Figure 1.

Myc activation enhances basal and receptor tyrosine kinase-stimulated Ras/Mapk activity. (a) Wild-type MEFs expressing MycER were treated with 4-OHT to activate Myc or ethanol (EtOH) vehicle control. Mek1/2 phosphorylation and Erk1/2 phosphorylation, as measures of Mapk activity, were assessed by western blot. (b) Murine fibroblasts (NIH3T3 cells) expressing MycER were treated with 4-OHT or EtOH control, washed with PBS, and then treated with complete media containing 10% serum (top panel) or serum-free media containing 100 ng/ml EGF (bottom panel). Erk1/2 phosphorylation was assessed by western blot. (c) MEFs from Ksr1+/+ and Ksr1−/− embryos expressing MycER were treated with 4-OHT to activate MycER, and basal Erk1/2 phosphorylation was assessed by western blot. Relative levels of phosphorylated Erk1/2 and Mek1/2 are indicated