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Publications (3)18.12 Total impact

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    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.
    Blood 01/2000; 94(12):4186-94. · 9.06 Impact Factor
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    ABSTRACT: The beta3 cytoplasmic domain of the alpha v beta3 integrin is essential for intracellular signals required for cytoskeletal rearrangements. Expression of beta3Ser752Pro mutation in heterologous cells profoundly affects cell spreading and beta3 localization into focal contacts. However, the beta3Ser752Ala substitution mostly restores normal integrin functions, suggesting that the presence of Pro is responsible for the receptor's loss of function. To further assess the role of the Ser752 of the beta3 cytoplasmic domain in the cytoskeletal organization of adherent cells, we developed a computer-assisted method of image analysis allowing the automatic classification of spread cells according to the quantitative analysis of their cell morphology. We compared adhesion and spreading to von Willebrand factor (vWF) or fibrinogen (Fg) of cells expressing beta3 wild type, beta3Ser752Pro or beta3Ser752Ala mutated integrin subunit as a chimeric alpha v beta3 receptor. The beta3Ser752Ala substitution did not impair the general ability of cells to spread, but resulted in a delayed and reduced spreading on both vWF and Fg. Moreover, the beta3Ser752Ala mutation produced modifications of the morphology of spread cells, suggesting a disorganization of their cytoskeleton. Attachment studies showed that the beta3Ser752Ala mutation did not modify the capacity of cells to attach to the substrate, indicating no change in the ligand binding affinity of the alpha v beta3 integrin. Furthermore, we identified a slight defect of beta3Ser752Pro cell attachment to vWF and Fg, beside their impairment of spreading. Taken together, these results suggest a role of Ser752 of the beta3 cytoplasmic domain in the optimal cytoskeletal organization of adherent cells.
    Cell adhesion and communication 02/1998; 6(4):335-48.
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    ABSTRACT: Endothelial cell adhesion to von Willebrand Factor is mainly mediated through an interaction between the alpha vbeta3 integrin and the RGD sequence of von Willebrand factor (vWF). To define the potential involvement of glycoprotein Ib alpha (GPIb alpha) as an endothelial vWF receptor, we compared cell adhesion to three recombinant vWF, the wild-type (WT-rvWF) and two mutants, RGGS-rvWF (D1746G), defective for binding to platelet alphaIIb beta3, and deltaA1-rvWF with a deletion between amino-acids 478 and 716, which does not bind to platelet GPIb alpha. Adhesion of human umbilical vein endothelial cells to purified vWF recombinants was measured by automatized cell counting using an image analyzer. Whereas cell adhesion to delta A1-rvWF was unchanged compared with WT-rvWF, reaching a plateau of 40% total cells at a concentration of 2.5 microg/mL rvWF, adhesion to RGGS-rvWF was only 10% of total cells. Cell stimulation by tumor necrosis factor-alpha (TNF alpha), reported to upregulate the expression of the putative endothelial GPIb alpha, did not modify adhesion to these rvWF. Monoclonal antibodies to vWF or GPIb alpha, blocking vWF interaction with platelet GPIb alpha, were unable to inhibit endothelial cell adhesion to rvWF. In contrast, antibody 9 to vWF, blocking the alpha vbeta3-dependent endothelial cell adhesion to plasma vWF, inhibited adhesion to WT-rvWF as efficiently as to deltaA1-rvWF (50% inhibition at a concentration of 11 and 15 microg/mL, respectively). In agreement with the fact that endothelial cell adhesion to vWF appeared independent of the GPIb alpha-binding domain, we were unable to detect endothelial surface expression of GPIb alpha by flow cytometry or in cell lysates by immunoprecipitation followed by immunoblotting. Moreover, expression of GPIb alpha mRNA was undetectable in endothelial cells, even after stimulation by TNF alpha. These studies indicate that GPIb alpha is not expressed in human cultured endothelial cells and is not involved in adhesion to vWF-containing surfaces. Thus, in static conditions, cultured endothelial cells adhere to vWF through an alpha vbeta3-dependent, GPIb alpha-independent mechanism.
    Blood 10/1997; 90(6):2335-44. · 9.06 Impact Factor