Interferon-stimulated transcription and innate antiviral immunity require deacetylase activity and histone deacetylase 1

Histone Deacetylase Inhibitors Promote the Anticancer Activity of Cisplatin: Mechanisms and Potential

Cisplatin is a widely used DNA-targeting anticancer drug. Histone deacetylase inhibitors (HDACi) cause histone hyperacetylation, changing chromatin structure and accessibility of genomic DNA by the genotoxic drug. As a consequence, HDACi could promote cisplatin cytotoxicity. Hence, the underlying mechanisms by which HDACi alter the action pathways of cisplatin to promote its anticancer activity have attracted increasing attention during the past decades. It has been commonly accepted that HDACi elevate the acetylation level of histones to release genomic DNA to cisplatin attack, increasing the level of cisplatin-induced DNA lesions to promote cisplatin cytotoxicity. However, how the HDACi-enhanced cisplatin lesion on DNA impacts the downstream biological processes, and whether the promotion of HDACi to cisplatin activity is attributed to their inherent anticancer activity or to their induced elevation of histone acetylation, have been in debate. Several studies showed that HDACi-enhanced DNA lesion could promote cisplatin-induced apoptosis, cell cycle arrest, and reactive oxygen species (ROS) generation, subsequently promoting cisplatin efficiency. In contrast, HDACi-induced elimination of ROS and inhibition of ferroptosis were thought to be the main ways by which HDACi protect kidneys from acute injury caused by cisplatin. Based on our recent research, we herein review and discuss the advances in research on the mechanisms of HDACi-induced enhancement in cisplatin cytotoxicity. Given that histone acetyltransferase (HAT) inhibitors also show an effect enhancing cisplatin cytotoxicity, we will discuss the diverse roles of histone acetylation in cancer therapy in addition to the synergistic anticancer effect and potential of HDACi with genotoxic drugs and radiotherapy.

Seneca Valley virus 3C protease cleaves HDAC4 to antagonize type I interferon signaling

Seneca Valley virus (SVV) is a newly identified pathogen that poses a notable threat to the global pig industry. SVV has evolved multiple strategies to evade host antiviral innate immune responses. However, the underlying molecular mechanisms have not yet been fully elucidated. Histone deacetylases (HDACs) have been shown to function as host antiviral innate immune factors. In this study, we examined the mechanisms underlying SVV evasion of host innate immunity and found that SVV infection induced degradation and cleavage of HDAC4. Ectopic expression of HDAC4 suppressed SVV replication, whereas siRNA-mediated knockdown of HDAC4 enhanced SVV replication. Further studies showed that the viral 3C protease (3Cpro) degraded HDAC4 in a protease activity- and caspase pathway-dependent manner. In addition, 3Cpro cleaved HDAC4 at Q599, which blocked its ability to limit viral replication. We also found that HDAC4 interacted with the SVV viral RNA-dependent RNA polymerase 3D and induced its proteasomal degradation. The cleaved HDAC4 products did not block SVV replication or induce 3D degradation and did not induce type I interferon (IFN) activation and expression of IFN-stimulated genes (ISGs). Collectively, these findings identified HDAC4 as an antiviral factor with effects against SVV infection and provided mechanistic insights into how SVV 3Cpro antagonizes its function, which has implications for viral evasion of innate immunity.

IMPORTANCE

Seneca Valley virus (SVV) is an emerging pathogen that causes vesicular disease in pigs and poses a threat to the pork industry. Histone deacetylases (HDACs) are important in the regulation of innate immunity. However, little is known about their roles in SVV infection. Our results revealed HDAC4 as an anti-SVV infection factor that targets the viral RNA-dependent RNA polymerase, 3D, for degradation. The SVV proteinase 3Cpro targets HDAC4 for degradation and cleavage, and cleavage of HDAC4 abrogated its antiviral effect. HDAC4 promotes type I interferon (IFN) signaling, and SVV 3Cpro-mediated cleavage of HDAC4 antagonized induction of type I IFN and interferon-stimulated genes (ISGs). Our findings reveal a novel molecular mechanism by which SVV 3Cpro counteracts type I IFN signaling by targeting HDAC4.

Butyrate: A potential mediator of obesity and microbiome via different mechanisms of actions

Butyrate, a short-chain fatty acid, is a crucial product of gut microbial fermentation with significant implications for various metabolic and physiological processes. Dietary sources of butyrate are limited, primarily derived from the fermentation of dietary fibers by butyrate-producing gut bacteria. Butyrate exerts its effects primarily as a histone deacetylase (HDAC) inhibitor and through signaling pathways involving G protein-coupled receptors (GPCRs). Its diverse benefits include promoting gut health, enhancing energy metabolism, and potentially alleviating complications associated with obesity. However, the exact role of butyrate in obesity is still under investigation, with a limited number of human trials necessitating further research to determine its efficacy and safety profile. Moreover, butyrate impact on the gut-brain axis and its modulation of microbiome effect on behavior highlight its broader importance in regulating host physiology. A thorough understanding of the metabolic pathways and mechanisms of butyrate is essential for developing targeted interventions for metabolic disorders. Continued research is crucial to fully realize its therapeutic potential and optimize its clinical applications in human health. In summary, this review illuminates the multifaceted role of butyrate as a potential mediator of obesity and related metabolic changes.

Macrophage iron dyshomeostasis promotes aging-related renal fibrosis

Renal aging, marked by the accumulation of senescent cells and chronic low-grade inflammation, leads to renal interstitial fibrosis and impaired function. In this study, we investigate the role of macrophages, a key regulator of inflammation, in renal aging by analyzing kidney single-cell RNA sequencing data of C57BL/6J mice from 8 weeks to 24 months. Our findings elucidate the dynamic changes in the proportion of kidney cell types during renal aging and reveal that increased macrophage infiltration contributes to chronic low-grade inflammation, with these macrophages exhibiting senescence and activation of ferroptosis signaling. CellChat analysis indicates enhanced communications between macrophages and tubular cells during aging. Suppressing ferroptosis alleviates macrophage-mediated tubular partial epithelial-mesenchymal transition in vitro, thereby mitigating the expression of fibrosis-related genes. Using SCENIC analysis, we infer Stat1 as a key age-related transcription factor promoting iron dyshomeostasis and ferroptosis in macrophages by regulating the expression of Pcbp1, an iron chaperone protein that inhibits ferroptosis. Furthermore, through virtual screening and molecular docking from a library of anti-aging compounds, we construct a docking model targeting Pcbp1, which indicates that the natural small molecule compound Rutin can suppress macrophage senescence and ferroptosis by preserving Pcbp1. In summary, our study underscores the crucial role of macrophage iron dyshomeostasis and ferroptosis in renal aging. Our results also suggest Pcbp1 as an intervention target in aging-related renal fibrosis and highlight Rutin as a potential therapeutic agent in mitigating age-related renal chronic low-grade inflammation and fibrosis.

Transcriptional control of interferon-stimulated genes

Interferon-induced genes are among the best-studied groups of coregulated genes. Nevertheless, intense research into their regulation, supported by new technologies, is continuing to provide insights into their many layers of transcriptional regulation and to reveal how cellular transcriptomes change with pathogen-induced innate and adaptive immunity. This article gives an overview of recent findings on interferon-induced gene regulation, paying attention to contributions beyond the canonical JAK-STAT pathways.

Saikosaponin A Recovers Impaired Filaggrin Levels in Inflamed Skin by Downregulating the Expression of FRA1 and c-Jun

Filaggrin (FLG) is an essential structural protein expressed in differentiated keratinocytes. Insufficient FLG expression contributes to the pathogenesis of chronic inflammatory skin diseases. Saikosaponin A (SSA), a bioactive oleanane-type triterpenoid, exerts anti-inflammatory activity. However, the effects of topically applied SSA on FLG expression in inflamed skin remain unclear. This study aimed to evaluate the biological activity of SSA in restoring reduced FLG expression. The effect of SSA on FLG expression in HaCaT cells was assessed through various biological methods, including reverse transcription PCR, quantitative real-time PCR, immunoblotting, and immunofluorescence staining. TNFα and IFNγ decreased FLG mRNA, cytoplasmic FLG protein levels, and FLG gene promoter-reporter activity compared to the control groups. However, the presence of SSA restored these effects. A series of FLG promoter-reporter constructs were generated to investigate the underlying mechanism of the effect of SSA on FLG expression. Mutation of the AP1-binding site (mtAP1) in the -343/+25 FLG promoter-reporter abrogated the decrease in reporter activities caused by TNFα + IFNγ, suggesting the importance of the AP1-binding site in reducing FLG expression. The SSA treatment restored FLG expression by inhibiting the expression and nuclear localization of FRA1 and c-Jun, components of AP1, triggered by TNFα + IFNγ stimulation. The ERK1/2 mitogen-activated protein kinase signaling pathway upregulates FRA1 and c-Jun expression, thereby reducing FLG levels. The SSA treatment inhibited ERK1/2 activation caused by TNFα + IFNγ stimulation and reduced the levels of FRA1 and c-Jun proteins in the nucleus, leading to a decrease in the binding of FRA1, c-Jun, p-STAT1, and HDAC1 to the AP1-binding site in the FLG promoter. The effect of SSA was evaluated in an animal study using a BALB/c mouse model, which induces human atopic-dermatitis-like skin lesions via the topical application of dinitrochlorobenzene. Topically applied SSA significantly reduced skin thickening, immune cell infiltration, and the expression of FRA1, c-Jun, and p-ERK1/2 compared to the vehicle-treated group. These results suggest that SSA can effectively recover impaired FLG levels in inflamed skin by preventing the formation of the repressor complex consisting of FRA1, c-Jun, HDAC1, and STAT1.

