title: 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.
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".
authors.affiliation: Université catholique de Louvain, Christian de Duve Institute of Cellular Pathology, CELL Unit, UCL 75.41, avenue Hippocrate, 75, B-1200 Brussels, Belgium.
authors.forename: Anna
authors.initials: A
authors.lastname: Platek
authors.forename: Vassil S
authors.initials: VS
authors.lastname: Vassilev
authors.forename: Philippe
authors.initials: P
authors.lastname: de Diesbach
authors.forename: Donatienne
authors.initials: D
authors.lastname: Tyteca
authors.forename: Marcel
authors.initials: M
authors.lastname: Mettlen
authors.forename: Pierre J
authors.initials: PJ
authors.lastname: Courtoy
mesh_terms: D000818:Animals; D002460:Cell Line; D002462:Cell Membrane / Q000201:enzymology* / Q000378:metabolism; D018385:Centrosome / Q000502:physiology; D002633:Chemotaxis; D003593:Cytoplasm / Q000201:enzymology / Q000378:metabolism; D003599:Cytoskeleton / Q000502:physiology; D004789:Enzyme Activation; D005347:Fibroblasts / Q000378:metabolism; D022001:Focal Adhesions / Q000378:metabolism; D022101:Microtubule-Organizing Center / Q000502:physiology; D015688:Oncogene Protein pp60(v-src) / Q000502:physiology*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D010982:Platelet-Derived Growth Factor / Q000494:pharmacology*; D051057:Proto-Oncogene Proteins c-akt / Q000235:genetics; D051381:Rats; D017479:Receptors, Platelet-Derived Growth Factor / Q000378:metabolism*; D015398:Signal Transduction
chemical_list: D010982:Platelet-Derived Growth Factor; D019869:Phosphatidylinositol 3-Kinases; D017479:Receptors, Platelet-Derived Growth Factor; D015688:Oncogene Protein pp60(v-src); D051057:Proto-Oncogene Proteins c-akt