title: Cephalostatin 1 inactivates Bcl-2 by hyperphosphorylation independent of M-phase arrest and DNA damage.
abstract: Cephalostatin 1 is a marine product that induces a novel cytochrome c-independent apoptotic pathway in Jurkat leukemia T cells (Cancer Res 63:8869-8876, 2003). Here, we show that overexpression of the antiapoptotic protein Bcl-2 protects cells only partially against cephalostatin 1-induced apoptosis. The mechanism of Bcl-2 inactivation by cephalostatin 1 is based on hyperphosphorylation of Bcl-2 on Thr69 and Ser87 because Jurkat cells overexpressing a Bcl-2 protein with mutations on both phosphorylation sites were completely protected against cephalostatin 1. In search of the kinase responsible for Bcl-2 phosphorylation, c-Jun NH2-terminal kinase (JNK) was found to be activated by cephalostatin 1. Reduction of Bcl-2 phosphorylation by the specific JNK inhibitor (anthra(1,3-cd)pyrazol-6(2H)-one) SP600125 suggested a crucial role for JNK in this process. JNK activation was not a consequence of DNA damage, a known stimulus of JNK, because cephalostatin 1 did not induce DNA lesions as shown by the comet assay. Arrest in M-phase is also demonstrated to be associated with JNK activation. However, cephalostatin 1 does not evoke an arrest in M-phase as shown by flow cytometry. Together, cephalostatin 1 is shown to induce JNK activation with subsequent Bcl-2 phosphorylation and inactivation. Reported triggers, such as the induction of an M-phase arrest or DNA damage are not involved in this process, suggesting a novel mechanism for cephalostatin 1-mediated Bcl-2 hyperphosphorylation.
authors.affiliation: Department of Pharmacy, Center of Drug Research, University of Munich, Germany.
authors.forename: Irina M
authors.initials: IM
authors.lastname: Müller
authors.forename: Verena M
authors.initials: VM
authors.lastname: Dirsch
authors.forename: Anita
authors.initials: A
authors.lastname: Rudy
authors.forename: Nancy
authors.initials: N
authors.lastname: López-Antón
authors.forename: George R
authors.initials: GR
authors.lastname: Pettit
authors.forename: Angelika M
authors.initials: AM
authors.lastname: Vollmar
mesh_terms: D002455:Cell Division / Q000187:drug effects* / Q000235:genetics; D004249:DNA Damage / Q000187:drug effects* / Q000235:genetics; D020868:Gene Silencing / Q000187:drug effects*; D019254:Genes, bcl-2 / Q000187:drug effects*; D006801:Humans; D019169:Jurkat Cells; D010619:Phenazines / Q000737:chemistry / Q000302:isolation & purification / Q000494:pharmacology*; D010766:Phosphorylation / Q000187:drug effects; D013141:Spiro Compounds / Q000737:chemistry / Q000302:isolation & purification / Q000494:pharmacology*; D013256:Steroids / Q000737:chemistry / Q000302:isolation & purification / Q000494:pharmacology*
chemical_list: D010619:Phenazines; D013141:Spiro Compounds; D013256:Steroids; C454806:cephalostatin I