Expression of the aryl hydrocarbon receptor (AhR) and the aryl hydrocarbon receptor nuclear translocator (ARNT) in fetal, benign hyperplastic, and malignant prostate

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

Background

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

Methods/Results

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

Conclusions

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

Potential protective mechanisms of aryl hydrocarbon receptor (AHR) signaling in benign prostatic hyperplasia

The aryl hydrocarbon receptor (AHR) is an evolutionarily conserved ligand activated transcription factor best known for its role in mediating toxic responses to dioxin-like environmental contaminants. However, AHR signaling has also emerged as an active participant in processes of normal development and disease progression. Here, we review the role of AHR signaling in prostate development and disease processes, with a particular emphasis on benign prostatic hyperplasia (BPH). Inappropriate AHR activation has recently been associated with a decreased risk of symptomatic BPH in humans and has been shown to impair prostate development and disrupt endocrine signaling in rodents. We highlight known physiological responses to AHR activation in prostate and other tissues and discuss potential mechanisms by which it may act in adult human prostate to protect against symptomatic BPH.

Modulation of aryl hydrocarbon receptor activity by four and a half LIM domain 2

The aryl hydrocarbon receptor (AhR) mediates transcriptional effects of a diverse array of ligands including environmental contaminants that have been linked to various cancers. The transcriptional activity of the AhR is modulated by different coregulators such as the p160 family members of coactivators and nuclear receptor coactivator 4 (NcoA4). In this study, we provide novel evidence that four and a half LIM only protein 2 (FHL2) interacts with and differentially modulates the transcriptional activity of AhR. Co-immunoprecipitation studies indicate that FHL2 interacts with AhR in a ligand-independent manner but not with its heterodimeric partner, AhR nuclear translocator (ARNT). Overexpression of FHL2 enhanced AhR-mediated expression of a luciferase reporter gene in a dose- and ligand-dependent manner in COS cells. Furthermore, FHL2 cooperated with NcoA4 to synergistically enhance AhR transcriptional activity in these cells. However, the impact of FHL2 on AhR transcriptional activity was cell-specific: FHL2 facilitated AhR action in MCF-7 and PC-3 cells, whereas it suppressed AhR activity in T47D and LNCaP cells. These results of reporter gene studies were corroborated by the impact of FHL2 overexpression on, an established target gene of AhR, cytochrome P450 (CYP1A1) expression. We also demonstrated a potential competition of AhR and androgen receptor (AR) for FHL2 availability in COS cells, as FHL2-facilitation was significantly decreased in the presence of liganded AR. These findings indicate a functional interaction between AhR and FHL2 that modulates the activity of AhR and therefore could affect its role in cancer progression or development.

AHR signaling in prostate growth, morphogenesis, and disease

Most evidence of aryl hydrocarbon receptor (AHR) signaling in prostate growth, morphogenesis, and disease stems from research using 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) to pharmacologically activate the AHR at various stages of development. This review discusses effects of TCDD on prostate morphogenesis and highlights interactions between AHR and other signaling pathways during normal and aberrant prostate growth. Although AHR signaling modulates estrogen and androgen signaling in other tissues, crosstalk between these steroid hormone receptors and AHR signaling cannot account for actions of TCDD on prostate morphogenesis. Instead, the AHR appears to act within a cooperative framework of developmental signals to regulate timing and patterning of prostate growth. Inappropriate activation of AHR signaling as a result of early life TCDD exposure disrupts the balance of these signals, impairs prostate morphogenesis, and has an imprinting effect on the developing prostate that predisposes to prostate disease in adulthood. Mechanisms of AHR signaling in prostate growth and disease are only beginning to be unraveled and recent studies have revealed its interactions with WNT5A, retinoic acid, fibroblast growth factor 10, and vascular endothelial growth factor signaling pathways.

