FOXP1 acts through a negative feedback loop to suppress FOXO-induced apoptosis

Cell Death Differ. 2013 Sep;20(9):1219-29. doi: 10.1038/cdd.2013.81. Epub 2013 Jul 5.

Abstract

Transcriptional activity of Forkhead box transcription factor class O (FOXO) proteins can result in a variety of cellular outcomes depending on cell type and activating stimulus. These transcription factors are negatively regulated by the phosphoinositol 3-kinase (PI3K)-protein kinase B (PKB) signaling pathway, which is thought to have a pivotal role in regulating survival of tumor cells in a variety of cancers. Recently, it has become clear that FOXO proteins can promote resistance to anti-cancer therapeutics, designed to inhibit PI3K-PKB activity, by inducing the expression of proteins that provide feedback at different levels of this pathway. We questioned whether such a feedback mechanism may also exist directly at the level of FOXO-induced transcription. To identify critical modulators of FOXO transcriptional output, we performed gene expression analyses after conditional activation of key components of the PI3K-PKB-FOXO signaling pathway and identified FOXP1 as a direct FOXO transcriptional target. Using chromatin immunoprecipitation followed by next-generation sequencing, we show that FOXP1 binds enhancers that are pre-occupied by FOXO3. By sequencing the transcriptomes of cells in which FOXO is specifically activated in the absence of FOXP1, we demonstrate that FOXP1 can modulate the expression of a specific subset of FOXO target genes, including inhibiting expression of the pro-apoptotic gene BIK. FOXO activation in FOXP1-knockdown cells resulted in increased cell death, demonstrating that FOXP1 prevents FOXO-induced apoptosis. We therefore propose that FOXP1 represents an important modulator of FOXO-induced transcription, promoting cellular survival.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adaptor Proteins, Signal Transducing / biosynthesis
  • Animals
  • Apoptosis / genetics*
  • Apoptosis Regulatory Proteins
  • Base Sequence
  • Cell Line
  • Cell Survival / genetics
  • Drug Resistance, Neoplasm / genetics*
  • Forkhead Box Protein O1
  • Forkhead Transcription Factors / genetics
  • Forkhead Transcription Factors / metabolism*
  • Gene Expression Regulation, Neoplastic
  • HEK293 Cells
  • Humans
  • Mice
  • Mitochondrial Proteins / biosynthesis
  • Neoplasms / drug therapy
  • Neoplasms / metabolism*
  • Phosphatidylinositol 3-Kinases / metabolism
  • Protein Binding
  • Proto-Oncogene Proteins c-akt / metabolism
  • RNA Interference
  • RNA, Small Interfering
  • Repressor Proteins / genetics
  • Repressor Proteins / metabolism*
  • Sequence Analysis, DNA
  • Signal Transduction
  • Transcription, Genetic

Substances

  • Adaptor Proteins, Signal Transducing
  • Apoptosis Regulatory Proteins
  • Bik protein, mouse
  • Forkhead Box Protein O1
  • Forkhead Transcription Factors
  • Foxo1 protein, mouse
  • Foxp1 protein, mouse
  • Mitochondrial Proteins
  • RNA, Small Interfering
  • Repressor Proteins
  • Proto-Oncogene Proteins c-akt