IRF5 is required for late-phase TNF secretion by human dendritic cells

Abstract

Spatially and temporally controlled expression of inflammatory mediators is critical for an appropriate immune response. In this study, we define the role for interferon regulatory factor 5 (IRF5) in secretion of tumor necrosis factor (TNF) by human dendritic cells (DCs). We demonstrate that DCs but not macrophages have high levels of IRF5 protein, and that IRF5 is responsible for the late-phase expression of TNF, which is absent in macrophages. Sustained TNF secretion is essential for robust T IntroductionTumor necrosis factor (TNF) is one of the major cytokines responsible for effector immune functions. As well as playing a central role in host defense against infection, TNF is a major factor in the pathogenesis of chronic inflammatory disease such as rheumatoid arthritis (RA). Consequently, tightly controlled regulation of its expression is critical for an appropriate immune response. This occurs at the transcriptional and posttranscriptional levels, with transcriptional regulation showing specificity for both stimulus and cell type. 1 The NF-B family of transcription factors (TFs) plays a major role in transcriptional up-regulation of the TNF gene by lipopolysaccharide (LPS) in both mouse and human myeloid cells. [2][3][4][5] Regulation of transcription for many immune genes in response to Toll-like receptor (TLR) signaling involves a combination of NF-B and interferon regulatory factor (IRF) factors. 6 IRFs appear to provide a mechanism for conferring signal specificity to a variety of target gene subsets, with IRF3 being essential for type I interferon (IFN) response, 7 and IRF5 playing a key role in induction of proinflammatory cytokines, including TNF, Consequently, IRF5 Ϫ/Ϫ mice show resistance to lethal shock induced by CpG-B or LPS. 8 Unlike other IRF family members, IRF5 contains 2 nuclear localization signals (NLSs), 1 in the N-terminus and the other in the C-terminus of the protein. This results in low levels of nuclear translocation and therefore weak trans-activation activity of IRF5, even in unstimulated cells. 9 The molecular pathways leading to IRF5 activation are not well understood, but it was shown that TLR signaling induces the formation of MyD88-IRF5-TRAF6 complexes, 8 and is probably followed by phosphorylation of specific sites within the IRF5 C-terminal autoinhibitory domain. 10 Human IRF5 is expressed as multiple spliced variants with distinct cell type-specific expression, cellular localization, differential regulation, and dissimilar functions. 11 Moreover, genetic polymorphisms in the IRF5 gene leading to expression of several unique isoforms have been implicated in autoimmune diseases, including systemic lupus erythematosis (SLE), RA and Sjogren syndrome. 12-15 IRF5 mRNA expression has been detected in B cells, dendritic cells (DCs), monocytes, and natural killer (NK) cells but not in T cells, 11 yet little is known about the IRF5 protein expression in these cells.Here, we demonstrate that human monocytes acquire high levels of IRF5 protein during differentiation into monocyte-d...

Multiple Interferon Regulatory Factor and NF-κB Sites Cooperate in Mediating Cell-Type- and Maturation-Specific Activation of the Human CD83 Promoter in Dendritic Cells

“…Moreover, cotransfection experiments in 293T cells identified that the combination of p65 or cRel with IRF-5 resulted in the strongest induction of the URE and MP-261, which is clearly in line with results shown by ChIP. Furthermore, this is in accordance with data reported previously by the group of Irina Udalova, which indicated that p65 induces basal transient transcriptional activity of the TNF-␣ promoter in DCs (33). Regarding their model, IRF-5 is first recruited to an upstream interferon regulatory element (ISRE) flanked by a NF-B site upon LPS stimulation, which then interacts at another downstream NF-B site directly with p65, resulting in an upregulated and prolonged induction of TNF-␣ expression.…”

“…IRF-5, however, is expressed constitutively in DCs but has been described to be expressed as multiple splice variants with distinct cell-type-specific expression and cellular localization, differential regulation/activation, and dissimilar functions (35)(36)(37). Although the functions of IRF-5 are not yet fully elucidated, it has been shown by the group of Irina Udalova to coinduce (i) gene expression in immune cells as an upstream promoter-binding factor (33) and (ii) CD83 expression in DCs after adenovirus-mediated overexpression (38), thereby indicating that IRF-5 is a factor for the fine regulation of human CD83 expression. Whereas a strong binding of an as-yet-unknown TF was observed for IRF site 2, IRF-1 and -2 were specified by EMSA to bind to IRF site 1 within the enhancer.…”

Constitutive expression of IRF-5 in HTLV-1-infected T cells

“…Tax can activate mouse TNF-α promoter through nuclear factor-κb (NF-κb) activation (51). Furthermore, IRF-5 can specifically interact with NF-κb RelA, and sustain TNF-α secretion in human dendritic cells (52). These findings suggest that Tax/NF-κb/IRF-5 may cooperate in HTLV-1-induced TNF-α promoter activation.…”

Evaluating mRNA Expression Levels of the TLR4/IRF5 Signaling Axis During Hepatic Ischemia-Reperfusion Injuries

“…6,[11][12][13] Therefore, a potential role in initial inflammatory phase of hepatic IRI can be suggested for IRF5. On the basis of previous findings, we aimed to evaluate the expression profile of TLR4/IRF5 axis in hepatic IRI.…”