Requirement of aryl hydrocarbon receptor overexpression for CYP1B1 up-regulation and cell growth in human lung adenocarcinomas

The Aryl Hydrocarbon Receptor: Impact on the Tumor Immune Microenvironment and Modulation as a Potential Therapy

The aryl hydrocarbon receptor (AhR) is a ubiquitous nuclear receptor with a broad range of functions, both in tumor cells and immune cells within the tumor microenvironment (TME). Activation of AhR has been shown to have a carcinogenic effect in a variety of organs, through induction of cellular proliferation and migration, promotion of epithelial-to-mesenchymal transition, and inhibition of apoptosis, among other functions. However, the impact on immune cell function is more complicated, with both pro- and anti-tumorigenic roles identified. Although targeting AhR in cancer has shown significant promise in pre-clinical studies, there has been limited efficacy in phase III clinical trials to date. With the contrasting roles of AhR activation on immune cell polarization, understanding the impact of AhR activation on the tumor immune microenvironment is necessary to guide therapies targeting the AhR. This review article summarizes the state of knowledge of AhR activation on the TME, limitations of current findings, and the potential for modulation of the AhR as a cancer therapy.

Deciphering the roles of aryl hydrocarbon receptor (AHR) in regulating carcinogenesis

Aryl hydrocarbon receptor (AHR) is a ligand-dependent receptor that belongs to the superfamily of basic helix-loop-helix (bHLH) transcription factors. The activation of the canonical AHR signaling pathway is known to induce the expression of cytochrome P450 enzymes, facilitating the detoxification metabolism in the human body. Additionally, AHR could interact with various signaling pathways such as epidermal growth factor receptor (EGFR), signal transducer and activator of transcription 3 (STAT3), hypoxia-inducible factor-1α (HIF-1α), nuclear factor ekappa B (NF-κβ), estrogen receptor (ER), and androgen receptor (AR) signaling pathways. Over the past 30 years, several studies have reported that various chemical, physical, or biological agents, such as tobacco, hydrocarbon compounds, industrial and agricultural chemical wastes, drugs, UV, viruses, and other toxins, could affect AHR expression or activity, promoting cancer development. Thus, it is valuable to overview how these factors regulate AHR-mediated carcinogenesis. Current findings have reported that many compounds could act as AHR ligands to drive the expressions of AHR-target genes, such as CYP1A1, CYP1B1, MMPs, and AXL, and other targets that exert a pro-proliferation or anti-apoptotic effect, like XIAP. Furthermore, some other physical and chemical agents, such as UV and 3-methylcholanthrene, could promote AHR signaling activities, increasing the signaling activities of a few oncogenic pathways, such as the phosphatidylinositol 3-kinase/protein kinase B (PI3K/AKT) and mitogen-activated protein kinase/extracellular signal-regulated kinase (MAPK/ERK) pathways. Understanding how various factors regulate AHR-mediated carcinogenesis processes helps clinicians and scientists plan personalized therapeutic strategies to improve anti-cancer treatment efficacy. As many studies that have reported the roles of AHR in regulating carcinogenesis are preclinical or observational clinical studies that did not explore the detailed mechanisms of how different chemical, physical, or biological agents promote AHR-mediated carcinogenesis processes, future studies should focus on conducting large-scale and functional studies to unravel the underlying mechanism of how AHR interacts with different factors in regulating carcinogenesis processes.

Phosphorylation of AHR by PLK1 promotes metastasis of LUAD via DIO2-TH signaling

Metastasis of Lung adenocarcinoma (LUAD) is a major cause of death in patients. Aryl hydrocarbon receptor (AHR) is an important transcription factor involved in the initiation and progression of lung cancer. Polo-like kinase 1 (PLK1), a serine/threonine kinase, is an oncogene that promotes the malignancy of multiple cancer types. Nonetheless, the interaction between these two factors and significance in lung cancer remains to be determined. Here, we demonstrate that PLK1 phosphorylates AHR at S489 in LUAD, which leads to epithelial-mesenchymal transition (EMT) and metastatic events. RNA-seq analyses show that type 2 deiodinase (DIO2) is responsible for EMT and enhanced metastatic potential. DIO2 converts tetraiodothyronine (T4) to triiodothyronine (T3), which then activates thyroid hormone signaling. In vitro and in vivo experiments demonstrate that treatment with T3 or T4 promotes the metastasis of LUAD, whereas depletion of DIO2 or deiodinase inhibitor disrupts this property. Taken together, our results identify the phosphorylation of AHR by PLK1 as a mechanism leading to the progression of LUAD and provide possible therapeutic interventions for this event.

When AHR signaling pathways meet viral infections

Aryl hydrocarbon receptor (AHR) is a ligand-dependent transcriptional factor widely expressed among immune, epithelial, endothelial and stromal cells in barrier tissues. It can be activated by small molecules provided by pollutants, microorganisms, food, and metabolism. It has been demonstrated that AHR plays an important role in modulating the response to many microbial pathogens, and the abnormal expression of AHR signaling pathways may disrupt endocrine, cause immunotoxicity, and even lead to the occurrence of cancer. Most humans are infected with at least one known human cancer virus. While the initial infection with these viruses does not cause major disease, the metabolic activity of infected cells changes, thus affecting the activation of oncogenic signaling pathways. In the past few years, lots of studies have shown that viral infections can affect disease progression by regulating the transmission of multiple signaling pathways. This review aims to discuss the potential effects of virus infections on AHR signaling pathways so that we may find a new strategy to minimize the adverse effects of the AHR pathway on diseases. Video Abstract.

Screening of medicinal plants for possible herb-drug interactions through modulating nuclear receptors, drug-metabolizing enzymes and transporters

ETHNOPHARMACOLOGICAL RELEVANCE

The last three decades have witnessed a surge in popularity and consumption of herbal products. An unintended consequence of such popularity is that chronic consumption of these products can often modulate the functions of various proteins involved in drug disposition and may, in turn, impose risks for herb-drug interactions (HDIs), leading to serious adverse health outcomes. Identifying plants that may give rise to clinically relevant HDIs is essential, and proactive dissemination of such research outcomes is necessary for researchers, clinicians, and average consumers.

AIM OF THE STUDY

The main objective of this study was to evaluate the HDI potential of plants commonly used as ingredients in many herbal products, including BDS.

MATERIALS AND METHODS

The dried material of 123 plants selected from the NCNPR repository was extracted with 95% ethanol. The extracts were screened for agonistic effects on nuclear receptors (PXR and AhR) by reporter gene assays in PXR-transfected HepG2 and AhR-reporter cells. For cytochrome P450 enzyme (CYP) inhibition studies, CYP450 baculosomes were incubated with enzyme-specific probe substrates by varying concentrations of extracts. The inhibitory effect on the efflux transporter P-glycoprotein (P-gp) was investigated via rhodamine (Rh-123) uptake assay in P-gp overexpressing MDR1-MDCK cells.

RESULTS

Out of 123 plants, 16 increased transcriptional activity of human PXR up to 4 to 7-fold at 60 μg/mL, while 18 plants were able to increase AhR activity up to 10 to 40-fold at 30 μg/mL. Thirteen plants inhibited the activity of CYP3A4, while 10 plants inhibited CYP1A2 activity with IC₅₀ values in the range of 1.3-10 μg/mL. Eighteen plants (at 50 μg/mL) increased intracellular accumulation of Rh-123 (>150%) in MDR1-MDCK cells. Additionally, other plants tested in this study were able to activate PXR, AhR, or both to lesser extents, and several inhibited the catalytic activity of CYPs at higher concentrations (IC₅₀ >10 μg/mL).

CONCLUSIONS

The results indicate that prolonged or excessive consumption of herbal preparations rich in such plants (presented in Figs. 1a, 2a, 3a, 4a, and 5a) may pose a risk for CYP- and P-gp-mediated HDIs, leading to unwanted side effects due to the altered pharmacokinetics of concomitantly ingested medications.

