Activation function 2 mediates dioxin-induced recruitment of estrogen receptor alpha to CYP1A1 and CYP1B1

We investigated the role of the activation function 1 (AF1) and AF2 domains of estrogen receptor alpha (ERα) in mediating dioxin-dependent recruitment of ERα to cytochrome P4501A1 (CYP1A1) and CYP1B1 in HuH-7 human hepatoma cells. Dioxin-induced recruitment of ERα wildtype (ERα-WT) and an ERα AF1 deletion mutant (ERα-ΔAF1), but not a transcriptional inactive AF2 mutant (ERα-AF2mut) to CYP1A1 and CYP1B1. Direct interactions between AHR and the AF1 and AF2 domains of ERα were observed, and were independent of mutations in the AF2. Expression of ERα-WT increased dioxin-induced CYP1A1 and CYP1B1-regulated reporter activity, and CYP1A1 and CYP1B1 mRNA levels. However, no increases in gene expression above vector controls were observed in cells transfected with ERα-ΔAF1 or ERα-AF2mut. Our data show that the AF2 domain contributes to dioxin-induced recruitment of ERα to AHR target genes, but that both the AF1 and AF2 domains are required for ERα-dependent increases in AHR activity.