Marc Delcommenne1, Clara Tan1, Virginia Gray1, Laurent Rue1, James R. Woodgett1, Shoukat Dedhar1
1British Columbia Cancer Agency, Jack Bell Research Centre, 2660 Oak Street, Vancouver, British Columbia V6H 3Z6 Canada; Department of Biochemistry and Molecular Biology, University of British Columbia, Vancouver, British Columbia V6T 1Z3 Canada; and Ontario Cancer Institute and Department of Medical Biophysics, University of Toronto, 810 University Avenue, Toronto, Ontario M5G 2M9 Canada
Tóm tắt
Integrin-linked kinase (ILK) is an ankyrin-repeat containing serine–threonine protein kinase capable of interacting with the cytoplasmic domains of integrin β1, β2, and β3 subunits. Overexpression of ILK in epithelial cells disrupts cell–extracellular matrix as well as cell–cell interactions, suppresses suspension-induced apoptosis (also called Anoikis), and stimulates anchorage-independent cell cycle progression. In addition, ILK induces nuclear translocation of β-catenin, where the latter associates with a T cell factor/lymphocyte enhancer-binding factor 1 (TCF/LEF-1) to form an activated transcription factor. We now demonstrate that ILK activity is rapidly, but transiently, stimulated upon attachment of cells to fibronectin, as well as by insulin, in a phosphoinositide-3-OH kinase [Pi(3)K]-dependent manner. Furthermore, phosphatidylinositol(3,4,5)trisphosphate specifically stimulates the activity of ILK
in vitro
, and in addition, membrane targetted constitutively active Pi(3)K activates ILK
in vivo
. We also demonstrate here that ILK is an upstream effector of the Pi(3)K-dependent regulation of both protein kinase B (PKB/AKT) and glycogen synthase kinase 3 (GSK-3). Specifically, ILK can directly phosphorylate GSK-3
in vitro
and when stably, or transiently, overexpressed in cells can inhibit GSK-3 activity, whereas the overexpression of kinase-deficient ILK enhances GSK-3 activity. In addition, kinase-active ILK can phosphorylate PKB/AKT on serine-473, whereas kinase-deficient ILK severely inhibits endogenous phosphorylation of PKB/AKT on serine-473, demonstrating that ILK is involved in agonist stimulated, Pi(3)K-dependent, PKB/AKT activation. ILK is thus a receptor-proximal effector for the Pi(3)K-dependent, extracellular matrix and growth factor mediated, activation of PKB/AKT, and inhibition of GSK-3.
