Modulation by heparin of the interaction of the A1 domain of Von Willebrand factor with glycoprotein Ib.
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.
Perrault
C
C
INSERM U143, Hopital de Bicetre, Bicetre, France.
Ajzenberg
N
N
Legendre
P
P
Rastegar-Lari
G
G
Meyer
D
D
Lopez
J A
JA
Baruch
D
D
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*
D005343:Fibrinolytic Agents; D019038:Platelet Glycoprotein GPIb-IX Complex; D014841:von Willebrand Factor; D006493:Heparin