Human umbilical vein endothelial cells possess binding sites for the globular domain of C1q.
Binding sites for both the collagen-like and globular domains of C1q have been described on a variety of cell types. HUVEC were previously shown to express the 60- to 67-kDa receptor recognizing the collagen-like domain of C1q. This study demonstrates the presence of a distinct 28- to 33-kDa HUVEC protein (gC1qR) that interacts with the globular head domain of C1q. Polyclonal Abs raised against the Raji cell gC1qR partially inhibited HUVEC interaction with immobilized C1q and recognized a 28- to 33-kDa protein on Western blots. The Ab also reacted strongly with poly-L-lysine-immobilized, glutaraldehyde-fixed, intact HUVEC in ELISA assays. No significant difference in reactivity was noted if HUVEC were permeabilized with 0.2% Triton X-100. However, unfixed HUVEC grown on gelatin-coated microtiter wells to 80% confluence failed to express significant amounts of gC1qR Ag. Quantitation of HUVEC gC1qR by gel scanning suggested the presence of 5.7 +/- 3.8 x 10(6) molecules/cell (mean +/- SD; n = 4). A quantitative sandwich ELISA procedure, however, detected only 3.7 +/- 0.6 x 10(5) gC1qR molecules/cell (mean +/- SD; n = 4), consistent with previously described gC1qR multimerization. The capacity of endothelial cells to recognize both the collagen-like and globular domains of C1q via distinct binding sites may have implications for the role of C1q in vascular inflammatory and thrombotic lesions.
Department of Pathology, State University of New York, Stony Brook 11794, USA.
E I
EI
Peerschke
S S
SS
Smyth
E I
EI
Teng
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Dalzell
B
B
Ghebrehiwet
D001665:Binding Sites; D002352:Carrier Proteins; D002478:Cells, Cultured; D015922:Complement C1q / Q000737:chemistry / Q000378:metabolism*; D004730:Endothelium, Vascular / Q000737:chemistry / Q000378:metabolism*; D006801:Humans; D018960:Hyaluronan Receptors; D008562:Membrane Glycoproteins; D024101:Mitochondrial Proteins; D017434:Protein Structure, Tertiary; D011951:Receptors, Complement / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D014471:Umbilical Veins
C087299:C1QBP protein, human; D002352:Carrier Proteins; D018960:Hyaluronan Receptors; D008562:Membrane Glycoproteins; D024101:Mitochondrial Proteins; D011951:Receptors, Complement; D011993:Recombinant Fusion Proteins; C032402:complement 1q receptor; D015922:Complement C1q