Pin Wang

MicroRNA-146a Feedback Inhibits RIG-I-Dependent Type I IFN Production in Macrophages by Targeting TRAF6, IRAK1, and IRAK2

Upon recognition of viral components by pattern recognition receptors, including TLRs and retinoic acid-inducible gene I (RIG-I)- like helicases, cells are activated to produce type I IFN and proinflammatory cytokines. These pathways are tightly regulated by host to prevent inappropriate cellular response, but viruses can down-regulate these pathways for their survival. Recently, identification of negative regulators for cytoplasmic RNA-mediated antiviral signaling, especially the RIG-I pathway, attract much attention. However, there is no report about negative regulation of RIG-I antiviral pathway by microRNAs (miRNA) to date. We found that vesicular stomatitis virus (VSV) infection up-regulated miR-146a expression in mouse macrophages in TLR-myeloid differentiation factor 88-independent but RIG-I-NF-κB-dependent manner. In turn, miR-146a negatively regulated VSV-triggered type I IFN production, thus promoting VSV replication in macrophages. In addition to two known miR-146a targets, TRAF6 and IRAK1, we proved that IRAK2 was another target of miR-146a, which also participated in VSV-induced type I IFN production. Furthermore, IRAK1 and IRAK2 participated in VSV-induced type I IFN production by associating with Fas-associated death domain protein, an important adaptor in RIG-I signaling, in a VSV infection-inducible manner. Therefore, we demonstrate that miR-146a, up-regulated during viral infection, is a negative regulator of the RIG-I-dependent antiviral pathway by targeting TRAF6, IRAK1, and IRAK2.

The STAT3-Binding Long Noncoding RNA lnc-DC Controls Human Dendritic Cell Differentiation

L[i]nc to Dendritic Cell Activation Long noncoding RNAs (lncRNAs) are important regulators of gene expression, but whether they are important regulators of the immune system is poorly understood. Wang et al. (p. 310) identify a lncRNA expressed exclusively in human dendritic cells (DC), called lnc-DC, that is required for optimal DC differentiation from human monocytes and that regulates DC activation of T cells. Lnc-DC interacts with the transcription factor STAT3, which is also required for DC development and function, to prevent interaction with and to block dephosphorylation by tyrosine phosphatase SHP1. A long noncoding RNA regulates dendritic cell differentiation and function. Long noncoding RNAs (lncRNAs) play important roles in diverse biological processes; however, few have been identified that regulate immune cell differentiation and function. Here, we identified lnc-DC, which was exclusively expressed in human conventional dendritic cells (DCs). Knockdown of lnc-DC impaired DC differentiation from human monocytes in vitro and from mouse bone marrow cells in vivo and reduced capacity of DCs to stimulate T cell activation. lnc-DC mediated these effects by activating the transcription factor STAT3 (signal transducer and activator of transcription 3). lnc-DC bound directly to STAT3 in the cytoplasm, which promoted STAT3 phosphorylation on tyrosine-705 by preventing STAT3 binding to and dephosphorylation by SHP1. Our work identifies a lncRNA that regulates DC differentiation and also broadens the known mechanisms of lncRNA action.

Inducible microRNA-155 Feedback Promotes Type I IFN Signaling in Antiviral Innate Immunity by Targeting Suppressor of Cytokine Signaling 1

Effective recognition of viral infection and subsequent triggering of antiviral innate immune responses are essential for the host antiviral defense, which is tightly regulated by multiple regulators, including microRNAs. Our previous study showed that a panel of microRNAs, including miR-155, was markedly upregulated in macrophages upon vesicular stomatitis virus infection; however, the biological function of miR-155 during viral infection remains unknown. In this paper, we show that RNA virus infection induces miR-155 expression in macrophages via TLR/MyD88-independent but retinoic acid-inducible gene I/JNK/NF-κB–dependent pathway. And the inducible miR-155 feedback promotes type I IFN signaling, thus suppressing viral replication. Furthermore, suppressor of cytokine signaling 1 (SOCS1), a canonical negative regulator of type I IFN signaling, is targeted by miR-155 in macrophages, and SOCS1 knockdown mediates the enhancing effect of miR-155 on type I IFN-mediated antiviral response. Therefore, we demonstrate that inducible miR-155 feedback positively regulates host antiviral innate immune response by promoting type I IFN signaling via targeting SOCS1.

