Abstract
The transduction of signals generated by protein kinases and phosphatases are critical for the ability of integrin αIIbβ3 to support stable platelet adhesion and thrombus formation. Unlike kinases, it remains unclear how serine/threonine phosphatases engage the signaling networks that are initiated following integrin ligation. Because protein-protein interactions form the backbone of signal transduction, we searched for proteins that interact with the catalytic subunit of protein phosphatase 2A (PP2Ac). In a yeast two-hybrid study, we identified a novel interaction between PP2Ac and an adaptor protein CIN85 (Cbl-interacting protein of 85 kDa). Truncation and alanine mutagenesis studies revealed that PP2Ac binds to the P3 block ((396)PAIPPKKPRP(405)) of the proline-rich region in CIN85. The interaction of purified PP2Ac with CIN85 suppressed phosphatase activity. Human embryonal kidney 293 αIIbβ3 cells overexpressing a CIN85 P3 mutant, which cannot support PP2Ac binding, displayed decreased adhesion to immobilized fibrinogen. Platelets contain the ∼85 kDa CIN85 protein along with the PP2Ac-CIN85 complex. A myristylated cell-permeable peptide derived from residues 395-407 of CIN85 protein (P3 peptide) disrupted the platelet PP2Ac-CIN85 complex and decreased αIIbβ3 signaling dependent functions such as platelet spreading on fibrinogen and thrombin-mediated fibrin clot retraction. In a phospho-profiling study P3 peptide treated platelets also displayed decreased phosphorylation of several signaling proteins including Src and GSK3β. Taken together, these data support a role for the novel PP2Ac-CIN85 complex in supporting integrin-dependent platelet function by dampening the phosphatase activity.
Highlights
The transduction of signals generated by protein kinases and phosphatases are critical for the ability of integrin ␣IIb3 to support stable platelet adhesion and thrombus formation
A myristylated cell-permeable peptide derived from residues 395– 407 of Cblinteracting protein of 85 kDa (CIN85) protein (P3 peptide) disrupted the platelet PP2Ac-CIN85 complex and decreased ␣IIb3 signaling dependent functions such as platelet spreading on fibrinogen and thrombin-mediated fibrin clot retraction
Because PP2Ac has not been identified in the CIN85 interactome, we evaluated this interaction in epitope-transfected HEK 293 cells
Summary
The transduction of signals generated by protein kinases and phosphatases are critical for the ability of integrin ␣IIb3 to support stable platelet adhesion and thrombus formation. In a phospho-profiling study P3 peptide treated platelets displayed decreased phosphorylation of several signaling proteins including Src and GSK3 Taken together, these data support a role for the novel PP2Ac-CIN85 complex in supporting integrindependent platelet function by dampening the phosphatase activity. The activated integrin can engage fibrinogen and generate outside-in signals that facilitate cytoskeletal reorganization and support a cascade of functional changes, including platelet spreading, stable adhesion, granule secretion, and clot retraction; all processes that augment the size of the platelet thrombi [2, 3]. The paucity of VOLUME 291 NUMBER 33 AUGUST 12, 2016
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