Mutual cross-talk between fibronectin integrins and the EGF receptor: Molecular basis and biological significance.

Extension of the plasma membrane is one of the first steps in cell migration. Understanding how cells "choose" between various types of membrane protrusion enhances our knowledge of both normal and cancer cell physiology. The EGF receptor is a paradigm for understanding how transmembrane receptor tyrosine kinases regulate intracellular signaling following ligand stimulation. Evidence from the past decade indicates that EGF receptors also form macromolecular complexes with integrin receptors leading to EGF receptor transactivation during cell adhesion. However, relatively little is known about how these complexes form and impact cell migration. Our recent work characterized a molecular complex between EGF receptor and β3 integrin which recognizes RGD motifs in extracellular matrix proteins. Complex formation requires a dileucine motif (679-LL) in the intracellular juxtamembrane region of the EGF receptor that also controls whether or not the receptor undergoes Src kinase-dependent phosphorylation at Tyr-845. In contrast to wild-type receptors, mutant EGF receptors defective for Tyr-845 phosphorylation form complexes with β1 integrin that also binds RGD motifs. In addition, we have discovered that EGF receptor antagonizes small GTPase RhoA by mediating membrane recruitment of its regulatory GAP p190RhoGAP. In this addendum we discuss a potential new role for Src-dependent EGF receptor transactivation in integrin/EGF receptor complex formation. We also discuss how our study fits with previous observations linking p190RhoGAP to RhoA-dependent cytoskeletal rearrangements involved in cell migration, and provide new data that the EGF receptor is compartmentalized to relatively immature zyxin-poor focal adhesions which are the likely site of p190RhoGAP signaling.