdrawn from the market in the 1980s, polychlorinated biphenyls (PCBs) are still found ubiquitously in the aquatic environment and pose a serious risk to biota due to their teratogenic potential. In fish, early life-stages are often considered most sensitive with regard to their exposure to PCBs and other dioxin-like compounds. However, little is known about the molecular drivers of the frequently observed teratogenic effects. Therefore, the aims of our study were to: (1) characterize the baseline transcriptome profiles at different embryonic life-stages in zebrafish (Danio rerio); and (2) to identify the molecular response to PCB exposure and life-stage specific-effects of the chemical on associated processes. For both objectives, embryos were sampled at 12, 48, and 96 h post-fertilization (hpf) and subjected to Illumina sequence-by-synthesis and RNAseq analysis. Results revealed that with increasing age more genes and related pathways were upregulated both in terms of number and magnitude. Yet, other transcripts followed an opposite pattern with greater transcript abundance at the earlier time points. Additionally, embryos were exposed to PCB126, a potent agonist of the aryl hydrocarbon receptor (AHR). ClueGO network analysis revealed significant enrichment of genes associated with basic cell metabolism, communication, and homeostasis as well as eye development, muscle formation, and skeletal formation. We selected eight genes involved in the affected pathways for an in-depth characterization of their regulation throughout normal embryogenesis and after exposure to PCB126 by quantification of transcript abundances every 12 h until 118 hpf. Among these, fgf7 and c9 stood out because of their strong upregulation by PCB126 exposure at 48 and 96 hpf, respectively. Cyp2aa12 was upregulated from 84 hpf on. Fabp10ab, myhz1.1, col8a1a, sulf1, and opn1sw1 displayed specific regulation depending on the developmental stage. Overall, we demonstrate that (1) the developmental transcriptome of zebrafish is highly dynamic, and (2) dysregulation of gene expression by exposure to PCB126 was significant and in several cases not directly connected to AHR-signaling. Hence, this study improves the understanding of linkages between molecular events and apical outcomes that are of regulatory relevance.

Acute 2,3,7,8-Tetrachlorodibenzo-p-dioxin exposure in adult mice does not alter the morphology or inflammatory response of cortical microglia

Microglia, the immune cells of the brain, have a canonical role in regulating responses to neurological disease or injury, but have also recently been implicated as regulators of neurophysiological processes such as learning and memory. Given these dual immune and physiological roles, microglia are a likely mechanism by which external toxic stimuli are converted into deficits in neuronal circuitry and subsequently function. However, while it is well established that exposure to environmental toxicants negatively affects the peripheral immune system, it remains unknown whether and how such exposure causes neuroinflammation which, in turn, may negatively impact microglial functions in vivo. Here, we examined how acute 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) exposure in adulthood, which negatively impacts immune cells in the periphery, affects microglial characteristics in the cortex of the mouse. We found that microglia density, distribution, morphology, inflammatory signaling, and response to a secondary, pathological activation were unaffected by acute TCDD exposure. These results suggest that acute, peripheral TCDD exposure in adulthood is not sufficient to induce an overt inflammatory phenotype in cortical microglia.

Roles of aryl hydrocarbon receptor in endothelial angiogenic responses†

Aryl hydrocarbon receptor (AhR) is a transcription factor, which can be activated by a plethora of structure-diverse ligands. Historically, AhR is known for its involvements in regulation of metabolism of xenobiotics. However, normal physiological roles of AhR have been defined in other essential biological processes, including vascular growth and function, reproduction, and immunoresponses. In contrast, aberrant expression and activation of the AhR signaling pathway occur in a variety of human diseases, many of which (e.g., preeclampsia, atherosclerosis, and hypertension) could be associated with endothelial dysfunction. Indeed, emerging evidence has shown that either exogenous or endogenous AhR ligands can induce endothelial dysfunction in either an AhR-dependent or AhR-independent manner, possibly reliant on the blood vessel origin (artery and vein) of endothelial cells. Given that the AhR signaling pathway has broad impacts on endothelial and cardiovascular function, AhR ligands, AhR, and their downstream genes could be considered novel therapeutic targets for those endothelial-related diseases. This review will discuss the current knowledge of AhR's mediation on endothelial function and potential mechanisms underlying these actions with a focus on placental endothelial cells.

Dual Specific Phosphatase 14 Deletion Rescues Retinal Ganglion Cells and Optic Nerve Axons after Experimental Anterior Ischemic Optic Neuropathy

PURPOSE

Understanding molecular changes is essential for designing effective treatments for nonarteritic anterior ischemic optic neuropathy (AION), the most common acute optic neuropathy in adults older than 50 years. We investigated changes in the mitogen-activated protein kinase (MAPK) pathway after experimental AION and focused on dual specificity phosphatase 14 (Dusp14), an atypical MAPK phosphatase that is downstream of Krüppel-like transcription factor (KLF) 9-mediated inhibition of retinal ganglion cell (RGC) survival and axonal regeneration.

MATERIALS AND METHODS

We induced severe AION in a photochemical thrombosis model in adult C57BL/6 wild-type and Dusp14 knockout mice. For comparison, some studies were performed using an optic nerve crush model. We assessed changes in MAPK pathway molecules using Western blot and immunohistochemistry, measured retinal thickness using optical coherence tomography (OCT), and quantified RGCs and axons using histologic methods.

RESULTS

Three days after severe AION, there was no change in the retinal protein levels of MAPK ERK1/2, phosphorylated-ERK1/2 (pERK1/2), downstream effector Elk-1 and phosphatase Dusp14 on Western blot. Western blot analysis of purified RGCs after a more severe model using optic nerve crush also showed no change in Dusp14 protein expression. Because of the known importance of the Dusp14 and MAPK pathway in RGCs, we examined changes after AION in Dusp14 knockout mice. Three days after AION, Dusp14 knockout mice had significantly increased pERK1/2⁺, Brn3A⁺ RGCs on immunohistochemistry. Three weeks after AION, Dusp14 knockout mice had significantly greater preservation of retinal thickness, increased number of Brn3A⁺ RGCs on whole mount preparation, and increased number of optic nerve axons compared with wild-type mice.

CONCLUSIONS

Genetic deletion of Dusp14, a MAPK phosphatase important in KFL9-mediated inhibition of RGC survival, led to increased activation of MAPK ERK1/2 and greater RGC and axonal survival after experimental AION. Inhibiting Dusp14 or activating the MAPK pathway should be examined further as a potential therapeutic approach to treatment of AION.

Abbreviations: AION: anterior ischemic optic neuropathy; Dusp14: dual specific phosphatase 14; ERK1/2: extracellular signal-regulated kinases 1/2; Elk-1: ETS Like-1 protein; GCC: ganglion cell complex; GCL: ganglion cell layer; inner nuclear layer; KO: knockout; MAPK: mitogen-activated phosphokinase; OCT: optical coherence tomography; RGC: retinal ganglion cell; RNFL: retinal nerve fiber layer.

