50-KD INTEGRIN-ASSOCIATED PROTEIN DOES NOT DETECTABLY INFLUENCE SEVERAL FUNCTIONS OF GLYCOPROTEIN IIB-IIIA COMPLEX IN HUMAN PLATELETS

A 50-kD integrin-associated protein (IAP) has been reported to be asso ciated with beta(3) integrins and to modulate their function, especial ly vitronectin receptor in human erythroleukemia (HEL) cells and leuko cyte response integrin in neutrophils. We studied the involvement of I AP in the function of platelet beta(3), integrin, glycoprotein (GP) II b-IIIa complex. IAP was a widely distributed protein and was also expr essed in the cells that do not have beta(3), integrin. Platelets from a patient with thrombasthenia, which lack GPIIb and IIIa, expressed IA P as well as normal platelets. Neither platelet aggregation nor intrac ellular Ca2+ elevation after stimulation was influenced by the anti-IA P antibody, B6H12, which was reported to be inhibitory for other beta( 3), integrins. The expression level of GPIIb-IIIa complex was not infl uenced by coexpression of human IAP in the transfected Chinese hamster ovary (CHO) cells. IAP did not facilitate the binding of soluble fibr inogen to the CHO cells expressing GPIIb-IIIa complex. Furthermore, ce ll adhesion onto the immobilized fibrinogen via GPIIb-IIIa complex was not inhibited by B6H12 in HEL cells and was not altered by coexpressi on of human IAP in CHO cells. We concluded that expression of IAP is r egulated independently with that of GPIIb-IIIa complex and that IAP do es not influence the function of GPIIb-IIIa complex. (C) 1995 by The A merican Society of Hematology.