FIGURE 1.

KSR1 is required for DNA damage-induced ERK phosphorylation. KSR1^–/– or KSR1^–/– MEFs expressing ectopic KSR1 were treated with MMC (0.5 μg/ml) for 2 h followed by incubation for the indicated times (A), UV radiation (5 J/m²) (B), or IR (8 Gy) (C) and lysed at the indicated times following treatment. D, for comparison, KSR1^–/– and KSR1^–/– MEFs expressing ectopic KSR1 were serum-starved for 4 h and treated with epidermal growth factor (100 ng/ml) for the indicated times. Total ERK and phospho-ERK were detected by Western blotting. E, KSR1 is not required for p38 or JNK MAPK activation in response to MMC. KSR1^–/– or KSR1^–/– MEFs expressing ectopic KSR1 were treated with MMC (0.5 μg/ml for 2 h), washed with PBS, and incubated for the indicated times. The cells were lysed, and total and phopsho-p38 and JNK were detected by Western blotting.