Romidepsin and Afatinib Abrogate Jak-Signal Transducer and Activator of Transcription Signaling and Elicit Synergistic Antitumor Effects in Cutaneous T-Cell Lymphoma

Cutaneous T-cell lymphomas are mature lymphoid neoplasias resulting from the malignant transformation of skin-resident T-cells. A distinctive clinical feature of cutaneous T-cell lymphomas is their sensitivity to treatment with histone deacetylase inhibitors. However, responses to histone deacetylase inhibitor therapy are universally transient and noncurative, highlighting the need for effective and durable drug combinations. In this study, we demonstrate that the combination of romidepsin, a selective class I histone deacetylase inhibitor, with afatinib, an EGFR family inhibitor, induces strongly synergistic antitumor effects in cutaneous T-cell lymphoma models in vitro and in vivo through abrogation of Jak-signal transducer and activator of transcription signaling. These results support a previously unrecognized potential role for histone deacetylase inhibitor plus afatinib combination in the treatment of cutaneous T-cell lymphomas.

JAK-STAT signaling maintains homeostasis in T cells and macrophages

Immune cells need to sustain a state of constant alertness over a lifetime. Yet, little is known about the regulatory processes that control the fluent and fragile balance that is called homeostasis. Here we demonstrate that JAK-STAT signaling, beyond its role in immune responses, is a major regulator of immune cell homeostasis. We investigated JAK-STAT-mediated transcription and chromatin accessibility across 12 mouse models, including knockouts of all STAT transcription factors and of the TYK2 kinase. Baseline JAK-STAT signaling was detected in CD8+ T cells and macrophages of unperturbed mice-but abrogated in the knockouts and in unstimulated immune cells deprived of their normal tissue context. We observed diverse gene-regulatory programs, including effects of STAT2 and IRF9 that were independent of STAT1. In summary, our large-scale dataset and integrative analysis of JAK-STAT mutant and wild-type mice uncovered a crucial role of JAK-STAT signaling in unstimulated immune cells, where it contributes to a poised epigenetic and transcriptional state and helps prepare these cells for rapid response to immune stimuli.

Design, Synthesis, and Structure-Activity Relationship of Novel Pyridazinone-Based PARP7/HDACs Dual Inhibitors for Elucidating the Relationship between Antitumor Immunity and HDACs Inhibition

Histone deacetylases (HDACs) inhibitors such as vorinostat (SAHA) has been used to treat hematologic malignancies (rather than solid tumors) and have been found to suppress the JAK/STAT, a critical signal pathway for antitumor immunity, while PARP7 inhibitor RBN-2397 could activate the type I interferons (IFN-I) pathway, facilitating downstream effects such as STAT1 phosphorylation and immune activation. To elucidate whether simultaneous inhibition of these two targets could interfere with these two signal pathways, a series of pyridazinone-based PARP7/HDACs dual inhibitors have been designed, synthesized, and evaluated in vitro and in vivo experiments. Compound 9l was identified as a potent and balanced dual inhibitor for the first time, exhibiting excellent antitumor capabilities both in vitro and in vivo. This suggests that 9l can be used as a valuable tool molecule for investigating the relationship between anticancer immunity and HDAC inhibition.

Mechanisms of mesothelial cell response to viral infections: HDAC1-3 inhibition blocks poly(I:C)-induced type I interferon response and modulates the mesenchymal/inflammatory phenotype

Infectious peritonitis is a leading cause of peritoneal functional impairment and a primary factor for therapy discontinuation in peritoneal dialysis (PD) patients. Although bacterial infections are a common cause of peritonitis episodes, emerging evidence suggests a role for viral pathogens. Toll-like receptors (TLRs) specifically recognize conserved pathogen-associated molecular patterns (PAMPs) from bacteria, viruses, and fungi, thereby orchestrating the ensuing inflammatory/immune responses. Among TLRs, TLR3 recognizes viral dsRNA and triggers antiviral response cascades upon activation. Epigenetic regulation, mediated by histone deacetylase (HDAC), has been demonstrated to control several cellular functions in response to various extracellular stimuli. Employing epigenetic target modulators, such as epidrugs, is a current therapeutic option in several cancers and holds promise in treating viral diseases. This study aims to elucidate the impact of TLR3 stimulation on the plasticity of human mesothelial cells (MCs) in PD patients and to investigate the effects of HDAC1-3 inhibition. Treatment of MCs from PD patients with the TLR3 agonist polyinosinic:polycytidylic acid (Poly(I:C)), led to the acquisition of a bona fide mesothelial-to-mesenchymal transition (MMT) characterized by the upregulation of mesenchymal genes and loss of epithelial-like features. Moreover, Poly(I:C) modulated the expression of several inflammatory cytokines and chemokines. A quantitative proteomic analysis of MCs treated with MS-275, an HDAC1-3 inhibitor, unveiled altered expression of several proteins, including inflammatory cytokines/chemokines and interferon-stimulated genes (ISGs). Treatment with MS-275 facilitated MMT reversal and inhibited the interferon signature, which was associated with reduced STAT1 phosphorylation. However, the modulation of inflammatory cytokine/chemokine production was not univocal, as IL-6 and CXCL8 were augmented while TNF-α and CXCL10 were decreased. Collectively, our findings underline the significance of viral infections in acquiring a mesenchymal-like phenotype by MCs and the potential consequences of virus-associated peritonitis episodes for PD patients. The observed promotion of MMT reversal and interferon response inhibition by an HDAC1-3 inhibitor, albeit without a general impact on inflammatory cytokine production, has translational implications deserving further analysis.

Gut microbiota-derived butyrate promotes coronavirus TGEV infection through impairing RIG-I-triggered local type I interferon responses via class I HDAC inhibition

Gut microbiota-derived metabolites are important for the replication and pathogenesis of many viruses. However, the roles of bacterial metabolites in swine enteric coronavirus (SECoV) infection remain poorly understood. Recent studies show that SECoVs infection in vivo significantly alters the composition of short-chain fatty acids (SCFAs)-producing gut microbiota. This prompted us to investigate whether and how SCFAs impact SECoV infection. Employing alphacoronavirus transmissible gastroenteritis virus (TGEV), a major cause of diarrhea in piglets, as a model, we found that SCFAs, particularly butyrate, enhanced TGEV infection both in porcine intestinal epithelial cells and swine testicular (ST) cells at the late stage of viral infection. This effect depended on the inhibited productions of virus-induced type I interferon (IFN) and downstream antiviral IFN-stimulated genes (ISGs) by butyrate. Mechanistically, butyrate suppressed the expression of retinoic acid-inducible gene I (RIG-I), a key viral RNA sensor, and downstream mitochondrial antiviral-signaling (MAVS) aggregation, thereby impairing type I IFN responses and increasing TGEV replication. Using pharmacological and genetic approaches, we showed that butyrate inhibited RIG-I-induced type I IFN signaling by suppressing class I histone deacetylase (HDAC). In summary, we identified a novel mechanism where butyrate enhances TGEV infection by suppressing RIG-I-mediated type I IFN responses. Our findings highlight that gut microbiota-derived metabolites like butyrate can be exploited by SECoV to dampen innate antiviral immunity and establish infection in the intestine.IMPORTANCESwine enteric coronaviruses (SECoVs) infection in vivo alters the composition of short-chain fatty acids (SCFAs)-producing gut microbiota, but whether microbiota-derived SCFAs impact coronavirus gastrointestinal infection is largely unknown. Here, we demonstrated that SCFAs, particularly butyrate, substantially increased alphacoronavirus TGEV infection at the late stage of infection, without affecting viral attachment or internalization. Furthermore, enhancement of TGEV by butyrate depended on impeding virus-induced type I interferon (IFN) responses. Mechanistically, butyrate suppressed the cytoplasmic viral RNA sensor RIG-I expression and downstream type I IFN signaling activation by inhibiting class I HDAC, thereby promoting TGEV infection. Our work reveals novel functions of gut microbiota-derived SCFAs in enhancing enteric coronavirus infection by impairing RIG-I-dependent type I IFN responses. This implies that bacterial metabolites could be therapeutic targets against SECoV infection by modulating antiviral immunity in the intestine.

Histone deacetylase inhibitor boosts anticancer potential of fusogenic oncolytic vaccinia virus by enhancing cell-cell fusion

Oncolytic viruses have two anticancer functions: direct oncolysis and elicitation of antitumor immunity. We previously developed a novel fusogenic oncolytic vaccinia virus (FUVAC) from a non-fusogenic vaccinia virus (VV) and, by remodeling the tumor immune microenvironment, we demonstrated that FUVAC induced stronger oncolysis and antitumor immune responses compared with non-fusogenic VV. These functions depend strongly on cell-cell fusion induction. However, FUVAC tends to have decreased fusion activity in cells with low virus replication efficacy. Therefore, another combination strategy was required to increase cell-cell fusion in these cells. Histone deacetylase (HDAC) inhibitors suppress the host virus defense response and promote viral replication. Therefore, in this study, we selected an HDAC inhibitor, trichostatin A (TSA), as the combination agent for FUVAC to enhance its fusion-based antitumor potential. TSA was added prior to FUVAC treatment of murine tumor B16-F10 and CT26 cells. TSA increased the replication of both FUVAC and parental non-fusogenic VV. Moreover, TSA enhanced cell-cell fusion and FUVAC cytotoxicity in these tumor cells in a dose-dependent manner. Transcriptome analysis revealed that TSA-treated tumors showed altered expression of cellular component-related genes, which may affect fusion tolerance. In a bilateral tumor-bearing mouse model, combination treatment of TSA and FUVAC significantly prolonged mouse survival compared with either treatment alone or in combination with non-fusogenic VV. Our findings demonstrate that TSA is a potent enhancer of cell-cell fusion efficacy of FUVAC.

