title: Kinase suppressor of ras is necessary for tumor necrosis factor alpha activation of extracellular signal-regulated kinase/mitogen-activated protein kinase in intestinal epithelial cells.
abstract: Mitogen-activated protein (MAP) kinase activity is essential for tumor necrosis factor (TNF) alpha receptor 1 regulation of intestinal epithelial cell proliferation. However, the mechanism of TNF-alpha mediated activation of extracellular signal-regulated kinase (ERK)/M1AP kinase has not been established clearly. Both TNF-alpha and cell-permeable ceramide have been reported to increase the kinase activity of kinase suppressor of Ras (KSR). To determine the role of KSR in TNF-alpha-induced ERK1/ERK2 activation, we studied young adult mouse colon cells expressing a dominant-negative, kinase-inactive (ki) KSR. We report that TNF-alpha, a cell-permeable ceramide, and sphingomyelinase stimulate ERK1/ERK2 activation and increase the phosphoserine content of KSR, which are inhibited by kiKSR expression in intact cells. Furthermore, TNF-alpha-induced Raf-1 threonine phosphorylation, kinase activity toward MEK1, and association with KSR are also inhibited by kiKSR expression. Our data also show by sequential in vitro kinase assays that TNF-alpha enhances KSR phosphorylation of Raf-1 on threonine, enhancing Raf-1 kinase activity toward MAP kinase kinase. We therefore conclude that KSR is an essential upstream regulator of TNF-alpha-stimulated ERK1/ERK2 activation, most likely mediated via direct phosphorylation of Raf-1.
authors.affiliation: Department of Pediatrics, Vanderbilt University School of Medicine, Nashville, Tennessee 37232, USA.
authors.forename: F
authors.initials: F
authors.lastname: Yan
authors.forename: D B
authors.initials: DB
authors.lastname: Polk
mesh_terms: D000818:Animals; D002460:Cell Line; D002518:Ceramides / Q000494:pharmacology; D003106:Colon / Q000166:cytology / Q000201:enzymology*; D004789:Enzyme Activation; D004847:Epithelial Cells / Q000201:enzymology; D007413:Intestinal Mucosa / Q000201:enzymology*; D048031:JNK Mitogen-Activated Protein Kinases; D048369:MAP Kinase Kinase 1; D048670:MAP Kinase Kinase 4; D020935:MAP Kinase Signaling System / Q000187:drug effects; D051379:Mice; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism*; D048052:Mitogen-Activated Protein Kinase 3; D020929:Mitogen-Activated Protein Kinase Kinases / Q000378:metabolism; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D010766:Phosphorylation; D010768:Phosphoserine / Q000378:metabolism; D010769:Phosphothreonine / Q000378:metabolism; D011494:Protein Kinases / Q000378:metabolism / Q000502:physiology*; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D019908:Proto-Oncogene Proteins c-raf / Q000378:metabolism; D013108:Sphingomyelin Phosphodiesterase / Q000494:pharmacology; D014409:Tumor Necrosis Factor-alpha / Q000037:antagonists & inhibitors / Q000494:pharmacology* / Q000502:physiology
chemical_list: D002518:Ceramides; D014409:Tumor Necrosis Factor-alpha; D010769:Phosphothreonine; D010768:Phosphoserine; D011494:Protein Kinases; C097199:KSR-1 protein kinase; D017346:Protein Serine-Threonine Kinases; D019908:Proto-Oncogene Proteins c-raf; D048031:JNK Mitogen-Activated Protein Kinases; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases; D048369:MAP Kinase Kinase 1; D048670:MAP Kinase Kinase 4; C482127:Map2k1 protein, mouse; D020929:Mitogen-Activated Protein Kinase Kinases; D013108:Sphingomyelin Phosphodiesterase