Fig. 4. Effect of Ha-Ras expression on p21 regulation by growth factors. ras8 cells were cultured with or without IPTG (10 mM) for 812 h to induce Ras expression. The cells were transferred to low serum for 4 h, followed by culturing the cells for indicated times with FGF-2 (5 ng/ml; A), PDGF (10 ng/ml; B), or TGF-ß1 (250 pM; C) in the presence or absence of IPTG. Immunoblotting was performed with anti-p21, anti-phospho-ERK1/2, anti-ERK2, and anti-Ras antibodies as indicated. Fold inductions of p21 as compared with non-IPTG-treated cells grown in low serum for 6 h are shown below.