Activation of the Pro-survival Phosphatidylinositol 3-Kinase/AKT Pathway by Transforming Growth Factor-β1 in Mesenchymal Cells Is Mediated by p38 MAPK-dependent Induction of an Autocrine Growth Factor

Academic Article

Abstract

  • Transforming growth factor-β1 (TGF-β1) is a multifunctional cytokine involved in differentiation, growth, and survival of mesenchymal cells while inhibiting growth/survival of most other cell types. The mechanism(s) of pro-survival signaling by TGF-β1 in mesenchymal cells is unclear. In this report, we demonstrate that TGF-β1 protects against serum deprivation-induced apoptosis of mesenchymal cells isolated from patients with acute lung injury and of normal human fetal lung fibroblasts (IMR-90). TGF-β receptor(s)-activated signaling in these cells involves rapid activation of the Smad and p38 MAPK pathways within minutes of TGF-β1 treatment followed by a more delayed activation of the pro-survival phosphatidylinositol 3-kinase-protein kinase B (PKB)/Akt pathway. Pharmacological inhibition of p38 MAPK with SB203580 or expression of a p38 kinase-deficient mutant protein inhibits TGF-β1-induced PKB/Akt phosphorylation. Conditioned medium from TGF-β1-treated cells rapidly induces PKB/Akt activation in an SB203580- and suramin-sensitive manner, suggesting p38 MAPK-dependent production of a secreted growth factor that activates this pro-survival pathway by an autocrine/paracrine mechanism. Inhibition of the phosphatidylinositol 3-kinase-PKB/Akt pathway blocks TGF-β1-induced resistance to apoptosis. These results demonstrate the activation of a novel TGF-β1-activated pro-survival/anti-apoptotic signaling pathway in mesenchymal cells/fibroblasts that may explain cell-specific actions of TGF-β1 and provide mechanistic insights into its pro-fibrotic and tumor-promoting effects.
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    Digital Object Identifier (doi)

    Author List

  • Horowitz JC; Lee DY; Waghray M; Keshamouni VG; Thomas PE; Zhang H; Cui Z; Thannickal VJ
  • Start Page

  • 1359
  • End Page

  • 1367
  • Volume

  • 279
  • Issue

  • 2