Effect of IL-6 and IFN-β on p21^ras activation in U266 cells. U266 cells were deprived of serum for 14 hours, labeled with ³²P_i (0.2 mCi/mL) for the last 4 hours of serum deprivation and incubated for 50 minutes with or without IFN-β (500 U/mL) followed by IL-6 (25 ng/mL) for 2 minutes as indicated. Whole cell extracts from 1 × 10⁷ cells were prepared, Ras proteins immunoprecipitated with Y13-259 MoAb, and nucleotides bound analyzed by thin layer chromatography on polyethyleneimine cellulose F plates in 0.75 mol/L KH₂PO₄ . The positions of GDP and GTP are indicated. Results presented are representative of three separate experiments, with the mean values shown below.