Inhibition of the Binding of von Willebrand Factor to the Platelet Glycoprotein Ib-IX with an Inhibitor of 14-3-3 and Glycoprotein Ib-IX Interaction.

Platelet adhesion and activation are essential for thrombosis and hemostasis. In arteries and capillaries where blood flow shear rate is high, initial platelet adhesion is dependent on the binding of von Willebrand factor (VWF) to its platelet receptor, the glycoprotein (GP) Ib-IX-V complex (GPIb-IX), which consists of four subunits, GPIbα, GPIbβ, GPIX and GPV. We have shown previously that a phosphoserine-dependent intracellular signaling molecule, 14-3-3, interacts with the C-terminal SIRYSGHSL610 sequence in the cytoplasmic domain of GPIbα, and this interaction is dependent upon phosphorylation at Serine 609 of GPIbα. Here we show that a short cell-permeable myristoylated phospho-peptide corresponding to the 14-3-3 binding sequence of GPIbα inhibits VWF binding to platelets and VWF-mediated platelet adhesion. This peptide also specifically inhibits VWF-dependent platelet agglutination induced by ristocetin but has no significant effect on platelet aggregation induced by platelet agonists such as ADP and collagen. Furthermore, intravenous injection of this phospho-peptide caused significantly prolonged bleeding time in mice. Thus, 14-3-3 interaction with GPIbα plays critical roles in VWF binding function of GPIb-IX and hemostatic function of platelets. These results also suggest a new type of anti-platelet drugs that may potentially be useful in treating thrombosis.