title: Lateral clustering of platelet GP Ib-IX complexes leads to up-regulation of the adhesive function of integrin alpha IIbbeta 3.
abstract: Binding of von Willebrand factor (VWF) to GP Ib-IX mediates initial platelet adhesion and increases the subsequent adhesive function of alpha(IIb)beta(3). Because these responses are promoted most effectively by large VWF multimers, we hypothesized that receptor clustering modulates GP Ib-IX function. To test this, GP IX was fused at its cytoplasmic tail to tandem repeats of FKBP, and GP Ib-IX(FKBP)(2) and alpha(IIb)beta(3) were expressed in Chinese hamster ovary cells. Under flow conditions at wall shear rates of up to 2000 s(-1), GP Ib-IX(FKBP)(2) mediated cell tethering to immobilized VWF, just as in platelets. Conditional oligomerization of GP Ib-IX(FKBP)(2) by AP20187, a cell-permeable FKBP dimerizer, caused a decrease in cell translocation velocities on VWF (p < 0.001). Moreover, clustering of GP Ib-IX(FKBP)(2) by AP20187 led to an increase in alpha(IIb)beta(3) function, manifested under static conditions by increased cell adhesion to fibrinogen (p < 0.01) and under flow by increased stable cell adhesion to VWF (p < 0.04). Clustering of GP Ib-IX(FKBP)(2) also stimulated rapid tyrosine phosphorylation of ectopically expressed Syk, a putative downstream effector of GP Ib-IX in platelets. These studies establish that GP Ib-IX oligomerization, per se, affects the interaction of this receptor with VWF and its ability to influence the adhesive function of alpha(IIb)beta(3). By extrapolation, GP Ib-IX clustering in platelets may promote thrombus formation.
authors.affiliation: Departments of Cell Biology and Molecular and Experimental Medicine, The Scripps Research Institute, La Jolla, California 92037, USA.
authors.forename: Ana
authors.initials: A
authors.lastname: Kasirer-Friede
authors.forename: Jerry
authors.initials: J
authors.lastname: Ware
authors.forename: Lijun
authors.initials: L
authors.lastname: Leng
authors.forename: Patrizia
authors.initials: P
authors.lastname: Marchese
authors.forename: Zaverio M
authors.initials: ZM
authors.lastname: Ruggeri
authors.forename: Sanford J
authors.initials: SJ
authors.lastname: Shattil
mesh_terms: D000818:Animals; D001792:Blood Platelets / Q000378:metabolism; D016466:CHO Cells; D002448:Cell Adhesion; D002478:Cells, Cultured; D006224:Cricetinae; D019281:Dimerization; D004305:Dose-Response Relationship, Drug; D005340:Fibrinogen / Q000494:pharmacology; D006801:Humans; D010766:Phosphorylation; D010957:Plasmids / Q000378:metabolism; D019039:Platelet Glycoprotein GPIIb-IIIa Complex / Q000378:metabolism*; D019038:Platelet Glycoprotein GPIb-IX Complex; D011485:Protein Binding; D015398:Signal Transduction; D013050:Spectrometry, Fluorescence; D014162:Transfection; D014443:Tyrosine / Q000378:metabolism; D015854:Up-Regulation; D014841:von Willebrand Factor / Q000494:pharmacology
chemical_list: D019039:Platelet Glycoprotein GPIIb-IIIa Complex; D019038:Platelet Glycoprotein GPIb-IX Complex; D014841:von Willebrand Factor; D014443:Tyrosine; D005340:Fibrinogen