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The Src family kinases (SFKs) play essential roles in collagenand von Willebrand factor (VWF)-mediated platelet activation. However, the roles of SFKs in G protein-coupled receptor-mediated platelet activation and the molecular mechanisms whereby SFKs are activated by G protein-coupled receptor stimulation are not fully understood. Here we show that the thrombin receptor protease-activated receptor 4 agonist peptide AYPGKF elicited SFK phosphorylation in P2Y12 deficient platelets but stimulated minimal SFK phosphorylation in platelets lackingGq.We have previously shown that thrombin-induced SFK phosphorylation was inhibited by the calcium chelator 5,5'-dimethyl-bis- (o-aminophenoxy)ethane-N,N,Nα',N'-tetraacetic acid (dimethyl- BAPTA). The calcium ionophore A23187 induced SFK phosphorylation in both wild-type and Gq deficient platelets. Together, these results indicate that SFK phosphorylation in response to thrombin receptor stimulation is downstream from Gq/Ca2+ signaling. Moreover, A23187-induced thromboxane A2 synthesis, platelet aggregation, and secretion were inhibited by preincubation of platelets with a selective SFK inhibitor, PP2. AYPGKF-induced thromboxane A2 production in wild-type and P2Y12 deficient platelets was abolished by PP2, and AYPGKF-mediated P-selectin expression, integrin αIIbβ3 activation, and aggregation of P2Y12 deficient platelets were partially inhibited by the PKC inhibitor Ro-31-8220, PP2, dimethyl- BAPTA, or LY294002, but were abolished by Ro-31-8220 plus PP2, dimethyl-BAPTA, or LY294002. These data indicate that Ca2+/SFKs/PI3K andPKCrepresent two alternative signaling pathways mediating Gq-dependent platelet activation. [ABSTRACT FROM AUTHOR]

The Src family kinases (SFKs) have been proposed to play stimulatory and inhibitory roles in platelet activation. The mechanisms for these apparently contradictory roles are unclear. Here we show that SFK, mainly Lyn, is important in stimulating a common signaling pathway leading to secretion of platelet granules. Lyn knock-out or an isoform-nonselective SFK inhibitor, PP2, inhibited platelet secretion of both dense and α granules and the secretion-dependent platelet aggregation induced by thrombin, collagen, and thromboxane A2. The inhibitory effect of Lyn knock-out on platelet aggregation was reversed by supplementing granule content ADP, indicating that the primary role of Lyn is to stimulate granule secretion. Inhibitory effect of PP2 on platelet aggregation induced by thrombin and thromboxane A2 were also reversed by supplementing ADP. Furthermore, PP2 treatment or Lyn knock-out diminished agonist-induced Aktactivation and cyclic GMP production. The inhibitory effect of PP2 or Lyn knock-out on platelet response can be corrected by supplementing cyclic GMP. These data indicate that Lyn stimulates platelet secretion by activating the phosphoinositide 3-kinase-Akt-nitric oxide (NO)-cyclic GMP pathway and also provide an explanation why Lyn can both stimulate and inhibit platelet activation. [ABSTRACT FROM AUTHOR]

Thromboxane A[sub 2] (TX[sub A]2)-mediated platelet secretion and aggregation are important in thrombosis. Here, we present a novel finding that the stable TXA[sub 2] analogue, U46619, induces two waves of platelet secretion, each of which precedes a distinct wave of platelet aggregation. ADP released from platelets during the first wave of secretion played a major role in augmenting the first wave of platelet aggregation. The second wave of platelet secretion and aggregation required the first wave of both ADP secretion and aggregation and were blocked by either the integrin inhibitor RGDS or a P2Y12 receptor antagonist, indicating a requirement for both the integrin outside-in signal and ADP-activated Gi pathway. U46619 stimulated phosphoinositide 3-kinase (PI3K)-dependent phosphorylation of Akt, which was augmented by ADP but did not require integrin outside-in signaling. Platelets from PI3Kγ knock-out mice or PI3K inhibitor-treated platelets showed an impaired second wave of platelet secretion and aggregation. However, the second wave of platelet aggregation was restored by addition of exogenous ADP to PI3Kγ deficient or PI3K inhibitor-treated platelets. Thus, our data indicate that PI3K, together with the integrin outside-in signaling, play a central role in inducing the second wave of platelet secretion, which leads to the second wave of irreversible platelet aggregation. [ABSTRACT FROM AUTHOR]

Cu2O/amorphous TiO2 core-shell nanocomposites with uniform cubic structure were prepared by a hydrolysis method and CuO/TiO2 core-shell nanocomposites were obtained by a post-calcination process. The structure and morphology of the products were characterized by powder X-ray diffraction, transmission electron microscopy, and scanning electron microscopy. The results showed that the cubic Cu2O/TiO2 core-shell nanocomposites were of 110-140nm in side length and the as-hydrolyzed TiO2 shell layer was amorphous. The products transformed to quasi-spheric CuO/TiO2 (anatase) nanocomposites after calcination. The visible-light photocatalytic properties of different products towards methyl orange (MO) were investigated. The results showed that the photocatalytic activity of the cubic Cu2O/amorphous TiO2 core-shell nanocomposites was higher than that of pure Cu2O nanocubes, pure TiO2 nanoparticles, and the spheric CuO/TiO2 core-shell nanocomposites. [ABSTRACT FROM AUTHOR]