Syndecan-1–mediated growth inhibition requires an intact proteoglycan. ARH-77 cells were incubated with intact purified syndecan-1 ectodomain (4 nmol/L), syndecan-1 (4 nmol/L) pretreated with heparitinase (Heparitinase), glycosaminoglycan (GAGs) chains purified from syndecan-1, or heparin (1 and 10 μg/mL) or in media alone (as control) for 72 hours. Cell growth is expressed as a percentage of control.