Nuclear translocation of ␤-catenin and its association with Tcf/Lef factors are key steps in transduction of the Wnt signal, which is aberrantly activated in a variety of human cancers. In a search for new ␤-catenin-Tcf target genes, we analyzed ␤-catenin-induced alterations of gene expression in primary human hepatocytes, after transduction of either dominant stable ␤-catenin or its truncated, transactivation-deficient counterpart by means of a lentiviral vector. cDNA microarray analysis revealed a limited set of up-regulated genes, including known Wnt targets such as matrilysin and keratin-1. In this screen, we identified the CXC chemokine interleukin 8 (IL-8) as a direct target of ␤-catenin-Tcf4. IL-8 is constitutively expressed in various cancers, and it has been implicated in tumor progression through its mitogenic, motogenic, and angiogenic activities. The IL-8 promoter contains a unique consensus Tcf/Lef site that is critical for IL-8 activation by ␤-catenin. We show here that the p300 coactivator was required for efficient transactivation of ␤-catenin on this promoter. Ectopic expression of ␤-catenin in hepatoma cells promoted IL-8 secretion, which stimulated endothelial cell migration. These data define IL-8 as a Wnt target and suggest that IL-8 induction by ␤-catenin might be implicated in developmental and tumorigenic processes.

IL-33, a new member of the IL-1 family, has been described as an important inducer of Th2 cytokines and mediator of inflammatory responses. In this study, we demonstrate that murine basophils sorted directly from the bone marrow, without prior exposure to IL-3 or FcεR cross-linking, respond to IL-33 alone by producing substantial amounts of histamine, IL-4, and IL-6. These cells express ST2 constitutively and generate a cytokine profile that differs from their IL-3-induced counterpart by a preferential production of IL-6. In vivo, IL-33 promotes basophil expansion in the bone marrow (BM) through an indirect mechanism of action depending on signaling through the βc chain shared by receptors for IL-3, GM-CSF, and IL-5. IL-3 can still signal through its specific βIL-3 chain in these mutant mice, which implies that it is not the unique growth-promoting mediator in this setup, but requires IL-5 and/or GMCSF. Our results support a major role of the latter growth factor, which is readily generated by total BM cells as well as sorted basophils in response to IL-33 along with low amounts of IL-3. Furthermore, GM-CSF amplifies IL-3-induced differentiation of basophils from BM cells, whereas IL-5 that is also generated in vivo, affects neither their functions nor their growth in vitro or in vivo. In conclusion, our data provide the first evidence that IL-33 not only activates unprimed basophils directly, but also promotes their expansion in vivo through induction of GM-CSF and IL-3.

In order to provide additional insight into the in vivo significance of serotonin [5-hydroxytryptamine (5-HT)] in inflammation, we examined its effect on the production of tumor necrosis factor (TNF)-alpha, IL-1alpha, IL-1beta, IL-6, IL-10 and IL-1 receptor antagonist in lipopolysaccharide (LPS)-stimulated human peripheral blood mononuclear cells (PBMC). 5-HT inhibited TNF-alpha production and increased IL-1beta production in PBMC. The level of IL-1beta-converting enzyme/caspase-1 remained unchanged, suggesting that the effect of 5-HT is not directly related to the IL-1beta maturation process. TNF-alpha mRNA and IL-1beta mRNA content did not change in the presence of 5-HT. 5-HT did not have any effect on the production of other cytokines studied. The inhibitory effect of 5-HT on TNF-alpha production was antagonized by ketanserin, a selective 5-HT(2A) antagonist, and mimicked by DOI, a selective 5-HT(2A/2C) agonist. These findings suggest that the inhibition of TNF-alpha production by 5-HT involves the participation of the 5-HT(2A) receptor subtypes in PBMC. Accordingly, we detected the presence of 5-HT(2A) receptors in PBMC by Western blot analysis. Our data support a role of 5-HT in inflammation through its effect on cytokine production in PBMC.

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