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PTEN-induction in U251 glioma cells decreases the expression of insulin-like growth factor binding protein-2

Randy J Levitt1, Maria-Magdalena Georgescu, Michael Pollak

  • 1Lady Davis Institute for Medical Research, Jewish General Hospital, Department of Medicine, Division of Experimental Medicine, McGill University, Montreal, Que., Canada.

Biochemical and Biophysical Research Communications
|September 13, 2005
PubMed

Insights

Restoring PTEN tumor suppressor function reduces insulin-like growth factor binding protein-2 (IGFBP-2) in glioma cells. This suggests high IGFBP-2 levels in poor prognosis gliomas may reflect PTEN loss, not IGFBP-2

Area of Science:

  • Molecular Biology
  • Oncology
  • Cancer Genetics

Background:

  • PTEN is a critical tumor suppressor gene frequently lost in human cancers.
  • Insulin-like growth factor binding protein-2 (IGFBP-2) is increasingly linked to poor prognosis in malignancies like gliomas, despite its classical role as a growth inhibitor.
  • The relationship between PTEN status and IGFBP-2 expression in aggressive cancers remains unclear.

Purpose of the Study:

  • To investigate the effect of PTEN restoration on IGFBP-2 expression in PTEN-null glioma cells.
  • To elucidate the molecular mechanisms by which PTEN influences IGFBP-2 levels.
  • To explore the functional significance of the PTEN-IGFBP-2 axis in glioma progression.

Main Methods:

  • Utilized an inducible PTEN expression system in the U251 PTEN-null glioma cell line.
  • Assessed proliferation, apoptosis, and IGFBP-2 expression following PTEN induction.
  • Employed PI3-kinase inhibitor (LY294002) and mTOR inhibitor (CCI-779) to probe signaling pathways.
  • Investigated the functional impact of IGFBP-2 using recombinant protein and siRNA.

Main Results:

  • PTEN induction in U251 cells led to reduced proliferation, increased apoptosis, and significantly decreased IGFBP-2 expression.
  • The PTEN-mediated reduction in IGFBP-2 was mimicked by PI3-kinase inhibition, highlighting PTEN's lipid phosphatase activity.
  • mTOR signaling inhibition did not affect IGFBP-2 levels, suggesting it's not involved in this PTEN-dependent regulation.
  • Exogenous IGFBP-2 did not rescue U251-PTEN cells from PTEN's anti-proliferative effects, and IGFBP-2 knockdown did not alter cell growth.

Conclusions:

  • Loss of PTEN function, common in aggressive gliomas, may contribute to elevated IGFBP-2 levels.
  • The observed correlation between high IGFBP-2 and poor prognosis in gliomas might be, in part, a consequence of PTEN loss.
  • These findings support further translational research into the PTEN-IGFBP-2 relationship for understanding glioma aggressiveness.

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