Potential therapeutic significance of increased expression of aryl hydrocarbon receptor in human gastric cancer

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.

Differential Expression of Genes Involved in Metabolism and Immune Response in Diffuse and Intestinal Gastric Cancers, a Pilot Ptudy

Gastric cancer (GC) is one of the major causes of cancer-related mortality worldwide. The vast majority of GC cases are adenocarcinomas including intestinal and diffuse GC. The incidence of diffuse GCs, often associated with poor overall survival, has constantly increased in USA and Europe The molecular basis of diffuse GC aggressivity remains unclear. Using mRNA from diffuse and intestinal GC tumor samples of a Western cohort, this study reports the expression level of the immunomodulatory aryl-hydrocarbon receptor (AhR), and genes involved in immune suppression (PD1, PD-L1, PD-L2) and the early steps of tryptophan metabolism (IDO1, IDO2, TDO2). Strongly increased expression of IDO1 (p < 0.001) and PD1 (p < 0.003) was observed in the intestinal sub-type. The highest expression of IDO1 and PDL1 correlated with early clinical stage and absence of lymphatic invasion (×25 p = 0.004, ×3 p = 0.04, respectively). Our results suggest that kynurenine, produced by tryptophan catabolism, and AhR activation play a central role in creating an immunosuppressive environment. Correspondingly, as compared to intestinal GCs, expression levels of IDO1-TDO2 and PD-L1 were less prominent in diffuse GCs which also had less infiltration of immune cells, suggesting an inactive immune response in the advanced diffuse GC. Confirmation of these patterns of gene expression will require a larger cohort of early and advanced stages of diffuse GC samples.

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.

The footprint of kynurenine pathway in every cancer: a new target for chemotherapy

Treatment of cancers has always been a challenge for physicians. Typically, several groups of anti-cancer medications are needed for effective management of an invasive and metastatic cancer. Recently, therapeutic potentiation of immune system markedly improved treatment of cancers. Kynurenine pathway has an interwoven correlation with immune system. Kynurenine promotes T Reg (regulatory) differentiation, which leads to increased production of anti-inflammatory cytokines and suppression of cytotoxic activity of T cells. Overactivation of kynurenine pathway in cancers provides an immunologically susceptible microenvironment for mutant cells to survive and invade surrounding tissues. Interestingly, kynurenine pathway vigorously interacts with other molecular pathways involved in tumorigenesis. For instance, kynurenine pathway interacts with phospoinosisitide-3 kinase (PI3K), extracellular signal-regulated kinase (ERK), Wnt/β-catenin, P53, bridging integrator 1 (BIN-1), cyclooxygenase 2 (COX-2), cyclin-dependent kinase (CDK) and collagen type XII α1 chain (COL12A1). Overactivation of kynurenine pathway, particularly overactivation of indoleamine 2,3-dioxygenase (IDO) predicts poor prognosis of several cancers such as gastrointestinal cancers, gynecological cancers, hematologic malignancies, breast cancer, lung cancer, glioma, melanoma, prostate cancer and pancreatic cancer. Furthermore, kynurenine increases the invasion, metastasis and chemoresistance of cancer cells. Recently, IDO inhibitors entered clinical trials and successfully passed their safety tests and showed promising therapeutic efficacy for cancers such as melanoma, brain cancer, renal cell carcinoma, prostate cancer and pancreatic cancer. However, a phase III trial of epacadostat, an IDO inhibitor, could not increase the efficacy of treatment with pembrolizumab for melanoma. In this review the expanding knowledge towards kynurenine pathway and its application in each cancer is discussed separately.

