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Transforming growth factor beta enhances epithelial cell survival via Akt-dependent regulation of FKHRL1

I Shin1, A V Bakin, U Rodeck

  • 1Department of Medicine, Vanderbilt University School of Medicine, Nashville, Tennessee 37232, USA.

Molecular Biology of the Cell
|November 6, 2001
PubMed

Insights

Transforming growth factor beta (TGF-β) promotes epithelial cell survival by regulating the Forkhead factor FKHRL1 through the Akt pathway. This mechanism involves FKHRL1 phosphorylation and cytoplasmic retention, influencing apoptosis.

Area of Science:

  • Molecular Biology
  • Cell Biology
  • Biochemistry

Background:

  • The Forkhead family of transcription factors is involved in regulating genes related to cell death.
  • Transforming growth factor beta (TGF-β) signaling plays a crucial role in cellular processes, including apoptosis and survival.

Purpose of the Study:

  • To investigate the role of TGF-β in regulating the Forkhead factor FKHRL1.
  • To elucidate the involvement of the Akt signaling pathway in TGF-β-mediated FKHRL1 regulation and its impact on epithelial cell survival.

Main Methods:

  • Utilized mammary epithelial cells (NMuMG, 4T1) and keratinocytes (HaCaT).
  • Employed LY294002 (phosphatidylinositol-3 kinase inhibitor) and dominant-negative Akt expression.
  • Generated and expressed wild-type (WT) and mutant FKHRL1 constructs (triple phosphorylation mutant TM-FKHRL1, transactivation domain deletion mutant).
  • Assessed FKHRL1 phosphorylation, subcellular localization (cytoplasmic retention, nuclear exclusion), and transcriptional activity.
  • Evaluated apoptosis induction and nuclear fragmentation in response to FKHRL1 expression and TGF-β treatment.
  • Investigated the effect of dominant-negative Akt on TGF-β's antiapoptotic function.

Main Results:

  • TGF-β induced FKHRL1 phosphorylation and cytoplasmic retention in NMuMG and 4T1 cells, reducing its transcriptional activity.
  • LY294002 and dominant-negative Akt inhibited TGF-β-induced FKHRL1 phosphorylation and nuclear exclusion.
  • A triple mutant FKHRL1 (TM-FKHRL1) resistant to Akt phosphorylation did not translocate to the cytoplasm upon TGF-β stimulation.
  • Forced expression of WT-FKHRL1 or TM-FKHRL1 induced apoptosis in NMuMG cells, evidenced by nuclear fragmentation.
  • Exogenous TGF-β prevented the apoptotic effect of WT-FKHRL1 but not TM-FKHRL1.
  • TGF-β inhibited serum starvation-induced apoptosis in NMuMG and HaCaT cells.
  • Dominant-negative Akt blocked the antiapoptotic effect of TGF-β.

Conclusions:

  • TGF-β promotes epithelial cell survival through the Akt-dependent regulation of FKHRL1.
  • TGF-β-induced FKHRL1 phosphorylation and cytoplasmic retention are key mechanisms mediating its antiapoptotic effects.
  • The Akt pathway acts as a critical mediator in TGF-β's role in maintaining epithelial cell viability.

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