The aryl hydrocarbon receptor (AhR) inhibits vanadate-induced vascular endothelial growth factor (VEGF) production in TRAMP prostates

Hypoxia-inducible factor-1 alpha (HIF-1alpha) and aryl hydrocarbon receptor nuclear translocator (ARNT) are basic helix-loop-helix/per-arnt-sim (PAS) family transcription factors. During angiogenesis and tumor growth, HIF-1alpha dimerizes with ARNT, inducing expression of many genes, including vascular endothelial growth factor (VEGF). ARNT also dimerizes with the aryl hydrocarbon receptor (AhR). AhR-null (Ahr(-/-)) transgenic adenocarcinoma of the mouse prostate (TRAMP) mice develop prostate tumors with greater frequency than AhR wild-type (Ahr(+/+)) TRAMP mice, even though prevalence of prostate epithelial hyperplasia is not inhibited. This suggests that Ahr inhibits prostate carcinogenesis. In TRAMP mice, prostatic epithelial hyperplasia results in stabilized HIF-1alpha, inducing expression of VEGF, a prerequisite for tumor growth and angiogenesis. Since ARNT is a common dimerization partner of AhR and HIF-1alpha, we hypothesized that the AhR inhibits prostate tumor formation by competing with HIF-1alpha for ARNT, thereby limiting VEGF production. Prostates from Ahr(+/+), Ahr(+/-) and Ahr(-/-) C57BL/6J TRAMP mice were cultured in the presence of graded concentrations of vanadate, an inducer of VEGF through the HIF-1alpha-ARNT pathway. Vanadate induced VEGF protein in a dose-dependent fashion in Ahr(+/-) and Ahr(-/-) TRAMP cultures, but not in Ahr(+/+) cultures. However, vanadate induced upstream proteins in the phosphatidylinositol 3-kinase-signaling cascade to a similar extent in TRAMPs of each Ahr genotype, evidenced by v-akt murine thymoma viral oncogene homolog (Akt) phosphorylation. These findings suggest that AhR sequesters ARNT, decreasing interaction with HIF-1alpha reducing VEGF production. Since VEGF is required for tumor vascularization and growth, these studies further suggest that reduction in VEGF correlates with inhibited prostate carcinogenesis in Ahr(+/+) TRAMP mice.

Integrating transcription factor binding site information with gene expression datasets

MOTIVATION

Microarrays are widely used to measure gene expression differences between sets of biological samples. Many of these differences will be due to differences in the activities of transcription factors. In principle, these differences can be detected by associating motifs in promoters with differences in gene expression levels between the groups. In practice, this is hard to do.

RESULTS

We combine correspondence analysis, between group analysis and co-inertia analysis to determine which motifs, from a database of promoter motifs, are strongly associated with differences in gene expression levels. Given a database of motifs and gene expression levels from a set of arrays, the method produces a ranked list of motifs associated with any specified split in the arrays. We give an example using the Gene Atlas compendium of gene expression levels for human tissues where we search for motifs that are associated with expression in central nervous system (CNS) or muscle tissues. Most of the motifs that we find are known from previous work to be strongly associated with expression in CNS or muscle. We give a second example using a published prostate cancer dataset where we can simply and clearly find which transcriptional pathways are associated with differences between benign and metastatic samples.

AVAILABILITY

The source code is freely available upon request from the authors.

Using a combination of cytochrome P450 1B1 and beta-catenin for early diagnosis and prevention of colorectal cancer

BACKGROUND

Although fecal occult blood test and invasive endoscopic examination are common used to detect colorectal adenomas and cancers, non-invasive and specific biomarkers are still under investigation. The objective is to evaluate the biomarker CYP1B1 alone or in combination with aryl hydrocarbon receptor (AhR), nuclear beta-catenin, p53 or bcl-2 for early diagnosis and prevention of colorectal cancer.

METHODS

These biomarkers were analyzed semi-quantified across 231 colonic tissues including 97 adenocarcinomas, 85 adenomas and 49 non-neoplastic colons using immunohistochemistry. In order to differentiate non-neoplastic colons from colorectal neoplasms (adenoma and carcinoma), the values for CYP1B1, AhR, nuclear beta-catenin, p53 and bcl-2 expressions were subjected to discrimination analysis, then the cross-validation, sensitivity and specificity of these models were calculated.

