Effect of IL-6 and IFN-β on the tyrosine phosphorylation of Shc isoforms and Shc-associated proteins in U266 cells. Serum-deprived U266 cells were pretreated with IFN-β (500 U/mL) for 50 minutes and then exposed to IL-6 (25 ng/mL) for the times indicated. Whole-cell extracts were prepared from 1 × 10⁷ cells, immunoprecipitated with an anti-Shc MoAb and subjected to immunoblotting with an anti-pTyr MoAb. The p52^shc and p46^shc isoforms, and the p145 and p45 Shc-associated proteins discussed in the text are indicated by arrows. Representative of four separate experiments.