MAPK3 and lung adenocarcinoma: We treated A549 lung adenocarcinoma cells containing mutations in KRAS (homozygous G12S mutation) with either ERK1/2 or MEK inhibitors (SCH772984 and PD0325901, respectively) prior to stimulation with EGF, similar to the protocols that we used for HeLa cells (Supplemental Fig. S8A).