RESULTS

Expressions of CYP1B1, p53, nuclear beta-catenin and bcl-2 were significantly associated with colorectal carcinogenesis (p<0.01 for the trend test). The overexpression rates for CYP1B1, p53, nuclear beta-catenin and bcl-2 were significantly higher in the adenoma and carcinoma groups than in the non-neoplastic colon group (p<0.05). The discrimination models showed that a combination of two biomarkers was better than a single biomarker, and provided specificity ranging from 39% to 100% and sensitivity ranging from 43% to 82% for colorectal carcinoma.

CONCLUSIONS

The increase in expression of CYP1B1 occurred not only in colorectal carcinoma and but also in adenoma. Moreover, a screening panel of CYP1B1 in combination with nuclear beta-catenin was the most suitable marker pair to screen for colorectal carcinoma based on this study.

Identification of Aryl Hydrocarbon Receptor as a Putative Wnt/β-Catenin Pathway Target Gene in Prostate Cancer Cells

Recent genetic and functional analyses have implicated the wnt/beta-catenin signaling pathway in prostate cancer (CaP) pathogenesis. Thus, there is much interest in understanding the consequences of wnt signaling in CaP; target gene expression is one important area of inquiry and is the focus of this report. Adenoviral-mediated overexpression of a mutant, hyperactive form of beta-catenin in CWR22-Rv1 CaP cells led to increased aryl hydrocarbon receptor (AhR, or dioxin receptor) and transmembrane protein 2 RNA transcript expression, as detected by cDNA-microarray analyses. Validating these results, reverse transcription-PCR assays demonstrated that in CWR22-Rv1 cells as well as in LAPC-4 CaP cells, increased putative target gene RNA expression occurs with transient overexpression of mutant beta-catenin, treatment of cells with lithium chloride, or with wnt3a-conditioned medium, three distinct modes of experimental wnt/beta-catenin pathway activation. This beta-catenin-associated expression of AhR and transmembrane protein 2 does not require de novo protein synthesis and may only involve a certain subset of CaP cell lines. Western and immunofluorescence analyses were undertaken to assess the relationship between the wnt/beta-catenin-stimulated increase in AhR transcripts and AhR protein expression; we provide evidence that an association exists whereby up-regulation of AhR RNA by wnt or beta-catenin is coupled with augmented AhR protein levels. Intriguingly, these studies also demonstrated that nuclear beta-catenin staining may not be a sole deciding factor when predicting the status of wnt/beta-catenin signaling in CaP cells. Finally, the extent to which wnt signaling may synergize with an environmental agonist of AhR (2,3,7,8-tetrachlorodibenzo-p-dioxin) to potentiate AhR transcriptional activity was examined. Considering previous work linking AhR to processes of development and carcinogenesis, our data may highlight one particular role for wnt/beta-catenin signaling in prostate tumor biology.

Cell selective cAMP induction of rat CYP1B1 in adrenal and testis cells. Identification of a novel cAMP-responsive far upstream enhancer and a second Ah receptor-dependent mechanism

CYP1B1 is unique among P450 cytochromes in exhibiting inductive responses mediated by both the Ah receptor (AhR) and cAMP. cAMP induction was mediated either by a 189bp far upstream enhancer region (FUER, -5110 to -5298) or by a 230bp AhR-responsive enhancer region (AhER) (-797 to -1026). CYP1B1 luciferase reporters respond selectively to cAMP and TCDD in adrenal Y-1 cells (only cAMP), testis MA10 cells (cAMP>TCDD), and C3H10T1/2 mouse embryo fibroblasts (only TCDD). In Y-1 cells, which lack AhR, cAMP induction is totally dependent on the FUER, including absolute requirements for upstream and downstream halves of this region, and for CREB activity at a CRE sequence located at the 3(')-end. cAMP stimulation of the FUER was remarkably high (27-fold) and equally effective when linked to an HSV-TK promoter, indicating direct cAMP activation of the FUER. Binding of CREB to the essential CRE was demonstrated along with dominant negative effects of functionally impaired mutants. cAMP induction in MA10 cells was partially mediated by the FUER mechanism but was regulated additionally by AhER through AhR activity. MA10 cells also exhibit cAMP-dependent AhR down-regulation and AhR/Arnt complex formation. Mutations in AhER including XRE5 were similarly inhibitory to cAMP stimulation in MA10 cells and to TCDD stimulation in C3H10T1/2 cells. Transfection of AhR into the AhR-deficient Y-1 cells did not introduce this second mechanism, which indicated a need for additional components that are present in MA10 cells.

