Brd4 modulates the innate immune response through Mnk2-eIF4E pathway-dependent translational control of IκBα

BRD4 as a therapeutic target for atrial fibrosis and atrial fibrillation

OBJECTIVE

This study aimed to elucidate the molecular mechanisms by which BRD4 play a role in atrial fibrillation (AF).

METHODS AND RESULTS

We used a discovery-driven approach to detect BRD4 expression in the atria of patients with AF and in various murine models of atrial fibrosis. We used a BRD4 inhibitor (JQ1) and atrial fibroblast (aFB)-specific BRD4-knockout mice to elucidate the role of BRD4 in AF. We further examined the underlying mechanisms using RNA-seq and ChIP-seq analyses in vitro, to identify key downstream targets of BRD4. We found that BRD4 expression is significantly increased in patients with AF, with accompanying atrial fibrosis and aFB differentiation. We showed that JQ1 treatment and shRNA-based molecular silencing of BRD4 blocked ANG-II-induced extracellular matrix production and cell-cycle progression in aFBs. BRD4-related RNA-seq and ChIP-seq analyses in aFBs demonstrated enrichment of a subset of promoters related to the expression of profibrotic and proliferation-related genes. The pharmacological inhibition of BRD4 in vivo or in aFB-specific BRD4-knockout in mice limited ANG-II-induced atrial fibrosis, atrial enlargement, and AF susceptibility.

CONCLUSION

Our findings suggest that BRD4 plays a key role in pathological AF, at least partially by activating aFB proliferation and ECM synthesis. This study provides mechanistic insights into the development of BRD4 inhibitors as targeted antiarrhythmic therapies.

Targeting BRD4: Potential therapeutic strategy for head and neck squamous cell carcinoma (Review)

As a member of BET (bromodomain and extra-terminal) protein family, BRD4 (bromodomain‑containing protein 4) is a chromatin‑associated protein that interacts with acetylated histones and actively recruits regulatory proteins, leading to the modulation of gene expression and chromatin remodeling. The cellular and epigenetic functions of BRD4 implicate normal development, fibrosis and inflammation. BRD4 has been suggested as a potential therapeutic target as it is often overexpressed and plays a critical role in regulating gene expression programs that drive tumor cell proliferation, survival, migration and drug resistance. To address the roles of BRD4 in cancer, several drugs that specifically target BRD4 have been developed. Inhibition of BRD4 has shown promising results in preclinical models, with several BRD4 inhibitors undergoing clinical trials for the treatment of various cancers. Head and neck squamous cell carcinoma (HNSCC), a heterogeneous group of cancers, remains a health challenge with a high incidence rate and poor prognosis. Conventional therapies for HNSCC often cause adverse effects to the patients. Targeting BRD4, therefore, represents a promising strategy to sensitize HNSCC to chemo‑ and radiotherapy allowing de‑intensification of the current therapeutic regime and subsequent reduced side effects. However, further studies are required to fully understand the underlying mechanisms of action of BRD4 in HNSCC in order to determine the optimal dosing and administration of BRD4‑targeted drugs for the treatment of patients with HNSCC.

Apoptotic body-inspired nanotherapeutics efficiently attenuate osteoarthritis by targeting BRD4-regulated synovial macrophage polarization

Bromodomain-containing protein 4 (BRD4) is the most well-studied BET protein that is important for the innate immune response. We recently revealed that targeting BRD4 triggers apoptosis in tumor-associated macrophages, but its role in synovial macrophages and joint inflammation is largely unknown. Herein, we demonstrated that BRD4 was highly expressed in the iNOS-positive M1 macrophages in the human and mouse osteoarthritis (OA) synovium, and conditional knockout of BRD4 in the myeloid lineage using Lyz2-cre; BRD4flox/flox mice significantly abolished anterior cruciate ligament transection (ACLT)-induced M1 macrophage accumulation and synovial inflammation. Accordingly, we successfully constructed apoptotic body-inspired phosphatidylserine-containing nanoliposomes (PSLs) loaded with the BRD4 inhibitor JQ1 to regulate inflammatory macrophages. JQ1-loaded PSLs (JQ1@PSLs) exhibited a higher cellular uptake by macrophages than fibroblast-like synoviocytes (FLSs) in vitro and in vivo, as well as the reduction in proinflammatory M1 macrophage polarization. Intra-articular injections of JQ1@PSLs showed prolonged retention within the joint, and remarkably reduced synovial inflammation and joint pain via suppressing M1 polarization accompanied by reduced TRPA1 expression by targeted inhibition of BRD4 in the macrophages, thus attenuating cartilage degradation during OA development. The results show that BRD4-inhibiting JQ1@PSLs can targeted-modulate macrophage polarization, which opens a new avenue for efficient OA therapy via a "Trojan horse".

Successes and challenges in the development of BD1-selective BET inhibitors: a patent review

INTRODUCTION

Bromodomain and ExtraTerminal (BET) domain proteins are transcriptional cofactors that, recognizing acetylated lysines of histone and non-histone proteins, can modulate gene expression. The BET family consists of four members, each of which contains two bromodomains (BD1 and BD2) able to recognize the acetylated mark. Pan-BET inhibitors (BETi) have shown a promising anticancer potential in many clinical trials; however, their further development has been in part hampered by the side effects due to their lack of selectivity. Mounting evidence suggests that BD1 is primarily involved in cancer and that its selective inhibition can phenocopy the anticancer effects of pan-BETi with increased tolerability. Therefore, the development of BD1 selective inhibitors is highly pursed in both academia and industry.