MicroRNA-466l Upregulates IL-10 Expression in TLR-Triggered Macrophages by Antagonizing RNA-Binding Protein Tristetraprolin-Mediated IL-10 mRNA Degradation

MicroRNAs (miRNAs) are generally recognized as regulating gene expression posttranscriptionally by inhibiting translation or inducing target mRNA degradation. New mechanisms for miRNAs to regulate gene expression also still attract much attention. More and more novel miRNAs are discovered by the advanced sequencing technology, but yet their biological functions are largely unknown. Up to now, the function of miR-466l, a miRNA discovered in mouse embryonic stem cells, remains unclear. In this study, we report that miR-466l can upregulate both mRNA and protein expression of IL-10 in TLR-triggered macrophages. Furthermore, we show that miR-466l can competitively bind to the IL-10 3′ untranslated region AU-rich elements, which is a typical binding site for RNA-binding protein (RBP). Tristetraprolin is a well-known RBP, and mediates rapid degradation of IL-10 mRNA. miRNA always mediates target mRNA degradation or translation repression modestly; thus, the net effect of miR-466l’s binding to IL-10 AU-rich elements is to prevent IL-10 mRNA degradation mediated by tristetraprolin, resulting in extended t1/2 of IL-10 mRNA and elevated IL-10 expression. Thus, competitive binding with RBP to the same target mRNA and subsequent stabilization of target mRNA is an alternative mechanism for gene regulation by miRNAs. Also, a mechanism for regulation of IL-10 by miRNAs is outlined.

Identification of Resting and Type I IFN-Activated Human NK Cell miRNomes Reveals MicroRNA-378 and MicroRNA-30e as Negative Regulators of NK Cell Cytotoxicity

NK cells are important innate immune cells with potent cytotoxicity that can be activated by type I IFN from the host once infected. How NK cell cytotoxicity is activated by type I IFN and then tightly regulated remain to be fully elucidated. MicroRNAs (miRNAs, or miRs) are important regulators of innate immune response, but the full scale of miRNome in human NK cells remains to be determined. In this study, we reported an in-depth analysis of miRNomes in resting and IFN-α–activated human NK cells, found two abundant miRNAs, miR-378 and miR-30e, markedly decreased in activated NK cells by IFN-α, and further proved that miR-378 and miR-30e directly targeted granzyme B and perforin, respectively. Thus, IFN-α activation suppresses miR-378 and miR-30e expression to release cytolytic molecule mRNAs for their protein translation and then augments NK cell cytotoxicity. Importantly, the phenomena are also confirmed in human NK cells activated by other cytokines and even in the sorted CD16+CD56dimCD69+ human NK cell subset. Finally, miR-378 and miR-30e were proved to be suppressors of human NK cell cytotoxicity. Taken together, our results reveal that downregulated miR-378 and miR-30e during NK cell activation are negative regulators of human NK cell cytotoxicity, providing a mechanistic explanation for regulation of NK cell function by miRNAs.

Phosphatase PTP1B negatively regulates MyD88- and TRIF-dependent proinflammatory cytokine and type I interferon production in TLR-triggered macrophages.

Toll-like receptors (TLRs) are primary sensors to detect conserved patterns on microorganisms, thus acting as the important components of innate immunity against invading pathogens. Protein tyrosine phosphatase-1B (PTP1B) has been shown to be a critical negative regulator of insulin pathway and other cellular signaling, however, whether and how PTP1B regulates TLR-triggered innate response remain to be investigated. We report here that PTP1B can markedly decrease TNF-alpha, IL-6 and IFN-beta production by macrophages stimulated with LPS, CpG ODN, or Poly I:C. Accordingly, knockdown of endogenous PTP1B expression increases production of TNF-alpha, IL-6 and IFN-beta in macrophages stimulated with TLR ligands. Phosphatase activity-disrupted mutant PTP1B cannot inhibit TLR-triggered production of proinflammatory cytokines and IFN-beta, indicating PTP1B exerts its suppressive activity in phosphatase-dependent manner. PTP1B inhibits TLR ligands-induced activation of MAPKs, NF-kappaB, and IRF3, furthermore, co-transfection of PTP1B inhibits both MyD88- and TRIF-induced transcription of TNF-alpha and IFN-beta reporter genes in a dose-dependent manner. In addition, PTP1B inhibits LPS-induced Tyk2 and STAT1 activation. Therefore, we demonstrate that phosphatase PTP1B is a physiological negative regulator of TLR signaling via suppression of both MyD88- and TRIF-dependent production of proinflammatory cytokine and IFN-beta in macrophages. Our results provide new mechanistic explanation for negative regulation TLR response and suggest PTP1B as a potential target for the intervention of the inflammatory diseases.

