Intracellular chloride regulates the G₁/S cell cycle progression in gastric cancer cells

Recent studies show that ion channels/transporters play important roles in fundamental cellular functions. Several reports indicating the important roles of Cl(-) channels/transporters on cell proliferation suggest that the intracellular chloride concentration ([Cl(-)](i)) regulated by them would be one of critical messengers. We investigated whether the [Cl(-)](i) controls cell proliferation and cell cycle progression in human gastric cancer cells. Our studies indicated that furosemide, a blocker of Na(+)/K(+)/2Cl(-) cotransporter (NKCC), diminished cell growth by delaying the G(1)-S phase progression in gastric cancer cells with high expression and activity of NKCC. Furthermore, we found that the culture in the low Cl(-) medium (replacement of Cl(-) by NO(3) (-)) decreased the [Cl(-)](i) and inhibited cell growth of gastric cancer cells and that this inhibition of cell growth was due to cell cycle arrest at the G(0)/G(1) phase caused by diminution of CDK2 and phosphorylated Rb. The culture of cells in the low Cl(-) medium significantly increased expressions of p21 mRNA and protein. In addition, the low Cl(-) medium induced phosphorylation of mitogen activated protein kinases (MAPKs). Treatment with an inhibitor of p38 or JNK significantly suppressed p21 upregulation caused by culture in a low Cl(-) medium and rescued gastric cancer cells from the low Cl(-)-induced G(1) cell cycle arrest. These findings revealed that the [Cl(-)](i) affects the cell proliferation via activation of MAPKs through upregulation of p21 in gastric cancer cells. Our results suggest that the [Cl(-)](i) regulates important cellular functions in gastric cancer cells, leading to the development of novel therapeutic strategies.