Critical role of a survivin/TGF-β/mTORC1 axis in IGF-I-mediated growth of prostate epithelial cells

PLoS One. 2013 May 1;8(5):e61896. doi: 10.1371/journal.pone.0061896. Print 2013.

Abstract

Survivin is a unique member of the inhibitor of apoptosis (IAP) proteins that is overexpressed in numerous cancers through poorly defined mechanisms. One such mechanism may be through constitutive activation of the insulin-like growth factor-I (IGF-I) signaling pathway, implicated in the development and progression of prostate cancer. Using the pre-neoplastic NRP-152 rat prostate cell line as a model, we showed that IGF-I induces Survivin expression, and that silencing Survivin by lentiviral-mediated small hairpin RNA (shRNA) represses IGF-I-stimulated cell growth, implicating Survivin as a mediator of this growth response. Moreover, our data support that the induction of Survivin by IGF-I occurs through a transcriptional mechanism that is mediated in part by the PI3K/Akt/mTORC1 pathway. Use of various Survivin promoter-luciferase constructs revealed that the CDE and CHR response elements in the proximal region of the Survivin promoter are involved in this IGF-I response. Transforming growth factor (TGF-β) signaling antagonists similarly activated the Surivin promoter and rendered cells refractory to further promoter activation by IGF-I. IGF-I suppressed levels of phospho-Smads 2 and 3 with kinetics similar to that of Survivin induction. Suppression of TGF-β signaling, either by TGF-β receptor kinase inhibitors or by silencing Smads 2 and 3, induced Survivin expression and promoted cell growth similar to that induced by IGF-I. TGF-β receptor antagonists also rescued cells from down-regulation of Survivin expression and growth suppression by pharmacological inhibitors of PI3K, Akt, MEK and mTOR. Sh-RNA gene silencing studies suggest that mTORC1 induces while mTORC2 represses the expression of Survivin by IGF-I. Taken together, these results suggest that IGF-I signaling through a PI3K/Akt/mTORC1 mechanism elevates expression of Survivin and promotes growth of prostate epithelial cells by suppressing Smad-dependent autocrine TGF-β signaling.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Animals
  • Autocrine Communication
  • Cell Proliferation
  • Epithelial Cells / physiology*
  • HEK293 Cells
  • Humans
  • Insulin-Like Growth Factor I / analogs & derivatives*
  • Insulin-Like Growth Factor I / pharmacology
  • Insulin-Like Growth Factor I / physiology
  • MAP Kinase Signaling System
  • Male
  • Mechanistic Target of Rapamycin Complex 1
  • Microtubule-Associated Proteins / genetics*
  • Microtubule-Associated Proteins / metabolism
  • Multiprotein Complexes / antagonists & inhibitors
  • Multiprotein Complexes / metabolism
  • Phosphatidylinositol 3-Kinases / metabolism
  • Phosphoinositide-3 Kinase Inhibitors
  • Prostate / cytology*
  • Protein Kinase Inhibitors / pharmacology
  • Proto-Oncogene Proteins c-akt / antagonists & inhibitors
  • Proto-Oncogene Proteins c-akt / metabolism
  • Rats
  • Receptors, Transforming Growth Factor beta / metabolism
  • Retinoblastoma Protein / metabolism
  • Smad Proteins / metabolism
  • Survivin
  • TOR Serine-Threonine Kinases / antagonists & inhibitors
  • TOR Serine-Threonine Kinases / metabolism
  • Transcription, Genetic
  • Transcriptional Activation
  • Transforming Growth Factor beta1 / physiology*

Substances

  • Birc5 protein, rat
  • LR(3)IGF-I
  • Microtubule-Associated Proteins
  • Multiprotein Complexes
  • Phosphoinositide-3 Kinase Inhibitors
  • Protein Kinase Inhibitors
  • Receptors, Transforming Growth Factor beta
  • Retinoblastoma Protein
  • Smad Proteins
  • Survivin
  • Tgfb1 protein, rat
  • Transforming Growth Factor beta1
  • Insulin-Like Growth Factor I
  • Mechanistic Target of Rapamycin Complex 1
  • Proto-Oncogene Proteins c-akt
  • TOR Serine-Threonine Kinases