title: Requirement of alpha and beta subunit transmembrane helix separation for integrin outside-in signaling.
abstract: Adhesion to extracellular ligands through integrins regulates cell shape, migration, growth, and survival. How integrins transmit signals in the outside-to-in direction remains unknown. Whereas in resting integrins the alpha and beta subunit transmembrane domains are associated, ligand binding promotes dissociation and separation of these domains. Here we address whether such separation is required for outside-in signaling. By introduction of an intersubunit disulfide bond, we generated mutant integrin alphaIIbbeta3 with blocked transmembrane separation that binds ligand, mediates adhesion, adopts an extended conformation after ligand binding, and forms antibody-induced macroclusters on the cell surface similarly to wild type. However, the mutant integrin exhibits a profound defect in adhesion-induced outside-in signaling as measured by cell spreading, actin stress-fiber and focal adhesion formation, and focal adhesion kinase activation. This defect was rescued by reduction of the disulfide bond. Our results demonstrate that the separation of transmembrane domains is required for integrin outside-in signal transduction.
authors.affiliation: The CBR Institute for Biomedical Research and Department of Pathology, Harvard Medical School, Boston, MA 02115, USA.
authors.forename: Jieqing
authors.initials: J
authors.lastname: Zhu
authors.forename: Christopher V
authors.initials: CV
authors.lastname: Carman
authors.forename: Minsoo
authors.initials: M
authors.lastname: Kim
authors.forename: Motomu
authors.initials: M
authors.lastname: Shimaoka
authors.forename: Timothy A
authors.initials: TA
authors.lastname: Springer
authors.forename: Bing-Hao
authors.initials: BH
authors.lastname: Luo
mesh_terms: D000818:Animals; D002448:Cell Adhesion; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism*; D006224:Cricetinae; D004220:Disulfides / Q000378:metabolism; D004789:Enzyme Activation; D051416:Focal Adhesion Protein-Tyrosine Kinases / Q000378:metabolism; D006801:Humans; D008024:Ligands; D009154:Mutation / Q000235:genetics; D019000:Phosphotyrosine / Q000378:metabolism; D019039:Platelet Glycoprotein GPIIb-IIIa Complex / Q000235:genetics / Q000378:metabolism*; D021122:Protein Subunits / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction; D012995:Solubility
chemical_list: D004220:Disulfides; D008024:Ligands; D019039:Platelet Glycoprotein GPIIb-IIIa Complex; D021122:Protein Subunits; D019000:Phosphotyrosine; D051416:Focal Adhesion Protein-Tyrosine Kinases