AREAS COVERED

This review aims at giving an overview of the patent literature of BD1-selective BETi between 2014 and 2023. WIPO, USPTO, EPO, and SciFinder® databases were used for the search of patents.

EXPERT OPINION

The development of BD1-selective BETi, despite challenging, is highly desirable as it could have a great impact on the development of new safer anticancer therapeutics. Several strategies could be applied to discover potent and selective compounds with limited side effects.

Discovery of D25, a Potent and Selective MNK Inhibitor for Sepsis-Associated Acute Spleen Injury

Mitogen-activated protein kinase-interacting protein kinases (MNKs) and phosphorylate eukaryotic initiation factor 4E (p-eIF4E) play a critical role in regulating mRNA translation and protein synthesis associated with the development of cancer, metabolism, and inflammation. This study undertakes the modification of a 4-(3-(piperidin-4-yl)-1H-pyrazol-5-yl)pyridine structure, leading to the discovery of 4-(3-(piperidin-4-yl)-1H-pyrazol-5-yl)-1H-pyrrolo[2,3-b]pyridine (D25) as a potent and selective MNK inhibitor. D25 demonstrated inhibitory activity, with IC50 values of 120.6 nM for MNK1 and 134.7 nM for MNK2, showing exceptional selectivity. D25 inhibited the expression of pro-inflammation cytokines in RAW264.7 cells, such as inducible NO synthase, cyclooxygenase-2, and interleukin-6 (IL-6). In the lipopolysaccharide-induced sepsis mouse model, D25 significantly reduced p-eIF4E in spleen tissue and decreased the expression of tumor necrosis factor α, interleukin-1β, and IL-6, and it also reduced the production of reactive oxygen species, resulting in improved organ injury caused by inflammation. This suggests that D25 may provide a potential treatment for sepsis and sepsis-associated acute spleen injury.

Bromodomain protein 4 is a key molecular driver of TGFβ1-induced hepatic stellate cell activation

Liver fibrosis is characterized by the excessive deposition of extracellular matrix in liver. Chronic liver injury induces the activation of hepatic stellate cell (HSCs), a key step in liver fibrogenesis. The activated HSC is the primary source of ECM and contributes significantly to liver fibrosis. TGFβ1 is the most potent pro-fibrotic cytokine. Bromodomain protein 4 (BrD4), an epigenetic reader of histone acetylation marks, was crucial for profibrotic gene expression in HSCs. The present study aimed to investigate the roles of BRD4 in TGFβ1-dependent HSC activation and liver fibrosis, focusing on TGFβ1-induced alterations of the levels of the fibrotic-related important proteins in HSCs by employing the heterozygous TGFβ1 knockout mice and BrD4 knockdown in vivo and in vitro. Results revealed that BrD4 protein level was significantly upregulated by TGFβ1 and BrD4 knockdown reduced TGFβ1-induced HSC activation and liver fibrosis. BrD4 was required for the influences of TGFβ1 on PDGFβ receptor and on the pathways of Smad3, Stat3, and Akt. BrD4 also mediated TGFβ1-induced increases in histone acetyltransferase p300, the pivotal pro-inflammatory NFkB p65, and tissue inhibitor of metalloproteinase 1 whereas BrD4 reduced Caspase-3 protein levels in HSCs during liver injury, independent of TGFβ1. Further experiments indicated the interaction between TGFβ1-induced BrD4 and NFkB p65 in HSCs and in liver of TAA-induced liver injury. Human cirrhotic livers were demonstrated a parallel increase in the protein levels of BrD4 and NFkB p65 in HSCs. This study revealed that BrD4 was a key molecular driver of TGFβ1-induced HSC activation and liver fibrosis.

BRD4 Regulates Glycolysis-Dependent Nos2 Expression in Macrophages Upon H pylori Infection

BACKGROUND & AIMS

Metabolic reprogramming is essential for the activation and functions of macrophages, including bacterial killing and cytokine production. Bromodomain-containing protein 4 (BRD4) has emerged as a critical regulator of innate immune response. However, the potential role of BRD4 in the metabolic reprogramming of macrophage activation upon Helicobacter pylori infection remains unclear.

METHODS

Bone marrow-derived macrophages (BMDMs) from wild-type (WT) and Brd4-myeloid deletion conditional knockout (Brd4-CKO) mice were infected with H pylori. RNA sequencing was performed to evaluate the differential gene expression between WT and Brd4-deficient BMDMs upon infection. An in vivo model of H pylori infection using WT and Brd4-CKO mice was used to confirm the role of BRD4 in innate immune response to infection.

RESULTS

Depletion of Brd4 in BMDMs showed impaired H pylori-induced glycolysis. In addition, H pylori-induced expression of glycolytic genes, including Slc2a1 and Hk2, was decreased in Brd4-deficient BMDMs. BRD4 was recruited to the promoters of Slc2a1 and Hk2 via hypoxia-inducible factor-1α, facilitating their expression. BRD4-mediated glycolysis stabilized H pylori-induced nitric oxide synthase (Nos2) messenger RNA to produce nitric oxide. The NO-mediated killing of H pylori decreased in Brd4-deficient BMDMs, which was rescued by pyruvate. Furthermore, Brd4-CKO mice infected with H pylori showed reduced gastric inflammation and increased H pylori colonization with reduced inducible NO synthase expression in gastric macrophages.

