R.Winzen and M.Kracht contributed equally to this workStabilization of mRNAs contributes to the strong and rapid induction of genes in the inflammatory response. The signaling mechanisms involved were investigated using a tetracycline-controlled expression system to determine the half-lives of interleukin (IL)-6 and IL-8 mRNAs. Transcript stability was low in untreated HeLa cells, but increased in cells expressing a constitutively active form of the MAP kinase kinase kinase MEKK1. Destabilization and signal-induced stabilization was transferred to the stable β-globin mRNA by a 161-nucleotide fragment of IL-8 mRNA which contains an AU-rich region, as well as by defined AU-rich elements (AREs) of the c-fos and GM-CSF mRNAs. Of the different MEKK1-activated signaling pathways, no significant effects on mRNA degradation were observed for the SAPK/JNK, extracellular regulated kinase and NF-κB pathways. Selective activation of the p38 MAP kinase (⍧SAPK2) pathway by MAP kinase kinase 6 induced mRNA stabilization. A dominant-negative mutant of p38 MAP kinase interfered with MEKK1 and also IL-1-induced stabilization. Furthermore, an active form of the p38 MAP kinase-activated protein kinase (MAPKAP K2 or MK2) induced mRNA stabilization, whereas a negative interfering MK2 mutant interfered with MAP kinase kinase 6-induced stabilization. These findings indicate that the p38 MAP kinase pathway contributes to cytokine/stress-induced gene expression by stabilizing mRNAs through an MK2-dependent, ARE-targeted mechanism.

Human fibroblasts in primary culture released reactive oxygen species upon stimulation with cytokines such as interleukin-1 alpha (IL-1) or tumour necrosis factor-alpha (TNF). The primary radical produced was O2.- as determined by e.s.r. spin trapping and cytochrome c reduction. In contrast to the oxidative burst in granulocytes and monocytes, radical formation took place continuously for at least 4 h. Low-level chemiluminescence was increased by stimulation with IL-1 and TNF. Spectral characteristics and tests with azide led to the conclusion that the photoemissive species were excited carbonyls and not singlet oxygen. Further, there was a liberation of ethane from the cells. Radical production and light emission were not altered by either xanthine or allopurinol, nor by azide, cyanide or rotenone. O2.- production increased in the presence of NADH or NADPH, making an NAD(P)H oxidase a likely source.

Phosphorylation of NF-B p65(RelA) serine 536 is physiologically induced in response to a variety of proinflammatory stimuli, but the responsible pathways have not been conclusively unraveled, and the function of this phosphorylation is largely elusive. In contrast to previous studies, we found no evidence for a role of c-Jun N-terminal kinase, p38 kinase, extracellular signal-regulated kinase, or phosphatidylinositol 3-kinase in interleukin-1-or tumor necrosis factor-induced Ser-536 phosphorylation, as revealed by pharmacological inhibitors. We were not able to suppress Ser-536 phosphorylation by either RNA interference directed at IB kinase (IKK)-␣/␤ (the best characterized Ser-536 kinases so far) or the IKK␤ inhibitor SC-514 or dominant negative mutants of either IKK. A green fluorescent protein p65 fusion protein was phosphorylated at Ser-536 in the absence of IKK activation, suggesting the existence of IKK␣/␤-independent Ser-536 kinases. Chromatographic fractionation of cell extracts allowed the identification of two distinct enzymatic activities phosphorylating Ser-536. Peak 1 represents an unknown kinase, whereas peak 2 contained IKK␣, IKK␤, IKK⑀, and TBK1. Overexpressed IKK⑀ and TBK1 phosphorylate Ser-536 in vivo and in vitro. Reconstitution of mutant p65 proteins in p65-deficient fibroblasts that either mimicked phosphorylation (S536D) or preserved a predicted hydrogen bond between Ser-536 and Asp-533 (S536N) revealed that phosphorylation of Ser-536 favors interleukin-8 transcription mediated by TATA-binding protein-associated factor II31, a component of TFIID. In the absence of phosphorylation, the hydrogen bond favors binding of the corepressor amino-terminal enhancer of split to the p65 terminal transactivation domain. Collectively, our results provide evidence for at least five kinases that converge on Ser-536 of p65 and a novel function for this phosphorylation site in the recruitment of components of the basal transcriptional machinery to the interleukin-8 promoter.The transcription factor NF-B regulates the expression of a large number of genes with important functions in the immune response, inflammation, cellular stress reactions, carcinogenesis, and apoptosis. In resting cells NF-B is trapped in the cytoplasm by its interaction with the inhibitor IB. A central step in activation of NF-B is the stimulus-induced phosphorylation of IB by IB kinases (IKK) 1 ␣ and ␤. Both IKKs, IB, and NF-B subunits form a large signaling complex (1). Phosphorylation of IB results in targeting of IB to the proteasome followed by release and nuclear translocation of NF-B. Recent evidence suggests that NF-B activity is determined by additional mechanisms. Cells lacking the protein kinases glycogen synthase kinase 3␤ (2), TBK1/NF-kB-activating kinase (3, 4), IKK⑀ (5), NF-kB-inducing kinase (6), and protein kinase C (7) show a normal IB degradation pathway but impaired activation of NF-B-dependent gene expression.Furthermore, biochemical and genetic experiments in cells deficient for IKK␣ or IKK␤ strongly suggest that d...