Project description:Background: The Aryl hydrocarbon receptor (AHR) is a ligand-activated transcription factor that is activated by xenobiotic chemicals that function as AHR ligands. The response to xenobiotic AHR ligands is toxicity and the induction of drug metabolizing enzymes. The impact of AHR knockdown on gene expression and pathways in human breast cancer cells in absence of xenobiotic AHR ligands has not been investigated on a genome-wide scale. Methods: MCF-7 cells were used as a model of human breast cancer. The AHR was silenced with short interfering RNA against AHR (siAHR). RNA-sequencing coupled with Ingenuity pathway analysis (IPA) was used to determine the impact of AHR knockdown on gene expression and pathways in the absence of xenobiotic AHR ligands. Western blot analysis and recombinant tumor necrosis factor (TNF) was used to investigate the impact of AHR knockdown on TNF induction of MNSOD expression. Results: We found that the AHR is transcriptionally active in MCF-7 breast cancer cells in the absence of xenobiotic AHR ligands. In total, the expression of 634 genes was significantly changed in AHR knockdown cells compared to controls at a false discovery rate of < 10%. The analysis confirmed that drug metabolizing enzymes were AHR targets; however, we found that AHR also promoted the expression of genes that were not directly related to the metabolism of xenobiotics, such as those involved in lipid and eicosanoid synthesis. Gene pathway analysis of the AHR regulated gene dataset predicted TNF activity to be reduced in AHR knockdown cells. Our finding that AHR knockdown inhibited TNF-stimulated increases in MNSOD expression confirmed this IPA prediction. Conclusions: This is the first gene expression profiling study of AHR knockdown breast cancer cells. Several known and novel AHR targets were identified. The results suggest that endogenous AHR regulation impacts eicosanoid synthesis by regulating gene expression. The IPA prediction of reduced TNF activity in AHR knockdown cells was confirmed by showing that TNF-induced increases in MNSOD expression was inhibited in AHR knockdown cells. The requirement of AHR for MNSOD activation is novel and provides a new link by which AHR may impact reactive oxidative species (ROS) signaling. Expression profiles by mRNA sequencing were generated for human MCF-7 cells transfected with cRNAi (6 replicates) or AHR-siRNA (5 replicates) for 36hr. Sequencing was performed on an Illumina HiSeq 1000 using a 2x100 base paired-end strategy.

Project description:Background: The Aryl hydrocarbon receptor (AHR) is a ligand-activated transcription factor that is activated by xenobiotic chemicals that function as AHR ligands. The response to xenobiotic AHR ligands is toxicity and the induction of drug metabolizing enzymes. The impact of AHR knockdown on gene expression and pathways in human breast cancer cells in absence of xenobiotic AHR ligands has not been investigated on a genome-wide scale. Methods: MCF-7 cells were used as a model of human breast cancer. The AHR was silenced with short interfering RNA against AHR (siAHR). RNA-sequencing coupled with Ingenuity pathway analysis (IPA) was used to determine the impact of AHR knockdown on gene expression and pathways in the absence of xenobiotic AHR ligands. Western blot analysis and recombinant tumor necrosis factor (TNF) was used to investigate the impact of AHR knockdown on TNF induction of MNSOD expression. Results: We found that the AHR is transcriptionally active in MCF-7 breast cancer cells in the absence of xenobiotic AHR ligands. In total, the expression of 634 genes was significantly changed in AHR knockdown cells compared to controls at a false discovery rate of < 10%. The analysis confirmed that drug metabolizing enzymes were AHR targets; however, we found that AHR also promoted the expression of genes that were not directly related to the metabolism of xenobiotics, such as those involved in lipid and eicosanoid synthesis. Gene pathway analysis of the AHR regulated gene dataset predicted TNF activity to be reduced in AHR knockdown cells. Our finding that AHR knockdown inhibited TNF-stimulated increases in MNSOD expression confirmed this IPA prediction. Conclusions: This is the first gene expression profiling study of AHR knockdown breast cancer cells. Several known and novel AHR targets were identified. The results suggest that endogenous AHR regulation impacts eicosanoid synthesis by regulating gene expression. The IPA prediction of reduced TNF activity in AHR knockdown cells was confirmed by showing that TNF-induced increases in MNSOD expression was inhibited in AHR knockdown cells. The requirement of AHR for MNSOD activation is novel and provides a new link by which AHR may impact reactive oxidative species (ROS) signaling.

Project description:The Aryl hydrocarbon Receptor (AhR) is a signal regulated transcription factor, which is canonically activated by the direct binding of xenobiotics. In addition, switching cells from adherent to suspension culture also activates the AhR, representing a non-xenobiotic, physiological activation of AhR signaling. Here, we show that the AhR is recruited to target gene enhancers in both ligand (YH439) treated and suspension cells, suggesting a common mechanism of target gene induction between these two routes of AhR activation. However, gene expression profiles critically differ between xenobiotic and suspension activated AhR signaling. Por, and Cldnd1 were regulated predominately by ligand treatments, while in contrast, ApoER2 and Ganc were regulated predominately by the suspension condition. Classic xenobiotic metabolizing AhR targets such as Cyp1a1, Cyp1b1, and Nqo1 were regulated by both ligand and suspension conditions. Temporal expression patterns of AhR target genes were also found to vary, with examples of transient activation, transient repression, or sustained alterations in expression. Furthermore, sequence analysis coupled with ChIP assays and reporter gene analysis identified a functional XRE (xenobiotic response element) within the mouse Tiparp gene that features a concatemer of 4 XRE cores (GCGTG) residing in the first intron ~1.2kb downstream of the Tiparp transcription start site. Our data suggest that this XRE concatemer site concurrently regulates the expression of both Tiparp gene and its cis anti-sense non-coding RNA following ligand or suspension induced AhR activation. This work lends novel insights into how AhR signaling drives different transcriptional programs via the ligand versus suspension modes of activation. Reference: Murray IA et al. (2005) Evidence that ligand binding is a key determinant of Ah receptor-mediated transcriptional activity. Arch Biochem Biophys 442(1):59-71. Reference: Monk SA et al. (2001) Transient expression of CYP1A1 in rat epithelial cells cultured in suspension. Arch Biochem Biophys 393(1):154-162. Reference: Chua SW et atl. (2006) A novel normalization method for effective removal of systematic variation in microarray data. Nucleic acids research 34(5):e38. 18 microarray samples consisting of AhR null and reconstituted hepatocytes subjected to 10M-NM-<M YH439, 0.1% DMSO carrier control or grown in suspension culture for 8 hours in 3 biologial replicates.

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