Effect on blocking MAPK on cell response to EphB2 activation. (a–c) Collapse assays were performed to determine the effect of ephrinB1-Fc on EphB2+GFP cells in the absence (a) or presence (b) of blocking ERK activation with 20 μM U0126 or after iFGFR activation (c). The cells were incubated at 4°C with Qdot605-labeled anti-EphB2 antibodies to label cell surface EphB2. The cells were incubated with culture medium at 37°C containing 1 μg/ml ephrinB1-Fc, and time-lapse images were collected. Control EphB2 cells undergo collapse after the addition of ephrinB1-Fc but do not collapse when the MAPK pathway is blocked or after activation of iFGFR (right).