Identification of new candidate drugs for primary Sjögren's syndrome using a drug repurposing transcriptomic approach

OBJECTIVES

To date, no immunomodulatory drug has demonstrated its efficacy in primary SS (pSS). We sought to analyse potential commonalities between pSS transcriptomic signatures and signatures of various drugs or specific knock-in or knock-down genes.

METHODS

Gene expression from peripheral blood samples of patients with pSS was compared with that of healthy controls in two cohorts and three public databases. In each of the five datasets, we analysed the 150 most up- and downregulated genes between pSS patients and controls with regard to the differentially expressed genes resulting from the biological action on nine cell lines of 2837 drugs, 2160 knock-in and 3799 knock-down genes in the Connectivity Map database.

RESULTS

We analysed 1008 peripheral blood transcriptomes from five independent studies (868 patients with pSS and 140 healthy controls). Eleven drugs could represent potential candidate drugs, with histone deacetylases and PI3K inhibitors among the most significantly associated. Twelve knock-in genes were associated with a pSS-like profile and 23 knock-down genes were associated with a pSS-revert profile. Most of those genes (28/35, 80%) were interferon-regulated.

CONCLUSION

This first drug repositioning transcriptomic approach in SS confirms the interest of targeting interferons and identifies histone deacetylases and PI3K inhibitors as potential therapeutic targets.

N-terminal domain of classical swine fever virus Npro induces proteasomal degradation of specificity protein 1 with reduced HDAC1 expression to evade from innate immune responses

IMPORTANCE

Of the flaviviruses, only CSFV and bovine viral diarrhea virus express Npro as the non-structural protein which is not essential for viral replication but functions to dampen host innate immunity. We have deciphered a novel mechanism with which CSFV uses to evade the host antiviral immunity by the N-terminal domain of its Npro to facilitate proteasomal degradation of Sp1 with subsequent reduction of HDAC1 and ISG15 expression. This is distinct from earlier findings involving Npro-mediated IRF3 degradation via the C-terminal domain. This study provides insights for further studies on how HDAC1 plays its role in antiviral immunity, and if and how other viral proteins, such as the core protein of CSFV, the nucleocapsid protein of porcine epidemic diarrhea virus, or even other coronaviruses, exert antiviral immune responses via the Sp1-HDAC1 axis. Such research may lead to a deeper understanding of viral immune evasion strategies as part of their pathogenetic mechanisms.

Epigenetic reprogramming around IFN1 and IFNy2 promoters in rainbow trout cells inoculated with infectious pancreatic necrosis virus (IPNV)

Infectious pancreatic necrosis virus (IPNV) has proven to effectively evade the host antiviral responses. This study clarifies whether the modulation of the antiviral immune response exerted by IPNV involves epigenetic mechanisms. An in-silico characterization of the rainbow trout IFN1 and IFNγ2 promoters was performed, identifying the islands or sequences rich in CpG dinucleotides and the putative transcription factor binding sites (TBS) for both gene promoters. RTS11 cells (rainbow trout monocyte/macrophage) were infected with IPNV, and the course of viral infection was followed up to 48 h post infection (hpi). Infected cells showed increased IFN1 and IFNγ2 transcriptional expression at 6 and 24 hpi, respectively. IPNV infection caused increases and decreases in global IFNγ2 promoter methylation at 6 and 24 hpi, respectively. The CpG dinucleotides at positions -392 and + 38 of this promoter were the most sensitive to methylation changes. The IFN1 promoter remained fully unmethylated during the course of the infection, similar to the control. The changes in the methylation pattern observed for the IFNγ2 promoter were coincident with the changes in DNA methyltransferase (DNMT) expression levels, increasing at 6 hpi and decreasing below basal level at 24 hpi. Similarly, the H4 histones associated with the IFN1 and IFNγ2 promoters were hyperacetylated at 6 hpi, subsequently decreasing their acetylation below basal levels at 24 hpi, in both promoters. Coincidentally with the above, overexpression of histone acetyltransferase (HAT) was observed at 6 hpi and of histone deacetylase (HDAC) at 24 hpi, with return to baseline of HAT. These results suggest that IPNV would epigenetically modulate the expression of IFN1 by changing acetylation levels of the histones H4 associated with its promoter. Also, the modulation of the expression of IFNy2 would be by switching methylation/demethylation levels of its promoter, in addition to changes in acetylation levels of histones H4 associated with this promoter. This study is the first to demonstrate the effect of epigenetic reprogramming after IPNV infection in salmonid cells, demonstrating that promoter methylation/demethylation level and changes in the histone code associated with promoters may play a role in the modulation of the immune response induced by the virus.

The HDAC inhibitor domatinostat induces type I interferon α in Merkel cell carcinoma by HES1 repression

BACKGROUND

Class I selective histone deacetylase inhibitors (HDACi) have been previously demonstrated to not only increase major histocompatibility complex class I surface expression in Merkel cell carcinoma (MCC) cells by restoring the antigen processing and presentation machinery, but also exert anti-tumoral effect by inducing apoptosis. Both phenomena could be due to induction of type I interferons (IFN), as has been described for HDACi. However, the mechanism of IFN induction under HDACi is not fully understood because the expression of IFNs is regulated by both activating and inhibitory signaling pathways. Our own preliminary observations suggest that this may be caused by suppression of HES1.

METHODS

The effect of the class I selective HDACi domatinostat and IFNα on cell viability and the apoptosis of MCPyV-positive (WaGa, MKL-1) and -negative (UM-MCC 34) MCC cell lines, as well as, primary fibroblasts were assessed by colorimetric methods or measuring mitochondrial membrane potential and intracellular caspase-3/7, respectively. Next, the impact of domatinostat on IFNA and HES1 mRNA expression was measured by RT-qPCR; intracellular IFNα production was detected by flow cytometry. To confirm that the expression of IFNα induced by HDACi was due to the suppression of HES1, it was silenced by RNA interference and then mRNA expression of IFNA and IFN-stimulated genes was assessed.

RESULTS

Our studies show that the previously reported reduction in viability of MCC cell lines after inhibition of HDAC by domatinostat is accompanied by an increase in IFNα expression, both of mRNA and at the protein level. We confirmed that treatment of MCC cells with external IFNα inhibited their proliferation and induced apoptosis. Re-analysis of existing single-cell RNA sequencing data indicated that induction of IFNα by domatinostat occurs through repression of HES1, a transcriptional inhibitor of IFNA; this was confirmed by RT-qPCR. Finally, siRNA-mediated silencing of HES1 in the MCC cell line WaGa not only increased mRNA expression of IFNA and IFN-stimulated genes but also decreased cell viability.

CONCLUSION

Our results demonstrate that the direct anti-tumor effect of HDACi domatinostat on MCC cells is at least in part mediated via decreased HES1 expression allowing the induction of IFNα, which in turn causes apoptosis.

Epigenetic signals that direct cell type-specific interferon beta response in mouse cells

The antiviral response induced by type I interferon (IFN) via the JAK-STAT signaling cascade activates hundreds of IFN-stimulated genes (ISGs) across human and mouse tissues but varies between cell types. However, the links between the underlying epigenetic features and the ISG profile are not well understood. We mapped ISGs, binding sites of the STAT1 and STAT2 transcription factors, chromatin accessibility, and histone H3 lysine modification by acetylation (ac) and mono-/tri-methylation (me1, me3) in mouse embryonic stem cells and fibroblasts before and after IFNβ treatment. A large fraction of ISGs and STAT-binding sites was cell type specific with promoter binding of a STAT1/2 complex being a key driver of ISGs. Furthermore, STAT1/2 binding to putative enhancers induced ISGs as inferred from a chromatin co-accessibility analysis. STAT1/2 binding was dependent on the chromatin context and positively correlated with preexisting H3K4me1 and H3K27ac marks in an open chromatin state, whereas the presence of H3K27me3 had an inhibitory effect. Thus, chromatin features present before stimulation represent an additional regulatory layer for the cell type-specific antiviral response.

Analysis of microbiota-host communication mediated by butyrate in Atlantic Salmon

Butyrate is a microbiota-produced metabolite, sensed by host short-chain fatty acid receptors FFAR2 (Gpr43), FFAR3 (Gpr41), HCAR2 (Gpr109A), and Histone deacetylase (HDAC) that promotes microbiota-host crosstalk. Butyrate influences energy uptake, developmental and immune response in mammals. This microbial metabolite is produced by around 79 anaerobic genera present in the mammalian gut, yet little is known about the role of butyrate in the host-microbiota interaction in salmonid fish. To further our knowledge of this interaction, we analyzed the intestinal microbiota and genome of Atlantic salmon (Salmo salar), searching for butyrate-producing genera and host butyrate receptors. We identified Firmicutes, Proteobacteria, and Actinobacteria as the main butyrate-producing bacteria in the salmon gut microbiota. In the Atlantic salmon genome, we identified an expansion of genes orthologous to FFAR2 and HCAR2 receptors, and class I and IIa HDACs that are sensitive to butyrate. In addition, we determined the expression levels of orthologous of HCAR2 in the gut, spleen, and head-kidney, and FFAR2 in RTgutGC cells. The effect of butyrate on the Atlantic salmon immune response was evaluated by analyzing the pro and anti-inflammatory cytokines response in vitro in SHK-1 cells by RT-qPCR. Butyrate decreased the expression of the pro-inflammatory cytokine IL-1β and increased anti-inflammatory IL-10 and TGF-β cytokines. Butyrate also reduced the expression of interferon-alpha, Mx, and PKR, and decreased the viral load at a higher concentration (4 mM) in cells treated with this molecule before the infection with Infectious Pancreatic Necrosis Virus (IPNV) by mechanisms independent of FFAR2, FFAR3 and HCAR2 expression that probably inhibit HDAC. Moreover, butyrate modified phosphorylation of cytoplasmic proteins in RTgutGC cells. Our data allow us to infer that Atlantic salmon have the ability to sense butyrate produced by their gut microbiota via different specific targets, through which butyrate modulates the immune response of pro and anti-inflammatory cytokines and the antiviral response.

