Estrogen and aryl hydrocarbon receptor expression and crosstalk in human Ishikawa endometrial cancer cells

Regulation of the aryl hydrocarbon receptor in cancer and cancer stem cells of gynecological malignancies: An update on signaling pathways

Gynecological malignancies are a female type of cancers that affects the reproductive system. Cancer metastasis or recurrence mediated by cellular invasiveness occurs at advanced stages of cancer progression. Cancer Stem Cells (CSCs) enrichment in tumors leads to chemoresistance, which results in cancer mortality. Exposure to environmental pollutants such as polycyclic aromatic hydrocarbons is associated with an increased the risk of CSC enrichment in gynecological cancers. One of the important pathways that mediates the metabolism and bioactivation of these environmental chemicals is the transcription factor, aryl hydrocarbon receptor (AhR). The present review explores the molecular mechanisms regulating the crosstalk and interaction of the AhR with cancer-related signaling pathways, such as apoptosis, epithelial-mesenchymal transition, immune checkpoints, and G-protein-coupled receptors in several gynecological malignancies such as ovarian, uterine, endometrial, and cervical cancers. The review also discusses the potential of targeting the AhR pathway as a novel chemotherapy for gynecological cancers.

Involvement of sirtuins (Sirt1 and Sirt3) and aryl hydrocarbon receptor (AhR) in the effects of triclosan (TCS) on production of neurosteroids in primary mouse cortical neurons cultures

Epidemiological studies have shown the presence of triclosan (TCS) in the brain due to its widespread use as an antibacterial ingredient. One of the confirmed mechanisms of its action is the interaction with the aryl hydrocarbon receptor (AhR). In nerve cells, sirtuins (Sirt1 and Sirt3) act as cellular sensors detecting energy availability and modulate metabolic processes. Moreover, it has been found that Sirt1 inhibits the activation of estrogen receptors, regulates the androgen receptor, and may interact with the AhR receptor. It is also known that Sirt3 stimulates the production of estradiol (E₂) via the estradiol receptor β (Erβ). Therefore, the aim of the present study was to evaluate the effect of TCS alone or in combination with synthetic flavonoids on the production of neurosteroids such as progesterone (P₄), testosterone (T), and E₂ in primary neural cortical neurons in vitro. The contribution of Sirt1 and Sirt3 as well as AhR to these TCS-induced effects was investigated as well. The results of the experiments showed that both short and long exposure of neurons to TCS increased the expression of the Sirt1 and Sirt3 proteins in response to AhR stimulation. After an initial increase in the production of all tested neurosteroids, TCS acting for a longer time lowered their levels in the cells. This suggests that TCS activating AhR as well as Sirt1 and Sirt3 in short time intervals stimulates the levels of P₄, T, and E₂ in neurons, and then the amount of neurosteroids decreases despite the activation of AhR and the increase in the expression of the Sirt1 and Sirt3 proteins. The use of both the AhR agonist and antagonist prevented changes in the expression of Sirt1, Sirt3, and AhR and the production of P₄, T, and E₂, which confirmed that this receptor is a key in the mechanism of the TCS action.

Endocrine Disruptors and Endometrial Cancer: Molecular Mechanisms of Action and Clinical Implications, a Systematic Review

It has been widely demonstrated that endocrine disruptors play a central role in various physiopathological processes of human health. In the literature, various carcinogenic processes have been associated with endocrine disruptors. A review of the molecular mechanisms underlying the interaction between endocrine disruptors and the endometrial cancer has been poorly developed. A systematic review was performed using PubMed^®/MEDLINE. A total of 25 in vivo and in vitro works were selected. Numerous endocrine disruptors were analyzed. The most relevant results showed how Bisphenol A (BPA) interacts with the carcinogenesis process on several levels. It has been demonstrated how BPA can interact with hormonal receptors and with different transcription proliferative and antiproliferative factors. Furthermore, the effect of Polycyclic aromatic hydrocarbons on Aryl hydrocarbon receptors was investigated, and the role of flame retardants in promoting proliferation and metastasis was confirmed. The results obtained demonstrate how the mechanisms of action of endocrine disruptors are manifold in the pathophysiology of endometrial cancer, acting on different levels of the cancerogenesis process.

AHR agonistic effects of 6-PN contribute to potential beneficial effects of Hops extract

Hops (Humulus lupulus) is used as an alternative to hormone replacement therapy due to the phytoestrogen, 8-prenylnaringenin (8-PN). To examine the potential risks/benefits of hops extract and its compounds (8-PN and 6-prenylnaringenin, 6-PN), we aimed to evaluate the estrogen receptor α (ERα) and aryl hydrocarbon receptor (AHR) signaling pathways in human endometrial cancer cells. Hops extract, 8-PN and 6-PN showed estrogenic activity. Hops extract and 6-PN activated both ERα and AHR pathways. 6-PN increased the expression of the tumor suppressor gene (AHRR), and that of genes involved in the estrogen metabolism (CYP1A1, CYP1B1). Although 6-PN might activate the detoxification and genotoxic pathways of estrogen metabolism, hops extract as a whole only modulated the genotoxic pathway by an up-regulation of CYP1B1 mRNA expression. These data demonstrate the relevant role of 6-PN contained in the hops extract as potential modulator of estrogen metabolism due to its ERα and AHR agonist activity.

Cigarette Smoking and Estrogen-Related Cancer

Cigarette smoking is a known cause of many cancers, yet epidemiologic studies have found protective associations with the risk of four "estrogen-related" malignancies: endometrial cancer, endometrioid and clear cell ovarian cancers, and thyroid cancer. This review considers epidemiologic and biological aspects of these associations, focusing particularly on estrogen signaling, and contrasts them with those for breast cancer, another estrogen-related malignancy. The observational findings regarding the inverse associations are consistent and remain after adjustment for possible confounding factors. In general, women who smoke do not have lower circulating estrogen levels than nonsmokers, eliminating one possible explanation for reduced risks of these malignancies. For endometrial and endometrioid ovarian cancer, the negative associations could plausibly be explained by interference with signaling through the estrogen receptor α. However, this is unlikely to explain the lower risks of thyroid and clear cell ovarian cancers. For thyroid cancer, an anti-inflammatory effect of nicotine and reduced TSH levels from smoking have been proposed explanations for the inverse association, but both lack convincing evidence. While the overall impact of cigarette smoking is overwhelmingly negative, protective associations such as those discussed here can provide potential clues to disease etiology, treatment, and prevention.

Roles of aryl hydrocarbon receptor in endothelial angiogenic responses†

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

Environmental polycyclic aromatic hydrocarbons mixture, in human blood levels, decreased oestradiol secretion by granulosa cells via ESR1 and GPER1 but not ESR2 receptor

Tissue-dependent oestrogenic and anti-oestrogenic activity of polycyclic aromatic hydrocarbons (PAHs) has been suggested. In this study, the effect of two PAH mixtures, M1 composed of all 16 priority pollutants and M2 composed of five (noted in the highest levels) compounds, on follicle-stimulating hormone receptor (FSHR) expression, basal or FSH-induced oestradiol (E2) secretion and aromatase cytochrome P450 (P450arom) protein expression, by non-luteinised human granulosa cell line (HGrC1) was determined. In addition, the consequences of gene silencing of oestrogen receptor alfa (siESR1), oestrogen receptor beta (siESR2) and a G protein-coupled receptor (siGPER1) on the above parameters were described. Neither PAH mixture had an effect on basal FSHR protein expression; however, both mixtures increased FSH-induced FSHR expression. Decreased E2 secretion and P450arom expression was also demonstrated. In both basal and FSH treated cells, siESR1 and siGPER1 reversed the inhibitory effect of the mixtures on E2 secretion; however, in siESR2 cells, the inhibitory effect was still observed. This study showed that both classic ESR1 and GPER1 were involved in the inhibitory effect of both PAH mixtures on E2 secretion and confirmed that expression of P450arom could be downregulated through the aryl hydrocarbon receptor and additionally through the ESR2.

