SAR1 enhances HbF expression through the activation of JNK/Jun signaling. (A) Western blot analysis of SAR1- or vector control–stably transfected K562 cells for expression of phospho- and total c-Jun and phospho- and total JNK. (B) Western blot analysis of SAR1- or vector control–stably transfected K562 cells for expression of phospho- and total c-Jun and phospho- and total JNK after incubation in the absence or presence of the JNK phosphorylation inhibitor SP600125 (12.5 μM) for 5 days. β-actin was used as a loading control. (C) SAR1- or vector control–stably transfected K562 cells incubated in the absence or presence of SP600125 (12.5 μM) for 5 days were stained with PE-conjugated anti-HbF antibody and subjected to flow cytometry for measurement of HbF-positive cells. Left panels, representative flow cytometry results. Right panel, Graphical representation of flow cytometry data for HbF protein expression in SAR1- or vector control–stably transfected K562 cells with or without SP600125 treatment. *P < .001 vs vector control–transfected cells without SP600125 treatment, **P < .001 vs SAR1-transfected cells without SP600125 treatment. Error bars represent SD of the mean of >3 independent experiments. (D) Western blot analysis of SAR1- or vector control–transfected CD34⁺ cells for expression of phospho- and total c-Jun (left panel) and γ-globin chain (right panel) after incubation in the presence or absence of SP600125 (20 µM) for 3 days. β-actin was used as a loading control. CD34⁺ cells were transfected at day 5 of differentiation.