Synergistic efficacy of telomerase-specific oncolytic adenoviral therapy and histone deacetylase inhibition in human hepatocellular carcinoma

The telomerase-specific oncolytic adenovirus Telomelysin and the histone deacetylase inhibitor AR42 have demonstrated anticancer effects in preclinical models of human hepatocellular carcinoma (HCC). However, the clinical development of Telomelysin may be hindered by human antiviral immunity and tumor resistance. Combining oncolytic and epigenetic therapies is a viable approach for treating various cancers. This study investigated the potential synergism of Telomelysin and AR42 and the relevant underlying mechanisms. Telomelysin and AR42 exhibited synergistic antiproliferative effects in human HCC models in vitro and in vivo. Apoptosis induced by Telomelysin was significantly enhanced by AR42 in both PLC5 and Hep3B HCC cells. AR42 treatment unexpectedly attenuated the expression of the coxsackievirus and adenovirus receptor and the mRNA levels of human telomerase reverse transcriptase, which may be positively associated with the cytotoxicity of Telomelysin. Meanwhile, the cellular antiviral interferon response was not altered by AR42 treatment. Further, we found that Telomelysin enhanced Akt phosphorylation in HCC cells. AR42 reduced Telomelysin-induced phospho-Akt activation and enhanced Telomelysin-induced apoptosis. The correlation of Akt phosphorylation with drug-induced apoptosis was validated in HCC cells with upregulated or downregulated Akt signaling. Combination therapy with Telomelysin and AR42 demonstrated synergistic anti-HCC efficacy. Clinical trials investigating this new combination regimen are warranted.

The main protease of SARS-CoV-2 cleaves histone deacetylases and DCP1A, attenuating the immune defense of the interferon-stimulated genes

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), which causes coronavirus disease 2019, constitutes an emerging human pathogen of zoonotic origin. A critical role in protecting the host against invading pathogens is carried out by interferon-stimulated genes (ISGs), the primary effectors of the type I interferon (IFN) response. All coronaviruses studied thus far have to first overcome the inhibitory effects of the IFN/ISG system before establishing efficient viral replication. However, whether SARS-CoV-2 evades IFN antiviral immunity by manipulating ISG activation remains to be elucidated. Here, we show that the SARS-CoV-2 main protease (M^pro) significantly suppresses the expression and transcription of downstream ISGs driven by IFN-stimulated response elements in a dose-dependent manner, and similar negative regulations were observed in two mammalian epithelial cell lines (simian Vero E6 and human A549). Our analysis shows that to inhibit the ISG production, M^pro cleaves histone deacetylases (HDACs) rather than directly targeting IFN signal transducers. Interestingly, M^pro also abolishes the activity of ISG effector mRNA-decapping enzyme 1a (DCP1A) by cleaving it at residue Q343. In addition, M^pro from different genera of coronaviruses has the protease activity to cleave both HDAC2 and DCP1A, even though the alphacoronaviruse M^pro exhibits weaker catalytic activity in cleaving HDAC2. In conclusion, our findings clearly demonstrate that SARS-CoV-2 M^pro constitutes a critical anti-immune effector that modulates the IFN/ISG system at multiple levels, thus providing a novel molecular explanation for viral immune evasion and allowing for new therapeutic approaches against coronavirus disease 2019 infection.

African swine fever virus pA104R protein acts as a suppressor of type I interferon signaling

This study evaluates the role of the late viral protein, pA104R, in African swine fever virus immunosuppression. ASFV-encoded pA104R is a putative histone-like protein that is highly conserved throughout different virulent and non-virulent isolates. Previous studies have demonstrated that pA104R plays a vital role in the ASFV replication cycle and is a potential target for antiviral therapy. Here, we demonstrated that pA104R is a potent antagonist of type I interferon signaling. IFN-stimulated response element activity and subsequent transcription of co-transfected and endogenous interferon-stimulated genes were attenuated by pA104R treatment in HEK-293 T cells. Immunoprecipitation assay and reciprocal pull-down showed that pA104R does not interact directly with STAT1, STAT2, or IRF9. However, pA104R could inhibit IFN signaling by attenuating STAT1 phosphorylation, and we identified the critical amino acid residues (R/H69,72 and K/R92,94,97) involved through the targeted mutation functional assays. Although pA104R is a histone-like protein localized to the nucleus, it did not inhibit IFN signaling through its DNA-binding capacity. In addition, activation of the ISRE promoter by IRF9-Stat2(TA), a STAT1-independent pathway, was inhibited by pA104R. Further results revealed that both the transcriptional activation and recruitment of transcriptional stimulators by interferon-stimulated gene factor 3 were not impaired. Although we failed to determine a mechanism for pA104R-mediated IFN signaling inhibition other than attenuating the phosphorylation of STAT1, these results might imply a possible involvement of epigenetic modification by ASFV pA104R. Taken together, these findings support that pA104R is an antagonist of type I interferon signaling, which may interfere with multiple signaling pathways.

The JAK-STAT pathway at 30: Much learned, much more to do

The discovery of the Janus kinase (JAK)-signal transducer and activator of transcription (STAT) pathway arose from investigations of how cells respond to interferons (IFNs), revealing a paradigm in cell signaling conserved from slime molds to mammals. These discoveries revealed mechanisms underlying rapid gene expression mediated by a wide variety of extracellular polypeptides including cytokines, interleukins, and related factors. This knowledge has provided numerous insights into human disease, from immune deficiencies to cancer, and was rapidly translated to new drugs for autoimmune, allergic, and infectious diseases, including COVID-19. Despite these advances, major challenges and opportunities remain.

FRA1:c-JUN:HDAC1 complex down-regulates filaggrin expression upon TNFα and IFNγ stimulation in keratinocytes

Filaggrin (FLG), an essential structural protein for skin barrier function, is down-regulated under chronic inflammatory conditions, leading to disruption of the skin barrier. However, the detailed molecular mechanisms of how FLG changes in the context of chronic inflammation are poorly understood. Here, we identified the molecular mechanisms by which inflammatory cytokines inhibit FLG expression in the skin. We found that the AP1 response element within the -343/+25 of the FLG promoter was necessary for TNFα + IFNγ-induced down-regulation of FLG promoter activity. Using DNA affinity precipitation assay, we observed that AP1 subunit composition binding to the FLG promoter was altered from c-FOS:c-JUN (at the early time) to FRA1:c-JUN (at the late time) in response to TNFα + IFNγ stimulation. Knockdown of FRA1 or c-JUN abrogated TNFα + IFNγ-induced FLG suppression. Histone deacetylase (HDAC) 1 interacted with FRA1:c-JUN under TNFα + IFNγ stimulation. Knockdown of HDAC1 abrogated the inhibitory effect of TNFα + IFNγ on FLG expression. The altered expression of FLG, FRA1, c-JUN, and HDAC1 was confirmed in mouse models of 2,4-dinitrochlorobenzene-induced atopic dermatitis and imiquimod-induced psoriasis. Thus, the current study demonstrates that TNFα + IFNγ stimulation suppresses FLG expression by promoting the FRA1:c-JUN:HDAC1 complex. This study provides insight into future therapeutic strategies targeting the FRA1:c-JUN:HDAC1 complex to restore impaired FLG expression in chronic skin inflammation.

Porcine Deltacoronavirus Infection Cleaves HDAC2 to Attenuate Its Antiviral Activity

Protein acetylation plays an important role during virus infection. Thus, it is not surprising that viruses always evolve elaborate mechanisms to regulate the functions of histone deacetylases (HDACs), the essential transcriptional and epigenetic regulators for deacetylation. Porcine deltacoronavirus (PDCoV), an emerging enteropathogenic coronavirus, causes severe diarrhea in suckling piglets and has the potential to infect humans. In this study, we found that PDCoV infection inhibited cellular HDAC activity. By screening the expressions of different HDAC subfamilies after PDCoV infection, we unexpectedly found that HDAC2 was cleaved. Ectopic expression of HDAC2 significantly inhibited PDCoV replication, while the reverse effects could be observed after treatment with an HDAC2 inhibitor (CAY10683) or the knockdown of HDAC2 expression by specific siRNA. Furthermore, we demonstrated that PDCoV-encoded nonstructural protein 5 (nsp5), a 3C-like protease, was responsible for HDAC2 cleavage through its protease activity. Detailed analyses showed that PDCoV nsp5 cleaved HDAC2 at glutamine 261 (Q261), and the cleaved fragments (amino acids 1 to 261 and 262 to 488) lost the ability to inhibit PDCoV replication. Interestingly, the Q261 cleavage site is highly conserved in HDAC2 homologs from other mammalian species, and the nsp5s encoded by seven tested mammalian coronaviruses also cleaved HDAC2, suggesting that cleaving HDAC2 may be a common strategy used by different mammalian coronaviruses to antagonize the antiviral role of HDAC2. IMPORTANCE As an emerging porcine enteropathogenic coronavirus that possesses the potential to infect humans, porcine deltacoronavirus (PDCoV) is receiving increasing attention. In this work, we found that PDCoV infection downregulated cellular histone deacetylase (HDAC) activity. Of particular interest, the viral 3C-like protease, encoded by the PDCoV nonstructural protein 5 (nsp5), cleaved HDAC2, and this cleavage could be observed in the context of PDCoV infection. Furthermore, the cleavage of HDAC2 appears to be a common strategy among mammalian coronaviruses, including the emerging severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), to antagonize the antiviral role of HDAC2. To our knowledge, PDCoV nsp5 is the first identified viral protein that can cleave cellular HDAC2. Results from our study provide new targets to develop drugs combating coronavirus infection.

