A [Lys⁴⁹]phospholipase A₂ from Protobothrops flavoviridis Venom Induces Caspase-Independent Apoptotic Cell Death Accompanied by Rapid Plasma-Membrane Rupture in Human Leukemia Cells

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Protobothrops flavoviridis venom contains plural phospholipase A₂ (PLA₂) isozymes. A [Lys⁴⁹]PLA₂ called BPII induced cell death in human leukemia cells. PLA2, an [Asp⁴⁹]PLA₂ that has much stronger lipolytic activity than BPII, failed to induce cell death. BPII-treated cells showed morphological changes, DNA fragmentation, and nuclear condensation. This BPII-induced apoptotic cell death was neither inhibited by inhibitors of caspases 3 and 6 nor accompanied by activation of procaspase 3, indicating that BPII-induced cell death is caspase independent. Since inactive p-bromophenacylated BPII induced cell death, BPII-induced apoptotic cell death is independent of PLA₂ lipolytic activity. Rapid externalization of phosphatidylserine in BPII-treated cells was observed for fluorescein isothiocyanate (FITC)-labeled annexin V. In the cells treated with BPII, this spread over the cell membranes, implying that the cell toxicity of BPII is mediated via its cell-surface receptor.