Adverse outcome pathway from activation of the AhR to breast cancer-related death

Adverse outcome pathways (AOPs) are formalized and structured linear concepts that connect one molecular initiating event (MIE) to an adverse outcome (AO) via different key events (KE) through key event relationships (KER). They are mainly used in eco-toxicology toxicology, and regulatory health issues. AOPs must respond to specific guidelines from the Organization for Economic Co-operation and Development (OECD) to weight the evidence between each KE. Breast cancer is the deadliest cancer in women with a poor prognosis in case of metastatic breast cancer. The role of the environments in the formation of metastasis has been suggested. We hypothesized that activation of the AhR (MIE), a xenobiotic receptor, could lead to breast cancer related death (AO), through different KEs, constituting a new AOP. An artificial intelligence tool (AOP-helpfinder), which screens the available literature, was used to collect all existing scientific abstracts to build a novel AOP, using a list of key words. Four hundred and seven abstracts were found containing at least a word from our MIE list and either one word from our AO or KE list. A manual curation retained 113 pertinent articles, which were also screened using PubTator. From these analyses, an AOP was created linking the activation of the AhR to breast cancer related death through decreased apoptosis, inflammation, endothelial cell migration, angiogenesis, and invasion. These KEs promote an increased tumor growth, angiogenesis and migration which leads to breast cancer metastasis and breast cancer related death. The evidence of the proposed AOP was weighted using the tailored Bradford Hill criteria and the OECD guidelines. The confidence in our AOP was considered strong. An in vitro validation must be carried out, but our review proposes a strong relationship between AhR activation and breast cancer-related death with an innovative use of an artificial intelligence literature search.

Genome-wide evaluation of transcriptomic responses of human tissues to smoke: A systems biology study

The harmful compounds in various sources of smoke threaten human health. So far, many studies have investigated the effects of compounds of smoke on transcriptome changes in different human tissues. However, no study has been conducted on the effects of these compounds on transcriptome changes in different human tissues simultaneously. Hence, the present study was conducted to identify smoke-related genes (SRGs) and their response mechanisms to smoke in various human cells and tissues using systems biology based methods. A total of 6,484 SRGs were identified in the studied tissues, among which 4,095 SRGs were up-regulated and 2,389 SRGs were down-regulated. Totally, 459 SRGs were smoke-related transcription factors (SRTFs). Gene regulatory network analysis showed that the studied cells and tissues have different gene regulation and responses to compounds of smoke. The comparison of different tissues revealed no common SRG among the all studied tissues. However, the CYP1B1 gene was common among seven cells and tissues, and had the same expression trend. Network analysis showed that the CYP1B1 is a hub gene among SRGs in various cells and tissues. To the best of our knowledge, for the first time, our results showed that compounds of smoke induce and increase the expression of CYP1B1 key gene in all target and non-target tissues of human. Moreover, despite the specific characteristics of CYP1B1 gene and its identical expression trend in target and non-target tissues, it can be used as a biomarker for diagnosis and prognosis.

Gene-gene interaction of AhRwith and within the Wntcascade affects susceptibility to lung cancer

BACKGROUND

Aberrant Wnt signalling, regulating cell development and stemness, influences the development of many cancer types. The Aryl hydrocarbon receptor (AhR) mediates tumorigenesis of environmental pollutants. Complex interaction patterns of genes assigned to AhR/Wnt-signalling were recently associated with lung cancer susceptibility.

AIM

To assess the association and predictive ability of AhR/Wnt-genes with lung cancer in cases and controls of European descent.

METHODS

Odds ratios (OR) were estimated for genomic variants assigned to the Wnt agonist and the antagonistic genes DKK2, DKK3, DKK4, FRZB, SFRP4 and Axin2. Logistic regression models with variable selection were trained, validated and tested to predict lung cancer, at which other previously identified SNPs that have been robustly associated with lung cancer risk could also enter the model. Furthermore, decision trees were created to investigate variant × variant interaction. All analyses were performed for overall lung cancer and for subgroups.

RESULTS

No genome-wide significant association of AhR/Wnt-genes with overall lung cancer was observed, but within the subgroups of ever smokers (e.g., maker rs2722278 SFRP4; OR  = 1.20; 95% CI 1.13-1.27; p  = 5.6 × 10-10) and never smokers (e.g., maker rs1133683 Axin2; OR  = 1.27; 95% CI 1.19-1.35; p  = 1.0 × 10-12). Although predictability is poor, AhR/Wnt-variants are unexpectedly overrepresented in optimized prediction scores for overall lung cancer and for small cell lung cancer. Remarkably, the score for never-smokers contained solely two AhR/Wnt-variants. The optimal decision tree for never smokers consists of 7 AhR/Wnt-variants and only two lung cancer variants.

CONCLUSIONS

The role of variants belonging to Wnt/AhR-pathways in lung cancer susceptibility may be underrated in main-effects association analysis. Complex interaction patterns in individuals of European descent have moderate predictive capacity for lung cancer or subgroups thereof, especially in never smokers.

UCH-L3 structure and function: Insights about a promising drug target

In the past few years, researchers have shed light on the immense importance of ubiquitin in numerous regulatory pathways. The post-translational addition of mono or poly-ubiquitin molecules namely "ubiquitinoylation" is therefore pivotal to maintain the cell's vitality, maturation, differentiation, and division. Part of conserving homeostasis stems from maintaining the ubiquitin pool in the vicinity of the cell's intracellular environment; this crucial role is played by deubiquitylating enzymes (DUBs) that cleave ubiquitin molecules from target molecules. To date, they are categorized into 7 families with ubiquitin carboxyl c-terminal de-hydrolase family (UCH) as the most common and well-studied. Ubiquitin C-terminal hydrolase L (UCH-L3) is a significant protein in this family as it has been implicated in many molecular and cellular processes with its mRNA identified in a range of body tissues including the brain. It goes without saying that it manifests in maintaining health and when abnormally regulated in disease. As it is an attractive small molecule drug target, scientists have used high throughput screening (HTS) and other drug discovery methods to discover inhibitors for this enzyme for the treatment of cancer and neurodegenerative diseases. In this review we present an overview of UCH-L3 catalytic mechanism, structure, its role in DNA repair and cancer along with the inhibitors discovered so far to halt its activity.

Enhancing immunotherapy in cancer by targeting emerging immunomodulatory pathways

The discovery and clinical implementation of immune-checkpoint inhibitors (ICIs) targeting CTLA4, PD-1 and PD-L1 has revolutionized the treatment of cancer, as recognized by the 2018 Nobel Prize for Medicine and Physiology. This groundbreaking new approach has improved the outcomes of patients with various forms of advanced-stage cancer; however, the majority of patients receiving these therapies, even in combination, do not derive clinical benefit. Further development of agents targeting additional immune checkpoints, co-stimulatory receptors and/or co-inhibitory receptors that control T cell function is therefore critical. In this Review, we discuss the translational potential and clinical development of agents targeting both co-stimulatory and co-inhibitory T cell receptors. Specifically, we describe their mechanisms of action, and provide an overview of ongoing clinical trials involving novel ICIs including those targeting LAG3, TIM3, TIGIT and BTLA as well as agonists of the co-stimulatory receptors GITR, OX40, 41BB and ICOS. We also discuss several additional approaches, such as harnessing T cell metabolism, in particular via adenosine signalling, inhibition of IDO1, and targeting changes in glucose and fatty acid metabolism. We conclude that further efforts are needed to optimize the timing of combination ICI approaches and, most importantly, to individualize immunotherapy based on both patient-specific and tumour-specific characteristics.

Monocytic differentiation and AHR signaling as Primary Nodes of BET Inhibitor Response in Acute Myeloid Leukemia

To understand mechanisms of response to BET inhibitors (BETi), we mined the Beat AML functional genomic dataset and performed genome-wide CRISPR screens on BETi- sensitive and BETi- resistant AML cells. Both strategies revealed regulators of monocytic differentiation, SPI1, JUNB, FOS, and aryl-hydrocarbon receptor signaling (AHR/ARNT), as determinants of BETi response. AHR activation synergized with BETi while inhibition antagonized BETi-mediated cytotoxicity. Consistent with BETi sensitivity dependence on monocytic differentiation, ex vivo sensitivity to BETi in primary AML patient samples correlated with higher expression of monocytic markers CSF1R, LILRs, and VCAN. In addition, HL-60 cell line differentiation enhanced its sensitivity to BETi. Further, screens to rescue BETi sensitivity identified BCL2 and CDK6 as druggable vulnerabilities. Finally, monocytic AML patient samples refractory to venetoclax ex vivo were significantly more sensitive to combined BETi + venetoclax. Together, our work highlights mechanisms that could predict BETi response and identifies combination strategies to overcome resistance.

