Ling Xiang, Cheng Qiuying, Black Jennifer D, Li Fengzhi
Department of Pharmacology and Therapeutics, Grace Cancer Drug Center, Roswell Park Cancer Institute, Buffalo, New York 14263.
Department of Pharmacology and Therapeutics, Grace Cancer Drug Center, Roswell Park Cancer Institute, Buffalo, New York 14263.
J Biol Chem. 2007 Sep 14;282(37):27204-27214. doi: 10.1074/jbc.M705161200. Epub 2007 Jul 25.
It has been previously shown that both survivin and the survivin splice variant survivin-2B are localized in mitochondria. Whereas the mechanism involved in blockade of mitochondria-mediated apoptosis by survivin has been extensively studied, the role of survivin-2B in regulation of apoptosis has not been well defined. In the present study, we report that in addition to mitochondria, survivin-2B is also localized in the microtubule organization center (MTOC) and, in contrast to other survivin isoforms (i.e. survivin and survivin-DeltaEx3), behaves as a proapoptotic molecule. We show that forced expression of survivin-2B blocks tubulin polymerization, ablates mitotic cells, and induces mitochondria-dependent apoptosis. The mitochondria-mediated apoptosis induced by survivin-2B was indicated by Smac release from mitochondria, activation of caspases 9 and 3, and loss of mitochondrial potential, while caspase-8 remained inactive. Further analysis of the mechanism for the mitochondria-associated events of apoptosis induced by forced expression of survivin-2B revealed down-regulation of the pro-survival factor Bcl-2 and up-regulation of the pro-apoptotic factor Bax in mitochondria, while the apoptosis-inducing factor (AIF) remains unchanged. Our studies further showed that taxol (paclitaxel) treatment of cancer cells not only up-regulates survivin but also down-regulates survivin-2B and that forced expression of survivin-2B sensitizes cells to taxol-induced cell growth inhibition and cell death, while silencing of endogenous survivin-2B transcripts by survivin-2B-specific siRNA made cells resistant to taxol treatment. These findings advance our current knowledge about survivin-2B and may help to develop novel approaches for cancer treatment.
先前的研究表明，生存素和生存素剪接变体生存素-2B均定位于线粒体。虽然生存素阻断线粒体介导的细胞凋亡的机制已得到广泛研究，但生存素-2B在细胞凋亡调控中的作用尚未明确界定。在本研究中，我们报告称，除了线粒体，生存素-2B还定位于微管组织中心（MTOC），并且与其他生存素异构体（即生存素和生存素-DeltaEx3）不同，它表现为一种促凋亡分子。我们发现，强制表达生存素-2B会阻断微管蛋白聚合，消除有丝分裂细胞，并诱导线粒体依赖性细胞凋亡。生存素-2B诱导的线粒体介导的细胞凋亡表现为Smac从线粒体释放、半胱天冬酶9和3的激活以及线粒体膜电位的丧失，而半胱天冬酶-8仍无活性。对强制表达生存素-2B诱导的细胞凋亡相关线粒体事件机制的进一步分析表明，线粒体中促生存因子Bcl-2下调，促凋亡因子Bax上调，而凋亡诱导因子（AIF）保持不变。我们的研究还表明，用紫杉醇处理癌细胞不仅会上调生存素，还会下调生存素-2B，并且强制表达生存素-2B会使细胞对紫杉醇诱导的细胞生长抑制和细胞死亡敏感，而用生存素-2B特异性siRNA沉默内源性生存素-2B转录本会使细胞对紫杉醇处理产生抗性。这些发现推进了我们目前对生存素-2B的认识，并可能有助于开发新的癌症治疗方法。
