Fig. 1.

EGFR activity is dependent on uPAR expression. a The mitogenic effect of EGF depends on uPAR expression on the cell surface. Comparison of the effects of increasing doses of EGF in the presence or in the absence of suPAR on HEK-293 (devoid of uPAR) and HEK-293-uPAR cells (expressing uPAR). Cell numbers expressed as mean ± SD (n = 3) were determined at day 4. The number of cells cultured without EGF and suPAR is considered to be 100% cell proliferation (control). *p < 0.01 compared to control (white bar). b Serum-starved HEK-293 and HEK-293-uPAR cells were stimulated with either 1 ng/ml EGF or 100 pM D2A. When present, cells were pretreated for 15 min with the EGFR tyrosine kinase inhibitor AG1478 before being further stimulated for 10 min with EGF or D2A. Then, cells were lysed, and immunoprecipitated EGFR was blotted for phosphotyrosine (EGFR-P, upper pictures) and total EGFR (EGFR total, middle pictures) as described in the “Materials and methods” section. Each panel is representative of one independent experiment out of at least three. The bar graphs show the standardized densitometric analysis expressed as mean ± SD (n = 3, left panel; n = 4, right panel) of the ratio EGFR-P/EGFR total. Control (C, without AG1478) was given the arbitrary value of 100%. *p < 0.05 and **p < 0.01 compared to control