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

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Abstract
Recently, we reported that reduction of intracellular Cl− concentration ([Cl−]i) inhibited proliferation of MKN28 gastric cancer cells by diminishing the transition rate from G1 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 G1/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 G1/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 G1 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.

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