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AHR (Ah Receptor) belongs to a family of proteins comprised of its dimerization partner ARNT (HIF-1 Beta) and the Drosophila proteins PER and SIM. AHR contains an N-terminal sequence of approximately 200 amino acids termed the PAS domain. AHR, found in a variety of tissues, binds to a specific DNA enhancer sequence and initiates transcription of the mRNA for the cytochrome P-450 (CYPIA1) gene. The gene for AHR encodes a ligand-activated transcription factor involved in the regulation of biological responses to planar aromatic hydrocarbons. AHR has been shown to regulate xenobiotic-metabolizing enzymes such as cytochrome P450, and its ligands included a variety of aromatic hydrocarbons. AHR is a ligand-activated helix/loop/helix transcription factor found in a variety of vertebrate species. The known ligands for AHR are foreign planar aromatic compounds, such as polycyclic aromatic compounds and halogenated aromatic compounds such as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Unlike the steroid/thyroid hormone receptors, there is no known physiological ligand for AHR. Studies indicate that in non-ligand activated cells, AHR is found complexed with HSP90 predominantly in the cytoplasm. Upon binding to an agonist, the ligand-activated AhR is believed to transform to a nuclear, DNA binding form, and this transformation process appears to involve dissociation of HSP90 from AhR followed by formation of a heterodimer with AhR nuclear translocator protein (Arnt). Diseases associated with AHR include eosinophilic fasciitis and seborrheic dermatitis.
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Protein Aliases: Ah receptor; AH-receptor; aromatic hydrocarbon receptor; Aryl hydrocarbon receptor; bHLHe76; Class E basic helix-loop-helix protein 76; dioxin receptor
Gene Aliases: Ah; Ahh; AHR; Ahre; BHLHE76; In
Molecular Function: basic helix-loop-helix transcription factor