title: The mechanism of kindlin-mediated activation of integrin αIIbβ3.
abstract: Increased ligand binding to cellular integrins ("activation") plays important roles in processes such as development, cell migration, extracellular matrix assembly, tumor metastasis, hemostasis, and thrombosis. Integrin activation encompasses both increased integrin monomer affinity and increased receptor clustering and depends on integrin-talin interactions. Loss of kindlins results in reduced activation of integrins. Kindlins might promote talin binding to integrins through a cooperative mechanism; however, kindlins do not increase talin association with integrins. Here, we report that, unlike talin head domain (THD), kindlin-3 has little effect on the affinity of purified monomeric αIIbβ3, and it does not enhance activation by THD. Furthermore, studies with ligands of varying valency show that kindlins primarily increase cellular αIIbβ3 avidity rather than monomer affinity. In platelets or nucleated cells, loss of kindlins markedly reduces αIIbβ3 binding to multivalent but not monovalent ligands. Finally, silencing of kindlins reduces the clustering of ligand-occupied αIIbβ3 as revealed by total internal reflection fluorescence and electron microscopy. Thus, in contrast to talins, kindlins have little primary effect on integrin αIIbβ3 affinity for monovalent ligands and increase multivalent ligand binding by promoting the clustering of talin-activated integrins.
authors.affiliation: Department of Medicine, University of California, San Diego, La Jolla, CA 92093, USA.
authors.forename: Feng
authors.initials: F
authors.lastname: Ye
authors.affiliation: Department of Medicine, University of California, San Diego, La Jolla, CA 92093, USA.
authors.forename: Brian G
authors.initials: BG
authors.lastname: Petrich
authors.affiliation: Department of Medicine, University of California, San Diego, La Jolla, CA 92093, USA.
authors.forename: Praju
authors.initials: P
authors.lastname: Anekal
authors.affiliation: La Jolla Institute for Allergy & Immunology, La Jolla, CA 92093, USA.
authors.forename: Craig T
authors.initials: CT
authors.lastname: Lefort
authors.affiliation: Department of Medicine, University of California, San Diego, La Jolla, CA 92093, USA.
authors.forename: Ana
authors.initials: A
authors.lastname: Kasirer-Friede
authors.affiliation: Department of Medicine, University of California, San Diego, La Jolla, CA 92093, USA.
authors.forename: Sanford J
authors.initials: SJ
authors.lastname: Shattil
authors.affiliation: Department of Molecular Medicine, Max Planck Institute of Biochemistry, 82152 Martinsried, Germany.
authors.forename: Raphael
authors.initials: R
authors.lastname: Ruppert
authors.affiliation: Department of Molecular Medicine, Max Planck Institute of Biochemistry, 82152 Martinsried, Germany.
authors.forename: Markus
authors.initials: M
authors.lastname: Moser
authors.affiliation: Department of Molecular Medicine, Max Planck Institute of Biochemistry, 82152 Martinsried, Germany.
authors.forename: Reinhard
authors.initials: R
authors.lastname: Fässler
authors.affiliation: Department of Medicine, University of California, San Diego, La Jolla, CA 92093, USA. Electronic address: mhginsberg@ucsd.edu.
authors.forename: Mark H
authors.initials: MH
authors.lastname: Ginsberg
mesh_terms: D000818:Animals; D001792:Blood Platelets / Q000378:metabolism; D003598:Cytoskeletal Proteins / Q000235:genetics / Q000378:metabolism; D057809:HEK293 Cells; D006801:Humans; D008024:Ligands; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D009363:Neoplasm Proteins / Q000235:genetics / Q000378:metabolism*; D019039:Platelet Glycoprotein GPIIb-IIIa Complex / Q000235:genetics / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism
chemical_list: D003598:Cytoskeletal Proteins; C475301:FERMT1 protein, human; C477322:FERMT3 protein, human; D008024:Ligands; D008565:Membrane Proteins; D009363:Neoplasm Proteins; D019039:Platelet Glycoprotein GPIIb-IIIa Complex; D011994:Recombinant Proteins; C527818:kindlin-3 protein, mouse