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Research Articles: Therapeutics, Targets, and Development

Docetaxel-induced apoptosis in melanoma cells is dependent on activation of caspase-2

Immunology and Oncology Unit, Newcastle Misericordiae Hospital, Newcastle, New South Wales, Australia

Requests for reprints: Peter Hersey or Xu Dong Zhang, Immunology and Oncology Unit, Royal Newcastle Hospital, Room 443, David Maddison Clinical Sciences Building, Corner King and Watt Streets, Newcastle, NSW 2300, Australia. Phone: 61-2-49-236828; Fax: 61-2-49236184. E-mail: Peter.Hersey{at}newcastle.edu.au or Xu.Zhang{at}newcastle.edu.au

Abstract

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. [Mol Cancer Ther 2007;6(2):752–61]

Grant support: New South Wales State Cancer Council and National Health and Medical Research Council, Australia. X.D. Zhang is a Cancer Institute NSW Fellow.

The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

¹ In preparation.

Received 9/13/06; revised 11/20/06; accepted 12/20/06.

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