Abstract
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.
Publication types
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Research Support, Non-U.S. Gov't
MeSH terms
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Apoptosis
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Caspase 3
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Caspase 8
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Caspases / metabolism
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Cathepsin D / metabolism
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Cell Membrane / chemistry
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Cell-Free System
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Ceramides / pharmacology
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Cytochromes c / metabolism
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Fluorescent Antibody Technique
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Gene Expression
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Green Fluorescent Proteins / genetics
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HeLa Cells
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Humans
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Mitochondria / ultrastructure*
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Niemann-Pick Diseases / enzymology
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Protein Conformation / drug effects
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Protein Conformation / radiation effects
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Proto-Oncogene Proteins c-bcl-2 / chemistry*
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Proto-Oncogene Proteins c-bcl-2 / genetics
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Proto-Oncogene Proteins c-bcl-2 / physiology
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Proto-Oncogene Proteins c-bcl-2 / radiation effects
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RNA, Small Interfering / pharmacology
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Signal Transduction
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Sphingomyelin Phosphodiesterase / deficiency
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Sphingomyelin Phosphodiesterase / genetics
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Sphingomyelin Phosphodiesterase / physiology*
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Ultraviolet Rays*
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bcl-2-Associated X Protein
Substances
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BAX protein, human
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Ceramides
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Proto-Oncogene Proteins c-bcl-2
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RNA, Small Interfering
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bcl-2-Associated X Protein
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Green Fluorescent Proteins
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Cytochromes c
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Sphingomyelin Phosphodiesterase
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CASP3 protein, human
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CASP8 protein, human
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Caspase 3
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Caspase 8
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Caspases
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Cathepsin D