The p38 MAP kinase inhibitor SB203580 enhances nuclear factor‐kappa B transcriptional activity by a non‐specific effect upon the ERK pathway

In the present study we investigated a possible role for the p38 mitogen‐activated protein (MAP) kinase pathway in mediating nuclear factor‐kappa B (NF‐κB) transcriptional activity in the erythroleukaemic cell line TF‐1. TF‐1 cells stimulated with the phosphatase inhibitor okadaic acid (OA) demonstrated enhanced NF‐κB and GAL4p65‐regulated transcriptional activity which was associated with elevated p38 phosphorylation. However, pretreatment with the p38 MAPK specific inhibitor SB203580 (1 μ M ) or overexpression of kinase‐deficient mutants of MKK3 or MKK6 did not affect OA‐enhanced NF‐κB transcriptional potency, as determined in transient transfection assays. In fact, 5 and 10 μ M SB203580 enhanced rather than inhibited NF‐κB‐mediated promoter activity by 2 fold, which was independent of phosphorylation of the p65 subunit. The SB203580‐mediated increase in NF‐κB transcriptional activity was associated with enhanced phosphorylation of extracellular signal‐regulated kinase (ERK)1/2 and c‐Jun N‐terminal kinase (JNK), but not p38 kinase. Overexpression of kinase‐deficient mutants belonging to the ERK1/2, JNK, and p38 pathways showed that only dominant‐negative Raf‐1 abrogated SB203580‐enhanced NF‐κB activity. This would implicate the involvement of the ERK1/2 pathway in the enhancing effects of SB203580 on NF‐κB‐mediated gene transcription. This study demonstrates that the p38 MAP kinase pathway is not involved in the OA‐induced activation of NF‐κB. SB203580 at higher concentrations activates the ERK pathway, which subsequently enhances NF‐κB transcriptional activity.British Journal of Pharmacology (2000) 131 , 99–107; doi: 10.1038/sj.bjp.0703534