Cytosolic chloride ion is a key factor in lysosomal acidification and function of autophagy in human gastric cancer cell

The purpose of the present study was to clarify roles of cytosolic chloride ion (cl-) in regulation of lysosomal acidification [intra-lysosomal ph (phlys)] and autophagy function in human gastric cancer cell line (mkn28). the mkn28 cells cultured under a low cl- condition elevated phlys and reduced the intra-lysosomal cl- concentration ([cl-]lys) via reduction of cytosolic cl- concentration ([cl-]c),showing abnormal accumulation of lc3ii and p62 participating in autophagy function (dysfunction of autophagy) accompanied by inhibition of cell proliferation via g0/g1 arrest without induction of apoptosis. we also studied effects of direct modification of h+ transport on lysosomal acidification and autophagy. application of bafilomycin a1 (an inhibitor of v-type h+-atpase) or ethyl isopropyl amiloride [eipa; an inhibitor of na+/h+ exchanger (nhe)] elevated phlys and decreased [cl-]lys associated with inhibition of cell proliferation via induction of g0/g1 arrest similar to the culture under a low cl- condition. however,unlike low cl- condition,application of the compound,bafilomycin a1 or eipa,induced apoptosis associated with increases in caspase 3 and 9 without large reduction in [cl-]c compared with low cl- condition. these observations suggest that the lowered [cl-]c primarily causes dysfunction of autophagy without apoptosis via dysfunction of lysosome induced by disturbance of intra-lysosomal acidification. this is the first study showing that cytosolic cl- is a key factor of lysosome acidification and autophagy. © 2014 the authors. journal of cellular and molecular medicine published by john wiley & sons ltd and foundation for cellular and molecular medicine.