THE ARYL-HYDROCARBON RECEPTOR COMPLEX

The heteromeric unliganded aryl hydrocarbon receptor complex (AHRC) co ntains the aryl hydrocarbon receptor monomer (AHR). Binding of polycyc lic or halogenated aromatic hydrocarbon (PAH and HAH) ligand causes re lease of AHR, which then associates with the AHR nuclear translocator protein (ARNT) to generate the heterodimeric ''transformed'' AHRC, AHR and ARNT belong to a novel subclass of basic helix-loop-helix-contain ing transcription factors. The transformed AHRC binds xenobiotic respo nsive elements in responsive genes and turns on their transcription. C ertain of these genes encode enzymes involved in the metabolic activat ion of PAHs to mutagenic derivatives. HAHs are not genotoxic: Their pa thogenicity depends on the AHRC but not on their metabolism, Current r esearch includes investigations directed towards delineating the pathw ays of HAH pathogenesis, ascertaining whether AHR can mediate signal t ransduction independently of DNA binding, understanding the mechanism of transcriptional activation, and investigating the potential roles o f AHR and ARNT in development.