Cultured human endothelial cells synthesize a plasma membrane protein complex immunologically related to the platelet glycoprotein IIb/IIIa complex

Abstract

We have previously demonstrated that endothelial cells synthesize a plasma membrane protein indistinguishable from platelet glycoprotein (GP) IIa. The present study provides evidence for a further analogy between the platelet and the endothelial cell membrane by showing that cultured endothelial cells also synthesize a membrane protein complex immunologically related to the platelet GP IIb/GP IIIa complex. This evidence is based on the following observations: (1) C17, a murine monoclonal antiplatelet GP IIIa antibody, consistently precipitates two proteins, apparent molecular weights, respectively, 115,000 and 125,000 reduced and 95,000 and 135,000 nonreduced, from metabolically (35S- methionine) as well as surface 125I-labeled cultured human endothelial cells; (2) upon crossed immunoelectrophoresis of solubilized endothelial cells against a polyclonal rabbit antiplatelet antiserum and 125I-labeled C17 IgG, a single precipitate of the protein(s) recognized by C17 is observed. As judged by their mobility in 9% polyacrylamide gels, both endothelial proteins appear to have a somewhat larger molecular weight than their platelet counterparts. Patterns obtained by crossed immunoelectrophoresis are also indicative of a difference in electrophoretic behavior of the platelet GP IIb/IIIa complex and the endothelial cell protein complex.

The platelet glycoprotein IIb/IIIa-like protein in human endothelial cells promotes adhesion but not initial attachment to extracellular matrix.

“…8). The GPIIb/Ma complex was immunoprecipitated from t25I-surface labeled HUVE with the anti-GPIIb/IIIa antibody (data not shown), similar to results described by others (Fitzgerald et al, 1985;Leeksma et al, 1986;Newman et al, 1986). Additionally, with platelet sample the polyclonal antibody cross-reacts with GPIIb (Fig.…”

“…Unlike its counterpart on platelets, the formation of the GPIIb/IIIa complex on endothelial cells does not seem to be Ca2+-dependent (Fitzgerald et al, 1985). The molecular weights of GPIlb/IIIa-like proteins in endothelial cells are also slightly different from platelets (Thiagarajan et al, 1985;Fitzgerald et al, 1985;Leeksma et al, 1986). In that platelet GPIIb/IIIa binds to molecules contained in the extracellular matrix, it is possible that HUVE detachment by anti-GPIlb/IIIa IgG is due to disruption of interactions of GPIlb/IIIa complex with fibronectin, vitronectin, thrombospondin, or some other protein(s) located in the subendothelial matrix .…”

“…weight of 100,000 unreduced and 117,000 reduced. The decrease in mobility with reduction is characteristic of GPIIIa in platelets, BAE, and HUVE (Fitzgerald et al, 1985;Leeksma et al, 1986). The amount of the 65-kD band appears to be independent of detachment condition.…”

The platelet glycoprotein Ia‐IIa‐associated Br‐alloantigen system is expressed by cultured endothelial cells

“…Since it does not recognize other GPIIa-containing complexes, the epitope probably resides on GPIa. Monoclonal antibody CLB-C17, directed against GPIIIa, has been described before (Tetteroo et al, 1983;Leeksma et al, 1986). Monoclonal antibodies Sam-1, GoH3 and K20 are directed against epitopes on different VLA subunits: Sam-1 against an epitope on VLAa5 (unpublished), GoH3 against an epitope on VLAa6 (Sonnenberg et al, 1987;Hemler at al, 1988) and K20 against an epitope on VLAB (Leucocyta Typing IV, 1989).…”

Inhibitory effects of TTP sera on binding of anti‐platelet glycoprotein IIb‐IIIa monoclonal antibodies to human vascular endothelial cells

“…HUVE synthesizes GPIIIb, GPII,, and GPIIbIII,-like substances, and antibodies for human platelet might bind to HUVE [3,4,9,10]. Therefore, we studied the binding of anti-platelet GPII&I, (a major component of platelet membrane) monoclonal antibodies to HUVE after its exposure to TTP sera and found that treatment with TTP sera significantly lowered the binding rate.…”