Publications

TLRs initiate immune responses by direct detection of molecular motifs that distinguish invading microbes from host cells. Five intracellular adaptor proteins, each containing a Toll/IL-1R (TIR) domain, are used by TLRs and play key roles in dictating gene expression patterns that are tailored to the invader. Such gene expression is mediated by transcription factors, and although TIR adaptor-induced activation of NF-κB and the IFN regulatory factors have been intensively studied, there is a dearth of information on the role of TIR adaptors in regulating CREB. In this paper, we describe a role for the TIR adaptor Mal in enhancing activation of CREB. Mal-deficient murine bone marrow-derived macrophages show a loss in responsiveness to TLR2 and TLR4 ligands with respect to activation of CREB. Mal-deficient cells also fail to express the CREB-responsive genes IL-10 and cyclooxygenase 2 in response to Pam(2)Cys-Ser-(Lys)4 and LPS. We reveal that Mal-mediated activation of CREB is dependent on Pellino3 and TNFR-associated factor 6, because CREB activation is greatly diminished in Pellino3 knockdown cells and TNFR-associated factor 6-deficient cells. We also demonstrate the importance of p38 MAPK in this pathway with the p38 inhibitor SB203580 abolishing activation of CREB in murine macrophages. MAPK-activated protein kinase 2 (MK2), a substrate for p38 MAPK, is the likely downstream mediator of p38 MAPK in this pathway, because Mal is shown to activate MK2 and inhibition of MK2 decreases TLR4-induced activation of CREB. Overall, these studies demonstrate a new role for Mal as a key upstream regulator of CREB and as a contributor to the expression of both pro- and anti-inflammatory genes.

The pathogenic basis for increased thrombotic risk in individuals with inflammatory diseases is poorly understood. Myeloid cell “trained immunity” describes persistent innate immune cell memory arising from prior exposure to an inflammatory stimulus, leading to an enhanced immune response to subsequent unrelated stimuli. We identify enhanced myeloid cell prothrombotic activity as a maladaptive consequence of trained immunity. Lipopolysaccharide (LPS) stimulation of macrophages trained previously with β-glucan or heme exhibited significantly enhanced procoagulant activity compared to macrophages stimulated with LPS alone, which was mediated by enhanced acid sphingomyelinase–mediated tissue factor decryption. Furthermore, splenic monocytes isolated from β-glucan–trained mice revealed enhanced procoagulant activity up to 4 weeks after β-glucan administration compared to monocytes from control mice over the same time period. Moreover, hematopoietic progenitor cells and bone marrow interstitial fluid from β-glucan–trained mice had enhanced procoagulant activity compared to control mice. Trained immunity and associated metabolic perturbations may therefore represent an opportunity for targeted intervention in immunothrombotic disease development.

T1/ST2 is a member of the interleukin (IL)-1 receptor superfamily, possessing three immunoglobulin domains extracellularly and a Toll/IL1R (TIR) domain intracellularly. The ligand for T1/ST2 is not known. T1/ST2 is expressed on Type 2 T helper (Th2) cells, and its role appears to be in the regulation of Th2 cell function. Here, we have investigated T1/ST2 signal transduction, using either transient overexpression of T1/ST2 or a cross-linking monoclonal antibody to activate cells. We demonstrate that T1/ST2 does not activate the transcription factor NF-κB when overexpressed in murine thymoma EL4 cells, or in the mast cell line P815 treated with the anti-T1/ST2 antibody. However, a chimera comprising the extracellular domain of the type 1 IL-1 receptor and the intracellular domain of T1/ST2 activates NF-κB both by overexpression and in response to IL-1. This artificial activation requires the IL1RAcP recruited via the extracellular portion (IL1R1) of the chimera. T1/ST2 is, however, able to activate the transcription factor activator protein-1 (AP-1), increase phosphorylation of c-Jun, and activate the MAP kinases c-Jun N-terminal kinase (JNK), p42/p44 and p38. Anti-T1/ST2 also induces the selective expression of IL-4 but not IFN-γ in naive T cells. Importantly, this effect is blocked by prior treatment with the JNK inhibitor SP600125 confirming that JNK as a key effector in T1/ST2 signaling. The lack of effect on NF-κB when T1/ST2 is homodimerized identifies T1/ST2 as the first member of the IL-1 receptor superfamily so far studied that is apparently unable to activate NF-κB, consistent with evidence indicating the lack of a role for NF-κB in Th2 cell function.

