Analysis of the AHR gene proximal promoter GGGGC-repeat polymorphism in lung, breast, and colon cancer

Sinomenine increases the methylation level at specific GCG site in mPGES-1 promoter to facilitate its specific inhibitory effect on mPGES-1

Prostaglandin E₂ (PGE₂) in cancer and inflammatory diseases is a key mediator of disease progression. Non-steroidal anti-inflammatory drugs (NSAIDs) are widely used to inhibit the expression of PGE₂ by depressing cyclooxygenase (COX) in inflammatory treatments. However, the inhibition to COXs may cause serious side effects. Thus, it is urgent to develop new anti-inflammatory drugs aiming new targets to inhibit PGE₂ production. Microsomal prostaglandin E synthase 1 (mPGES-1) catalyzes the final step of PGE₂ biosynthesis. Therefore, the selective inhibition of mPGES-1 has become a promising strategy in the treatments of cancer and inflammatory diseases. Our previous studies confirmed that sinomenine (SIN) is a specific mPGES-1 inhibitor. However, the exact mechanism by which SIN inhibits mPGES-1 remains unknown. This study aimed to explain the regulation effect of SIN to mPGES-1 gene expression by its DNA methylation induction effect. We found that the demethylating agent 5-azacytidine (5-AzaC) reversed the inhibitory effect of SIN to mPGES-1. Besides, SIN selectively increased the methylation level of the promoter region in the mPGES-1 gene while the pretreatment of 5-AzaC suppressed this effect. The results also shows that pretreatment with SIN increased the methylation level of specific GCG sites in the promoter region of mPGES-1. This specific methylation site may become a new biomarker for predicting and diagnosing RA and cancer with high expression of mPGES-1. Also, our research provides new ideas and solutions for clinical diagnosis and treatment of diseases related to mPGES-1 and for targeted methylation strategy in drug development.

Cullin 4-DCAF Proteins in Tumorigenesis

Cullin-RING ligase 4 (CRL4), a member of the cullin-RING ligase family, orchestrates a variety of critical cellular processes and pathophysiological events. Recent results from mouse genetics, clinical analyses, and biochemical studies have revealed the impact of CRL4 in development and cancer etiology and elucidated its in-depth mechanism on catalysis of ubiquitination as a ubiquitin E3 ligase. Here, we summarize the versatile roles of the CRL4 E3 ligase complexes in tumorigenesis dependent on the evidence obtained from knockout and transgenic mouse models as well as biochemical and pathological studies.

The citrus flavonone hesperetin attenuates the nuclear translocation of aryl hydrocarbon receptor

The environmental polycyclic aromatic hydrocarbons (PAH) and dioxins are carcinogens and their adverse effects have been largely attributed to the activation of AhR. Hesperetin is a flavonone found abundantly in citrus fruits and has been shown to be a biologically active agent. In the present study, the effect of hesperetin on the nuclear translocation of AhR and the downstream gene expression was investigated in MCF-7 cells. Confocal microscopy indicated that 7, 12-dimethylbenz[α]anthracene (DMBA) or 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) -induced nuclear translocation of AhR was deterred by hesperetin treatment. The reduced nuclear translocation could also be observed in Western analysis. Reporter-gene assay further illustrated that the induced XRE transactivation was weakened by the treatment of hesperetin. Quantitative reverse transcriptase-polymerase chain reaction (RT-PCR) assay demonstrated that the gene expressions of CYP1A1, 1A2, and 1B1 followed the same pattern of AhR translocation. These results suggested that hesperetin counteracted AhR transactivation and suppressed the downstream gene expression.

