The effect of magnolol on Ca(2+) homeostasis and its related physiology in human oral cancer cells.

OBJECTIVE: Magnolol, a polyphenol compound from herbal medicines, was shown to alter physiology in various cell models. However, the effect of magnolol on Ca(2+) homeostasis and its related physiology in oral cancer cells is unclear. This study examined whether magnolol altered Ca(2+) signaling and cell viability in OC2 human oral cancer cells. METHODS: Cytosolic Ca(2+) concentrations ([Ca(2+)](i)) in suspended cells were measured by using the fluorescent Ca(2+)-sensitive dye fura-2. Cell viability was examined by 4-[3-[4-lodophenyl]-2-4(4-nitrophenyl)-2H-5-tetrazolio-1,3-benzene disulfonate] water soluble tetrazolium-1 (WST-1) assay. RESULTS: Magnolol at concentrations of 20-100 muM induced [Ca(2+)](i) rises. Ca(2+) removal reduced the signal by approximately 50%. Magnolol (100 muM) induced Mn(2+) influx suggesting of Ca(2+) entry. Magnolol-induced Ca(2+) entry was partially suppressed by protein kinase C (PKC) regulators, and inhibitors of store-operated Ca(2+) channels. In Ca(2+)-free medium, treatment with the endoplasmic reticulum Ca(2+) pump inhibitor 2,5-di-tert-butylhydroquinone (BHQ) abolished magnolol-evoked [Ca(2+)](i) rises. Conversely, treatment with magnolol abolished BHQ-evoked [Ca(2+)](i) rises. Inhibition of phospholipase C (PLC) with U73122 partially inhibited magnolol-induced [Ca(2+)](i) rises. Magnolol at 20-100 muM decreased cell viability, which was not reversed by pretreatment with the Ca(2+) chelator 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid-acetoxymethyl ester (BAPTA/AM). CONCLUSIONS: Together, in OC2 cells, magnolol induced [Ca(2+)](i) rises by evoking partially PLC-dependent Ca(2+) release from the endoplasmic reticulum and Ca(2+) entry via PKC-sensitive store-operated Ca(2+) entry. Magnolol also caused Ca(2+)-independent cell death. Therefore, magnolol-induced cytotoxicity may not be involved in activation mechanisms associated with intracellular Ca(2+) mobilization in oral cancer cells.