Resveratrol Rescue Indoxyl Sulfate-Induced Deterioration of Osteoblastogenesis via the Aryl Hydrocarbon Receptor /MAPK Pathway

Indoxyl sulfate (IS), a uremic toxin derived from dietary tryptophan metabolism by the gut microbiota, is an endogenous aryl hydrocarbon receptor (AhR) agonist and a key player in bone remodeling. Resveratrol (RSV), an AhR antagonist, plays a protective role in shielding against AhR ligands. Our study explored the impact of IS on osteoblast differentiation and examined the possible mechanism of IS in controlling the expression of osteoblastogenesis markers through an in-depth investigation of AhR signaling. In vivo, we found histological architectural disruption of the femoral bones in 5/6 nephrectomies of young adult IS exposed mice, including reduced Runx2 antigen expression. RSV improved the diaphysis architecture, Runx2 expression, and trabecular quality. In vitro data suggest that IS at 500 and 1000 μM disturbed osteoblastogenesis through suppression of the ERK and p38 mitogen-activated protein kinase (MAPK) pathways, which were found to be downstream of AhR. RSV proved to ameliorate the anti-osteoblastogenic effects of IS through the inhibition of AhR and downstream signaling. Taken together, we demonstrated that the IS/AhR/MAPK signaling pathway plays a crucial role in the inhibition of osteoblastogenesis, and RSV has a potential therapeutic role in reversing the IS-induced decline in osteoblast development and suppressing abnormal bone turnover in chronic kidney disease patients.

Regulation of the aryl hydrocarbon receptor activity in bovine cumulus-oocyte complexes during in vitro maturation: The role of EGFR and post-EGFR ERK1/2 signaling cascade

The aryl hydrocarbon receptor (AhR) has been extensively characterized as an environmental sensor with major roles in xenobiotic-induced toxicity. Evidence is accumulating that these functions serve as adaptive mechanisms overlapping its physiological roles. We previously described a critical role of constitutive AhR activation for the correct progress of mammalian oocyte maturation but the signaling pathway through which AhR controls maturation remains unclear. The aim of this study was to investigate whether the AhR interacts with the epidermal growth factor receptor (EGFR) and p42/44 extracellular regulated kinases (ERK1/2), both key factors in the signaling network that finely regulates the oocyte maturation. As experimental model we used bovine cumulus-oocyte complexes (COCs) during in vitro maturation (IVM). Blocking ERK1/2 signaling in COCs during IVM with the specific EGFR inhibitor AG1478 or the mitogen-activated protein kinase kinase (MEK) inhibitor PD98059 downregulated the expression of the AhR-target gene Cyp1a1. Inhibition of AhR activity was associated with a reduction in the oocytes' ability to progress in meiosis resumption. In contrast, exposure to the AhR antagonist resveratrol reduced both CYP1A1 expression and the oocytes' maturation competence, without affecting ERK1/2 signaling. These findings strongly indicate the EGFR/ERKs signaling network as an upstream regulator of the AhR activation in COCs, offering a new understanding of the finely tuned physiological mechanism leading to oocyte maturation. This information may provide fresh opportunities for improving oocyte in vitro maturation, and therefore boosting the efficiency of assisted reproduction techniques in mammals.

Catalpol protects against 2,3,7,8-tetrachlorodibenzo-p-dioxin-induced cytotoxicity in osteoblastic MC3T3-E1 cells

2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) is a well-known environmental contaminant that produces a wide variety of adverse effects in humans. Catalpol, a major bioactive compound enriched in the dried root of Rehmannia glutinosa, is a major iridoid glycoside that alleviates bone loss. However, the detailed mechanisms underlying the effects of catalpol remain unclear. The present study evaluated the effects of catalpol on TCDD-induced cytotoxicity in osteoblastic MC3T3-E1 cells. Catalpol inhibited TCDD-induced reduction in cell viability and increases in apoptosis and autophagic activity in osteoblastic MC3T3-E1 cells. Additionally, pretreatment with catalpol significantly decreased the nitric oxide and nitrite levels compared with a control in TCDD-treated cells and significantly inhibited TCDD-induced increases in the levels of cytochrome P450 1A1 and extracellular signal-regulated kinase. Pretreatment with catalpol also effectively restored the expression of superoxide dismutase and extracellular signal-regulated kinase 1 and significantly enhanced the expression of glutathione peroxidase 4 and osteoblast differentiation markers, including alkaline phosphatase and osterix. Taken together, these findings demonstrate that catalpol has preventive effects against TCDD-induced damage in MC3T3-E1 osteoblastic cells.

The aryl hydrocarbon receptor is a novel negative regulator of interleukin-17-mediated signaling and inflammation in vitro

Interleukin (IL)-17 plays a critical role in the pathogenesis of inflammation and autoimmune diseases. The aryl hydrocarbon receptor (AHR) is a transcription factor responsible for the elimination of xenobiotic chemicals. However, it remains unknown whether AHR is involved in IL-17 signaling. Here, we demonstrate that knockdown of AHR significantly enhances, while overexpression or activation of AHR inhibits IL-17-induced inflammation in Hela cells. AHR specifically suppresses IL-17-induced p38 activation, and inhibition of p38 activity markedly reverses the effect of AHR knockdown on IL-17-induced inflammation. Mechanistically, AHR physically interacts with TAK1 and mitogen-activated protein kinase kinase 3/6 (MKK3/6) and disrupts TAK1-MKK3/6 interaction, leading to impaired IL-17 signaling. Thus, our study indicates that AHR negatively regulates IL-17-mediated signaling and inflammation at least partially through interfering with the interaction between TAK1 and MKK3/6.

27-Deoxyactein prevents 2,3,7,8-tetrachlorodibenzo-p-dioxin-induced cellular damage in MC3T3-E1 osteoblastic cells

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is a well-known environmental contaminant that exerts its toxicity through a variety of signaling mechanisms. The present study evaluated the effects of 27-deoxyactein, one of the major constituents isolated from Cimicifuga racemosa, on TCDD-induced toxicity in osteoblastic MC3T3-E1 cells. TCDD reduced cell survival, markedly increased apoptosis, and enhanced autophagy activity. However, pre-treatment with 27-deoxyactein attenuated all TCDD-induced effects and significantly decreased intracellular calcium (Ca²⁺) concentrations, the collapse of the mitochondrial membrane potential (MMP), the level of reactive oxygen species (ROS), and cardiolipin peroxidation compared to the TCDD-treated controls. Additionally, TCDD-induced increases in the levels of aryl hydrocarbon receptor (AhR), cytochrome P450 1A1 (CYP1A1), and extracellular signal-regulated kinase (ERK) were significantly inhibited by 27-deoxyactein. The mRNA levels of superoxide dismutase (SOD), ERK1, and nuclear factor kappa B (NF-κB) were also effectively restored by pre-treatment with 27-deoxyactein. Furthermore, 27-deoxyactein significantly increased the expressions of genes associated with osteoblast differentiation, including alkaline phosphatase (ALP), osteocalcin, bone sialoprotein (BSP), and osterix. Taken together, the present findings demonstrate the preventive effects of 27-deoxyactein on TCDD-induced damage in osteoblasts.

