Docetaxel-induced apoptosis of human melanoma is mediated by activation of c-Jun NH2-terminal kinase and inhibited by the mitogen-activated protein kinase extracellular signal-regulated kinase 1/2 pathway.
OBJECTIVE
Our studies have shown variable sensitivity of cultured melanoma cells to docetaxel. To better understand this response, we studied the role of signal transduction pathways in modulating docetaxel-induced melanoma killing.


METHODS
Involvement of c-Jun NH(2)-terminal kinase (JNK), extracellular signal-regulated kinase 1/2 (ERK1/2), p38 mitogen-activated protein kinase, and Akt signaling was studied by evaluating their extent of activation in melanoma cells after treatment with docetaxel. The effect of their activation on docetaxel-induced apoptosis was assessed using biochemical inhibitors of the pathways and Western blot analysis of proteins involved.


RESULTS
Docetaxel induced activation of both JNK and ERK1/2 but not p38 mitogen-activated protein kinase or Akt kinases. Apoptosis was dependent on activation of JNK and mediated through activation of caspase-2 and caspase-dependent changes in Bax and Bak. The levels of activated JNK in individual lines showed a close correlation with the levels of apoptosis. In contrast, activation of ERK1/2 by docetaxel inhibited apoptosis and the levels of activation in individual lines were inversely correlated to the degree of apoptosis. Studies on the Bcl-2 family proteins seemed to reflect changes induced by activation of JNK and ERK1/2 pathways. Docetaxel-induced JNK activation was required for Bcl-2 phosphorylation as well as caspase-2-dependent activation of Bax and Bak and subsequent mitochondrial release of apoptosis-inducing factor and cytochrome c. In contrast, activation of ERK1/2 resulted in degradation of BH3-only protein Bim and phosphorylation of Bad.


CONCLUSIONS
These studies provide further insights into sensitivity of melanoma cells to taxanes and provide a basis for the current rationale of combining taxanes with inhibitors of the Raf-ERK1/2 pathway.
Mhaidat
Nizar M
NM
Immunology and Oncology Unit, Royal Newcastle Hospital, Newcastle, New South Wales, Australia.
Zhang
Xu Dong
XD
Jiang
Chen Chen
CC
Hersey
Peter
P
D000970:Antineoplastic Agents / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects*; D053143:Caspase 2 / Q000378:metabolism; D045744:Cell Line, Tumor; D000077143:Docetaxel; D004789:Enzyme Activation; D019254:Genes, bcl-2; D006801:Humans; D048031:JNK Mitogen-Activated Protein Kinases / Q000378:metabolism*; D020935:MAP Kinase Signaling System / Q000187:drug effects; D008545:Melanoma / Q000188:drug therapy* / Q000201:enzymology* / Q000473:pathology; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism*; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism*; D051058:Oncogene Protein v-akt / Q000378:metabolism; D043823:Taxoids / Q000494:pharmacology*; D050998:bcl-2 Homologous Antagonist-Killer Protein / Q000378:metabolism; D051028:bcl-2-Associated X Protein / Q000378:metabolism; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism
D000970:Antineoplastic Agents; D043823:Taxoids; D050998:bcl-2 Homologous Antagonist-Killer Protein; D051028:bcl-2-Associated X Protein; D000077143:Docetaxel; D051058:Oncogene Protein v-akt; D048031:JNK Mitogen-Activated Protein Kinases; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D048051:p38 Mitogen-Activated Protein Kinases; D053143:Caspase 2