Microtubule dysfunction induced by paclitaxel initiates apoptosis through both c-Jun N-terminal kinase (JNK)-dependent and -independent pathways in ovarian cancer cells

The antineoplastic agent paclitaxel (Taxol(TM)), a microtubule stabilizing agent, is known to arrest cells at the G(2)/M phase of the cell cycle and i nduce apoptosis. We and others have recently demonstrated that paclitaxel a lso activates the c-Jun N-terminal kinase/stress-activated protein kinase ( JNK/SAPK) signal transduction pathway in various human cell types, however, no clear role has been established for JNK/SAPK in paclitaxel-induced apop tosis. To further examine the role of JNK/SAPK signaling cascades in apopto sis resulting from microtubular dysfunction induced by paclitaxel, we have coexpressed dominant negative (dn) mutants of signaling proteins of the JNK /SAPK pathway (Ras, ASK1, Rac, JNKK, and JNK) in human ovarian cancer cells with a selectable marker to analyze the apoptotic characteristics of cells expressing dn vectors following exposure to paclitaxel, Expression of thes e dn signaling proteins had no effect on Bcl-2 phosphorylation, yet inhibit ed apoptotic changes induced by paclitaxel up to 16 h after treatment. Coex pression of these dn signaling proteins had no protective effect after 48 h of paclitaxel treatment. Our data indicate that: (i) activated JNK/SAPK ac ts upstream of membrane changes and caspase-3 activation in paclitaxel-init iated apoptotic pathways, independently of cell cycle stage, (ii) activated JNK/SAPK is not responsible for paclitaxel-induced phosphorylation of Bcl- 2, and (iii) apoptosis resulting from microtubule damage may comprise multi ple mechanisms, including a JNK/SAPK-dependent early phase and a JNK/SAPK-i ndependent late phase.