Mhaidat Nizar M, Wang Yufang, Kiejda Kelly A, Zhang Xu Dong, Hersey Peter
Immunology and Oncology Unit, Royal Newcastle Hospital, Room 443, David Maddison Clinical Sciences Building, Corner King and Watt Streets, Newcastle, NSW 2300, Australia.
Mol Cancer Ther. 2007 Feb;6(2):752-61. doi: 10.1158/1535-7163.MCT-06-0564.
Taxanes have a broad spectrum of activity against various human cancers, including melanoma. In this study, we have examined the molecular mechanism of docetaxel-induced apoptosis of human melanoma. We report that docetaxel induced varying degrees of apoptosis in a panel of melanoma cell lines but not in normal fibroblasts. Induction of apoptosis was caspase dependent and associated with changes in mitochondrial membrane potential that could be inhibited by overexpression of Bcl-2. Docetaxel induced changes in Bax that correlated with sensitivity to docetaxel-induced apoptosis. These changes in Bax were not inhibited by overexpression of Bcl-2. Kinetic studies of caspase-2 activation by Western blotting and fluorogenic assays revealed that activation of caspase-2 seemed to be the initiating event. Inhibition of caspase-2 with z-VDVAD-fmk or by small interfering RNA knockdown inhibited changes in Bax and mitochondrial membrane potential and events downstream of mitochondria. Activation of caspase-8 and Bid seemed to be a late event, and docetaxel was able to induce apoptosis in cells deficient in caspase-8 and Bid. p53 did not seem to be involved as a p53 null cell line was sensitive to docetaxel and an inhibitor of p53 did not inhibit apoptosis. Small interfering RNA knockdown of PUMA and Noxa also did not inhibit apoptosis. These results suggest that docetaxel induces apoptosis in melanoma cells by pathways that are dependent on activation of caspase-2, which initiates mitochondrial dependent apoptosis by direct or indirect activation of Bax.
紫杉烷对包括黑色素瘤在内的多种人类癌症具有广泛的活性。在本研究中，我们研究了多西他赛诱导人黑色素瘤细胞凋亡的分子机制。我们报告多西他赛在一组黑色素瘤细胞系中诱导了不同程度的凋亡，但在正常成纤维细胞中未诱导凋亡。凋亡的诱导是半胱天冬酶依赖性的，并且与线粒体膜电位的变化有关，这种变化可被Bcl-2的过表达所抑制。多西他赛诱导的Bax变化与对多西他赛诱导凋亡的敏感性相关。Bcl-2的过表达并未抑制这些Bax的变化。通过蛋白质印迹法和荧光测定法对半胱天冬酶-2激活进行的动力学研究表明，半胱天冬酶-2的激活似乎是起始事件。用z-VDVAD-fmk或通过小干扰RNA敲低抑制半胱天冬酶-2可抑制Bax和线粒体膜电位的变化以及线粒体下游的事件。半胱天冬酶-8和Bid的激活似乎是一个晚期事件，并且多西他赛能够在缺乏半胱天冬酶-8和Bid的细胞中诱导凋亡。p53似乎未参与其中，因为p53缺失的细胞系对多西他赛敏感，并且p53抑制剂并未抑制凋亡。PUMA和Noxa的小干扰RNA敲低也未抑制凋亡。这些结果表明，多西他赛通过依赖于半胱天冬酶-2激活的途径诱导黑色素瘤细胞凋亡，半胱天冬酶-2通过直接或间接激活Bax启动线粒体依赖性凋亡。
