Effect of IGF-1 and EGF on receptor activation in keratinocytes. C50 cells were serum and growth factor starved for 24 hours, stimulated with either IGF-1 (25 ng/mL) or EGF (10 ng/mL) and harvested at multiple time points (0–120 minutes). A, Western blot analyses evaluating EGFR, erbB2 and IGF-1R activation in cell lysates. B, Quantitation. Data shown represents mean ± SEM of three independent experiments (IRS-1, white bars; EGFR, black bars; erbB2, gray bars). IGF-1 stimulation significantly increased activation of all targets at all time points, while EGF stimulation significantly increased EGFR and erbB2 activation at all time points (p < 0.05; Student’s t-test).