title: Junctional adhesion molecule-A suppresses platelet integrin αIIbβ3 signaling by recruiting Csk to the integrin-c-Src complex.
abstract: 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 Y(529) in its regulatory domain. Absence of JAM-A results in impaired c-SrcY(529) 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.
authors.affiliation: Delaware Cardiovascular Research Center, and.
authors.forename: Meghna U
authors.initials: MU
authors.lastname: Naik
authors.forename: Jeffrey L
authors.initials: JL
authors.lastname: Caplan
authors.forename: Ulhas P
authors.initials: UP
authors.lastname: Naik
mesh_terms: D000293:Adolescent; D000328:Adult; D000818:Animals; D001792:Blood Platelets / Q000378:metabolism*; D000081247:CSK Tyrosine-Protein Kinase; D015815:Cell Adhesion Molecules / Q000502:physiology*; D002478:Cells, Cultured; D015536:Down-Regulation; D006801:Humans; D051379:Mice; D018345:Mice, Knockout; D046912:Multiprotein Complexes / Q000378:metabolism; D010766:Phosphorylation; D019039:Platelet Glycoprotein GPIIb-IIIa Complex / Q000378:metabolism*; D011485:Protein Binding; D016392:Proto-Oncogene Proteins pp60(c-src) / Q000378:metabolism*; D011956:Receptors, Cell Surface / Q000502:physiology*; D015398:Signal Transduction; D055815:Young Adult; D019061:src-Family Kinases / Q000378:metabolism*
chemical_list: D015815:Cell Adhesion Molecules; C407243:F11R protein, human; D046912:Multiprotein Complexes; D019039:Platelet Glycoprotein GPIIb-IIIa Complex; D011956:Receptors, Cell Surface; D000081247:CSK Tyrosine-Protein Kinase; D016392:Proto-Oncogene Proteins pp60(c-src); D019061:src-Family Kinases; C000631346:CSK protein, human