Distinct Mechanisms for Induction and Tolerance Regulate the Immediate Early Genes Encoding Interleukin 1β and Tumor Necrosis Factor α

Interleukin-1β and Tumor Necrosis Factor α play related, but distinct, roles in immunity and disease. Our study revealed major mechanistic distinctions in the Toll-like receptor (TLR) signaling-dependent induction for the rapidly expressed genes (IL1B and TNF) coding for these two cytokines. Prior to induction, TNF exhibited pre-bound TATA Binding Protein (TBP) and paused RNA Polymerase II (Pol II), hallmarks of poised immediate-early (IE) genes. In contrast, unstimulated IL1B displayed very low levels of both TBP and paused Pol II, requiring the lineage-specific Spi-1/PU.1 (Spi1) transcription factor as an anchor for induction-dependent interaction with two TLR-activated transcription factors, C/EBPβ and NF-κB. Activation and DNA binding of these two pre-expressed factors resulted in de novo recruitment of TBP and Pol II to IL1B in concert with a permissive state for elongation mediated by the recruitment of elongation factor P-TEFb. This Spi1-dependent mechanism for IL1B transcription, which is unique for a rapidly-induced/poised IE gene, was more dependent upon P-TEFb than was the case for the TNF gene. Furthermore, the dependence on phosphoinositide 3-kinase for P-TEFb recruitment to IL1B paralleled a greater sensitivity to the metabolic state of the cell and a lower sensitivity to the phenomenon of endotoxin tolerance than was evident for TNF. Such differences in induction mechanisms argue against the prevailing paradigm that all IE genes possess paused Pol II and may further delineate the specific roles played by each of these rapidly expressed immune modulators. © 2013 Adamik et al

PPARγ Controls Dectin-1 Expression Required for Host Antifungal Defense against Candida albicans

We recently showed that IL-13 or peroxisome proliferator activated receptor γ (PPARγ) ligands attenuate Candida albicans colonization of the gastrointestinal tract. Here, using a macrophage-specific Dectin-1 deficient mice model, we demonstrate that Dectin-1 is essential to control fungal gastrointestinal infection by PPARγ ligands. We also show that the phagocytosis of yeast and the release of reactive oxygen intermediates in response to Candida albicans challenge are impaired in macrophages from Dectin-1 deficient mice treated with PPARγ ligands or IL-13. Although the Mannose Receptor is not sufficient to trigger antifungal functions during the alternative activation of macrophages, our data establish the involvement of the Mannose Receptor in the initial recognition of non-opsonized Candida albicans by macrophages. We also demonstrate for the first time that the modulation of Dectin-1 expression by IL-13 involves the PPARγ signaling pathway. These findings are consistent with a crucial role for PPARγ in the alternative activation of macrophages by Th2 cytokines. Altogether these data suggest that PPARγ ligands may be of therapeutic value in esophageal and gastrointestinal candidiasis in patients severely immunocompromised or with metabolic diseases in whom the prevalence of candidiasis is considerable

Interferon inducible X-linked gene CXorf21 may contribute to sexual dimorphism in Systemic Lupus Erythematosus.

Systemic lupus erythematosus (SLE) is an autoimmune disease, characterised by increased expression of type I interferon (IFN)-regulated genes and a striking sex imbalance towards females. Through combined genetic, in silico, in vitro, and ex vivo approaches, we define CXorf21, a gene of hitherto unknown function, which escapes X-chromosome inactivation, as a candidate underlying the Xp21.2 SLE association. We demonstrate that CXorf21 is an IFN-response gene and that the sexual dimorphism in expression is magnified by immunological challenge. Fine-mapping reveals a single haplotype as a potential causal cis-eQTL for CXorf21. We propose that expression is amplified through modification of promoter and 3'-UTR chromatin interactions. Finally, we show that the CXORF21 protein colocalises with TLR7, a pathway implicated in SLE pathogenesis. Our study reveals modulation in gene expression affected by the combination of two hallmarks of SLE: CXorf21 expression increases in a both an IFN-inducible and sex-specific manner

TH2 cytokines and allergic challenge induce Ym1 expression in macrophages by a STAT6-dependent mechanism.

