Dioxin-Mediated Up-Regulation of Aryl Hydrocarbon Receptor Target Genes Is Dependent on the Calcium/Calmodulin/CaMKIα Pathway

Abstract

Regulation of genes targeted by the ligand-activated aryl hydrocarbon receptor (AhR) has been shown to be controlled by calcium (Ca(2+)) changes induced by AhR agonists such as the environmental contaminant 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). The present study was designed to characterize this link between Ca(2+) and the AhR pathway. We report that fast elevation of intracellular Ca(2+) in TCDD-exposed mammary MCF-7 cells was associated with transient enhanced activity of the Ca(2+)/calmodulin (CaM)-dependent protein kinase (CaMK) pathway. Chemical inhibition of this pathway using the CaM antagonist W7 or the CaMK inhibitor KN-93 strongly reduced TCDD-mediated induction of the AhR target gene CYP1A1. Small interfering RNA (siRNA)-mediated knockdown expression of CaMKIalpha, one of the CaMK isoforms, similarly prevented CYP1A1 up-regulation. Both KN-93 and siRNA targeting CaMKIalpha were found to abolish TCDD-mediated activation of CYP1A1 promoter and TCDD-triggered nuclear import of AhR, a crucial step of the AhR signaling pathway. TCDD-mediated inductions of various AhR targets, such as the drug metabolizing CYP1B1, the cytokine interleukin-1beta, the chemokines interleukin-8 and CCL1, the adhesion molecule beta7 integrin, and the AhR repressor, were also prevented by KN-93 in human macrophages. Taken together, these data identified the Ca(2+)/CaM/CaMKIalpha pathway as an important contributing factor to AhR-mediated genomic response.