Fig. 4. Murine uPAR rescues the EGF response in uPAR-KO keratinocytes. (A) uPAR-KO keratinocytes were infected with either a murine or human uPAR (muPAR or huPAR, respectively) retroviral expression vector and the expression analyzed by western blot using an anti-uPAR antibody (kindly provided by Steven Rosenberg) that recognizes both the human and mouse receptor. An empty vector was used as a negative control. (B,C) The growth rate of infected uPAR-KO keratinocytes was monitored in the presence (C) or absence (B) of exogenous EGF (10 ng/ml). (D) Semi-confluent puromycin-selected cells were serum-starved for 18 hours and then stimulated with EGF (10 ng/ml) for 15 minutes. After protein extraction, the levels of huPAR, muPAR, active ERK (pERK1/2) and total ERK (totERK2) were determined by western blot analysis on total cell lysates.