Structure-Activity Relationships of the Main Bioactive Constituents of Euodia rutaecarpa on Aryl Hydrocarbon Receptor Activation and Associated Bile Acid Homeostasis

Rutaecarpine (RUT), evodiamine (EOD), and dehydroevodiamine (DHED) are the three main bioactive indoloquinazoline alkaloids isolated from Euodia rutaecarpa, a widely prescribed traditional Chinese medicine. Here, the structure-activity relationships of these analogs for aryl hydrocarbon receptor (AHR) activation were explored by use of Ahr-deficient (Ahr^-/-) mice, primary hepatocyte cultures, luciferase reporter gene assays, in silico ligand-docking studies, and metabolomics. In vitro, both mRNA analysis of AHR target genes in mouse primary hepatocytes and luciferase reporter assays in hepatocarcinoma cell lines demonstrated that RUT, EOD, and DHED significantly activated AHR, with an efficacy order of RUT > DHED > EOD. Ligand-docking analysis predicted that the methyl substitute at the N-14 atom was a key factor affecting AHR activation. In vivo, EOD was poorly orally absorbed and failed to activate AHR, whereas RUT and DHED markedly upregulated expression of the hepatic AHR gene battery in wild-type mice, but not in Ahr^-/- mice. Furthermore, RUT, EOD, and DHED were not hepatotoxic at the doses used; however, RUT and DHED disrupted bile acid homeostasis in an AHR-dependent manner. These findings revealed that the methyl group at the N-14 atom of these analogs and their pharmacokinetic behaviors were the main determinants for AHR activation, and suggest that attention should be given to monitoring bile acid metabolism in the clinical use of E. rutaecarpa.

AHR and CYP1A expression link historical contamination events to modern day developmental effects in the American alligator

The aryl hydrocarbon receptor (AHR) is a ligand-activated transcription factor that initiates a transcriptional pathway responsible for the expression of CYP1A subfamily members, key to the metabolism of xenobiotic compounds. Toxic planar halogenated aromatic hydrocarbons, including dioxin and PCBs, are capable of activating the AHR, and while dioxin and PCB inputs into the environment have been dramatically curbed following strict regulatory efforts in the United States, they persist in the environment and exposures remain relevant today. Little is known regarding the effects that long-term chronic exposures to dioxin or dioxin-like compounds might have on the development and subsequent health of offspring from exposed individuals, nor is much known regarding AHR expression in reptilians. Here, we characterize AHR and CYP1A gene expression in embryonic and juvenile specimen of a long-lived, apex predator, the American alligator (Alligator mississippiensis), and investigate variation in gene expression profiles in offspring collected from sites conveying differential exposures to environmental contaminants. Both age- and tissue-dependent patterning of AHR isoform expression are detected. We characterize two downstream transcriptional targets of the AHR, CYP1A1 and CYP1A2, and describe conserved elements of their genomic architecture. When comparisons across different sites are made, hepatic expression of CYP1A2, a direct target of the AHR, appears elevated in embryos from a site associated with a dioxin point source and previously characterized PCB contamination. Elevated CYP1A2 expression is not persistent, as site-specific variation was absent in juveniles originating from field-collected eggs but reared under lab conditions. Our results illustrate the patterning of AHR gene expression in a long-lived environmental model species, and indicate a potential contemporary influence of historical contamination. This research presents a novel opportunity to link contamination events to critical genetic pathways during embryonic development, and carries significant potential to inform our understanding of potential health effects in wildlife and humans.

Aryl hydrocarbon receptor gene transitions (c.-742C>T; c.1661G>A) and idiopathic male infertility: a case-control study with in silico and meta-analysis

Aryl hydrocarbon receptor (AHR) is responsible for crucial events in male reproductive biology. Here, the association of the AHR transitions c.-742C>T and c.1661G>A with idiopathic male infertility was investigated in a case-control study, which is followed by a meta-analysis and a bioinformatic investigation. Blood and semen samples were obtained from a total of 135 idiopathic infertile men and 130 healthy controls. Participants were genotyped for the transitions using a PCR-RFLP method. A meta-analysis of five sets of data evaluated the association of c.1661G>A with male infertility, and using an in silico analysis, the possible molecular effects of the transitions predicted. Genotypes and alleles of AHR-c.-742C>T and c.1661G>A polymorphisms were not associated with the risk of male infertility significantly. However, the frequency of C/A haplotype was significantly associated with the increased risk of male infertility, and T/A haplotype was higher among controls significantly. Also, the frequencies of combined genotypes CT/GG, CT/GA and TT/GG were significantly associated with decreased risk of infertility. And, the meta-analysis showed that the AA versus GA/GG recessive model is associated with decreased risk of male infertility among the Iranian population. In silico analysis predicted that c.-742C>T does not alter the binding sites of the proposed transcription factors, but c.1661G>A poses a tolerable structural disturbance in AHR protein. In conclusion, these results showed that AHR c.-742C>T and c.1661G>A transitions separately could not be nominated as a risk or protective factor for male infertility. However, some combined models could affect infertility risk, especially among Iranian men.

