p38 MAPK inhibitor reducesHOXB4level. (A) UT-7/TPO cells were cultured in 10 ng/mL TPO and treated with 50 μM SB203580, 20 μM PD98059, or 20 μM LY294002 for 72 hours and total RNA was extracted. HOXB4 expression levels were analyzed by real-time RT-PCR; each column represents an average ± SD of several independent experiments (n = 5, control; n = 5, SB203580; n = 3, PD98059; n = 3, LY294002). (B) UT-7/TPO cells were cultured with the indicated concentrations of SB203580 for 72 hours. After each culture period, whole cell lysates were prepared and the activation of p38 MAPK was analyzed by Western blotting. (C) UT-7/TPO cells were cultured with the indicated concentrations of SB203580 and cell number was counted; *P < .05, **P < .01. (D) EML cells were cultured with SCF plus TPO and treated with SB203580 for 72 hours; total cell lysates were prepared and subjected to Western blotting with antiphospho-p38 MAPK, anti-p38 MAPK, and anti-HoxB4 antibodies. (E) EML cells were cultured with SCF plus TPO and treated with 20 μ M SB203580 for 24 hours. Then Hoxb4 levels were analyzed by real-time RT-PCR. Each column represents an average ± SD of several independent experiments (n = 5, control; n = 3, SB203580). (F) EML cells were cultured with SCF plus TPO and various concentrations of SB203580 and cell numbers were counted; *P < .05, **P < .01.