Transforming growth factor beta enhances epithelial cell survival via Akt-dependent regulation of FKHRL1.
The Forkhead family of transcription factors participates in the induction of death-related genes. In NMuMG and 4T1 mammary epithelial cells, transforming growth factor beta (TGF beta) induced phosphorylation and cytoplasmic retention of the Forkhead factor FKHRL1, while reducing FHKRL1-dependent transcriptional activity. TGF beta-induced FKHRL1 phosphorylation and nuclear exclusion were inhibited by LY294002, an inhibitor of phosphatidylinositol-3 kinase. A triple mutant of FKHRL1, in which all three Akt phosphorylation sites have been mutated (TM-FKHRL1), did not translocate to the cytoplasm in response to TGF beta. In HaCaT keratinocytes, expression of dominant-negative Akt prevented TGF beta-induced 1) reduction of Forkhead-dependent transcription, 2) FKHRL1 phosphorylation, and 3) nuclear exclusion of FKRHL1. Forced expression of either wild-type (WT) or TM-FKHRL1, but not a FKHRL1 mutant with deletion of the transactivation domain, resulted in NMuMG mammary cell apoptosis. Evidence of nuclear fragmentation colocalized to cells with expression of WT- or TM-FKHRL1. The apoptotic effect of WT-FKHRL1 but not TM-FKHRL1 was prevented by exogenous TGF beta. Serum starvation-induced apoptosis was also inhibited by TGF beta in NMuMG and HaCaT cells. Finally, dominant-negative Akt abrogated the antiapoptotic effect of TGF beta. Taken together, these data suggest that TGF beta may play a role in epithelial cell survival via Akt-dependent regulation of FKHRL1.
Shin
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I
Department of Medicine, Vanderbilt University School of Medicine, Nashville, Tennessee 37232, USA.
Bakin
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AV
Rodeck
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U
Brunet
A
A
Arteaga
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CL
D021581:Active Transport, Cell Nucleus; D000818:Animals; D017209:Apoptosis; D002455:Cell Division; D002467:Cell Nucleus / Q000378:metabolism; D002470:Cell Survival; D004268:DNA-Binding Proteins / Q000378:metabolism*; D004847:Epithelial Cells / Q000166:cytology; D000071316:Forkhead Box Protein O3; D051858:Forkhead Transcription Factors; D051379:Mice; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins / Q000235:genetics / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt; D014157:Transcription Factors / Q000378:metabolism*; D014158:Transcription, Genetic; D016212:Transforming Growth Factor beta / Q000378:metabolism*
D004268:DNA-Binding Proteins; D000071316:Forkhead Box Protein O3; D051858:Forkhead Transcription Factors; C474033:FoxO3 protein, mouse; D011518:Proto-Oncogene Proteins; D014157:Transcription Factors; D016212:Transforming Growth Factor beta; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt