Dose-dependent effect of rapamycin (for 24 h) on phosphorylation of Smad1/5/8, repression of cyclin Ds (A) and activation of the Id1 promoter (C) was assessed in LNCaP cells. Time-dependent effects 200 nmol/L of rapamycin on the phosphorylation of Smad1/5/8 (B), activation of the Id1 promoter (D), and induction of Id1 mRNA (E) were assessed in LNCaP cells. F, Time-dependent phosphorylation of Smad1/5/8 by 200 nmol/L of rapamycin was determined in PC3 cells. Combined effects of rapamycin (200 nmol/L) and BMP4 (5 ng/ml) on Id1 promoter activity (28 h treatment, left panel) and apoptosis (72 h treatment, right panel) were assessed in LNCaP cells. Apoptotic cells were enumerated under fluorescence and phase contrast microscopy at 200X following staining with Hoechst dye. In the case of the promoter assay, BMP4 was added 4 h prior to harvesting cells. Columns, average of triplicate determinations; bar, ±S.E. Data is representative of three independent experiments.