Effect of diindolylmethane on Ca super(2+) movement and viability in HA59T human hepatoma cells

The effect of diindolylmethane, a natural compound derived from indole-3-carbinol in cruciferous vegetables, on cytosolic Ca super(2+) concentrations ([Ca super(2+)] sub(i)) and viability in HA59T human hepatoma cells is unclear. This study explored whether diindolylmethane changed [Ca super(2+)] sub(i) in HA59T cells. The Ca super(2+)-sensitive fluorescent dye fura-2 was applied to measure [Ca super(2+)] sub(i). Diindolylmethane at concentrations of 1-50 mu M evoked a [Ca super(2+)] sub(i) rise in a concentration-dependent manner. The signal was reduced by removing Ca super(2+). Diindolylmethane-induced Ca super(2+) influx was not inhibited by nifedipine, econazole, SK&F96365, and protein kinase C modulators but was inhibited by aristolochic acid. In Ca super(2+)-free medium, treatment with the endoplasmic reticulum Ca super(2+) pump inhibitors thapsigargin or 2,5-di-tert-butylhydroquinone (BHQ) inhibited or abolished diindolylmethane-induced [Ca super(2+)] sub(i) rise. Incubation with diindolylmethane inhibited thapsigargin or BHQ-induced [Ca super(2+)] sub(i) rise. Inhibition of phospholipase C with U73122 reduced diindolylmethane-induced [Ca super(2+)] sub(i) rise. At concentrations of 10-75 mu M, diindolylmethane killed cells in a concentration-dependent manner. The cytotoxic effect of diindolylmethane was not reversed by chelating cytosolic Ca super(2+) with 1,2-bis(2-aminophenoxy)ethane-N,N ,N',N'-tetraacetic acid. Propidium iodide staining data suggest that diindolylmethane (25-50 mu M) induced apoptosis in a concentration-dependent manner. Collectively, in HA59T cells, diindolylmethane induced a [Ca super(2+)] sub(i) rise by causing phospholipase C-dependent Ca super(2+) release from the endoplasmic reticulum and Ca super(2+) influx via phospholipase A sub(2)-sensitive channels. Diindolylmethane induced cell death that may involve apoptosis.