Histone Deacetylase-2 Controls IL-1β Production through the Regulation of NLRP3 Expression and Activation in Tuberculosis Infection

Histone deacetylases (HDACs) are critical immune regulators. However, their roles in interleukin-1β (IL-1β) production remain unclear. By screening 11 zinc-dependent HDACs with chemical inhibitors, we found that HDAC1 inhibitor, 4-(dimethylamino)-N-[6-(hydroxyamino)-6-oxohexyl]-benzamide (DHOB), enhanced IL-1β production by macrophage and dendritic cells upon TLR4 stimulation or Mycobacterium tuberculosis infection through IL-1β maturation via elevated NLRP3 expression, increased cleaved caspase-1, and enhanced ASC oligomerization. DHOB rescued defective IL-1β production by dendritic cells infected with M. tuberculosis with ESAT-6 deletion, a virulence factor shown to activate NLRP3 inflammasome. DHOB increased IL-1β production and NLRP3 expression in a tuberculosis mouse model. Although DHOB inhibited HDAC activities of both HDAC1 and HDAC2 by direct binding, knockdown of HDAC2, but not HDAC1, increased IL-1β production and NLRP3 expression in M. tuberculosis-infected macrophages. These data suggest that HDAC2, but not HDAC1, controls IL-1β production through NLRP3 inflammasome activation, a mechanism with a significance in chronic inflammatory diseases including tuberculosis.

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HDAC1 inhibitor, DHOB, increased IL-1β production via NLRP3 inflammasome activation

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DHOB suppressed deacetylase activities of both HDAC1 and HDAC2 by direct interaction

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Deletion of HDAC2, but not HDAC1, increased IL-β production by increased NLRP3 expression

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DHOB increased IL-1β and NLRP3 expression in a mouse model of TB infection

Butyrate Prevents Induction of CXCL10 and Non-Canonical IRF9 Expression by Activated Human Intestinal Epithelial Cells via HDAC Inhibition

Non-communicable diseases are increasing and have an underlying low-grade inflammation in common, which may affect gut health. To maintain intestinal homeostasis, unwanted epithelial activation needs to be avoided. This study compared the efficacy of butyrate, propionate and acetate to suppress IFN-γ+/−TNF-α induced intestinal epithelial activation in association with their HDAC inhibitory capacity, while studying the canonical and non-canonical STAT1 pathway. HT-29 were activated with IFN-γ+/−TNF-α and treated with short chain fatty acids (SCFAs) or histone deacetylase (HDAC) inhibitors. CXCL10 release and protein and mRNA expression of proteins involved in the STAT1 pathway were determined. All SCFAs dose-dependently inhibited CXCL10 release of the cells after activation with IFN-γ or IFN-γ+TNF-α. Butyrate was the most effective, completely preventing CXCL10 induction. Butyrate did not affect phosphorylated STAT1, nor phosphorylated NFκB p65, but inhibited IRF9 and phosphorylated JAK2 protein expression in activated cells. Additionally, butyrate inhibited CXCL10, SOCS1, JAK2 and IRF9 mRNA in activated cells. The effect of butyrate was mimicked by class I HDAC inhibitors and a general HDAC inhibitor Trichostatin A. Butyrate is the most potent inhibitor of CXCL10 release compared to other SCFAs and acts via HDAC inhibition. This causes downregulation of CXCL10, JAK2 and IRF9 genes, resulting in a decreased IRF9 protein expression which inhibits the non-canonical pathway and CXCL10 transcription.

Discovery of Genes that Modulate Flavivirus Replication in an Interferon-Dependent Manner

Establishment of the interferon (IFN)-mediated antiviral state provides a crucial initial line of defense against viral infection. Numerous genes that contribute to this antiviral state remain to be identified. Using a loss-of-function strategy, we screened an original library of 1156 siRNAs targeting 386 individual curated human genes in stimulated microglial cells infected with Zika virus (ZIKV), an emerging RNA virus that belongs to the flavivirus genus. The screen recovered twenty-one potential host proteins that modulate ZIKV replication in an IFN-dependent manner, including the previously known IFITM3 and LY6E. Further characterization contributed to delineate the spectrum of action of these genes towards other pathogenic RNA viruses, including Hepatitis C virus and SARS-CoV-2. Our data revealed that APOL3 acts as a proviral factor for ZIKV and several other related and unrelated RNA viruses. In addition, we showed that MTA2, a chromatin remodeling factor, possesses potent flavivirus-specific antiviral functions induced by IFN. Our work identified previously unrecognized genes that modulate the replication of RNA viruses in an IFN-dependent manner, opening new perspectives to target weakness points in the life cycle of these viruses.

HDAC inhibition as neuroprotection in COVID-19 infection

The SARS-CoV-2 virus is responsible of COVID-19 affecting millions of humans around the world. COVID-19 shows diverse clinical symptoms (fever, cough, fatigue, diarrhea, body aches, headaches, anosmia and hyposmia). Approximately 30% of the patients with COVID-19 showed neurological symptoms, these going from mild to severe manifestations including headache, dizziness, impaired consciousness, encephalopathy, anosmia, hypogeusia, hyposmia, psychology and psychiatry among others. The neurotropism of SARS-CoV-2 virus explains its neuroinvasion provoking neurological damage as acute demyelination, neuroinflammation etc. At molecular level, the COVID-19 patients had higher levels of cytokines and chemokines known as cytokines storms which disrupt the blood brain barrier allowing the entrance of monocytes and lymphocytes causing neuroinflammation, neurodegeneration and demyelination. In addition, ischemic, hemorrhagic strokes, seizures and encephalopathy have been observed due to the proinflammatory cytokines. In this sense, to avoid or decrease neurological damage due to SARS-CoV-2 infection, an early neuroprotective management should be adopted. Several approaches can be used; one of them includes the use of HDAC inhibitors (HDACi) due to their neuroprotective effects. Also, the HDACi down regulates the pro-inflammatory cytokines (IL-6 and TNF- decreasing the neurotoxicity. HDACi can also avoid and prevent the entrance of the virus into the Central nervous System (CNS) as well as decrease the virus replication by downregulating the virus receptors. Here we review the mechanisms that could explain how the SARS-CoV-2 virus could reach the CNS, induce the neurological damage and symptoms, as well as the possibility to use HDACi as neuroprotective therapy.

Knockout of HDAC9 Gene Enhances Foot-and-Mouth Disease Virus Replication

Foot-and-mouth disease virus (FMDV) is a highly contagious viral disease that mainly infects cloven-hoofed animals. Propagation of FMDV by cell culture is an important method to preserve viral biological and antigenic characteristics, which is crucial in FMD monitoring and vaccine production. However, only a few cell lines are sensitive to FMDV, and there is still a lot of room for improvement. Acetylation is an important post-translational modification, which is dynamically regulated by histone acetyltransferases (HATs) and histone deacetylases (HDACs). However, the study of the relationship between FMDV and HDACs is still unclear. HDAC9 belongs to the class II of HDACs family; in this study, HDAC9 knockout (KO) BHK-21 cells were successfully established using CRISPR/cas9 technology. The results of karyotype analysis, growth curve analysis, and morphological observation showed that the HDAC9 knockout cell line was stable in growth and morphological characteristics. After infection with FMDV, the expression of viral RNA and protein, viral titers, and the copies of viral RNA in HDAC9-KO cells were significantly higher than those in NC cells. Meanwhile, RNA-seq technology was used to sequence HDAC9-KO cells and NC cells infected and uninfected with FMDV. It was found that the differentially expressed innate immune factors containing NFKBIA, SOD2, IL2RG, BCL2L1, CXCL1/2/3, and IL1RAP have significantly enriched in the Jak-STAT, NOD-like receptor, Toll-like receptor, NF-κB, and MAPK signaling pathway. RT-qPCR was performed to detect the expression level of differentially expressed genes and showed consistency with the RNA-seq data. These results preliminarily reveal the role of HDAC9 in host antiviral innate immune response, and the HDAC9-KO cell line could also serve as a useful tool for FMDV research.

Chasing a Breath of Fresh Air in Cystic Fibrosis (CF): Therapeutic Potential of Selective HDAC6 Inhibitors to Tackle Multiple Pathways in CF Pathophysiology

Compelling new support has been provided for histone deacetylase isoform 6 (HDAC6) as a common thread in the generation of the dysregulated proinflammatory and fibrotic phenotype in cystic fibrosis (CF). HDAC6 also plays a crucial role in bacterial clearance or killing as a direct consequence of its effects on CF immune responses. Inhibiting HDAC6 functions thus eventually represents an innovative and effective strategy to tackle multiple aspects of CF-associated lung disease. In this Perspective, we not only showcase the latest evidence linking HDAC(6) activity and expression with CF phenotype but also track the new dawn of HDAC(6) modulators in CF and explore potentialities and future perspectives in the field.

