Phosphorylation of raf-1 by kinase suppressor of ras is inhibited by "MEK-specific" inhibitors PD 098059 and U0126 in differentiating HL60 cells

Exp Cell Res. 2001 Aug 15;268(2):294-300. doi: 10.1006/excr.2001.5292.


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.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Butadienes / pharmacology
  • Calcitriol / pharmacology*
  • Cell Differentiation
  • Enzyme Inhibitors / pharmacology
  • Flavonoids / pharmacology
  • HL-60 Cells
  • Humans
  • MAP Kinase Kinase Kinase 1*
  • Mitogen-Activated Protein Kinase 1 / metabolism
  • Mitogen-Activated Protein Kinase 3
  • Mitogen-Activated Protein Kinases / metabolism
  • Models, Biological
  • Monocytes / cytology*
  • Nitriles / pharmacology
  • Phosphorylation / drug effects
  • Protein Kinases / drug effects
  • Protein Kinases / metabolism*
  • Protein-Serine-Threonine Kinases / antagonists & inhibitors*
  • Proto-Oncogene Proteins c-raf / metabolism*
  • Ribosomal Protein S6 Kinases / metabolism
  • Signal Transduction


  • Butadienes
  • Enzyme Inhibitors
  • Flavonoids
  • Nitriles
  • U 0126
  • Protein Kinases
  • KSR-1 protein kinase
  • Protein-Serine-Threonine Kinases
  • Proto-Oncogene Proteins c-raf
  • Ribosomal Protein S6 Kinases
  • Mitogen-Activated Protein Kinase 1
  • Mitogen-Activated Protein Kinase 3
  • Mitogen-Activated Protein Kinases
  • MAP Kinase Kinase Kinase 1
  • MAP3K1 protein, human
  • Calcitriol
  • 2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one