Variable apoptotic response of NSCLC cells to inhibition of the MEK/ERK pathway by small molecules or dominant negative mutants.
To evaluate the role of the MEK/ERK pathway in NSCLC survival, we analyzed NSCLC cell lines that differed in tumor histology and status of p53, Rb, and K-ras. Constitutive ERK1/2 activity was demonstrated in 17 of 19 cell lines by maintenance of ERK1/2 phosphorylation with serum deprivation. Phosphorylation of ERK1/2 correlated with phosphorylation of MEK1/2 and p90RSK, but was inversely correlated with phosphorylation of c-Raf at S259. With serum deprivation, the MEK inhibitors, PD98059 and U0126, inhibited ERK1/2 activity but did not increase apoptosis. PD98059 and U0126 induced cell cycle arrest in G(0)/G(i) in cells with the highest levels of ERK1/2 activity, which correlated with induction of p27 but not p21. To confirm the cytostatic response to MEK inhibitors, we performed transient transfections with dominant negative forms of MEK or ERK. Surprisingly, dominant negative MEK and ERK mutants increased apoptosis without affecting cell cycle or p27 levels. When combined with paclitaxel, MEK inhibitors had no effect on apoptosis. In contrast, dominant negative ERK2 potentiated paclitaxel-induced apoptosis. Our studies show that constitutive ERK1/2 activity in NSCLC cells promotes cellular survival and chemotherapeutic resistance. Moreover, our data are the first to demonstrate divergent cellular responses to inhibition of the MEK/ERK pathway by small molecule inhibitors or dominant negative mutants.
Cancer Therapeutics Branch, Center for Cancer Research, National Cancer Institute, Bethesda, MD 20889, USA.
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Brognard
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Dennis
D000970:Antineoplastic Agents / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects / Q000235:genetics*; D002289:Carcinoma, Non-Small-Cell Lung / Q000188:drug therapy / Q000201:enzymology* / Q000235:genetics; D002470:Cell Survival / Q000187:drug effects / Q000235:genetics; D019008:Drug Resistance, Neoplasm / Q000235:genetics; D004791:Enzyme Inhibitors / Q000494:pharmacology; D014644:Genetic Variation / Q000187:drug effects / Q000235:genetics; D006801:Humans; D008175:Lung Neoplasms / Q000188:drug therapy / Q000201:enzymology* / Q000235:genetics; D048369:MAP Kinase Kinase 1; D020935:MAP Kinase Signaling System / Q000187:drug effects / Q000235:genetics*; D020929:Mitogen-Activated Protein Kinase Kinases / Q000037:antagonists & inhibitors / Q000235:genetics*; D020928:Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors / Q000235:genetics*; D009154:Mutation / Q000187:drug effects / Q000235:genetics; D010766:Phosphorylation / Q000187:drug effects; D017346:Protein Serine-Threonine Kinases / Q000037:antagonists & inhibitors / Q000235:genetics*; D016192:Resting Phase, Cell Cycle / Q000187:drug effects / Q000235:genetics; D014162:Transfection; D014407:Tumor Cells, Cultured; D015854:Up-Regulation / Q000187:drug effects / Q000235:genetics
D000970:Antineoplastic Agents; D004791:Enzyme Inhibitors; D017346:Protein Serine-Threonine Kinases; D020928:Mitogen-Activated Protein Kinases; D048369:MAP Kinase Kinase 1; C482125:MAP2K1 protein, human; D020929:Mitogen-Activated Protein Kinase Kinases