Primary endometrial 3D co-cultures: A comparison between human and rat endometrium

Human and rat reproductive systems differ significantly with respect to hormonal cyclicity and endometrial cell behavior. However, species-differences in endometrial cell responses upon hormonal stimulation and exposure to potentially toxic compounds are poorly characterized. In this study, human and rat endometrial hormonal responses were assessed in vitro using a 3D co-culture model of primary human and rat endometrial cells. The models were exposed to the aryl hydrocarbon receptor (AHR) ligands 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), laquinimod, and its AHR active metabolite DELAQ. In both the human and rat endometrial models, estrogen receptor and progesterone receptor gene expression was modulated by the hormonal treatments, comparable to the in vivo situation. AHR gene expression in the human endometrial model did not change when exposed to hormones. In contrast, AHR expression decreased 2-fold in the rat model when exposed to predominantly progesterone, which resulted in a 2.8-fold attenuation of gene expression induction of cytochrome P450 1A1 (CYP1A1) by TCDD. TCDD and DELAQ, but not laquinimod, concentration-dependently induced CYP1A1 gene expression in both human and rat endometrial models. Interestingly, the relative degree of DELAQ to induce CYP1A1 was higher than that of TCDD in the human model, while it was lower in the rat model. These data clearly show species-differences in response to hormones and AHR ligands between human and rat endometrial cells in vitro, which might greatly affect the applicability of the rat as translational model for human endometrial effects. This warrants further development of human relevant, endometrium-specific test methods for risk assessment purposes.

Anti-tumor properties of methoxylated analogues of resveratrol in malignant MCF-7 but not in non-tumorigenic MCF-10A mammary epithelial cell lines

Resveratrol is a plant-derived polyphenol that is known for its anti-inflammatory and anti-tumorigenic properties in in vitro and in vivo models. Recent studies show that some resveratrol analogues might be more potent anti-tumor agents, which may partly be attributed to their ability to activate the aryl hydrocarbon receptor (AHR). Here, the anti-tumorigenic properties of resveratrol and structural analogues oxyresveratrol, pinostilbene, pterostilbene and tetramethoxystilbene (TMS) were studied in vitro, using in the malignant human MCF-7 breast cancer cell line and non-tumorigenic breast epithelial cell line MCF-10A. Cell viability and migration assays showed that methoxylated analogues of resveratrol are more potent anti-tumorigenic compounds than resveratrol and its hydroxylated analogue oxyresveratrol, with 2,3',4,5'-tetramethoxy-trans-stilbene (TMS) being the most potent compound. TMS decreased MCF-7 tumor cell viability with 50% at 3.6 μM and inhibited migration with 37.5 ± 14.8% at 3 μM. In addition, TMS activated the AHR more potently (EC50 in a reporter gene assay 2.0 μM) and induced AHR-mediated induction of cytochrome P450 1A1 (CYP1A1) activity (EC50 value of 0.7 μM) more than resveratrol and the other analogues tested. Cell cycle analysis showed that TMS induced a shift in cell cycle status from the G1 to the G2/M phase causing a cell cycle arrest in the MCF-7 cells, while no effect of TMS was observed in the non-tumorigenic MCF-10A mammary epithelial cell line. Gene expression analysis showed that 3 μM TMS increased gene expression of CYP1A1 (289-fold), CYP1B1 (5-fold) and Nqo1 (2-fold), and decreased gene expression of IL-8 (3-fold) in MCF-7 cells. In MCF-10A cells, 10 μM TMS also increased gene expression of CYP1A1 (5-fold) and CYP1B1 (2-fold), but decreased gene expression of Nqo1 (1.4-fold) in contrast to MCF-7 cells. TMS displays more potent anti-tumorigenic properties and activates the AHR more effectively than resveratrol. In addition, this is the first study to show that TMS, but not resveratrol, selectively inhibits the cell cycle of breast tumor cells and not the non-tumorigenic cells. Our study provides more insight in the anti-tumor properties of the methoxylated analogues of resveratrol in breast cells in vitro.

Activation of Aryl Hydrocarbon Receptor Suppresses Invasion of Esophageal Squamous Cell Carcinoma Cell Lines

Aims and Background

Esophageal cancer is the eighth most common malignancy and sixth leading cause of cancer deaths in the world. Recent studies have shown the potential role of the aryl hydrocarbon receptor (AhR) in tumor development; however, little is known about its role in esophageal squamous cell carcinoma. In the present study, we evaluated AhR expression in esophageal tumor tissues as well as cell lines and investigated the effects of AhR activation by its agonist BNF on esophageal squamous cell carcinoma invasion using Eca109 and TE-13 cells as a model.

Methods

Western blotting was performed to detect the AhR and CYP1A1 protein expression. Transwell migration assays were carried out to study the effects of BNF on esophageal squamous cell carcinoma cell invasion. AhR-specific siRNA was used to knock down the expression of AhR protein.

Results

Our results showed that AhR was highly expressed in esophageal squamous cell carcinoma tissues and cell lines when compared with its expression in normal tissue. AhR siRNA robustly decreased AhR protein expression in both Eca109 and TE-13 cells. BNF significantly inhibited invasion of human esophageal squamous cell carcinoma cells via activation of AhR.

Conclusions

The obtained results provide critical information on the roles of BNF in mediating esophageal squamous cell carcinoma invasion. This information could be useful for future therapeutic intervention in this lethal human disease.

Aryl hydrocarbon receptor and unexplained miscarriage

AIM

The aim of this study was to carry out a preliminary investigation of the expression of aryl hydrocarbon receptor (AhR) in decidua and villus and the relationship between AhR and unexplained miscarriage.

METHODS

The expression of AhR mRNA and protein from decidua and villus were measured using real-time reverse transcription-polymerase chain reaction, western blot and immunohistochemistry in 34 patients with unexplained miscarriage (miscarriage group) and 38 women with normal early pregnancy (control group).

RESULTS

The AhR mRNA and protein expression was increased significantly in the villus in both groups compared with decidua (P < 0.05, P < 0.05). In decidua, AhR mRNA and protein expression in the miscarriage group was increased significantly compared with the control group (P < 0.05, P < 0.05). In villus, AhR mRNA and protein expression in the miscarriage group was increased significantly compared with the control group (P < 0.05, P < 0.05). AhR is expressed mostly in the cytoplasm of syncytiotrophoblasts in villus, and also in the cytoplasm of decidual cells.

CONCLUSIONS

AhR was expressed more in the villus than in the decidua, and the upregulation of AhR mRNA and protein expression is associated with the pathogenesis of unexplained miscarriage.

The role of the SDF-1/ CXCR7 axis on the growth and invasion ability of endometrial cancer cells

PURPOSE

Stroma-derived factor-1 (SDF-1) and its receptor C-X-C chemokine receptor-4 (CXCR4) are involved in human endometrial carcinoma (EC) progression. CXCR7 is another important receptor of SDF-1 and has a higher affinity with SDF-1 compared with that of CXCR4. This paper aims to study the effects of the SDF-1/CXCR7 axis on the growth and invasion ability of EC cells.

METHODS

CXCR7 expression was evaluated by quantitative RT-PCR, immunohistochemistry, immunocytochemistry and Western blotting in EC cell lines and 30 cases of primary EC tissue from patients. EC cell line proliferation and migration were assessed following knockdown of CXCR7 by MTT and transwell assays.

RESULTS

The results showed that CXCR7 was highly expressed at both mRNA and protein levels in the EC cells and tissue. siCXCR7 effectively silenced CXCR7 in Ishikawa and AN3CA cells. Treatment with 17β-oestradiol (17β-E2) significantly increased the levels of CXCR7 and SDF-1 in Con, siCon and siCXCR7 treated Ishikawa. siCXCR7 persistently inhibited CXCR7 expression, even in cells treated with 17β-E2. Moreover, in vitro functional analyses, silencing CXCR7 resulted in decreased proliferation in Ishikawa and AN3CA cells. Treatment with 17β-E2 and SDF-1 significantly promoted the growth and migration in siCon treated Ishikawa and AN3CA. Interestingly, in response to 17β-E2 and SDF-1 stimulation, siCXCR7 continuously inhibited the growth and invasion of Ishikawa and AN3CA cells.

CONCLUSION

Our results indicate that SDF-1/CXCR7 plays a positive role in the proliferation and invasion of EC cells. CXCR7 inhibition treatment may provide a promising strategy for anti-tumour therapy for EC.

