Ceramide induces p38 MAPK and JNK activation through a mechanism involving a thioredoxin-interacting protein-mediated pathway.
Ceramide, a tumor-suppressor lipid, is generated by sphingomyelin hydrolysis or by de novo synthesis when cells are activated by various stress stimuli as well as when cancer cells are subjected to genotoxic chemotherapy. Ceramide may modulate apoptotic signaling pathways; however, its transcription-dependent effects remain unclear. Our data showed that actinomycin D partially inhibited ceramide-induced apoptosis. Using microarray analysis, we found that ceramide up-regulated a tumor suppressor gene called thioredoxin-interacting protein (Txnip). Similarly, the chemotherapeutic agent etoposide induced Txnip expression en route to apoptosis, which was blocked by inhibitors of ceramide production. Txnip colocalized with thioredoxin and reduced its activity, which caused dissociation of thioredoxin from apoptosis signal-regulating kinase 1 (ASK1). Cells expressing ASK1 siRNA were more resistant to ceramide-induced apoptosis. Ceramide caused ASK1-regulated p38 mitogen-activated protein kinase (MAPK) and JNK activation, as well as activation of the endoplasmic reticulum (ER) stress cascade, and pharmacologic or siRNA-mediated inhibition of p38 MAPK or JNK partially reduced ceramide-induced mitochondria-mediated apoptosis. Furthermore, ceramide-induced ASK1, p38, and JNK phosphorylation and cell apoptosis were inhibited by Txnip siRNA transfection. Taken together, we show that ceramide exhibits a mechanism of transcriptional regulation involving up-regulation of Txnip expression, also induced by etoposide, which results in ASK1 activation, ER stress, and p38 and JNK phosphorylation, all leading to apoptosis.
Chen
Chia-Ling
CL
Institute of Basic Medical Sciences, National Cheng Kung University Medical College, Tainan, Taiwan.
Lin
Chiou-Feng
CF
Chang
Wen-Tsan
WT
Huang
Wei-Ching
WC
Teng
Chiao-Fang
CF
Lin
Yee-Shin
YS
D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D002518:Ceramides / Q000494:pharmacology*; D003609:Dactinomycin / Q000494:pharmacology; D015536:Down-Regulation / Q000187:drug effects; D004789:Enzyme Activation / Q000187:drug effects; D005047:Etoposide / Q000494:pharmacology; D015973:Gene Expression Regulation, Leukemic / Q000187:drug effects; D006801:Humans; D048031:JNK Mitogen-Activated Protein Kinases / Q000378:metabolism*; D019169:Jurkat Cells; D048848:MAP Kinase Kinase Kinase 5 / Q000378:metabolism; D051379:Mice; D020411:Oligonucleotide Array Sequence Analysis; D010766:Phosphorylation / Q000187:drug effects; D021381:Protein Transport / Q000187:drug effects; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D013879:Thioredoxins / Q000378:metabolism; D014158:Transcription, Genetic / Q000187:drug effects; D015854:Up-Regulation / Q000187:drug effects; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism*
D002352:Carrier Proteins; D002518:Ceramides; D012333:RNA, Messenger; C486715:TXNIP protein, human; D003609:Dactinomycin; D013879:Thioredoxins; D005047:Etoposide; D048031:JNK Mitogen-Activated Protein Kinases; D048051:p38 Mitogen-Activated Protein Kinases; D048848:MAP Kinase Kinase Kinase 5; C482858:MAP3K5 protein, human