Estradiol-17β (E2) may participate in carcinoma of mammary cells containing estradiol receptors (
ER) at sufficient levels. Hence, the regulation of ER levels may be important for the progression of estrogen-dependent mammary carcinomas. Our previous findings that the progest
erone metabolite, 5
x3b1;-pregnane-3,20-dione (5
x3b1;P), exhibits marked mitogenic and metastatic prop
erties, wh
ereas the progest
erone metabolites, 4-pregnen-3
x3b1;-ol-20-one (3
x3b1;HP) and 4-pregnen-20
x3b1;-ol-3-one (20
x3b1;HP), oppose these actions, prompted examination of the possible effects of these progest
erone metabolites on ER concentration in MCF-7 breast canc
er cells. Cells w
ere exposed for 24 h to 0 (control) or 10
−10 to 10
−6 M E2, 5
x3b1;P, 3
x3b1;HP, 20
x3b1;HP or combinations of these st
eroids, and ER concentrations w
ere det
ermined for intracellular estrogen receptors by specific binding of [
3H]E2. The total ER numb
er (nuclear plus cytosolic) in control samples was 2551 ± 164 p
er cell. E2 and 5
x3b1;P resulted in significant dose-dependent increases in total ER numb
ers (
![not, v<font color=](http://www.sciencedirect.com/scidirimg/entities/223c.gif)
ert, similar" bord
er=0>1.6-fold and
![not, v<font color=](http://www.sciencedirect.com/scidirimg/entities/223c.gif)
ert, similar" bord
er=0>2.2-fold at 10
−6 M, respectively). In combination, E2 + 5
x3b1;P resulted in additive increases in ER numb
ers. Individually, 3
x3b1;HP and 20
x3b1;HP each resulted in dose-dependent decreases (43%and 54%at 10
−6 M, respectively) in total ER numb
ers and inhibited the E2- or 5
x3b1;P-induced increases in ER levels. In combination, 3
x3b1;HP + 20
x3b1;HP resulted in dose-dependent additive suppression of ER levels. Treatment with cycloheximide or actinomycin D indicated that both transcription and translation are involved in 5
x3b1;P and 3
x3b1;HP action on ER numb
ers. Real time RT-PCR showed increases in expression of ER
x3b1; transcripts due to 5
x3b1;P and increases in expression of ERβ due to 3
x3b1;HP; expression levels of eith
er ER
x3b1; or ERβ w
ere not significantly alt
ered when cells w
ere treated with 5
x3b1;P + 3
x3b1;HP. The results are the first to show that the pro- and anti-canc
er progest
erone metabolites also have marked selective (up or down) regulatory effects on ER levels in MCF-7 breast canc
er cells.