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 A₂ (PLA₂) from 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 PLA₂-treated cells. Moreover, PLA₂ treatment increased Fas and FasL protein expression. Upon exposure to PLA₂, activation of p38 MAPK (mitogen-activated protein kinase) and JNK (c-Jun NH ₂-terminal kinase) was found in K562 cells. SB202190 (p38 MAPK inhibitor) pretreatment enhanced cytotoxic effect of PLA₂ and led to prolonged JNK activation, but failed to affect PLA₂-induced upregulation of Fas and FasL protein expression. Sustained JNK activation aggravated caspase8/mitochondria-dependent death pathway, downregulated Bcl-2 expression and increased mitochondrial translocation of Bax. SP600125 (JNK inhibitor) abolished the cytotoxic effect of PLA₂ and PLA ₂-induced autocrine Fas death pathway. Transfection ASK1 siRNA and overexpression of dominant negative p38α MAPK proved that ASK1 pathway was responsible for PLA₂-induced p38 MAPK and JNK activation and p38α MAPK activation suppressed dynamically persistent JNK activation. Downregulation of FADD abolished PLA₂-induced procaspase-8 degradation and rescued viability of PLA₂-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.