Aryl Hydrocarbon Receptor and Its Diverse Ligands and Functions: An Exposome Receptor

The aryl hydrocarbon receptor (AhR) is a transcriptional factor that regulates multiple functions following its activation by a variety of ligands, including xenobiotics, natural products, microbiome metabolites, and endogenous molecules. Because of this diversity, the AhR constitutes an exposome receptor. One of its main functions is to regulate several lines of defense against chemical insults and bacterial infections. Indeed, in addition to its well-established detoxication function, it has several functions at physiological barriers, and it plays a critical role in immunomodulation. The AhR is also involved in the development of several organs and their homeostatic maintenance. Its activity depends on the type of ligand and on the time frame of the receptor activation, which can be either sustained or transient, leading in some cases to opposite modes of regulations as illustrated in the regulation of different cancer pathways. The development of selective modulators and their pharmacological characterization are important areas of research. Expected final online publication date for the Annual Review of Pharmacology and Toxicology, Volume 62 is January 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

The smoking estrogens - a potential synergy between estradiol and benzo(a)pyrene

According to recent statistics, Lung Cancer (LC) is one of the most frequently diagnosed tumor types, representing nearly 12% of all global cancer cases. Moreover, in recent years, an increased mortality rate and incidence of this cancer were observed, especially among nonsmokers. Lung cancer patients are often characterized by poor prognosis and low survival rates, which encourages the scientific community to investigate the biochemical and molecular processes leading to the development of this malignancy. Furthermore, the mechanisms of LC formation and progression are not yet fully elucidated due to their high complexity, as well as a multitude of environmental, genetic, and molecular factors involved. Even though LC's association with exposure to cigarette smoke is indisputable, current research provides evidence that the development of this cancer can also be affected by the presence of estrogens and their interaction with several tobacco smoke components. Hence, the main goal of this brief review was to investigate reports of a possible synergy between 17β estradiol (E2), the most biologically active estrogen, and benzo(a)pyrene (BaP), a strongly carcinogenic compound produced as a result of incomplete tobacco combustion. The literature sources demonstrate a possible carcinogenic synergy between estrogens, especially E2, and BaP, a toxic tobacco smoke component. Therefeore, the combined effect of disturbed estrogen production in cancer cells, as well as the molecular influence exerted by BaP, could explain the increased aggressiveness and rate of LC development. Summarizing, the synergistic effect of these risk factors is an interesting area of further research.

Evaluation of aryl hydrocarbon receptor expression in oral squamous cell carcinoma and normal oral mucosa using western blot

Background

Aryl hydrocarbon receptor (AHR) is a ligand-activated transcription factor that acts as a binding site for toxic chemicals, particularly the dioxin group of chemicals. Elevated levels of AHR have been observed in various human cancers, including lung carcinomas, hepatic carcinomas and in mammary tumors. However, the expression of AHR in oral squamous cell carcinoma (OSCC) patients who are tobacco users are less explored.

Aims and Objectives

The aim of the present study is to evaluate and compare AHR levels in OSSC patients and in normals using Western blot technique in an attempt to explore the possible role of AHR in oral carcinogenesis.

Materials and Methods

The study sample consisted of ten oral squamous cell carcinoma cases which were diagnosed clinically and confirmed histopathologically as OSCC and four samples of the normal oral mucosa. AHR protein expression was evaluated using Western blot technique and chemiluminescence detection kit. The densitometry was performed on a Microtek scan maker MSP flatbed scanner and quantified using Image J software. Mean AHR protein levels were calculated and compared between OSCC and normal oral mucosa using Student's t-test.

Results

The mean AHR protein level in OSCC samples (n = 10) was 2878.90 ± 1231.27 and 975.75 ± 227.27 in the normal oral mucosa (n = 4). The OSCC samples showed significantly higher levels of AHR protein compared to the normal oral mucosa (P = 0.008).

Conclusion

The study showed a significantly higher expression of AHR in oral squamous cell carcinoma samples when compared to the normal oral mucosa, suggesting a possible role of AHR in the initiation, promotion and progression of oral squamous cell carcinoma.

LMP2A suppresses the role of AHR pathway through ERK signal pathway in EBV-associated gastric cancer

OBJECTIVE

To investigate the function of the aryl hydrocarbon receptor (AHR) pathway in Epstein-Barr Virus (EBV)-associated gastric cancer (EBVaGC) and to explore the relationship between EBV and AHR expression.

METHODS

The expression of AHR in EBVaGC and EBV negative GC (EBVnGC) tissues was detected by immunohistochemistry (IHC). Real-time qPCR (RT-qPCR) and Western blot analysis were used to examine the expression of AHR, cytochrome P450 1A1 (CYP1A1), and cytochrome P450 1B1 (CYP1B1) in gastric cancer cells. The cell proliferation and migration assay were tested by CCK8 and transwell analysis. EBV-encoded latent membrane protein 2A (LMP2A) was over-expressed in SGC7901 cells and silenced in AGS-EBV cells to further identify its role in EBV positive GC cells.

RESULTS

It was found that EBV infection inhibited the expression of AHR in gastric cancer tissues and cell lines. We also found that the activation of AHR pathway can promote cell proliferation and migration. However, the function was restricted in EBVaGC cell lines compared with EBVnGC. LMP2A can suppress AHR expression and pathway activation by activating phosphorylation of extracellular signal-regulated kinase (ERK) in EBV positive GC cell lines.

CONCLUSION

EBV-encoded LMP2A regulated the function of the AHR pathway by activating the ERK signal pathway in EBV positive GC cell lines.

Cigarette smoke-induced alterations in blood: A review of research on DNA methylation and gene expression

Worldwide, smoking remains a threat to public health, causing preventable diseases and premature mortality. Cigarette smoke is a powerful inducer of DNA methylation and gene expression alterations, which have been associated with negative health consequences. Here, we review the current knowledge on smoking-related changes in DNA methylation and gene expression in human blood samples. We identified 30 studies focused on the association between active smoking, DNA methylation modifications, and gene expression alterations. Overall, we identified 1,758 genes with differentially methylated sites (DMS) and differentially expressed genes (DEG) between smokers and nonsmokers, of which 261 were detected in multiple studies (≥4). The most frequently (≥10 studies) reported genes were AHRR, GPR15, GFI1, and RARA. Functional enrichment analysis of the 261 genes identified the aryl hydrocarbon receptor repressor and T cell pathways (T helpers 1 and 2) as influenced by smoking status. These results highlight specific genes for future mechanistic and translational research that may be associated with cigarette smoke exposure and smoking-related diseases. (PsycInfo Database Record (c) 2021 APA, all rights reserved).

Functional screening identifies aryl hydrocarbon receptor as suppressor of lung cancer metastasis

Lung cancer mortality largely results from metastasis. Despite curative surgery many patients with early-stage non-small cell lung cancer ultimately succumb to metastatic relapse. Current risk reduction strategies based on cytotoxic chemotherapy and radiation have only modest activity. Against this background, we functionally screened for novel metastasis modulators using a barcoded shRNA library and an orthotopic lung cancer model. We identified aryl hydrocarbon receptor (AHR), a sensor of xenobiotic chemicals and transcription factor, as suppressor of lung cancer metastasis. Knockdown of endogenous AHR induces epithelial–mesenchymal transition signatures, increases invasiveness of lung cancer cells in vitro and metastasis formation in vivo. Low intratumoral AHR expression associates with inferior outcome of patients with resected lung adenocarcinomas. Mechanistically, AHR triggers ATF4 signaling and represses matrix metalloproteinase activity, both counteracting metastatic programs. These findings link the xenobiotic defense system with control of lung cancer progression. AHR-regulated pathways are promising targets for innovative anti-metastatic strategies.

