Aryl hydrocarbon receptor agonists directly activate estrogen receptor α in MCF-7 breast cancer cells

The aryl hydrocarbon receptor (AhR) binds with high affinity to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and related halogenated aromatics, but also binds with lower affinity to structurally diverse exogenous and endogenous chemicals. One study reported that 3-methylcholanthrene (3MC) activated the estrogen receptor (ER) through the AhR, which acts as co-regulatory protein, whereas a recent report showed that 3MC directly bound and activated ER alpha. This study also shows that the AhR agonists benzo[a]pyrene, 3,3',4,4'-tetrachlorobiphenyl, chrysin, 6-methyl-1,3,8-trichlorodibenzofuran, and 3,3'-diindolylmethane also induce ER alpha-dependent transactivation. Moreover, in chromatin immunoprecipitation assays, these compounds induce binding of AhR and ER alpha to the CYP1A1 and pS2 gene promoters, which is consistent with their activities as both selective AhR modulators (SAhRMs) and selective ER modulators (SERMs).