1,25D-induced upregulation of AP-1 and p21 luciferase reporters occurs only in the presence of a classic VDR. Native (Non-T), control vector transfected (V-T), and siRNA VDR transfected (siRNA-T) SaOS-2cells co-transfected with AP-1 (x7) enhancer (A) or p21-promoter luciferase constructs (B) were cultured in the presence of 10 nM 1,25D for 15 min (open bars) or 3 days (filled bars). Relative light units (RLU) from luciferase activity were measured as a function of AP-1 enhancer and p21 promoter activities. *, p<0.001, n=3. RLU values were normalized for transfection efficiency with β-galactosidase activity.