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The β isoform of the catalytic subunit of protein phosphatase 2B restrains platelet function by suppressing outside‐in α II b β 3 integrin signaling
Author(s) -
Khatlani T.,
Pradhan S.,
Da Q.,
Gushiken F. C.,
Bergeron A. L.,
Langlois K. W.,
Molkentin J. D.,
Rumbaut R. E.,
Vijayan K. V.
Publication year - 2014
Publication title -
journal of thrombosis and haemostasis
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.947
H-Index - 178
eISSN - 1538-7836
pISSN - 1538-7933
DOI - 10.1111/jth.12761
Subject(s) - integrin , gene isoform , protein subunit , microbiology and biotechnology , platelet , chemistry , protein phosphatase 2 , function (biology) , phosphatase , protein phosphatase 1 , biochemistry , phosphorylation , immunology , biology , receptor , gene
Summary Background Calcium‐dependent signaling mechanisms play a critical role in platelet activation. Unlike calcium‐activated protease and kinase, the contribution of calcium‐activated protein serine/threonine phosphatase in platelet activation is poorly understood. Objective To assess the role of catalytic subunit of protein phosphatase 2B ( PP 2B) or calcineurin in platelet function. Results Here, we showed that an increase in PP 2B activity was associated with agonist‐induced activation of human and murine platelets. Pharmacological inhibitors of the catalytic subunit of protein phosphatase 2B ( PP 2B‐A) such as cyclosporine A or tacrolimus ( FK 506) potentiated aggregation of human platelets. Murine platelets lacking the β isoform of PP 2B‐A ( PP 2B‐Aβ −/− ) displayed increased aggregation with low doses of agonist concentrations. Loss of PP 2B‐Aβ did not affect agonist‐induced integrin α II b β 3 inside‐out signaling, but increased basal Src activation and outside‐in α II b β 3 signaling to p38 mitogen‐activated protein kinase ( MAPK ), with a concomitant enhancement in platelet spreading on immobilized fibrinogen and greater fibrin clot retraction. Fibrinogen‐induced increased p38 activation in PP 2B‐Aβ −/− platelets were blocked by Src inhibitor. Both PP 2B‐Aβ −/− platelets and PP 2B‐Aβ‐depleted human embryonal kidney 293 α II b β 3 cells displayed increased adhesion to immobilized fibrinogen. Filamin A, an actin crosslinking phosphoprotein that is known to associate with β 3 , was dephosphorylated on Ser 2152 in fibrinogen‐adhered wild‐type but not in PP 2B‐Aβ −/− platelets. In a FeCl 3 injury thrombosis model, PP 2B‐Aβ −/− mice showed decreased time to occlusion in the carotid artery. Conclusion These observations indicate that PP 2B‐Aβ by suppressing outside‐in α II b β 3 integrin signaling limits platelet response to vascular injury.