MATERIALS AND METHODS

Cell Culture and Stable Transfection Human breast cancer MCF-7 cells were cultured in Dulbecco’s Modified Eagle’s Medium (DMEM, GIBCO) containing 5% fetal bovine serum (FBS) and penicillin–streptomycin in humidified 5% CO2 at 37 C. The human AhRR coding sequence amplified by reverse transcription–polymerase chain reaction (RT-PCR) utilizing 5-GCGGGATCCATGATCCCCCCGCCGGGGGAG-3 as a sense primer (start codon underlined, BamHI site in italics) and 5-GATGGTGGTCACTGCGCTATGGAAT-3 as an antisense primer (stop codon underlined) was ligated to the BamHI and EcoRV sites of expression vector pcDNA 5/TO (Invitrogen) to make pcDNA-hAhRR. The cells were transfected with pcDNA-hAhRR using TransFast (Promega). On the following day, the medium was changed to another containing hygromycin (500mg/ml). After 2 weeks, single colonies were picked up and subcultured in 24-well plates. The stable expression of