Phosphorylation and nuclear exclusion of the forkhead transcription factor FKHR after epidermal growth factor treatment in human breast cancer cells

Oncogene. 2000 Sep 21;19(40):4574-81. doi: 10.1038/sj.onc.1203825.

Abstract

Akt, when activated by IGF/insulin, can phosphorylate forkhead transcription factors. We undertook this study to determine whether epidermal growth factor (EGF) treatment could produce a signaling cascade resulting in phosphorylation of the forkhead transcription factor FKHR in a breast cancer cell line, MDA-MB-231. After establishing ErbB1, cbl, PI3 kinase and Akt were activated in EGF treated MDA-MB-231, we determined by immunoblot with FKHR antiserum that the electrophoretic mobility of FKHR was retarded after EGF treatment. This mobility retardation was reversible by treatment with alkaline phosphatase, and immunoblot with phospho-Ser256 FKHR antibody further confirmed phosphorylation on an Akt consensus site after EGF treatment. EGF stimulated FKHR phosphorylation was blocked by the PI3 kinase inhibitor LY294002, and the ErbB1 inhibitor AG1478. FKHR immunoblotting after purification of nuclear and cytoplasmic proteins showed that EGF induced a simultaneous increase of FKHR in the cytoplasm and decrease in the nucleus. This finding was confirmed by immunofluorescence staining. Treatment of cells with pharmacological inhibitors of PI3 kinase or ErbB1 blocked this effect. Thus, these results demonstrate the phosphorylation and nuclear exclusion of FKHR after EGF treatment by a PI3 kinase dependent mechanism, and represent the first report of growth factor regulation of endogenous FKHR localization.

Publication types

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

MeSH terms

  • Alkaline Phosphatase / pharmacology
  • Biological Transport / drug effects
  • Breast Neoplasms / genetics
  • Breast Neoplasms / metabolism
  • Breast Neoplasms / pathology*
  • Cell Nucleus / metabolism*
  • Chromones / pharmacology
  • Cytoplasm / metabolism
  • DNA-Binding Proteins / metabolism*
  • Epidermal Growth Factor / pharmacology*
  • ErbB Receptors / drug effects
  • ErbB Receptors / physiology*
  • Female
  • Forkhead Box Protein O1
  • Forkhead Transcription Factors
  • Gene Expression Regulation, Neoplastic / drug effects*
  • Humans
  • Macromolecular Substances
  • Morpholines / pharmacology
  • Neoplasm Proteins / metabolism*
  • Phosphatidylinositol 3-Kinases / physiology*
  • Phosphoinositide-3 Kinase Inhibitors
  • Phosphorylation / drug effects
  • Protein Processing, Post-Translational / drug effects*
  • Protein-Serine-Threonine Kinases*
  • Proto-Oncogene Proteins / metabolism*
  • Proto-Oncogene Proteins / physiology
  • Proto-Oncogene Proteins c-akt
  • Proto-Oncogene Proteins c-cbl
  • Quinazolines
  • Signal Transduction / drug effects*
  • Transcription Factors / metabolism*
  • Tumor Cells, Cultured / drug effects
  • Tumor Cells, Cultured / metabolism
  • Tyrphostins / pharmacology
  • Ubiquitin-Protein Ligases*

Substances

  • Chromones
  • DNA-Binding Proteins
  • FOXO1 protein, human
  • Forkhead Box Protein O1
  • Forkhead Transcription Factors
  • Macromolecular Substances
  • Morpholines
  • Neoplasm Proteins
  • Phosphoinositide-3 Kinase Inhibitors
  • Proto-Oncogene Proteins
  • Quinazolines
  • Transcription Factors
  • Tyrphostins
  • RTKI cpd
  • 2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one
  • Epidermal Growth Factor
  • Proto-Oncogene Proteins c-cbl
  • Ubiquitin-Protein Ligases
  • ErbB Receptors
  • AKT1 protein, human
  • Protein-Serine-Threonine Kinases
  • Proto-Oncogene Proteins c-akt
  • Alkaline Phosphatase
  • CBL protein, human