Elevated levels of syndecan-1 expression confer potent serum-dependent growth in human 293T cells

Syndecan-1 is the best studied integral membrane proteoglycan and functions to modulate epithelial cell attachment and physiology. Extracellularly, syndecan-1 binds both growth factors and extracellular matrix components, and intracellularly, its cytoplasmic portion interacts with cytoskeletal components. To investigate the possible role of syndecan-1 in epithelial cell transformation that is characterized by alteration in extracellular matrix interactions and cytoskeleton architecture, we established stable transfectants of syndecan-1 in a highly transformed human renal epithelial line expressing two viral oncogenes, adenovirus E1a and SV40 large T antigen (293T cell line). Expression of syndecan-1 core protein and appropriate posttranslational attachment of glycosaminoglycan chains was confirmed by enzymatic digestion and Western blot analysis. Overexpresser cells grew at a significantly faster rate than the vector-transfected control cells in serum-rich media but showed a proliferative disadvantage in serum-reduced media. In addition to this serum dependency, syndecan-1 overexpression caused a partial reversal of the transformed phenotype with the expressing clones becoming more anchorage dependent and less motile than the vector-transfected counterparts. Surprisingly, the overexpressers were more tumorigenic when injected s.c. into nude mice. These results indicate that syndecan-1 expression plays a role in the control of cell proliferation and suggest that serum-dependent growth may be the more reflective of tumorigenicity in nude mice.