Cross-talk between the PI-3K and MAPK pathways and MAPK regulation of p70S6 kinase.

H929 cells were cultured in serum-free medium for 16 hours followed by treatment for 1 hour with increasing concentrations of the PI-3K inhibitor LY294002 (panel A) or the MAPK (Mek1/2) inhibitor PD98059 (panel B). Cells were then stimulated with IGF-I (100 ng/mL, 5 minutes) and lysates were analyzed as described in Figure 1 by use of the indicated antibodies. The upper band (**) in panel B designates phosphorylated p85S6 kinase as described in Figure 3.