Decrease in β-globin gene expression in differentiated MEL cells exposed to calcium ionophore. A, treatment of DMSO-induced MEL cells with the calcium ionophore A23187 leads to proteolytic cleavage of USF. DMSO-treated MEL cells were incubated in the presence or absence of 0.9 μg/ml A23187 and subjected to Western blot analysis using a USF2-specific antibody. B, treatment of DMSO-induced MEL cells with the calcium ionophore A23187 reduces βmaj-globin gene expression. MEL cells were grown in the absence (MEL/without DMSO) or in the presence (MEL/DMSO) of 2% DMSO for 48 h. MEL cells grown with DMSO were incubated with 0.3 or 0.9 μg/ml A23187 for 3, 8, or 16 h as indicated. RNA was isolated from these cells, reverse transcribed, and subjected to quantitative PCR using primers specific for the βmaj-globin gene. Error bars reflect S.D. from two independent experiments.