A novel mechanism underlying phytate-mediated biological action-phytate hydrolysates induce intracellular calcium signaling by a Gαq protein-coupled receptor and phospholipase C-dependent mechanism in colorectal cancer cells.

Phytate (inositol hexa-phosphate, IP6) possesses multiple biological functions including anticancer activity. IP6 is converted to inositol di-, tri-, and tetra-phosphates (IP2, IP3, and IP4) by phytase in large intestinal microbes; however, their contribution to the IP6-mediated functions has not been investigated. We have developed the preparations of IP2-4 and IP3-rich phytate hydrolysate (IP3-RPH) by IP6 digestion using microbial phytase, and examined the induction of intracellular Ca(2+) signaling in response to the preparations in colorectal cancer cells. IP2-4, but not inositol (IP0) and IP6, induced increases in intracellular Ca(2+) concentration ([Ca(2+)](i)) in Caco-2 cells with the following rank order: IP3>IP2=IP4. Inositol tri-phosphate (IP3)-RPH induced increases in [Ca(2+)](i) in both undifferentiated Caco-2 and HT-29 cells, but not in differentiated Caco-2. The IP3-RPH-induced [Ca(2+)](i) increase was resistant to extracellular Ca(2+) depletion, however, it was impaired by inhibitors of phospholipase C, inositol 1, 4, 5 tri-phosphate receptor, ryanodine receptor, and Galphaq protein. These results show that the putative G protein-coupled receptor on the plasma membrane senses the IP6 hydrolysates and activates phospholipase Cbeta, resulting in Ca(2+) mobilization through Ca(2+) channels coupled with the inositol 1, 4, 5 tri-phosphate and ryanodine receptors on the sarco-endoplasmic reticulum Ca(2+) store in colorectal cancer cells.