Actein alleviates 2,3,7,8-tetrachlorodibenzo-p-dioxin-mediated cellular dysfunction in osteoblastic MC3T3-E1 cells

The environmental pollutant 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) is known to affect bone metabolism. We evaluated the protective effects of the triterpene glycoside actein from the herb black cohosh against TCDD-induced toxicity in MC3T3-E1 osteoblastic cells. We found that TCDD significantly reduced cell viability and increased apoptosis and autophagy in MC3T3-E1 osteoblastic cells (P < .05). In addition, TCDD treatment resulted in a significant increase in intracellular calcium concentration, mitochondrial membrane potential collapse, reactive oxygen species (ROS) production, and cardiolipin peroxidation, whereas pretreatment with actein significantly mitigated these effects (P < .05). The effects of TCDD on extracellular signal-related kinase (ERK), aryl hydrocarbon receptor, aryl hydrocarbon receptor repressor, and cytochrome P450 1A1 levels in MC3T3-E1 cells were significantly inhibited by actein. The levels of superoxide dismutase, ERK1, and nuclear factor kappa B mRNA were also effectively restored by pretreatment with actein. Furthermore, actein treatment resulted in a significant increase in alkaline phosphatase (ALP) activity and collagen content, as well as in the expression of genes associated with osteoblastic differentiation (ALP, type I collagen, osteoprotegerin, bone sialoprotein, and osterix). This study demonstrates the underlying molecular mechanisms of cytoprotection exerted by actein against TCDD-induced oxidative stress and osteoblast damage.

ITE Suppresses Angiogenic Responses in Human Artery and Vein Endothelial Cells: Differential Roles of AhR

Aryl hydrocarbon receptor (AhR), a ligand-activated transcription factor is involved in regulation of many essential biological processes including vascular development and angiogenesis. 2-(1'H-indole-3'-carbonyl)-thiazole-4-carboxylic acid methyl ester (ITE) is an AhR ligand, which regulates immune responses and cancer cell growth. However, the roles of the ITE/AhR pathway in mediating placental angiogenesis remains elusive. Here, we determined if ITE affected placental angiogenic responses via AhR in human umbilical vein (HUVECs) and artery endothelial (HUAECs) cells in vitro. We observed that ITE dose- and time-dependently inhibited proliferation and viability of HUAECs and HUVECs, whereas it inhibited migration of HUAECs, but not HUVECs. While AhR siRNA significantly suppressed AhR protein expression in HUVECs and HUAECs, it attenuated the ITE-inhibited angiogenic responses of HUAECs, but not HUVECs. Collectively, ITE suppressed angiogenic responses of HUAECs and HUVECs, dependent and independent of AhR, respectively. These data suggest that ITE may regulate placental angiogenesis.

Paternal smoking and germ cell death: A mechanistic link to the effects of cigarette smoke on spermatogenesis and possible long-term sequelae in offspring

Paternal exposure to constituents of cigarette smoke (CS) is reportedly associated with infertility, birth defects and childhood cancers even though the mechanism behind this relationship is still unclear. Chronic cigarette smoking by men leads to poor sperm quality and quantity mainly through oxidative stress and also direct assault by CS metabolites. Among several carcinogenic and teratogenic components of cigarette smoke condensate (CSC), polycyclic aromatic hydrocarbons (PAHs) display a preeminent role in accelerating germ cell death via the cytoplasmic transcription factor, aryl hydrocarbon receptor (AHR) that is present across all stages of spermatogenesis. Activation of AHR by growth factors though benefits normal cellular functions, its mediation by CSC in a spermatocyte cell line [Gc2(spd)ts] adversely affects the expression of a battery of genes associated with antioxidant mechanisms, cell proliferation and apoptosis, and cell cycle progress. Besides, the CSC-mediated cross talk either between AHR and NRF2 or AHR-NRF2 and MAPKs pathways inhibits normal proliferation of the spermatogenic GC-2spd(ts) cells in vitro and cell death of spermatocytes in vivo. Pharmacological inactivation of CSC-induced AHR but not its genetic manipulation seems preventing DNA and cell membrane damage in Gc2(spd)ts. Data from recent reports suggest that the cigarette smoke affects both the genomic and epigenomic components of the sperm and attributes any associated changes to developmental defects in the offspring. Thus, the studies discussed here in this review shed light on possible mechanistic factors that could probably be responsible for the paternally mediated birth defects in the offspring following exposure to the toxic constituents of cigarette smoke.

Signalling pathways in trophic skeletal development and morphogenesis: Insights from studies on teleost fish

During the development of the vertebrate feeding apparatus, a variety of complicated cellular and molecular processes participate in the formation and integration of individual skeletal elements. The molecular mechanisms regulating the formation of skeletal primordia and their development into specific morphological structures are tightly controlled by a set of interconnected signalling pathways. Some of these pathways, such as Bmp, Hedgehog, Notch and Wnt, are long known for their pivotal roles in craniofacial skeletogenesis. Studies addressing the functional details of their components and downstream targets, the mechanisms of their interactions with other signals as well as their potential roles in adaptive morphological divergence, are currently attracting considerable attention. An increasing number of signalling pathways that had previously been described in different biological contexts have been shown to be important in the regulation of jaw skeletal development and morphogenesis. In this review, I provide an overview of signalling pathways involved in trophic skeletogenesis emphasizing studies of the most species-rich group of vertebrates, the teleost fish, which through their evolutionary history have undergone repeated episodes of spectacular trophic diversification.

A constitutive active MAPK/ERK pathway due to BRAFV600E positively regulates AHR pathway in PTC

The aryl hydrocarbon receptor (AHR) is a ligand-activated transcription factor mediating the toxicity and tumor-promoting properties of dioxin. AHR has been reported to be overexpressed and constitutively active in a variety of solid tumors, but few data are currently available concerning its role in thyroid cancer. In this study we quantitatively explored a series of 51 paired-normal and papillary thyroid carcinoma (PTC) tissues for AHR-related genes. We identified an increased AHR expression/activity in PTC, independently from its nuclear dimerization partner and repressor but strictly related to a constitutive active MAPK/ERK pathway. The AHR up-regulation followed by an increased expression of AHR target genes was confirmed by a meta-analysis of published microarray data, suggesting a ligand-independent active AHR pathway in PTC. In-vitro studies using a PTC-derived cell line (BCPAP) and HEK293 cells showed that BRAF^V600E may directly modulate AHR localization, induce AHR expression and activity in an exogenous ligand-independent manner. The AHR pathway might represent a potential novel therapeutic target for PTC in the clinical practice.

Identification of aryl hydrocarbon receptor signaling pathways altered in TCDD-treated red seabream embryos by transcriptome analysis

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) induces a broad spectrum of toxic effects including craniofacial malformation and neural damage in fish embryos. These effects are mainly mediated by the aryl hydrocarbon receptor (AHR). However, the mode of action between TCDD-induced AHR activation and adverse outcomes is not yet understood. To provide a comprehensive picture of the AHR signaling pathway in fish embryos exposed to TCDD, red seabream (Pagrus major) embryos were treated with graded concentrations of TCDD (0.3-37nM) in seawater, or with a mixture of TCDD and 500nM CH223191, an AHR-specific antagonist. The transcriptome of red seabream embryos was analyzed using a custom-made microarray with 6000 probes specifically prepared for this species. A Jonckheere-Terpstra test was performed to screen for genes that demonstrated altered mRNA expression levels following TCDD exposure. The signals of 1217 genes (as human homologs) were significantly altered in a TCDD concentration-dependent manner (q-value<0.2). Notably, the TCDD-induced alteration in mRNA expression was alleviated by co-exposure to CH223191, suggesting that the mRNA expression level of these genes was regulated by AHR. To identify TCDD-activated pathways, the microarray data were further subjected to gene set enrichment analysis (GSEA) and functional protein-protein interaction (PPI) network analysis. GSEA demonstrated that the effects of TCDD on sets of genes involved calcium, mitogen-activated protein kinase (MAPK), actin cytoskeleton, chemokine, T cell receptor, melanoma, vascular endothelial growth factor (VEGF), axon guidance, and renal cell carcinoma signaling pathways. These results suggest the hypotheses that TCDD induces immunosuppression via the calcium, MAPK, chemokine, and T cell receptor signaling pathways, neurotoxicity via VEGF signaling, and axon guidance alterations and teratogenicity via the dysregulation of the actin cytoskeleton and melanoma and renal cell carcinoma signaling pathways. Furthermore, the PPI network analysis indicated that the adverse outcome pathways of TCDD in the embryos might be propagated through several hub genes such as cell division control protein 42, phosphoinositide-3-kinase regulatory subunit 1, and guanine nucleotide-binding proteins. Understanding these pathways potentially allows for exploring the adverse outcome pathway of the effects of TCDD on the red seabream embryos.

