Although interleukin-1 (IL-1) induces expression of interferon regulatory factor 1 (IRF1), its roles in immune and inflammatory responses and mechanisms of activation remain elusive. Here, we show that IRF1 is essential for IL-1-induced expression of chemokines CXCL10 and CCL5 that recruit mononuclear cells into sites of sterile inflammation. Newly synthesized IRF1 acquires K63-linked polyubiquitylation mediated by cellular inhibitor of apoptosis 2 (cIAP2), which is enhanced by the bioactive lipid sphingosine-1 phosphate (S1P). In response to IL-1, cIAP2 and sphingosine kinase 1, the enzyme that generates S1P, form a complex with IRF1, which leads to its activation. Thus, IL-1 triggers a hitherto unknown signaling cascade that controls induction of IRF1-dependent genes important for sterile inflammation.

Nuclear factor I-X3 (NFI-X3) is a newly identified splice variant of NFI-X that regulates expression of several astrocyte-specific markers, such as glial fibrillary acidic protein. Here, we identified a set of genes regulated by NFI-X3 that includes a gene encoding a secreted glycoprotein YKL-40. Although YKL-40 expression is up-regulated in glioblastoma multiforme, its regulation and functions in nontransformed cells of the central nervous system are widely unexplored. We find that expression of YKL-40 is activated during brain development and also differentiation of neural progenitors into astrocytes in vitro. Furthermore, YKL-40 is a migration factor for primary astrocytes, and its expression is controlled by both NFI-X3 and STAT3, which are known regulators of gliogenesis. Knockdown of NFI-X3 and STAT3 significantly reduced YKL-40 expression in astrocytes, whereas overexpression of NFI-X3 dramatically enhanced YKL-40 expression in glioma cells. Activation of STAT3 by oncostatin M induced YKL-40 expression in astrocytes, whereas expression of a dominant-negative STAT3 had a suppressive effect. Mechanistically, NFI-X3 and STAT3 form a complex that binds to weak regulatory elements in the YKL-40 promoter and activates transcription. We propose that NFI-X3 and STAT3 control the migration of differentiating astrocytes as well as migration and invasion of glioma cells via regulating YKL-40 expression.Astrocytes, the most abundant CNS cells, are critical for many functions of normal and pathological brains (1, 2). Generation and differentiation of astrocytes from neural progenitors is controlled by activation of the JAK-STAT3, BMP-SMAD, and Notch-HES pathways in vivo (3, 4) and promoted by cytokines of the IL-6 family that activate STAT3 in vitro (5, 6). In addition to these pathways, evolutionarily conserved NFI 3 transcription factors, consisting of NFI-A, -B, -C, and -X, regulate astrocyte differentiation (7,8). NFIs are expressed in overlapping patterns during embryogenesis, with high expression levels of NFI-A, -B, and -X found in the developing neocortex (9, 10). Consequently, Nfia, Nfib, and Nfix knock-out mice show severe brain anatomical defects, including agenesis of corpus callosum (9, 10), whereas NPs from Nfix knock-out mice show defects in proliferation and migration (9, 10). NFI-A and -B control gliogenesis in chick embryonic spinal cord (7), whereas NFI-X and -C regulate the expression of late astrocyte markers during the differentiation of human NPs in vitro (7,8). Expression of NFI-A is induced by Notch signaling in NP and leads to the demethylation of astrocyte-specific genes (11), as well as down-regulation of Notch signaling via repression of Notch effector Hes1 (12). Each of the NFI transcripts undergoes alternative splicing, generating as many as nine different NFI splice variants (13), likely possessing distinctive functions. We have recently characterized a novel human NFI-X3 splice variant, which is a potent activator of gene expression in astrocytes (14). NFI-X3 contains a unique transcri...

