Sp17 promotes syndecan-1–mediated cell-cell adhesion.

(A) In the absence of rSp17, syndecan-1–transfected ARH-77 cells (syn-1) aggregate significantly more than wild-type (wt) cells that lack syndecan-1 expression (compare solid bars of syn-1 vs wt;P < .00000001). This illustrates the requirement of syndecan-1 for cell aggregation. Addition of rSp17 to syndecan-1–transfected cells significantly increases the extent of their aggregation (compare solid and hatched bars of syn-1;P < .0000001). In contrast, rSp17 has no effect on aggregation of the syndecan-1–negative wild-type cells (compare solid and hatched bars of wt). Addition of heparin blocks aggregation of the syndecan-1–transfected ARH-77 cells in either the absence or presence of rSP17 (syn-1 plus heparin). Addition of rSp17 also promotes aggregation of syndecan-1–expressing ARP-1 cells (compare solid vs hatched bars; P < .0001). Values represent the mean of a minimum of 3 experiments ± SE. In control experiments, addition of 100 μg/mL rGST had no effect on the extent of aggregation (not shown). (B) Dose-response experiments with rSp17 demonstrate a significant increase in aggregation of ARH-77 cells (syn-1) at 10 μg/mL (P < .005). An increase in aggregation is also noted at 1 μg/mL although at this level the change was not stastistically significant (P < .06).