Figure 4

Rac1 activates p38 in papilloma cells in response to EGFR signaling, but does not activate p38 in normal cells. (A) Cells were transfected with either Rac1 or luciferase siRNAs as in Figure 1, analyzed by Western blot followed by densitometry with intensity normalized to β-actin. Representative Western blots are shown. Results are the mean ± SD of the ratio of phosphorylated to total p38 in three separate experiments with each type of cells, normalized to actin and expressed relative to the ratio in normal cells transfected with luciferase siRNA (*P < 0.05). (B) Papilloma cells cultured in serum-free KGM containing both EGF and insulin were treated with PD153035 to inhibit the EGFR, PD98059 to inhibit MEK and thus prevent Erk activation, and LY294002, a specific inhibitor of PI3K. A representative Western blot from three separate experiments is shown.