Transforming Growth Factor (cid:1) 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 (TGF ) induced phosphorylation and cytoplasmic retention of the Forkhead factor FKHRL1, while reducing FHKRL1-dependent transcriptional activity. TGF -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 (TMFKHRL1), did not translocate to the cytoplasm in response to TGF . In HaCaT keratinocytes, expression of dominant-negative Akt prevented TGF -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 WTor TM-FKHRL1. The apoptotic effect of WT-FKHRL1 but not TM-FKHRL1 was prevented by exogenous TGF . Serum starvation-induced apoptosis was also inhibited by TGF in NMuMG and HaCaT cells. Finally, dominant-negative Akt abrogated the antiapoptotic effect of TGF . Taken together, these data suggest that TGF may play a role in epithelial cell survival via Akt-dependent regulation of FKHRL1.

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