Aryl hydrocarbon receptor mediates Jak2/STAT3 signaling for non-small cell lung cancer stem cell maintenance

Cancer stem cells (CSCs) play an important role in shaping the invasive cancer phenotype by contributing to tumor initiation, metastasis, relapse, and therapeutic resistance in non-small cell lung cancer (NSCLC). The Aryl hydrocarbon receptor (AhR), a ligand activated transcription factor, which is well known for mediating the toxicity and tumorigenesis of a variety of environmental pollutants, has been extensively recognized as an important mediator in NSCLC development. Here, evidence showed that AhR was overexpressed in NSCLC tissues, and a high AhR protein level was associated with an aggressive tumor phenotype. Knockdown of AhR suppressed cell proliferation, invasion and migration, as well as CSC-like properties, while upregulation and activation of AhR enhanced CSC-like properties and increased stem cell-associated gene expression in NSCLC cells. Elevated and activated AhR leads to phosphorylation of janus kinase 2 (Jak2), as well as its downstream effector, activator of transcription 3 (STAT3), while inhibition of Jak2/STAT3 signaling by pharmacologic approach attenuates the effects of AhR-mediated NSCLC cell stemness, suggesting a role for the Jak2/STAT3 pathway in AhR-regulated NSCLC stemness. In summary, our study uncovers a transcriptional-independent mechanism of AhR through which AhR mediates NSCLC stemness via Jak2/STAT3 signaling pathway, indicating a promising target for the treatment of NSCLC.

The deubiquitylase UCHL3 maintains cancer stem-like properties by stabilizing the aryl hydrocarbon receptor

Cancer stem cells (CSCs) exhibit highly aggressive and metastatic features and resistance to chemotherapy and radiotherapy. Aryl hydrocarbon receptor (AhR) expression varies among non-small cell lung cancers (NSCLCs), and the mechanisms that support abnormal AhR expression in CSCs remain elusive. Here, we identified ubiquitin carboxyl terminal hydrolase L3 (UCHL3), a DUB enzyme in the UCH protease family, as a bona fide deubiquitylase of the AhR in NSCLC. UCHL3 was shown to interact with, deubiquitylate, and stabilize AhR in a manner dependent on its deubiquitylation activity. Moreover, we showed that UCHL3 promotes the stem-like characteristics and potent tumorigenic capacity of NSCLC cells. UCHL3 increased AhR stability and the binding of AhR to the promoter regions of the “stemness” genes ATP-binding cassette subfamily G member 2 (ABCG2), KLF4, and c-Myc. Depletion of UCHL3 markedly downregulated the “stemness” genes ABCG2, KLF4, and c-Myc, leading to the loss of self-renewal and tumorigenesis in NSCLCs. Furthermore, the UCHL3 inhibitor TCID induced AhR degradation and exhibited significantly attenuated efficacy in NSCLC cells with stem cell-like properties. Additionally, UCHL3 was shown to indicate poor prognosis in patients with lung adenocarcinoma. In general, our results reveal that the UCHL3 deubiquitylase is pivotal for AhR protein stability and a potential target for NSCLC-targeted therapy.

Live-cell screening platform using human-induced pluripotent stem cells expressing fluorescence-tagged cytochrome P450 1A1

Human-induced pluripotent stem cells (hiPSCs) are invaluable sources for drug screening and toxicity tests because of their differentiation potential and proliferative capacity. Recently, the CRISPR-Cas9-mediated homologous recombination system has enabled reporter knock-ins at desired loci in hiPSCs, and here, we generated a hiPSC reporter line expressing mCherry-tagged cytochrome P450 1A1 (CYP1A1), which can be utilized to screen for the modulators of aryl hydrocarbon receptor (AHR) in live cells. CYP1A1-mCherry hiPSCs exhibited typical characteristics of pluripotent stem cells such as marker expression, differentiation potential, and normal karyotype. After differentiation into hepatocyte-like cells (HLCs), CYP1A1-mCherry fusion protein was expressed and localized at the endoplasmic reticulum, and induced by AHR agonists. We obtained 23 hits modulating CYP1A1 expression from high-content screening with 241 hepatotoxicity chemicals and nuclear receptor ligands, and identified three upregulating chemicals and two downregulating compounds. Responses of hiPSC-HLCs against an AHR agonist were more similar to human primary hepatocytes than of HepG2 hepatocellular carcinoma cells. This platform has the advantages of live-cell screening without sacrificing cells (unlike previously available CYP1A1 reporter cell lines), as well as an indefinite supply of cells, and can be utilized in a wide range of screening related to AHR- and CYP1A1-associated diseases in desired cell types.

CYP1B1 gene: Implications in glaucoma and cancer

Glaucoma is a serious disease that can lead to irreversible loss of vision. Patients with primary congenital glaucoma may have elevated intraocular pressure. Hypertension causes damages to intraocular structures and affects the Schlemm's canal, collector channels, trabecular meshwork, and optic nerve's molecular structures. An important gene that is defective in patients with glaucoma is CYP1B1, a gene associated with optic nerve deterioration. CYP1B1is a key enzyme involved in the metabolism of exogenous and endogenous compounds. Also, it is critical in the detoxification of pre-carcinogens, such as polycyclic aromatic hydrocarbons and estrogen. It catalyzes their conversion into metabolites subsequently eliminated from the body. In malignant tumors, the CYP1B1 promoter is hypomethylated. CYP1B1 overexpression results in the conversion of estrogens to quinone forms, which bind with DNA and create a predisposition for cancer in several organs, such as the brain, breast, and ovary. Increased cytokine interleukin-6 and leptin lead to elevated CYP1B1 activity, which possibly causes cancer. In addition, the expression of aromatic hydrocarbon receptors is increased in tumor tissues, and it elevates oxidative stress and cell growth. TCGA database analysis showed increased survival at bladder and renal carcinoma when CYP1B1 expression is low. Therefore, alteration of CYP1B1 expression may suggest a therapeutic benefit for multiple diseases such as glaucoma and cancer.

TCDD inhibited the osteogenic differentiation of human fetal palatal mesenchymal cells through AhR and BMP-2/TGF-β/Smad signaling

Exposure to environmental toxicant 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) causes cleft palate at high rates, but little is known about the underlying biological mechanisms. In the present study, we cultured osteoblasts from human fetal palate mesenchymal cells (hFPMCs) to explore the effects of TCDD on osteogenic differentiation. The results showed that TCDD significantly decreased cell proliferation, alkaline phosphatase (ALP) activity and calcium deposition. RNA analyses and protein detection demonstrated that TCDD downregulated a wide array of pro-osteogenic biomarkers. Further investigation of the underlying molecular mechanisms revealed that exposure to TCDD activated aryl hydrocarbon receptor (AhR) signaling and inhibited BMP-2/TGF-β1/Smad pathway molecules. The inactivation of AhR signaling using CRISPR/Cas9-mediated AhR deletion or by genetic siRNA knockdown significantly blocked the effects induced by TCDD, suggesting a critical role of AhR activation in the TCDD-mediated inhibition of hFPMC osteogenic differentiation. The cotreatment with TGF-β1 or BMP-2 and TCDD significantly relieved the activation of AhR and rescued the impairment of osteogenesis caused by TCDD. Taken together, our findings indicated that TCDD inhibited the osteogenic differentiation of hFPMCs via crosstalk between AhR and BMP-2/TGF-β1/Smad signaling pathway.

Biomarkers of Exposure and Effect in the Lungs of Smokers, Nonsmokers, and Electronic Cigarette Users

BACKGROUND

Nicotine-containing electronic cigarette (e-cig) use has become widespread. However, understanding the biological impact of e-cigs compared with smoking on the lung is needed. There are major gaps in knowledge for chronic effects and for an etiology to recent acute lung toxicity leading to death among vapers.

METHODS

We conducted bronchoscopies in a cross-sectional study of 73 subjects (42 never-smokers, 15 e-cig users, and 16 smokers). Using bronchoalveolar lavage and brushings, we examined lung inflammation by cell counts, cytokines, genome-wide gene expression, and DNA methylation.

RESULTS

There were statistically significant differences among never-smokers, e-cig users, and smokers for inflammatory cell counts and cytokines (FDR q < 0.1). The e-cig users had values intermediate between smokers and never-smokers, with levels for most of the biomarkers more similar to never-smokers. For differential gene expression and DNA methylation, e-cig users also more like never-smokers; many of these genes corresponded to smoking-related pathways, including those for xenobiotic metabolism, aryl hydrocarbon receptor signaling, and oxidative stress. Differentially methylated genes were correlated with changes in gene expression, providing evidence for biological effects of the methylation associations.

