Increased p38 MAPK phosporylation and acetylation of histone H4 by thalidomide inhibited by the antioxidants catalase and DMTU, and p38 inhibitor SB203580. CD34⁺ cells cultured in EPO medium for 7 days were pretreated with the antioxidants catalase (4000 U/mL) or DMTU (10 mM) (A) or with 5, 10, or 20 μM of the p38 MAPK inhibitor SB203580 (B) for 30 minutes, then coincubated with 100 μM thalidomide in the presence of indicated inhibitors for 30 minutes. Cell lysates (30 μg) were analyzed by Western blot using phosphorylated p38 MAPK and acetyl-histone H4 antibodies. Total p38 MAPK and histone H4 were analyzed as loading controls as described in Figure 3.