Background: Alloplastic implants such as those employed in hernia repair induce distinct local inflammation and seroma production. As monocytes take a key position in the inflammatory foreign body reaction, their specific release of cytokines was investigated in vitro after incubation with alloplastic materials.Methods: Human blood monocytes were isolated from buffy coats of 42 healthy blood donors. Cells were cultivated in polystyrene culture wells (4 × 10 6 cells/well) on polypropylene-polyglactin mesh, on polytetrafluoroethylene, in control wells with the addition of 1 µg lipopolysaccharide (LPS) and on pure polystyrene. Supernatant was taken after 1 h and 5 days, and concentrations of tumour necrosis factor (TNF) α, interleukin (IL) 6 and IL-10 were determined. Donors were defined as 'high' or 'low' responders when concentrations of TNF-α were above the 75th or below the 25th percentiles, respectively. Results:In contact with biomaterials, the monocytes liberated TNF-α, IL-6 and IL-10, similar to levels observed after stimulation with LPS. Median cytokine concentrations were not normally distributed and were influenced by donor, timepoint and applied stimulus. One donor matched the criteria for low responder and three for high responder. Conclusion:The individual was identified as an independent factor for the inflammatory response of monocytes to biomaterials. Moreover, high and low responders could be identified. The variability of cytokine release and the lack of a normal distribution suggest that a larger sample size should be used in future studies of cellular response.

The secreted protein, YKL-40, has been proposed as a biomarker of a variety of human diseases characterized by ongoing inflammation, including chronic neurological pathologies such as multiple sclerosis (MS)2 and Alzheimer’s disease. However, inflammatory mediators and the molecular mechanism responsible for enhanced expression of YKL-40 remained elusive. Using several mouse models of inflammation, we now show that YKL-40 expression correlated with increased expression of both IL-1 and IL-6. Furthermore, IL-1 together with IL-6 or the IL-6 family cytokine, oncostatin M (OSM), synergistically upregulated YKL-40 expression in both primary human and mouse astrocytes in vitro. The robust cytokine-driven expression of YKL-40 in astrocytes required both STAT3 and NF-κB binding elements of the YKL-40 promoter. Additionally, YKL-40 expression was enhanced by constitutively active STAT3 and inhibited by dominant-negative IκBα. Surprisingly, cytokine-driven expression of YKL-40 in astrocytes was independent of the p65 subunit of NF-κB and instead required subunits RelB and p50. Mechanistically, we show that IL-1-induced RelB/p50 complex formation was further promoted by OSM and that these complexes directly bound to the YKL-40 promoter. Moreover, we found that expression of RelB was strongly upregulated during inflammation in vivo and by IL-1 in astrocytes in vitro. We propose that IL-1 and the IL-6 family of cytokines regulate YKL-40 expression during sterile inflammation via both STAT3 and RelB/p50 complexes. These results suggest that IL-1 may regulate the expression of specific anti-inflammatory genes in non-lymphoid tissues via the canonical activation of the RelB/p50 complexes.

The neuroinflammation associated with multiple sclerosis involves activation of astrocytes that secrete and respond to inflammatory mediators such as IL-1. IL-1 stimulates expression of many chemokines, including C-C motif ligand (CCL) 5, that recruit immune cells, but it also stimulates sphingosine kinase-1, an enzyme that generates sphingosine-1-phosphate (S1P), a bioactive lipid mediator essential for inflammation. We found that whereas S1P promotes IL-1-induced expression of IL-6, it inhibits IL-1-induced CCL5 expression in astrocytes. This inhibition is mediated by the S1P receptor (S1PR)-2 via an inhibitory G-dependent mechanism. Consistent with this surprising finding, infiltration of macrophages into sites of inflammation increased significantly in S1PR2(-/-) animals. However, activation of NF-κB, IFN regulatory factor-1, and MAPKs, all of which regulate CCL5 expression in response to IL-1, was not diminished by the S1P in astrocytes. Instead, S1PR2 stimulated inositol 1,4,5-trisphosphate-dependent Ca(++) release and Elk-1 phosphorylation and enhanced c-Fos expression. In our study, IL-1 induced the IFNβ production that supports CCL5 expression. An intriguing finding was that S1P induced c-Fos-inhibited CCL5 directly and also indirectly through inhibition of the IFN-β amplification loop. We propose that in addition to S1PR1, which promotes inflammation, S1PR2 mediates opposing inhibitory functions that limit CCL5 expression and diminish the recruitment of immune cells.