CONCLUSIONS

These data indicate that e-cigs are associated with less toxicity than cigarettes for smoking-related pathways. What is unknown may be unique effects for e-cigs not measured herein, and a comparison of smokers completely switching to e-cigs compared with former smokers. Clinical trials for smokers switching to e-cigs who undergo serial bronchoscopy and larger cross-sectional studies of former smokers with and without e-cig use, and for e-cigs who relapse back to smoking, are needed.

IMPACT

These data can be used for product regulation and for informing tobacco users considering or using e-cigs. What is unknown may be unique effects for e-cigs not measured herein, and clinical trials with serial bronchoscopy underway can demonstrate a direct relationship for changes in lung biomarkers.

The role of AhR in transcriptional regulation of immune cell development and function

The aryl hydrocarbon receptor (AhR) is a ligand-activated transcriptional factor (TF) that is a member of the Per-Arnt-Sim family of proteins. AhR regulates diverse processes, including malignant transformation, hematopoietic cell development, and fate determination of immune cell lineages. Moreover, AhR forms a crucial link between innate and adaptive arms of the immune system. Malignant cells frequently evolve multiple mechanisms for suppressing tumor-specific responses, including the induction of suppressive pathways involving AhR and its metabolic byproducts in the tumor microenvironment that promote immune evasion and tumor progression. Thus, interest is high in further defining the role of AhR in carcinogenesis and immune development and regulation, particularly regarding the therapeutic interventions that unleash immune responses to cancer cells. Here, we provide an overview of the role of AhR in the regulation of innate and adaptive immune response and discuss the implications of targeting this pathway to augment the immune response in cancer patients.

Effect of Dioxins in Milk on the 3D Cultured Primary Buffalo Hepatocyte Model System

Cow and human milk have been reported to contain dioxins ranging from 0.023 to 26.46 and 0.88 to 19 pg/g of fat, respectively. However, the toxic effects of the dioxins in the milk in this range of concentrations were not explored. Therefore, considering the outbred livestock tissues as better models than inbred laboratory animals, the present study targeted to study the effect of dioxins present in the milk on three-dimensionally (3D) cultured buffalo primary hepatocyte spheroids. The spheroids were treated with a model dioxin, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), directly and also through milk fat at different concentrations (i.e, 0.02-20 pg/mL) for 24 h. Among the liver-cell-specific (ALB, HNF4α, and AFP) genes, a similar ALB and upregulated HNF4α expression at all treatments indicated the functional and transcriptionally active hepatocyte spheroids. Supportingly, no significant difference in the antiapoptotic gene expression between the treatments of milk fat and milk fat containing dioxins indicated the survivability of the spheroids during dioxin treatments. Among the selected TCDD responsive (CYP1A1, CYP1A2, AHR, CYP1B1, and TIPARP) genes, a nonsignificant increasing trend of the CYP1A1 expression was observed from 0.2 to 10 pg/mL of TCDD concentration through milk fat. This pattern was similar to the reported insensitive response of human primary hepatocytes toward dioxins than that of rat primary hepatocytes. This may indicate that the buffalo hepatocyte spheroids could be better models than rats for TCDD hepatotoxic studies. Further, TCDD in the milk in the range of 0.02-20 pg/mL concentration may not be very hepatotoxic.

Involvement of Aryl Hydrocarbon Receptor in L-Kynurenine-Mediated Parathyroid Hormone-Related Peptide Expression

Parathyroid hormone-related peptide (PTHrP), produced by specific cancers such as lung cancer, profoundly influences the formation of bone metastatic lesions via the "vicious cycle" of tumor growth and bone resorption. The changes in gene expression regulated by the abnormal microenvironment components play key roles in maintaining the biological characteristics of cells, such as the organotropism of cancer metastasis. A recent study has shown that L-kynurenine (L-Kyn), one of microenvironment components, induced a substantial increase in the metastasis of lung cancer cells. What remains unclear, however, is the linkage between L-Kyn and bone metastatic lesions. In the present paper, we found that a significant upregulation of PTHrP expression was detected when 95D cells, a lung cancer cell line, were incubated with 50 μM of L-Kyn. Meanwhile, L-Kyn (50/100 μM) strongly strengthened aryl hydrocarbon receptor (Ahr) expression. Additionally, L-Kyn (50 μM) increased the expression of the nuclear translocation of Ahr and cytochrome P450 1A1. Most importantly, the L-Kyn-induced upregulation of migration was significantly reduced when cells were co-incubated with siRNA_Ahr. Notably, the L-Kyn-mediated increase in PTHrP was also substantially attenuated upon siRNA_Ahr treatment in 95D cells. These results suggest that Ahr is involved in the L-Kyn-induced enhancement of PTHrP expression.

Marine biogenics in sea spray aerosols interact with the mTOR signaling pathway

Sea spray aerosols (SSAs) have profound effects on our climate and ecosystems. They also contain microbiota and biogenic molecules which could affect human health. Yet the exposure and effects of SSAs on human health remain poorly studied. Here, we exposed human lung cancer cells to extracts of a natural sea spray aerosol collected at the seashore in Belgium, a laboratory-generated SSA, the marine algal toxin homoyessotoxin and a chemical inhibitor of the mammalian target of rapamycin (mTOR) pathway. We observed significant increased expression of genes related to the mTOR pathway and Proprotein convertase subtilisin/kexin type 9 (PCSK9) after exposure to homoyessotoxin and the laboratory-generated SSA. In contrast, we observed a significant decrease in gene expression in the mTOR pathway and of PCSK9 after exposure to the natural SSA and the mTOR inhibitor, suggesting induction of apoptosis. Our results indicate that marine biogenics in SSAs interact with PCSK9 and the mTOR pathway and can be used in new potential pharmaceutical applications. Overall, our results provide a substantial molecular evidence base for potential beneficial health effects at environmentally relevant concentrations of natural SSAs.

Mediation effect of AhR expression between polycyclic aromatic hydrocarbons exposure and oxidative DNA damage among Chinese occupational workers

Polycyclic aromatic hydrocarbons (PAH) are well-known to be carcinogenic and the mechanisms that it contributes to oxidative DNA damage and aryl hydrocarbon receptor (AhR)-dependent induction are also well understood. However, little is known about the associations between PAH exposure, AhR expression, and oxidative DNA damage. We investigated their associations of AhR expression and oxidative DNA damage related to PAH exposure among 310 workers from a coke-oven plant in China. Urine biomarkers of PAH exposure (2-hydroxynaphthalene, 2-NAP; 2-hydroxyfluorene, 2-FLU; 9-hydroxyphenanthren, 9-PHE; and 1-hydroxypyrene, 1-OHP) and a marker of oxidative damage (8-hydroxy- 2'- deoxyguanosine, 8-OHdG) were measured by high performance liquid chromatography. AhR expression in venous blood was measured by reverse transcription -polymerase chain reaction. The results showed that increasing levels of urinary 1-OHP was positively associated with high 8-OHdG (OR (95% CI) was 4.01 (1.41-11.45) for 4th quartile, compared with 1st quartile, P for trend = 0.013). The similar associations were also found between urinary 1-OHP and high-AhR expressions (4th vs. 1st quartile = 3.50, 95% CI: 1.24-9.87, P for trend = 0.029). A significant association between AhR expression and high 8-OHdG was also found (4th vs. 1st quartile = 2.44, 95% CI: 1.05-5.70, P for trend = 0.027). In addition, mediation analysis showed the AhR expression could explain 35.9% of the association of oxidative DNA damage related to PAH exposure. Our findings implicated that the association between PAH exposure and oxidative DNA damage may be mediated by AhR expression among Chinese occupational workers.

Aryl Hydrocarbon Receptor (AhR) Ligands as Selective AhR Modulators: Genomic Studies

The aryl hydrocarbon receptor (AhR) binds structurally diverse ligands that vary from the environmental toxicant 2,3,7,8-tetrachlorodibenzo-B-dioxin (TCDD) to AhR- active pharmaceuticals and health-promoting phytochemicals. There are remarkable differences in the toxicity of TCDD and related halogenated aromatics (HAs) vs. health promoting AhR ligands, and genomic analysis shows that even among the toxic HAs, there are differences in their regulation of genes and pathways. Thus, like ligands for other receptors, AhR ligands are selective AhR modulators (SAhRMs) which exhibit variable tissue-, organ- and species-specific genomic and functional activities.

