Distinct roles of ligand affinity and cytoskeletal anchorage in alphaIIbbeta3 (GP IIb/IIIa)-mediated cell aggregation and adhesion.

Platelet integrin alphaIIbbeta3 (GP IIb/IIla) is functionally modulated by changes in ligand affinity or in cytoskeletal anchorage. CHO cells transfected with wild-type/mutated alphaIIbbeta3 allow the dissection of the relative contributions of the two regulatory mechanisms in alphaIIbbeta3-mediated adhesion and aggregation. Mutations included a truncation of the cytoplasmic domain of the beta-subunit, resulting in a loss of cytoskeletal anchorage of alphaIIbbeta3, and a VGFFK-deletion of the alpha-subunit, resulting in a permanent high affinity state. alphaIIbbeta3-mediated cell aggregation is dependent on the high affinity state but only partially on the cytoskeletal anchorage of alphaIIbbeta3. In contrast, alphaIIbbeta3-mediated cell adhesion is dependent on the cytoskeletal anchorage but only partially on the high affinity state of alphaIIbbeta3. Thus, the functional evaluation of mutated alphaIIbbeta3 implies a differential role of affinity state and cytoskeletal anchorage for alphaIIbbeta3-mediated cell adhesion and aggregation.