The Aryl Hydrocarbon Receptor (AHR) is a ligand-activated transcription factor that belongs to the basic helix-loop-helix (bHLH)/Per-Arnt-Sim (PAS) family of proteins. It is primarily found in the cytoplasm of cells and acts as a sensor for a wide range of environmental toxicants and endogenous compounds. The AHR is known to bind to a variety of structurally diverse molecules, including polycyclic aromatic hydrocarbons (PAHs), dioxins, and other xenobiotic chemicals.
Upon ligand binding, the AHR undergoes a conformational change that allows it to translocate to the nucleus, where it forms a complex with another protein called ARNT (Aryl Hydrocarbon Receptor Nuclear Translocator). This complex then binds to specific DNA regulatory regions called xenobiotic response elements (XREs), leading to the transcriptional activation or repression of various downstream genes.
The AHR is involved in the regulation of numerous physiological processes, including xenobiotic metabolism, detoxification, immune responses, and cell differentiation. It plays a crucial role in the metabolism and elimination of many environmental toxins, as well as in the pathogenesis of several diseases, including cancer, immune disorders, and developmental abnormalities.
Understanding the function and regulation of the AHR has important implications in environmental health sciences, toxicology, and pharmacology. It has also become a target for the development of therapeutics aimed at modulating AHR activity for the treatment of various diseases and conditions.