[Aryl-hydrocarbon receptor as a potential target for anticancer therapy]

Aryl-hydrocarbon receptor (Aryl Hydrocarbon Receptor, AHR) is a ligand-dependent transcription factor, whose functions are related to xenobiotic detoxification, response to inflammation, and maintenance of tissue homeostasis. Recent investigations suggest that AHR also plays an important role in the processes of carcinogenesis. Increased expression of AHR is observed in several types of tumors and tumor cell lines. In addition, it turned out that the composition of pharmaceutical drugs used in oncotherapy includes some ligands AHR. These facts allow us to consider an aryl-hydrocarbon receptor as a potential target for anticancer therapy, especially for the treatment of severe cancers whose treatment options are very limited or do not exist at all. In this review the examples of AHR ligands' effect on tumor cell cultures and on model mice lines with AHR-dependent response are discussed.

Towards Resolving the Pro- and Anti-Tumor Effects of the Aryl Hydrocarbon Receptor

We have postulated that the aryl hydrocarbon receptor (AHR) drives the later, more lethal stages of some cancers when chronically activated by endogenous ligands. However, other studies have suggested that, under some circumstances, the AHR can oppose tumor aggression. Resolving this apparent contradiction is critical to the design of AHR-targeted cancer therapeutics. Molecular (siRNA, shRNA, AHR repressor, CRISPR-Cas9) and pharmacological (AHR inhibitors) approaches were used to confirm the hypothesis that AHR inhibition reduces human cancer cell invasion (irregular colony growth in 3D Matrigel cultures and Boyden chambers), migration (scratch wound assay) and metastasis (human cancer cell xenografts in zebrafish). Furthermore, these assays were used for a head-to-head comparison between AHR antagonists and agonists. AHR inhibition or knockdown/knockout consistently reduced human ER⁻/PR⁻/Her2⁻ and inflammatory breast cancer cell invasion, migration, and metastasis. This was associated with a decrease in invasion-associated genes (e.g., Fibronectin, VCAM1, Thrombospondin, MMP1) and an increase in CDH1/E-cadherin, previously associated with decreased tumor aggression. Paradoxically, AHR agonists (2,3,7,8-tetrachlorodibenzo-p-dioxin and/or 3,3′-diindolylmethane) similarly inhibited irregular colony formation in Matrigel and blocked metastasis in vivo but accelerated migration. These data demonstrate the complexity of modulating AHR activity in cancer while suggesting that AHR inhibitors, and, under some circumstances, AHR agonists, may be useful as cancer therapeutics.

The Aryl Hydrocarbon Receptor and Tumor Immunity

The aryl hydrocarbon receptor (AhR) is an important cytosolic, ligand-dependent transcription factor. Emerging evidence suggests the promoting role of the AhR in the initiation, promotion, progression, invasion, and metastasis of cancer cells. Studies on various tumor types and tumor cell lines have shown high AhR expression, suggesting that AhR is activated constitutively in tumors and facilitates their growth. Interestingly, immune evasion has been recognized as an emerging hallmark feature of cancer. A connection between the AhR and immune system has been recognized, which has been suggested as an immunosuppressive effector on different types of immune cells. Certain cancers can escape immune recognition via AhR signaling pathways. This review discusses the role of the AhR in tumor immunity and its potential mechanism of action in the tumor microenvironment.

Activation of the Aryl Hydrocarbon Receptor Leads to Resistance to EGFR TKIs in Non-Small Cell Lung Cancer by Activating Src-mediated Bypass Signaling

Purpose: The aryl hydrocarbon receptor (AhR) has been generally recognized as a ligand-activated transcriptional factor that responds to xenobiotic chemicals. Recent studies have suggested that the expression of AhR varies widely across different cancer types and cancer cell lines, but its significance in cancer treatment has yet to be clarified.Experimental Design: AhR expression in non-small cell lung cancer (NSCLC) was determined by Western blotting and IHC staining. In vitro and in vivo functional experiments were performed to determine the effect of AhR on sensitivity to targeted therapeutics. A panel of biochemical assays was used to elucidate the underlying mechanisms.Results: A high AhR protein level indicated an unfavorable prognosis for lung adenocarcinoma. Inhibition of AhR signaling sensitized EGFR tyrosine kinase inhibitors (TKIs) in NSCLC cells that express high level of endogenous AhR protein. Notably, activation of AhR by pharmacologic and molecular approaches rendered EGFR-mutant cells resistant to TKIs by restoring PI3K/Akt and MEK/Erk signaling through activation of Src. In addition, we found that AhR acts as a protein adaptor to mediate Jak2-Src interaction, which does not require the canonical transcriptional activity of AhR.Conclusions: Our results reveal a transcription-independent function of AhR and indicate that AhR may act as a protein adaptor that recruits kinases bypassing EGFR and drives resistance to TKIs. Accordingly, targeting Src would be a strategy to overcome resistance to EGFR TKIs in AhR-activated NSCLC. Clin Cancer Res; 24(5); 1227-39. ©2017 AACR.

Role of the aryl hydrocarbon receptor in carcinogenesis and potential as an anti-cancer drug target

The aryl hydrocarbon receptor (AhR) was initially identified as the receptor that binds and mediates the toxic effects induced by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and structurally related halogenated aromatics. Other toxic compounds including some polynuclear aromatic hydrocarbons act through the AhR; however, during the last 25 years, it has become apparent that the AhR plays an essential role in maintaining cellular homeostasis. Moreover, the scope of ligands that bind the AhR includes endogenous compounds such as multiple tryptophan metabolites, other endogenous biochemicals, pharmaceuticals and health-promoting phytochemicals including flavonoids, indole-3-carbinol and its metabolites. It has also been shown that like other receptors, the AhR is a drug target for multiple diseases including cancer, where both AhR agonists and antagonists effectively block many of the critical hallmarks of cancer in multiple tumor types. This review describes the anti-cancer activities of AhR ligands and demonstrates that it is time to separate the AhR from TCDD and exploit the potential of the AhR as a novel target for cancer chemotherapy.

Diesel exhaust particles (DEP) pre-exposure contributes to the anti-oxidant response impairment in hCMEC/D3 during post-oxygen and glucose deprivation damage

Recently, air pollution has been identified as a significant modifiable risk factor to the increasing stroke burden. Diesel exhaust particles, characterized by high polycyclic aromatic hydrocarbons content, constitute an important component of outdoor air pollution and is known to cause oxidative stress, and could therefore contribute to and exacerbate the effects of ROS in post-ischemic injury. hCMEC/D3 cells have been submitted to 48h treatment with diesel exhaust particles (25μg/ml and 50μg/ml, DEP50) or alternatively to 3h of oxygen and glucose deprivation, followed by 1h of oxygen and glucose restoration. The combined treatment consisted in 48h of diesel exhaust particles (25μg/ml and 50μg/ml, DEP50) followed by 3h of oxygen and glucose deprivation and 1h of restoration. A panel of markers related to oxidative stress and inflammatory responses, such as transcription factors (Nrf2 and HIF-1α), anti-oxidant proteins (HO-1, SOD-1, Hsp70) and proteins potentially inducing further oxidative-stress or inflammation (Cyp1b1, iNOS, COX-2, TNF-α, IL-1α, IL-1β, IL-8, VEGF), have been examined. Data obtained showed that diesel exhaust particles and oxygen and glucose deprivation treatments alone elicited the antioxidants response, each by means of a different transcription factor, while the combined treatment led to a dysregulation of the antioxidant response during ischemic injury reperfusion.

