Activation status of FLT3 receptor mutants. The indicated FLT3 constructs and vector alone (mock) were transiently overexpressed in HEK 293 cells. The FLT3 WT expressing cells were either untreated or stimulated with FLT3 ligand (FL). (A) FLT3 was immunoprecipitated from whole cell lysates and immunoblotted with antiphosphotyrosine antibody (upper panel). Subsequently, the blots were stripped and reblotted with anti-FLT3 antibody (lower panel). (B) Activation of STAT5 was demonstrated by immunoblotting the total cell lysates with anti-pSTAT5 antibody (upper panel). After stripping the membrane was reprobed with total anti-STAT5 antibody (lower panel).