Cot protooncoprotein activates the dual specificity kinases MEK-1 and SEK-1 and induces differentiation of PC12 cells.
Mitogenic signals initiated at the plasma membrane are transmitted to the nucleus through an intricate signalling network. We identified the protooncoprotein Cot as a new component of mitogenic signalling cascades, which activates both the classic cytoplasmic cascade and the SAPK stress pathway. Wildtype and activated Cot phosphorylate and activate MEK-1 and SEK-1 in vitro. These findings are consistent with the sequence homology between Cot and the rat gene Tpl-2. Expression of oncogenic Cot in 293, NIH3T3 and PC12 cells leads to in vivo phosphorylation of endogenous c-Jun and Erk-1/2 suggesting that the serine/threonine kinase Cot functions beside c-Raf-1 and Mos as a direct activator of MEK-1. Furthermore, we have examined the biological effects of Cot on the phenotype of fibroblastic and neuronal cells. In order to test a potential c-Raf-1 dependency of Cot transformation, the effect of oncogenic Cot on Raf revertant CHP25 cells was determined. Cot could restore the transformed phenotype indicating that Cot transformation is not dependent on active c-Raf-1 and that Cot is not a target for the putative Raf inhibitor, which is presumably active in the revertant cell line. Expression of oncogenic versions of Raf as well as v-Mos leads to differentiation of PC12 cells. Cot also induces neurite outgrowth of PC12 cells. These data are consistent with the role of Cot in the classic mitogenic cascade and suggest that the simultaneously activated JNK/SAPK stress pathway has no antagonistic effects in this context.
Institut für la Medizinische Strahlenkunde und Zellforschung, University of Würzburg, Germany.
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Hagemann
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Troppmair
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UR
Rapp
D016475:3T3 Cells; D000818:Animals; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000235:genetics / Q000378:metabolism; D002454:Cell Differentiation; D002461:Cell Line, Transformed; D004789:Enzyme Activation; D005326:Fetal Proteins / Q000378:metabolism*; D048369:MAP Kinase Kinase 1; D020930:MAP Kinase Kinase Kinases; D051379:Mice; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020929:Mitogen-Activated Protein Kinase Kinases; D020928:Mitogen-Activated Protein Kinases; D016716:PC12 Cells; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D011518:Proto-Oncogene Proteins / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D016755:Proto-Oncogene Proteins c-jun / Q000378:metabolism; D051381:Rats; D020794:Receptor Protein-Tyrosine Kinases / Q000378:metabolism*; D036122:Receptor, EphA4; D048051:p38 Mitogen-Activated Protein Kinases
D005326:Fetal Proteins; D011518:Proto-Oncogene Proteins; D016755:Proto-Oncogene Proteins c-jun; D011505:Protein-Tyrosine Kinases; D020794:Receptor Protein-Tyrosine Kinases; D036122:Receptor, EphA4; D017346:Protein Serine-Threonine Kinases; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases; D048051:p38 Mitogen-Activated Protein Kinases; D020930:MAP Kinase Kinase Kinases; C069937:MAP3K8 protein, human; D048369:MAP Kinase Kinase 1; C482125:MAP2K1 protein, human; C482127:Map2k1 protein, mouse; D020929:Mitogen-Activated Protein Kinase Kinases