Paclitaxel induces prolonged activation of the Ras/MEK/ERK pathway independently of activating the programmed cell death machinery.
Paclitaxel is a widely used chemotherapeutic agent and is known to induce programmed cell death (apoptosis) in a variety of cell types, but the precise underlying mechanisms are poorly understood. To elucidate these mechanisms, we challenged human esophageal squamous cancer cell lines with paclitaxel and investigated its effects upon signal transduction pathways. Physiologically relevant concentrations of paclitaxel (1-1,000 nm) induced apoptosis. All three mitogen-activated protein kinase (MAPK) family members, c-Jun N-terminal kinase (JNK), p38 MAPK, and extracellular signal-regulated kinase (ERK) were activated upon paclitaxel treatment. Interestingly, JNK activation and p38 MAPK activation were delayed and peaked at 48 h, whereas ERK activity was sustained over 72 h. In addition, Ras activation and MAPK/ERK kinase (MEK) phosphorylation were observed in concordance with ERK activation. While ERK activation was completely ablated by MEK inhibitors, immunoprecipitation and Western blot analysis revealed that neither MEK-1 nor MEK-2 was involved, but instead another member of the MEK family may potentially participate. Although pretreatment with a general caspase inhibitor, benzyloxycarbonyl-Val-Ala-Asp-fluoromethylketone rescued the cell death, it did not prevent Ras or ERK activation. Furthermore, inhibition of JNK, p38 MAPK, or MEK did not alter PARP cleavage and the cell death induced by paclitaxel. These results in aggregate suggest that the delayed activation of JNK, p38 MAPK, and ERK was not linked to activation of the cell death machinery.
Division of Gastroenterology, Cancer Center, Department of Genetics, and Abramson Family Cancer Research Institute, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA.
Okano J
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D000590:Amino Acid Chloromethyl Ketones / Q000494:pharmacology; D000972:Antineoplastic Agents, Phytogenic / Q000494:pharmacology*; D017209:Apoptosis; D015153:Blotting, Western; D053179:Caspase 7; D020169:Caspases / Q000378:metabolism; D002467:Cell Nucleus / Q000378:metabolism; D002470:Cell Survival; D004305:Dose-Response Relationship, Drug; D004789:Enzyme Activation; D004815:Epidermal Growth Factor / Q000494:pharmacology; D005434:Flow Cytometry; D006801:Humans; D048031:JNK Mitogen-Activated Protein Kinases; D048369:MAP Kinase Kinase 1; D048370:MAP Kinase Kinase 2; D020935:MAP Kinase Signaling System; D020929:Mitogen-Activated Protein Kinase Kinases / Q000378:metabolism*; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D008954:Models, Biological; D017239:Paclitaxel / Q000494:pharmacology*; D010766:Phosphorylation; D011233:Precipitin Tests; D020033:Protein Isoforms; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D015398:Signal Transduction; D013997:Time Factors; D014407:Tumor Cells, Cultured; D048051:p38 Mitogen-Activated Protein Kinases; D018631:ras Proteins / Q000378:metabolism*
D000590:Amino Acid Chloromethyl Ketones; D000972:Antineoplastic Agents, Phytogenic; D020033:Protein Isoforms; C096713:benzyloxycarbonylvalyl-alanyl-aspartyl fluoromethyl ketone; D004815:Epidermal Growth Factor; C482128:MAP2K2 protein, human; D011505:Protein-Tyrosine Kinases; D017346:Protein Serine-Threonine Kinases; D048031:JNK Mitogen-Activated Protein Kinases; D020928:Mitogen-Activated Protein Kinases; D048051:p38 Mitogen-Activated Protein Kinases; D048369:MAP Kinase Kinase 1; D048370:MAP Kinase Kinase 2; C482125:MAP2K1 protein, human; D020929:Mitogen-Activated Protein Kinase Kinases; C505520:CASP7 protein, human; D053179:Caspase 7; D020169:Caspases; D018631:ras Proteins; D017239:Paclitaxel