Abstract
Small cell lung cancer (SCLC) accounts for 25% of all lung cancers, and is almost uniformly fatal. Unlike other lung cancers, ras mutations have not been reported in SCLC, suggesting that activation of ras-associated signal transduction pathways such as the raf-MEK mitogen-activated protein kinases (MAPK) are associated with biological consequences that are unique from other cancers. The biological effects of raf activation in small cell lung cancer cells was determined by transfecting NCI-H209 or NCI-H510 SCLC cells with a gene encoding a fusion protein consisting of an oncogenic form of human Raf-1 and the hormone binding domain of the estrogen receptor (DeltaRaf-1:ER), which can be activated with estradiol. DeltaRaf-1:ER activation resulted in phosphorylation of MAPK. Activation of this pathway caused a dramatic loss of soft agar cloning ability, suppression of growth capacity, associated with cell accumulation in G1 and G2, and S phase depletion. Raf activation in these SCLC cells was accompanied by a marked induction of the cyclin-dependent kinase (cdk) inhibitor p27(kip1), and a decrease in cdk2 protein kinase activities. Each of these events can be inhibited by pretreatment with the MEK inhibitor PD098059. These data demonstrate that MAPK activation by DeltaRaf-1:ER can activate growth inhibitory pathways leading to cell cycle arrest. These data suggest that raf/MEK/ MAPK pathway activation, rather than inhibition, may be a therapeutic target in SCLC and other neuroendocrine tumors.
Publication types
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Research Support, Non-U.S. Gov't
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Research Support, U.S. Gov't, P.H.S.
MeSH terms
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Adenovirus E1A Proteins / pharmacology
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CDC2 Protein Kinase / metabolism
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CDC2-CDC28 Kinases*
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Calcium-Calmodulin-Dependent Protein Kinases / metabolism
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Carcinoma, Small Cell / pathology*
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Cell Cycle
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Cell Cycle Proteins*
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Cell Division
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Cyclin-Dependent Kinase 2
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Cyclin-Dependent Kinase Inhibitor p27
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Cyclin-Dependent Kinases / antagonists & inhibitors
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Cyclin-Dependent Kinases / metabolism
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Cyclins / metabolism
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Enzyme Inhibitors / metabolism
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Estradiol / pharmacology
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Flavonoids / pharmacology
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Humans
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Lung Neoplasms / pathology*
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Microtubule-Associated Proteins / metabolism
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Mitogen-Activated Protein Kinase Kinases
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Phosphorylation
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Protein Kinases / metabolism
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Protein Serine-Threonine Kinases / metabolism
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Proto-Oncogene Proteins c-raf / biosynthesis
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Proto-Oncogene Proteins c-raf / genetics
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Proto-Oncogene Proteins c-raf / metabolism*
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Receptors, Estrogen / genetics
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Receptors, Estrogen / metabolism
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Recombinant Fusion Proteins / biosynthesis
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Recombinant Fusion Proteins / genetics
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Recombinant Fusion Proteins / metabolism
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Tamoxifen / analogs & derivatives
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Tamoxifen / pharmacology
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Tumor Cells, Cultured
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Tumor Suppressor Proteins*
Substances
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Adenovirus E1A Proteins
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Cell Cycle Proteins
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Cyclins
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Enzyme Inhibitors
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Flavonoids
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Microtubule-Associated Proteins
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Receptors, Estrogen
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Recombinant Fusion Proteins
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Tumor Suppressor Proteins
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Tamoxifen
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Cyclin-Dependent Kinase Inhibitor p27
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afimoxifene
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Estradiol
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Protein Kinases
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Protein Serine-Threonine Kinases
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Proto-Oncogene Proteins c-raf
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Calcium-Calmodulin-Dependent Protein Kinases
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CDC2 Protein Kinase
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CDC2-CDC28 Kinases
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CDK2 protein, human
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Cyclin-Dependent Kinase 2
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Cyclin-Dependent Kinases
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Mitogen-Activated Protein Kinase Kinases
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2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one