title: Integrin alpha3beta1-dependent beta-catenin phosphorylation links epithelial Smad signaling to cell contacts.
abstract: Injury-initiated epithelial to mesenchymal transition (EMT) depends on contextual signals from the extracellular matrix, suggesting a role for integrin signaling. Primary epithelial cells deficient in their prominent laminin receptor, alpha3beta1, were found to have a markedly blunted EMT response to TGF-beta1. A mechanism for this defect was explored in alpha3-null cells reconstituted with wild-type (wt) alpha3 or point mutants unable to engage laminin 5 (G163A) or epithelial cadherin (E-cadherin; H245A). After TGF-beta1 stimulation, wt epithelial cells but not cells expressing the H245A mutant internalize complexes of E-cadherin and TGF-beta1 receptors, generate phospho-Smad2 (p-Smad2)-pY654-beta-catenin complexes, and up-regulate mesenchymal target genes. Although Smad2 phosphorylation is normal, p-Smad2-pY654-beta-catenin complexes do not form in the absence of alpha3 or when alpha3beta1 is mainly engaged on laminin 5 or E-cadherin in adherens junctions, leading to attenuated EMT. These findings demonstrate that alpha3beta1 coordinates cross talk between beta-catenin and Smad signaling pathways as a function of extracellular contact cues and thereby regulates responses to TGF-beta1 activation.
authors.affiliation: Pulmonary and Critical Care Division, Department of Medicine, and Cardiovascular Research Institute, University of California, San Francisco, San Francisco, CA 94143, USA.
authors.forename: Young
authors.initials: Y
authors.lastname: Kim
authors.forename: Matthias C
authors.initials: MC
authors.lastname: Kugler
authors.forename: Ying
authors.initials: Y
authors.lastname: Wei
authors.forename: Kevin K
authors.initials: KK
authors.lastname: Kim
authors.forename: Xiaopeng
authors.initials: X
authors.lastname: Li
authors.forename: Alexis N
authors.initials: AN
authors.lastname: Brumwell
authors.forename: Harold A
authors.initials: HA
authors.lastname: Chapman
mesh_terms: D000818:Animals; D002448:Cell Adhesion; D004847:Epithelial Cells / Q000378:metabolism; D004848:Epithelium / Q000378:metabolism; D005455:Fluorescent Antibody Technique; D039201:Integrin alpha3beta1 / Q000378:metabolism*; D051379:Mice; D008822:Mice, Transgenic; D010766:Phosphorylation; D015398:Signal Transduction / Q000502:physiology*; D051785:Smad Proteins / Q000378:metabolism*; D053773:Transforming Growth Factor beta1 / Q000378:metabolism; D051176:beta Catenin / Q000378:metabolism*
chemical_list: D039201:Integrin alpha3beta1; D051785:Smad Proteins; D053773:Transforming Growth Factor beta1; D051176:beta Catenin