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) role in hematopoiesis and in hematologic diseases: A critical review

Dioxin exposure and its effect on hematopoiesis and cancer have been largely investigated in both human and non-human settings. Here we systematically reviewed literature to address the question of what we know about TCDD biology and exposure. Most effects are due to TCDD interaction with a receptor of xenobiotics called AHR, which is ubiquitously represented and also works on hematopoietic myeloid and lymphoid stem cells, inducing proliferation and stem cell release from bone marrow to peripheral circulation. Epidemiologic studies on TCDD exposure demonstrated an association with onco-hematologic diseases, particularly with non Hodgkin lymphomas and multiple myeloma, and non hematologic cancers, such as sarcomas, although these relationships are affected by multiple confounding factors.

The inflammation and estrogen metabolism impacts of polychlorinated biphenyls on endometrial cancer cells

Polychlorinated biphenyls (PCBs) are persistent and bio-accumulative chemicals that provoke a wide range of toxic effects. Their adverse impacts on the reproductive system are of great concern, however, the effects of PCBs on endometrium are still unclear. In the study, the endometrial adenocarcinoma Ishikawa cells were exposed to both dioxin-like CB126 and non-dioxin-like CB153 at the nominal concentrations of 0.3, 3, and 30μM. The inflammatory and endocrine effects were detected after treatment by PCBs. Results showed that CB126 stimulated the proliferation of Ishikawa cells at lower concentrations of 0.3 and 3μM. By contrast, CB153 did not affect the viability of the cells. Both congeners exerted the stimulatory effects on the enzymatic activity of SOD1. CB126 decreased the abundance of Interleukin-8 both at the mRNA and protein levels. Blocking of estrogen receptor or aryl hydrocarbon receptor by the antagonist abolished the effects of CB126 on the expressions of inflammatory factors. The levels of testosterone and 17beta-estradiol were not changed after exposure to lower doses of PCBs. In accordance, PCBs did not affect the mRNA expressions of estrogen metabolism-related genes. In all, our study revealed that PCBs affected the expression of inflammatory factors through ER and AHR receptors, however, no toxic effects were observed on estrogen metabolism.

2-(4-Hydroxy-3-methoxyphenyl)-benzothiazole suppresses tumor progression and metastatic potential of breast cancer cells by inducing ubiquitin ligase CHIP

Breast cancer is the most common malignancy among women and has poor survival and high recurrence rates for aggressive metastatic disease. Notably, triple-negative breast cancer (TNBC) is a highly aggressive cancer and there is no preferred agent for TNBC therapy. In this study, we show that a novel agent, 2-(4-hydroxy-3-methoxyphenyl)-benzothiazole (YL-109), has ability to inhibit breast cancer cell growth and invasiveness in vitro and in vivo. In addition, YL-109 repressed the sphere-forming ability and the expression of stem cell markers in MDA-MB-231 mammosphere cultures. YL-109 increased the expression of carboxyl terminus of Hsp70-interacting protein (CHIP), which suppresses tumorigenic and metastatic potential of breast cancer cells by inhibiting the oncogenic pathway. YL-109 induced CHIP transcription because of the recruitment of the aryl hydrocarbon receptor (AhR) to upstream of CHIP gene in MDA-MB-231 cells. Consistently, the antitumor effects of YL-109 were depressed by CHIP or AhR knockdown in MDA-MB-231 cells. Taken together, our findings indicate that a novel agent YL-109 inhibits cell growth and metastatic potential by inducing CHIP expression through AhR signaling and reduces cancer stem cell properties in MDA-MB-231 cells. It suggests that YL-109 is a potential candidate for breast cancer therapy.

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

PURPOSE

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

METHODS

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

RESULTS

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

CONCLUSION

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

Endocrine disruption of oestrogen action and female reproductive tract cancers

Endocrine disrupting chemicals (EDC) are ubiquitous and persistent compounds that have the capacity to interfere with normal endocrine homoeostasis. The female reproductive tract is exquisitely sensitive to the action of sex steroids, and oestrogens play a key role in normal reproductive function. Malignancies of the female reproductive tract are the fourth most common cancer in women, with endometrial cancer accounting for most cases. Established risk factors for development of endometrial cancer include high BMI and exposure to oestrogens or synthetic compounds such as tamoxifen. Studies on cell and animal models have provided evidence that many EDC can bind oestrogen receptors and highlighted early life exposure as a window of risk for adverse lifelong effects on the reproductive system. The most robust evidence for a link between early life exposure to EDC and adverse reproductive health has come from studies on women who were exposed in utero to diethylstilbestrol. Demonstration that EDC can alter expression of members of the HOX gene cluster highlights one pathway that might be vulnerable to their actions. In summary, evidence for a direct link between EDC exposure and cancers of the reproductive system is currently incomplete. It will be challenging to attribute causality to any single EDC when exposure and development of malignancy may be separated by many years and influenced by lifestyle factors such as diet (a source of phytoestrogens) and adiposity. This review considers some of the evidence collected to date.

Dioxin and estrogen signaling in lung adenocarcinoma cells with different aryl hydrocarbon receptor/estrogen receptor α phenotypes

Evidence suggests that estrogen affects the pulmonary response to carcinogenic pollutants, such as dioxins. In this study, we examined dioxin and estrogen signaling cross-talk in lung adenocarcinoma cell lines that were engineered to exhibit different aryl hydrocarbon receptor (AhR)/estrogen receptor (ER) α phenotypes. Data showed that 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) weakly antagonized estrogen-activated ERα activity in cells expressing abundant ERα, but little AhR. Increase of AhR expression or presence of a dioxin-responsive element in proximity silenced the antiestrogenic effect of TCDD. AhR was bound to dioxin-responsive element and transcriptionally active in both TCDD-untreated and -treated lung adenocarcinoma cells. 17β-estradiol (E2) reduced basal and TCDD-induced AhR activity only in ERα-positive cells. AhR and ERα exhibited a protein-protein interaction in the presence of E2. Cotreatment with TCDD moderated this protein interaction. Colocalization of ERα and AhR at the estrogen-responsive site under E2 and TCDD/E2 treatments implied that E2 ∣ ERα might hijack AhR away from the dioxin-responsive site. Increasing the relative expression of AhR to ERα counteracted inhibition of AhR activity by E2 ∣ ERα. When AhR and ERα were both highly expressed, TCDD and E2 up-regulated expression of dual-responsive genes cytochrome P450 (CYP) 1A1 and CYP1B1 in a cumulative manner, increasing the danger of metabolic activation of carcinogens. Whereas TCDD ∣ AhR and E2 ∣ ERα appeared to regulate CYP1B1 separately through their binding sites, E2 ∣ ERα increased the TCDD responsiveness and mRNA expression of CYP1A1 in a noncanonical way. In conclusion, AhR/ERα expression pattern, estrogen level, and promoter context determine the genomic action of dioxin in lung adenocarcinoma cells.

Role of the aryl hydrocarbon receptor in carcinogenesis and potential as a drug target

The aryl hydrocarbon receptor (AHR) is highly expressed in multiple organs and tissues, and there is increasing evidence that the AHR plays an important role in cellular homeostasis and disease. The AHR is expressed in multiple tumor types, in cancer cell lines, and in tumors from animal models, and the function of the AHR has been determined by RNA interference, overexpression, and inhibition studies. With few exceptions, knockdown of the AHR resulted in decreased proliferation and/or invasion and migration of cancer cell lines, and in vivo studies in mice overexpressing the constitutively active AHR exhibited enhanced stomach and liver cancers, suggesting a pro-oncogenic role for the AHR. In contrast, loss of the AHR in transgenic mice that spontaneously develop colonic tumors and in carcinogen-induced liver tumors resulted in increased carcinogenesis, suggesting that the receptor may exhibit antitumorigenic activity prior to tumor formation. AHR ligands also either enhanced or inhibited tumorigenesis, and these effects were highly tumor specific, demonstrating that selective AHR modulators that exhibit agonist or antagonist activities represent an important new class of anticancer agents that can be directed against multiple tumors.