CONCLUSIONS

Our study identified BRD4 as a key regulator of hypoxia-inducible factor-1α-dependent glycolysis and macrophage activation. Furthermore, we show a novel regulatory role of BRD4 in innate immunity through glycolysis to stabilize Nos2 messenger RNA for NO production to eliminate H pylori infection.

BRD4 Inhibition Enhances the Antitumor Effects of Radiation Therapy in a Murine Breast Cancer Model

Bromodomain-containing protein 4 (BRD4) is an intracellular protein that regulates expression of various cellular functions. This study investigated whether BRD4 inhibition can alter the immunomodulatory and antitumor effects of radiation therapy (RT). A murine breast cancer cell line was implanted into BALB/c mice. The dual-tumor model was used to evaluate the abscopal effects of RT. A total of 24 Gy was delivered and BRD4 inhibitor was injected intravenously. Tumor size was measured, and in vivo imaging was performed to evaluate tumor growth. Flow cytometry and immunohistochemistry were performed to examine immunologic changes upon treatment. The combination of BRD4 inhibitor and RT significantly suppressed tumor growth compared to RT alone. BRD4 inhibitor reduced the size of the unirradiated tumor, indicating that it may induce systemic immune responses. The expression of HIF-1α and PD-L1 in the tumor was significantly downregulated by the BRD4 inhibitor. The proportion of M1 tumor-associated macrophages (TAMs) increased, and the proportion of M2 TAMs decreased upon BRD4 inhibition. BRD4 inhibitor expanded CD4+ and CD8+ T cell populations in the tumor microenvironment. Additionally, splenic monocytic myeloid derived suppressor cells, which were increased by RT, were reduced upon the addition of BRD4 inhibitor. Therefore, the addition of BRD4 inhibitor significantly enhanced the systemic antitumor responses of local RT.

MAPK/MAK/MRK overlapping kinase (MOK) controls microglial inflammatory/type-I IFN responses via Brd4 and is involved in ALS

Amyotrophic lateral sclerosis (ALS) is a fatal and incurable neurodegenerative disease affecting motor neurons and characterized by microglia-mediated neurotoxic inflammation whose underlying mechanisms remain incompletely understood. In this work, we reveal that MAPK/MAK/MRK overlapping kinase (MOK), with an unknown physiological substrate, displays an immune function by controlling inflammatory and type-I interferon (IFN) responses in microglia which are detrimental to primary motor neurons. Moreover, we uncover the epigenetic reader bromodomain-containing protein 4 (Brd4) as an effector protein regulated by MOK, by promoting Ser492-phospho-Brd4 levels. We further demonstrate that MOK regulates Brd4 functions by supporting its binding to cytokine gene promoters, therefore enabling innate immune responses. Remarkably, we show that MOK levels are increased in the ALS spinal cord, particularly in microglial cells, and that administration of a chemical MOK inhibitor to ALS model mice can modulate Ser492-phospho-Brd4 levels, suppress microglial activation, and modify the disease course, indicating a pathophysiological role of MOK kinase in ALS and neuroinflammation.

The role of eIF4F-driven mRNA translation in regulating the tumour microenvironment

Cells can rapidly adjust their proteomes in dynamic environments by regulating mRNA translation. There is mounting evidence that dysregulation of mRNA translation supports the survival and adaptation of cancer cells, which has stimulated clinical interest in targeting elements of the translation machinery and, in particular, components of the eukaryotic initiation factor 4F (eIF4F) complex such as eIF4E. However, the effect of targeting mRNA translation on infiltrating immune cells and stromal cells in the tumour microenvironment (TME) has, until recently, remained unexplored. In this Perspective article, we discuss how eIF4F-sensitive mRNA translation controls the phenotypes of key non-transformed cells in the TME, with an emphasis on the underlying therapeutic implications of targeting eIF4F in cancer. As eIF4F-targeting agents are in clinical trials, we propose that a broader understanding of their effect on gene expression in the TME will reveal unappreciated therapeutic vulnerabilities that could be used to improve the efficacy of existing cancer therapies.

BRD4: New Hope in the Battle Against Glioblastoma

The BET family proteins, comprising BRD2, BRD3 and BRD4, represent epigenetic readers of acetylated histone marks that play pleiotropic roles in the tumorigenesis and growth of multiple human malignancies, including glioblastoma (GBM). A growing body of investigation has proven BET proteins as valuable therapeutic targets for cancer treatment. Recently, several BRD4 inhibitors and degraders have been reported to successfully suppress GBM in preclinical and clinical studies. However, the precise role and mechanism of BRD4 in the pathogenesis of GBM have not been fully elucidated or summarized. This review focuses on summarizing the roles and mechanisms of BRD4 in the context of the initiation and development of GBM. In addition, several BRD4 inhibitors have been evaluated for therapeutic purposes as monotherapy or in combination with chemotherapy, radiotherapy, and immune therapies. Here, we provide a critical appraisal of studies evaluating various BRD4 inhibitors and degraders as novel treatment strategies against GBM.

Bromodomain and Extra-Terminal Proteins in Brain Physiology and Pathology: BET-ing on Epigenetic Regulation

BET proteins function as histone code readers of acetylated lysins that determine the positive regulation in transcription of genes involved in cell cycle progression, differentiation, inflammation, and many other pathways. In recent years, thanks to the development of BET inhibitors, interest in this protein family has risen for its relevance in brain development and function. For example, experimental evidence has shown that BET modulation affects neuronal activity and the expression of genes involved in learning and memory. In addition, BET inhibition strongly suppresses molecular pathways related to neuroinflammation. These observations suggest that BET modulation may play a critical role in the onset and during the development of diverse neurodegenerative and neuropsychiatric disorders, such as Alzheimer’s disease, fragile X syndrome, and Rett syndrome. In this review article, we summarize the most recent evidence regarding the involvement of BET proteins in brain physiology and pathology, as well as their pharmacological potential as targets for therapeutic purposes.