Prognostic Role of Aryl Hydrocarbon Receptor Interacting Protein (AIP) Immunohistochemical Expression in Patients with Resected Gastric Carcinomas

Aryl hydrocarbon receptor (AHR) interacting protein (AIP) is a chaperone which binds to inactive AHR in the cell cytoplasm. AHR is best known for mediating the toxicity of halogenated aromatics, but it has also been linked to carcinogenesis and tumor progression in several tumor types. Our aims are to assess the features of AIP immunohistochemical (IHC) staining and to evaluate its possible role as a prognostic marker in gastric cancer (GC). Retrospective study of 147 cases of resected GC. Clinicopathological features were collected, tissue microarrays were constructed for AIP IHC and statistical analysis were performed. AIP staining was observed in 50.3% of tumors. All AIP-positive cases exhibited cytoplasmic or membranous staining, variably associated with nuclear co-staining. 93.2% of AIP-positive tumors showed AIP immunoreactivity in 100% of cells. Staining intensity was mild, moderate and intense in 33.8%, 13.5% and 52.7% of cases. Tumors were stratified according to AIP staining intensity into low expression (no or mild AIP immunoreactivity) and high expression (moderate or intense AIP immunoreactivity). 36.6% of our cases showed high AIP expression. High AIP expression was significantly and independently correlated to tumor progression and cancer death. Tumors with high AIP expression showed lower survival and higher progression rates. AIP expression might be useful for determining GC prognosis. More studies are needed to clarify the role of AHR pathway in GC, AIP expression and its potential use as a surrogate marker for selecting patients for AHR modulation therapy.

Effects of high-fat diet and intestinal aryl hydrocarbon receptor deletion on colon carcinogenesis

Consumption of a high-fat diet has been associated with an increased risk of developing colorectal cancer (CRC). However, the effects of the interaction between dietary fat content and the aryl hydrocarbon receptor (AhR) on colorectal carcinogenesis remain unclear. Mainly known for its role in xenobiotic metabolism, AhR has been identified as an important regulator for maintaining intestinal epithelial homeostasis. Although previous research using whole body AhR knockout mice has revealed an increased incidence of colon and cecal tumors, the unique role of AhR activity in intestinal epithelial cells (IECs) and modifying effects of fat content in the diet at different stages of sporadic CRC development are yet to be elucidated. In the present study, we have examined the effects of a high-fat diet on IEC-specific AhR knockout mice in a model of sporadic CRC. Although loss of AhR activity in IECs significantly induced the development of premalignant lesions, in a separate experiment, no significant changes in colon mass incidence were observed. Moreover, consumption of a high-fat diet promoted cell proliferation in crypts at the premalignant colon cancer lesion stage and colon mass multiplicity as well as β-catenin expression and nuclear localization in actively proliferating cells in colon masses. Our data demonstrate the modifying effects of high-fat diet and AhR deletion in IECs on tumor initiation and progression.NEW & NOTEWORTHY Through the use of an intestinal-specific aryl hydrocarbon receptor (AhR) knockout mouse model, this study demonstrates that the expression of AhR in intestinal epithelial cells is required to reduce the formation of premalignant colon cancer lesions. Furthermore, consumption of a high-fat diet and the loss of AhR in intestinal epithelial cells influences the development of colorectal cancer at various stages.

Histopathological features of the proper gastric glands in FVB/N-background mice carrying constitutively-active aryl-hydrocarbon receptor

Background

Aryl-hydrocarbon receptor (AhR) is a multiple ligand-activated transcription factor that has important roles in xenobiotic, physiological, or pathological functions. Transgenic mice systemically expressing constitutively-active AhR (CA-AhR) have been created to mimic activated AhR signaling in vivo. However, their detailed histopathological features are unclear. In the present study, we generated CA-AhR-expressing FVB/N mice (FVB-CA-AhR mice) and clarified their phenotypes in detail.

Methods

Male and female FVB-CA-AhR and wild-type mice were histopathologically examined from 6 to 33 weeks of age.

Results

Among the systemic organs, only the stomachs in FVB-CA-AhR mice showed pathological changes including cystic structures beneath the serosa; in addition, stomach weights increased with age. Histopathologically, cystic structures and alcian blue-positive metaplasia were observed in the mucosa of the proper gastric glands, and these two histometric parameters were positively correlated. Furthermore, proliferating cells shifted from the isthmus to the base of the glands, and parietal cells decreased. Age-related histopathological changes were clearer in females than in males. Importantly, in FVB-CA-AhR mice, intramucosal cysts developed as extramucosal cysts beneath the serosa, penetrating the lamina muscularis mucosae and the muscularis propria. Their incidence reached 100% in 28-week-old male mice and 33-week-old female mice. Extramucosal cysts contained alcian blue-, Griffonia simplicifolia lectin II-, or trefoil factor 2-positive cells, suggesting a stomach origin for the cysts and spasmolytic polypeptide-expressing metaplasia-like lesions.

