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

Abstract

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 nonxenobiotic, physiological activation of AhR signaling. Here, we show that the AhR is recruited to target gene enhancers in both ligand [isopropyl-2-(1,3-dithietane-2-ylidene)-2-[N-(4-methylthiazol-2-yl)carbamoyl]acetate (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 predominantly by ligand treatments, whereas, in contrast, ApoER2 and Ganc were regulated predominantly by the suspension condition. Classic xenobioticmetabolizing 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 chromatin immunoprecipitation assays and reporter gene analysis identified a functional xenobiotic response element (XRE) in the intron 1 of the mouse Tiparp gene, which was also bound by hypoxia-inducible factor-1␣ during hypoxia and features a concatemer of four XRE cores (GCGTG). Our data suggest that this XRE concatemer site concurrently regulates the expression of both the Tiparp gene and its cis antisense noncoding RNA after ligand-or suspension-induced AhR activation. This work provides novel insights into how AhR signaling drives different transcriptional programs via the ligand versus suspension modes of activation.

Collagen density regulates xenobiotic and hypoxic response of mammary epithelial cells

“…Promoter activity of a purified XRE is identified in cells cultured in collagen matrices, consistent with previous findings that increased activation of the XRE signals occurs in cells suspended in semisolid media containing 1.68% methylcellulose (Sadek and Allen-Hoffmann 1994, Hao et al 2012) or cultures within ultralow attachment plates (Sengupta et al 2014). Despite the decrease in XRE activity in HD matrices, the expression of CYP1B1 and CYP4B1, which are regulated in part by XRE elements, are significantly increased in HD matrices.…”

Aryl Hydrocarbon Receptor Repressor and TiPARP (ARTD14) Use Similar, but also Distinct Mechanisms to Repress Aryl Hydrocarbon Receptor Signaling

“…Little is known about the AHR-dependent regulation of the TiPARP upstream regulatory region. The isolated mouse TiPARP promoter was unresponsive to TCDD, which might be due to its high constitutive expression levels [21]. These findings might also suggest a more complex mechanism of regulation of TiPARP .…”

Intersection of AHR and Wnt Signaling in Development, Health, and Disease

“…The AHR-ARNT heterodimer binds to dioxin response elements (DREs) in the promoter region of downstream target genes and directly upregulates their expression [38]. Activated AHR is also capable of downregulating expression, and multiple studies have reported a larger number of genes being downregulated rather than upregulated following AHR activation [41,42,43,44,45,46,47]. However, it is less clear whether transcriptional downregulation is the result of AHR binding directly to the promoter, or if it is an indirect effect due to (1) AHR-induced upregulation of transcriptional inhibitors or (2) AHR-induced degradation of other transcriptional activators (discussed below).…”