An endogenous aryl hydrocarbon receptor ligand inhibits proliferation and migration of human ovarian cancer cells

The aryl hydrocarbon receptor (AhR), a ligand-activated transcription factor mediates many biological processes. Herein, we investigated if 2-(1'H-indole-3'-carbonyl)-thiazole-4-carboxylic acid methyl ester (ITE, an endogenous AhR ligand) regulated proliferation and migration of human ovarian cancer cells via AhR. We found that AhR was widely present in many histotypes of ovarian cancer tissues. ITE suppressed OVCAR-3 cell proliferation and SKOV-3 cell migration in vitro, which were blocked by AhR knockdown. ITE also suppressed OVCAR-3 cell growth in mice. These data suggest that the ITE might potentially be used for therapeutic intervention for at least a subset of human ovarian cancer.

Inhibition of constitutive aryl hydrocarbon receptor (AhR) signaling attenuates androgen independent signaling and growth in (C4-2) prostate cancer cells

The aryl hydrocarbon receptor is a member of the basic-helix-loop-helix family of transcription factors. AhR mediates the biochemical and toxic effects of a number of polyaromatic hydrocarbons such as 2,3,7,8,-tetrachloro-dibenzo-p-dioxin (TCDD). AhR is widely known for regulating the transcription of drug metabolizing enzymes involved in the xenobiotic metabolism of carcinogens and therapeutic agents, such as cytochrome P450-1B1 (CYP1B1). Additionally, AhR has also been reported to interact with multiple signaling pathways during prostate development. Here we investigate the effect of sustained AhR signaling on androgen receptor function in prostate cancer cells. Immunoblot analysis shows that AhR expression is increased in androgen independent (C4-2) prostate cancer cells when compared to androgen sensitive (LNCaP) cells. RT-PCR studies revealed constitutive AhR signaling in C4-2 cells without the ligand induced activation required in LNCaP cells. A reduction of AhR activity by short RNA mediated silencing in C4-2 cells reduced expression of both AhR and androgen responsive genes. The decrease in androgen responsive genes correlates to a decrease in phosphorylated androgen receptor and androgen receptor expression in the nucleus. Furthermore, the forced decrease in AhR expression resulted in a 50% decline in the growth rate of C4-2 cells. These data indicates that AhR is required to maintain hormone independent signaling and growth by the androgen receptor in C4-2 cells. Collectively, these data provide evidence of a direct role for AhR in androgen independent signaling and provides insight into the molecular mechanisms responsible for sustained androgen receptor signaling in hormone refractory prostate cancer.

Inhibition of AHR transcription by NF1C is affected by a single-nucleotide polymorphism, and is involved in suppression of human uterine endometrial cancer

Involvement of the aryl hydrocarbon receptor (AHR) in carcinogenesis has been suggested in many studies. Upregulation of AHR has been reported in some cancer species, and an association between single-nucleotide polymorphisms (SNPs) of AHR and cancer risk or cancer development has also been reported. This evidence suggests the involvement of some specific SNPs in AHR transcriptional regulation in the process of carcinogenesis or cancer development, but there have been no studies to elucidate the mechanism involved. In this study, we identified the transcription factor Nuclear Factor 1-C (NF1C) as a candidate to regulate AHR transcription in a polymorphism-dependent manner. SNP rs10249788 was included in a consensus binding site for NF1C. Our results suggested that NF1C preferred the C allele to the T allele at rs10249788 for binding. Forced expression of NF1C suppressed the activity of the AHR promoter with C at rs10249788 stronger than that with T. Moreover, expression analysis of human uterine endometrial cancer (HEC) specimens showed greater upregulation of AHR and downregulation of NF1C than those of normal endometrium specimens. Sequence analysis showed HEC patients at advanced stages tended to possess T/T alleles more frequently than healthy women. We also demonstrated that NF1C suppressed proliferation, motility and invasion of HEC cells. This function was at least partially mediated by AHR. This study is the first to report that a polymorphism on the AHR regulatory region affected transcriptional regulation of the AHR gene in vitro. Because NF1C is a tumor suppressor, our new insights into AHR deregulation and its polymorphisms could reveal novel mechanisms of genetic susceptibility to cancer.

The aryl hydrocarbon receptor ligands 2,3,7,8-tetrachlorodibenzo-p-dioxin and 3-methylcholanthrene regulate distinct genetic networks

The two estrogen receptor isoforms ERα and ERβ mediate biological effects of estrogens, but are also targets for endocrine disruptive chemicals (EDCs), compounds that interfere with hormonal signaling. 3-Methylcholanthrene (3-MC) and dioxin (TCDD) are EDCs and prototypical aryl hydrocarbon receptor (AhR) agonists, and can inhibit ER signaling. However, in contrast to TCDD, 3-MC gives rise to metabolites with estrogenic properties. We compared gene expression profiles in HepG2 cells after exposure to 3-MC, TCDD, and the synthetic estrogen diethylstilbestrol (DES). Interestingly, we observed little overlap between the genetic networks activated by 3-MC and TCDD, two compounds sometimes considered as interchangeable AhR ligands. Like DES, 3-MC induced a number of ER-regulated genes and lead to recruitment of ERα to the promoters of such genes. Interestingly, in contrast to DES, the estrogenic effects exerted by 3-MC were exclusively observed in ERα, but not in ERβ-expressing cells, suggesting ER isoform selectivity of 3-MC-derived metabolites.

Possible aryl hydrocarbon receptor-independent pathway of 2,3,7,8-tetrachlorodibenzo-p-dioxin-induced antiproliferative response in human breast cancer cells

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is a ligand with high affinity for the aryl hydrocarbon receptor (AhR). It suppresses 17β-estradiol (E2)-induced cell proliferation in human breast cancer cells. Although it has been theorized that the AhR is involved in TCDD-induced antiestrogenic activity and antiproliferation in human breast cancer cells, some evidence suggests that these activities of chlorinated aromatic compounds also occur by AhR-independent pathways. Here, we investigated the possibility of TCDD-induced antiproliferative responses in human breast cancer cells through AhR-independent pathways. Compared with that in vehicle-treated controls, DNA synthesis was significantly suppressed in MCF-7 cells and ZR75-1 cells treated with TCDD at a very low concentration (0.01 nM), whereas that in human ovarian carcinoma OVCAR3 cells, human cervical carcinoma HeLa cells and human choriocarcinoma JEG-3 cells was unaffected, even by exposure to 10 nM TCDD. The suppression induced by TCDD was not associated with the estrogen receptor α-signaling pathway. Another AhR agonist, 3,3',4,4',5-pentachlorobiphenyl, had no effect on DNA synthesis in MCF-7 cells at concentrations high enough to induce the transactivation function of the AhR. Furthermore, in MCF-7 cells, knockdown of the AhR by RNA interference had no effect on TCDD-induced antiproliferation. These findings suggest that the principal pathways of TCDD-induced antiproliferation in breast cancer cells are not AhR dependent.

A new model for embryo implantation: coculture of blastocysts and Ishikawa cells

OBJECTIVE

To explore and develop a new in vitro implantation model that reflects the main process of embryo attachment and invasion.

STUDY DESIGN

One of the limitations in human embryo implantation research is lack of an available in vitro model that faithfully replicates human embryo-uterine interactions. In the present study, we examined the attachment and invasiveness of blastocysts from mice in Ishikawa cell (IK), a human endometrial cell, to clarify whether this new model is suitable to study implantation of embryos. We used IK and placed it in contact with blastocysts to initiate coculture experiments using a specifically designed medium. The culture medium was composed of Ham F-12/Dulbecco's modified Eagle medium (1:1), 30% fetal calf serum, 63.5 nmol/L progesterone, 7.14 nmol/L estradiol-17β, 100 mg/ml of insulin, and 20 ng/ml epidermal growth factor. The culture for 24 h clearly demonstrated that embryos were capable of attachment to the IK and displayed partial invasion.

RESULTS

Our results showed that embryos attached to the IK and displayed partial invasion after coculture of blastocysts with IK for 48 h.

CONCLUSIONS

The model is capable of demonstrating the procedure of attachment and invasion of embryo into the endometrial cells and has promises to be used in studies related to early embryo implantation in human endometrium.

