The regulation mechanisms of AhR by molecular chaperone complex

Abstract

The AhR, so called the dioxin receptor, is a member of the nuclear receptor superfamily. The ligand-free AhR forms a cytosolic protein complex with the molecular chaperone HSP90, co-chaperone p23, and XAP2 in the cytoplasm. Following ligand binding like 2, 3, 7, 8-tetrachlorodibenzo-p-dioxin (TCDD), the AhR translocates into the nucleus. Although it has been reported that HSP90 regulates the translocation of the AhR to the nucleus, the precise activation mechanisms of the AhR have not yet been fully understood. AhR consists of the N-terminal bHLH domain containing NLS and NES, the middle PAS domain and the C-terminal transactivation domain. The PAS domain is familiar as a ligand and HSP90 binding domain. In this study, we focused on the bHLH domain that was thought to be a HSP90 binding domain. We investigated the binding properties of bHLH to HSP90. We analyzed the direct interaction of bHLH with HSP90, p23 and XAP2 using purified proteins. We found that not only the PAS domain but also the bHLH domain bound to HSP90. The bHLH domain forms complex with HSP90, p23 and XAP2. We also determined the bHLH binding domain was HSP90 N-domain. The bHLH domain makes a complex with HSP90, p23 and XAP2 via the HSP90 N-domain. Although the NLS is closed in the absence of a ligand, the structure of AhR will be changed in the presence of a ligand, which leads to NLS open, result in the nuclear translocation of AhR.

Transitional States in Ligand-Dependent Transformation of the Aryl Hydrocarbon Receptor into Its DNA-Binding Form

“…It shows that hsp90 is in the closed conformation [53] and the client protein threads through the two hsp90 subunits due to a partial unfolding of two β-strands, leaving its two lobes on the opposite sides of the chaperone. By analogy, we hypothesize that the two AhR PAS domains could also arrange on the opposite sides of hsp90 (initial arrangement in Figure 6A), with the bHLH bound to the N-terminal domain of hsp90, as previously proposed [54]. Similarly to CDK4, the arrangement of the two PAS domains of AhR could be associated with a partial unfolding of the N-terminal β-sheets of the PASB.…”

Indoxyl Sulfate Induces Renal Fibroblast Activation through a Targetable Heat Shock Protein 90-Dependent Pathway

“…First, we set up an in vivo experimental design consisting in a chronic supplementation of moderate amount of IS to mice with a preserved renal function (Supplementary 1); then, to buttress our ex vivo observation, we evaluated in vitro the potential for moderate IS concentration, such as 20 μ M, to prime the renal fibroblast phenotype. Finally, since the cytoplasmic receptor of IS, AhR, is tightly regulated by the molecular complex with the chaperone HSP90 [21], we tested whether the profibrotic effects of IS occur through the HSP90/Smad 2/3 pathway.…”

AhR and Cancer: from Gene Profiling to Targeted Therapy

“…low-molecularweight planar ligands that can exhibit tissue-specific agonist or antagonist activities [4] [5]. In the absence of a ligand, AhR makes up part of a cytosolic multiprotein complex, consisting of c-Src kinase, Hsp90, and the chaperones p23 and XAP2 [6] [7]. Binding of a ligand to AhR induces conformational changes, leading to dissociation of the protein complex and nuclear translocation of AhR.…”