MAPK1 and squamous cell lung carcinoma: To determine whether an initial, transient increase in P-ERK occurred after nearly complete knockdown of DUSP6, preceding the observed reduction in viable cells, we measured P-ERK in two cell lines with mutations in EGFR (PC9 and H1975 cells), one cell line with a mutation in KRAS (A549 cells) and a lung squamous cell carcinoma with wildtype EGFR and KRAS (HCC95 cells) 24 hr after addition of DUSP6 siRNA.