A critical role for 14-3-3ζ protein in regulating the VWF binding function of platelet glycoprotein Ib-IX and its therapeutic implications

The platelet receptor for von Willebrand factor (VWF), glycoprotein (GP) lb-IX, mediates platelet adhesion and activation. The cytoplasmic domains of the GPIb alpha and beta subunits contain binding sites for the phosphorylation-dependent signaling molecule, 14-3-3 zeta. Here we show that a novel membrane-permeable inhibitor of 14-3-3 zeta GPlb alpha interaction, MP alpha C, potently inhibited VWF binding to platelets and VWF-mediated platelet adhesion under flow conditions. MP alpha C also inhibited VWF-dependent platelet agglutination induced by ristocetin. Furthermore, activation of the VWF binding function of GPIb-IX induced by GPIb beta dephosphorylation is diminished by mutagenic disruption of the 14-3-3 zeta binding site in the C-terminal domain of GPIb alpha, mimicking MP alpha C-induced inhibition, indicating that the inhibitory effect of MPaC is likely to be caused by disruption of 14-3-3 zeta bindIng to GPIb alpha. These data suggest a novel 14-3-3 zeta-depenclent regulatory mechanism that controls the VWF binding function of GPIb-IX, and also suggest a new type of antiplatelet agent that may be potentially useful in preventing or treating thrombosis.