title: Raf-1/bcl-2 phosphorylation: a step from microtubule damage to cell death.
abstract: Recent studies have shown that paclitaxel leads to activation of Raf-1 kinase and have suggested that this activation is essential for bcl-2 phosphorylation and apoptosis. In the present study, we demonstrate that, in addition to paclitaxel, other agents that interact with tubulin and microtubules also induce Raf-1/bcl-2 phosphorylation, whereas DNA-damaging drugs, antimetabolites, and alkylating agents do not. Activation of Raf-1 kinase by paclitaxel is linked to tubulin polymerization; the effect is blunted in paclitaxel-resistant cells, the tubulin of which does not polymerize following the addition of paclitaxel. In contrast, vincristine and vinblastine, drugs to which the paclitaxel-resistant cells retain sensitivity were able to bring about Raf-1 phosphorylation. The requirement for disruption of microtubules in this signaling cascade was strengthened further using paclitaxel analogues by demonstrating a correlation between tubulin polymerization, Raf-1/bcl-2 phosphorylation, and cytotoxicity. Inhibition of RNA or protein synthesis prevents Raf-1 activation and bcl-2 phosphorylation, suggesting that an intermediate protein(s) acts upstream of Raf-1 in this microtubule damage-activating pathway. A model is proposed that envisions a pathway of Raf-1 activation and bcl-2 phosphorylation following disruption of microtubular architecture, serving a role similar to p53 induction following DNA damage.
authors.affiliation: Howard Hughes Medical Institute, University of Pennsylvania School of Medicine, Philadelphia 19104, USA.
authors.forename: M V
authors.initials: MV
authors.lastname: Blagosklonny
authors.forename: P
authors.initials: P
authors.lastname: Giannakakou
authors.forename: W S
authors.initials: WS
authors.lastname: el-Deiry
authors.forename: D G
authors.initials: DG
authors.lastname: Kingston
authors.forename: P I
authors.initials: PI
authors.lastname: Higgs
authors.forename: L
authors.initials: L
authors.lastname: Neckers
authors.forename: T
authors.initials: T
authors.lastname: Fojo
mesh_terms: D000970:Antineoplastic Agents / Q000494:pharmacology; D000972:Antineoplastic Agents, Phytogenic / Q000494:pharmacology*; D004351:Drug Resistance; D004789:Enzyme Activation; D005260:Female; D006801:Humans; D008870:Microtubules / Q000187:drug effects*; D017239:Paclitaxel / Q000494:pharmacology*; D010766:Phosphorylation; D011108:Polymers / Q000378:metabolism; D047428:Protein Kinase Inhibitors; D011494:Protein Kinases / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism*; D019908:Proto-Oncogene Proteins c-raf; D014404:Tubulin / Q000187:drug effects* / Q000378:metabolism; D014407:Tumor Cells, Cultured / Q000187:drug effects / Q000378:metabolism
chemical_list: D000970:Antineoplastic Agents; D000972:Antineoplastic Agents, Phytogenic; D011108:Polymers; D047428:Protein Kinase Inhibitors; D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D014404:Tubulin; D011494:Protein Kinases; D017346:Protein Serine-Threonine Kinases; D019908:Proto-Oncogene Proteins c-raf; D017239:Paclitaxel