STAT3 is constitutively phosphorylated on tyrosine 705 and serine 727 in IC2 cells expressing D814Y Kit. (A) Whole cell lysate protein (35 μg per lane) from IC2 cells expressing WT or D814Y Kit was run on SDS-PAGE, transferred to immobilon-P, and immunoblotted with antibodies specific for phosphotyrosine 705 STAT3 or phosphoserine 727 STAT3. (B) Immunoblots were stripped and reprobed with an antibody specific for STAT3. (C) An identical control panel was immunoblotted with normal rabbit IgG. These data are representative of 3 independent experiments.