The diverse functions of macrophages as participants in innate and acquired immune responses are regulated by the specific milieu of environmental factors, cytokines, and other signaling molecules that are encountered at sites of inflammation. Microarray analysis of the transcriptional response of mouse peritoneal macrophages to the T(H)2 cytokine interleukin-4 (IL-4) identified Ym1 and arginase as the most highly up-regulated genes, exhibiting more than 68- and 88-fold induction, respectively. Molecular characterization of the Ym1 promoter in transfected epithelial and macrophage cell lines revealed the presence of multiple signal transducers and activators of transcription 6 (STAT6) response elements that function in a combinatorial manner to mediate transcriptional responses to IL-4. The participation of STAT6 as an obligate component of protein complexes binding to these sites was established by analysis of nuclear extracts derived from STAT6-deficient macrophages. Macrophage expression of Ym1 was highly induced in vivo by an IL-4- and STAT6-dependent mechanism during the evolution of allergic peritonitis, supporting the biological relevance of the IL-4-dependent pathway characterized ex vivo in peritoneal macrophages. These studies establish Ym1 as a highly inducible STAT6-dependent transcript in T(H)2-biased inflammation and define Cis-active elements in the Ym1 promoter that are required for this transcriptional response

TH2 cytokines and allergic challenge induce Ym1 expression in macrophages by a STAT6-dependent mechanism.

The diverse functions of macrophages as participants in innate and acquired immune responses are regulated by the specific milieu of environmental factors, cytokines, and other signaling molecules that are encountered at sites of inflammation. Microarray analysis of the transcriptional response of mouse peritoneal macrophages to the T(H)2 cytokine interleukin-4 (IL-4) identified Ym1 and arginase as the most highly up-regulated genes, exhibiting more than 68- and 88-fold induction, respectively. Molecular characterization of the Ym1 promoter in transfected epithelial and macrophage cell lines revealed the presence of multiple signal transducers and activators of transcription 6 (STAT6) response elements that function in a combinatorial manner to mediate transcriptional responses to IL-4. The participation of STAT6 as an obligate component of protein complexes binding to these sites was established by analysis of nuclear extracts derived from STAT6-deficient macrophages. Macrophage expression of Ym1 was highly induced in vivo by an IL-4- and STAT6-dependent mechanism during the evolution of allergic peritonitis, supporting the biological relevance of the IL-4-dependent pathway characterized ex vivo in peritoneal macrophages. These studies establish Ym1 as a highly inducible STAT6-dependent transcript in T(H)2-biased inflammation and define Cis-active elements in the Ym1 promoter that are required for this transcriptional response

Selective inhibition of the FcɛRI-induced de novo synthesis of mediators by an inhibitory receptor

Aggregation of the type 1 Fcɛ receptors (FcɛRI) on mast cells initiates a network of biochemical processes culminating in secretion of both granule-stored and de novo-synthesized inflammatory mediators. A strict control of this response is obviously a necessity; nevertheless, this regulation is hardly characterized. Here we report that a prototype inhibitory receptor, the mast cell function-associated antigen (MAFA), selectively regulates the FcɛRI stimulus–response coupling network and the subsequent de novo production and secretion of inflammatory mediators. Specifically, MAFA suppresses the PLC-γ2–[Ca(2+)](i), Raf-1–Erk1/2, and PKC–p38 coupling pathways, while the Fyn–Gab2-mediated activation of PKB and Jnk is essentially unaffected. Hence, the activities of several transcription/nuclear factors for inflammatory mediators (NF-κB, NFAT) are markedly reduced, while those of others (Jun, Fos, Fra, p90rsk) are unaltered. This results in a selective inhibition of gene transcription of cytokines including IL-1β, IL-4, IL-8, and IL-10, while that of TNF-α, MCP-1, IL-3, IL-5, or IL-13 remains unaffected. Taken together, these results illustrate the capacity of an immunoreceptor tyrosine-based inhibitory motif-containing receptor to cause tight and specific control of the production and secretion of inflammatory mediators by mast cells