Identification of a novel mechanism of regulation of Ah (dioxin) receptor function

Ah receptor (AhR) is a ligand-activated transcription factor that mediates pleiotropic effects of environmental pollutants such as 2,3,7,8-tetrachloro dibenzo-p-dioxin on host animals. In addition to induction of drug-metaboli zing enzymes, the liganded AM complex was found to activate gene expression of a factor designated AhR repressor (AhRR), which inhibits AhR function b y competing with AhR for dimerizing with Amt and binding to the XRE sequenc e. Thus, AhR and AhRR form a regulatory circuit in the xenobiotic signal tr ansduction pathway and provide a novel mechanism of regulation of AhR funct ion that may determine tissue-specific sensitivity to environmental polluta nts.