Role of membrane sphingomyelin and ceramide in platform formation for Fas-mediated apoptosis.
Engagement of the Fas receptor (CD95) initiates multiple signaling pathways that lead to apoptosis, such as the formation of death-inducing signaling complex (DISC), activation of caspase cascades, and the generation of the lipid messenger, ceramide. Sphingomyelin (SM) is a major component of lipid rafts, which are specialized structures that enhance the efficiency of membrane receptor signaling and are a main source of ceramide. However, the functions of SM in Fas-mediated apoptosis have yet to be clearly defined, as the responsible genes have not been identified. After cloning a gene responsible for SM synthesis, SMS1, we established SM synthase-defective WR19L cells transfected with the human Fas gene (WR/Fas-SM(-)), and cells that have been functionally restored by transfection with SMS1 (WR/Fas-SMS1). We show that expression of membrane SM enhances Fas-mediated apoptosis through increasing DISC formation, activation of caspases, efficient translocation of Fas into lipid rafts, and subsequent Fas clustering. Furthermore, WR/Fas-SMS1 cells, but not WR/Fas-SM(-) cells, showed a considerable increase in ceramide generation within lipid rafts upon Fas stimulation. These data suggest that a membrane SM is important for Fas clustering through aggregation of lipid rafts, leading to Fas-mediated apoptosis.
Miyaji
Michihiko
M
Department of Rheumatology and Clinical Immunology, Graduate School of Medicine, Kyoto University, Sakyo-ku, Kyoto 606-8507, Japan.
Jin
Zhe-Xiong
ZX
Yamaoka
Shohei
S
Amakawa
Ryuichi
R
Fukuhara
Shirou
S
Sato
Satoshi B
SB
Kobayashi
Toshihide
T
Domae
Naochika
N
Mimori
Tsuneyo
T
Bloom
Eda T
ET
Okazaki
Toshiro
T
Umehara
Hisanori
H
D000818:Animals; D017209:Apoptosis / Q000235:genetics / Q000502:physiology*; D020169:Caspases / Q000378:metabolism; D045744:Cell Line, Tumor; D002518:Ceramides / Q000378:metabolism*; D017353:Gene Deletion; D006801:Humans; D021962:Membrane Microdomains / Q000378:metabolism*; D051379:Mice; D021381:Protein Transport / Q000235:genetics / Q000502:physiology; D015398:Signal Transduction / Q000235:genetics / Q000502:physiology*; D013109:Sphingomyelins / Q000378:metabolism*; D014162:Transfection; D017855:Transferases (Other Substituted Phosphate Groups) / Q000235:genetics / Q000378:metabolism; D019014:fas Receptor / Q000235:genetics / Q000378:metabolism*
D002518:Ceramides; D013109:Sphingomyelins; D019014:fas Receptor; D017855:Transferases (Other Substituted Phosphate Groups); C070186:phosphatidylcholine-ceramide phosphocholine transferase; D020169:Caspases