JQ1 attenuates neuroinflammation by inhibiting the inflammasome-dependent canonical pyroptosis pathway in SAE

Sepsis-associated encephalopathy (SAE) manifests clinically in hyperneuroinflammation. Pyroptosis, which can induce an inflammatory cascade response, has been considered to be a causative factor of SAE. Evidence has shown that the bromo- and extraterminal (BET) proteins (including BRD2, BRD3, BRD4 and BRDT) inhibitor JQ1 can inhibit inflammation and suppress pyroptosis in various diseases. Therefore, we examined the effect of JQ1 on inflammasome-induced pyroptosis in the hippocampus in a mouse model of sepsis induced by lipopolysaccharide (LPS) injection. The results showed that JQ1 treatment alleviated sepsis-related symptoms, protected the blood-brain barrier (BBB), as indicated by upregulated expression of the tight junction proteins occludin and ZO-1, and remarkably rescued neuronal damage in SAE mice. Mechanistically, we demonstrated that JQ1 intervention inhibited the expression of BRD proteins and decreased the expression of inflammasomes by blocking phospho-nuclear factor kappa B (p-NF-κB) signalling, attenuating the canonical pyroptosis (mediated by cleaved-Caspase1/11) pathway and the release of proinflammatory factors in the hippocampus of septic mice. Interestingly, we also found that JQ1 selectively suppressed the activation of hippocampal microglia in SAE mice. Thus, JQ1 protected the hippocampal BBB and neuronal damage through the attenuation of neuroinflammation by inhibiting the inflammasome-dependent canonical pyroptosis pathway induced by LPS injection in mice, and JQ1 may be a promising target for the prevention of SAE.

Identification of diagnostic mRNA biomarkers in whole blood for ankylosing spondylitis using WGCNA and machine learning feature selection

Ankylosing spondylitis (AS) is a common inflammatory spondyloarthritis affecting the spine and sacroiliac joint that finally results in sclerosis of the axial skeleton. Aside from human leukocyte antigen B27, transcriptomic biomarkers in blood for AS diagnosis still remain unknown. Hence, this study aimed to investigate credible AS-specific mRNA biomarkers from the whole blood of AS patients by analyzing an mRNA expression profile (GSE73754) downloaded Gene Expression Omnibus, which includes AS and healthy control blood samples. Weighted gene co-expression network analysis was performed and revealed three mRNA modules associated with AS. By performing gene set enrichment analysis, the functional annotations of these modules revealed immune biological processes that occur in AS. Several feature mRNAs were identified by analyzing the hubs of the protein-protein interaction network, which was based on the intersection between differentially expressed mRNAs and mRNA modules. A machine learning-based feature selection method, SVM-RFE, was used to further screen out 13 key feature mRNAs. After verifying by qPCR, IL17RA, Sqstm1, Picalm, Eif4e, Srrt, Lrrfip1, Synj1 and Cxcr6 were found to be significant for AS diagnosis. Among them, Cxcr6, IL17RA and Lrrfip1 were correlated with severity of AS symptoms. In conclusion, our findings provide a framework for identifying the key mRNAs in whole blood of AS that is conducive for the development of novel diagnostic markers for AS.

BET protein inhibition promotes non-myeloid cell mediated neuroprotection after rodent spinal cord contusion

Spinal cord injuries (SCI) often lead to multiple neurological deficits as a result from the initial trauma and also the secondary damage that follows. Despite abundant preclinical data proposing anti-inflammatory therapies to minimize secondary injury and improve functional recovery, the field still lacks an effective neuroprotective treatment. Epigenetic proteins, such as bromodomain and extraterminal domain (BET) proteins, are emerging as new targets to regulate inflammation. More importantly, pharmacological inhibition of BET proteins suppresses pro-inflammatory gene transcription after SCI. In this study, we tested the therapeutic potential of inhibiting BET proteins after SCI with clinically relevant compounds, and investigated the role of the BET protein BRD4 in macrophages during progression of SCI pathology. Systemic inhibition of BET proteins with I-BET762 significantly reduced lesion size 8 weeks after a contusion injury in rats. However, we observed no histological or locomotor improvements after SCI when we deleted Brd4 in macrophages through the use of myeloid-specific Brd4 knockout mice or after macrophage-targeted pharmacological BET inhibition. Taken together, our data indicate that systemic I-BET762 treatment is neuroprotective, and the histopathological improvement observed is likely to be a result of effects on non-macrophage targets. Expanding our understanding on the role of BET proteins after SCI is necessary to identify novel therapeutic targets that can effectively promote repair after SCI.

