17-BETA-ESTRADIOL-MEDIATED GROWTH-INHIBITION OF MDA-MB-468 CELLS STABLY TRANSFECTED WITH THE ESTROGEN-RECEPTOR - CELL-CYCLE EFFECTS

Estrogen receptor (ER)-negative MDA-MB-468 human breast cancer cells w ere stably transfected with wild-type human ER and utilized as a model for investigating estrogen-and aryl hydrocarbon (Ah)-responsiveness. Treatment of the stably transfected cells with 10 nM 17 beta-estradiol (E2) resulted in a significant inhibition (> 60%) of cell proliferati on and DNA synthesis, which was blocked by 10(-7) M ICI 182780. Analys is by flow cytometry indicated that treatment with E2 increased the pe rcentage of cells in G0/G1 (from 68.8 to 89.4) and decreased cells in S (from 18.4 to 3.4) and G2/M (from 12.8 to 7.2) phases of the cell cy cle. The effects of E2 on the major cyclins, cyclin-dependent kinases and cyclin-dependent kinase inhibitors, retinoblastoma protein (RE), E 2F-1, and cyclin-dependent kinase activities were also investigated in the stably transfected MDA-MB-468 cells. The results demonstrated tha t the growth inhibitory effects of 10(-8) M E2 in ER stably transfecte d MDA-MB-468 cells were associated with modulation of several factors required for cell cycle progression and DNA synthesis, including signi ficant induction of the cyclin-dependent kinase inhibitor p21(cip-1) ( > 4-fold increase after 12 h) and decreased E2F1 and PCNA. protein lev els. These results show that the growth-inhibitory effects of E2 in th e stably transfected cells were due to multiple factors which result i n growth arrest in G0/G1 and inhibition of DNA synthesis. (C) 1997 Els evier Science Ireland Ltd.