Estrogen and aryl hydrocarbon responsiveness of ECC-1 endometrial cancer cells

ECC-1 endometrial cancer cells express estrogen receptor alpha (ERalpha), a nd 17 beta-estradiol (E2) induces cell proliferation, cathepsin D mRNA leve ls, and reporter gene activity in cells transiently transfected with constr ucts derived from the human cathepsin D and creatine kinase B (pCD and pCKB , respectively) gene promoters. The comparative antiestrogenic activity of aryl hydrocarbon receptor (AhR) agonists and ERalpha antagonists were also determined in these endometrial cancer cells. A functional AhR was expresse d in ECC-1 cells and AhR agonists including 2,3,7,8-tetrachlorodibenzo-p-di oxin (TCDD) inhibited E2-induced cell proliferation and transactivation. Th is was comparable to inhibitory AhR-ER crosstalk in breast cancer cell line s. The pure ER antagonist ICI 182,780 also exhibited antiestrogenic activit y in ECC-1 cells; however, the results obtained for 4'-hydroxytamoxifen wer e response-specific. 4'-Hydroxytamoxifen alone did not induce ECC-1 cell pr oliferation but completely inhibited E2-induced cell proliferation. 4'-Hydr oxytamoxifen primarily exhibited ER antagonist activities in transactivatio n assays and this contrasted to the predominant ER agonist responses observ ed in other endometrial cancer cell lines. The unique cellular context of E CC-1 cells was confirmed using pCKB and constructs expressing wild-type ER or ER variants expressing activation function 1 (AF1) or AF2 (ER-AF1 and ER -AF2, respectively). 4'-Hydroxytamoxifen did not induce reporter gene activ ity in cells cotransfected with pCKB and ER-AF1 or ER-AF2; however, in cotr eatment studies (4'-hydroxytamoxifen plus E2), 4'-hydroxytamoxifen inhibite d E2-induced transcriptional activation by ER-AF1 or ER-AF2. Thus, the prim arily antiestrogenic activity observed for 4'-hydroxytamoxifen in ECC-1 cel ls may be related to the inability to activate gene expression through AF1- dependent pathways. (C) 1999 Elsevier Science Ireland Ltd. All rights reser ved.