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The Talin Head Domain Binds to Integrin β Subunit Cytoplasmic Tails and Regulates Integrin Activation*

Open AccessPublished:October 01, 1999DOI:https://doi.org/10.1074/jbc.274.40.28071
      The β subunit cytoplasmic domains of integrin adhesion receptors are necessary for the connection of these receptors to the actin cytoskeleton. The cytoplasmic protein, talin, binds to β integrin cytoplasmic tails and actin filaments, hence forming an integrin-cytoskeletal linkage. We used recombinant structural mimics of β1A, β1D and β3integrin cytoplasmic tails to characterize integrin-binding sites within talin. Here we report that an integrin-binding site is localized within the N-terminal talin head domain. The binding of the talin head domain to integrin β tails is specific in that it is abrogated by a single point mutation that disrupts integrin localization to talin-rich focal adhesions. Integrin-cytoskeletal interactions regulate integrin affinity for ligands (activation). Overexpression of a fragment of talin containing the head domain led to activation of integrin αIIbβ3; activation was dependent on the presence of both the talin head domain and the integrin β3 cytoplasmic tail. The head domain of talin thus binds to integrins to form a link to the actin cytoskeleton and can thus regulate integrin function.
      The connection of integrin adhesion receptors to the actin cytoskeleton regulates cell shape, adhesion, and migration (
      • Schoenwaelder S.M.
      • Burridge K.
      ). Talin, a cytoplasmic protein composed of ∼270-kDa subunits binds to integrin β cytoplasmic tails, vinculin and actin filaments (
      • Pfaff M.
      • Liu S.
      • Erle D.J.
      • Ginsberg M.H.
      ,
      • Knezevic I.
      • Leisner T.
      • Lam S.
      ,
      • Sampath R.
      • Gallagher P.J.
      • Pavalko F.M.
      ,
      • Hemmings L.
      • Rees D.J.
      • Ohanian V.
      • Bolton S.J.
      • Gilmore A.P.
      • Patel B.
      • Priddle H.
      • Trevithick J.E.
      • Hynes R.O.
      • Critchley D.R.
      ,
      • Muguruma M.
      • Nishimuta S.
      • Tomisaka Y.
      • Ito T.
      • Matsumura S.
      ), and co-localizes with integrins at sites of cell-substratum contact (
      • Burridge K.
      • Chrzanowska-Wodnicka M.
      ). It plays an important role in the establishment and maintenance of integrin-cytoskeleton connections, and loss of talin expression leads to impaired cell adhesion, spreading, and migration (
      • Priddle H.
      • Hemmings L.
      • Monkley S.
      • Woods A.
      • Patel B.
      • Sutton D.
      • Dunn G.A.
      • Zicha D.
      • Critchley D.R.
      ). Talin consists of an N-terminal ∼50-kDa globular head domain and an ∼220-kDa C-terminal rod domain (
      • Rees D.J.
      • Ades S.E.
      • Singer S.J.
      • Hynes R.O.
      ). The N-terminal talin head domain contains an ∼200-residue region similar to a region within the membrane-binding N-terminal ERM association domain (N-ERMAD) in the ezrin, radixin, and moesin (ERM) family of proteins (
      • Rees D.J.
      • Ades S.E.
      • Singer S.J.
      • Hynes R.O.
      ). The N-ERMAD domain of ERM proteins binds to the cytoplasmic domain of transmembrane receptors (e.g. CD44), and the C-terminal domain binds to actin, linking the receptor to the cytoskeleton (
      • Mangeat P.
      • Roy C.
      • Martin M.
      ). In contrast to ERM proteins, previous studies indicate that the C-terminal rod domain of talin contains the integrin-binding site and the vinculin- and actin-binding sites (
      • Hemmings L.
      • Rees D.J.
      • Ohanian V.
      • Bolton S.J.
      • Gilmore A.P.
      • Patel B.
      • Priddle H.
      • Trevithick J.E.
      • Hynes R.O.
      • Critchley D.R.
      ,
      • Muguruma M.
      • Nishimuta S.
      • Tomisaka Y.
      • Ito T.
      • Matsumura S.
      ,
      • Horwitz A.
      • Duggan K.
      • Buck C.A.
      • Beckerle M.C.
      • Burridge K.
      ). Thus, talin might differ from other ERM proteins in the manner in which it connects membrane proteins to actin filaments.
      Talin binds to recombinant structural mimics of dimerized integrin β cytoplasmic tails (
      • Pfaff M.
      • Liu S.
      • Erle D.J.
      • Ginsberg M.H.
      ). Here, we examined the interaction of the talin head domain with three of these integrin β cytoplasmic tails and report that either recombinant or proteolytically derived talin head domains bind specifically to all three β tails. Furthermore, overexpression of the talin fragments containing the head domain “activated” integrin αIIbβ3 as judged by increased ligand-binding affinity. Consequently, the talin head domain binds to several integrin β tails and can thus mediate the linkage of these integrins to the actin cytoskeleton and modulate integrin function.

      Note Added in Proof

      The paper by Patil et al.(Patil, S., Jedsadayanmata, A., Wencel-Drake, J. D., Wang, W., Knezevic, I., and Lam, S. C.-T. (1999) J. Biol. Chem. 274, 28575–28583) describes the interaction of the talin head domain with integrin αIIbβ3.

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