Human Umbilical Vein Endothelial Cells Synthesize S‐Protein (Vitronectin) In Vitro

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Abstract
S‐protein, also named vitronectin, is a multifunctional glycoprotein with molecular weight (MW) of about 75 kDa and a serum concentration of 0.14‐0.60 mg/ml. It is synthesized mainly in the liver, but synthesis has also been found in monocytes/macrophages. We used human umbilical vein endothelial cells (EC) which were incubated wilh agarose beads, an activator of the alternative complement pathway. By radioimmunoassay (RIA) based on monoclonal and polyclonal S‐protein antibodies, we delected S‐protein on harvested agarose beads. The time dependent increase m the amount of S‐protein was significantly reduced by the presence of cycloheximide (10 μg/ml) in the cell cultures. We also found a strong binding of S‐protein antibodies to agarose beads preincubated in native serum, which was strongly reduced (70‐80%) by inactivation of the alternative complement pathway (50°C, 20 min). Our results show that EC synthesize S‐protein in vitro.