Intracellular chloride regulates cell proliferation through the activation of stress‐activated protein kinases in MKN28 human gastric cancer cells

Recently, we reported that reduction of intracellular Cl − concentration ([Cl − ] i ) inhibited proliferation of MKN28 gastric cancer cells by diminishing the transition rate from G 1 to S cell‐cycle phase through upregulation of p21, cyclin‐dependent kinase inhibitor, in a p53‐independent manner. However, it is still unknown how intracellular Cl − regulates p21 expression level. In this study, we demonstrate that mitogen‐activated protein kinases (MAPKs) are involved in the p21 upregulation and cell‐cycle arrest induced by reduction of [Cl − ] i . Culture of MKN28 cells in a low Cl − medium significantly induced phosphorylation (activation) of MAPKs (ERK, p38, and JNK) and G 1 /S cell‐cycle arrest. To clarify the involvement of MAPKs in p21 upregulation and cell growth inhibition in the low Cl − medium, we studied effects of specific MAPKs inhibitors on p21 upregulation and G 1 /S cell‐cycle arrest in MKN28 cells. Treatment with an inhibitor of p38 or JNK significantly suppressed p21 upregulation caused by culture in a low Cl − medium and rescued MKN28 cells from the low Cl − ‐induced G 1 cell‐cycle arrest, whereas treatment with an ERK inhibitor had no significant effect on p21 expression or the growth of MKN28 cells in the low Cl − medium. These results strongly suggest that the intracellular Cl − affects the cell proliferation via activation of p38 and/or JNK cascades through upregulation of the cyclin‐dependent kinase inhibitor (p21) in a p53‐independent manner in MKN28 cells. J. Cell. Physiol. 223:764–770, 2010. © 2010 Wiley‐Liss, Inc.