Tyrosine phosphorylation of STAT3.

Platelets from 1 unaffected (IV-8) and 2 thrombocytopenic family members (IV-10 and V-14) were either unstimulated (−) or stimulated (+) with recombinant human TPO for 10 minutes, 10 ng/mL. Cellular extracts were analyzed by Western blot (7.5% acrylamide gel) and probed with a phospho-STAT3–specific antibody. Below, the blot was stripped and reprobed with a STAT3 antibody to confirm equal protein in each lane. At left, extracts from parental Ba/F3 and Ba/F3-mMpl cells (a cell line engineered to express the murine Mpl receptor) were used as negative and positive control, respectively, for TPO-dependent STAT3 phosphorylation.