Synergistic adhesive interactions and signaling mechanisms operating between platelet gp ib/ix and integrin αiibβ3: studies in human platelets and transfected K562 and CHO cells

S. P. Jackson, T. Domagala, S. C. Hughan, S. L. Cranmer, W. S. Nesbitt, S. Kulkarni, S. M. Dopheide, Y. Yuan, F. Lanza, C. L. Yap

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This study investigates 3 aspects of the adhesive interaction operating between platelet GPIb/lX and integrin o-4βj. These include ( 1 ) examining the sufficiency of GPIb/lX and integrin Otllbβ3 to mediate irreversible cell adhesion on a vWf matrix under flow; (2) the ability of the vWf-GPIb interaction to induce integrin Ollbβ3 activation independent of endogenous platelet stimuli; and (3) the identification of key second messengers linking the vWf-GPIb/IX interaction to integrin <xllbβ3 activation. Using CHO or K562 cells transfected with GPIb/lX and integrin <xnbβ3, we demonstrate that these receptors are both necessary and sufficient to mediate irreversible cell adhesion under flow, wherein GPIb/IX mediates cell tethering and rolling on immobilized vWf and integrin o-4βj mediates cell arrest. Moreover, we demonstrate direct signaling between GPIb/IX and integrin allbβ3. Studies on human platelets pretreated with inhibitors of ADP and TXA2, demonstrate that vWf binding to GPIb/IX is able to induce integrin (x,-4 activation independent of endogenous platelet stimuli under both static and physiological flow conditions (150 s-1, 600 s ' or 1800 s'). Similarly, K562 cells expressing GPIb/IX and integrin O1]bβ3 were able to adhere and spread on vWf and specifically bound the activation specific anti-integrin Ctnbβ3 mAb, PAC-1. Analysis of the key second messengers linking the vWf-GPIb interaction to integrin (XIIbβ3 activation demonstrated a key role for cytoplasmic calcium and PKC in this process. The first step in the activation process involves the mobilization of calcium from internal stores, whereas transmembrane calcium influx is a secondary event, potentiating integrin ot-4βj activation. Taken together, our studies demonstrate the existence of direct signaling pathways operating between GPIb/IX and integrin allbβ3 in platelets and transfected cell lines. Furthermore, they establish a critical role for intracellular calcium mobilization in initiating GPIb/IX-mediated integrin Otllbβ3 activation.

Original languageEnglish
Issue number11 PART I
Publication statusPublished - 1 Dec 2000

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