Figure 5. Syndecan-1 mediates binding of VLDL.

(A) Wild-type cells were incubated with the indicated concentrations of ¹²⁵I-VLDL in the absence (filled circles) or presence (open circles) of 10 U heparin for 1 hour at 4°C. The amount of binding observed in the presence of heparin was subtracted from the total to obtain specific binding (dashed line, gray circles). (B) Wild-type (filled circles) and Sdc1^–/– (filled squares) hepatocytes were incubated with the indicated concentrations of ¹²⁵I-VLDL for 1 hour at 4°C. A parallel set of cells was incubated under identical conditions with 250 μg/ml of non-radioactive VLDL. Addition of non-radioactive VLDL decreased binding in wild-type hepatocytes (open circles) to nearly the level measured in Sdc1^–/– cells (open squares). (C) Deletion of syndecan-1 reduced maximal binding. The counts bound in the presence of excess non-radioactive VLDL in B were subtracted from the raw data, and the net counts were converted to μg VLDL protein bound/mg of cell protein, based on radiospecific activity of the particles (140 cpm/ng). Each data point represents the average of triplicate analyses, which varied by less than the height of the symbol.