Estradiol and progesterone regulate oxytocin receptor binding and expression in human breast cancer cell lines

The effects of estradiol (E-2) and progesterone on the oxytocin receptor (OTR) were investigated in MCF-7 and Hs 578T human breast cancer cell lines. OTR messenger RNA and protein were identified by reverse transcriptase polymerase chain reaction (PCR) and solution-phase hybridization-RNase protection assay, and Western blot analysis, respectively, in cell lines and in cancerous breast tissue removed from women at mastectomy. Cells were exposed to E-2, progesterone, or vehicle (each steroid, 10(-10)-10(-6) M) for 24 h and harvested for extraction of RNA. The OTR PCR product was increased by E-2 (10(-7) M, p < 0.05, or 10(-6) M, p < 0.01 vs control) and decreased by progesterone (control vs 10(-7) or 10(-6) M, each p < 0.005). Hs578T cells were cultured in the presence or absence of E-2 (10(-6) M) or progesterone (10(-6) M) for 24 h and binding was measured. For the E-2-exposed cells, the K-d (p < 0.05), and B max (p < 0.01) were higher whereas for the progesterone-treated cells the K-d (p < 0.05) and B-max were lower than control cells. E-2 and progesterone not only regulate OTR expression and binding in normal mammary myoepithelium but also in malignant mammary cell lines.