Type I Transforming Growth Factor β Receptor Binds to and Activates Phosphatidylinositol 3-Kinase

Abstract

We have examined the interaction of transforming growth factor (TGF)␤ receptors with phosphatidylinositol 3-(PI3) kinase in epithelial cells. In COS7 cells, treatment with TGF␤ increased PI3 kinase activity as measured by the ability of p85-associated immune complexes to phosphorylate inositides in vitro. Both type I and type II TGF␤ receptors (T␤R) associated with p85, but the association of T␤RII appeared to be constitutive. The interaction of T␤RI with p85 was induced by treatment with TGF␤. The receptor association with PI3 kinase was not direct as 35 S-labeled rabbit reticulocyte p85 did not couple with fusion proteins containing type I and type II receptors. A kinase-dead, dominant-negative mutant of T␤RII blocked ligand-induced p85-⌻␤RI association and PI3 kinase activity. In T␤RI-null R1B cells, TGF␤ did not stimulate PI3 kinase activity. This stimulation was restored upon reconstitution of T␤RI by transfection. In R1B and NMuMG epithelial cells, overexpression of a dominant active mutant form of T␤RI markedly enhanced ligand-independent PI3 kinase activity, which was blocked by the addition of the T␤RI kinase inhibitor LY580276, suggesting a causal link between T␤RI function and PI3 kinase. Overexpressed Smad7 also prevented ligand-induced PI3 kinase activity. Taken together, these data suggest that 1) TGF␤ receptors can indirectly associate with p85, 2) both receptors are required for ligand-induced PI3 kinase activation, and 3) the activated T␤RI serine-threonine kinase can potently induce PI3 kinase activity.Transforming growth factor ␤ (TGF␤) 1 binds to a heteromeric complex of transmembrane serine-threonine kinases, the type I and II TGF␤ receptors (T␤RI or Alk5 and T␤RII). Following ligand binding to T␤RII, the type I receptor is recruited to the ligand-receptor complex where the constitutively active T␤RII transactivates T␤RI (1). Activated T␤RI phosphorylates the receptor-specific Smad2 and Smad3, which then associate with Smad4 and, as a heteromeric complex, translocate to the nucleus where they regulate the transcription of TGF␤ target genes (1). The Smad signaling pathway mediates the antiproliferative effect of TGF␤ in epithelial cells (2, 3) and is the best characterized. Several non-Smad pathways have also been implicated in mediating the cellular effects of TGF␤. These include the extracellular signal-regulated kinase (Erk), c-Jun N-terminal kinase (Jnk), p38 mitogen-activated protein kinase (MAPK), phosphatidylinositol-3 (PI3) kinase, and the family of Rho GTPases (4, 5).Activated PI3 kinase increases the formation of intracellular 3Ј-phosphorylated inositol lipids, signal transducers that are essential for the regulation of cell cycle progression, glucose metabolism, cell motility, epithelial-to-mesenchymal transition, and apoptosis among others (6, 7). In Swiss 3T3 cells, TGF␤ stimulates PI3 kinase activity, as measured by the ability of immune complexes precipitated with an antibody against p85, the regulatory subunit of PI3 kinase, to induce the formation of phosphatidylinositol-3 mo...

HAb18G/CD147 promotes epithelial–mesenchymal transition through TGF-β signaling and is transcriptionally regulated by Slug

“…PI3K function is also required for TGF-b-mediated EMT and cell migration (Bakin et al, 2000). The TGF-b type-1 receptor (ALK5) can bind to p85, the regulatory subunit of PI3K, and activate the PI3K pathway (Yi et al, 2005). Our study showed that HAb18G/CD147 expression was driven by the TGF-b/PI3K/Akt pathway, which exerted resistance to apoptosis.…”

Activated type I TGFβ receptor kinase enhances the survival of mammary epithelial cells and accelerates tumor progression

“…Both TbRII and Alk5 have been shown to associate indirectly with p85. Although the association of p85 with TbRII is constitutive, the Alk5-p85 interaction is ligand-dependent (Yi et al, 2005). TGFb-mediated cell motility and protection from apoptosis are blocked by LY294002 and/or expression of dominant-negative Akt (Bakin et al, 2000;Shin et al, 2001;Horowitz et al, 2004;Muraoka-Cook et al, 2004).…”

“…In transformed cells, treatment with TGFb enhances survival via Akt-induced phosphorylation of FKHRL1 (Shin et al, 2001). TGFb has been shown to activate PI3K and its target Akt (Higaki and Shimokado, 1999;Bakin et al, 2000;Yi et al, 2005). Although the signaling programs regulating TGFb-mediated protection from cell death are not completely understood, this protection is blocked by the PI3K inhibitor LY294002 and/or expression of dominantnegative Akt (Shin et al, 2001;Horowitz et al, 2004;Muraoka-Cook et al, 2004).…”

High glucose activates PKC-ζ and NADPH oxidase through autocrine TGF-β1 signaling in mesangial cells

“…For instance, T␤RI activates ERK by directly phosphorylating ShcA (27). PI3 kinase associates indirectly with T␤RI (66), and TGF-␤ 1 -induced Akt phosphorylation occurs independently of Smads in fibroblasts (60). Transactivation of the EGF receptor (EGFR) by TGF-␤ 1 can also stimulate PI3 kinase and Akt (22,36,37,52).…”