W593A mutation impairs TEL-PDGFβR-dependent phosphorylation and activation of downstream signaling components. (A) Phosphorylation of STAT5 by TEL-PDGFβR in Ba/F3 cells. Ba/F3 cells transduced with empty retroviral vector were included as control. STAT5 proteins were blotted with antibody against STAT5b that also recognizes STAT5a (middle). STAT5 phosphorylated at Tyr-694 was detected with specific anti-phospho-STAT5 antibody as shown in the top panel. The bottom panel shows almost equal protein expression among distinct TEL-PDGFβR variants. (B) Phosphorylation of PI3K by TEL-PDGFβR. PI3K-p85 was immunoprecipitated and probed with 4G10 antiphosphotyrosine antibody. Antibody heavy chains (HCs) in the immunoprecipitates are shown (top). PI3K-p85 expression was assessed by immunoblotting whole-cell lysates with p85 antibody (bottom). (C) Tyrosine phosphorylation of STAT3. The immunoprecipitates of STAT3 were blotted with specific antibody against STAT3 phosphorylated at Tyr-704 (top). Expression of STAT3 and distinct TEL-PDGFβR variants were detected by immunoblotting in each sample (bottom).