Time course of tyrosine phosphorylation of the FLT4 receptor after VRP treatment. HEL-JW cells were serum-starved and stimulated with VRP for the indicated times. TCLs were immunoprecipitated with anti-FLT4 antibody, and subjected to serial immunoblotting with antiphosphotyrosine antibody (A) and anti-FLT4 antibody (B). The phosphorylated proteins are indicated by arrows in (A). The increase in tyrosine phosphorylation of FLT4 is indicated (by fold increase) based on the densitometry values. Normal rabbit IgG was used as a negative control for the immunoprecipitations.