Arsenic trioxide-induced growth inhibition is SEK1-dependent in MEF cells.SEK1^+/+ and SEK1^-/- cells were treated for 5 days with 1 or 2.5 μM As₂O₃ (A) or with 0.5 or 1.0 μg/mL doxorubicin (B). Growth inhibition after this time was assessed by counting live, trypan blue-negative cells, and was expressed as percentage of viable cells for each treatment relative to its respective untreated control. Trypan blue-positive cells never exceeded 3%. Apoptosis was detected by PI staining and quantitated by flow cytometric measurement of PI-positive cells. Each bar represents an average of 3 independent samples, and standard deviation error bars are shown.