HDAC inhibitors: Targets for tumor therapy, immune modulation and lung diseases

Histone deacetylases (HDACs) are enzymes that play a key role in the epigenetic regulation of gene expression by remodeling chromatin. Inhibition of HDACs is a prospective therapeutic approach for reversing epigenetic alteration in several diseases. In preclinical research, numerous types of HDAC inhibitors were discovered to exhibit powerful and selective anticancer properties. However, such research has revealed that the effects of HDAC inhibitors may be far broader and more intricate than previously thought. This review will provide insight into the HDAC inhibitors and their mechanism of action with special emphasis on the significance of HDAC inhibitors in the treatment of Chronic Obstructive Pulmonary Disease and lung cancer. Nanocarrier-mediated HDAC inhibitor delivery and new approaches for targeting HDACs are also discussed.

Interactions, structural aspects, and evolutionary perspectives of the yeast 'START'-regulatory network

Molecular signal transduction networks which conduct transcription at the G1 to S phase transition of the eukaryotic cell division cycle have been identified in diverse taxa from mammals to baker´s yeast with analogous functional organization. However, regarding some network components, such as the transcriptional regulators STB1 and WHI5, only few orthologs exist which are confined to individual Saccharomycotina species. While Whi5 has been characterized as yeast analog of human Rb protein, in the particular case of Stb1 (Sin three binding protein 1) identification of functional analogs emerges as difficult because to date its exact functionality still remains obscured. By aiming to resolve Stb1´s enigmatic role this Perspectives article especially surveys works covering relations between Cyclin/CDKs, the heteromeric transcription factor complexes SBF (Swi4/Swi6) and MBF (Mbp1/Swi6), as well as additional coregulators (Whi5, Sin3, Rpd3, Nrm1) which are collectively associated with the orderly transcription at 'Start' of the Saccharomyces cerevisiae cell cycle. In this context, interaction capacities of the Sin3-scaffold protein are widely surveyed because its four PAH domains (Paired Amphiphatic Helix) represent a 'recruitment-code' for gene-specific targeting of repressive histone deacetylase activity (Rpd3) via different transcription factors. Here Stb1 plays a role in Sin3´s action on transcription at the G1/S-boundary. Through bioinformatic analyses a potential Sin3-interaction domain (SID) was detected in Stb1, and beyond that, connections within the G1/S-regulatory network are discussed in structural and evolutionary context thereby providing conceptual perspectives.

Porcine Epidemic Diarrhea Virus Inhibits HDAC1 Expression To Facilitate Its Replication via Binding of Its Nucleocapsid Protein to Host Transcription Factor Sp1

Porcine epidemic diarrhea virus (PEDV) is an enteric coronavirus causing acute intestinal infection in pigs, with high mortality often seen in neonatal pigs. The newborns rely on innate immune responses against invading pathogens because of lacking adaptive immunity. However, how PEDV disables the innate immunity of newborns toward severe infection remains unknown. We found that PEDV infection led to reduced expression of histone deacetylases (HDACs), especially HDAC1, in porcine IPEC-J2 cells. HDACs are considered important regulators of innate immunity. We hypothesized that PEDV interacts with certain host factors to regulate HDAC1 expression in favor of its replication. We show that HDAC1 acted as a negative regulator of PEDV replication in IPEC-J2 cells, as shown by chemical inhibition, gene knockout, and overexpression. A GC-box (GCCCCACCCCC) within the HDAC1 promoter region was identified for Sp1 binding in IPEC-J2 cells. Treatment of the cells with Sp1 inhibitor mithramycin A inhibited HDAC1 expression, indicating direct regulation of HDAC1 expression by Sp1. Of the viral proteins that were overexpressed in IPEC-J2 cells, the N protein was found to be present in the nuclei and more inhibitory to HDAC1 transcription. The putative nuclear localization sequence ²⁶¹PKKNKSR²⁶⁷ contributed to its nuclear localization. The N protein interacted with Sp1 and interfered with its binding to the promoter region, thereby inhibiting its transcriptional activity for HDAC1 expression. Our findings reveal a novel mechanism of PEDV evasion of the host responses, offering implications for studying the infection processes of other coronaviruses. IMPORTANCE The enteric coronavirus porcine epidemic diarrhea virus (PEDV) causes fatal acute intestinal infection in neonatal pigs that rely on innate immune responses. Histone deacetylases (HDACs) play important roles in innate immune regulation. Our study found PEDV suppresses HDAC1 expression via the interaction of its N protein and porcine Sp1, which identified a novel mechanism of PEDV evasion of the host responses to benefit its replication. This study suggests that other coronaviruses, including SARS-CoV and SARS-CoV-2, also make use of their N proteins to intercept the host immune responses in favor of their infection.

Expression of HDACs 1, 3 and 8 Is Upregulated in the Presence of Infiltrating Lymphocytes in Uveal Melanoma

Simple Summary

Uveal melanoma (UM) is an ocular malignancy which is derived from melanocytes in the uveal tract. Epigenetic regulators such as Histone Deacetylase (HDACs) inhibitors are being tested as treatment of UM metastases. Expression of different HDACs is variable, and some are increased in high-risk tumors with loss of one chromosome 3. As this genetic abnormality is also associated with an inflammatory phenotype, we analyzed whether HDAC expression was influenced by inflammation. In two cohorts of UM cases, expression of several HDACs showed a positive correlation with tumor-infiltrating T cells, while HDACs 2 and 11 showed a negative association with macrophages. Interferon-γ stimulated expression of some HDACs on UM cell lines. These data suggest that cytokines produced by T cells may be responsible for the increased expression of some HDACs in UM with monosomy 3.

Abstract

In Uveal Melanoma (UM), an inflammatory phenotype is strongly associated with the development of metastases and with chromosome 3/BAP1 expression loss. As an increased expression of several Histone Deacetylases (HDACs) was associated with loss of chromosome 3, this suggested that HDAC expression might also be related to inflammation. We analyzed HDAC expression and the presence of leukocytes by mRNA expression in two sets of UM (Leiden and TCGA) and determined the T lymphocyte fraction through ddPCR. Four UM cell lines were treated with IFNγ (50IU, 200IU). Quantitative PCR (qPCR) was used for mRNA measurement of HDACs in cultured cells. In both cohorts (Leiden and TCGA), a positive correlation occurred between expression of HDACs 1, 3 and 8 and the presence of a T-cell infiltrate, while expression of HDACs 2 and 11 was negatively correlated with the presence of tumor-infiltrating macrophages. Stimulation of UM cell lines with IFNγ induced an increase in HDACs 1, 4, 5, 7 and 8 in two out of four UM cell lines. We conclude that the observed positive correlations between HDAC expression and chromosome 3/BAP1 loss may be related to the presence of infiltrating T cells.

BRD9 is a druggable component of interferon-stimulated gene expression and antiviral activity

Interferon (IFN) induction of IFN-stimulated genes (ISGs) creates a formidable protective antiviral state. However, loss of appropriate control mechanisms can result in constitutive pathogenic ISG upregulation. Here, we used genome-scale loss-of-function screening to establish genes critical for IFN-induced transcription, identifying all expected members of the JAK-STAT signaling pathway and a previously unappreciated epigenetic reader, bromodomain-containing protein 9 (BRD9), the defining subunit of non-canonical BAF (ncBAF) chromatin-remodeling complexes. Genetic knockout or small-molecule-mediated degradation of BRD9 limits IFN-induced expression of a subset of ISGs in multiple cell types and prevents IFN from exerting full antiviral activity against several RNA and DNA viruses, including influenza virus, human immunodeficiency virus (HIV1), and herpes simplex virus (HSV1). Mechanistically, BRD9 acts at the level of transcription, and its IFN-triggered proximal association with the ISG transcriptional activator, STAT2, suggests a functional localization at selected ISG promoters. Furthermore, BRD9 relies on its intact acetyl-binding bromodomain and unique ncBAF scaffolding interaction with GLTSCR1/1L to promote IFN action. Given its druggability, BRD9 is an attractive target for dampening ISG expression under certain autoinflammatory conditions.

Histone deacetylase 2 knockout suppresses immune escape of triple-negative breast cancer cells via downregulating PD-L1 expression

The PD-L1 overexpression is an important event of immune escape and metastasis in triple-negative breast cancer (TNBC), but the molecular mechanism remains to be determined. Interferon gamma (IFNγ) represents a major driving force behind PD-L1 expression in tumor microenvironment, and histone deacetylase 2 (HDAC2) is required for IFN signaling. Here, we investigated the regulation of HDAC2 on the IFNγ-induced PD-L1 expression in TNBC cells. We found the HDAC2 and PD-L1 expression in TNBC was significantly higher than that in non-TNBC, and HDAC2 was positively correlated with PD-L1 expression. HDAC2 promoted PD-L1 induction by upregulating the phosphorylation of JAK1, JAK2, and STAT1, as well as the translocation of STAT1 to the nucleus and the recruitment of STAT1 to the PD-L1 promoter. Meanwhile, HDAC2 was recruited to the PD-L1 promoter by STAT1, and HDAC2 knockout compromised IFNγ-induced upregulation of H3K27, H3K9 acetylation, and the BRD4 recruitment in PD-L1 promoter. In addition, significant inhibition of proliferation, colony formation, migration, and cell cycle of TNBC cells were observed following knockout of HDAC2 in vitro. Furthermore, HDAC2 knockout reduced IFNγ-induced PD-L1 expression, lymphocyte infiltration, and retarded tumor growth and metastasis in the breast cancer mouse models. This study may provide evidence that HDAC2 promotes IFNγ-induced PD-L1 expression, suggesting a way for enhanced antitumor immunity when targeting the HDAC2 in TNBC.

