Effect of IGF-I on Forkhead transcription factors.

IGF-I induces time- and dose-dependent phosphorylation of Forkhead transcription factors FKHRL1, FKHR, and AFX. H929 cells were cultured in serum-free medium for 16 hours and stimulated with 100 ng/mL IGF-I for indicated times (panels A and B) or increasing concentrations of IGF-I (1 to 100 ng/mL) for 5 minutes (panel C). Cell lysates were analyzed as described in Figure 1 with the use of the antibodies indicated. Anti-FKHRL1 recognizes 2 bands, of which the upper band represents the phosphorylated form.