Possible involvement of cytosolic phospholipase A(2) in cell death induced by 1-methyl-4-phenylpyridinium ion, a dopaminergic neurotoxin, in GH3 cells.

Previously we reported that 1-methyl-4-phenylpyridinium ion (MPP(+)), a dopaminergic neurotoxin, induced apoptosis of GH3 cells established from rat anterior pituitary. In the present study, the role of MPP(+) along with that of other apoptotic factors such as Ca(2+) and H(2)O(2) in cell death was examined. Ionomycin induced DNA fragmentation and lactate dehydrogenase (LDH) leakage in GH3 cells. H(2)O(2) also induced LDH leakage. Co-addition of MPP(+), in conditions where MPP(+) had no effect by itself, enhanced ionomycin- and H(2)O(2)-induced cell death. Because the stimulation of phospholipase A(2) (PLA(2)) causing arachidonic acid (AA) release has been proposed to be involved in neuronal cell death, the effect of MPP(+) on AA release in GH3 cells was investigated. MPP(+) treatment for 8 h enhanced ionomycin- and H(2)O(2)-stimulated AA release mediated by activation of cytosolic PLA(2) in a concentration-dependent manner, although MPP(+) by itself had no effect on AA release. An inhibitor of cytosolic PLA(2) inhibited MPP(+)-induced cell death. These findings suggest a synergistic effect of MPP(+) on Ca(2+)- and H(2)O(2)-induced cell death, and the involvement of cytosolic PLA(2) activation in MPP(+)-induced cell death in GH3 cells. Pretreatment with a caspase inhibitor or EGF did not modify the ionomycin- or H(2)O(2)-induced AA release, or enhancement by MPP(+), but the pretreatment inhibited the cell death in the presence and absence of MPP(+). The involvement of caspase(s) on activation of PLA(2) by MPP(+) was excluded, and EGF inhibited MPP(+)-induced cell death downstream of the AA release.