Department of Oral and Craniofacial Molecular Biology, School of Dentistry, Massey Cancer Center, Virginia Commonwealth University, Richmond, Virginia, USA.
PLoS One. 2013;8(4):e60685. doi: 10.1371/journal.pone.0060685. Epub 2013 Apr 5.
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.
紫杉醇（泰素）诱导的细胞死亡需要内在的细胞死亡途径，但具体的参与者和确切的机制还不清楚。先前的研究表明，BH3 仅蛋白 BIM（BCL-2 相互作用介导细胞死亡的介质）在紫杉醇诱导的细胞凋亡中发挥作用。我们在这里表明，在使用 bim(-/-) MEFs（小鼠胚胎成纤维细胞）、bim(-/-) 小鼠乳腺癌模型和 shRNA 介导的人乳腺癌细胞中 BIM 下调的情况下，BIM 在紫杉醇诱导的细胞凋亡中是可有可无的。相比之下，bak(-/-) MEFs 和 shRNA 下调 BAK 的人乳腺癌细胞对紫杉醇的耐药性更高。然而，bax(-/-) MEFs 或 shRNA 下调 BAX 的人乳腺癌细胞中紫杉醇的敏感性不受影响，表明紫杉醇诱导的细胞凋亡依赖于 BAK，但不依赖于 BAX。在人乳腺癌细胞中，紫杉醇处理导致 MCL-1 降解，而蛋白酶体抑制剂 MG132 可阻止这种降解。Cdk 抑制剂罗西维林阻断紫杉醇诱导的 MCL-1 降解和凋亡，表明有丝分裂阻滞时 Cdk 的激活可以以蛋白酶体依赖的方式诱导随后的 MCL-1 降解。在未处理的细胞中，BAK 与 MCL-1 相关联，并与 MCL-1 表达的丧失及其从复合物中的释放协同激活。我们的数据表明，BAK 是紫杉醇诱导的细胞凋亡的介质，可能是克服紫杉醇耐药性的替代靶标。
