title: Betulinic acid as new activator of NF-kappaB: molecular mechanisms and implications for cancer therapy.
abstract: Recent evidence demonstrates that the anticancer activity of betulinic acid (BetA) can be markedly increased by combination protocols, for example with chemotherapy, ionizing radiation or TRAIL. Since nuclear factor-kappaB (NF-kappaB), a key regulator of stress-induced transcriptional activation, has been implicated in mediating apoptosis resistance, we investigated the role of NF-kappaB in BetA-induced apoptosis. Here, we provide for the first time evidence that BetA activates NF-kappaB in a variety of tumor cell lines. NF-kappaB DNA-binding complexes induced by BetA consisted of p50 and p65 subunits. Nuclear translocation of p65 was also confirmed by immunofluorescence microscopy. BetA-induced NF-kappaB activation involved increased IKK activity and phosphorylation of IkappaB-alpha at serine 32/36 followed by degradation of IkappaB-alpha. Reporter assays revealed that NF-kappaB activated by BetA is transcriptionally active. Interestingly, inhibition of BetA-induced NF-kappaB activation by different chemical inhibitors (proteasome inhibitor, antioxidant, IKK inhibitor) attenuated BetA-induced apoptosis. Importantly, specific NF-kappaB inhibition by transient or stable expression of IkappaB-alpha super-repressor inhibited BetA-induced apoptosis in SH-EP neuroblastoma cells, while transient expression of IkappaB-alpha super-repressor had no influence on BetA-induced apoptosis in two other cell lines. Thus, our findings that activation of NF-kappaB by BetA promotes BetA-induced apoptosis in a cell type-specific fashion indicate that NF-kappaB inhibitors in combination with BetA would have no therapeutic benefit or could even be contraproductive in certain tumors, which has important implications for the design of BetA-based combination protocols.
authors: Department of Hematology, Oncology, University Children's Hospital, Prittwitzstr. 43, Ulm D-89075, Germany.
authors: Hubert
authors: H
authors: Kasperczyk
authors: Katia
authors: K
authors: La Ferla-Brühl
authors: Mike Andrew
authors: MA
authors: Westhoff
authors: Lars
authors: L
authors: Behrend
authors: Ralf Michael
authors: RM
authors: Zwacka
authors: Klaus-Michael
authors: KM
authors: Debatin
authors: Simone
authors: S
authors: Fulda
mesh_terms: D017209:Apoptosis; D001483:Base Sequence; D045744:Cell Line, Tumor; D017931:DNA Primers; D006801:Humans; D006868:Hydrolysis; D020672:I-kappa B Proteins / Q000378:metabolism; D000072000:NF-KappaB Inhibitor alpha; D016328:NF-kappa B / Q000378:metabolism*; D009369:Neoplasms / Q000628:therapy*; D053978:Pentacyclic Triterpenes; D014315:Triterpenes / Q000494:pharmacology*; D000094062:Betulinic Acid
chemical_list: D017931:DNA Primers; D020672:I-kappa B Proteins; D016328:NF-kappa B; C000606204:NFKBIA protein, human; D053978:Pentacyclic Triterpenes; D014315:Triterpenes; D000072000:NF-KappaB Inhibitor alpha; D000094062:Betulinic Acid