EGF Receptor Mediates Adhesion-Dependent Activation of the Rac GTPase: A Role for Phosphatidylinositol 3-kinase and Vav2

Oncogene. 2003 Sep 4;22(38):6100-6. doi: 10.1038/sj.onc.1206712.

Abstract

Organization of the actin cytoskeleton in eucaryotic cells is controlled by small GTPases of the Rho family. Rac becomes activated by growth factor stimulation and integrin-mediated cell adhesion to extracellular matrix and is known to have a crucial role in lamellipodia formation, cell spreading and migration. At present, the intracellular pathways that connect cell surface receptors to Rac activation are poorly characterized. It has been reported previously that integrin-mediated cell attachment induces activation of the EGF receptor (EGFR) in the absence of EGF. We demonstrate here that this activation is instrumental for integrin-dependent Rac activation. Thus, we found that cells in which EGFR activity had been inhibited failed to spread and form lamellipodia on fibronectin. Failure to spread coincided with inhibition of adhesion-induced GTP loading of Rac and also with inhibition of the phosphatidylinositol 3-kinase (PI 3-kinase)/Akt pathway. Subsequent studies demonstrated that an activated form of PI 3-kinase restored Rac GTP loading in the presence of EGFR inhibition, while a dominant-negative form of PI 3-kinase blocked Rac GTP loading in fibronectin-adherent cells. Our further functional studies identified Vav2, a known exchange factor for Rac, as a crucial downstream component in EGFR- and PI 3-kinase-dependent Rac activation upon integrin-mediated cell adhesion. Our results provide a mechanistic insight into integrin-dependent Rac activation, and identify a novel role for EGFR, PI 3-kinase and Vav2 in this pathway.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Actins / metabolism
  • Actins / ultrastructure
  • Animals
  • COS Cells
  • Cell Adhesion / physiology*
  • Cells, Cultured
  • Cytoskeleton / metabolism
  • Cytoskeleton / ultrastructure
  • Enzyme Activation / physiology
  • Enzyme Inhibitors / pharmacology
  • ErbB Receptors / antagonists & inhibitors
  • ErbB Receptors / genetics
  • ErbB Receptors / metabolism*
  • Focal Adhesion Kinase 1
  • Focal Adhesion Protein-Tyrosine Kinases
  • Guanosine Triphosphate / metabolism
  • Humans
  • JNK Mitogen-Activated Protein Kinases
  • Mitogen-Activated Protein Kinases / drug effects
  • Mitogen-Activated Protein Kinases / metabolism
  • Oncogene Proteins / genetics
  • Oncogene Proteins / metabolism*
  • Phosphatidylinositol 3-Kinases / genetics
  • Phosphatidylinositol 3-Kinases / metabolism*
  • Phosphoinositide-3 Kinase Inhibitors
  • Phosphorylation
  • Protein-Tyrosine Kinases / metabolism
  • Proto-Oncogene Proteins c-vav
  • Quinazolines
  • Tyrosine
  • Tyrphostins / pharmacology
  • rac GTP-Binding Proteins / genetics
  • rac GTP-Binding Proteins / metabolism*

Substances

  • Actins
  • Enzyme Inhibitors
  • Oncogene Proteins
  • Phosphoinositide-3 Kinase Inhibitors
  • Proto-Oncogene Proteins c-vav
  • Quinazolines
  • Tyrphostins
  • VAV2 protein, human
  • RTKI cpd
  • Tyrosine
  • Guanosine Triphosphate
  • ErbB Receptors
  • Protein-Tyrosine Kinases
  • Focal Adhesion Kinase 1
  • Focal Adhesion Protein-Tyrosine Kinases
  • PTK2 protein, human
  • JNK Mitogen-Activated Protein Kinases
  • Mitogen-Activated Protein Kinases
  • rac GTP-Binding Proteins