Down-regulation of FoxO-dependent c-FLIP expression mediates TRAIL-induced apoptosis in activated hepatic stellate cells

Cell Signal. 2009 Oct;21(10):1495-503. doi: 10.1016/j.cellsig.2009.05.008. Epub 2009 May 24.

Abstract

Activated hepatic stellate cells which contribute to liver fibrosis have represented an important target for antifibrotic therapy. In this study, we found that TRAIL inhibited PI3K/Akt-dependent FoxO phosphorylation and relocated FoxO proteins into the nucleus from the cytosol in activated human hepatic stellate LX-2 cells. The accumulated FoxO proteins in the nucleus led to down-regulation of c-FLIP(L/S) expression, resulting in the activation of apoptosis-related signaling molecules including the activation of caspase-8, -3, and Bid, as well as mitochondrial cytochrome c release. These results were supported by showing that siRNA-mediated knockdown of FoxO led to restoration of c-FLIP(L/S) expression and resistance to TRAIL-induced apoptosis after treatment of LX-2 cells with TRAIL. Furthermore, c-FLIP(L/S)-transfected LX-2 cells showed the decreased sensitivity to TRAIL-induced apoptosis. Collectively, our data suggest that sequential activation of FoxO proteins under conditions of suppressed PI3K/Akt signaling by TRAIL can down-regulate c-FLIP(L/S), consequently promoting TRAIL-induced apoptosis in LX-2 cells. Therefore, the present study suggests TRAIL may be an effective strategy for antifibrotic therapy in liver fibrosis.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Apoptosis*
  • CASP8 and FADD-Like Apoptosis Regulating Protein / metabolism*
  • Caspase 3 / metabolism
  • Caspase 8 / metabolism
  • Cell Line
  • Down-Regulation
  • Forkhead Box Protein O1
  • Forkhead Transcription Factors / genetics
  • Forkhead Transcription Factors / metabolism*
  • Hepatic Stellate Cells / metabolism*
  • Humans
  • Phosphatidylinositol 3-Kinases / metabolism
  • Proto-Oncogene Proteins c-akt / metabolism
  • RNA, Small Interfering / metabolism
  • Signal Transduction
  • TNF-Related Apoptosis-Inducing Ligand / pharmacology*

Substances

  • CASP8 and FADD-Like Apoptosis Regulating Protein
  • CFLAR protein, human
  • FOXO1 protein, human
  • Forkhead Box Protein O1
  • Forkhead Transcription Factors
  • RNA, Small Interfering
  • TNF-Related Apoptosis-Inducing Ligand
  • Phosphatidylinositol 3-Kinases
  • Proto-Oncogene Proteins c-akt
  • Caspase 3
  • Caspase 8