Ex Vivo Culture Models of Hidradenitis Suppurativa for Defining Molecular Pathogenesis and Treatment Efficacy of Novel Drugs

Hidradenitis suppurativa (HS) is a complex and debilitating inflammatory skin disease for which no effective treatment is available currently. This is partly because of the lack of adequate human or animal models for defining the pathobiology of the disease. Here, we describe the development of air-liquid (A-L) interface, liquid-submersion (L-S), and bioreactor (Bio) ex vivo skin culture models. All three ex vivo platforms were effective for culturing skin samples for up to 14 days. Tissue architecture and integrity remained intact for at least 3 days for healthy skin and 14 days for HS skin. Up to day 3, no significant differences were observed in % early apoptotic cells among all three platforms. However, late apoptotic/necrotic cell death was increased in HS skin at day 3 in A-L and Bio culture. These cultures efficiently support the growth of various cells populations, including keratinocytes and immune cells. Profiling inflammatory gene signatures in HS skin from these ex vivo cultures showed dynamic changes in expression at day 3 and day 14. All three culture platforms were necessary to represent the inflammatory gene status of HS skin at day 0, suggesting that not all gene clusters were identically altered in each culture method. Similarly, cytokine/chemokine profiling of the supernatants from vehicle- and drug-treated ex vivo HS cultures again showed a better prediction of drug efficacy against HS. Overall, development of these three culture systems collectively provides a powerful tool to uncover the pathobiology of HS progression and screen various drugs against HS.

Discovery, X-ray Crystallography, and Anti-inflammatory Activity of Bromodomain-containing Protein 4 (BRD4) BD1 Inhibitors Targeting a Distinct New Binding Site

Bromodomain-containing protein 4 (BRD4) is an emerging epigenetic drug target for intractable inflammatory disorders. The lack of highly selective inhibitors among BRD4 family members has stalled the collective understanding of this critical system and the progress toward clinical development of effective therapeutics. Here we report the discovery of a potent BRD4 bromodomain 1 (BD1)-selective inhibitor ZL0590 (52) targeting a unique, previously unreported binding site, while exhibiting significant anti-inflammatory activities in vitro and in vivo. The X-ray crystal structural analysis of ZL0590 in complex with human BRD4 BD1 and the associated mutagenesis study illustrate a first-in-class nonacetylated lysine (KAc) binding site located at the helix αB and αC interface that contains important BRD4 residues (e.g., Glu151) not commonly shared among other family members and is spatially distinct from the classic KAc recognition pocket. This new finding facilitates further elucidation of the complex biology underpinning bromodomain specificity among BRD4 and its protein-protein interaction partners.

PROTACs technology for treatment of Alzheimer's disease: Advances and perspectives

Neurodegenerative diseases (NDs) are characteristic with progression of neuron degeneration, resulting in dysfunction of cognition and mobility. Many neurodegenerative diseases are because of proteinopathies that results from unusual protein accumulations and aggregations. The aggregation of misfolded proteins like β-amyloid, α-synuclein, tau, and polyglutamates are hallmarked in Alzheimer's disease (AD), which are undruggable targets, and usually do not respond to conventional small-molecule agents. Therefore, developing novel technology and strategy for reducing the levels of protein aggregates would be critical for treatment of AD. Recently, the emerging proteolysis targeting chimeras (PRPTACs) technology has been significantly considered for artificial and selective degradation of aberrant target proteins. These engineered bifunctional molecules engage target proteins to be degraded by either the cellular degradation machinery in the ubiquitin-proteasome system (UPS) or via the autophagy-lysosome degradation pathway. Although the application of PROTACs technology is preferable than oligonucleotide and antibodies for treatment of NDs, many limitations such as their pharmacokinetic properties, tissue distribution and cell permeabilities, still need to be corrected. Herein, we review the recent advances in PROTACs technology with their limitation for pharmaceutical targeting of aberrant proteins involved in Alzheimer's diseases. We also review therapeutic potential of dysregulated signaling such as PI3K/AKT/mTOR axis for the management of AD.

The Role of mRNA Translational Control in Tumor Immune Escape and Immunotherapy Resistance

Tremendous advances have been made in cancer immunotherapy over the last decade. Among the different steps of gene expression, translation of mRNA is emerging as an essential player in both cancer and immunity. Changes in mRNA translation are both rapid and adaptive, and translational reprogramming is known to be necessary for sustaining cancer cell proliferation. However, the role of mRNA translation in shaping an immune microenvironment permissive to tumors has not been extensively studied. Recent studies on immunotherapy approaches have indicated critical roles of mRNA translation in regulating the expression of immune checkpoint proteins, tuning the secretion of inflammation-associated factors, modulating the differentiation of immune cells in the tumor microenvironment, and promoting cancer resistance to immunotherapies. Careful consideration of the role of mRNA translation in the tumor-immune ecosystem could suggest more effective therapeutic strategies and may eventually change the current paradigm of cancer immunotherapy. In this review, we discuss recent advances in understanding the relationship between mRNA translation and tumor-associated immunity, the potential mechanisms of immunotherapy resistance in cancers linked to translational reprogramming, and therapeutic perspectives and potential challenges of modulating translational regulation in cancer immunotherapy.

BRD4 in physiology and pathology: ''BET'' on its partners

Bromodomain-containing 4 (BRD4), a member of Bromo and Extra-Terminal (BET) family, recognizes acetylated histones and is of importance in transcription, replication, and DNA repair. It also binds non-histone proteins, DNA and RNA, contributing to development, tissue growth, and various physiological processes. Additionally, BRD4 has been implicated in driving diverse diseases, ranging from cancer, viral infection, inflammation to neurological disorders. Inhibiting its functions with BET inhibitors (BETis) suppresses the progression of several types of cancer, creating an impetus for translating these chemicals to the clinic. The diverse roles of BRD4 are largely dependent on its interaction partners in different contexts. In this review we discuss the molecular mechanisms of BRD4 with its interacting partners in physiology and pathology. Current development of BETis is also summarized. Further understanding the functions of BRD4 and its partners will facilitate resolving the liabilities of present BETis and accelerate their clinical translation.

