Bruton’s Tyrosine Kinase Is Essential for Botrocetin/vWf-Induced Signaling and GPIb-Dependent Thrombus Formation In Vivo.

Botrocetin (bt) facilitated binding of von Willebrand factor (vWf) to the platelet membrane glycoprotein (GP) Ib-IX-V complex on platelets in suspension initiates a signaling cascade that causes αIIbβ3 activation and platelet aggregation. Previous work has demonstrated that bt/vWf-mediated agglutination activates αIIbβ3 and elicits ATP secretion in a thromboxane A2 (TxA2)-dependent manner. The signaling that results in TxA2 production is initiated by Lyn, enhanced by Src and propagated through Syk, SLP-76, PI3K, PLCγ2 and PKC. Here, we demonstrate that the signaling elicited by GPIb-mediated agglutination that results in TxA2 production is dependent on Bruton’s tyrosine kinase (Btk). The results demonstrate that Btk is downstream of Lyn, Syk, SLP-76 and PI3K, upstream of ERK1/2, PLCγ2 and PKC, and greatly enhances Akt phosphorylation. The relationship(s), if any between ERK1/2, PLCγ2 and PKC were not elucidated. The requirement for Btk and TxA2 receptor function in GPIb-dependent arterial thrombosis was confirmed in vivo by characterizing blood flow in ferric chloride treated mouse carotid arteries. These results demonstrate that the Btk family kinase, Tec, cannot provide the function(s) missing because of the absence of normal Btk function, and that Btk is essential for both bt/vWf-mediated agglutination-induced TxA2 production and GPIb-dependent stable arterial thrombus formation in vivo. Finally, consistent with the TxA2 receptor requirement for stable arterial thrombus formation in vivo, aspirin (at the appropriate concentration) prevented GPIb-dependent stable thrombus formation in vivo on ferric chloride damaged arterial endothelium.