Identification of the motif in versican G3 domain that plays a dominant-negative effect on astrocytoma cell proliferation through inhibiting versican secretion and binding

This study was designed to investigate the mechanisms by which mutant versican constructs play a dominant-negative effect on astrocytoma cell proliferation. Although a mini-versican or a versican G3 construct promoted growth of U87 astrocytoma cells, a mini-versican lacking epidermal growth factor (EGF) motifs (versican Delta EGF) and a G3 mutant (G3 Delta EGF) exerted a dominant-negative effect on cell proliferation. G3 Delta EGF-transfected cells formed smaller colonies, arrested cell cycle at G(1) phase, inhibited expression of cell cycle proteins cdk4 and cyclin D1, and contained multiple nucleoli, In cell surface binding assays, G3 products expressed in COS-7 cells and bacteria bound to U87 cell surface. G3 Delta EGF products exhibited decreased binding activity, but higher levels of G3 Delta EGF products were able to inhibit the binding of G3 to the cell surface, G3 Delta EGF expression inhibited secretion of endogenous versican in astrocytoma cells and also inhibited the secretion of mini-versican in COS-7 cells co-transfected with the mini-versican and G3 Delta EGF constructs. The effect seems to depend on the expression efficiency of G3 Delta EGF, and it occurred via the carbohydrate recognition domain.