Constitutive JAK/STAT signaling is the primary mechanism of resistance to JAKi in TYK2-rearranged acute lymphoblastic leukemia

Activating TYK2-rearrangements have recently been identified and implicated in the leukemogenesis of high-risk acute lymphoblastic leukemia (HR-ALL) cases. Pre-clinical studies indicated the JAK/TYK2 inhibitor (JAKi), cerdulatinib, as a promising therapeutic against TYK2-rearranged ALL, attenuating the constitutive JAK/STAT signaling resulting from the TYK2 fusion protein. However, following a period of clinical efficacy, JAKi resistance often occurs resulting in relapse. In this study, we modeled potential mechanisms of JAKi resistance in TYK2-rearranged ALL cells in vitro in order to recapitulate possible clinical scenarios and provide a rationale for alternative therapies. Cerdulatinib resistant B-cells, driven by the MYB-TYK2 fusion oncogene, were generated by long-term exposure to the drug. Sustained treatment of MYB-TYK2-rearranged ALL cells with cerdulatinib led to enhanced and persistent JAK/STAT signaling, co-occurring with JAK1 overexpression. Hyperactivation of JAK/STAT signaling and JAK1 overexpression was reversible as cerdulatinib withdrawal resulted in re-sensitization to the drug. Importantly, histone deacetylase inhibitor (HDACi) therapies were efficacious against cerdulatinib-resistant cells demonstrating a potential alternative therapy for use in TYK2-rearranged B-ALL patients who have lost response to JAKi treatment regimens.

Cytokines and pregnancy: Potential regulation by histone deacetylases

Cytokines are important regulators of pregnancy and parturition. Aberrant expression of proinflammatory cytokines during pregnancy contributes towards preterm labor, pre-eclampsia, and gestational diabetes mellitus. The regulation of cytokine expression in human cells is highly complex, involving interactions between environment, transcription factors, and feedback mechanisms. Recent developments in epigenetic research have made tremendous advancements in exploring histone modifications as a key epigenetic regulator of cytokine expression and the effect of their signaling molecules on various organ systems in the human body. Histone acetylation and subsequent deacetylation by histone deacetylases (HDACs) are major epigenetic regulators of protein expression in the human body. The expression of various proinflammatory cytokines, their role in normal and abnormal pregnancy, and their epigenetic regulation via HDACs will be discussed in this review.

HDAC Inhibition Increases HLA Class I Expression in Uveal Melanoma

Simple Summary

Chemotherapy and immunotherapy are both used to treat malignancies. The immunotherapy of cancer often involves T cells, which recognise the antigens presented in HLA molecules. Uveal melanoma (UM) is an intraocular malignancy, which often gives rise to metastases. We determined whether high-risk tumours expressed the target of two drugs, histone deacetylase (HDAC) inhibitor Quisinostat and Tazemetostat, an inhibitor of Enhancer of zeste homologue 2 (EZH2). We observed that especially high-risk UM tumours (monosomy 3, gain of 8q, loss of BAP1) expressed several HDACs, and showed a high HLA Class I expression. We further tested whether these drugs influenced HLA Class I expression on three UM cell lines. The drug Quisinostat led to an upregulation of HLA protein and mRNA levels in three UM cell lines, while Tazemetostat had little effect. We concluded that the use of drugs that influence epigenetic regulators may impact immunotherapy approaches.

Abstract

The treatment of uveal melanoma (UM) metastases or adjuvant treatment may imply immunological approaches or chemotherapy. It is to date unknown how epigenetic modifiers affect the expression of immunologically relevant targets, such as the HLA Class I antigens, in UM. We investigated the expression of HDACs and the histone methyl transferase EZH2 in a set of 64 UMs, using an Illumina HT12V4 array, and determined whether a histone deacetylase (HDAC) inhibitor and EZH2 inhibitor modified the expression of HLA Class I on three UM cell lines. Several HDACs (HDAC1, HDAC3, HDAC4, and HDAC8) showed an increased expression in high-risk UM, and were correlated with an increased HLA expression. HDAC11 had the opposite expression pattern. While in vitro tests showed that Tazemetostat did not influence cell growth, Quisinostat decreased cell survival. In the three tested cell lines, Quisinostat increased HLA Class I expression at the protein and mRNA level, while Tazemetostat did not have an effect on the cell surface HLA Class I levels. Combination therapy mostly followed the Quisinostat results. Our findings indicate that epigenetic drugs (in this case an HDAC inhibitor) may influence the expression of immunologically relevant cell surface molecules in UM, demonstrating that these drugs potentially influence immunotherapy.

Butyrate Reprograms Expression of Specific Interferon-Stimulated Genes

Butyrate is an abundant metabolite produced by gut microbiota. While butyrate is a known histone deacetylase inhibitor that activates expression of many genes involved in immune system pathways, its effects on virus infections and on the antiviral type I interferon (IFN) response have not been adequately investigated. We found that butyrate increases cellular infection with viruses relevant to human and animal health, including influenza virus, reovirus, HIV-1, human metapneumovirus, and vesicular stomatitis virus. Mechanistically, butyrate suppresses levels of specific antiviral IFN-stimulated gene (ISG) products, such as RIG-I and IFITM3, in human and mouse cells without inhibiting IFN-induced phosphorylation or nuclear translocation of the STAT1 and STAT2 transcription factors. Accordingly, we discovered that although butyrate globally increases baseline expression of more than 800 cellular genes, it strongly represses IFN-induced expression of 60% of ISGs and upregulates 3% of ISGs. Our findings reveal that there are differences in the IFN responsiveness of major subsets of ISGs depending on the presence of butyrate in the cell environment, and overall, they identify a new mechanism by which butyrate influences virus infection of cells.IMPORTANCE Butyrate is a lipid produced by intestinal bacteria. Here, we newly show that butyrate reprograms the innate antiviral immune response mediated by type I interferons (IFNs). Many of the antiviral genes induced by type I IFNs are repressed in the presence of butyrate, resulting in increased virus infection and replication. Our research demonstrates that metabolites produced by the gut microbiome, such as butyrate, can have complex effects on cellular physiology, including dampening of an inflammatory innate immune pathway resulting in a proviral cellular environment. Our work further suggests that butyrate could be broadly used as a tool to increase growth of virus stocks for research and for the generation of vaccines.

Quantitative Temporal Proteomic Analysis of Vaccinia Virus Infection Reveals Regulation of Histone Deacetylases by an Interferon Antagonist

Vaccinia virus (VACV) has numerous immune evasion strategies, including multiple mechanisms of inhibition of interferon regulatory factor 3 (IRF-3), nuclear factor κB (NF-κB), and type I interferon (IFN) signaling. Here, we use highly multiplexed proteomics to quantify ∼9,000 cellular proteins and ∼80% of viral proteins at seven time points throughout VACV infection. A total of 265 cellular proteins are downregulated >2-fold by VACV, including putative natural killer cell ligands and IFN-stimulated genes. Two-thirds of these viral targets, including class II histone deacetylase 5 (HDAC5), are degraded proteolytically during infection. In follow-up analysis, we demonstrate that HDAC5 restricts replication of both VACV and herpes simplex virus type 1. By generating a protein-based temporal classification of VACV gene expression, we identify protein C6, a multifunctional IFN antagonist, as being necessary and sufficient for proteasomal degradation of HDAC5. Our approach thus identifies both a host antiviral factor and a viral mechanism of innate immune evasion.

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Temporal proteomic analysis quantifies host and viral dynamics during vaccinia infection

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Host protein families are proteasomally degraded over the course of vaccinia infection

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Vaccinia protein C6 targets HDAC5 for proteasomal degradation

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HDAC5 is a host antiviral factor that restricts different families of DNA viruses

iNOS/NO is required for IRF1 activation in response to liver ischemia-reperfusion in mice

Background

Ischemia and reperfusion (I/R) induces cytokines, and up-regulates inducible nitric oxide synthase (iNOS), interferon regulatory factor-1(IRF1) and p53 up-regulated modulator of apoptosis (PUMA), which contribute to cell death and tissue injury. However, the mechanisms that I/R induces IRF1-PUMA through iNOS/NO is still unknown.

Methods

Ischemia was induced by occluding structures in the portal triad (hepatic artery, portal vein, and bile duct) to the left and median liver lobes for 60 min, and reperfusion was initiated by removal of the clamp. Induction of iNOS, IRF1 and PUMA in response to I/R were analyzed. I/R induced IRF1 and PUMA expression were compared between iNOS wild-type and iNOS knockout (KO) mice. Human iNOS gene transfected-cells were used to determine iNOS/NO signals targeting IRF1. To test whether HDAC2 was involved in the mediation of iNOS/NO-induced IRF1 transcriptional activities and its target gene (PUMA and p21) expression, NO donors were used in vitro and in vivo.

Results

IRF1 nuclear translocation and PUMA transcription elevation were markedly induced following I/R in the liver of iNOS wild-type mice compared with that in knock-out mice. Furthermore, I/R induced hepatic HDAC2 expression and activation, and decreased H3AcK9 expression in iNOS wild-type mice, but not in the knock-out mice. Mechanistically, over-expression of human iNOS gene increased IRF1 transcriptional activity and PUMA expression, while iNOS inhibitor L-NIL reversed these effects. Cytokine-induced PUMA through IRF1 was p53 dependent. IRF1 and p53 synergistically up-regulated PUMA expression. iNOS/NO-induced HDAC2 mediated histone H3 deacetylation and promoted IRF1 transcriptional activity. Moreover, treating the cells with romidepsin, an HDAC1/2 inhibitor decreased NO-induced IRF1 and PUMA expression.

Conclusions

This study demonstrates a novel mechanism that iNOS/NO is required for IRF1/PUMA signaling through a positive-feedback loop between iNOS and IRF1, in which HDAC2-mediated histone modification is involved to up-regulate IRF1 in response to I/R in mice.

