Table 1.

Estrogen Stimulates G1-Phase to S-Phase Transition of MCF-7 Cells.

Treatment	G1	S	G2/M
4 days in DMEM	65.0	34.5	0.5
After 24 hr in DMEM	40.5	59.0	0.5
E2	28.0	71.5	0.5
TMX	54.6	42.0	3.4
TMX + E2	35.2	61.2	3.6

MCF-7 cells were precultured for 4 days in phenol red-free DMEM containing 5% charcoal dextran-stripped FBS. Then cells were cultured for 24 hours in basal DMEM or DMEM supplemented with 10 nM E₂, 1 µM TMX, or their combination. Cell were stained with propidium iodide and used for flow cytometry. Cell cycle distribution profiles were recorded with a FACscan (Becton Dickinson) using a CELLQuest program.