Regional Induction of CYP1A1 in Rat Liver Following Treatment with Mixtures of PCB 126 and PCB 153

Liver enzyme induction has been shown previously to be regional with clear borders between induced and uninduced regions in vivo, and cells either fully induced or not induced in vitro. The current study examined this phenomenon in vivo by evaluating enzyme induction after exposure to PCB 126 and PCB 153 in female Fisher 344 (F344) and male Sprague—Dawley (SD) rats. IHC revealed a regional induction of CYP1A1 after exposure to PCB 126, apparent in the centrilobular region at lower doses and progressing to panlobular with higher doses. PCB 153 exposure induced CYP2B1/2 in the centrilobular region, which spread to the midzonal region as the dose increased, but never became panlobular even at the highest dosage tested. In rats treated with PCB 126 in combination with high doses of PCB 153, induction of CYP1A1 occurred preferentially in the periportal region, a reversal from the pattern seen with PCB 126 alone. This CYP1A1 induction pattern reversal is a unique example of complex biological interactions between coplanar (PCB 126) and noncoplanar (PCB 153) halogenated aromatic hydrocarbons.

β-naphthoflavone interferes with cyp1c1, cox2 and IL-8 gene transcription and leukotriene B4 secretion in Atlantic cod (Gadus morhua) head kidney cells during inflammation

The objective of this study was to evaluate how β-naphthoflavone interacts with lipopolysaccharide (LPS) and polyinosinic acid: polycytidylic acid (poly I: C) induced innate immune parameters as well as phase I and phase II detoxification enzymes in head kidney cells isolated from Atlantic cod. β-naphthoflavone is a pure agonist of aryl hydrocarbon receptor (AhR) while LPS and poly I: C are not. β-naphthoflavone was added to head kidney leukocytes alone or together with LPS or poly I: C and the responses were evaluated in terms of protein and gene expression. The results showed that β-naphthoflavone (25 nM), with and without LPS, significantly induced cytochrome P450 (cyp1c) transcription in cod head kidney cells. β-naphthoflavone (100 nM) in the presence of the virus mimic, poly I: C, also increased cyp1c1transcription. LPS induced cyp1c1, cyclooxygenase 2 (cox2), interleukin 1β (IL-1β), interleukin 6 (IL-6) and interleukin 8 (IL-8) transcription, genes that were not affected by the tested β-naphthoflavone concentrations alone. However, β-naphthoflavone (25 and 50 nM) strengthened LPS induced cox2 and IL-8 transcription. Cod head kidney cells exposed to β-naphthoflavone concentrations ranging from 25 to 100 nM, with and without LPS or poly I: C, expressed AhR protein. LPS or β-naphthoflavone (5-50 nM) significantly induced leukotriene B4 (LTB4) secretion compared to control. In conclusion, this study suggests that β-naphthoflavone could interfere with LPS induced immune cell signaling in cod head kidney cells.

Epidermal Growth Factor Receptor Kinase Inhibitors Synergize with TCDD to Induce CYP1A1/1A2 in Human Breast Epithelial MCF10A Cells

CYP1A1 and CYP1A2 are transcriptionally activated in the human normal breast epithelial cell line MCF10A following exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Shifting MCF10A cultures to medium deficient in serum and epidermal growth factor (EGF) caused rapid reductions in the activated (i.e., phosphorylated) forms of extracellular regulated kinases (ERKs) and the epidermal growth factor receptor (EGFR). Shifting to serum/EGF-deficient medium also enhanced TCDD-mediated induction of cytochrome P450 (CYP)1A1 Treatment of cells cultured in complete medium with the EGFR inhibitors gefitinib (Iressa), AG1478, and CI-1033 resulted in concentration-dependent reductions of active EGFR and ERKs, and increased CYP1A1 mRNA content ∼3- to 18-fold above basal level. EGFR inhibitors synergized with TCDD and resulted in transient CYP1A1 and CYP1A2 mRNA accumulations ∼8-fold greater (maximum at 5 hours) than that achieved with only TCDD. AG1478, gefitinib, and TCDD individually induced small increases (∼1.2- to 2.5-fold) in CYP1A1 protein content but did not cause additive or synergistic accumulations of CYP1A1 protein when used in combination. The mitogen-activated protein kinase kinase inhibitor PD184352 inhibited ERK and EGFR activation in a concentration-dependent fashion without causing CYP1A1 mRNA accumulation. However, cotreatment with PD184352 potentiated TCDD-mediated CYP1A1 induction. TCDD-mediated induction of CYP1A1 in MCF7-TET on-EGFR cells, a MCF7 variant in which EGFR expression can be controlled, was not affected by the activity status of EGFR or ERKs. Hence, EGFR signaling mutes both basal and ligand-induced expression of two aryl hydrocarbon receptor-responsive P450s in MCF10A cultures. However, these effects are cell context-dependent. Furthermore, CYP1A1 mRNA and protein abundance are not closely coupled in MCF10A cultures.

2,3',4,4',5-Pentachlorobiphenyl Induces Inflammatory Responses in the Thyroid Through JNK and Aryl Hydrocarbon Receptor-Mediated Pathway

Polychlorinated biphenyls (PCBs) are durable and widely distributed environmental contaminants that can compromise the normal functions of multiple organs and systems; one important mechanism is the induction of inflammatory disorders. In this study, we explored the influences of 2,3',4,4',5-pentachlorobiphenyl (PCB118) on inflammatory responses and its underlying mechanisms in the thyroid. Wistar rats were administered PCB118 intraperitoneally at 0, 10, 100, and 1000 μg/kg/d, 5 days a week for 13 weeks; rat thyroid FRTL-5 cells were treated with PCB118 (0, 0.25, 2.5, and 25 nM) for indicated time. Results revealed that PCB118 promoted the generation of interleukin-6 (IL-6), tumor necrosis factor-α (TNF-α), and intercellular adhesion molecule-1 (ICAM-1) in a time- and dose-related manner and decreased sodium/iodide symporter (NIS) protein expression. Moreover, stimulation with PCB118 resulted in the upregulation of the aryl hydrocarbon receptor (AhR)-responsive gene cytochrome P450 1A1 in FRTL-5 cells; whereas pretreatment with the AhR inhibitor α-naphthoflavone or AhR small interfering RNA (siRNA) suppressed AhR, CYP1A1, IL-6, and ICAM-1 and restored NIS expression. In vivo and in vitro studies also suggested that the c-Jun N-terminal kinase (JNK) pathway was activated on PCB118 exposure, and the experiments using siRNA for JNK partially blocked PCB118-induced upregulation of IL-6 and ICAM-1 and downregulation of NIS. Altogether, PCB118 stimulates production of IL-6, TNF-α, and ICAM-1 in the thyroid through AhR and JNK activations and subsequently interferes with NIS expression, resulting in the disruption of thyroid structure and function.

