Effect of diindolylmethane on Ca2+ homeostasis and viability in PC3 human prostate cancer cells

The effect of the natural product diindolylmethane on cytosolic Ca2+ concentrations ([Ca2+](i)) and viability in PC3 human prostate cancer cells was explored. The Ca2+-sensitive fluorescent dye fura-2 was applied to measure [Ca2+](i). Diindolylmethane at concentrations of 20-50 mu M induced [Ca2+](i) rise in a concentration-dependent manner. The response was reduced partly by removing Ca2+. Diindolylmethane-evoked Ca2+ entry was suppressed by nifedipine, econazole, SK&F96365, protein kinase C modulators and aristolochic acid. In the absence of extracellular Ca2+, incubation with the endoplasmic reticulum Ca2+ pump inhibitor thapsigargin or 2,5-di-tert-butylhydroquinone (BHQ) inhibited or abolished diindolylmethane-induced [Ca2+](i) rise. Incubation with diindolylmethane also inhibited thapsigargin or BHQ-induced [Ca2+](i) rise. Inhibition of phospholipase C with U73122 reduced diindolylmethane-induced [Ca2+](i) rise. At concentrations of 50-100 mu M, diindolylmethane killed cells in a concentration-dependent manner. This cytotoxic effect was not altered by chelating cytosolic Ca2+ with 1,2-bis(2-aminophenoxy) ethane-N, N,N',N'-tetraaceticacid (BAPTA). Annexin V/PI staining data implicate that diindolylmethane (50 and 100 mu M) induced apoptosis in a concentration-dependent manner. In conclusion, diindolylmethane induced a [Ca2+](i) rise in PC3 cells by evoking phospholipase C-dependent Ca2+ release from the endoplasmic reticulum and Ca2+ entry via phospholipase A(2)-sensitive store-operated Ca2+ channels. Diindolylmethane caused cell death in which apoptosis may participate.