The leukemic cell lines M1 and HEL do not respond to exogenous VEGF.

(A) KDR phosphorylation. PAE, PAE-KDR, M1, HEL, and U937 were incubated in the presence (+) or absence (−) of VEGF₁₆₅ (20 ng/mL) for 30 minutes on ice and then shifted to 37°C for 7 minutes, as described in “Materials and methods.” Cells were lysed and proteins were absorbed on ConA Sepharose and resolved by a 6% SDS-PAGE. Proteins were blotted onto polyvinylidenefluoride (PVDF) membrane, which was subsequently probed with antiphosphotyrosine antibodies. Phosphorylated KDR (Phos KDR) was detected as a band with a molecular weight of approximately 220 kd. (B) Cell proliferation. M1 and HEL cells were incubated in the presence (VEGF) or the absence (control) of VEGF (10 ng/mL) in serum-free medium, as described in “Materials and methods.” Cell numbers were obtained after 24 and 48 hours. Cell numbers represent the average of 3 individual wells.