Estrogen and aryl hydrocarbon receptor expression and crosstalk in human Ishikawa endometrial cancer cells

Ishikawa endometrial cancer cells express the estrogen receptor (ER), and t his study investigates aryl hydrocarbon receptor (AhR) expression and inhib itory AhR-ER crosstalk in this cell line. Treatment of Ishikawa cells with the AhR agonist [H-3]2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) gave a radi olabeled nuclear complex that sedimented at 6.0 S in sucrose density gradie nts, and Western blot analysis confirmed that Ishikawa cells expressed huma n AhR and AhR nuclear translocator (Amt) proteins. Treatment of Ishikawa ce lls with 10 nM TCDD induced a 9.7-fold increase in CYP1A1-dependent ethoxyr esorufin O-deethylase (EROD) activity and a 10.5-ford increase in chloramph enicol acetyltransferase (CAT) activity in cells transfected with pRNH11c c ontaining an Ah-responsive human CYP1A1 gene promoter insert (-1142 to + 24 34). Inhibitory AhR-ER crosstalk was investigated in Ishikawa cells using E 2-induced cell proliferation and transcriptional activation assays in cells transfected with E2-responsive constructs containing promoter inserts from the progesterone receptor and vitellogenin A2 genes. AhR agonists includin g TCDD, benzo[a]pyrene (BaP) and 6-methyl,3,8-trichlorodibenzofuran, inhibi ted 32-47% of the E2-induced responses. In contrast, neither estrogen nor p rogesterone inhibited EROD activity induced by TCDD in Ishikawa cells, wher eas inhibitory ER-AhR crosstalk was observed in ECC-1 endometrial cells sug gesting that these interactions were cell context-dependent. (C) 2000 Elsev ier Science Ltd. All rights reserved.