The MLK3 inhibitor K252a prevents LPS-induced MLK3/JNK signaling cascades and TNF-α production. BV-2 cells were pretreated with vehicle or 100 nM (A) or various concentrations (B) of K252a for 30 min followed by treatment with 100 ng/ml LPS for the indicated times (western blotting) or 6 h (TNF-α). Western analysis was performed as described in Fig. 7. Released TNF-α (B) was measured by ELISA. Data are presented as mean ± SEM of three independent experiments. **p < 0.01 compared with LPS-stimulated alone cultures. The TNF-α content in untreated cultures was not detectable. The level of TNF-α in cells treated with LPS alone was 4.26 ± 0.14 ng/ml.