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.
- Received June 25, 2004.
- Accepted February 8, 2005.
- The American Society for Pharmacology and Experimental Therapeutics
MolPharm articles become freely available 12 months after publication, and remain freely available for 5 years.Non-open access articles that fall outside this five year window are available only to institutional subscribers and current ASPET members, or through the article purchase feature at the bottom of the page.
|