Compendium of TCDD-mediated transcriptomic response datasets in mammalian model systems

Background

2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) is the most potent congener of the dioxin class of environmental contaminants. Exposure to TCDD causes a wide range of toxic outcomes, ranging from chloracne to acute lethality. The severity of toxicity is highly dependent on the aryl hydrocarbon receptor (AHR). Binding of TCDD to the AHR leads to changes in transcription of numerous genes. Studies evaluating the transcriptional changes brought on by TCDD may provide valuable insight into the role of the AHR in human health and disease. We therefore compiled a collection of transcriptomic datasets that can be used to aid the scientific community in better understanding the transcriptional effects of ligand-activated AHR.

Results

Specifically, we have created a datasets package – TCDD.Transcriptomics – for the R statistical environment, consisting of 63 unique experiments comprising 377 samples, including various combinations of 3 species (human derived cell lines, mouse and rat), 4 tissue types (liver, kidney, white adipose tissue and hypothalamus) and a wide range of TCDD exposure times and doses. These datasets have been fully standardized using consistent preprocessing and annotation packages (available as of September 14, 2015). To demonstrate the utility of this R package, a subset of “AHR-core” genes were evaluated across the included datasets. Ahrr, Nqo1 and members of the Cyp family were significantly induced following exposure to TCDD across the studies as expected while Aldh3a1 was induced specifically in rat liver. Inmt was altered only in liver tissue and primarily by rat-AHR.

Conclusions

Analysis of the “AHR-core” genes demonstrates a continued need for studies surrounding the impact of AHR-activity on the transcriptome; genes believed to be consistently regulated by ligand-activated AHR show surprisingly little overlap across species and tissues. Until now, a comprehensive assessment of the transcriptome across these studies was challenging due to differences in array platforms, processing methods and annotation versions. We believe that this package, which is freely available for download (http://labs.oicr.on.ca/boutros-lab/tcdd-transcriptomics) will prove to be a highly beneficial resource to the scientific community evaluating the effects of TCDD exposure as well as the variety of functions of the AHR.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-016-3446-z) contains supplementary material, which is available to authorized users.

Aryl hydrocarbon receptor (AhR)-dependent regulation of pulmonary miRNA by chronic cigarette smoke exposure

The aryl hydrocarbon receptor (AhR) is a ligand-activated transcription factor historically known for its toxic responses to man-made pollutants such as dioxin. More recently, the AhR has emerged as a suppressor of inflammation, oxidative stress and apoptosis from cigarette smoke by mechanisms that may involve the regulation of microRNA. However, little is known about the AhR regulation of miRNA expression in the lung in response to inhaled toxicants. Therefore, we exposed Ahr^−/− and Ahr^+/− mice to cigarette smoke for 4 weeks and evaluated lung miRNA expression by PCR array. There was a dramatic regulation of lung miRNA by the AhR in the absence of exogenous ligand. In response to cigarette smoke, there were more up-regulated miRNA in Ahr^−/− mice compared to Ahr^+/− mice, including the cancer-associated miRNA miR-96. There was no significant change in the expression of the AhR regulated proteins HuR and cyclooxygenase-2 (COX-2). There were significant increases in the anti-oxidant gene sulfiredoxin 1 (Srxn1) and FOXO3a- predicted targets of miR-96. Collectively, these data support a prominent role for the AhR in regulating lung miRNA expression. Further studies to elucidate a role for these miRNA may further uncover novel biological function for the AhR in respiratory health and disease.