Phosphorylation of raf-1 by kinase suppressor of ras is inhibited by "MEK-specific" inhibitors PD 098059 and U0126 in differentiating HL60 cells.
Determination of the involvement of MAP kinase cascades in signaling cell growth or differentiation is aided by the use of the inhibitors PD 098059 [2-(2'-amino-3'-methoxyphenyl)oxananphthalen-4-one] and U0126 [1,4-diamino-2,3-dicyano-1,4-bis(2-aminophenylthio)butadiene], believed to be MEK-specific kinase inhibitors. We report here that the activity of kinase suppressor of ras (KSR-1), a kinase upstream of raf-1, is inhibited by both these compounds at concentrations similar to those that inhibit MEK-1. Further, in HL60 cells induced to differentiate with 1,25-dihydroxyvitamin D(3) raf-1 and p90RSK, but not ERK1/2, are coregulated, and their expression as well as monocytic differentiation is inhibited in parallel by PD 098059. Thus, in this system raf-1 is phosphorylated by KSR-1, and PD 098059 as well as U0126 inhibits this phosphorylation. This suggests great caution in the interpretation of experiments that utilize these pharmacological inhibitors of kinase activity as evidence for a role for the MEK--ERK module in ras or raf-1 signaling.
Wang
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Department of Pathology and Laboratory Medicine, UMD-New Jersey Medical School, Newark, New Jersey 07103, USA.
Studzinski
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GP
D002070:Butadienes / Q000494:pharmacology; D002117:Calcitriol / Q000494:pharmacology*; D002454:Cell Differentiation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005419:Flavonoids / Q000494:pharmacology; D018922:HL-60 Cells; D006801:Humans; D048728:MAP Kinase Kinase Kinase 1; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D008954:Models, Biological; D009000:Monocytes / Q000166:cytology*; D009570:Nitriles / Q000494:pharmacology; D010766:Phosphorylation / Q000187:drug effects; D011494:Protein Kinases / Q000187:drug effects / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases / Q000037:antagonists & inhibitors*; D019908:Proto-Oncogene Proteins c-raf / Q000378:metabolism*; D019893:Ribosomal Protein S6 Kinases / Q000378:metabolism; D015398:Signal Transduction
D002070:Butadienes; D004791:Enzyme Inhibitors; D005419:Flavonoids; D009570:Nitriles; C113580:U 0126; D011494:Protein Kinases; C097199:KSR-1 protein kinase; D017346:Protein Serine-Threonine Kinases; D019908:Proto-Oncogene Proteins c-raf; D019893:Ribosomal Protein S6 Kinases; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases; D048728:MAP Kinase Kinase Kinase 1; C482576:MAP3K1 protein, human; D002117:Calcitriol; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one