Eicosapentaenoic acid prevents TCDD-induced oxidative stress and inflammatory response by modulating MAP kinases and redox-sensitive transcription factors

BACKGROUND AND PURPOSE

Oxidative stress and subsequent activation of inflammatory responses is a widely accepted consequence of exposure to environmental toxins. TCDD (2,3,7,8-tetrachlorodibenzo-p-dioxin), a well-known environmental toxin, exerts its toxicity through many signalling mechanisms, with liver being the principal organ affected. However, an effective antidote to TCDD-induced toxicity is unknown. The present study evaluated the effect of eicosapentaenoic acid (EPA), an n3 fatty acid, on TCDD-induced toxicity.

EXPERIMENTAL APPROACH

In cultures of HepG2 cells, the EPA/AA ratio was determined using gas chromatography, oxidative stress and inflammatory responses through reactive oxygen species (ROS) levels, antioxidant status, [Ca(2+) ]i , nuclear migration of two redox-sensitive transcription factors, NF-κB p65 and Nrf-2, expression of MAP kinase (p-Erk, p-p38), NF-κB p65, COX-2 and Nrf-2. Cellular changes in ΔΨm, acidic vesicular organelle formation, cell cycle analysis and scanning electron microscopy analysis were performed.

KEY RESULTS

EPA offered significant cytoprotection by increasing EPA/AA ratios in cell membranes, inhibiting ROS generation, enhancing antioxidant status and modulating nuclear translocation of redox-sensitive transcription factors (NF-κB p65 and Nrf-2) and expression of NF-κB p65, COX-2 and Nrf-2. Furthermore, TCDD-induced upstream events of MAPK phosphorylation, the increase in [Ca(2+) ]i levels and cell surface changes in microvilli were significantly inhibited by EPA. EPA treatment maintained ΔΨm and prevented formation of acidic vesicular organelles.

CONCLUSION AND IMPLICATIONS

The present study demonstrates for the first time some underlying molecular mechanisms of cytoprotection exerted by EPA against TCDD-induced oxidative stress and inflammatory responses.

2,3,7,8-Tetrachlorodibenzo-p-dioxin differentially suppresses angiogenic responses in human placental vein and artery endothelial cells

Placental angiogenesis is dramatically increased during pregnancy in association with the elevated placental blood flows to support the rapidly growing fetus. 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is an environmental toxicant and a ligand of aryl hydrocarbon receptor (AhR). Herein, we investigated the effects of TCDD on proliferation, migration, and viability of fetoplacental endothelial cells in response to a complete growth medium which contained serum and growth supplement using human umbilical cord vein (HUVECs) and artery (HUAECs) cells as models. We found that TCDD dose- and time-dependently inhibited (p < 0.05) proliferation of HUVECs and HUAECs. Treatment with TCDD at 10 nM for 6 days inhibited (p < 0.05) migration (by ∼ 30%) of HUAECs, but not HUVECs. TCDD at 10nM also decreased (p < 0.05) viability of HUVECs and HUAECs. Interestingly, specific AhR siRNA blocked (p < 0.05) the TCDD-inhibited cellular responses in HUAECs, but not HUVECs. Nonetheless, TCDD at 10nM neither affected the cell cycle progression, nor did it induce cell apoptosis in HUVECs and HUAECs. In addition, TCDD at 10 nM also did not alter activation of ERK1/2 and AKT1 in HUVECs and HUAECs. Collectively, TCDD suppresses proliferation and/or migration (two key steps of angiogenesis) of HUVECs and HUAECs independent and dependent of AhR, respectively. These data suggest that TCDD inhibited growth of HUVECs and HUAECs via decreasing cell viability. Thus, TCDD may inhibit fetoplacental angiogenesis, leading to negative pregnancy outcomes.

Ligand-Specific Transcriptional Mechanisms Underlie Aryl Hydrocarbon Receptor-Mediated Developmental Toxicity of Oxygenated PAHs

Polycyclic aromatic hydrocarbons (PAHs) are priority environmental contaminants that exhibit mutagenic, carcinogenic, proinflammatory, and teratogenic properties. Oxygen-substituted PAHs (OPAHs) are formed during combustion processes and via phototoxidation and biological degradation of parent (unsubstituted) PAHs. Despite their prevalence both in contaminated industrial sites and in urban air, OPAH mechanisms of action in biological systems are relatively understudied. Like parent PAHs, OPAHs exert structure-dependent mutagenic activities and activation of the aryl hydrocarbon receptor (AHR) and cytochrome p450 metabolic pathway. Four-ring OPAHs 1,9-benz-10-anthrone (BEZO) and benz(a)anthracene-7,12-dione (7,12-B[a]AQ) cause morphological aberrations and induce markers of oxidative stress in developing zebrafish with similar potency, but only 7,12-B[a]AQ induces robust Cyp1a protein expression. We investigated the role of the AHR in mediating the toxicity of BEZO and 7,12-B[a]AQ, and found that knockdown of AHR2 rescued developmental effects caused by both compounds. Using RNA-seq and molecular docking, we identified transcriptional responses that precede developmental toxicity induced via differential interaction with AHR2. Redox-homeostasis genes were affected similarly by these OPAHs, while 7,12-B[a]AQ preferentially activated phase 1 metabolism and BEZO uniquely decreased visual system genes. Analysis of biological functions and upstream regulators suggests that BEZO is a weak AHR agonist, but interacts with other transcriptional regulators to cause developmental toxicity in an AHR-dependent manner. Identifying ligand-dependent AHR interactions and signaling pathways is essential for understanding toxicity of this class of environmentally relevant compounds.

Gene-Environment Interactions Target Mitogen-activated Protein 3 Kinase 1 (MAP3K1) Signaling in Eyelid Morphogenesis

Gene-environment interactions determine the biological outcomes through mechanisms that are poorly understood. Mouse embryonic eyelid closure is a well defined model to study the genetic control of developmental programs. Using this model, we investigated how exposure to dioxin-like environmental pollutants modifies the genetic risk of developmental abnormalities. Our studies reveal that mitogen-activated protein 3 kinase 1 (MAP3K1) signaling is a focal point of gene-environment cross-talk. Dioxin exposure, acting through the aryl hydrocarbon receptor (AHR), blocked eyelid closure in genetic mutants in which MAP3K1 signaling was attenuated but did not disturb this developmental program in either wild type or mutant mice with attenuated epidermal growth factor receptor or WNT signaling. Exposure also markedly inhibited c-Jun phosphorylation in Map3k1(+/-) embryonic eyelid epithelium, suggesting that dioxin-induced AHR pathways can synergize with gene mutations to inhibit MAP3K1 signaling. Our studies uncover a novel mechanism through which the dioxin-AHR axis interacts with the MAP3K1 signaling pathways during fetal development and provide strong empirical evidence that specific gene alterations can increase the risk of developmental abnormalities driven by environmental pollutant exposure.