Conclusions

Disease onset occurred earlier in FVB-CA-AhR mice than previously reported in C57BL/6-derived CA-AhR mice. Importantly, the histopathological features were partly similar with gastritis cystica profunda in humans and animals. Excessive activation of AhR signaling aggravated abnormalities in the gastric mucosa and were affected by both genetic- and sex-related factors.

Electronic supplementary material

The online version of this article (10.1186/s12876-019-1009-x) contains supplementary material, which is available to authorized users.

Involvement of Aryl Hydrocarbon Receptor and Aryl Hydrocarbon Receptor Repressor in Helicobacter Pylori-related Gastric Pathogenesis

Background: Persistent Helicobacter pylori (H. pylori) infection leads to various gastric diseases. Multiple studies have demonstrated that aryl hydrocarbon receptor (AHR) plays roles in the antibacterial response and aryl hydrocarbon receptor repressor (AHRR) is downregulated in stomach cancer. However, the role of AHR or AHRR in H. pylori-related gastric diseases remains unclear. Aims: To investigate whether AHR or AHRR is involved in H. pylori-related gastric diseases. Methods: Patients with gastritis or gastric adenocarcinoma were enrolled randomly, and gastric tissue specimens were diagnosed pathologically. AHR, AHRR, and H. pylori infection status in tissues were detected by immunohistochemistry. Human gastric cells were cocultured with H. pylori. siRNAs were used to silence AHR or AHRR, and a C57bl/6 mouse model colonized by H. pylori was established. Protein expression was determined by western blotting analysis, and TNF, IL-8 and IL-1β in cell supernatants were measured by ELISA. Results: AHR and AHRR were expressed in gastritis tissues and gastric cancer tissues without H. pylori infection, and principally located in the cytoplasm and nucleus. AHR expression was significantly correlated with AHRR expression in gastric tissues without H. pylori infection (P=0.008). However, their expressions were negatively correlated with H. pylori infection status. H. pylori coculture inhibited AHR and AHRR expression in stomach mucosa in vitro and in vivo. Gastric cells produced more TNF, IL-8 and IL-1β when AHR or AHRR was silenced. Conclusions: This preliminary study indicates that AHR and AHRR may be involved in H. pylori-related gastric pathogenesis, and helps toward understanding of inflammation-initiated carcinogenesis of gastric cancer.

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.

Overexpression of aryl hydrocarbon receptor (AHR) signalling pathway in human meningioma

Aryl hydrocarbon receptor (AHR) is a ligand activated transcription factor and involved in tumorigenesis of many cancers. However there are no reports on AHR in human meningioma. Therefore we examined the status of the AHR and its signalling molecules in human meningioma by using tumor biopsy samples and autopsy control meninges. We report the up regulation of AHR pathway genes like aryl hydrocarbon receptor nuclear translocator (ARNT), aldehyde dehydrogenase1family memberA3 (ALDH1A3), cytochrome P450, family1, subfamily A polypeptide1 (CYP1A1) and TCCD induced poly ADP ribose polymerase (TIPARP) gene expression in human meningioma. Further, AHR protein expression was found to be up regulated in all grades of human meningioma. We found that AHR localized in the nucleus for high grade anaplastic meningioma through immunohistochemical analysis. Since AHR signalling pathway was known to involve in inhibition of apoptosis in cancer cells, we evaluated the cyclophilin D levels which maintains mitochondrial permeability transition pore a critical event during apoptosis. We report that cyclophilin D levels were upregulated in all grades of human meningioma compared to control meninges. Finally we also evaluated c-Fos protein levels as its levels were regulated by AHR. Here we report that c-Fos protein levels were down regulated in all grades of human meningioma compared to control meninges. To sum-up we found that AHR signalling pathway components were upregulated, as the grade of the meningioma progresses from low to high grade, suggesting an important role of AHR signalling pathway in human meningioma.