Prostate cancer cell-intrinsic interferon signaling regulates dormancy and metastatic outgrowth in bone

The latency associated with bone metastasis emergence in castrate-resistant prostate cancer is attributed to dormancy, a state in which cancer cells persist prior to overt lesion formation. Using single-cell transcriptomics and ex vivo profiling, we have uncovered the critical role of tumor-intrinsic immune signaling in the retention of cancer cell dormancy. We demonstrate that loss of tumor-intrinsic type I IFN occurs in proliferating prostate cancer cells in bone. This loss suppresses tumor immunogenicity and therapeutic response and promotes bone cell activation to drive cancer progression. Restoration of tumor-intrinsic IFN signaling by HDAC inhibition increased tumor cell visibility, promoted long-term antitumor immunity, and blocked cancer growth in bone. Key findings were validated in patients, including loss of tumor-intrinsic IFN signaling and immunogenicity in bone metastases compared to primary tumors. Data herein provide a rationale as to why current immunotherapeutics fail in bone-metastatic prostate cancer, and provide a new therapeutic strategy to overcome the inefficacy of immune-based therapies in solid cancers.

Induction of Samhd1 by interferon gamma and lipopolysaccharide in murine macrophages requires IRF1

SAMHD1 is an enzyme with phosphohydrolase activity. Mutations in SAMHD1 have been linked to the development of Aicardi-Goutières syndrome in humans. This enzyme also has the capacity to restrict HIV virus replication in macrophages. Here, we report that Samhd1 is highly expressed in murine macrophages and is regulated by proinflammatory (IFN-γ and LPS) but not by anti-inflammatory (IL-4 or IL-10) activators. The induction of Samhd1 follows the pattern of an intermediate gene that requires protein synthesis. In transient transfection experiments using the Samhd1 promoter, we found that a fragment of 27 bps of this gene, falling between -937 and -910 bps relative to the transcription start site, is required for IFN-γ-dependent activation. Using EMSAs, we determined that IFN-γ treatment led to the elimination of a protein complex. Chromatin immunoprecipitation assays and siRNA experiments revealed that IRF1 is required for IFN-γ- or LPS-induced Samhd1 expression. Therefore, our results indicate that Samhd1 is stimulated by proinflammatory agents IFN-γ and LPS. Moreover, they reveal that these two agents, via IRF1, eliminate a protein complex that may be related to a repressor, thereby, triggering Samhd1 expression.

Histone deacetylases 1 and 2 restrain CD4+ cytotoxic T lymphocyte differentiation

Some effector CD4+ T cell subsets display cytotoxic activity, thus breaking the functional dichotomy of CD4+ helper and CD8+ cytotoxic T lymphocytes. However, molecular mechanisms regulating CD4+ cytotoxic T lymphocyte (CD4+ CTL) differentiation are poorly understood. Here we show that levels of histone deacetylases 1 and 2 (HDAC1-HDAC2) are key determinants of CD4+ CTL differentiation. Deletions of both Hdac1 and 1 Hdac2 alleles (HDAC1cKO-HDAC2HET) in CD4+ T cells induced a T helper cytotoxic program that was controlled by IFN-γ-JAK1/2-STAT1 signaling. In vitro, activated HDAC1cKO-HDAC2HET CD4+ T cells acquired cytolytic activity and displayed enrichment of gene signatures characteristic of effector CD8+ T cells and human CD4+ CTLs. In vivo, murine cytomegalovirus-infected HDAC1cKO-HDAC2HET mice displayed a stronger induction of CD4+ CTL features compared with infected WT mice. Finally, murine and human CD4+ T cells treated with short-chain fatty acids, which are commensal-produced metabolites acting as HDAC inhibitors, upregulated CTL genes. Our data demonstrate that HDAC1-HDAC2 restrain CD4+ CTL differentiation. Thus, HDAC1-HDAC2 might be targets for the therapeutic induction of CD4+ CTLs.

Interferon-γ signaling is associated with BRCA1 loss-of-function mutations in high grade serous ovarian cancer

Loss-of-function mutations of the breast cancer type 1 susceptibility protein (BRCA1) are associated with breast (BC) and ovarian cancer (OC). To identify gene signatures regulated by epigenetic mechanisms in OC cells carrying BRCA1 mutations, we assessed cellular responses to epigenome modifiers and performed genome-wide RNA- and chromatin immunoprecipitation-sequencing in isogenic OC cells UWB1.289 (carrying a BRCA1 mutation, BRCA1-null) and UWB1.289 transduced with wild-type BRCA1 (BRCA1+). Increased sensitivity to histone deacetylase inhibitors (HDACi) was observed in BRCA1-null vs. BRCA1+ cells. Gene expression profiles of BRCA1-null vs. BRCA1+ cells and treated with HDACi were integrated with chromatin mapping of histone H3 lysine 9 or 27 acetylation. Gene networks activated in BRCA1-null vs. BRCA1 + OC cells related to cellular movement, cellular development, cellular growth and proliferation, and activated upstream regulators included TGFβ1, TNF, and IFN-γ. The IFN-γ pathway was altered by HDACi in BRCA1+ vs. BRCA1-null cells, and in BRCA1-mutated/or low vs. BRCA1-normal OC tumors profiled in the TCGA. Key IFN-γ-induced genes upregulated at baseline in BRCA1-null vs. BRCA1+OC and BC cells included CXCL10, CXCL11, and IFI16. Increased localization of STAT1 in the promoters of these genes occurred in BRCA1-null OC cells, resulting in diminished responses to IFN-γ or to STAT1 knockdown. The IFN-γ signature was associated with improved survival among OC patients profiled in the TCGA. In all, our results support that changes affecting IFN-γ responses are associated with inactivating BRCA1 mutations in OC. This signature may contribute to altered responses to anti-tumor immunity in BRCA1-mutated cells or tumors.

NOS1 inhibits the interferon response of cancer cells by S-nitrosylation of HDAC2

Background

The dysfunction of type I interferon (IFN) signaling is an important mechanism of immune escape and metastasis in tumors. Increased NOS1 expression has been detected in melanoma, which correlated with dysfunctional IFN signaling and poor response to immunotherapy, but the specific mechanism has not been determined. In this study, we investigated the regulation of NOS1 on the interferon response and clarified the relevant molecular mechanisms.

Methods

After stable transfection of A375 cells with NOS1 expression plasmids, the transcription and expression of IFNα-stimulated genes (ISGs) were assessed using pISRE luciferase reporter gene analysis, RT-PCR, and western blotting, respectively. The effect of NOS1 on lung metastasis was assessed in melanoma mouse models. A biotin-switch assay was performed to detect the S-nitrosylation of HDAC2 by NOS1. ChIP-qPCR was conducted to measure the binding of HDAC2, H4K16ac, H4K5ac, H3ac, and RNA polymerase II in the promoters of ISGs after IFNα stimulation. This effect was further evaluated by altering the expression level of HDAC2 or by transfecting the HDAC2-C262A/C274A site mutant plasmids into cells. The coimmunoprecipitation assay was performed to detect the interaction of HDAC2 with STAT1 and STAT2. Loss-of-function and gain-of-function approaches were used to examine the effect of HDAC2-C262A/C274A on lung metastasis. Tumor infiltrating lymphocytes were analyzed by flow cytometry.

Results

HDAC2 is recruited to the promoter of ISGs and deacetylates H4K16 for the optimal expression of ISGs in response to IFNα treatment. Overexpression of NOS1 in melanoma cells decreases IFNα-responsiveness and induces the S-nitrosylation of HDAC2-C262/C274. This modification decreases the binding of HDAC2 with STAT1, thereby reducing the recruitment of HDAC2 to the ISG promoter and the deacetylation of H4K16. Moreover, expression of a mutant form of HDAC2, which cannot be nitrosylated, reverses the inhibition of ISG expression by NOS1 in vitro and decreases NOS1-induced lung metastasis and inhibition of tumor infiltrating lymphocytes in a melanoma mouse model.

Conclusions

This study provides evidence that NOS1 induces dysfunctional IFN signaling to promote lung metastasis in melanoma, highlighting NOS1-induced S-nitrosylation of HDAC2 in the regulation of IFN signaling via histone modification.

Histone deacetylase 4 promotes type I interferon signaling, restricts DNA viruses, and is degraded via vaccinia virus protein C6

Interferons (IFNs) represent an important host defense against viruses. Type I IFNs induce JAK-STAT signaling and expression of IFN-stimulated genes (ISGs), which mediate antiviral activity. Histone deacetylases (HDACs) perform multiple functions in regulating gene expression and some class I HDACs and the class IV HDAC, HDAC11, influence type I IFN signaling. Here, HDAC4, a class II HDAC, is shown to promote type I IFN signaling and coprecipitate with STAT2. Pharmacological inhibition of class II HDAC activity, or knockout of HDAC4 from HEK-293T and HeLa cells, caused a defective response to IFN-α. This defect in HDAC4-/- cells was rescued by reintroduction of HDAC4 or catalytically inactive HDAC4, but not HDAC1 or HDAC5. ChIP analysis showed HDAC4 was recruited to ISG promoters following IFN stimulation and was needed for binding of STAT2 to these promoters. The biological importance of HDAC4 as a virus restriction factor was illustrated by the observations that (i) the replication and spread of vaccinia virus (VACV) and herpes simplex virus type 1 (HSV-1) were enhanced in HDAC4-/- cells and inhibited by overexpression of HDAC4; and (ii) HDAC4 is targeted for proteasomal degradation during VACV infection by VACV protein C6, a multifunctional IFN antagonist that coprecipitates with HDAC4 and is necessary and sufficient for HDAC4 degradation.