Overexpression of Phospholipase D suppresses Taxotere-induced cell death in stomach cancer cells

Abstract

Phspholipase D (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 both of PLD isozymes are involved in a diverse range of cellular processes that include receptor signaling, control of intracellular membrane transport, and reorganization of the actin cytoskeleton. Several recent studies reported that PLD has a role 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 poorly differentiated stomach cancer cells (SNU 484). While NSC showed a high level of basal PLD activity, SNU484 had a low level of basal PLD activity. Taxotere treatment resulted in increasing not only PLDs expression but also PLD activity. When PLD was selectively inhibited by treatment with 1-butanol, taxotere-induced apoptosis was exacerbated in both of NSC and SNU484. To confirm the role of PLD in taxorere-induced apoptosis, we transfected the PLDs into SNU 484. Overexpression of PLD isozymes resulted in inhibition of taxotere-induced apoptotic cell death, respectively, showing that by decreased degradation of chromosomal DNA and increased cell viability. Concurrently, bcl-2 expression was up-regulated and taxotere-induced activation of procaspase-3 was inhibited after the transfection of PLDs. Treatment of SNU 484 with PA, the product of PLD isozymes, also resulted in up-regualtion of bcl-2. While, PA-induced bcl-2 expression was blocked by mepacrine, an inhibitor of phospholiase A2 (PLA2), increased bcl-2 expression by PA was not inhibited by propranolol, inhibitor of PA phospholyhydrolase (PAP), indicating that PLA2 is very important in bcl-2 expression induced by PLD. Taken together, both PLD and PA play protective role against taxotere-induced cell death, resulting in increased bcl-2 expression in SNU 484 cells.