ADAP interactions with talin and kindlin promote platelet integrin ?IIb?3 activation and stable fibrinogen binding.

ABSTRACT: ADAP is a hematopoietic-restricted adapter protein that promotes integrin activation and is a carrier for other adapter proteins, Src kinase-associated phosphoprotein 1 (SKAP1) and SKAP2. In T lymphocytes, SKAP1 is the ADAP-associated molecule that activates integrins through direct linkages with Rap1 effectors (regulator of cell adhesion and polarization enriched in lymphoid tissues; Rap1-interacting adapter molecule). ADAP also promotes integrin ?IIb?3 activation in platelets, which lack SKAP1, suggesting an ADAP integrin-regulatory pathway different from those in lymphocytes. Here we characterized a novel association between ADAP and 2 essential integrin-? cytoplasmic tail-binding proteins involved in ?IIb?3 activation, talin and kindlin-3. Glutathione S-transferase pull-downs identified distinct regions in ADAP necessary for association with kindlin or talin. ADAP was physically proximal to talin and kindlin-3 in human platelets, as assessed biochemically, and by immunofluorescence microscopy and proximity ligation. Relative to wild-type mouse platelets, ADAP-deficient platelets exhibited reduced co-localization of talin with ?IIb?3, and reduced irreversible fibrinogen binding in response to a protease activated receptor 4 (PAR4) thrombin receptor agonist. When ADAP was heterologously expressed in Chinese hamster ovary cells co-expressing ?IIb?3, talin, PAR1, and kindlin-3, it associated with an ?IIb?3/talin complex and enabled kindlin-3 to promote agonist-dependent ligand binding to ?IIb?3. Thus, ADAP uniquely promotes activation of and irreversible fibrinogen binding to platelet ?IIb?3 through interactions with talin and kindlin-3.

SUBMITTER: Kasirer-Friede A 

PROVIDER: S-EPMC4023421 | biostudies-literature | 2014 May

REPOSITORIES: biostudies-literature