Efficient Surface Expression of Platelet GPIIb-IIIa Requires Both Subunits

• Published in: Blood 1989-07, Vol.74 (1), p.14-18
• Main Authors: O'Toole, Timothy E., Loftus, Joseph C., Plow, Edward F., Glass, Alison A., Harper, John R., Ginsberg, Mark H.
• Format: Article
• Language: English
• Subjects: Animals; Antigens, Surface - physiology; Biological and medical sciences; Blood Platelets - physiology; Blood Platelets - ultrastructure; Cell Adhesion; Cell Line; Chlorocebus aethiops; Cloning, Molecular; Fundamental and applied biological sciences. Psychology; Gene expression; Humans; In Vitro Techniques; Macromolecular Substances; Molecular and cellular biology; Molecular genetics; Platelet Membrane Glycoproteins - physiology; Platelet Membrane Glycoproteins - ultrastructure; Protein Processing, Post-Translational; Structure-Activity Relationship; Transfection
• ISSN: 0006-4971; 1528-0020
• DOI: 10.1182/blood.V74.1.14.14

Platelet membrane GPIIb-IIIa is a member of the integrin family of heterodimeric adhesion receptors. Processing and export of certain leukocyte and melanoma integrins is disrupted in cells lacking one subunit. We found that surface expression of GPIIb-IIIa, measured by fluorescent activated cell sorting or by surface labeling, required cotransfection of both subunits. In contrast, surface expression was not detected when the subunits were transfected individually. Immunoprecipitation of metaboli- cally labeled transfected cells confirmed the presence of comparable levels of intracellular protein in all cases. When both subunits were transfected, post-translational cleavage of Pro-GPIIb to yield GPIIb heavy chain was also seen, while transfection with GPIIb alone resulted in coprecipitation of Pro-GPIIb with a second band that may be an endogenous β subunit. Pro-GPIIb in these transfectants was not processed to yield GPIIb heavy chain. When transfected into COS cells alone, transiently expressed GPIIIa remained intracellular and did not appear to complex with any endogenous proteins. Thus, surface expression of processed GPIIb-IIIa depends on the presence of both subunits; the coordinate reduction of both subunits observed in some cases of Glanzmann's thrombasthenia may result from mutation affecting only one.