Ah receptor and NF-kappaB interactions: mechanisms and physiological implications.

The aryl hydrocarbon (Ah) receptor mediates most of the toxic effects induced by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and related compounds, which are ubiquitous environmental contaminants causing toxic responses in human and wildlife. Nuclear factor kappa B (NF-kappaB) is a pleiotropic transcription factor that plays a pivotal role in a wide array of physiological and pathological responses including immune modulation, inflammatory responses and apoptosis. Many physiological functions adversely affected by TCDD are also known to be regulated by NF-kappaB, such as immune activation, maintenance of skin differentiation, control of cell proliferation and survival, as well as induction of xenobiotic metabolizing enzymes. In the past few years, evidence has emerged to show that the Ah receptor and NF-kappaB interact and transcriptionally modulate each other. This review discusses Ah receptor-NF-kappaB interactions and examines potential mechanistic explanations for toxic responses as a result of TCDD exposure and the suppression of cytochrome P450 1A1/1A2 by stress stimuli such as inflammation and infection.