Reduction of intracellular Cl⁻ concentration induces the G₁/S cell cycle arrest through the activation of stress-activated protein kinases in MKN28 human gastric cancer cells.

Abstract

Our recent studies demonstrate that the reduction of intracellular Cl⁻ concentration bring the inhibitory effect on the cell proliferation of MKN28 gastric cancer cell by diminishing the transition rate from G₁ to S cell cycle phase through a p21, CDK inhibitor, upregulation in a p53-independen manner. However, it is still unknown how the intracellular Cl⁻ regulates the p21 expression level. In this study, we show that stress-activated protein kinases (SAPKs) are involved in p21 upregulation and cell cycle arrest induced by the reduction of the intracellular Cl⁻ concentration. In MKN28 cells, culture in the Cl⁻-replaced medium (replacement of NaCl by NaNO3) significantly induced SAPKs (ERK, p38, and JNK) phosphorylation and G₁/S cell cycle arrest. To clarify the involvement of SAPKs in p21 induction and cell growth inhibition in the Cl⁻-replaced medium, we studied the effects of specific SAPKs inhibitors on the p21-induced G₁/S cell cycle arrest in MKN28 cells. The cell cycle arrest observed in the Cl⁻-replaced media was partially eliminated by the addition of inhibitors of SAPKs. The effects of SPAKs inhibitors on the p21 and its downstream signaling molecules will also be discussed. [J Physiol Sci. 2008;58 Suppl:S207]