Transcriptional activation of cathepsin D gene expression by 17β-estradiol: Mechanism of aryl hydrocarbon receptor-mediated inhibition

17β-estradiol (E2) induces cathepsin D gene expression in MCF-7 human breast cancer cells and this response is inhibited by aryl hydrocarbon receptor (AhR) agonists, such as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Analysis of the cathepsin D gene promoter initially identified a pentanucleotide GCGTG core dioxin responsive element (DRE) that blocked E2 action by inhibiting formation of a transcriptionally active estrogen receptor (ER)-Sp1 complex. A second functional downstream inhibitory DRE (iDRE2) (-130 to -126) has now been identified in the cathepsin D gene promoter and inhibition of E2-induced transactivation involves inhibitory AhR crosstalk with the E2-responsive adenovirus major late promoter element (MLPE) at -124 to -104 in the cathepsin D gene promoter. The MLPE site primarily binds USF1/USF2 and ERα, and gel mobility shift and DNA footprinting assays show that the AhR complex decreases binding of these transcription factors to the MLPE.