Effect of TNF-α on GATA1 expression is partially mediated through p38 MAPK activation. (A) p38 MAPK phosphorylation is increased in RPS19-deficient CD71⁺ fetal liver cells before and after a 10-minute stimulation with 100 ng/mL TNF-α, as measured by phospho-flow cytometry 5 days after transduction. (B) Treatment of CD34⁺ cord blood cells with SB203580 for 24 hours increased GATA1 protein expression in the cells. (C) Quantification of GATA1 protein increase from western blot in (B). (D) Treatment of RPS19-deficient cord blood cells with SB203580 partially rescues their erythropoiesis and myelopoiesis in methylcellulose. (E) Treatment of CD34⁺ cord blood cells with SB203580, a p38 MAPK inhibitor, increases the level of GATA1 protein in the cells, whereas treatment with CHX, a translation inhibitor, shows decreased GATA1 protein levels in the absence of SB203580. (F) Treatment of CD34⁺ cord blood cells with SB203580 and/or MG132, a proteasome inhibitor, increases GATA1 stability in the cells. Data are representative of 2 independent experiments. *P < .05; **P < .01; ***P < .001.