Effects of the EGFR inhibitor gefitinib on phosphorylation of signalling proteins and DNA synthesis. A) MH1C1 cells were treated with gefitinib (1 μM) for 30 min before stimulation with EGF (10 nM) or PGE2 (100 μM) for 5 min. B) Hepatocytes were treated with gefitinib (1 μM) for 30 min before stimulation with EGF (10 nM) or PGE2 (100 μM) for 5 min. C) Gefitinib (1 μM) was added 30 min prior to stimulation with either PGE2 (100 μM) or PGF2α (100 μM) for 5 min. Cells were harvested and subjected to SDS-PAGE followed by immunoblotting with antibodies and detection with enhanced chemiluminescence as described in Materials and Methods. All blots are representative of at least 3 independent experiments. D) Effect of gefitinib on DNA synthesis in MH1C1 cells. Increasing concentrations of gefitinib were added to serum-starved MH1C1 cells. [3 H]thymidine was added, and DNA synthesis was assessed as described under Materials and Methods. The results are presented as percent of control ± S.E.M of four independent experiments.