Recruitment of Dioxin Receptor to Active Transcription Sites

Abstract

The aryl hydrocarbon receptor (AhR or dioxin receptor) is a ligand-activated transcription factor that heterodimerizes with the AhR nuclear translocator (ARNT/HIF-1beta) to form an AhR/ARNT transcription factor complex. This complex binds to specific DNA sites in the regulatory domains of numerous target genes and mediates the biological effects of exogenous ligands. Herein, we have investigated the subcellular distribution of the AhR/ARNT complex in response to ligand stimulation, by using live-cell confocal and high-resolution deconvolution microscopy. We found that unliganded AhR shows a predominantly cytoplasmic diffuse distribution in mouse hepatoma cells. On addition of ligand, AhR rapidly translocates to the nucleus and accumulates in multiple bright foci. Inhibition of transcription prevented the formation of AhR foci. Dual- and triple-immunolabeling experiments, combined with labeling of nascent RNA, showed that the foci are transcription sites, indicating that upon ligand stimulation, AhR is recruited to active transcription sites. The interaction of AhR with ARNT was both necessary and sufficient for the recruitment of AhR to transcription sites. These results indicate that AhR/ARNT complexes are recruited to specific subnuclear compartments in a ligand-dependent manner and that these foci represent the sites of AhR target genes.

Antiandrogens prevent stable DNA-binding of the androgen receptor

“…4) (Tyagi et al, 2000;Tomura et al, 2001). For the aryl hydrocarbon receptor it was shown that foci correlated with transcription sites (Elbi et al, 2002) whereas for the GR, no clear correlation of foci with pre-mRNA synthesis sites could be demonstrated (van Steensel et al, 1995). Our results (Fig.…”

Id Proteins Negatively Regulate Basic Helix-Loop-Helix Transcription Factor Function by Disrupting Subnuclear Compartmentalization

“…The functional importance of subnuclear localization of transcription factors to discrete foci in chromatin has been widely reported (18,26,28,29), although studies on subnuclear diffusion dynamics have largely focused on the family of ligand-dependent nuclear hormone receptors. For example, the glucocorticoid receptor (27,35,36), thyroid hormone receptor (37), dioxin receptor (38), and proliferation-activated receptor (39) reportedly undergo liganddependent intranuclear redistribution into discrete foci representing transcriptional complexes. The pools of nuclear receptor in these foci undergo rapid (within seconds) exchange with a more highly mobile fraction in the nucleoplasm.…”

Phosphorylation of p53 at serine 37 is important for transcriptional activity and regulation in response to DNA damage

“…We compared the nucleoplasmic distribution of p53 to that of the PP2Ac by high-resolution dual-staining indirect immunofluorescence microscopy (Van Steensel et al, 1996;Elbi et al, 2002). We observed significant colocalizations (yellow-orange) between p53 (red) and PP2Ac (green) 2 and 4 h after g-irradiation (panels g and j).…”

“…Indirect immunofluorescence was performed as previously described (Elbi et al, 2002). Briefly, after exposure to 8 Gy -irradiation, cells were fixed with 2% paraformaldehyde in PBS.…”