Thrombopoietin activates STAT5 in UT7/TPO cells. Growth factor-deprived UT-7/TPO cells were stimulated with 100 ng/mL thrombopoietin and nuclear extracts were prepared. Nuclear extracts were subject to EMSA using a β-casein probe. Lane 1, nuclear extracts from unstimulated cells; lane 2, nuclear extracts from thrombopoietin-stimulated cells; lane 3, the same as in lane 2 in the presence of 50-fold excess cold probe; lane 4, the same as in lane 2, except that the nuclear extracts were incubated with STAT5 antisera (2 μg/mL) before EMSA; lane 5, + Crkl antisera (2 μg/mL); lane 6, + STAT3 antisera (2 μg/mL). Shift, probe complex in the absence of the antibodies; Super Shift 1, the supershifted band in the presence of STAT5 antisera; Super Shift 2, the supershifted band in the presence of Crkl antisera.