HUMAN PLATELET GLYCOPROTEIN-V - ITS ROLE IN ENHANCING EXPRESSION OF THE GLYCOPROTEIN-IB RECEPTOR

Platelet adhesion to an injured blood vessel wall is a critical initia ting step in hemostasis mediated by a four member receptor complex (gl ycoprotein Ib/V/IX) interacting with plasma von Willebrand factor (vWF ). The function of the GPV subunit within this complex is presently un defined. To study the role of glycoprotein (GP) V within the GPIb rece ptor complex, we transfected the GPV subunit gene into a hematopoietic cell line that constitutively expresses the other three subunits (hum an erythroleukemia [HEL] cells). Using flow cytometry, we found transf ected GPV was surface expressed in HEL cells; this, in turn, led to in creased surface expression of the ligand-binding GPIb alpha and GPIX s ubunits. Radioligand binding assays showed that GPV-transfected HEL ce lls bound more vWF than their non- or mock-transfected counterparts. W e employed confocal microscopy of GPV-transfected HEL cells to show th at GPV colocalizes with GPIb alpha on the cell surface. These findings suggest that the GPV subunit plays a role within the GPIb receptor co mplex by enhancing Ib alpha surface expression. (C) 1995 by The Americ an Society of Hematology.