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.
Peerschke
E I
EI
Department of Pathology, State University of New York, Stony Brook 11794, USA.
Smyth
S S
SS
Teng
E I
EI
Dalzell
M
M
Ghebrehiwet
B
B
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