Abstract
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.
Copyright 2001 Academic Press.
Publication types
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Research Support, U.S. Gov't, P.H.S.
MeSH terms
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Butadienes / pharmacology
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Calcitriol / pharmacology*
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Cell Differentiation
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Enzyme Inhibitors / pharmacology
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Flavonoids / pharmacology
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HL-60 Cells
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Humans
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MAP Kinase Kinase Kinase 1*
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Mitogen-Activated Protein Kinase 1 / metabolism
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Mitogen-Activated Protein Kinase 3
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Mitogen-Activated Protein Kinases / metabolism
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Models, Biological
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Monocytes / cytology*
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Nitriles / pharmacology
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Phosphorylation / drug effects
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Protein Kinases / drug effects
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Protein Kinases / metabolism*
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Protein Serine-Threonine Kinases / antagonists & inhibitors*
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Proto-Oncogene Proteins c-raf / metabolism*
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Ribosomal Protein S6 Kinases / metabolism
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Signal Transduction
Substances
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Butadienes
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Enzyme Inhibitors
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Flavonoids
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Nitriles
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U 0126
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Protein Kinases
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KSR-1 protein kinase
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Protein Serine-Threonine Kinases
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Proto-Oncogene Proteins c-raf
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Ribosomal Protein S6 Kinases
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Mitogen-Activated Protein Kinase 1
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Mitogen-Activated Protein Kinase 3
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Mitogen-Activated Protein Kinases
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MAP Kinase Kinase Kinase 1
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MAP3K1 protein, human
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Calcitriol
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2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one