TY - JOUR
T1 - Phosphorylation and nuclear exclusion of the forkhead transcription factor FKHR after epidermal growth factor treatment in human breast cancer cells
AU - Jackson, James G.
AU - Kreisberg, Jeffrey I.
AU - Koterba, Alan P.
AU - Yee, Douglas
AU - Brattain, Michael G.
N1 - Funding Information:
The authors wish to thank Delfino R Garza for technical help with FKHR immunoblotting. This work was supported by grants CA54807, CA34432 (MG Brattain) and CA74285, CA54174 (D Yee); JI Kreisberg is supported by a merit review and Career Scientist Award from the Department of Veterans Affairs.
PY - 2000/9/21
Y1 - 2000/9/21
N2 - 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.
AB - 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.
KW - Breast cancer
KW - EGF
KW - FKHR
KW - Forkhead
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U2 - 10.1038/sj.onc.1203825
DO - 10.1038/sj.onc.1203825
M3 - Article
C2 - 11030146
AN - SCOPUS:0034699325
SN - 0950-9232
VL - 19
SP - 4574
EP - 4581
JO - Oncogene
JF - Oncogene
IS - 40
ER -