Sema4D stimulation induces Met tyrosine phosphorylation in HUVECs. (A) HUVEC lysates were immunoprecipitated using the indicated antibodies, and Western blot was probed with Met-specific antibodies (top blot) or Plexin B1 antibodies (bottom blot). As shown, Met and Plexin B1 coprecipitated, whereas an unrelated protein, such as N-cadherin, did not show association with Met. (B) HUVECs were stimulated for 15 minutes with HGF or Sema4D, and cellular extracts were immunoprecipitated with α-Met antibodies. Probing of the blot with antiphosphotyrosine antibodies showed that Sema4D treatment triggered Met tyrosine phosphorylation (top blot). The control of the amount of the immunoprecipitated protein is shown in the intermediate panel. Quantification of tyrosine phosphorylation is shown in the bottom blot.