Ulcerative colitis and Crohn's disease are the two entities of chronic inflammatory bowel diseases (IBD). One of the main pathogenic mechanisms is probably a dysregulated immune response triggered by products of the enteric bacterial flora. The goal of this study was to evaluate the effects of the p38 mitogen-activated protein kinase (MAPK) inhibitor SB203580 on inflammatory responses using the DSS-induced experimental colitis model in mice reflecting human IBD. We found that SB203580 improved the clinical score, ameliorates the histological alterations, and reduces the mRNA levels of proinflammatory cytokines. In addition to p38 kinase activity, the "classical" and the "alternative" NF-kappaB pathways were also strongly activated during colitis induction. All three pathways were drastically down-regulated by SB203580 treatment. An analysis of the molecular basis of NF-kappaB activation revealed that Rip-like interacting caspase-like apoptosis-regulatory protein kinase (RICK), a key component of a pathway leading to NF-kappaB induction, is also strongly inhibited by SB203580. Since RICK is an effector kinase of NOD2, an intracellular receptor of bacterial peptidoglycan, these results support the notion that NOD signaling could play a pivotal role in the IBD pathogenesis. Thus, RICK could represent a novel target for future therapies in human IBD.

Nuclear factor-B (NF-B) is the main target of antiinflammatory therapies in human chronic inflammatory bowel diseases (IBD), Crohn disease, and ulcerative colitis. This study investigates the molecular anti-inflammatory mechanisms of SB203580, an inhibitor of the mitogen-activated protein kinase p38. The murine trinitrobenzene sulfonic acid (TNBS)-induced colitis was used as an established model of human Crohn disease. Here we show that SB203580 improved the clinical condition, reduced intestinal inflammation, and suppressed mRNA levels of pro-inflammatory cytokines elevated upon induction of colitis. Besides p38 kinase activity, the "classical" I B-dependent NF-B pathway was strongly up-regulated during colitis induction, whereas the "alternative" was not. SB203580 treatment resulted in a drastic down-regulation of p38 and NF-B activity. The molecular analysis of NF-B activation revealed that Rip-like interacting caspase-like apoptosis-regulatory protein kinase (RICK), a key component of a pathway leading to NF-B induction, is also strongly inhibited by SB203580. In contrast, SB203580 had no effect on the colitis-induced activation of other potential NF-Bactivating kinases such as protein kinase C (PKC ), mixed lineage kinase 3, and the oncogene product Cot/ TPL2. Thus, the inhibitory effect of SB203580 on NF-B activation is to a large extent mediated by RICK inhibition. RICK is the effector kinase of the intracellular receptor of bacterial peptidoglycan NOD. Because bacterial products are suggested to be the key pathogenic agents triggering IBD, inhibition of the NOD/RICK pathway may serve as a novel target of future therapies in human IBD.Crohn disease is characterized by chronic intestinal inflammation frequently relapsing with clinical manifestations including diarrhea, blood in the stool, abdominal pain, and weight loss. The etiology of Crohn disease is so far unknown (1) but epidemiological and linkage studies suggest a genetic predisposition of the patient and the involvement of environmental factors (1, 2). Furthermore, several observations strongly implicate a pathogenic role of the intestinal flora during the initiation process of the immunological dysregulation (3-5).

The immediate early transcription factor nuclear factor (IjBs) kappa B (NF-jB) is crucially involved in the regulation of numerous physiological or pathophysiological processes such as inflammation and tumourigenesis. Therefore, the control of NF-jB activity, which is mainly regulated by signal-induced degradation of cytoplasmic inhibitors of NF-jB (IjBs), is of high relevance. One known alternative pathway of NF-jB regulation is the stimulus-induced proteasomal degradation of RelB, a component of the NF-jB dimer. Here, we identified the serine/threonine protein kinase glycogen synthase kinase-3b (GSK-3b) as a critical signalling component leading to RelB degradation. In Jurkat leukaemic T cells as well as in primary human T cells, tetradecanoylphorbolacetate/ionomycinand CD3/CD28-induced RelB degradation were impaired by a GSK-3b-specific pharmacological inhibitor, an ectopically expressed dominant-negative GSK-3b mutant and by small-interfering RNA-mediated silencing of GSK-3b expression. Furthermore, a physical interaction between RelB and GSK-3b was shown by co-immunoprecipitation, which was already notable in unstimulated cells. Most importantly, as demonstrated by in vitro kinase assays, human RelB is inducibly phosphorylated by GSK-3b, indicating a direct substrate-enzyme relationship. The serine residue 552 is a target of GSK-3b-mediated phosphorylation in vitro and in vivo. We conclude that GSK-3b is a crucial regulator of RelB degradation, stressing the relevant linkage between the NF-jB system and GSK-3b.

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