Cytosolic phospholipase A2-{alpha} is an early apoptotic activator in PEDF-induced endothelial cell apoptosis

Departments of 1 Medical Research and 6 Ophthalmology, Mackay Memorial Hospital; 2 Department of Microbiology, School of Medicine, National Taiwan University; 3 Department of Ophthalmology and 4 School of Medicine, Taipei Medical University; and 5 Department of Microbiology and Immunology, The National Defense Medical Center, Taipei, Taiwan Submitted 22 August 2008 ; accepted in final form 4 December 2008 Pigment epithelium-derived factor (PEDF) is an intrinsic antiangiogenic factor and a potential therapeutic agent. Previously, we discovered the mechanism of PEDF-induced apoptosis of human umbilical vein endothelial cells (HUVECs) as sequential induction/activation of p38 mitogen-activated protein kinase (MAPK), peroxisome proliferator-activated receptor gamma (PPAR- ), and p53. In the present study, we investigated the signaling role of cytosolic calcium-dependent phospholipase A 2 - (cPLA 2 - ) to bridge p38 MAPK and PPAR- activation. PEDF induced cPLA 2 - activation in HUVECs and in endothelial cells in chemical burn-induced vessels on mouse cornea. The cPLA 2 - activation is evident from the phosphorylation and nuclear translocation of cPLA 2 - as well as arachidonic acid release and the cleavage of PED6, a synthetic PLA 2 substrate. Such activation can be abolished by p38 MAPK inhibitor. The PEDF-induced PPAR- activation, p53 expression, caspase-3 activity, and apoptosis can be abolished by both cPLA 2 inhibitor and small interfering RNA targeting cPLA 2 - . Our observation not only establishes the signaling role of cPLA 2 - but also for the first time demonstrates the sequential activation of p38 MAPK, cPLA 2 - , PPAR- , and p53 as the mechanism of PEDF-induced endothelial cell apoptosis. pigment epithelium-derived factor; p38 mitogen-activated protein kinase; peroxisome proliferator-activated receptor- Address for reprint requests and other correspondence: Y.-P. Tsao, Dept. of Medical Research, Mackay Memorial Hospital, Taipei, Taiwan (e-mail: yptsao{at}yahoo.com )