Japanese encephalitis virus infection activates caspase-8 and -9 in a FADD-independent and mitochondrion-dependent manner.
Japanese encephalitis virus (JEV), a mosquito-borne flavivirus, replicates primarily at the endoplasmic reticulum and thereby triggers apoptosis of infected cells. This study investigated the hierarchical activation of the caspase network induced by JEV infection. It was found that JEV activated the initiators caspase-8 and -9, as well as effector caspase-3, in infected baby hamster kidney and mouse neuroblastoma (N18) cells. In neuronal N18 cells, JEV infection triggered cytochrome c release from mitochondria, which in turn activated caspase-9 and -3. Treatment of JEV-infected N18 cells with cyclosporin A or ruthenium red, which attenuate mitochondrial injuries, blocked activation of caspase-9 or -3, typifying that, in neuronal cells, this apoptosis involves the mitochondrial pathway. Alternatively, in caspase-3-deficient MCF-7 cells, JEV persisted and readily triggered a typical apoptotic response, including cytochrome c release and full activation of caspase-9 and -8 along with caspase-6, indicating that JEV did not require caspase-3 to manifest caspase-8 activation and apoptosis. Interestingly, a Fas-associated death-domain-containing protein (FADD) dominant-negative mutant, which interfered with transmission of the extracellular death signals into cells through the Fas/tumour necrosis factor (TNF) receptor, failed to block JEV-induced apoptosis and caspase-8 activation, implying that receptor oligomerization of the Fas/TNF pathway might not participate in JEV-induced apoptosis. Taken together, these results illustrate that JEV infection triggers caspase cascades involving the initiators caspase-8 and -9, probably through FADD-independent but mitochondrion-dependent pathways.
Tsao
Chang-Huei
CH
Graduate Institute of Life Sciences, National Defense Medical Center, Taiwan, ROC.
Su
Hong-Lin
HL
The Department of Life Sciences, National Chung-Hsing University, Taiwan, ROC.
Lin
Yi-Ling
YL
Institute of Biomedical Sciences, Academia Sinica, Taiwan, ROC.
Yu
Han-Pang
HP
Institute of Biomedical Sciences, Academia Sinica, Taiwan, ROC.
Kuo
Shu-Ming
SM
The Department of Life Sciences, National Chung-Hsing University, Taiwan, ROC.
Shen
Ching-I
CI
The Department of Veterinary Medicine, National Chung-Hsing University, Taiwan, ROC.
Chen
Ching-Wen
CW
The Department of Life Sciences, National Chung-Hsing University, Taiwan, ROC.
Liao
Ching-Len
CL
Department of Microbiology and Immunology, National Defense Medical Center, Taiwan, ROC.
D000818:Animals; D017209:Apoptosis; D053181:Caspase 8 / Q000378:metabolism*; D053453:Caspase 9 / Q000378:metabolism*; D002460:Cell Line; D045744:Cell Line, Tumor; D006224:Cricetinae; D004664:Encephalitis Virus, Japanese / Q000472:pathogenicity*; D004789:Enzyme Activation; D053200:Fas-Associated Death Domain Protein / Q000378:metabolism*; D006801:Humans; D051379:Mice; D008928:Mitochondria / Q000378:metabolism*
C505533:FADD protein, human; D053200:Fas-Associated Death Domain Protein; D053181:Caspase 8; D053453:Caspase 9