Immunohistochemical analysis of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) toxicity on the developmental dentate gyrus and hippocampal fimbria in fetal mice

Dioxins are widespread persistent environmental contaminants with adverse impacts on humans and experimental animals. Behavioral and cognitive functions are impaired by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) exposure. TCDD exerts its toxicity via the aryl hydrocarbon receptor (AhR), a ligand-activated transcription factor. The hippocampus, which plays important roles in episodic memory and spatial function, is considered vulnerable to TCDD-induced neurotoxicity, because it contains the AhR. We herein investigated the effects of TCDD toxicity on hippocampal development in embryonic mice. TCDD was administered to dams at 8.5 days postcoitum with a single dose of 20, 200, 2,000 and 5,000 ng/kg body weight (groups T20, T200, T2000 and T5000, respectively), and the brains were dissected from their pups at embryonic day 18.5. Immunohistochemical analysis demonstrated that the Glial Fibrillary Acidic Protein (GFAP) immunoreactivities in the dentate gyrus (DG) were reduced in the T5000 group. Granular GFAP immunoreactivity was observed in the hippocampal fimbria, and the number of immunoreactive fimbria was significantly decreased in the T5000 group. The number of Proliferating Cell Nuclear Antigen (PCNA)-positive cells was decreased in all TCDD-exposed groups and significantly reduced in the T20, T200 and T5000 groups. Together, these results demonstrate that maternal TCDD exposure has adverse impacts on neural stem cells (NSCs), neural precursor cells (NPCs) and granular cells in the DG and disrupts the NSC maintenance and timing of differentiation in the hippocampal fimbria, which in turn interrupt neuronal development in future generations of mice.

Combined 17β-Estradiol with TCDD Promotes M2 Polarization of Macrophages in the Endometriotic Milieu with Aid of the Interaction between Endometrial Stromal Cells and Macrophages

The goal of this study is to elucidate the effects of 17β-estradiol and TCDD (2,3,7,8-tetrachlorodibenzo-p-dioxin) on macrophage phenotypes in the endometriotic milieu. Co-culture of endometrial stromal cells (ESCs) and U937 cells (macrophage cell line) was performed to simulate the endometriotic milieu and to determine the effects of 17β-estradiol and/or TCDD on IL10, IL12 production and HLA-DR, CD86 expression by U937 macrophages. We found that combining 17β-estradiol with TCDD has a synergistic effect on inducing M2 activation when macrophages are co-cultured with ESCs. Moreover, the combination of 17β-estradiol and TCDD significantly enhanced STAT3 and P38 phosphorylation in macrophages. Differentiation of M2 macrophages induced by 17β-estradiol and TCDD were effectively abrogated by STAT3 and P38MAPK inhibitors, but not by ERK1/2 and JNK inhibitors. In conclusion, 17β-estradiol and TCDD in the ectopic milieu may lead to the development of endometriosis by inducing M2 polarization of macrophages through activation of the STAT3 and P38MAPK pathways.

Polycyclic aromatic hydrocarbons reciprocally regulate IL-22 and IL-17 cytokines in peripheral blood mononuclear cells from both healthy and asthmatic subjects

Pollution, including polycyclic aromatic hydrocarbons (PAH), may contribute to increased prevalence of asthma. PAH can bind to the Aryl hydrocarbon Receptor (AhR), a transcription factor involved in Th17/Th22 type polarization. These cells produce IL17A and IL-22, which allow neutrophil recruitment, airway smooth muscle proliferation and tissue repair and remodeling. Increased IL-17 and IL-22 productions have been associated with asthma. We hypothesized that PAH might affect, through their effects on AhR, IL-17 and IL-22 production in allergic asthmatics. Activated peripheral blood mononuclear cells (PBMCs) from 16 nonallergic nonasthmatic (NA) and 16 intermittent allergic asthmatic (AA) subjects were incubated with PAH, and IL-17 and IL-22 productions were assessed. At baseline, activated PBMCs from AA exhibited an increased IL-17/IL-22 profile compared with NA subjects. Diesel exhaust particle (DEP)-PAH and Benzo[a]Pyrene (B[a]P) stimulation further increased IL-22 but decreased IL-17A production in both groups. The PAH-induced IL-22 levels in asthmatic patients were significantly higher than in healthy subjects. Among PBMCs, PAH-induced IL-22 expression originated principally from single IL-22- but not from IL-17- expressing CD4 T cells. The Th17 transcription factors RORA and RORC were down regulated, whereas AhR target gene CYP1A1 was upregulated. IL-22 induction by DEP-PAH was mainly dependent upon AhR whereas IL-22 induction by B[a]P was dependent upon activation of PI3K and JNK. Altogether, these data suggest that DEP-PAH and B[a]P may contribute to increased IL22 production in both healthy and asthmatic subjects through mechanisms involving both AhR -dependent and -independent pathways.

Aryl Hydrocarbon Receptor Ligand 5F 203 Induces Oxidative Stress That Triggers DNA Damage in Human Breast Cancer Cells

Breast tumors often show profound sensitivity to exogenous oxidative stress. Investigational agent 2-(4-amino-3-methylphenyl)-5-fluorobenzothiazole (5F 203) induces aryl hydrocarbon receptor (AhR)-mediated DNA damage in certain breast cancer cells. Since AhR agonists often elevate intracellular oxidative stress, we hypothesize that 5F 203 increases reactive oxygen species (ROS) to induce DNA damage, which thwarts breast cancer cell growth. We found that 5F 203 induced single-strand break formation. 5F 203 enhanced oxidative DNA damage that was specific to breast cancer cells sensitive to its cytotoxic actions, as it did not increase oxidative DNA damage or ROS formation in nontumorigenic MCF-10A breast epithelial cells. In contrast, AhR agonist and procarcinogen benzo[a]pyrene and its metabolite, 1,6-benzo[a]pyrene quinone, induced oxidative DNA damage and ROS formation, respectively, in MCF-10A cells. In sensitive breast cancer cells, 5F 203 activated ROS-responsive kinases: c-Jun-N-terminal kinase (JNK) and p38 mitogen activated protein kinase (p38). AhR antagonists (alpha-naphthoflavone, CH223191) or antioxidants (N-acetyl-l-cysteine, EUK-134) attenuated 5F 203-mediated JNK and p38 activation, depending on the cell type. Pharmacological inhibition of AhR, JNK, or p38 attenuated 5F 203-mediated increases in intracellular ROS, apoptosis, and single-strand break formation. 5F 203 induced the expression of cytoglobin, an oxidative stress-responsive gene and a putative tumor suppressor, which was diminished with AhR, JNK, or p38 inhibition. Additionally, 5F 203-mediated increases in ROS production and cytoglobin were suppressed in AHR100 cells (AhR ligand-unresponsive MCF-7 breast cancer cells). Our data demonstrate 5F 203 induces ROS-mediated DNA damage at least in part via AhR, JNK, or p38 activation and modulates the expression of oxidative stress-responsive genes such as cytoglobin to confer its anticancer action.

Cadmium interference with ERK1/2 and AhR signaling without evidence for cross-talk

The possibility that Cd may activate AhR indirectlyviaERK1/2 phosphorylation was tested as a function of enterocytic differentiation status in the human Caco-2 cells.

