Taiwan Cobra Phospholipase A2-Elicited JNK Activation is Responsible for Autocrine Fas-Mediated Cell Death and Modulating Bcl-2 and Bax Protein Expression in Human Leukemia K562 Cells

Phospholipase A(2) (PLA(2)) Front Naja naja atra venom induced apoptotic death of human leukemia K562 cells. Degradation of procaspases, production of tBid, loss of mitochondrial membrane potential, Bcl-2 degradation, mitochondrial translocation of Bax, and cytochrome c release were observed in PLA(2)-treated cells. Moreover, PLA(2) treatment increased Fas and FasL protein expression. Upon exposure to PLA(2), activation or p38 MAPK (mitogen-activated protein kinase) and JNK (c-Jun NH2-terminal kinase) was found in K562 cells. SB202 190 (p38 MAPK inhibitor) pretreatment enhanced cytotoxic effect of PLA(2) and led to prolonged JNK activation, but failed to affect PLA(2)-induced upregulation of Fas and FasL protein expression. Sustained JNK activation aggravated caspase9/mitochondria-dependent death pathway, downregulated Bcl-2 expression and increased mitochondrial translocation of Bax. SP600125 (JNK inhibitor) abolished the cytotoxic effect of PLA(2) and PLA(2)-induced autocrine Fas death pathway. Transfection ASK I siRNA and overexpression of dominant negative p38 alpha MAPK proved that ASK1 pathway was responsible For PLA(2)-induced p38 MAPK and JNK activation and p389 alpha MAPK activation suppressed dynamically persistent JNK activation. Downregulation of FADD abolished PLA(2)-induced procaspase-8 degradation and rescued viability of PLA(2)-treated cells. Taken together, our results indicate that JNK-mediated autocrine Fas/FasL apoptotic mechanism and modulation of Bcl-2 Family proteins are involved in PLA(2)-induced death of K562 cells. J. Cell. Biochem. 109: 245-254, 2010. (C) 2009 Wiley-Liss, Inc.