Intrinsic signaling functions of the beta4 integrin intracellular domain
Department of Cancer Biology
Cell Line, Tumor; Cell Movement; Cluster Analysis; Humans; Integrin beta4; Intercellular Signaling Peptides and Proteins; Mitogen-Activated Protein Kinase 1; Mitogen-Activated Protein Kinase 3; Protein Structure, Tertiary; Proto-Oncogene Proteins c-akt; Receptor, trkB; Recombinant Fusion Proteins; Signal Transduction; Tyrosine; src-Family Kinases
Cancer Biology | Life Sciences | Medicine and Health Sciences
A key issue regarding the role of alpha6beta4 in cancer biology is the mechanism by which this integrin exerts its profound effects on intracellular signaling, including growth factor-mediated signaling. One approach is to evaluate the intrinsic signaling capacity of the unique beta4 intracellular domain in the absence of contributions from the alpha6 subunit and tetraspanins and to assess the ability of growth factor receptor signaling to cooperate with this domain. Here, we generated a chimeric receptor composed of the TrkB extracellular domain and the beta4 transmembrane and intracellular domains. Expression of this chimeric receptor in beta4-null cancer cells enabled us to assess the signaling potential of the beta4 intracellular domain alone or in response to dimerization using brain-derived neurotrophic factor, the ligand for TrkB. Dimerization of the beta4 intracellular domain results in the binding and activation of the tyrosine phosphatase SHP-2 and the activation of Src, events that also occur upon ligation of intact alpha6beta4. In contrast to alpha6beta4 signaling, however, dimerization of the chimeric receptor does not activate either Akt or Erk1/2. Growth factor stimulation induces tyrosine phosphorylation of the chimeric receptor but does not enhance its binding to SHP-2. The chimeric receptor is unable to amplify growth factor-mediated activation of Akt and Erk1/2, and growth factor-stimulated migration. Collectively, these data indicate that the beta4 intracellular domain has some intrinsic signaling potential, but it cannot mimic the full signaling capacity of alpha6beta4. These data also question the putative role of the beta4 intracellular domain as an "adaptor" for growth factor receptor signaling.
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Citation: J Biol Chem. 2007 Oct 12;282(41):30322-30. Epub 2007 Aug 21. Link to article on publisher's site