Junctional adhesion molecule-A suppresses platelet integrin αIIbβ3 signaling by recruiting Csk to the integrin-c–Src complex

• Published in: Blood 2014-02, Vol.123 (9), p.1393-1402
• Main Authors: Naik, Meghna U., Caplan, Jeffrey L., Naik, Ulhas P.
• Format: Article
• Language: English
• Subjects: Adolescent; Adult; Animals; Blood Platelets - metabolism; Cell Adhesion Molecules - physiology; Cells, Cultured; CSK Tyrosine-Protein Kinase; Down-Regulation; Humans; Mice; Mice, Knockout; Multiprotein Complexes - metabolism; Phosphorylation; Platelet Glycoprotein GPIIb-IIIa Complex - metabolism; Protein Binding; Proto-Oncogene Proteins pp60(c-src) - metabolism; Receptors, Cell Surface - physiology; Signal Transduction; src-Family Kinases - metabolism; Thrombosis and Hemostasis; Young Adult
• ISSN: 0006-4971; 1528-0020
• DOI: 10.1182/blood-2013-04-496232

Fibrinogen binding to activated integrin induces outside-in signaling that results in stable platelet aggregates and clot retraction. How integrin αIIbβ3 is discouraged from spontaneous activation is not known. We have recently shown that junctional adhesion molecule-A (JAM-A) renders protection from thrombosis by suppressing integrin outside-in signaling. In this study, we show that JAM-A associates with integrin αIIbβ3 in resting platelets and dissociates upon platelet activation by agonists. We also show that integrin-associated JAM-A is tyrosine phosphorylated and is rapidly dephosphorylated upon platelet activation. C-terminal Src kinase (Csk) binds to tyrosine phosphorylated JAM-A through its Src homology 2 domain. Thus, JAM-A recruits Csk to the integrin-c–Src complex in resting platelets. Csk, in turn, keeps integrin-associated c-Src in an inactive state by phosphorylating Y529 in its regulatory domain. Absence of JAM-A results in impaired c-SrcY529 phosphorylation and augmentation of outside-in signaling-dependent c-Src activation. Our results strongly suggest that tyrosine-phosphorylated JAM-A is a Csk-binding protein and functions as an endogenous inhibitor of integrin signaling. JAM-A recruits Csk to the integrin-c–Src complex, where Csk negatively regulates c-Src activation, thereby suppressing the initiation of outside-in signaling. Upon agonist stimulation, JAM-A is dephosphorylated on the tyrosine, allowing the dissociation of Csk from the integrin complex, and thus facilitating outside-in signaling. •Phosphorylated JAM-A associates with resting integrin αIIbβ3.•JAM-A suppresses outside-in signaling by recruiting Csk to the integrin-c–Src complex.