Involvement of the cytokine-IDO1-AhR loop in zinc oxide nanoparticle-induced acute pulmonary inflammation

Zinc oxide nanoparticles (ZnONPs) are widely used in our daily life, such as in sunscreens and electronic nanodevices. However, pulmonary exposure to ZnONPs causes acute pulmonary inflammation, which is considered as an initial event for various respiratory diseases. Thus, elucidation of the underlying cellular mechanisms of ZnONPs can help us in predicting their potential effects in respiratory diseases. In this study, we observed that ZnONPs increased proinflammatory cytokines, accompanied with an increased expression of aryl hydrocarbon receptor (AhR) and its downstream target cytochrome P450 1A1 (CYP1A1) in macrophages in vitro and in mouse lung epithelia in vivo. Moreover, zinc nitrate, but not silica or titanium dioxide nanoparticles (NPs), had similar effects on macrophages, indicating that the zinc element or ion released from ZnONPs is likely responsible for the activation of the AhR pathway. Cotreatment with an AhR antagonist or AhR knockout reduced ZnONPs-induced cytokine secretion in macrophages or mice, respectively. Furthermore, kynurenine (KYN), an endogenous AhR agonist and a tryptophan metabolite catalyzed by indoleamine 2,3-dioxygenase (IDO), was increased in the serums of mice that aspirated ZnONPs. Consistently, ZnONPs increased IDO1 expression in lung cells in vitro and in vivo. Finally, AhR knockout reduced ZnONPs-induced pulmonary inflammation, cytokine secretion and KYN production in mice, suggesting that AhR activation is involved in ZnONPs-induced cytokine secretion and pulmonary inflammation. In summary, we demonstrated that the pulmonary exposure of ZnONPs stimulated the cytokine-IDO1-AhR loop in the lungs, which has been implied to play roles in immune dysfunctions.

An Aryl Hydrocarbon Receptor-Mediated Amplification Loop That Enforces Cell Migration in ER-/PR-/Her2- Human Breast Cancer Cells

The endogenous ligand-activated aryl hydrocarbon receptor (AHR) plays an important role in numerous biologic processes. As the known number of AHR-mediated processes grows, so too does the importance of determining what endogenous AHR ligands are produced, how their production is regulated, and what biologic consequences ensue. Consequently, our studies were designed primarily to determine whether ER⁻/PR⁻/Her2⁻ breast cancer cells have the potential to produce endogenous AHR ligands and, if so, how production of these ligands is controlled. We postulated that: 1) malignant cells produce tryptophan-derived AHR ligand(s) through the kynurenine pathway; 2) these metabolites have the potential to drive AHR-dependent breast cancer migration; 3) the AHR controls expression of a rate-limiting kynurenine pathway enzyme(s) in a closed amplification loop; and 4) environmental AHR ligands mimic the effects of endogenous ligands. Data presented in this work indicate that primary human breast cancers, and their metastases, express high levels of AHR and tryptophan-2,3-dioxygenase (TDO); representative ER⁻/PR⁻/Her2⁻ cell lines express TDO and produce sufficient intracellular kynurenine and xanthurenic acid concentrations to chronically activate the AHR. TDO overexpression, or excess kynurenine or xanthurenic acid, accelerates migration in an AHR-dependent fashion. Environmental AHR ligands 2,3,7,8-tetrachlorodibenzo[p]dioxin and benzo[a]pyrene mimic this effect. AHR knockdown or inhibition significantly reduces TDO2 expression. These studies identify, for the first time, a positive amplification loop in which AHR-dependent TDO2 expression contributes to endogenous AHR ligand production. The net biologic effect of AHR activation by endogenous ligands, which can be mimicked by environmental ligands, is an increase in tumor cell migration, a measure of tumor aggressiveness.

Genetic variants of the CYP1B1 gene as predictors of biochemical recurrence after radical prostatectomy in localized prostate cancer patients

Clinically localized prostate cancer is curative. Nevertheless many patients suffered from biochemical recurrence (BCR) after radical prostatectomy (RP). Mounting evidence suggest that estrogen and xenobiotic carcinogens play an essential role in progression of prostate cancervia oxidative estrogen metabolism. CYP1B1 is an enzyme involved in the hydroxylation of estrogens, a reaction of key relevance in estrogen metabolism. Given the role of CYP1B1 in the oxidative metabolism of endogenous/exogenous estrogen and compounds, CYP1B1 polymorphisms have the potential to modify its expression and subsequently lead to progression. We hypothesize that genetic variants of the CYP1B1 gene may influence clinical outcome in clinically localized prostate cancer patients. In this cohort study, we genotyped 9 tagging single nucleotide polymorphisms (SNPs) from the CYP1B1 gene in 312 patients treated with RP. For replication, these SNPs were genotyped in an independent cohort of 426 patients. The expression level of CYP1B1 in the adjacent normal prostate tissues was quantified by reverse transcription and real-time polymerase chain reaction. Kaplan-Meier analysis and Cox proportional hazard models were utilized to identify SNPs that correlated with BCR. CYP1B1 rs1056836 was significantly associated with BCR (hazard ratio [HR]: 0.69; 95% confidence interval [CI]: 0.40-0.89, P = 0.002) and relative CYP1B1 mRNA expression. Our findings suggest inherited genetic variation in the CYP1B1 gene may contribute to variable clinical outcomes for patients with clinically localized prostate cancer.

The role of the aryl hydrocarbon receptor in the development of cells with the molecular and functional characteristics of cancer stem-like cells

BACKGROUND

Self-renewing, chemoresistant breast cancer stem cells are believed to contribute significantly to cancer invasion, migration and patient relapse. Therefore, the identification of signaling pathways that regulate the acquisition of stem-like qualities is an important step towards understanding why patients relapse and towards development of novel therapeutics that specifically target cancer stem cell vulnerabilities. Recent studies identified a role for the aryl hydrocarbon receptor (AHR), an environmental carcinogen receptor implicated in cancer initiation, in normal tissue-specific stem cell self-renewal. These studies inspired the hypothesis that the AHR plays a role in the acquisition of cancer stem cell-like qualities.

RESULTS

To test this hypothesis, AHR activity in Hs578T triple negative and SUM149 inflammatory breast cancer cells were modulated with AHR ligands, shRNA or AHR-specific inhibitors, and phenotypic, genomic and functional stem cell-associated characteristics were evaluated. The data demonstrate that (1) ALDH(high) cells express elevated levels of Ahr and Cyp1b1 and Cyp1a1, AHR-driven genes, (2) AHR knockdown reduces ALDH activity by 80%, (3) AHR hyper-activation with several ligands, including environmental ligands, significantly increases ALDH1 activity, expression of stem cell- and invasion/migration-associated genes, and accelerates cell migration, (4) a significant correlation between Ahr or Cyp1b1 expression (as a surrogate marker for AHR activity) and expression of stem cell- and invasion/migration-associated gene sets is seen with genomic data obtained from 79 human breast cancer cell lines and over 1,850 primary human breast cancers, (5) the AHR interacts directly with Sox2, a master regulator of self-renewal; AHR ligands increase this interaction and nuclear SOX2 translocation, (6) AHR knockdown inhibits tumorsphere formation in low adherence conditions, (7) AHR inhibition blocks the rapid migration of ALDH(high) cells and reduces ALDH(high) cell chemoresistance, (8) ALDH(high) cells are highly efficient at initiating tumors in orthotopic xenografts, and (9) AHR knockdown inhibits tumor initiation and reduces tumor Aldh1a1, Sox2, and Cyp1b1 expression in vivo.

CONCLUSIONS

These data suggest that the AHR plays an important role in development of cells with cancer stem cell-like qualities and that environmental AHR ligands may exacerbate breast cancer by enhancing expression of these properties.

Diastereoisomer-specific effects of hexabromocyclododecanes on hepatic aryl hydrocarbon receptors and cytochrome P450s in zebrafish (Danio rerio)

In order to elucidate the mechanism for diastereoisomer-specific toxicity and metabolism of hexabromocyclododecanes (HBCDs) in biota, zebrafish (Danio rerio) were exposed to different concentrations of individual HBCD diastereoisomers (α-, β- and γ-HBCD) in water for 7 and 21d. We examined the gene expression of aryl hydrocarbon receptor (AHR) and cytochrome P450 (CYP), as well as ethoxyresorufin-O-deethylase (EROD) activity in zebrafish livers. Exposure to different HBCD diastereoisomers caused different expression of AHRs in zebrafish livers. For instance, 10 and 100μgL(-1) of α- and β-HBCD up-regulated the expressions of ahr1a and ahr1b in zebrafish liver, whereas 10 and 100μgL(-)(1) of γ-HBCD down-regulated them after 7d exposure. α-HBCD showed the most significant up-regulation of ahr1a and ahr1b expression, whereas γ-HBCD showed the most significant down-regulation of their expression among three HBCD diastereoisomers. Moreover, HBCDs could affect the expression of CYP1s as well as EROD activity in a gene-specific and diastereoisomer-specific manner. α-, β- and γ-HBCD inhibited cyp1a expression but enhanced the expression of cyp1b1 and cyp1c1. α-, β- and γ-HBCD showed different degrees of effect on the same CYP1 gene in a concentration-dependent way. The different effects of HBCD diastereoisomers on these genes we examined and EROD activity not only indicate diastereoisomer-specific toxic effect, but also in turn explain diastereoisomer-specific accumulation of HBCDs in zebrafish.