Unexpected hormonal activity of a catechol equine estrogen metabolite reveals reversible glutathione conjugation

4-Hydroxyequilenin (4-OHEN) is a major phase I metabolite of the equine estrogens present in widely prescribed hormone replacement formulations. 4-OHEN is autoxidized to an electrophilic o-quinone that has been shown to redox cycle, generating ROS, and to covalently modify proteins and DNA and thus potentially to act as a chemical carcinogen. To establish the ability of 4-OHEN to act as a hormonal carcinogen at the estrogen receptor (ER), estrogen responsive gene expression and proliferation were studied in ER(+) breast cancer cells. Recruitment by 4-OHEN of ER to estrogen responsive elements (ERE) of DNA in MCF-7 cells was also studied and observed. 4-OHEN was a potent estrogen, with additional weak activity associated with binding to the arylhydrocarbon receptor (AhR). The potency of 4-OHEN toward classical ERalpha mediated activity was unexpected given the reported rapid autoxidation and trapping of the resultant quinone by GSH. Addition of thiols to cell cultures did not attenuate the estrogenic activity of 4-OHEN, and preformed thiol conjugates added to cell incubations only marginally reduced ERE-luciferase induction. On reaction of the 4OHEN-GSH conjugate with NADPH, 4-OHEN was observed to be regenerated at a rate dependent upon NADPH concentration, indicating that intracellular nonenzymatic and enzymatic regeneration of 4-OHEN accounts for the observed estrogenic activity of 4-OHEN. 4-OHEN is therefore capable of inducing chemical and hormonal pathways that may contribute to estrogen-dependent carcinogenesis, and trapping by cellular thiols does not provide a mechanism of termination of these pathways.

Genomic characterization of gene copy-number aberrations in endometrial carcinoma cell lines derived from endometrioid-type endometrial adenocarcinoma

Endometrial carcinoma is one of the most common cancers in women. A limited number of endometrial carcinoma cell lines are available for studies of signal transduction pathways and experimental therapeutics in vitro. However, these cell lines have not been comprehensively characterized. In this study, we used genome-wide microarray-based comparative genomic hybridization (aCGH) technology to characterize five of the more commonly used endometrial cancer cell lines. We detected DNA copy-number gains in chromosomal regions 2q, 3p, 3q, 5q, 7p, 17q, and 19q in all five cell lines. Other common sites of copy-number gains, which were detected in four of five cell lines, included segments of chromosomes 1, 6, 8, 9, 11, 12, and 16. In all five cell lines, we found DNA copy-number losses in regions 3p, 10p, 10q, 11q, 11p, 14q, 15q, 18p, and 21q. Other common sites of genetic aberrations included segments of chromosomes 1, 2, 4, 5, 6, 16, 20, and 22. The genes involved in the copy-number alterations included the oncogenes PIK3CA (3q26.3), K-ras (12p12.1), R-ras (19q13.3-qter), Raf-1 (3p25), EGFR (7p12), Akt1 (14q32.32), and Akt2 (19q13.1-q13.2). A pathway analysis showed that genes in the PI3K and Wnt pathways are commonly affected. Our characterization of genomic alterations in these five commonly used endometrial cancer cell lines provides valuable genomic information for research that focuses on these key oncogenic pathways in endometrial cancer.

Comparison of hormonal activity of isoflavone-containing supplements used to treat menopausal complaints

OBJECTIVES

The isoflavones present in red clover and soy are used as an alternative treatment for menopausal complaints and are commercially available as high-dose food supplements. These preparations contain varying amounts of active ingredients, often without detailed specifications. Thus, it is difficult to derive a recommended daily dose, and the reliability of these products is rather low.

METHODS

We quantified the isoflavone content of 19 different isoflavone-containing preparations and compared their binding and transactivational activities with regard to estrogen receptor alpha, estrogen receptor beta, androgen receptor, progesterone receptor, peroxisome-proliferator-activated receptor, and aryl hydrocarbon receptor.

RESULTS

The food supplements that we tested bound to and transactivated both the estrogen receptors and the other receptors. After comparing the isoflavone content quantified by us with the isoflavone content specified on the package labels, we found that at least the specified isoflavone content or more could be detected in only 5 of the 19 food supplements that we tested.

CONCLUSIONS

Preparations containing isoflavones should be standardized for the isoflavone aglycone content to facilitate the prediction of theoretical hormonal activity, facilitate the intake of a controlled amount of isoflavones, and ensure greater product reliability.

The aryl hydrocarbon receptor as a target for estrogen receptor-negative breast cancer chemotherapy

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) and the relatively non-toxic selective aryl hydrocarbon receptor (AhR) modulator 6-methyl-1,3,8-trichlorodibenzo-furan (MCDF) induced CYP1A1-dependent ethoxyresorufin O-deethylase activity and inhibited proliferation of seven estrogen receptor (ER) negative breast cancer cell lines. MCDF, TCDD and structurally related 2,3,7,8-tetrachlorodibenzofuran, 1,2,3,7,8-pentachlorodibenzo-p-dioxin, 2,3,4,7,8-pentachlorodibenzofuran, and 3,3',4,4',5-pentachlorobiphenyl induced CYP1A1 and inhibited proliferation of BT-474 and MDA-MB-468 cells. In BT474 and MDA-MB-468 cells transfected with a small inhibitory RNA for the AhR, the antiproliferative activity of the chlorinated aromatic compounds was reversed, whereas for MCDF, only partial reversal was observed, suggesting that this compound acts through both AhR-dependent and AhR-independent pathways in these two cell lines. MCDF also inhibited tumor growth in athymic nude mice in which MDA-MB-468 cells were injected directly into the mammary fat pad. These results suggest that the AhR is a potential drug target for treatment of ER-negative breast cancer.

Morphological and functional disorders of the immature rat uterus after postnatal exposure to benz[a]anthracene and benzo[k]fluoranthene

We investigated the effects of postnatal exposure to benz[a]anthracene (B[a]A) and benzo[k]fluoranthene (B[k]F) on the development of the rat uterus. Neonates were injected on each postnatal days 1-14 with B[a]A (0.1, 1.0 or 10.0mg/kg), B[k]F (0.1, 1.0 or 5.0mg/kg), ethynylestradiol (EE; 1.0μg/kg) or a vehicle. The rats were killed on day 23. All doses of B[a]A and B[k]F induced a reduction of the uterine weight, a reduction of the estrogen receptor α expression in the luminal epithelium, glandular epithelium and stromal cells. Moreover, the uterotrophic response to EE (3-day administration of 1.0μg/kg on postnatal days 20-22) in rats exposed to B[a]A, B[k]F and EE was lower than in controls. The study showed that postnatal exposure to B[a]A and B[k]F resultes in morphological and functional disorders of the immature rat uterus.

Characterization of antiestrogenic activity of the Chinese herb, prunella vulgaris, using in vitro and in vivo (Mouse Xenograft) models

Prunella vulgaris (PV), a commonly used Chinese herb, also known as Self-heal, has a wide range of reported medicinal activities. By screening multiple herbs using the endometrial cancer cell line, ECC-1, and an alkaline phosphatase detection assay, we found that PV displayed significant antiestrogenic activity. We investigated the possible usefulness of antiestrogenic activity using both in vitro and in vivo models of endometrial function. Using the well-differentiated, hormone-responsive endometrial cell line, ECC-1, PV extract, at concentrations that were not toxic to the cells, significantly reduced alkaline phosphatase activity and cell proliferation in response to estrogen in a dose-dependent manner. The expression of CYR61, an estrogen-induced protein, was blocked in ECC-1 cells by both the antiestrogen ICI 182,780 and PV extract. Interestingly, PV extract did not appear to directly inhibit estrogen signaling. Rather, we found that its activities were probably related to an ability to function as an aryl hydrocarbon receptor (AHR) agonist in ECC-1 cells. In support of this hypothesis, we noted that PV induced CYP1A1, CYP1B1, and AHR repressor expression in a dose-dependent manner--responses that were blocked by small interfering RNA treatment to reduce AHR and specific AHR antagonists. Ovariectomized immunodeficient RAG-2/gamma(c) knockout mice implanted with human endometrial xenografts developed implants only when treated with estrogen. Mice treated with estrogen and PV tea in their drinking water had fewer and smaller xenograft implants compared with their estrogen-treated counterparts that drank only water (P < 0.05). Analysis of the resulting implants by immunohistochemistry demonstrated persistent estrogen receptor (ER), but reduced proliferation and CYR61 expression. Mouse uterine tissue weight in PV-treated mice was not different from controls, and cycle fecundity of intact C57 female mice was unaffected by PV tea treatment. PV, or Self-heal, exhibits significant antiestrogenic properties, both in vitro and in vivo. This activity is likely due to the ability of PV-activated AHR to interfere with estrogen. This herb may be useful as an adjunct for the treatment of estrogen-dependent processes like endometriosis and breast and uterine cancers. Full characterization of this herb will likely provide new insights into the crosstalk between AHR and ESR1, with potential for therapeutic applications in women.