Cigarette smoke-induced cell cycle arrest in spermatocytes [GC-2spd(ts)] is mediated through crosstalk between Ahr-Nrf2 pathway and MAPK signaling

Our earlier studies have demonstrated that the cigarette smoke in the form of cigarette smoke condensate (CSC) causes growth arrest of a mouse spermatocyte cell line [GC-2spd(ts)] through activation of the AHR-NRF2 pathway. The present study demonstrates the CSC-activated p38 and ERK MAPK signaling in GC-2spd(ts) via arylhydrocarbon receptor (AHR). Pharmacological inhibition by using AHR-antagonist, or p38 MAPK and ERK (MEK1) inhibitors significantly abrogates CSC-induced growth arrest by AHR and MAPK inactivation. QRT-PCR, western blot, and immunofluorescence of Ahr-target of Nrf2, and stress-inducible growth suppressive Atf3 and E2f4 following treatments indicate a crosstalk among these pathways. Regulation of Atf3 by Nrf2 and Ahr through RNA interference suggests the existence of a cross-regulatory loop between the targets. CSC induction of E2f4 via Atf3 and its regulation by pharmacological inhibitors reveal a possible regulatory mechanism of growth inhibitory CSC. SiRNA silencing of Ahr, Nrf2, Atf3, and E2f4 genes and downregulation of cyclins by CSC corroborate the growth inhibitory effect of cigarette smoke. Thus, the data obtained suggest that the CSC-mediated MAPKs and AHR-NRF2 crosstalks lay the molecular basis for the growth arrest and cell death of spermatocytes.

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) inhibits human ovarian cancer cell proliferation

PURPOSE

The aryl hydrocarbon receptor (AhR), a ligand-activated transcription factor, mediates a broad spectrum of biological processes, including ovarian growth and ovulation. Recently, we found that an endogenous AhR ligand (ITE) can inhibit ovarian cancer proliferation and migration via the AhR. Here, we tested whether 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD, an exogenous AhR ligand) may exert similar anti-ovarian cancer activities using human ovarian cancer and non-cancerous human ovarian surface epithelial cells.

METHODS

Two human ovarian cancer cell lines (SKOV-3 and OVCAR-3) and one human ovarian surface epithelial cell line (IOSE-385) were used. Cell proliferation and migration activities were determined using crystal violet and FluoroBlok insert system assays, respectively. AhR protein expression was assessed by Western blotting. Expression of cytochrome P450, family 1, member A1 (CYP1A1) and member B1 (CYP1B1) mRNA was assessed by qPCR. Small interfering RNAs (siRNAs) were used to knock down AhR expression.

RESULTS

We found that TCDD dose-dependently suppressed OVCAR-3 cell proliferation, with a maximum effect (~70% reduction) at 100 nM. However, TCDD did not affect SKOV-3 and IOSE-385 cell proliferation and migration. The estimated IC50 of TCDD for inhibiting OVCAR-3 cell proliferation was 4.6 nM. At 10 nM, TCDD time-dependently decreased AhR protein levels, while it significantly increased CYP1A1 and CYP1B1 mRNA levels in SKOV-3, OVCAR-3 and IOSE-385 cells, indicating activation of AhR signaling. siRNA-mediated AhR knockdown readily blocked TCDD-mediated suppression of OVCAR-3 cell proliferation.

CONCLUSION

Our data indicate that TCDD can suppress human ovarian cancer cell proliferation via the AhR signaling pathway and that TCDD exhibits an anti-proliferative activity in at least a subset of human ovarian cancer cells.

Aryl hydrocarbon receptor protein and Cyp1A1 gene induction by LPS and phenanthrene in Atlantic cod (Gadus morhua) head kidney cells

The objective of this study was to evaluate interactions between environmental toxicants and cod immune cells during inflammation. Phenanthrene is abundant in plant oils (rapeseed, palm, and soya oil) as compared to fish oils, and consequently constitute an undesirable element in plant replacement diets in aquaculture. Phenanthrene was added to head kidney cell cultures, alone or together with LPS (lipopolysaccharide) or poly I: C (polyinosinic acid: polycytidylic acid), and the responses were evaluated in terms of protein and gene expression. The results showed that LPS, poly I: C or phenanthrene, added to the cultures separately, induced aryl hydrocarbon receptor (AhR) protein expression. Phenanthrene treatment in combination with LPS induced AhR protein expression and Cyp1A1 gene transcription, which not was observed combining poly I: C and phenanthrene. Phenanthrene exposure up regulated the transcription of common stress and detoxification enzymes like catalase, caspase 3 and glutathione S-transferase alfa 3 subunit B (GSTAB3), while LPS exposure alone or combined with phenanthrene down regulated GSTAB3 and catalase in cod leukocytes. It seems clear that immune regulation and phenanthrene induced signaling pathways interact; transcriptional down regulation of detoxification and antioxidant enzymes by LPS could indicate that combating bacterial infections is the number one priority in these cells, and that AhR and Cyp1A1 is somehow involved in this signaling cascade. LPS seems to affect the mitogen activated protein kinases (MAPKs) pathways (P-p38 and ERK1/2) thus modulating the AhR protein and Cyp1A1 gene transcription, while phenanthrene possibly activates AhR by ligand binding.

AHR over-expression in papillary thyroid carcinoma: clinical and molecular assessments in a series of Italian acromegalic patients with a long-term follow-up

AIM

Acromegaly reportedly carries an increased risk of malignant and benign thyroid tumors, with a prevalence of thyroid cancer of around 3-7%. Germline mutations in the aryl-hydrocarbon receptor (AHR) interacting protein (AIP) have been identified in familial forms of acromegaly. The molecular and endocrine relationships between follicular thyroid growth and GH-secreting pituitary adenoma have yet to be fully established. Our aim was to study the prevalence of differentiated thyroid cancer (DTC) in acromegaly, focusing on the role of genetic events responsible for the onset of thyroid cancer.

METHODS

Germline mutations in the AIP gene were assessed in all patients; BRAF and H-N-K RAS status was analyzed by direct sequencing in thyroid specimens, while immunohistochemistry was used to analyze the protein expression of AIP and AHR. A set of PTCs unrelated to acromegaly was also studied.

RESULTS

12 DTCs (10 papillary and 2 follicular carcinomas) were identified in a cohort of 113 acromegalic patients. No differences in GH/IGF-1 levels or disease activity emerged between patients with and without DTC, but the former were older and more often female. BRAF V600E was found in 70% of the papillary thyroid cancers; there were no RAS mutations. AIP protein expression was similar in neoplastic and normal cells, while AHR protein was expressed more in PTCs carrying BRAF mutations than in normal tissue, irrespective of acromegaly status.

CONCLUSIONS

The prevalence of DTC in acromegaly is around 11% and endocrinologists should bear this in mind, especially when examining elderly female patients with uninodular goiter. The DTC risk does not seem to correlate with GH/IGF-1 levels, while it may be associated with BRAF mutations and AHR over-expression. Genetic or epigenetic events probably play a part in promoting thyroid carcinoma.

TCDD promotes lung tumors via attenuation of apoptosis through activation of the Akt and ERK1/2 signaling pathways

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is a multiple-site, multiple-species carcinogen that induces cancer in multiple organs. The molecular mechanisms underlying TCDD-induced lung tumorigenesis remain unclear. In the present study, a two-stage lung tumorigenesis model was established by administrating a single low dose of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) combined with TCDD to female A/J mice. The results indicated that TCDD combined with low-dose NNK has a significant tumor-promoting effect compared with TCDD or low-dose NNK alone. Resistance to apoptosis is a hallmark of cancer and is thought to be one of the tumor-promoting mechanisms regulated by TCDD. We performed an additional series of experiments in the normal human bronchial epithelial cell line Beas2B cells, in which TCDD was combined with the apoptosis inducer staurosporine. Our in vitro results confirmed that TCDD could rescue cells from apoptosis induced by staurosporine. The inhibition of apoptosis is likely mediated by the activation of the Akt and ERK1/2 pathways, as determined by the effectiveness of pathway-specific inhibitors in abrogating the anti-apoptotic activity of TCDD. In conclusion, we demonstrated that TCDD promoted NNK-induced lung tumorigenesis and revealed that TCDD inhibits staurosporine-induced apoptosis, at least in part, through the Akt and ERK1/2 signaling pathways.