Inhibitory effect of the low-toxic exogenous aryl hydrocarbon receptor modulator 3'3-diindolylmethane on gastric cancer in mice

3'3-Diindolylmethane (DIM) has been proved to exhibit anticancer properties in many solid tumors. In our previous study, we demonstrated that DIM inhibited SGC7901 cell proliferation by inducing apoptosis and delaying cell cycle progression. Herein, we further explored the anti-tumor effect of DIM on SGC-7901 tumor bearing mice. Tumors were excised, weighed, and tested by western blot and TdT-UTP nick-end labeling (TUNEL) assay. Blood samples were collected for biochemical analysis. The expression levels of AhR and cytochrome P450, family 1, subfamily A, polypeptide 1 (CYP1A1) protein were evaluated by western-blot assay. Our data show that with the increase of DIM dose (0, 5, 10, 20 mg/kg/day), AhR protein gradually decreased as CYP1A1 protein increased. The weight of the tumors found in the treated animals was significantly lower than that of the control group (0.845±0.096 vs. 1.275±0.236 g, 0.768±0.161 vs. 1.275±0.236 g, 0.607±0.106 vs. 1.275±0.236 g, P<0.05). TUNEL test showed that DIM induced increased apoptosis in the treatment groups in a dose-dependent manner. Blood tests also indicated that DIM showed no toxic effect on animal weight or liver and kidney function. These results indicated that DIM agent could be a safe and potent drug in therapy of gastric cancer.

Polychlorinated biphenyls and its potential role in endometriosis

With the progress of global industrialization and environmental deterioration, the relationship between human health and the living environment has become an increasing focus of attention. Polychlorinated biphenyls (PCBs, including dioxin-like polychlorinated biphenyls and non-dioxin-like polychlorinated biphenyls), as part of the organic chlorine contaminants, have been suspected as playing a role in the etiopathogenesis of endometriosis. Several population-based studies have proposed that exposure to PCBs may increase the risk of developing endometriosis, while some epidemiological studies have failed to find any association between PCBs and endometriosis. The purpose of this review is to discuss the potential pathophysiological relationship between endometriosis and PCBs with a focus on both dioxin-like polychlorinated biphenyls and non-dioxin-like polychlorinated biphenyls.

Effect of dioxin and 17β-estradiol on the expression of cytochrome P450 1A1 gene via an estrogen receptor dependent pathway in cellular and xenografted models

Cytochrome P450 (CYP) 1A1 plays a major role in the metabolic activation of procarcinogens to carcinogens via aryl hydrocarbon receptor (AhR) pathway. Especially, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) is known as an agonist of AhR. In estrogen responsive cancers, 17β-estradiol (E2) may influence on AhR dependent expression of CYP1 family via the interaction between estrogen receptor (ER) and AhR. In the present study, the effect of E2/ER on the expression of AhR and CYP1A1 genes was investigated for MCF-7 clonal variant (MCF-7 CV) breast cancer cells expressing ER. In reverse transcription-PCR and Western blot analysis, mRNA expression level of AhR was not altered, but its protein expression level was increased by TCDD or E2. The transcriptional and translational levels of CYP1A1 appeared to be increased by TCDD or E2. The increased expression of AhR and CYP1A1 induced by E2 was restored to the control level by the co-treatment of ICI 182,780, indicating that E2 induced the protein expression levels of AhR and CYP1A1 like TCDD via an ER dependent pathway. In an in vivo xenograft mouse model transplanted with MCF-7 CV cells, the protein expression levels of AhR and CYP1A1 of tumor masses were also increased by E2 or TCDD. Taken together, these results indicate that E2 may promote AhR dependent expression of CYP1A1 via ER dependent pathway in MCF-7 CV cells expressing ER in the absence of TCDD, an agonist of AhR. The relevance of E2 and ER in CYP1A1 activation of estrogen responsive cancers may be targeted for developing more effective cancer treatments.