The aryl hydrocarbon receptor complex and the control of gene expression

The aryl hydrocarbon receptor (AhR) is a ligand-activated transcription factor that controls the expression of a diverse set of genes. The toxicity of the potent AhR ligand 2,3,7,8-tetrachlorodibenzo-p-dioxin is almost exclusively mediated through this receptor. However, the key alterations in gene expression that mediate toxicity are poorly understood. It has been established through characterization of AhR-null mice that the AhR has a required physiological function, yet how endogenous mediators regulate this orphan receptor remains to be established. A picture as to how the AhR/ARNT heterodimer actually mediates gene transcription is starting to emerge. The AhR/ARNT complex can alter transcription both by binding to its cognate response element and through tethering to other transcription factors. In addition, many of the coregulatory proteins necessary for AhR-mediated transcription have been identified. Cross talk between the estrogen receptor and the AhR at the promoter of target genes appears to be an important mode of regulation. Inflammatory signaling pathways and the AhR also appear to be another important site of cross talk at the level of transcription. A major focus of this review is to highlight experimental efforts to characterize nonclassical mechanisms of AhR-mediated modulation of gene transcription.

Red clover isoflavones biochanin A and formononetin are potent ligands of the human aryl hydrocarbon receptor

Aryl hydrocarbon receptor (AhR) activation affects the cell cycle and drives cells to apoptosis. Thus, selective AhR modulators (SAhRMs) have previously been implicated in cancer therapy and prevention, particularly for hormone-dependent cancers. In the present study, isoflavones a remedy used to ameliorate menopausal complaints were tested for their potential in transactivating AhR in order to investigate the biological function of red clover isoflavones. The results were compared to the transactivation potentials of other flavonoids and plant-derived indole compounds. We found that the isoflavones biochanin A and formononetin were potent AhR agonists in vitro, with EC(50) values of 2.5 x 10(-7) and 1.3 x 10(-7)mol/l, respectively. These isoflavones are 10 times more potent compared to the indole compounds indole-3-carbinol and diindolylmethane, publicised as powerful AhR agonists with EC(50) values of 5.8 x 10(-6) and 1.1 x 10(-6)mol/l, respectively. Because activated AhR crosstalks with estrogen receptor alpha, future risk-benefit assessments of isoflavones should take into consideration their AhR transactivating potential.

The transcription factor aryl hydrocarbon receptor nuclear translocator functions as an estrogen receptor beta-selective coactivator, and its recruitment to alternative pathways mediates antiestrogenic effects of dioxin

The biological effects of dioxins are mediated by the aryl hydrocarbon receptor (AhR) and its dimerization partner, the AhR nuclear translocator (ARNT), and include interference with hormonal signaling pathways like the response to estrogens. The effects of estrogens are mediated by two estrogen receptor (ER) isoforms, ERalpha and ERbeta, which belong to the family of nuclear receptors. We have previously shown that ARNT can act as coactivator of the ERs. In this study, we show that recruitment of ARNT to AhR or hypoxia-inducible factor-1alpha signaling pathways as well as small interfering RNA-mediated down-regulation of ARNT levels lead to a reduction in ER transcriptional activity. Using chromatin immunoprecipitation assays, we demonstrate that this decrease coincides with reduced recruitment of ARNT to estradiol-regulated promoters. We show further that coactivation by ARNT as well as inhibition by dioxin acts stronger on ERbeta than on ERalpha activity. Additionally, we demonstrate that the effects of ARNT are dependent on the A/B domain of the ERs with the A/B domain of ERbeta being considerably stronger in mediating the coactivating effects of ARNT. Taken together, our studies show that recruitment of ARNT to the AhR after dioxin treatment can account for the antiestrogenic effect of dioxins. Moreover, we show for the first time that the inhibitory effects of dioxin are more pronounced on ERbeta than on ERalpha.

Inhibition of estrogen-mediated uterine gene expression responses by dioxin

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) exhibits antiestrogenic properties, including the inhibition of estrogen-induced uterine growth and proliferation. The inhibition of estrogen-mediated gene expression through ER/AhR cross-talk has been proposed as a plausible mechanism; however, only a limited number of inhibited responses have been investigated that are unlikely to fully account for the antiuterotrophic effects of TCDD. Therefore, the effects of TCDD on ethynyl estradiol (EE)-mediated uterine gene expression were investigated using cDNA microarrays with complementary physiological and histological phenotypic anchoring. Mice were gavaged with vehicle, 3 daily doses of 10 mug/kg EE, a single dose of 30 mug/kg TCDD, or a combination of EE plus TCDD and sacrificed after 4, 12, 24, and 72 h. TCDD cotreatment inhibited EE-induced uterine wet weight by 37, 23, and 45% at 12, 24, and 72 h, respectively. TCDD cotreatment also reduced EE-mediated stromal edema, hypertrophy, and hyperplasia and induced marked luminal epithelial cell apoptosis. A 2 x 2 factorial microarray design was used to identify EE- and TCDD-specific differential gene expression responses as well as their interactive effects. Only 133 of the 2753 EE-mediated differentially expressed genes were significantly modulated by TCDD cotreatment, indicating a gene-specific inhibitory response. The EE-mediated induction of many genes, including trefoil factor 1 and keratin 14, were inhibited by greater than 90% by TCDD. Functional annotation of inhibited responses was associated with cell proliferation, water and ion transport, and maintenance of cellular structure and integrity. These inhibited responses correlate with the observed histological alterations and may contribute to the antiuterotrophic effects of TCDD.

Effect of postnatal exposure to benzo[a]pyrene on the uterus of immature rats

The objective of this study was to investigate the morphological effects of postnatal exposure to benzo[a]pyrene (B[a]P) on the development of the uterus, uterine estrogen receptor (ERalpha) expression, and the uterine response to estrogen stimulation using the uterotrophic bioassay in rats. Neonates were injected on each postnatal day (PND) 1-14 with B[a]P (0.1, 1.0 and 10.0mg/kg), ethynylestradiol (EE; 1.0 microg/kg) or vehicle (control group). All animals were killed on PND 23. Postnatal administration of B[a]P with doses of 1.0 and 10.0 mg/kg induced significant (P<0.01) reduction of uterine weight and significantly lowered (P<0.05) ERalpha expression in the luminal epithelium. The increase in uterine weight and luminal epithelium heights after EE stimulation (1.0 microg/kg) on PND 20-22 was significantly higher (P<0.01) in all groups in comparison with corresponding non-stimulated groups. However, the uterotrophic response in rats postnatally exposed to EE and B[a]P was significantly lower (P<0.01) than in controls. In the control and EE groups, EE stimulation on PND 20-22 induced a significant (P<0.01) decrease in ERalpha immunoreactivity of the luminal epithelium. In contrast, rats postnatally treated with B[a]P showed no change in the density of ERalpha immunostaining when detected after estrogenic stimulation. The present study showed that postnatal exposure to B[a]P caused pathological changes in constitution and maturation of uterine ERalpha resulting in disturbed morphological development and uterine dysfunction in immature rats.