Glaucoma in iran and contributions of studies in iran to the understanding of the etiology of glaucoma

Epidemiologic and genetic/molecular research on glaucoma in Iran started within the past decade. A population-based study on the epidemiology of glaucoma in Yazd, a city in central Iran, revealed that 4.4% of studied individuals were affected with glaucoma: 1.6% with high tension primary open angle glaucoma (POAG), 1.6% with normal tension POAG, and 0.4% each with primary angle closure glaucoma (PACG) and pseudoexfoliation glaucoma (PEXG), and other types of secondary glaucoma. Two notable observations were the relatively high frequency of normal tension glaucoma cases (1.6%) and the large fraction of glaucoma affected individuals (nearly 90%) who were unaware of their condition. The first and most subsequent genetic studies on glaucoma in Iran were focused on primary congenital glaucoma (PCG) showing that cytochrome P450 1B1 (CYP1B1) is the cause of PCG in the majority of Iranian patients, many different CYP1B1 mutations are present among Iranian patients but only four mutations constitute the vast majority, and the origins of most mutations in the Iranians are identical by descent (IBD) with the same mutations in other populations. Furthermore, most of the PCG patients are from the northern and northwestern provinces of Iran. A statistically significant male predominance of PCG was observed only among patients without CYP1B1 mutations. Clinical investigations on family members of PCG patients revealed that CYP1B1 mutations exhibit variable expressivity, but almost complete penetrance. A great number of individuals harboring CYP1B1 mutations become affected with juvenile onset POAG. Screening of JOAG patients showed that an approximately equal fraction of the patients harbor CYP1B1 and (myocilin) MYOC mutations; MYOC is a well-known adult onset glaucoma causing gene. Presence of CYP1B1 mutations in JOAG patients suggests that in some cases, the two conditions may share a common etiology. Further genetic analysis of Iranian PCG patients led to identification of Latent-transforming growth factor beta-binding protein 2 (LTBP2) as a causative gene for both PCG and several diseases which are often accompanied by glaucomatous presentations, such as Weill-Marchesani syndrome 3 (WMS3). The findings on LTBP2 have contributed to recognize the importance of the extracellular matrix in pathways leading to glaucoma.

Expression of CYP1A1 and GSTP1 in human brain tumor tissues in Pakistan

Most of the exogenous and endogenous chemical compounds are metabolized by enzymes of xenobiotic processing pathways, including the phase I cytochrome p450 species. Carcinogens and their metabolites are generally detoxified by phase II enzymes like glutathione-S-transferases (GST). The balance of enzymes determines whether metabolic activation of pro-carcinogens or inactivation of carcinogens occurs. Under certain conditions, deregulated expression of xenobiotic enzymes may also convert endogenous substrates to metabolites that can facilitate DNA adduct formation and ultimately lead to cancer development. In this study, we aimed to test the association between deregulation of metabolizing genes and brain tumorigenesis. The expression profile of metabolizing genes CYP1A1 and GSTP1 was therefore studied in a cohort of 36 brain tumor patients and controls using Western blotting. In a second part of the study we analyzed protein expression of GSTs in the same study cohort by ELISA. CYP1A1 expression was found to be significantly high (p<0.001) in brain tumor as compared to the normal tissues, with ~4 fold (OR=4, 95%CI=0.43-37) increase in some cases. In contrast, the expression of GSTP1 was found to be significantly low in brain tumor tissues as compared to the controls (p<0.02). This down regulation was significantly higher (OR=0.05, 95%CI=0.006-0.51; p<0.007) in certain grades of lesions. Furthermore, GSTs levels were significantly down-regulated (p<0.014) in brain tumor patients compared to controls. Statistically significant decrease in GST levels was observed in the more advanced lesions (III-IV, p<0.005) as compared to the early tissue grades (I-II). Thus, altered expression of these xenobiotic metabolizing genes may be involved in brain tumor development in Pakistani population. Investigation of expression of these genes may provide information not only for the prediction of individual cancer risk but also for the prevention of cancer.

Aryl hydrocarbon receptor in breast cancer—a newly defined prognostic marker

Aryl hydrocarbon receptor (AhR) has been reported to exert various anticancer effects upon breast carcinoma cells in vitro but its details have remained largely unknown. Therefore, we first examined the AhR status in 90 invasive ductal carcinoma patients using immunohistochemistry. We then performed in vitro studies including wound healing assay, invasion assay, and matrix metalloproteinase (MMP) protein array in order to further elucidate the roles of AhR signaling in breast carcinoma. The status of AhR immunoreactivity was inversely correlated with histological grade (P = 0.0135) and Ki-67 labeling index (LI; P = 0.0087) of the patients. In addition, results of both uni- and multivariate analyses revealed that AhR in carcinoma cells turned out an independent prognostic factor with a protective relative risk (P = 0.0179). An administration of 10 nM 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), a ligand of AhR, significantly decreased Ki-67 LI in an AhR-dependent fashion in MCF-7, T47D, ZR75-1, and MDA-MB-231. Wound healing and invasion assays performed in T47D and ZR75-1 further demonstrated that 10 nM TCDD inhibited estrogen-induced migration and invasion of cells. MMP proteins associated with AhR in breast carcinoma cells were also firstly identified. These results demonstrated that AhR in breast carcinoma cells is considered a newly defined histological prognostic parameter of the breast cancer patients and effects of AhR activation on proliferation and MMPs expression may be related to the relatively good clinical outcome of AhR-positive breast cancer patients.

The aryl hydrocarbon receptor is constitutively active in advanced prostate cancer cells

Background

Distant prostate cancers are commonly hormone refractory and exhibit increased growth no longer inhibited by androgen deprivation therapy. Understanding all molecular mechanisms contributing to uncontrolled growth is important to obtain effective treatment strategies for hormone refractory prostate cancers (HRPC). The aryl hydrocarbon receptor (AhR) affects a number of biological processes including cell growth and differentiation. Several studies have revealed that exogenous AhR ligands inhibit cellular proliferation but recent evidence suggests AhR may possess intrinsic functions that promote cellular proliferation in the absence of exogenous ligands.

Methods/Results

qRT-PCR and western blot analysis was used to determine AhR mRNA and protein expression in hormone sensitive LNCaP cells as well as hormone refractory DU145, PC3 and PC3M prostate cancer cell lines. LNCaP cells express AhR mRNA and protein at a much lower level than the hormone refractory cell models. Cellular fractionation and immunocytochemistry revealed nuclear localization of AhR in the established hormone refractory cell lines while LNCaP cells are devoid of nuclear AhR protein. qRT-PCR analysis used to assess basal CYP1B1 levels and a xenobiotic responsive element binding assay confirmed ligand independent transcriptional activity of AhR in DU145, PC3 and PC3M cells. Basal CYP1B1 levels were decreased by treatment with specific AhR inhibitor, CH223191. An in vitro growth assay revealed that CH223191 inhibited growth of DU145, PC3 and PC3M cells in an androgen depleted environment. Immunohistochemical staining of prostate cancer tissues revealed increased nuclear localization of AhR in grade 2 and grade 3 cancers compared to the well differentiated grade 1 cancers.

Conclusions

Together, these results show that AhR is constitutively active in advanced prostate cancer cell lines that model hormone refractory prostate cancer. Chemical ablation of AhR signaling can reduce the growth of advanced prostate cancer cells, an effect not achieved with androgen receptor inhibitors or growth in androgen depleted media.