Aryl hydrocarbon receptor promotes hepatocellular carcinoma tumorigenesis by targeting intestine-specific homeobox expression

The aryl hydrocarbon receptor (AHR), a major chemical sensor, is thought to play a role in various biological contexts, including cell cycle regulation and tumorigenesis. However, its regulatory mechanisms remain unclear. We propose herein a novel mechanism through which AHR promotes tumorigenesis by targeting expression of the oncogene intestine-specific homeobox (ISX) in hepatocellular carcinoma (HCC). Compared to paired tumor-adjacent tissues and non-HCC tumors, HCCs exhibited an increased and hierarchical pattern of AHR expression. Patients exhibiting high AHR expression had a significantly shorter survival duration, compared to those with low and medium expression. Functionally, AHR was found to target the newly discovered proto-oncogene, ISX, resulting in the increased expression of this gene and its downstream targets, CCND1 and E2F1. Ablation of AHR or ISX in hepatoma cells suppressed cell growth, whereas overexpression promoted cell proliferation and led to enhanced tumorigenic activity in vitro and in vivo. These results provide evidence to support a critical role for the AHR/ISX axis in HCC tumorigenesis and suggest its potential utility as a new therapeutic and prognostic target for HCC.

Cytoplasmic aryl hydrocarbon receptor regulates glycogen synthase kinase 3 beta, accelerates vimentin degradation, and suppresses epithelial-mesenchymal transition in non-small cell lung cancer cells

Aryl hydrocarbon receptor (AHR), a ligand-activated transcription factor, has been studied extensively in carcinogenesis through the genomic pathway. In recent years, AHR has also been reported to exert positive or negative effects on epithelial–mesenchymal transition (EMT), the crucial step in tumor malignant progression. However, the detailed mechanism remains controversial. Analysis of AHR-expression levels in non-small cell lung cancer cell lines and lung cancer tissues revealed an inverse correlation between AHR protein levels and tumor cell invasion and metastasis. Overexpression of wild-type AHR in H1299 cells (AHR poorly expressed, potently invasive) not only accelerated mesenchymal vimentin degradation, but also prevented cell invasion in vitro and in vivo. In the absence of AHR agonists, the overexpressed AHR protein was predominantly localized in the cytoplasm, where it interacted with vimentin and functioned as an E3 ubiquitin ligase. A 6-h incubation with the proteasome inhibitor MG-132 fully rescued vimentin from AHR-mediated proteasomal degradation. In AHR-overexpressing H1299 cells, either vimentin degradation or invasive suppression could be reversed when glycogen synthase kinase 3 beta (GSK3β) was inactivated by CHIR-99021 treatment. In contrast, silencing of AHR in A549 cells (AHR highly expressed, weakly invasive) resulted in the downregulation of epithelial biomarkers (E-cadherin and claudin-1), augmentation of mesenchymal vimentin level, and GSK3β Ser-9 hyper-phosphorylation, which led to enhanced invasiveness. This work demonstrates that cytoplasmic, resting AHR protein may act as an EMT suppressor via a non-genomic pathway. Depletion of cytoplasmic AHR content represents a potential switch for EMT, thereby leading to the scattering of tumor cells.

Benzo[a]pyrene promotes gastric cancer cell proliferation and metastasis likely through the Aryl hydrocarbon receptor and ERK-dependent induction of MMP9 and c-myc

Gastric cancer (GC) is the fifth most common cancer worldwide and the third leading cause of global cancer-related death. Benzo[a]pyrene (BaP), a Group Ⅰ carcinogen categorized by the IARC, is a cumulative foodborne carcinogen and ubiquitous environmental pollutant with potent carcinogenic properties. However, the function and mechanism of BaP exposure on GC progression remains unclear. We investigated the role of BaP in human GC progression to identify potential mechanism underlining its carcinogenic activity. After exposure to various concentrations of BaP, human GC cells SGC-7901 and MNK-45 showed an increased capability of proliferation, migration and invasion. Further study indicated that BaP promotes the expression of matrix metalloproteinase-9 (MMP9) and c-myc at mRNA and protein level, and activates Aryl hydrocarbon receptor (AhR) and ERK pathway. Moreover, BaP-induced overexpression of MMP9 and c-myc were attenuated by the ERK inhibitor U0126 and AhR inhibitor resveratrol, respectively. These data suggest that BaP promotes proliferation and metastasis of GC cells through upregulation of MMP9 and c-myc expression, and this was likely mediated via the AhR and ERK signaling pathway.

