Acid sphingomyelinase is indispensable for UV light-induced Bax conformational change at the mitochondrial membrane.
Ultraviolet light-induced apoptosis can be caused by DNA damage but also involves immediate-early cell death cascades characteristic of death receptor signaling. Here we show that the UV light-induced apoptotic signaling pathway is unique, targeting Bax activation at the mitochondrial membrane independent of caspase-8 or cathepsin D activity. Cells deficient in acid sphingomyelinase (ASMase) do not show UV light-induced Bax activation, cytochrome c release, or apoptosis. In ASMase-deficient cells, the apoptotic UV light response is restored by stable or transient expression of human ASMase. Bax conformational change in ASMase(-/-) cells is also caused by synthetic C(16)-ceramide acting on intact cells or isolated mitochondria. The results suggest that UV light-triggered ASMase activation is essentially required for Bax conformational change leading to mitochondrial release of pro-apoptotic factors like cytochrome c and Smac.
Kashkar
Hamid
H
Institute for Medical Microbiology, Immunology and Hygiene and Center for Molecular Medicine Cologne, University of Cologne, 50935 Cologne, Germany.
Wiegmann
Katja
K
Yazdanpanah
Benjamin
B
Haubert
Dirk
D
Krönke
Martin
M
D017209:Apoptosis; D053148:Caspase 3; D053181:Caspase 8; D020169:Caspases / Q000378:metabolism; D002402:Cathepsin D / Q000378:metabolism; D002462:Cell Membrane / Q000737:chemistry; D002474:Cell-Free System; D002518:Ceramides / Q000494:pharmacology; D045304:Cytochromes c / Q000378:metabolism; D005455:Fluorescent Antibody Technique; D015870:Gene Expression; D049452:Green Fluorescent Proteins / Q000235:genetics; D006367:HeLa Cells; D006801:Humans; D008928:Mitochondria / Q000648:ultrastructure*; D009542:Niemann-Pick Diseases / Q000201:enzymology; D011487:Protein Conformation / Q000187:drug effects / Q000528:radiation effects; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000737:chemistry* / Q000235:genetics / Q000502:physiology / Q000528:radiation effects; D034741:RNA, Small Interfering / Q000494:pharmacology; D015398:Signal Transduction; D013108:Sphingomyelin Phosphodiesterase / Q000172:deficiency / Q000235:genetics / Q000502:physiology*; D014466:Ultraviolet Rays; D051028:bcl-2-Associated X Protein
C494826:BAX protein, human; D002518:Ceramides; D019253:Proto-Oncogene Proteins c-bcl-2; D034741:RNA, Small Interfering; D051028:bcl-2-Associated X Protein; D049452:Green Fluorescent Proteins; D045304:Cytochromes c; D013108:Sphingomyelin Phosphodiesterase; C505407:CASP3 protein, human; C505530:CASP8 protein, human; D053148:Caspase 3; D053181:Caspase 8; D020169:Caspases; D002402:Cathepsin D