Synthesis of interferon-β (IFN-β) is an innate response to cytoplasmic infection with bacterial pathogens. Our recent studies showed that Listeria monocytogenes limits immune detection and IFN-β synthesis via deacetylation of its peptidoglycan, which renders the bacterium resistant to lysozyme degradation. Here, we examined signaling requirements for the massive IFN-β production resulting from the infection of murine macrophages with a mutant strain of L. monocytogenes, ΔpgdA, which is unable to modify its peptidoglycan. We report the identification of unconventional signaling pathways to the IFN-β gene, requiring TLR2 and bacterial internalization. Induction of IFN-β was independent of the Mal/TIRAP adaptor protein but required TRIF and the transcription factors IRF3 and IRF7. These pathways were stimulated to a lesser degree by wild-type L. monocytogenes. They operated in both resident and inflammatory macrophages derived from the peritoneal cavity, but not in bone marrow-derived macrophages. The novelty of our findings thus lies in the first description of TLR2 and TRIF as two critical components leading to the induction of the IFN-β gene and in uncovering that individual macrophage populations adopt different strategies to link pathogen recognition signals to IFN-β gene expression.

In this study we describe a previously unreported function for NFκB2, an NFκB family transcription factor, in antiviral immunity. NFκB2 is induced in response to poly(I:C), a mimic of viral dsRNA. Poly(I:C), acting via TLR3, induces p52-dependent transactivation of a reporter gene in a manner that requires the kinase activity of IκB kinase ϵ (IKKϵ) and the transactivating potential of RelA/p65. We identify a novel NFκB2 binding site in the promoter of the transcription factor Sp1 that is required for Sp1 gene transcription activated by poly(I:C). We show that Sp1 is required for IL-15 induction by both poly(I:C) and respiratory syncytial virus, a response that also requires NFκB2 and IKKϵ. Our study identifies NFκB2 as a target for IKKϵ in antiviral immunity and describes, for the first time, a role for NFκB2 in the regulation of gene expression in response to viral infection. Background: IKKϵ can promote the ability of p52 to transactivate gene expression in a manner requiring p65. Results: p52 is induced by TLR3 activation and regulates Sp1 transcription. Sp1 promotes the transcription of IL-15. Both events require the presence of IKKϵ and p52. Conclusion: p52 is a target for IKKϵ in antiviral immunity. Significance: This study reports a role for NFκB2 in the induction of antiviral gene expression.

Metabolic reprogramming controls protective and pathogenic T helper 17 (T H 17) cell responses. When naïve T cells are differentiated into T H 17 cells in vitro, the presence of the cytokine activin A promotes their maturation into a nonpathogenic state. Here, we found that nonpathogenic T H 17 cells induced by activin A displayed reduced aerobic glycolysis and increased oxidative phosphorylation (OXPHOS). In response to activin A, signaling through the adenosine A 2A receptor (A 2A R) and AMP-activated protein kinase (AMPK) enhanced OXPHOS and reprogrammed pathogenic T H 17 cells toward nonpathogenic states that did not induce central nervous system autoimmunity in a mouse model of multiple sclerosis. In pathogenic T H 17 cells, the transcriptional coactivator p300/CBP-associated factor (PCAF) increased acetylation at histone 3 Lys 9 (H3K9ac) of genes involved in aerobic glycolysis and T H 17 pathogenic programs. In contrast, in nonpathogenic activin A–treated T H 17 cells, AMPK signaling suppressed PCAF-mediated H3K9ac modification of genes involved in aerobic metabolism and enhanced H3K9ac modification of genes involved in OXPHOS and nonpathogenic T H 17 programs. Together, our findings uncover A 2A R-AMPK signaling as a central metabolic checkpoint that suppresses T H 17 cell pathogenicity.

VOLUME 281 (2006) PAGES 10489–10495 PAGE 10492: There was an error in Fig. 2B. In the original data provided by the authors to the journal, lanes 1–6 of Fig. 2B were electrophoresed on a different gel from lanes 7 and 8. During figure assembly, the authors erroneously reused lane 4 to represent lane 7. The authors have repeated the experiment, and the results are shown. This error does not affect the results or conclusions of the work.