Effect of [6]-shogaol on cytosolic Ca2+ levels and proliferation in human oral cancer cells (OC2).

The effect of [6]-shogaol (1) on cytosolic free Ca(2+) concentrations (Ca(2+)) and viability has not been explored previously in oral epithelial cells. The present study has examined whether 1 alters Ca(2+) and viability in OC2 human oral cancer cells. Compound 1 at concentrations > or = 5 microM increased Ca(2+) in a concentration-dependent manner with a 50% effective concentration (EC(50)) value of 65 microM. The Ca(2+) signal was reduced substantially by removing extracellular Ca(2+). In a Ca(2+)-free medium, the 1-induced Ca(2+) elevation was mostly attenuated by depleting stored Ca(2+) with thapsigargin (an endoplasmic reticulum Ca(2+) pump inhibitor). The Ca(2+) signal was inhibited by La(3+) but not by L-type Ca(2+) channel blockers. The elevation of Ca(2+) caused by 1 in a Ca(2+)-containing medium was not affected by modulation of protein kinase C activity, but was inhibited by 82% with the phospholipase A2 inhibitor aristolochic acid I (20 microM). U73122, a selective inhibitor of phospholipase C, abolished 1-induced Ca(2+) release. At concentrations of 5-100 microM, 1 killed cells in a concentration-dependent manner. These findings suggest that [6]-shogaol induces a significant rise in Ca(2+) in oral cancer OC2 cells by causing stored Ca(2+) release from the thapsigargin-sensitive endoplasmic reticulum pool in an inositol 1,4,5-trisphosphate-dependent manner and by inducing Ca(2+) influx via a phospholipase A2- and La(3+)-sensitive pathway.