Functional Analysis of the Dioxin Response Elements (DREs) of the Murine CYP1A1 Gene Promoter: Beyond the Core DRE Sequence

Abstract

The aryl hydrocarbon receptor (AhR) is a ligand-dependent transcription factor that mediates the biological and toxicological effects of halogenated aromatic hydrocarbons, such as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). When activated by dioxin, the cytosolic AhR protein complex translocates into the nucleus and dimerizes with the ARNT (Ah receptor nuclear translocator) protein. The heteromeric ligand:AhR/Arnt complex then recognizes and binds to its specific DNA recognition site, the dioxin response element (DRE). DREs are located upstream of cytochrome P4501A1 (CYP1A1) and other AhR-responsive genes, and binding of the AhR complex stimulates their transcription. Although CYP1A1 expression has been used as the model system to define the biochemical and molecular mechanism of AhR action, there is still limited knowledge about the roles of each of the seven DREs located in the CYP1A1 promoter. These seven DREs are conserved in mouse, human and rat. Deletion analysis showed that a single DRE at −488 was enough to activate the transcription. Truncation analysis demonstrated that the DRE at site −981 has the highest transcriptional efficiency in response to TCDD. This result was verified by mutation analysis, suggesting that the conserved DRE at site −981 could represent a significant and universal AhR regulatory element for CYP1A1. The reversed substituted intolerant core sequence (5′-GCGTG-3′ or 5′-CACGC-3′) of seven DREs reduced the transcriptional efficiency, which illustrated that the adjacent sequences of DRE played a vital role in activating transcription. The core DRE sequence (5′-TNGCGTG-3′) tends to show a higher transcriptional level than that of the core DRE sequence (5′-CACGCNA-3′) triggered by TCDD. Furthermore, in the core DRE (5′-TNGCGTG-3′) sequence, when “N” is thymine or cytosine (T or C), the transcription efficiency was stronger compared with that of the other nucleotides. The effects of DRE orientation, DRE adjacent sequences and the nucleotide “N” in the core DRE (5′-TNGCGTG-3′) sequence on the AhR-regulated CYP1A1 transcription in response to TCDD were studied systematically, and our study laid a good foundation for further investigation into the AhR-dependent transcriptional regulation triggered by dioxin and dioxin-like compounds.

Effects of van der Waals density functional corrections on trends in furfural adsorption and hydrogenation on close-packed transition metal surfaces

“…They have been widely used to quickly estimate reaction kinetics in detailed mechanistic studies [51] and in trends-based analyses [47]. In this spirit, a BEP relationship can be developed for hydrogenation reactions associated with the intermediates discussed in the previous sections.…”

“…A bond-order based scaling correlation, with parameters determined by comparison to the results of selected DFT calculations, has been developed in a separate study for the estimation of the binding energies of glycerol dehydrogenation intermediates on transition metals, and this strategy has been successfully used to efficiently analyze a comparably large reaction network [14,[46][47][48][49]. To facilitate future studies of furfural reaction networks on transition metal surfaces, we briefly present a similar correlation based on the results of the calculated binding energies described in the previous section and in the Supporting Information.…”

“…We note that this correlation is quite similar to the correlation introduced previously for linear polyols although some differences are needed to account for the ring-like nature of the furfural derivatives. In addition to correlations for multiple intermediates on a given metal surface, it is possible to develop additional linear scaling relationships to relate the binding energies of hydrocarbon [50] and oxygenated hydrocarbon [47] species across different transition metals with reasonable accuracy:…”

Ah receptor pathway intricacies; signaling through diverse protein partners and DNA-motifs

“…Tumor promotion following DEN treatment has also been shown for the AHR in combination with various exogenous ligands 252-254 . Further, KLF6 has recently been suggested to function in T-cell activation 255 and in NF-κB signaling via p65-dependent transcription 256 ; the AHR has also been implicated in T-cell activation 257 and in NF-κB signaling with p65 258 . Moreover, while total knock-out of the AHR in mice is not lethal, it does result in significantly decreased litter sizes.…”

Glabridin attenuates antiadipogenic activity induced by 2,3,7,8‐tetrachlorodibenzo‐p‐dioxin in murine 3T3‐L1 adipocytes

“…Its diverse effects are thought to be mediated by the aryl hydrocarbon receptor (AhR), which localizes to the nucleus upon ligand binding. There, it associates with the nuclear protein AhR nuclear translocator, and the complex binds to dioxin‐response elements to activate transcription (Li, Pei, Zhang, Xie, & Zhao, ; Whitelaw, Pongratz, Wilhelmsson, Gustafsson, & Poellinger, ; Whitlock, ). TCDD is a persistent organic pollutant that is lipophilic and easily trapped in adipose tissue.…”