2,3,7,8-Tetrachlorodibenzo-p-dioxin induced cell-specific drug transporters with acquired cisplatin resistance in cisplatin sensitive cancer cells

2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) can induce drug transporter genes such as the ATP-binding cassette G member 2 (ABCG2), which contributes to multidrug resistance. We investigated the effect of TCDD pretreatment on drug transporters induction from cancer cells of various origins. Cell viabilities after treatment of cisplatin were measured to evaluate acquiring cisplatin resistance by TCDD. Acquring cisplatin resistance was found only in cisplatin senstivie cancer cells including gastric SNU601, colon LS180, brain CRT-MG and lymphoma Jurkat cells which showed a significant increase in cell viability after combined treatment with TCDD and cisplatin. High increase of ABCG2 gene expression was found in SNU601 and LS180 cells with a mild increase in the expression of the ABCC3, ABCC5,and SLC29A2 genes in SNU601 cells, and of major vault protein (MVP) in LS180 cells. The AhR inhibitor kaempferol suppressed the upregulation of ABCG2 expression and reversed the TCDD-induced increase in cell viability in LS180 cells. However, in CRT-MG cells, other transporter genes including ABCC1, ABCC5, ABCA3, ABCA2, ABCB4, ABCG1, and SLC29A1 were up-regulated. These findings suggested the acquiring cisplatin resistance by TCDD associated with cancer cell-type-specific induction of drug transporters.

6-shogaol, a major compound in ginger, induces aryl hydrocarbon receptor-mediated transcriptional activity and gene expression

Xenobiotics are usually detoxified by drug-metabolizing enzymes and excreted from the body. The expression of many of drug-metabolizing enzymes is regulated by the aryl hydrocarbon receptor (AHR). Some substances in vegetables have the potential to be AHR ligands. To search for vegetable components that exhibit AHR-mediated transcriptional activity, we assessed the activity of vegetable extracts and identified the active compounds using the previously established stable AHR-responsive HepG2 cell line. Among the hot water extracts of vegetables, the highest activity was found in ginger. The ethyl acetate fraction of the ginger hot water extract remarkably induced AHR-mediated transcriptional activity, and the major active compound was found to be 6-shogaol. Subsequently, the mRNA levels of AHR-targeting drug-metabolizing enzymes (CYP1A1, UGT1A1, and ABCG 2) and the protein level of CYP1A1 in HepG2 cells were shown to be increased by 6-shogaol. This is the first report that 6-shogaol can regulate the expression of detoxification enzymes by AHR activation.

Role of aryl hydrocarbon receptor in cancer

Aryl hydrocarbon receptor (AHR), a cytosolic ligand-activated transcription factor, belongs to the member of bHLH/PAS family of heterodimeric transcriptional regulators and is widely expressed in a variety of animal species and humans. Recent animal and human data suggested that AHR is involved in various signaling pathways critical to cell normal homeostasis, which covers multiple aspects of physiology, such as cell proliferation and differentiation, gene regulation, cell motility and migration, inflammation and others. Dysregulation of these physiological processes is known to contribute to events such as tumor initiation, promotion, and progression. Increasing epidemiological and experimental animal data provided substantial support for an association between abnormal AHR function and cancer, implicating AHR may be a novel drug-interfering target for cancers. The proposed underlying mechanisms of its actions in cancer involved multiple aspects, (a) inhibiting the functional expression of the key anti-oncogenes (such as p53 and BRCA1), (b) promoting stem cells transforming and angiogenesis, (c) altering cell survival, proliferation and differentiation by influencing the physiologic processes of cell-cycle, apoptosis, cell contact-inhibition, metabolism and remodel of extracellular matrix, and cell-matrix interaction, (d) cross-talking with the signaling pathways of estrogen receptor and inflammation. This review aims to provide a brief overview of recent investigations into the role of AHR and the underlying mechanisms of its actions in cancer, which were explored by the new technologies emerging in recent years.

