Methylmercury-induced toxicity is mediated by enhanced intracellular calcium through activation of phosphatidylcholine-specific phospholipase C.
Methylmercury (MeHg) is a ubiquitous environmental toxicant to which humans can be exposed by ingestion of contaminated food. MeHg has been suggested to exert its toxicity through its high reactivity to thiols, generation of arachidonic acid and reactive oxygen species (ROS), and elevation of free intracellular Ca(2+) levels ([Ca(2+)](i)). However, the precise mechanism has not been fully defined. Here we show that phosphatidylcholine-specific phospholipase C (PC-PLC) is a critical pathway for MeHg-induced toxicity in MDCK cells. D609, an inhibitor of PC-PLC, significantly reversed the toxicity in a time- and dose-dependent manner with concomitant inhibition of the diacylglycerol (DAG) generation and the phosphatidylcholine (PC)-breakdown. MeHg activated the group IV cytosolic phospholipase A(2) (cPLA(2)) and acidic form of sphingomyelinase (A-SMase) downstream of PC-PLC, but these enzymes as well as protein kinase C (PKC) were not linked to the toxicity by MeHg. Furthermore, MeHg produced ROS, which did not affect the toxicity. Addition of EGTA to culture media resulted in partial decrease of [Ca(2+)](i) and partially blocked the toxicity. In contrast, when the cells were treated with MeHg in the presence of Ca(2+) in the culture media, D609 completely prevented cell death with parallel decrease in [Ca(2+)](i). Our results demonstrated that MeHg-induced toxicity was linked to elevation of [Ca(2+)](i) through activation of PC-PLC, but not attributable to the signaling pathways such as cPLA(2), A-SMase, and PKC, or to the generation of ROS.
Kang
Mi Sun
MS
Department of Environmental and Health Chemistry, College of Pharmacy, Chung-Ang University, Seoul, 221 Huksuk-Dong, Dongjak-Ku, Seoul 156-756, South Korea.
Jeong
Ju Yeon
JY
Seo
Ji Heui
JH
Jeon
Hyung Jun
HJ
Jung
Kwang Mook
KM
Chin
Mi-Reyoung
MR
Moon
Chang-Kiu
CK
Bonventre
Joseph V
JV
Jung
Sung Yun
SY
Kim
Dae Kyong
DK
D000818:Animals; D001952:Bridged-Ring Compounds / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000187:drug effects; D002614:Chelating Agents / Q000494:pharmacology; D004075:Diglycerides / Q000378:metabolism; D004285:Dogs; D004305:Dose-Response Relationship, Drug; D004533:Egtazic Acid / Q000494:pharmacology; D004785:Environmental Pollutants / Q000633:toxicity*; D004789:Enzyme Activation / Q000187:drug effects; D006801:Humans; D007668:Kidney / Q000187:drug effects / Q000378:metabolism* / Q000473:pathology; D008767:Methylmercury Compounds / Q000633:toxicity*; D009447:Neuroblastoma / Q000188:drug therapy / Q000378:metabolism* / Q000473:pathology; D009636:Norbornanes; D010713:Phosphatidylcholines / Q000378:metabolism; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology; D010741:Phospholipases A / Q000378:metabolism; D017382:Reactive Oxygen Species / Q000378:metabolism; D013108:Sphingomyelin Phosphodiesterase / Q000378:metabolism; D013859:Thiocarbamates; D013871:Thiones / Q000494:pharmacology; D010738:Type C Phospholipases / Q000037:antagonists & inhibitors / Q000378:metabolism*
D001952:Bridged-Ring Compounds; D002614:Chelating Agents; D004075:Diglycerides; D004785:Environmental Pollutants; D008767:Methylmercury Compounds; D009636:Norbornanes; D010713:Phosphatidylcholines; D010726:Phosphodiesterase Inhibitors; D017382:Reactive Oxygen Species; D013859:Thiocarbamates; D013871:Thiones; D004533:Egtazic Acid; C046498:tricyclodecane-9-yl-xanthogenate; D010741:Phospholipases A; D010738:Type C Phospholipases; D013108:Sphingomyelin Phosphodiesterase; C105598:phosphatidylcholine-specific phospholipase C; C004925:methylmercuric chloride; D002118:Calcium