Opposing effects of PI3K/Akt and Smad-dependent signaling pathways in NAG-1-induced glioblastoma cell apoptosis

PLoS One. 2014 Apr 23;9(4):e96283. doi: 10.1371/journal.pone.0096283. eCollection 2014.

Abstract

Nonsteroidal anti-inflammatory drug (NSAID) activated gene-1 (NAG-1) is a divergent member of the transforming growth factor-beta (TGF-β) superfamily. NAG-1 plays remarkable multifunctional roles in controlling diverse physiological and pathological processes including cancer. Like other TGF-β family members, NAG-1 can play dual roles during cancer development and progression by negatively or positively modulating cancer cell behaviors. In glioblastoma brain tumors, NAG-1 appears to act as a tumor suppressor gene; however, the precise underlying mechanisms have not been well elucidated. In the present study, we discovered that overexpression of NAG-1 induced apoptosis in U87 MG, U118 MG, U251 MG, and T98G cell lines via the intrinsic mitochondrial pathway, but not in A172 and LN-229 cell lines. NAG-1 could induce the phosphorylation of PI3K/Akt and Smad2/3 in all six tested glioblastoma cell lines, except Smad3 phosphorylation in A172 and LN-229 cell lines. In fact, Smad3 expression and its phosphorylation were almost undetectable in A172 and LN-229 cells. The PI3K inhibitors promoted NAG-1-induced glioblastoma cell apoptosis, while siRNAs to Smad2 and Smad3 decreased the apoptosis rate. NAG-1 also stimulated the direct interaction between Akt and Smad3 in glioblastoma cells. Elevating the level of Smad3 restored the sensitivity to NAG-1-induced apoptosis in A172 and LN-229 cells. In conclusion, our results suggest that PI3K/Akt and Smad-dependent signaling pathways display opposing effects in NAG-1-induced glioblastoma cell apoptosis.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Apoptosis*
  • Cell Line, Tumor
  • Gene Expression Regulation, Neoplastic
  • Glioblastoma / metabolism
  • Glioblastoma / pathology*
  • Growth Differentiation Factor 15 / metabolism*
  • Humans
  • Membrane Potentials
  • Phosphatidylinositol 3-Kinases / metabolism
  • Phosphorylation
  • Protein Kinase Inhibitors / pharmacology
  • Proto-Oncogene Proteins c-akt / metabolism
  • Signal Transduction* / drug effects
  • Smad Proteins / metabolism*

Substances

  • GDF15 protein, human
  • Growth Differentiation Factor 15
  • Protein Kinase Inhibitors
  • Smad Proteins
  • Phosphatidylinositol 3-Kinases
  • Proto-Oncogene Proteins c-akt

Grant support

This work was partially supported by the National Natural Science Foundation of China (No. 81171086) (http://isisn.nsfc.gov.cn/egrantweb/) and the Natural Science Foundation of Shaanxi Province (No. 2013JQ4035). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.