Type I IFN Inhibits Innate IL-10 Production in Macrophages through Histone Deacetylase 11 by Downregulating MicroRNA-145

Innate immune responses must be tightly regulated to avoid overactivation and subsequent inflammatory damage to host tissue while eliminating invading pathogens. IL-10 is a crucial suppressor of inflammatory responses and its expression is under precise regulation involving complex regulatory networks and multiple feedback loops. MicroRNAs are now emerging as critical regulators in immune response. Our previous work showed that miR-143/145 cluster was markedly downregulated in macrophages upon vesicular stomatitis virus infection. However, the particular role of miR-143/145 cluster in the regulation of innate immune response remains unknown. In this study, we found that miR-143/145 cluster expression was also downregulated dramatically by TLR signals in macrophages, which was dependent on the subsequent type I IFN (IFN-I) production and downstream IFN-I receptor–JAK1–STAT1 signal cascade. Further studies demonstrated that miR-145, but not miR-143, promoted IL-10 expression in TLR4-triggered macrophages through directly targeting the epigenetic Il10 gene silencer histone deacetylase 11. Therefore, we demonstrate that miR-145, downregulated by IFN-I, targets histone deacetylase 11 to promote innate IL-10 expression in macrophages. Our findings suggest a new IFN-I–mediated negative feedback loop in the fine-tuning of innate IL-10 production that creates precise coordination of innate immune responses.

An interferon-independent lncRNA promotes viral replication by modulating cellular metabolism

Host RNA helps promote viral replication Viruses exploit host metabolic networks for survival. Wang et al. identified a long noncoding RNA (lncRNA) that enhances replication of multiple viruses in both mouse and human cells (see the Perspective by Kotzin et al). The expression of this cytoplasmic lncRNA was induced by viruses and independent of type I interferon. The lncRNA directly bound to and stimulated the metabolic enzyme glutamic-oxaloacetic transaminase. This viral strategy may have relevance for clinical diseases involving metabolic dysfunction and viral infection. Science, this issue p. 1051; see also p. 993 A virus-induced cytoplasmic long noncoding RNA enhances viral replication by regulating a host cell metabolic enzyme. Viruses regulate host metabolic networks to improve their survival. The molecules that are responsive to viral infection and regulate such metabolic changes are hardly known, but are essential for understanding viral infection. Here we identify a long noncoding RNA (lncRNA) that is induced by multiple viruses, but not by type I interferon (IFN-I), and facilitates viral replication in mouse and human cells. In vivo deficiency of lncRNA-ACOD1 (a lncRNA identified by its nearest coding gene Acod1, aconitate decarboxylase 1) significantly attenuates viral infection through IFN-I–IRF3 (interferon regulatory factor 3)–independent pathways. Cytoplasmic lncRNA-ACOD1 directly binds the metabolic enzyme glutamic-oxaloacetic transaminase (GOT2) near the substrate niche, enhancing its catalytic activity. Recombinant GOT2 protein and its metabolites could rescue viral replication upon lncRNA-ACOD1 deficiency and increase lethality. This work reveals a feedback mechanism of virus-induced lncRNA-mediated metabolic promotion of viral infection and a potential target for developing broad-acting antiviral therapeutics.

IFN-γ Primes Macrophage Activation by Increasing Phosphatase and Tensin Homolog via Downregulation of miR-3473b

The classical activation of macrophages, one of major innate effector cells, requires IFN-γ pretreatment (priming) and subsequent TLR stimuli (triggering). The priming effect of IFN-γ can promote macrophages to secrete higher level of proinflammatory cytokines but lower level of the anti-inflammatory cytokines, enhancing microbicidal and tumoricidal activity of macrophages. However, the underlying molecular mechanisms for IFN-γ–priming effect on macrophage activation remain to be fully understood. microRNAs (miRNAs) are now emerging as important regulators in immune response, including signaling transduction in immune cell function. In this study, we explored the effect of IFN-γ on miRNA expression profiling in macrophages and tried to identify the definite miRNA involved in the priming effect of IFN-γ. We discovered that miR-3473b, which was significantly downregulated after IFN-γ priming, could attenuate the priming effect of IFN-γ. miR-3473b promoted Akt/glycogen synthase kinase 3 signaling and IL-10 production through directly targeting phosphatase and tensin homolog (PTEN) to suppress activation of macrophages and inflammatory response. Our data indicate that IFN-γ beefs up macrophage innate response and cytotoxicity by downregulating miR-3473b to release PTEN from suppression, and then the increase of PTEN contributes to the full activation of IFN-γ–primed macrophages. Our results provide mechanistic insight to priming effect of IFN-γ on macrophage classical activation by identifying an IFN-γ/miR-3473b/PTEN regulatory loop in the regulation of macrophage function.