Aplysia Neurons as a Model of Alzheimer's Disease: Shared Genes and Differential Expression

Although Alzheimer’s disease (AD) is the most common form of dementia in the United States, development of therapeutics has proven difficult. Invertebrate alternatives to current mammalian AD models have been successfully employed to study the etiology of the molecular hallmarks of AD. The marine snail Aplysia californica offers a unique and underutilized system in which to study the physiological, behavioral, and molecular impacts of AD. Mapping of the Aplysia proteome to humans and cross-referencing with two databases of genes of interest in AD research identified 898 potential orthologs of interest in Aplysia. Included among these orthologs were alpha, beta and gamma secretases, amyloid-beta, and tau. Comparison of age-associated differential expression in Aplysia sensory neurons with that of late-onset AD in the frontal lobe identified 59 ortholog with concordant differential expression across data sets. The 21 concordantly upregulated genes suggested increased cellular stress and protein dyshomeostasis. The 47 concordantly downregulated genes included important components of diverse neuronal processes, including energy metabolism, mitochondrial homeostasis, synaptic signaling, Ca⁺⁺ regulation, and cellular cargo transport. Compromised functions in these processes are known hallmarks of both human aging and AD, the ramifications of which are suggested to underpin cognitive declines in aging and neurodegenerative disease.

Role of BET Proteins in Inflammation and CNS Diseases

Bromodomain and extra-terminal domain (BET) proteins consist of four mammalian members (BRD2, BRD3, BRD4, and BRDT), which play a pivotal role in the transcriptional regulation of the inflammatory response. Dysregulated inflammation is a key pathological process in various CNS disorders through multiple mechanisms, including NF-κB and Nrf2 pathways, two well-known master regulators of inflammation. A better mechanistic understanding of the BET proteins’ role in regulating the inflammatory process is of great significance since it could reveal novel therapeutic targets to reduce neuroinflammation associated with many CNS diseases. In this minireview, we first outline the structural features of BET proteins and summarize genetic and pharmacological approaches for BET inhibition, including novel strategies using proteolysis-targeting chimeras (PROTACs). We emphasize in vitro and in vivo evidence of the interplay between BET proteins and NF-κB and Nrf2 signaling pathways. Finally, we summarize recent studies showing that BET proteins are essential regulators of inflammation and neuropathology in various CNS diseases.

Brd4 Regulates the Homeostasis of CD8+ T-Lymphocytes and Their Proliferation in Response to Antigen Stimulation

CD8+ T cells are major components of adaptive immunity and confer robust protective cellular immunity, which requires adequate T-cell numbers, targeted migration, and efficient T-cell proliferation. Altered CD8+ T-cell homeostasis and impaired proliferation result in dysfunctional immune response to infection or tumorigenesis. However, intrinsic factors controlling CD8+ T-cell homeostasis and immunity remain largely elusive. Here, we demonstrate the prominent role of Brd4 on CD8+ T cell homeostasis and immune response. By upregulating Myc and GLUT1 expression, Brd4 facilitates glucose uptake and energy production in mitochondria, subsequently supporting naïve CD8+ T-cell survival. Besides, Brd4 promotes the trafficking of naïve CD8+ T cells partially through maintaining the expression of homing receptors (CD62L and LFA-1). Furthermore, Brd4 is required for CD8+ T cell response to antigen stimulation, as Brd4 deficiency leads to a severe defect in clonal expansion and terminal differentiation by decreasing glycolysis. Importantly, as JQ1, a pan-BRD inhibitor, severely dampens CD8+ T-cell immune response, its usage as an anti-tumor agent or latency-reversing agent for human immunodeficiency virus type I (HIV-1) should be more cautious. Collectively, our study identifies a previously-unexpected role of Brd4 in the metabolic regulation of CD8+ T cell-mediated immune surveillance and also provides a potential immunomodulation target.

Protective effect of surfactin on copper sulfate-induced inflammation, oxidative stress, and hepatic injury in zebrafish

Surfactin, an antibacterial peptide, produced by various Bacillus subtilis strains, have broad-spectrum antibacterial and immune-enhancing functions. In this study, we investigated the anti-inflammatory, antioxidant, and hepatoprotective effect of surfactin on zebrafish (Danio rerio) larvae following their exposure to copper sulfate (CuSO₄ ). The mature AB wild-type and a transgenic line of zebrafish larvae that expressed enhanced GFP (EGFP) named Tg (Lyz:EGFP) were exposed to 0, 20, 40, and 60 μg/mL surfactin after incubation with 3.2 μg/mL CuSO₄ for 2 h from 72 h postfertilization (hpf). Different endpoints, such as migration of GFP-labeled neutrophils, analysis of inflammatory cytokines and transaminases, markers of oxidation, expression of certain genes, and histological changes of liver, were studied to evaluate the function of surfactin. The protein expression levels of NF-κBp65, TNF-α, cyclooxygenase-2 (COX-2), and iNOS were determined in murine macrophage RAW 264.7 cells by western blotting. Our results show that surfactin reduced migration of neutrophils and relieved hepatic injury. In addition, surfactin reduced the index levels of inflammatory factors, oxidative stress response, and improved hepatic function. Surfactin also significantly inhibited the expression of IL-1β, IL-8, TNF-α, nitric oxide, NF-κBp65, COX-2, and iNOS, and increased the expression of IL-10. Thus, our results demonstrate that surfactin has anti-inflammatory, antioxidant, and hepatoprotective activities. Surfactin has potential as a novel inflammation and immune adjustment.

