Figure 3
SFK-mediated cytoplasmic localization of STAT5A is dominant over BCR-ABL induced nuclear accumulation. (A) HeLa T-REx BCR-ABL cells were transiently transfected with STAT5A-eYFP and either treated with 5 ng/ml doxycycline for 24 h to induce BCR-ABL expression (lower panel) or left untreated (upper panel). Fixation was performed with methanol. Fixed cells were stained for BCR-ABL using a cABL-specific primary antibody and a secondary antibody conjugated to Alexa Fluor-405. The subcellular distribution of STAT5A-eYFP was analyzed by confocal microscopy. Scale bars: 20 μm. (B) The subcellular distribution of STAT5A-eYFP was investigated in the presence of vSrc-dsRed (upper panel), vSrcK295N-dsRed (middle panel) or vSrcY416F-dsRed (lower panel) in HeLa T-REx BCR-ABL cells that were treated with 5 ng/ml doxycycline for 24 h. Fixation was performed with methanol. Fixed cells were stained for BCR-ABL using an Abl-specific primary antibody and a secondary antibody conjugated to Alexa Fluor-405. Scale bars: 20 μm. (C) HeLa T-REx BCR-ABL cells were co-transfected with vSrc-dsRed, or the respective kinase activity affecting mutants vSrcK295N-dsRed or vSrcY416F-dsRed and STAT5A-eYFP. The cells were either treated with 5 ng/ml doxycycline for 24 h (lanes 1–3) to induce the expression of BCR-ABL or left untreated (lane 4). Protein expression and phosphorylation in the cellular extracts was investigated by immunoblotting with antibodies against pY412-cABL, cABL, pY694/699-STAT5A/B, STAT5A, pY416-Src and Src. α-Tubulin served as a loading control.