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

The effect of the natural product diindolylmethane on cytosolic Ca ²⁺ 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 2050 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 50100 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′-tetraacetic acid (BAPTA). Annexin V/PI staining data implicate that diindolylmethane (50 and 100 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 A2-sensitive store-operated Ca²⁺ channels. Diindolylmethane caused cell death in which apoptosis may participate.