Paclitaxel-Induced Apoptosis Is BAK-Dependent, but BAX and BIM-Independent in Breast Tumor

Abstract

Paclitaxel (Taxol)-induced cell death requires the intrinsic cell death pathway, but the specific participants and the precise mechanisms are poorly understood. Previous studies indicate that a BH3-only protein BIM (BCL-2 Interacting Mediator of cell death) plays a role in paclitaxel-induced apoptosis. We show here that BIM is dispensable in apoptosis with paclitaxel treatment using bim−/− MEFs (mouse embryonic fibroblasts), the bim−/− mouse breast tumor model, and shRNA-mediated down-regulation of BIM in human breast cancer cells. In contrast, both bak −/− MEFs and human breast cancer cells in which BAK was down-regulated by shRNA were more resistant to paclitaxel. However, paclitaxel sensitivity was not affected in bax−/− MEFs or in human breast cancer cells in which BAX was down-regulated, suggesting that paclitaxel-induced apoptosis is BAK-dependent, but BAX-independent. In human breast cancer cells, paclitaxel treatment resulted in MCL-1 degradation which was prevented by a proteasome inhibitor, MG132. A Cdk inhibitor, roscovitine, blocked paclitaxel-induced MCL-1 degradation and apoptosis, suggesting that Cdk activation at mitotic arrest could induce subsequent MCL-1 degradation in a proteasome-dependent manner. BAK was associated with MCL-1 in untreated cells and became activated in concert with loss of MCL-1 expression and its release from the complex. Our data suggest that BAK is the mediator of paclitaxel-induced apoptosis and could be an alternative target for overcoming paclitaxel resistance.

BAK is a predictive and prognostic biomarker for the therapeutic effect of docetaxel treatment in patients with advanced gastric cancer

“…Taxane agents can stabilize microtubules by interfering with spindle microtubule dynamics, resulting in cell-cycle arrest [6]. Previous results indicated that the BAK and BIM proteins were important in the cytotoxicity of taxane agents in breast and lung cancer cells [31][32][33][34]. However, as these apoptosis-related proteins take part in a complex network [15], it is difficult to predict apoptotic responses by quantifying simple protein expression.…”

“…Gastric cancer cells from 40 patients enrolled in the UMIN 000000801 Trial [12] and 22 patients enrolled in the UMIN 000002361 Trial were also examined. At the time of analysis, the median followup time was 29.5 months (range, 3.6-96.4 months), and 46.4 % of the patients [32] had died. Thirty patients died of progressive disease, 1 patient died of a brain infarction, and 1 other patient died in a traffic accident.…”

Cisplatin-induced apoptosis in non-small-cell lung cancer cells is dependent on Bax- and Bak-induction pathway and synergistically activated by BH3-mimetic ABT-263 in p53 wild-type and mutant cells

“…Retroviral infection was performed as previously described [21]. The lentiviral sh-p53, sh-Bax and sh-Bak-expressing constructs were kindly provided by Dr. Harada (Virginia Commonwealth University, Richmond, VA, USA) [22].…”

A Bim-targeting strategy overcomes adaptive bortezomib resistance in myeloma through a novel link between autophagy and apoptosis

“…Human MM cell lines, 29,30 primary MM samples, and Bim knockout mouse embryonic fibroblasts (MEFs) 31 are described in supplemental Materials, available on the Blood Web site. To establish human MM cells adaptively resistant to bortezomib, RPMI8226 and U266 cells were continuously cultured in gradually increasing concentrations of bortezomib (initially 0.5 nM and increasing in stepwise increments of 0.2 nM) to 10 nM or 15 nM, respectively.…”