Effect of IGF-I on p70S6 kinase and GSK3β.

IGF-I induces phosphorylation of p70S6 kinase and GSK3β. H929 cells were cultured in serum-free growth medium for 16 hours and then stimulated with increasing concentrations of IGF-I (1-200 ng/mL) for 5 minutes (panel A) or with 100 ng/mL IGF-I for times indicated (panels B and C). Cell lysates were resolved on 8% SDS-polyacrylamide gels. Protein was transferred to membranes and blotted with the indicated antibodies. The upper band (**) in panel B designates the phosphorylated form of p85S6 kinase, an isoform of p70S6 kinase.