Abstract
Betulinic acid (BA), a pentacyclic triterpene, is an experimental cytotoxic agent for malignant melanoma. Here, we show that BA triggers apoptosis in five human glioma cell lines. BA-induced apoptosis requires new protein, but not RNA, synthesis, is independent of p53, and results in p21 protein accumulation in the absence of a cell cycle arrest. BA-induced apoptosis involves the activation of caspases that cleave poly(ADP ribose)polymerase. Interactions of death ligand/receptor pairs of the CD95/CD95 ligand family do not mediate BA-induced caspase activation. BA enhances the levels of BAX and BCL-2 proteins but does not alter the levels of BCL-xS or BCL-xL. Ectopic expression of BCL-2 prevents BA-induced caspase activation, DNA fragmentation, and cell death. Furthermore, BA induces the formation of reactive oxygen species that are essential for BA-triggered cell death. The generation of reactive oxygen species is blocked by BCL-2 and requires new protein synthesis but is unaffected by caspase inhibitors, suggesting that BA toxicity sequentially involves new protein synthesis, formation of reactive oxygen species, and activation of crm-A-insensitive caspases.
MeSH terms
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Antineoplastic Agents, Phytogenic / toxicity*
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Apoptosis / drug effects*
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Betulinic Acid
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Caspases / metabolism*
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Cell Cycle / drug effects
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Cell Division
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Cell Survival
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Cyclin-Dependent Kinase Inhibitor p21
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Cyclins / genetics
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Cycloheximide / pharmacology
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Cysteine Proteinase Inhibitors / pharmacology
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DNA Fragmentation
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Enzyme Activation
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Fas Ligand Protein
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Glioma
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Humans
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Kinetics
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Membrane Glycoproteins / pharmacology
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Oligopeptides / pharmacology
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Pentacyclic Triterpenes
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Proto-Oncogene Proteins / biosynthesis
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Proto-Oncogene Proteins c-bcl-2 / biosynthesis*
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Proto-Oncogene Proteins c-bcl-2 / genetics
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Proto-Oncogene Proteins c-bcl-2 / metabolism
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Reactive Oxygen Species / physiology*
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Triterpenes / toxicity*
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Tumor Cells, Cultured
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bcl-2-Associated X Protein
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bcl-X Protein
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fas Receptor / drug effects
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fas Receptor / physiology
Substances
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Antineoplastic Agents, Phytogenic
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BAX protein, human
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BCL2L1 protein, human
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CDKN1A protein, human
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Cyclin-Dependent Kinase Inhibitor p21
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Cyclins
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Cysteine Proteinase Inhibitors
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FASLG protein, human
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Fas Ligand Protein
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Membrane Glycoproteins
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Oligopeptides
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Pentacyclic Triterpenes
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Proto-Oncogene Proteins
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Proto-Oncogene Proteins c-bcl-2
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Reactive Oxygen Species
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Triterpenes
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aspartyl-glutamyl-valyl-aspartal
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bcl-2-Associated X Protein
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bcl-X Protein
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fas Receptor
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Cycloheximide
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Caspases
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Betulinic Acid