Lycopene and other carotenoids inhibit estrogenic activity of 17beta-estradiol and genistein in cancer cells

Epidemiological evidence suggests that carotenoids prevent several types of cancer, including mammary and endometrial cancers. On the other hand, such studies have also shown that estrogens are the most important risk factors for these cancer types. Genistein, the phytoestrogen mainly found in soy, also shows significant estrogenic activity when tested at concentrations found in human blood. The aim of this study was to determine whether carotenoids inhibit signaling of steroidal estrogen and phytoestrogen which could explain their cancer preventive activity. Similar to the known effect of 17beta-estradiol (E(2)), treatment of breast (T47D and MCF-7) and endometrial (ECC-1) cancer cells with phytoestrogens induced cell proliferation, cell-cycle progression and transactivation of the estrogen response element (ERE). However, each of the tested carotenoids (lycopene, phytoene, phytofluene, and beta-carotene) inhibited cancer cell proliferation induced by either E(2) or genistein. The inhibition of cell growth by lycopene was accompanied by slow down of cell-cycle progression from G1 to S phase. Moreover, the carotenoids inhibited estrogen-induced transactivation of ERE that was mediated by both estrogen receptors (ERs) ERalpha and ERbeta. The possibility that this inhibition results from competition of carotenoid-activated transcription systems on a limited pool of shared coactivators with the ERE transcription system was tested. Although cotransfection of breast and endometrial cancer cells with four different coactivators (SRC-1, SRC-2, SRC-3, and DRIP) strongly stimulated ERE reporter gene activity, it did not oppose the inhibitory effect of carotenoids. These results suggest that dietary carotenoids inhibit estrogen signaling of both 17beta-estradiol and genistein, and attenuate their deleterious effect in hormone-dependent malignancies.

Effects of bisphenol A-related diphenylalkanes on vitellogenin production in male carp (Cyprinus carpio) hepatocytes and aromatase (CYP19) activity in human H295r adrenocortical carcinoma cells

The present study investigated the effects of the known xenoestrogen bisphenol A (BPA) relative to eight BPA-related diphenylalkanes on estrogen receptor (ER)-mediated vitellogenin (vtg) production in hepatocytes from male carp (Cyprinus carpio), and on aromatase (CYP19) activity in the human adrenocortical H295R carcinoma cell line. Of the eight diphenylalkanes, only 4,4'-(hexafluoropropylidene)diphenol (BHF) and 2,2'-bis(4-hydroxy-3-methylphenyl)propane (BPRO) induced vtg, i.e., to a maximum of 3% to 4% (at 100 microM) compared with 8% for BPA relative to the maximum induction by 17beta-estradiol (E2, 1 microM). Bisphenol A diglycidyl ether (BADGE) was a potent antagonist of vtg production with an IC50 of 5.5 microM, virtually 100% inhibition of vtg at 20 microM, and an inhibitive (IC50) potency about one-tenth that of the known ER antagonist tamoxifen (IC50, 0.6 microM). 2,2'-Diallyl bisphenol A, 4,4'-(1,4-phenylene-diisopropylidene)bisphenol, BPRO, and BHF were much less inhibitory with IC50 concentrations of 20-70 microM, and relative potencies of 0.03 and 0.009 with tamoxifen. Bisphenol ethoxylate showed no anti-estrogenicity (up to 100 microM), and 4,4'-isopropylidene-diphenol diacetate was only antagonistic at 100 microM. When comparing the (anti)estrogenic potencies of these bisphenol A analogues/diphenylalkanes, anti-estrogenicity occurred at lower concentrations than estrogenicity. 4,4'-Isopropylidenebis(2,6-dimethylphenol) (IC50, 2.0 microM) reduced E2-induced (EC50, 100 nM) vtg production due to concentration-dependent cytotoxicity as indicated by a parallel decrease in MTT activity and vtg, whereas the remaining diphenylalkanes did not cause any cytotoxicity relative to controls. None of the diphenylalkanes (up to 100 microM) induced EROD activity indicating that concentration-dependent, CYP1A enzyme-mediated metabolism of E2, or any Ah-receptor-mediated interaction with the ER, was not a likely explanation for the observed anti-estrogenic effects. At concentrations as great as 100 microM, none of the diphenylalkanes directly inhibited aromatase (CYP19) activity in H295R cells. Environmental exposure of fish to BPA and related diphenylalkanes, depending on the structure, may pose anti-estrogenic, and to a lesser extent estrogenic, risks to development and reproduction.

Aryl hydrocarbon receptor-independent activation of estrogen receptor-dependent transcription by 3-methylcholanthrene

Aryl hydrocarbon receptor (AhR) is a ligand-activated transcription factor that stimulates transcription directed by xenobiotic response elements upstream of target genes. Recently, AhR ligands were reported to induce formation of an AhR-estrogen receptor (ER) complex, which can bind to estrogen response elements (EREs) and stimulate transcription of ER target genes. Presently, we investigate the effect of the AhR ligands 3-methylcholanthrene (3MC), 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and 3,3',4,4',5-pentachlorobiphenyl (BZ126) on ERE-regulated luciferase reporter activity and endogenous ER target gene expression. In MCF-7 human breast cancer cells, 3MC induced transcription of ER reporter genes containing native promoter sequences of the ER-responsive genes complement 3 and pS2 and heterologous promoters regulated by isolated EREs. Dose-response studies revealed that the concentration of 3MC required to half-maximally activate transcription (EC(50)) was >100-fold higher for an ER reporter (27-57 muM) than for an AhR reporter (86-250 nM) in both MCF-7 cells and in human endometrial cancer Ishikawa cells. 3MC also stimulated expression of the endogenous ER target genes amphiregulin, cathepsin D and progesterone receptor, albeit to a much lower extent than was achieved following stimulation with 17beta-estradiol. In Ishikawa cells, 3MC, but not BZ126 or TCDD, stimulated ERalpha-dependent reporter activity but did not induce expression of endogenous ER target genes. Finally, studies carried out in the AhR-positive rat hepatoma cell line 5L and the AhR-deficient variant BP8 demonstrated that ER reporter activity could be induced by 3MC in a manner that was independent of AhR and thus distinct from the AhR-ER 'hijacking' mechanism described recently. 3MC may thus elicit estrogenic activity by multiple mechanisms.

An aryl hydrocarbon receptor agonist amplifies the mitogenic actions of estradiol in granulosa cells: evidence of involvement of the cognate receptors

The aryl hydrocarbon receptor (AHR) is a ligand-activated transcription factor that, besides mediating toxic responses, may have a central role in ovarian physiology. Studying the actions of AHR ligands on granulosa cells function, we have found that beta-naphthoflavone amplifies the comitogenic actions of FSH and 17beta-estradiol in a dose-dependent manner. This amplification was even greater in cells that overexpress the AHR and was reversed by cotreatment with the AHR antagonist alpha-naphthoflavone, suggesting that this effect is mediated by the AHR. The estrogen receptor is likewise implicated in this phenomenon, because a pure antiestrogen abolished the described synergism. However, the more traditional inhibitory AHR-estrogen receptor interaction was observed on the estrogen response element-driven transcriptional activity. On the other hand, alpha-naphthoflavone inhibited dose-dependently the mitogenic actions of FSH and 17beta-estradiol. Beta-naphthoflavone induced the expression of Cyp1a1 and Cyp1b1 transcripts, two well-characterized AHR-inducible genes that code for hydroxylases that metabolize estradiol to catecholestrogens. Nevertheless, the positive effect of beta-naphthoflavone on proliferation was not caused by increased metabolism of estradiol to catecholestrogens, because these compounds inhibited the hormonally stimulated DNA synthesis. This latter inhibition exerted by catecholestrogens suggests that these hydroxylases would play a regulatory point in granulosa cell proliferation. Our study indicates that AHR ligands modulate the proliferation of rat granulosa cells, and demonstrates for the first time that an agonist of this receptor is able to amplify the comitogenic action of classical hormones through a mechanism that might implicate a positive cross-talk between the AHR and the estrogen receptor pathways.

2,3,7,8-Tetrachlorodibenzo-p-dioxin increases glycodelin gene and protein expression in human endometrium

CONTEXT

Glycodelin (GdA) is an immunosuppressive endometrial glycoprotein critical for embryonic implantation and pregnancy establishment.

OBJECTIVE

The aim of the present study was to examine the effect of dioxin [2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)] on GdA production in human endometrial cells.

DESIGN

Controlled endometrial explant (EE) and cell cultures were used in this study.

SETTING

Work was conducted at university hospital research laboratories in Bern, Switzerland, and in San Francisco, California.

PATIENTS

Ovulatory women provided endometrial biopsies in the proliferative or secretory phase.

