Mechanism of estrogens-induced increases in intracellular Ca²⁺ in PC3 human prostate cancer cells

BACKGROUND. The effect of estrogens (diethylstilbestrol [DES], 17β-estradiol) on intracellular Ca²⁺ concentrations ([Ca²⁺]_i) in hormone-insensitive PC3 human prostate cancer cells was examined. METHODS. [Ca²⁺]_i changes in suspended cells were measured by using the Ca²⁺-sensitive fluorescent dye fura-2. RESULTS. Estrogens (1-20 μM) increased [Ca²⁺]_i concentration-dependently with DES being more potent. Ca²⁺ removal inhibited 50 ± 10% of the signal. In Ca²⁺-free medium, pretreatment with 20 μM estrogens abolished the [Ca²⁺]_i increases induced by 2 μM carbonylcyanide m-chlorophenylhydrazone (CCCP, a mitochondrial uncoupler) and 1 μM thapsigargin (an endoplasmic reticulum Ca²⁺ pump inhibitor), but pretreatment with CCCP and thapsigargin did not alter DES-induced Ca²⁺ release and partly inhibited 17β-estradiol-induced Ca²⁺ release. Addition of 3 mM Ca²⁺ increased [Ca²⁺]_i in cells pretreated with 1-20 μM estrogens in Ca²⁺-free medium. Pretreatment with 1 μM U73122 to block phospholipase C-coupled inositol 1,4,5-trisphosphate formation did not alter estrogens-induced Ca²⁺ release. The effect of 20 μM estrogen on [Ca²⁺]_i was not affected by pretreatment with 0.1 μM estrogens. CONCLUSIONS. Estrogen induced significant Ca²⁺ release and Ca²⁺ influx in an inositol 1,4,5-trisphosphate-independent manner in PC3 cells. These effects of estrogens on Ca²⁺ signaling appear to be nongenomic.