Protein kinase C is activated in platelets subjected to pathological shear stress

High levels of fluid shear stress at the blood vessel wall directly stimulate von Willebrand factor (vWF)-mediated platelet adhesion and aggregation and thereby contribute to the pathogenesis of arterial thrombosis. We have found that a pathological level of arterial wall shear stress (90 dynes/cm²) induces platelet aggregation that is associated with the phosphorylation of pleckstrin, a M_r. 47,000 protein kinase C substrate (p47). Shear-induced p47 phosphorylation depends entirely on vWF binding to platelet glycoprotein (Gp) Ib and GpIIb-IIIa, and the specific inhibition of protein kinase C with the staurosporine analogue Ro 31-7549 inhibits the full aggregation response to shear. Shear stress-induced platelet p47 phosphorylation occurs independent of any measurable change in diacylglycerol mass or hydrolysis of phosphatidylinositol 4,5-bisphosphate. These results indicate that mechanical shear stress induces vWF to bind to platelet GpIb and GpIIb-IIIa, stimulating a diacylglycerol-independent pathway of protein kinase C activation that contributes to platelet aggregation in response to shear.