%0 Journal Article
%T Kindlins, Integrin Activation and the Regulation of Talin Recruitment to ¦ÁIIb¦Â3
%A Bryan N. Kahner
%A Hisashi Kato
%A Asoka Banno
%A Mark H. Ginsberg
%A Sanford J. Shattil
%A Feng Ye
%J PLOS ONE
%D 2012
%I Public Library of Science (PLoS)
%R 10.1371/journal.pone.0034056
%X Talins and kindlins bind to the integrin ¦Â3 cytoplasmic tail and both are required for effective activation of integrin ¦ÁIIb¦Â3 and resulting high-affinity ligand binding in platelets. However, binding of the talin head domain alone to ¦Â3 is sufficient to activate purified integrin ¦ÁIIb¦Â3 in vitro. Since talin is localized to the cytoplasm of unstimulated platelets, its re-localization to the plasma membrane and to the integrin is required for activation. Here we explored the mechanism whereby kindlins function as integrin co-activators. To test whether kindlins regulate talin recruitment to plasma membranes and to ¦ÁIIb¦Â3, full-length talin and kindlin recruitment to ¦Â3 was studied using a reconstructed CHO cell model system that recapitulates agonist-induced ¦ÁIIb¦Â3 activation. Over-expression of kindlin-2, the endogenous kindlin isoform in CHO cells, promoted PAR1-mediated and talin-dependent ligand binding. In contrast, shRNA knockdown of kindlin-2 inhibited ligand binding. However, depletion of kindlin-2 by shRNA did not affect talin recruitment to the plasma membrane, as assessed by sub-cellular fractionation, and neither over-expression of kindlins nor depletion of kindlin-2 affected talin interaction with ¦ÁIIb¦Â3 in living cells, as monitored by bimolecular fluorescence complementation. Furthermore, talin failed to promote kindlin-2 association with ¦ÁIIb¦Â3 in CHO cells. In addition, purified talin and kindlin-3, the kindlin isoform expressed in platelets, failed to promote each other's binding to the ¦Â3 cytoplasmic tail in vitro. Thus, kindlins do not promote initial talin recruitment to ¦ÁIIb¦Â3, suggesting that they co-activate integrin through a mechanism independent of recruitment.
%U http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0034056