Constitutive diffuse activation of phosphoinositide 3-kinase at the plasma membrane by v-Src suppresses the chemotactic response to PDGF by abrogating the polarity of PDGF receptor signalling

Exp Cell Res. 2007 Apr 1;313(6):1090-105. doi: 10.1016/j.yexcr.2007.01.020. Epub 2007 Feb 6.

Abstract

Cancer cells depend on chemotaxis for invasion and frequently overexpress and/or activate Src. We previously reported that v-Src accelerates motility by promoting phosphoinositide 3-kinase (PI3-K) signalling but abrogates chemotaxis. We here addressed the mechanism of the loss of chemotactic response to platelet-derived growth factor (PDGF) gradients in fibroblasts harbouring a thermosensitive v-Src kinase. At non-permissive temperature, PDGF receptor (PDGFR) signalling, assessed by phosphoY(751)-specific antibodies (a docking site for PI3-K), was not detected without PDGF and showed a concentration-dependent PDGF response. Both immunolabeling of PI3-K (p110) and live cell imaging of its product (phosphatidylinositol 3,4,5 tris-phosphate) showed PI3-K recruitment and activation at lamellipodia polarized towards a PDGF gradient. Centrosomes and PDGFR- and Src-bearing endosomes were also oriented towards this gradient. Upon v-Src thermoactivation, (i) Y(751) phosphorylation was moderately induced without PDGF and synergistically increased with PDGF; (ii) PI3-K was recruited and activated all along the plasma membrane without PDGF and did not polarize in response to a PDGF gradient; and (iii) polarization of centrosomes and of PDGFR-bearing endosomes were also abrogated. Thus, PDGF can further increase PDGFR auto-phosphorylation despite strong Src kinase activity, but diffuse downstream activation of PI3-K by Src abrogates cell polarization and chemotaxis: "signalling requires silence".

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Cell Line
  • Cell Membrane / enzymology*
  • Cell Membrane / metabolism
  • Centrosome / physiology
  • Chemotaxis*
  • Cytoplasm / enzymology
  • Cytoplasm / metabolism
  • Cytoskeleton / physiology
  • Enzyme Activation
  • Fibroblasts / metabolism
  • Focal Adhesions / metabolism
  • Microtubule-Organizing Center / physiology
  • Oncogene Protein pp60(v-src) / physiology*
  • Phosphatidylinositol 3-Kinases / metabolism*
  • Platelet-Derived Growth Factor / pharmacology*
  • Proto-Oncogene Proteins c-akt / genetics
  • Rats
  • Receptors, Platelet-Derived Growth Factor / metabolism*
  • Signal Transduction

Substances

  • Platelet-Derived Growth Factor
  • Phosphatidylinositol 3-Kinases
  • Receptors, Platelet-Derived Growth Factor
  • Oncogene Protein pp60(v-src)
  • Proto-Oncogene Proteins c-akt