Ku. Birkenkamp et al., The p38 MAP kinase inhibitor SB203580 enhances nuclear factor-kappa B transcriptional activity by a non-specific effect upon the ERK pathway, BR J PHARM, 131(1), 2000, pp. 99-107
1 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-kappa B) transcriptional activity in the erythroleukaemic cell line TF-
1.
2 TF-1 cells stimulated with the phosphatase inhibitor okadaic acid (OA) de
monstrated enhanced NF-kappa B and GAL4p65-regulated transcriptional activi
ty which was associated with elevated p38 phosphorylation. However, pretrea
tment with the p38 MAPK specific inhibitor SB203580 (1 mu M) or overexpress
ion of kinase-deficient mutants of MKK3 or MKK6 did not affect OA-enhanced
NF-kappa B transcriptional potency, as determined in transient transfection
assays. In fact, 5 and 10 mu M SB203580 enhanced rather than inhibited NF-
kappa B-mediated promoter activity by 2 fold, which was independent of phos
phorylation of the p65 subunit.
3 The SB203580-mediated increase in NF-kappa B 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.
4 Overexpression of kinase-deficient mutants belonging to the ERK1/2, JNK,
and p38 pathways showed that only dominant-negative Raf-l abrogated SB20358
0-enhanced NF-kappa B activity. This would implicate the involvement of the
ERK1/2 pathway in the enhancing effects of SB203580 on NF-kappa B-mediated
gene transcription.
5 This study demonstrates that the p38 MAP kinase pathway is not involved i
n the OA-induced activation of NF-kappa B. SB203580 at higher concentration
s activates the ERK pathway, which subsequently enhances NF-kappa B transcr
iptional activity.