Betulinic acid-induced apoptosis in glioma cells: A sequential requirement for new protein synthesis, formation of reactive oxygen species, and caspase

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, synthe-sis, is independent of p53, and results in p21 protein accumu-lation 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. Fur-thermore, BA induces the formation of reactive oxygen specie