Phospholipase D suppresses taxotere-induced cell death through bcl-2 retaining in stomach cancer cells

초록

Phospholipase (PLD) catalyses the hydrolysis of phosphatidylcholine to generate phosphatidic acid (PA) and choline. There are at least two PLD isozymes, PLD1 and PLD2. Genetic and pharmacological approaches implicate that both PLD isozymes are involved in a diverse range of cellular processes, including receptor signaling, membrane transport control, and actin cytoskeleton reorganization. Several recent studies reported that PLD has a role in signaling pathways that oppose apoptosis and promote cell survival in cancer. In this study, we examined the role of PLD in taxotere-induced apoptosis in stomach cell lines; normal stomach cells (NSC) and stomach cancer cells (SNU 484). Taxotere treatment resulted in increase of both PLDs expression and activity. When PLD was selectively inhibited by 1-butanol treatment, taxotere-induced apoptosis was exacerbated in both of NSC and SNU484 cells. To confirm the role of PLD in taxotere-induced apoptosis, PLDs were transfected into SNU 484 cells. Overexpression of PLD isozymes resulted in inhibition of taxotere-induced apoptotic cell death, evidenced by decreased degradation of chromosomal DNA and increased cell viability. Concurrently, bcl-2 expression was upregulated, and taxotere-induced activation of procaspase-3 was inhibited after PLDs transfection. Treatment of SNU 484 cells with PA, the product of PLDs, also resulted in upregulation of bcl-2. Although, PA-induced bcl-2 expression was blocked by mepacrine, an inhibitor of phospholipase A2 (PLA2), increased bcl-2 expression by PA was not abrogated by propranolol, on inhibitor of PA phospholyhydrolase (PAP). These results indicate that PLA2 is closely related with bcl-2 expression, but not with PAP, induced by PLD activation.