As shown in Figure 4A , 3D/4 cells were pre-treated with inhibitors of ERK1/2 (U0126), p38 (SB230058), and JNK1/2 (JNK InSolution), at concentrations of 10 mM, 5 mM, and 50 mM, respectively. While the phosphorylation of ERK1/2 was unaffected by treatment with the p38 and JNK inhibitors, it was completely abolished at both 18 and 30 hrs p.i. (lines 4-5) by the ERK1/2 inhibitor U0126 (Fig. 4A) . We noted that the basal level phosphorylation of ERK1/2 diminished in the presence of U0126. On the other hand, in light of the p38 and JNK inhibition with their specific inhibitors, the phosphorylation of ERK1/2 appeared to be enhanced (Fig. 4A, lines 6-9 ), indicating that a compensatory mechanism may exist among MAP kinases.