Downregulation of aryl hydrocarbon receptor expression decreases gastric cancer cell growth and invasion

Aryl hydrocarbon receptor (AhR) is a ligand-activated transcription factor associated with tumor initiation and progression. AhR expression is significantly increased in gastric cancer tissues and gastric cancer cell lines; however, the relationship between AhR and gastric cancer is still unclear. In the present study, we explored the effects of the inhibition of AhR expression by RNA interference on the biological behavior of gastric cancer cells (MKN45 and SGC7901), and elucidated the specific mechanisms of AhR action in the development of gastric cancer. Results showed that small interfering RNA (siRNA) against AhR effectively inhibited the expression of AhR, and decreased the expression of cytochrome P450 (CYP)1A1 and CYP1B1, which are classic target genes of the AhR pathway. Compared to the negative control group, AhR-siRNA-transfected cells showed decreased cellular growth, delayed G1-S cell cycle progression and increased apoptosis rate. Furthermore, inhibition of AhR expression by siRNA in SGC7901 cells led to decreased cell migratory and invasive ability, accompanied by downregulation of expression and activity of matrix metalloproteinase (MMP)-2 and MMP-9. Our results, therefore, suggest that AhR promotes the growth and invasiveness of gastric cancer cells and AhR may serve as a promising therapeutic target for gastric cancer.

AhR expression is increased in hepatocellular carcinoma

The aryl hydrocarbon receptor (AhR) is a ligand-activated transcription factor implicated in multiple cellular processes and its expression has been shown to play a critical role in tumorigenesis. However, the role of AhR in tumorigenesis of hepatocellular carcinoma remains unclear. In the current study, we investigated the role of AhR in hepatocellular carcinoma tumorigenesis and progression by (a) measuring the expression levels of AhR in liver lesions and (b) assessing the correlation between AhR expression and clinicopathologic parameters. The tissue microarray used in this study contained hepatocellular carcinoma tissues (n = 94), cancer adjacent normal hepatic tissues (n = 5) and normal hepatic tissues (n = 5), which were immunohistochemically assessed for AhR expression. Significantly stronger AhR staining was observed for hepatocellular carcinoma tissues than for cancer adjacent normal hepatic tissues (P = 0.003) and normal hepatic tissues (P = 0.004). In addition, AhR expression was associated with T stage (P = 0.03). The results from this study suggest that an increase in AhR expression is associated with hepatocellular carcinoma progression and may have a potential role in the treatment of hepatocellular carcinoma.

A selective aryl hydrocarbon receptor modulator 3,3'-Diindolylmethane inhibits gastric cancer cell growth

Background

Aryl hydrocarbon receptor (AhR) is a ligand-activated transcription factor associated with gastric carcinogenesis. 3,3'-Diindolylmethane (DIM) is a relatively non-toxic selective AhR modulator. This study was to detect the effects of DIM on gastric cancer cell growth.

Methods

Gastric cancer cell SGC7901 was treated with DIM at different concentrations (0,10,20,30,40,50 μmol/L) with or without an AhR antagonist, resveratrol. The expression of AhR and Cytochrome P4501A1 (CYP1A1), a classic target gene of AhR pathway, were detected by RT-PCR and Western blot; cell viability was measured by MTT assay, and the changes in cell cycle and apoptosis were analyzed by flow cytometry.

Results

RT-PCR and western-blot showed that with the increase of the concentration of DIM, AhR protein gradually decreased and CYP1A1 expression increased, suggesting that DIM activated the AhR pathway and caused the translocation of AhR from cytoplasm to nucleus. MTT assay indicated that the viability of SGC7901 cells was significantly decreased in a concentration- and time-dependent manner after DIM treatment and this could be partially reversed by resveratrol. Flow cytometry analysis showed that DIM arrested cell cycle in G1 phase and induced cell apoptosis.

Conclusion

Selective aryl hydrocarbon receptor modulator 3,3'-Diindolylmethane inhibits SGC7901 cell proliferation by inducing apoptosis and delaying cell cycle progression. AhR may be a potential therapeutic target for gastric cancer treatment.

