A human erythroleukemia cell line synthesizes a functionally active glycoprotein IIb-IIIa complex capable of binding...

The human erythroleukemia (HEL) cell line is known to express a number of platelet-megakaryocyte markers, including glycoproteins IIb and IIIa. Using [35S]methionine as well as monoclonal and polyclonal antibodies to glycoprotein IIb and IIIa, we have demonstrated synthesis of these two glycoproteins by this cell line. When Triton X-100-solubilized membranes were subjected to cross immunoelectrophoresis in 1% agarose, using a mixture of polyclonal antibodies to glycoproteins IIb and IIIa, a single peak was seen in the presence of Ca2+, whereas two distinct peaks were seen in the presence of 5 mM EDTA. When these crossed immunoelectrophoresis were overlaid with 125I-labelled fibrinogen, binding of fibrinogen to the glycoprotein IIb and IIIa complex peak was observed. When either the electrophoresis or the subsequent overlay was done in the presence of 5 mM EDTA, no 125I-fibrinogen binding was observed. These studies demonstrate that HEL cells contain glycoproteins IIb and IIIa capable of forming a Ca2+-dependent complex and capable of binding fibrinogen in a Ca2+-dependent reaction. Nevertheless, glycoprotein IIb- and IIIa-specific fibrinogen binding, of the type observed in platelets, could not be demonstrated in 'resting' or 'stimulated' intact HEL cells. The mechanism giving rise to this difference is currently unknown.