p38 MAPK activation and mitochondrial depolarization mediate the cytotoxicity of Taiwan cobra phospholipase A₂ on human neuroblastoma SK-N-SH cells

Modification of catalytic residue His-47 with p-bromophenacyl bromide (BPB) abolished the enzymatic activity of Naja naja atra phospholipase A₂ (PLA₂). Additionally, alterations in the global structure and the spatial positions of Trp residues were noted in His-modified PLA₂. The cell viability of human neuroblastoma SK-N-SH cells was decreased by approximately 40% and 20% after treatment with 10 μM PLA₂ and BPB-PLA₂, respectively. Native and His-modified PLA₂ induced a necrotic cell death accompanied with an activation of p38 MAPK, the loss of mitochondrial membrane potential (ΔΨ_m) and cytochrome c release. Pretreatment with SB202190 (p38 MAPK inhibitor) and cyclosporine A (inhibitor of mitochondria permeability transition pore) rescued cell viability, ΔΨ_m and cytochrome c release of PLA₂-treated cells. Taken together, our data indicate that PLA₂ activity does not play an indispensable role on the cytotoxicity of N. naja atra PLA₂, and suggest a novel function of secretory PLA₂ in inducing cell death of neuroblastoma. Moreover, the reduced cytotoxicity noted with BPB-PLA₂ may be partly attributed to conformational distortion after modification of His-47.