title: Modulation by heparin of the interaction of the A1 domain of Von Willebrand factor with glycoprotein Ib.
abstract: The conformation of the A1 domain of von Willebrand factor (vWF) is a critical determinant of its interaction with the glycoprotein (GP) Ib/V/IX complex. To better define the regulatory mechanisms of vWF A1 domain binding to the GPIb/V/IX complex, we studied vWF-dependent aggregation properties of a cell line overexpressing the GPIbalpha, GPIbbeta, and GPIX subunits (CHO-GPIbalphabeta/IX cells). We found that CHO-GPIbalphabeta/IX cell aggregation required the presence of both soluble vWF and ristocetin. Ristocetin-induced CHO-GPIbalphabeta/IX cell aggregation was completely inhibited by the recombinant VCL fragment of vWF that contains the A1 domain. Surprisingly, the substitution of heparin for ristocetin resulted in the formation of CHO-GPIbalphabeta/IX cell aggregates. Using monoclonal antibodies blocking vWF interaction with GPIb/V/IX or mocarhagin, a venom metalloproteinase that removes the amino-terminal fragment of GPIbalpha extending from aa 1 to 282, we demonstrated that both ristocetin- and heparin-induced aggregations involved an interaction between the A1 domain of vWF and the GPIbalpha subunit of the GPIb/V/IX complex. The involvement of heparin in cell aggregation was also demonstrated after treatment of heparin with heparinase that abolished CHO-GPIbalphabeta/IX cell aggregation. These results indicated that heparin was able to induce vWF-dependent CHO-GPIbalphabeta/IX cell aggregation. In conclusion, we demonstrated that heparin is capable of positively modulating the vWF interaction with the GPIb/V/IX complex.
authors.affiliation: INSERM U143, Hopital de Bicetre, Bicetre, France.
authors.forename: C
authors.initials: C
authors.lastname: Perrault
authors.forename: N
authors.initials: N
authors.lastname: Ajzenberg
authors.forename: P
authors.initials: P
authors.lastname: Legendre
authors.forename: G
authors.initials: G
authors.lastname: Rastegar-Lari
authors.forename: D
authors.initials: D
authors.lastname: Meyer
authors.forename: J A
authors.initials: JA
authors.lastname: Lopez
authors.forename: D
authors.initials: D
authors.lastname: Baruch
mesh_terms: D000818:Animals; D001792:Blood Platelets / Q000502:physiology*; D016466:CHO Cells; D006224:Cricetinae; D005343:Fibrinolytic Agents / Q000494:pharmacology; D006493:Heparin / Q000494:pharmacology; D006801:Humans; D015539:Platelet Activation; D019038:Platelet Glycoprotein GPIb-IX Complex / Q000378:metabolism*; D011485:Protein Binding; D014841:von Willebrand Factor / Q000378:metabolism*
chemical_list: D005343:Fibrinolytic Agents; D019038:Platelet Glycoprotein GPIb-IX Complex; D014841:von Willebrand Factor; D006493:Heparin