3-Methylcholanthrene Induces Differential Recruitment of Aryl Hydrocarbon Receptor to Human Promoters

Abstract

The aryl hydrocarbon receptor (AHR) is a ligand-activated protein that mediates the toxic actions of polycyclic aromatic and halogenated compounds. Identifying genes directly regulated by AHR is important in understanding the pathways regulated by this receptor. Here we used the techniques of chromatin immunoprecipitation and DNA microarrays (ChIP-chip) to detect AHR-bound genomic regions after 3-methylcholanthrene (3MC) treatment of T-47D human breast cancer cells. We identified 241 AHR-3MC-bound regions, and transcription factor-binding site analysis revealed a strong overrepresentation of the AHR-responsive element. Conventional ChIP confirmed recruitment of AHR to 26 regions with target gene responses to 3MC varying from activation to inhibition to having no effect. A comparison of identified AHR-3MC-bound regions with AHR-2,3,7,8-tetrchlorodibenzo-p-dioxin (TCDD)-bound regions from our previous study (Ahmed, S., Valen, E., Sandelin, A., and Matthews, J. (2009). Toxicol. Sci. 111, 254-266) revealed that 127 regions were common between the data sets. Time course ChIPs for six of the regions showed that 3MC induced gene-specific changes in histone H3 acetylation and methylation and induced differential oscillatory binding of AHR, with a periodicity between 1.5 and 2 h. Re-treatment of cells with 3MC failed to alter the oscillatory binding profiles of AHR or aryl hydrocarbon receptor nuclear translocator. Cells became responsive to 3MC but not TCDD after 24 h of exposure to 3MC, highlighting important differences in AHR responsiveness between the two ligands. Our results reveal a number of novel AHR-bound promoter regions and target genes that exhibit differential kinetic binding profiles and regulation by AHR.

Xenobiotics and Loss of Cell Adhesion Drive Distinct Transcriptional Outcomes by Aryl Hydrocarbon Receptor Signaling

“…Of note, AhR has been shown to be recruited to the XRE-like sequence (AhRE II) in some AhR-inducible genes (Boutros et al, 2004;Sogawa et al, 2004), and most recently a nonconventional, Arnt-independent XRE was defined (Huang and Elferink, 2012). Furthermore, in agreement with the above reports, genome-wide ChIP-on-chip studies suggested that a large proportion of the AhR binding sequences did not harbor canonical XREs (Ahmed et al, 2009;Pansoy et al, 2010).…”

FOXA1 Is Essential for Aryl Hydrocarbon Receptor–Dependent Regulation of Cyclin G2

“…Previously reported ChIP-chip data from our laboratory revealed that in both human cells and mouse tissue, FKH sites are significantly enriched in AHR-bound regions supporting a possible role for forkhead proteins in AHR signaling (8,9,46). In support of these data, we show that FOXA1 is critical for the AHR-dependent induction of CCNG2 levels.…”

“…Wellstudied AHR target genes include the phase I and II drug-metabolizing enzymes, such as cytochrome P450 1A1 (CYP1A1), CYP1B1, and glutathione S-transferases. Chromatin immunoprecipitation combined with microarrays (ChIP-chip) and gene expression microarray experiments revealed that AHR regulates numerous genes involved in diverse cellular pathways, including metabolism and cellcycle regulation (8)(9)(10). In support of these findings, previous studies have shown that TCDD inhibits cell proliferation (11)(12)(13).…”

“…Our previous ChIP-chip studies identified an AHR-bound AHRE-containing sequence in the upstream regulatory region of CCNG2. In contrast to estrogen, the AHR agonists, TCDD and 3MC, induced AHR recruitment to CCNG2 causing an increase in CCNG2 mRNA levels (8,9). However, the molecular mechanisms and characterization of the AHR-dependent regulation of CCNG2 remain elusive.…”

Aryl hydrocarbon receptor-dependence of dioxin’s effects on constitutive mouse hepatic cytochromes P450 and growth hormone signaling components

“…The parent MC molecule binds AHR with relatively high affinity (Riddick et al 1994) and alters expression of numerous AHR target genes (Kondraganti et al 2005;Pansoy et al 2010); however, studies with MC are complicated by time-dependent changes in biological potency caused by its rapid biotransformation to multiple metabolites (Poland and Glover 1974;Riddick et al 1994), some of which are highly reactive and toxic (Mathieu et al 2001). In contrast, TCDD is highly resistant to biotransformation and causes persistent AHR activation without being converted to reactive metabolites in the process, providing an opportunity for a cleaner assessment of the importance of AHR activation per se in a given biological response.…”