B chain is a functional subunit of beta-bungarotoxin for inducing apoptotic death of human neuroblastoma SK-N-SH cells.
beta-Bungarotoxin (beta-Bgt), a presynaptic phospholipase A(2) (PLA(2)) neurotoxin isolated from the venom of Bungarus multicinctus, consists of A chain and B chain. The goal of the present study is to explore the functional contribution of the two subunits to the toxicity of beta-Bgt. beta-Bgt was found to induce apoptotic death of SK-N-SH cells via elevating intracellular Ca(2+) and intracellular ROS production. Moreover, an activation of p38 MAPK was associated with the cytotoxicity of beta-Bgt. SB202190 (p38 MAPK inhibitor), N-acetylcysteine (antioxidant reagent), 1,2-bis(2-aminophenoxy)ethane-N,N,N,N-tetraacetic acid (BAPTA) (Ca(2+) chelator) and the inhibitors of Ca(2+) release from intracellular depots (ruthenium red and 2-aminoethoxydiphenyl borate) effectively attenuated the cytotoxicity of beta-Bgt. In sharp contrast to the inability of A chain, B chain was able to induce cytotoxic effects on SK-N-SH cells as beta-Bgt did. Abolishment of PLA(2) activity did not significantly alter the cytotoxic activity of beta-Bgt. MK801 (an NMDA receptor antagonist), antibodies against NMDA receptor and 4-aminopyridine (a potassium channel blocker) markedly reduced the cytotoxic effects of beta-Bgt, B chain and catalytically inactivated beta-Bgt. Moreover, antibodies against NMDA receptor blocked the binding of rhodamine-labeled beta-Bgt to SK-N-SH cells. Taken together, our data indicate that B chain is a functional subunit responsible for the cytotoxicity of beta-Bgt, and suggest that the cytotoxicity of beta-Bgt is mediated by NMDA receptor and potassium conductance.
Institute of Biomedical Sciences, National Sun Yat-Sen University-Kaohsiung Medical University Joint Research Center, National Sun Yat-Sen University, Kaohsiung 804, Taiwan.
Yun-Ching
YC
Cheng
Jeh-Jeng
JJ
Wang
Long-Sen
LS
Chang
D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D002038:Bungarotoxins / Q000008:administration & dosage / Q000494:pharmacology*; D017838:Bungarus; D002118:Calcium / Q000378:metabolism; D002121:Calcium Channel Blockers / Q000008:administration & dosage / Q000494:pharmacology*; D045744:Cell Line, Tumor; D006801:Humans; D009447:Neuroblastoma / Q000473:pathology; D009474:Neurons / Q000187:drug effects / Q000378:metabolism
D002038:Bungarotoxins; D002121:Calcium Channel Blockers; D002118:Calcium