Estrogen causes cell death of estrogen receptor stably transfected cells via apoptosis

We examined the effect of estrogen on the growth of estrogen receptor (ER) stably transfected cells (Rat1 + ER). 17-Beta-estradiol (E2, 10 nM) inhibited approximately 35-50% of Rat1 + ER growth after 3 d of treatment. The half-maximal growth inhibition occurred at 0.5-0.75 nM of E2 concentration and was saturated above 10 nM. This E2-induced antiproliferative effect was mediated through the ER since E2 did not cause any change in ER-negative parental Rat1 cells. Cells started to detach from plates and the adherent cells exhibited nuclear condensation. Apoptotic cell populations showed a 25% increase at 2 d of E2 treatment over controls that were quantified by fluorescence-activated cell sorter analysis. This indicates that E2 induced apoptosis in Rat1 + ER cells.