The aryl hydrocarbon receptor contributes to the proliferation of human medulloblastoma cells

The aryl hydrocarbon receptor (AhR), a ligand-activated member of the basic helix-loop-helix (bHLH)/PER-ARNT-SIM (PAS) transcription superfamily, is known to regulate the toxicity of polyaromatic halogenated hydrocarbon environmental chemicals, most notably dioxin. However, the AhR has also been implicated in multiple stages of tumorigenesis. Medulloblastoma (MB), a primary cerebellar brain tumor arising in infants and children, is thought to originate from abnormally proliferating cerebellar granule neuron precursors (GNPs). GNPs express high levels of the AhR in the external germinal layer of the developing cerebellum. Moreover, our laboratory has previously reported that either abnormal activation or deletion of the AhR leads to dysregulation of GNP cell cycle activity and maturation. These observations led to the hypothesis that the AhR promotes the growth of MB. Therefore, this study evaluated whether the AhR serves a pro-proliferative role in an immortalized MB tumor cell line (DAOY). We produced a stable AhR knockdown DAOY cell line [AhR short hairpin RNA (shRNA)], which exhibited a 70% reduction in AhR protein levels. Compared with wild-type DAOY cells, AhR shRNA DAOY cells displayed an impaired G(1)-to-S cell cycle transition, decreased DNA synthesis, and reduced proliferation. Furthermore, these cell cycle perturbations were correlated with decreased levels of the pro-proliferative gene Hes1 and increased levels of the cell cycle inhibitor p27(kip1). Supplementation experiments with human AhR restored the proliferative activity in AhR shRNA DAOY cells. Taken together, our data show that the AhR promotes proliferation of MB cells, suggesting that this pathway should be considered as a potential therapeutic target for MB treatment.

Aryl hydrocarbon receptor pathway activation enhances gastric cancer cell invasiveness likely through a c-Jun-dependent induction of matrix metalloproteinase-9

Background

Abberant aryl hydrocarbon receptor (AhR) expression and AhR pathway activation are involved in gastric carcinogenesis. However, the relationship between AhR pathway activation and gastric cancer progression is still unclear. In present study, we used 2,3,7,8-tetrachlorodibenzo-para-dioxin (TCDD), a classic and most potent ligand of AhR, to activate AhR pathway and investigated the effect of AhR pathway activation on human gastric cancer AGS cell invasion and explored the corresponding mechanism.

Results

To determine whether AhR pathway can be activated in AGS cells, we examined the expression of CYP1A1, a classic target gene of AhR pathway, following TCDD exposure. RT-PCR and western blot analysis showed that both CYP1A1 mRNA and protein expression were increased in a dose-dependent manner following TCDD treatment and AhR antagonist resveratrol (RSV) could reverse this TCDD-induced CYP1A1 expression. To determine whether TCDD treatment of AGS cells results in an induction of MMP-9 expression, we detected MMP-9 mRNA using RT-PCR and detected MMP-9 enzymatic activity using gelatin zymography. The results showed that both MMP-9 mRNA expression and enzymatic activity were gradually increased with the concentration increase of TCDD in media and these changes could be reversed by RSV treatment in a dose-dependent manner. To examine whether AhR activation-induced MMP-9 expression and activity in AGS cells results in increased migration and invasion, we performed wound healing migration assay and transwell migration and invasion assay. After TCDD treatment, the migration distance and the migration and invasion abilities of AGS cells were increased with a dose-dependent manner. To demonstrate AhR activation-induced MMP-9 expression is mediated by c-Jun, siRNA transfection was performed to silence c-Jun mRNA in AGS cells. The results showed that MMP-9 mRNA expression and activity in untreated control AGS cells were very weak; After TCDD (10 nmol/L) treatment, MMP-9 mRNA expression and activity were significant increased; This TCDD-induced MMP-9 expression and activity increase could be abolished by c-Jun siRNA transfection.

Conclusion

AhR pathway activation enhances gastric cancer cell invasiveness likely through a c-Jun-dependent induction of MMP-9. Our results provide insight into the mechanism and function of the AhR pathway and its impact on gastric cancer progression.