Association of the genetic polymorphism in cytochrome P450 (CYP) 1A1 with risk of familial prostate cancer in a Japanese population: a case-control study

Association between genetic polymorphisms of CYP1A1 and familial prostate cancer risk was examined by a case-control study of 185 individuals. Although the individual analysis of m1 or m2 genotype of CYP1A1 showed no significant association with prostate cancer risk, the presence of any mutated alleles significantly increased prostate cancer risk in comparison with wild-type genotypes by combination analysis (odds ratio [OR]=2.38; 95% confidence interval [CI]=1.72-3.29; P=0.0069). Furthermore, metastatic cancer had a significant association with mutated alleles of m1 and m2. These finding suggested that CYP1A1 polymorphisms has an association with prostate cancer risk, especially with progression of prostate cancer.

Overexpression of aryl hydrocarbon receptor in human lung carcinomas

Exposure to polycylic aromatic hydrocarbons (PAH) has been associated with increased risk of lung cancer. Aryl hydrocarbon receptor (AhR) is known to play an essential role in PAH-induced toxicity. The objectives of this study were to identify and evaluate AhR expression in normal human lung tissues and in lung carcinomas. AhR protein and mRNA levels in human lung cell lines were evaluated with immunoblot and quantitative real-time RT-PCR assays, respectively. AhR protein expression was high in cytosol homogenates of adenocarcinoma (AD) cell lines and AhR mRNA levels corresponded well with AhR protein levels in these cell lines. AhR expression in human lung tissues and carcinomas were examined by means of immunohistochemical staining method. In normal lung tissues, immunostaining was found in the cytosol of bronchiolar epithelial cells. AhR immunostaining was more intense in AD than in squamous cell carcinomas. When AhR expression was compared with noral bronchiolar epithelial cells and neoplastic cells in the same specimens, the neoplastic cells, especially those of AD, demonstrated an increased staining. The upregulation of AhR mRNA expression was also demonstrated among 2 of 4 paired tissues with the quantitative real-time RT-PCR assay. Our data indicated that AhR expression was upregulated in lung AD and suggested that AhR and its expression might play an important role in the development of lung AD.

Existence of xenobiotic response element binding in Dictyostelium

Xenobiotic response element (XRE) is a core nucleotide sequence at the upstream of inducible target genes for the transcription factor aryl hydrocarbon receptor (AhR) that is responsible for recognition of exogenous environmental pollutants in eukaryotic cells. Gel retardation electrophoresis revealed the presence of binding of a radiolabeled probe containing XRE in both cytosolic and nuclear preparations of the slime mold Dictyostelium. Unlabeled XRE probe was more potent in competing for XRE binding in both fractions than unlabeled XRE probe with a point mutation at the core element. Limited proteolysis by V8 protease did not markedly affect XRE binding in both fractions, while XRE binding decreased during in vitro incubation at 30 degrees C for up to 24 h at decline rates proportional to increasing pHs at a range of 6.5-8.5 in cytosolic fractions in a manner different from those in nuclear fractions. Deprivation of nutrients induced aggregation of cells within 4-8 h later, followed by formation of first finger tips around 12 h later and subsequent development to mobile slugs within 16 h and then to fruit bodies between 20 and 24 h later. The starvation led to a marked decrement of XRE binding in cytosolic fractions 4-36 h later, followed by a robust but transient increment of that in nuclear extracts 12-20 h afterward. However, XRE binding was not affected by antibodies against AhR-related proteins known to date in both fractions irrespective of nutritional conditions. These results suggest the abundance of as-yet unidentified proteins with high affinity for XRE in the slime mold Dictyostelium. The possibility that those proteins may be translocated from the cytoplasm to the nucleus in response to cellular development during starvation is feasible.