Mesenchymal stem cells-derived extracellular vesicles carrying microRNA-17 inhibits macrophage apoptosis in lipopolysaccharide-induced sepsis

OBJECTIVE

Sepsis, as a disease affecting the microcirculation and tissue perfusion, results in tissue hypoxia and multiple organ dysfunctions. Bone mesenchymal stem cell (BMSC)-derived extracellular vesicles (EVs) have been demonstrated to transfer trivial molecules (proteins/peptides, mRNA, microRNA and lipids) to alleviate sepsis. We sought to define the function of microRNA (miR)-17 carried in BMSC-EVs in sepsis.

METHODS

The purity of the extracted BMSCs was identified and confirmed by detection of the surface markers by flow cytometry, followed by osteoblastic, adipogenic, and chondrocyte differentiation experiments. Subsequently, EVs were collected from the medium of BMSCs. The uptake of PKH-67-labeled BMSC-EVs or EVs carrying cy3-miR-17 by RAW264.7 cells was observed under laser confocal microscopy. Furthermore, a series of gain- and loss-of-function approaches were conducted to test the effects of LPS, miR-17 and BRD4 on the inflammatory factors (IL-1β, IL-6 and TNF-α), number of M1 macrophages and M2 macrophages, inflammatory-related signal pathway factors (EZH2, c-MYC and TRAIL), macrophage proliferation, and apoptosis in sepsis. The survival rates were measured in vivo.

RESULTS

BMSC-EVs was internalized by the RAW264.7 cells. BDR4 was verified as a target of miR-17, while the expression pattern of miR-17 was upregulated in BMSC-EVs. MiR-17 carried by BMSC-EVs inhibited LPS-induced inflammation and apoptosis of RAW264.7 cells, but improved the viability of RAW264.7 cells. Next, in vitro experiments supported that miR-17 inhibited LPS-induced inflammation in RAW264.7 cells through BRD4/EZH2/TRAIL axis. BRD4 overexpression reversed the effects of miR-17. Moreover, the therapeutic function of BMSC-EVs carried miR-17 was verified by in vivo experiments.

CONCLUSIONS

MiR-17 derived from BMSCs-EVs regulates BRD4-mediated EZH2/TRAIL axis to essentially inhibit LPS-induced macrophages inflammation.

Brd4 modulates diet-induced obesity via PPARγ-dependent Gdf3 expression in adipose tissue macrophages

Macrophage-mediated inflammatory response has been implicated in the pathogenesis of obesity and insulin resistance. Brd4 has emerged as a key regulator in the innate immune response. However, the role of Brd4 in obesity-associated inflammation and insulin resistance remains uncharacterized. Here, we demonstrated that myeloid lineage-specific Brd4 knockout (Brd4-CKO) mice were protected from high-fat diet-induced (HFD-induced) obesity with less fat accumulation, higher energy expenditure, and increased lipolysis in adipose tissue. Brd4-CKO mice fed a HFD also displayed reduced local and systemic inflammation with improved insulin sensitivity. RNA-Seq of adipose tissue macrophages (ATMs) from HFD-fed WT and Brd4-CKO mice revealed that expression of antilipolytic factor Gdf3 was significantly decreased in ATMs of Brd4-CKO mice. We also found that Brd4 bound to the promoter and enhancers of Gdf3 to facilitate PPARγ-dependent Gdf3 expression in macrophages. Furthermore, Brd4-mediated expression of Gdf3 acted as a paracrine signal targeting adipocytes to suppress the expression of lipases and the associated lipolysis in cultured cells and mice. Controlling the expression of Gdf3 in ATMs could be one of the mechanisms by which Brd4 modulates lipid metabolism and diet-induced obesity. This study suggests that Brd4 could be a potential therapeutic target for obesity and insulin resistance.

Progress in developing MNK inhibitors

The MNKs (mitogen-activated protein kinase-interacting protein kinases) phosphorylate eIF4E (eukaryotic initiation factor 4 E) at serine 209; eIF4E plays an important role in the translation of cytoplasmic mRNAs, all of which possess a 5' 'cap' structure to which eIF4E binds. Elevated levels of eIF4E, p-eIF4E and/or the MNK protein kinases have been found in many types of cancer, including solid tumors and leukemia. MNKs also play a role in metabolic disease. Regulation of the activities of MNKs (MNK1 and MNK2), control the phosphorylation of eIF4E, which in turn has a close relationship with the processes of tumor development, cell migration and invasion, and energy metabolism. MNK knock-out mice display no adverse effects on normal cells or phenotypes suggesting that MNK may be a potentially safe targets for the treatment of various cancers. Several MNK inhibitors or 'degraders' have been identified. Initially, some of the inhibitors were developed from natural products or based on other protein kinase inhibitors which inhibit multiple kinases. Subsequently, more potent and selective inhibitors for MNK1/2 have been designed and synthesized. Currently, three inhibitors (BAY1143269, eFT508 and ETC-206) are in various stages of clinical trials for the treatment of solid cancers or leukemia, either alone or combined with inhibitors of other protein kinase. In this review, we summarize the diverse MNK inhibitors that have been reported in patents and other literature, including those with activities in vitro and/or in vivo.

