The aryl hydrocarbon receptor (AhR) is a nuclear helix-loop-helix transcription factor which forms a ligand-induced nuclear heterodimer with the AhR nuclear translocator (Arnt) protein. Research in this laboratory is focused on the molecular mechanism of crosstalk between the AhR and estrogen receptor (ER) signaling pathways in which the AhR inhibits estrogen-induced gene expression. The antiestrogenic activities of some AhR agonists are also being developed as drugs for clinical treatment of breast and endometrial cancers in women. Research on estrogen-dependent gene expression in various cancer cell lines is focused on analysis of several gene promoters to determine the mechanisms of ERa and ERb action. This includes several genes that are activated through interactions of the ER with Sp1 protein and other DNA-bound transcription factors.