INTERVENTION(S)

EEs and cells were cultured without and with TCDD.

MAIN OUTCOME MEASURE(S)

GdA protein and gene expression were quantified.

RESULTS

A 2.5-fold increase in GdA production was demonstrated in EEs treated with 10 nm TCDD for 9 d. Fluorography revealed a 3- to 4-fold increase in new GdA biosynthesis and secretion in TCDD-treated endometrial epithelial cells. Because the action of dioxin is mediated by the aryl hydrocarbon receptor (AhR), we ascertained that primary epithelial and Ishikawa cells express AhR. Dose responses to TCDD and expressed AhR were established in transiently transfected Ishikawa cells using luciferase fusion vectors containing 1.0 kb of 5' flanking DNA relative to the GdA transcriptional start site but not when shorter promoter constructs were used. A dioxin response element was mapped to nucleotides -539 to -533 of the gene promoter and verified by site-directed mutagenesis.

CONCLUSIONS

We demonstrated a direct AhR-mediated effect of dioxin on GdA gene transcription and protein secretion that might influence human female fertility.

Inhibition of breast cancer cell growth and induction of cell death by 1,1-bis(3'-indolyl)methane (DIM) and 5,5'-dibromoDIM

1,1-Bis(3'-indolyl)methane (DIM) and the 5,5'-dibromo ring substituted DIM (5,5'-diBrDIM) inhibited growth of MCF-7 and MDA-MB-231 breast cancer cells, and IC50 values were 10-20 and 1-5 microM, respectively, in both cell lines. DIM and 5,5'-diBrDIM did not induce p21 or p27 protein levels or alter expression of Sp1 or Sp3 proteins in either cell line. In contrast, 10 microM 5,5'-diBrDIM downregulated cyclin D1 protein in MCF-7 and MDA-MB-231 cells 12 and 24 h after treatment. DIM (20 microM) also decreased cyclin D1 in MCF-7 (24 h) and MDA-MB-231 (12 h), and the DIM/5,5'-diBrDIM-induced degradation of cyclin D1 was blocked by the proteasome inhibitor MG132. Both DIM and 5,5'-diBrDIM induced apoptosis in MCF-7 cells and this was accompanied by decreased Bcl-2, release of mitochondrial cytochrome c, and decreased mitochondrial membrane potential as determined by the red/green fluorescence of JC-1. DIM and 5,5'-diBrDIM induced extensive necrosis in MDA-MB-231 cells; however, this was accompanied by decreased mitochondrial membrane potential primarily in cells treated with 5,5'-diBrDIM but not DIM. Thus, DIM and 5,5'-diBrDIM induce cell death in MCF-7 and MDA-MB-231 cells by overlapping and different pathways, and the ring-substituted DIM represents a novel class of uncharged mitochondrial poisons that inhibit breast cancer cell and tumor growth.

Targets for indole-3-carbinol in cancer prevention

Mounting preclinical and clinical evidence indicate that indole-3-carbinol (I3C), a key bioactive food component in cruciferous vegetables, has multiple anticarcinogenic and antitumorigenic properties. Evidence that p21, p27, cyclin-dependent kinases, retinoblastoma, Bax/Bcl-2, cytochrome P-450 1A1 and GADD153 are targets for I3C already exists. Modification of nuclear transcription factors including Sp1, estrogen receptor, nuclear factor kappaB and aryl hydrocarbon receptor may represent a common site of action to help explain downstream cellular responses to dietary I3C and, ultimately, to its anticancer properties. While the current information is intriguing, future I3C research needs to focus on why these changes in nuclear transcription factors occur and how they relate to phenotypic responses and the quantity and duration of exposure to I3C and its dimer 3,3'-diindolylmethane.

Effect of PCB-126 on intracellular accumulation and transepithelial transport of vinblastine in LLC-PK1 and its transformant cells expressing human P-glycoprotein

The effects of 3, 3', 4, 4', 5-pentachlorobiphenyl (PCB-126), which is the most toxic congener of coplanar polychlorinated biphenyls (Co-PCBs), on intracellular accumulation and transepithelial transport of vinblastine were examined in porcine kidney cells, LLC-PK1, and its transformant cells expressing human P-glycoprotein (LLC-MDR1). The accumulation decreased less than one-tenth in LLC-MDR1 compared to LLC-PK1. In both cells, the accumulation increased with the addition of PCB-126 and cyclosporine A (CYA), which are P-glycoprotein modulators, though the magnitudes were different in these two cell groups as well as for these two chemicals. Thus, PCB-126 might inhibit extrusion of vinblastine through the drug extrusion system as does CYA. In both the cells, there might be an endogenous drug extrusion system other than P-glycoprotein that was inhibited by CYA or PCB-126. The net basal-to-apical transepithelial transport of vinblastine increased 1.7-fold more in LLC-MDR1 than in LLC-PK1. By adding PCB-126 on the apical side, the transport was greatly decreased by -76% in the monolayer of both cells. By adding PCB-126 and CYA on the basal side in LLC-MDR1 monolayer, the transports increased -1.7-fold, so that PCB-126 might inhibit the extrusion of vinblastine on both the apical and basal sides. One of the causes to be considered for the adverse effects of Co-PCBs, in addition to the binding with an aryl hydrocarbon receptor, might be the modification of drug transport by its interaction with the drug transport system.

Protective effects of ursodeoxycholic acid against 2,3,7,8-tetrachlorodibenzo-p-dioxin-induced testicular damage in mice

The protective effect of ursodeoxycholic acid (UDCA), a biliary component found in bears, on 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)-induced testicular damage in mice was investigated. Fifty C57BL/6J mice were equally divided into five groups. The mice in the control group received the vehicle and standard chow. The single TCDD treatment group received 27.5 microg/kg of TCDD subcutaneously. The UDCA-included treatment group received pulverized chow containing 0.125%, 0.25% and 0.5% UDCA, respectively, for 70 days starting 10 days before TCDD injections. The body and testicular weights were shown to be decreased in the single TCDD treatment group, while the decrease was prevented by UDCA added to the chow. In addition, the decrease in the serum-luteinizing hormone (LH) or the follicle stimulating hormone (FSH) secondary to a TCDD injection was not observed in the UDCA-included treatment group. Contrary to the single TCDD treatment group, the germinal epithelium and intercellular space were relatively well preserved in the UDCA-included treatment group. Adding UDCA also normalized TCDD-induced irregular ultrastructural changes such as development of phagolysosomes, inflated smooth endoplasmic reticulum (SER), dilated and altered mitochondria, necrosis and completely damaged seminiferous tubules. Moreover, in the experiment for Arnt expression, UDCA added to the chow suppressed the TCDD-induced relocation of Arnt from the cytoplasm to the nuclei. In conclusion, TCDD-induced testicular toxicity was effectively protected by UDCA. There was almost complete recovery of the testes in the UDCA-included treatment group. Thus, UDCA may be useful for the prevention and treatment of TCDD-induced testicular damage.

$3,3',4,4',5$ -Pentachlorobiphenyl Inhibits Drug Efflux Through P-Glycoprotein in KB-3 Cells Expressing Mutant Human P-Glycoprotein

The effects on the drug efflux of 3,3′,4,4′,5-pentachlorobiphenyl (PCB-126), the most toxic of all coplanar polychlorinated biphenyls (Co-PCBs), were examined in KB-3 cells expressing human wild-type and mutant P-glycoprotein in which the 61st amino acid was substituted for serine or phenylalanine (KB3-Phe⁶¹). In the cells expressing P-glycoproteins, accumulations of vinblastine and colchicine decreased form 85% to 92% and from 62% to 91%, respectively, and the drug tolerances for these chemicals were increased. In KB3-Phe⁶¹, the decreases in drug accumulation were inhibited by adding PCB-126 in a way similar to that with cyclosporine A: by adding 1 μM PCB-126, the accumulations of vinblastine and colchicine increased up to 3.3- and 2.3-fold, respectively. It is suggested that PCB-126 decreased the drug efflux by inhibiting the P-glycoprotein in KB3-Phe⁶¹. Since there were various P-glycoproteins and many congeners of Co-PCBs, this inhibition has to be considered a new cause of the toxic effects of Co-PCBs.