Phosphatidic acid produced by phospholipase D inhibits Fas-induced apoptosis via Bcl-2 upregulation in A20 murine B lymphoma cells

초록

Increased level of phospholipase D2 (PLD2) activity induced by PLD2 gene transfection, upregulated Bcl-2 expression and suppressed Fas-induced apoptosis at the same time. When the PLD2 activity was completely down regulated, Fas-induced apoptosis was not attenuated at all. These findings suggest that PLD2 activity suppress Fas-induced apoptosis in A20 cells. Pretreatment of phosphatidic acid (PA), the enzymatic product of PLD, in A20 cells also showed increased level of Bcl-2 expression and attenuated Fas-induced apoptosis. To determine the role of PA, we blocked the downstream signaling pathways of PA by propranolol, a phosphatidate phosphohydrolase inhibitor. Inhibition of phosphatidate phosphohydrolase resulted in the complete inhibition of Fas-mediated apoptosis and Bcl-2 upregulation. These results imply that PA produced by PLD plays a role in the increase of Bcl-2 expression and inhibition of apoptosis by Fas cross-linking. To confirm that PA itself can act as survival factor in Fas-mediated apoptosis in A20 cells, we blocked PLA2 using mepacrine, a well known PLA2 inhibitor. Interestingly, inhibition of PLA2 resulted in enhanced Fas-mediated apoptosis. This finding suggests that conversion of PA into lysophosphatidic acid (LPA) and arachidonic acid by PLA2 is necessary to show anti-apoptotic effect against Fas-induced cell death in A20 cells.