Decoding Cinnabarinic Acid-Specific Stanniocalcin 2 Induction by Aryl Hydrocarbon Receptor.

Aryl hydrocarbon receptor (AhR) is a ligand-mediated transcription factor known for regulating response to xenobiotics, including prototypical 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) through the activation of CYP1A1 expression. Upon ligand-binding, AhR translocates to the nucleus, interacts with the AhR nuclear translocator, and binds to xenobiotic response elements (XREs; GCGTG) present in the promoter region of AhR-regulated genes. Recently, we identified a novel tryptophan catabolite, cinnabarinic acid (CA), as an endogenous AhR agonist capable of activating expression of AhR target gene stanniocalcin 2 (stc2). The CA-driven stc2 induction bestowed cytoprotection against hepatotoxicity in an AhR-dependent manner. Interestingly, only CA but not TCDD was able to induce stc2 expression in liver, and CA was unable to upregulate the TCDD responsive cyp1a1 gene. In this report, we identified CA-specific histone H4 lysine 5 acetylation and H3 lysine 79 methylation at the AhR-bound stc2 promoter. Moreover, histone H4 lysine 5 acetylation writer, activating transcription factor 2 (Atf2), and H3 lysine 79 methylation writer, disruptor of telomeric silencing 1-like histone lysine methyltransferase (Dot1l), were interacting with the AhR complex at the stc2 promoter exclusively in response to CA treatment concurrent with the histone epigenetic marks. Suppressing Atf2 and Dot1l expression using RNA interference confirmed their role in stc2 expression. CRISPR/Cas9-assisted replacement of cyp1a1 promoter-encompassing XREs with stc2 promoter XREs resulted in CA-dependent induction of cyp1a1, underlining a fundamental role of quaternary structure of XRE sequence in agonist-specific gene regulation. In conclusion, CA-driven recruitment of specific chromatin regulators to the AhR complex and resulting histone epigenetic modifications may serve as a molecular basis for agonist-specific stc2 regulation by AhR. SIGNIFICANCE STATEMENT: Results reported here provide a mechanistic explanation for the agonist-specific differential gene regulation by identifying interaction of aryl hydrogen receptor with specific chromatin regulators concomitant with unique histone epigenetic marks. This study also demonstrated that the agonist-specific target-gene expression can be transferred with the gene-specific promoter xenobiotic response element-sequence in the context of chromatin architecture.

Patil NY ，Tang H ，Rus I ，Zhang K ，Joshi AD ... -  《-》

Epigenetic Regulation by Agonist-Specific Aryl Hydrocarbon Receptor Recruitment of Metastasis-Associated Protein 2 Selectively Induces Stanniocalcin 2 Expression.

The aryl hydrocarbon receptor (AhR) is a ligand-activated transcription factor that regulates a plethora of target genes. Historically, the AhR has been studied as a regulator of xenobiotic metabolizing enzyme genes, notably cytochrome P4501A1 encoded by CYP1A1, in response to the exogenous prototypical ligand 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). AhR activity depends on its binding to the xenobiotic response element (XRE) in partnership with the AhR nuclear translocator (Arnt). Recent studies identified stanniocalcin 2 (Stc2) as a novel AhR target gene responsive to the endogenous AhR agonist cinnabarinic acid (CA). CA-dependent AhR-XRE-mediated Stc2 upregulation is responsible for cytoprotection against ectoplasmic reticulum/oxidative stress-induced apoptosis both in vitro and in vivo. Significantly, CA but not TCDD induces expression of Stc2 in hepatocytes. In contrast to TCDD, CA is unable to induce the CYP1A1 gene, thus revealing an AhR agonist-specific mutually exclusive dichotomous transcriptional response. Studies reported here provide a mechanistic explanation for this differential response by identifying an interaction between the AhR and the metastasis-associated protein 2 (MTA2). Moreover, the AhR-MTA2 interaction is CA-dependent and results in MTA2 recruitment to the Stc2 promoter, concomitant with agonist-specific epigenetic modifications targeting histone H4 lysine acetylation. The results demonstrate that histone H4 acetylation is absolutely dependent on CA-induced AhR and MTA2 recruitment to the Stc2 regulatory region and induced Stc2 gene expression, which in turn confers cytoprotection to liver cells exposed to chemical insults.

Joshi AD ，Hossain E ，Elferink CJ 《-》

Single Nucleotide Polymorphisms (SNPs) Distant from Xenobiotic Response Elements Can Modulate Aryl Hydrocarbon Receptor Function: SNP-Dependent CYP1A1 Induction.

CYP1A1 expression can be upregulated by the ligand-activated aryl hydrocarbon receptor (AHR). Based on prior observations with estrogen receptors and estrogen response elements, we tested the hypothesis that single-nucleotide polymorphisms (SNPs) mapping hundreds of base pairs (bp) from xenobiotic response elements (XREs) might influence AHR binding and subsequent gene expression. Specifically, we analyzed DNA sequences 5 kb upstream and downstream of the CYP1A1 gene for putative XREs. SNPs located ±500 bp of these putative XREs were studied using a genomic data-rich human lymphoblastoid cell line (LCL) model system. CYP1A1 mRNA levels were determined after treatment with varying concentrations of 3-methylcholanthrene (3MC). The rs2470893 (-1694G>A) SNP, located 196 bp from an XRE in the CYP1A1 promoter, was associated with 2-fold variation in AHR-XRE binding in a SNP-dependent fashion. LCLs with the AA genotype displayed significantly higher AHR-XRE binding and CYP1A1 mRNA expression after 3MC treatment than did those with the GG genotype. Electrophoretic mobility shift assay (EMSA) showed that oligonucleotides with the AA genotype displayed higher LCL nuclear extract binding after 3MC treatment than did those with the GG genotype, and mass spectrometric analysis of EMSA protein-DNA complex bands identified three candidate proteins, two of which were co-immunoprecipitated with AHR. In conclusion, we have demonstrated that the rs2470893 SNP, which maps 196 bp from a CYP1A1 promoter XRE, is associated with variations in 3MC-dependent AHR binding and CYP1A1 expression. Similar "distant SNP effects" on AHR binding to an XRE motif and subsequent gene expression might occur for additional AHR-regulated genes.

Liu D ，Qin S ，Ray B ，Kalari KR ，Wang L ，Weinshilboum RM ... -  《-》

Aryl hydrocarbon receptor-dependent induction of cyp1a1 by bilirubin in mouse hepatoma hepa 1c1c7 cells.

Sinal CJ ，Bend JR 《MOLECULAR PHARMACOLOGY》

Analysis of the transcriptional regulation and molecular function of the aryl hydrocarbon receptor repressor in human cell lines.

Haarmann-Stemmann T ，Bothe H ，Kohli A ，Sydlik U ，Abel J ，Fritsche E ... -  《DRUG METABOLISM AND DISPOSITION》