p21 is required for OGF-induced growth inhibition. (A) BxPC-3 cells were transfected with p21 siRNAs or negative control siRNAs for 48, 72, 96, or 120 hours. Total proteins were isolated and separated by SDS-PAGE, and probed with antibodies specific to p21. (B-D) Growth curves for BxPC-3 (B), PANC-1 (C) and Capan-2 (D) cells transfected with either p21 siRNA or negative control siRNA, and grown in the presence or absence of 10-6 M OGF for 96 or 120 hours. Cells were harvested at 48, 72, 96 or 120 hours, and counted with a hemacytometer. Data represent means ± SE for 3 independent experiments. OGF had no effect on cell growth of any cell line transfected with p21 siRNA. Cell numbers for OGF-treated cultures transfected with negative control siRNA were significantly reduced from transfected cells receiving sterile water at *p < 0.05, **p < 0.01, or ***p < 0.001.