INTERACTION OF PLATELET GLYCOPROTEIN-V WITH GLYCOPROTEIN-IB-IX REGULATES EXPRESSION OF THE GLYCOPROTEINS AND BINDING OF VON-WILLEBRAND-FACTOR TO GLYCOPROTEIN-IB-IX IN TRANSFECTED CELLS

The goal of the present study was to determine whether platelet glycop rotein (GP) V interacts directly with the von Willebrand factor recept or GP Ib-IX and, if so, whether it affects the expression and function of this receptor. A melanoma cell line that does not contain actin-bi nding protein was transfected with the cDNAs coding for GP V and for e ach of the three subunits of GP Ib-IX. GP V co-immunoprecipitated and co-localized with GP Ib-IX. Although GP V could be expressed in the ab sence of GP Ib-IX, the amount incorporated in the membrane was markedl y increased when GP Ib-IX was present. Similarly, there was an enhance d expression of GP Ib-IX on the cell surface in the presence of GP V. The binding affinity of botrocetin-induced von Willebrand factor to GP Ib-IX was unaffected by the presence or absence of GP V. However, the binding capacity was increased by the presence of GP V. We conclude t hat GP V interacts directly with GP Ib-IX, that GP V must associate wi th GP Ib-IX to be efficiently expressed in the membrane, and that GP V increases the binding capacity of the cells for von Willebrand factor by enhancing the surface expression of the GP Ib-IX complex.