A Critical Role for 14-3-3 Protein in Regulating the VWF Binding Function of the Platelet Glycoprotein Ib-IX

Abstract number: P2095

Dai¹ K, Bodnar¹ R, Berndt² M, Du¹ X

¹¹University of Illinois, Chicago, USA ²²Monash University, Clayton, Australia

The platelet receptor for von Willebrand factor (VWF), glycoprotein (GP) Ib–IX mediates platelet adhesion and activation. Here we show that an intracellular signaling molecule, 14-3-3, plays a key role in the phosphorylation- and dephosphorylation-dependent regulation of the VWF binding function of GPIb-IX. Disruption of GPIbb phosphorylation by replacing GPIbb Ser¹⁶⁶ with an alanine or by an inhibitor of cAMP-dependent protein kinase enhanced VWF binding to GPIb-IX. This effect, however, was diminished in cells co-expressing a GPIba mutant with phosphoserine-609 to alanine substitution (S609A), which abolishes high affinity 14-3-3 binding. More importantly, we have developed a novel membrane-permeable inhibitor of 14-3-3-GPIba interaction, MPaC. MPaC potently inhibited VWF binding to platelets and VWF-mediated platelet adhesion under flow. MPaC also inhibited VWF-dependent platelet agglutination induced by ristocetin. These data suggest a novel 14-3-3-dependent regulatory mechanism that dynamically controls the VWF binding function of GPIb-IX, and also suggest a new type of anti-platelet agent that may be potentially useful in preventing or treating thrombosis.