Association of dioxin and other persistent organic pollutants (POPs) with diabetes: epidemiological evidence and new mechanisms of beta cell dysfunction

The worldwide explosion of the rates of diabetes and other metabolic diseases in the last few decades cannot be fully explained only by changes in the prevalence of classical lifestyle-related risk factors, such as physical inactivity and poor diet. For this reason, it has been recently proposed that other "nontraditional" risk factors could contribute to the diabetes epidemics. In particular, an increasing number of reports indicate that chronic exposure to and accumulation of a low concentration of environmental pollutants (especially the so-called persistent organic pollutants (POPs)) within the body might be associated with diabetogenesis. In this review, the epidemiological evidence suggesting a relationship between dioxin and other POPs exposure and diabetes incidence will be summarized, and some recent developments on the possible underlying mechanisms, with particular reference to dioxin, will be presented and discussed.

Characterization of natural aryl hydrocarbon receptor agonists from cassia seed and rosemary

Many recent studies have suggested that activation of the aryl hydrocarbon receptor (AhR) reduces immune responses, thus suppressing allergies and autoimmune diseases. In our continuing study on natural AhR agonists in foods, we examined the influence of 37 health food materials on the AhR using a reporter gene assay, and found that aqueous ethanol extracts of cassia seed and rosemary had particularly high AhR activity. To characterize the AhR-activating substances in these samples, the chemical constituents of the respective extracts were identified. From an active ethyl acetate fraction of the cassia seed extract, eight aromatic compounds were isolated. Among these compounds, aurantio-obtusin, an anthraquinone, elicited marked AhR activation. Chromatographic separation of an active ethyl acetate fraction of the rosemary extract gave nine compounds. Among these compounds, cirsimaritin induced AhR activity at 10-10² μM, and nepitrin and homoplantagenin, which are flavone glucosides, showed marked AhR activation at 10-10³ μM.

The aryl hydrocarbon receptor-activating effect of uremic toxins from tryptophan metabolism: a new concept to understand cardiovascular complications of chronic kidney disease

Patients with chronic kidney disease (CKD) have a higher risk of cardiovascular diseases and suffer from accelerated atherosclerosis. CKD patients are permanently exposed to uremic toxins, making them good candidates as pathogenic agents. We focus here on uremic toxins from tryptophan metabolism because of their potential involvement in cardiovascular toxicity: indolic uremic toxins (indoxyl sulfate, indole-3 acetic acid, and indoxyl-β-d-glucuronide) and uremic toxins from the kynurenine pathway (kynurenine, kynurenic acid, anthranilic acid, 3-hydroxykynurenine, 3-hydroxyanthranilic acid, and quinolinic acid). Uremic toxins derived from tryptophan are endogenous ligands of the transcription factor aryl hydrocarbon receptor (AhR). AhR, also known as the dioxin receptor, interacts with various regulatory and signaling proteins, including protein kinases and phosphatases, and Nuclear Factor-Kappa-B. AhR activation by 2,3,7,8-tetrachlorodibenzo-p-dioxin and some polychlorinated biphenyls is associated with an increase in cardiovascular disease in humans and in mice. In addition, this AhR activation mediates cardiotoxicity, vascular inflammation, and a procoagulant and prooxidant phenotype of vascular cells. Uremic toxins derived from tryptophan have prooxidant, proinflammatory, procoagulant, and pro-apoptotic effects on cells involved in the cardiovascular system, and some of them are related with cardiovascular complications in CKD. We discuss here how the cardiovascular effects of these uremic toxins could be mediated by AhR activation, in a “dioxin-like” effect.

The Ah receptor recruits IKKα to its target binding motifs to phosphorylate serine-10 in histone H3 required for transcriptional activation

Aryl hydrocarbon receptor (AHR) activation by xenobiotic ligands such as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) is key to their toxicity. Following activation and nuclear translocation, AHR heterodimerizes with the AHR nuclear translocator (ARNT) and binds to AHR response elements (AhREs) in the enhancer of target genes, of which Cyp1a1 is the prototype. Previously, we showed that concomitant with AHR binding, histone H3 in the Cyp1a1 enhancer-promoter AhRE cluster became phosphorylated in serine-10 (H3S10), suggesting that the ligand-activated AHR recruited one or more kinases to the enhancer chromatin to phosphorylate this residue. To test this hypothesis, we used mouse hepatoma Hepa-1c1c7 cells and their c35 mutant derivative, lacking a functional AHR, to search for candidate kinases that would phosphorylate H3S10 in an AHR dependent manner. Using chromatin immunoprecipitation with antibodies to a comprehensive set of protein kinases, we identified three kinases, IκB kinase α (IKKα), mitogen and stress activated protein kinase 1 (MSK1), and mitogen and stress activated protein kinase 2 (MSK2), whose binding to the Cyp1a1 enhancer was significantly increased by TCDD in Hepa-1c1c7 cells and absent in control c35 cells. Complexes of AHR, ARNT, and IKKα could be coimmunoprecipitated from nuclei of TCDD treated Hepa-1c1c7 cells and shRNA-mediated IKKα knockdown inhibited both H3S10 phosphorylation in the Cyp1a1 enhancer and the induction of Cyp1a1, Aldh3a1, and Nqo1 in TCDD-treated cells. We conclude that AHR recruits IKKα to the promoter of its target genes and that AHR-mediated H3S10 phosphorylation is a key epigenetic requirement for induction of AHR targets. Given the role of H3S10ph in regulation of chromosome condensation, AHR-IKKα cross-talk may be a mediator of chromatin remodeling by environmental agents.

Gene expression profiling of candidate genes in peripheral blood mononuclear cells for predicting toxicity of diesel exhaust particles

To validate gene expression profiling of peripheral blood mononuclear cells (PBMCs) as a surrogate for monitoring tissue expression, this study using RT-PCR-based TaqMan low-density array (TLDA) was initiated to investigate similarities in the mRNA expression of target genes altered by exposure to diesel exhaust particles (DEPs) in freshly prepared PBMCs and in lungs. Adult Wistar rats were treated transtracheally with a single dose of 7.5 or 15 or 30mg/kg DEPs and sacrificed 24h later. Blood and lungs were immediately taken out and processed for RT-PCR. DEP treatment induced similar patterns of increase in the expression of polycyclic aromatic hydrocarbon-responsive cytochrome P450s, the phase II enzymes, and their associated transcription factors in both lungs and PBMCs, at all doses. Similar to that seen in lungs, a dose-dependent increase was observed in the expression of genes involved in inflammation, such as cytokines, chemokines, and adhesion molecules, in PBMCs. The expression of various genes involved in DNA repair and apoptosis was also increased in a dose-dependent manner in PBMCs and lungs. The present TLDA data indicating similarities in the responsiveness of candidate genes involved in the toxicity of DEPs between PBMCs and lungs after exposure to DEPs demonstrate that expression profiles of genes in PBMCs could be used as a surrogate for monitoring the acute toxicity of fine and ultrafine particulate matter present in vehicular emissions.