Increased arylhydrocarbon receptor expression offers a potential therapeutic target for pancreatic cancer

The arylhydrocarbon receptor (AhR) was initially identified as a member of the adaptive metabolic and toxic response pathway to polycyclic aromatic hydrocarbons and to halogenated dibenzo-p-dioxins and dibenzofurans. In the present study, we sought to determine the functional significance of the AhR pathway in pancreatic carcinogenesis. AhR expression was analysed by Northern blotting. The exact site of AhR expression was analysed by in situ hybridization and immunohistochemistry. The effects of TCDD and four selective AhR agonists on pancreatic cancer cell lines were investigated by growth assays, apoptosis assays, and induction of the cyclin-dependent kinase inhibitor p21. There was strong AhR mRNA expression in 14 out of 15 pancreatic cancer samples, weak expression in chronic pancreatitis tissues, and faint expression in all normal pancreata. In pancreatic cancer tissues, AhR mRNA and protein expression were localized in the cytoplasm of pancreatic cancer cells. TCDD and the four AhR agonists inhibited pancreatic cancer cell growth in a dose-dependent manner, and decreased anchorage-independent cell growth. DAPI staining did not reveal nuclear fragmentation and CYP1A1 and was not induced by TCDD and AhR agonists. In contrast, TCDD and AhR agonists induced the expression of the cyclin-dependent kinase inhibitor p21. In conclusion, the relatively non-toxic AhR agonists caused growth inhibition in pancreatic cancer cells with high AhR expression levels via cell cycle arrest. In addition, almost all human pancreatic cancer tissues expressed this receptor at high levels, suggesting that these or related compounds may play a role in the therapy of pancreatic cancer in the future.

Differential expression of interleukin-15, a pro-inflammatory cytokine and T-cell growth factor, and its receptor in human prostate

BACKGROUND

Pro-inflammatory interleukin (IL)-15 plays a major role in host defense and chronic inflammation by stimulating T-lymphocyte recruitment and growth. Expression of IL-15 and IL-15 receptor (IL-15R) in human prostate was examined.

METHODS

Normal and benign hyperplastic (BPH) prostate specimens (n = 23) were analyzed for IL-15 and IL-15Ralpha-chain expression by immunohistochemistry and Real-Time-PCR/RT-PCR. Regulation of prostatic stromal cell (PSC) IL-15 mRNA and effect of IL-15 on prostatic cell growth were analysed in vitro.

RESULTS

In normal prostate, anti-IL-15 and anti-IL-15Ralpha-chain reactivity were restricted to smooth muscle and stromal cells. However, in BPH, in addition epithelial cells frequently exhibited discrete anti-IL-15R and often intense, membranous anti-IL-15 reactivity. IL-15/IL-15R mRNA were detected in all prostatic cells types. In BPH tissues, IL-15 mRNA content was variable (15-fold). IL-15 mRNA synthesis of PSC was significantly up-regulated by IFN-gamma. Furthermore IL-15 strongly stimulated the growth of BPH-T-lymphocytes and weakly that of carcinoma cell lines, but not of stromal cells.

CONCLUSIONS

Overexpression of IL-15 and IL-15Ralpha-chain in BPH and massive proliferation of BPH-T-lymphocytes induced by IL-15 suggest a role for IL-15 in prostatic inflammation. Since IFN-gamma, a T-lymphocyte product, stimulates prostatic IL-15 production; chronic inflammation might be triggered by this paracrine loop.