BRD4 targeting nanotherapy prevents lipopolysaccharide induced acute respiratory distress syndrome

Acute respiratory distress syndrome (ARDS) is a life threatening respiratory disease associated with pulmonary edema, alveolar dysfunction, hypoxia, and inflammatory cell accumulation. The most contagious form of COVID-19 associated with ARDS caused by SARS-CoV-2. SARS-CoV-2 majorly produces the cytokine storm and severe lung inflammation and ultimately leads to respiratory failure. ARDS is a complex disease and there is no proper therapeutics for effective therapy. Still, there is a huge scope to identify novel targets to combat respiratory illness. In the current study, we have identified the epigenetic regulating protein BRD4 and developed siRNA based nanomedicine to treat the ARDS. The liposomes were prepared by thin-film hydration method, where BRD4 siRNA complexed with cationic lipid and exhibited 96.24 ± 18.01 nm size and stable even in the presence of RNase. BRD4 siRNA lipoplexes (BRD4-siRNA-LP) inhibited inflammatory cells in lungs and suppressed the lipopolysaccharide (LPS) induced the neutrophil infiltration and mast cell accumulation. Also, BRD4 siRNA based nanomedicine significantly reduced the LPS induced cytokine storm followed by inflammatory signaling pathways. Interestingly, BRD4-siRNA-LP suppressed the LPS-induced p65 and STAT3 nuclear translocation and ameliorated the lung inflammation. Thus, BRD4-siRNA-LP could be a plausible therapeutic option for treating ARDS and might be useful for combating the COVID-19 associated respiratory illness.

Pharmacological Modulation of BET Family in Sepsis

The Third International Consensus Definitions for Sepsis and Septic Shock (Sepsis 3.0) recommended defining sepsis as a life-threatening organ dysfunction caused by the host's uncontrolled response to infection. The bromodomain and extra-terminal (BET) protein family (such as BRD2, BRD3, and BRD4), an epigenetic regulator of gene transcription, has recently been recognized as a significant septic regulator of inflammation and immune response, including cytokine and chemokine production. Mechanistically, the two N-terminal conserved tandem bromodomains (namely the first bromodomain [BD1] and the second bromodomain [BD2]) favor the binding of BETs to acetylated histones or transcription factors, thereby initiating gene transcription machinery after CycT1 and CDK9 (also known as P-TEFb) are recruited to gene promoters to phosphorylate RNA pol II. Notably, BD1 and BD2 are not functionally redundant because they have different target genes in innate immune cells. Small-molecule BET inhibitors (BETis) for different BDs, such as I-BET, JQ1, I-BET151, apabetalone, RVX-297, and dBET1 have shown promising therapeutic effects in experimental sepsis models. This mini-review summarizes the emerging roles of BETs and the applications of BETis in sepsis, discusses the existing shortcomings of BETis, and introduces possible future research directions in this area.

Brd4 regulates NLRC4 inflammasome activation by facilitating IRF8-mediated transcription of Naips

NLRC4 inflammasome activation and the subsequent maturation of IL-1β and IL-18 are critical for protection against infection by bacterial pathogens. The epigenetic regulator Brd4 has emerged as a key player in inflammation by regulating the expression of inflammatory cytokines. However, whether Brd4 has any role in inflammasome activation remains undetermined. Here, we demonstrated that Brd4 is an important regulator of NLRC4 inflammasome activation in response to Salmonella typhimurium infection. Brd4-deficient bone marrow-derived macrophages (BMDMs) displayed impaired caspase-1 activation, ASC oligomerization, IL-1β maturation, gasdermin-D cleavage, and pyroptosis in response to S.typhimurium infection. RNA sequencing and RT-PCR results revealed that the transcription of Naips was decreased in Brd4-deficient BMDMs. Brd4 formed a complex with IRF8/PU.1 and bound to the IRF8 and PU.1 binding motifs on the promoters of Naips to maintain the expression of Naips. Furthermore, myeloid lineage-specific Brd4 conditional knockout mice were more susceptible to S.typhimurium infection with increased mortality, bacterial loads, and tissue damage; impaired inflammasome-dependent cytokine production; and pyroptosis. Our studies identify a novel function of Brd4 in innate immunity by controlling inflammasome-mediated cytokine release and pyroptosis to effectively battle S.typhimurium infection.

The BET family in immunity and disease

Innate immunity serves as the rapid and first-line defense against invading pathogens, and this process can be regulated at various levels, including epigenetic mechanisms. The bromodomain and extraterminal domain (BET) family of proteins consists of four conserved mammalian members (BRD2, BRD3, BRD4, and BRDT) that regulate the expression of many immunity-associated genes and pathways. In particular, in response to infection and sterile inflammation, abnormally expressed or dysfunctional BETs are involved in the activation of pattern recognition receptor (e.g., TLR, NLR, and CGAS) pathways, thereby linking chromatin machinery to innate immunity under disease or pathological conditions. Mechanistically, the BET family controls the transcription of a wide range of proinflammatory and immunoregulatory genes by recognizing acetylated histones (mainly H3 and H4) and recruiting transcription factors (e.g., RELA) and transcription elongation complex (e.g., P-TEFb) to the chromatin, thereby promoting the phosphorylation of RNA polymerase II and subsequent transcription initiation and elongation. This review covers the accumulating data about the roles of the BET family in innate immunity, and discusses the attractive prospect of manipulating the BET family as a new treatment for disease.

BRD4 inhibition and FXR activation, individually beneficial in cholestasis, are antagonistic in combination

Activation of farnesoid X receptor (FXR) by obeticholic acid (OCA) reduces hepatic inflammation and fibrosis in patients with primary biliary cholangitis (PBC), a life-threatening cholestatic liver failure. Inhibition of bromodomain-containing protein 4 (BRD4) also has antiinflammatory, antifibrotic effects in mice. We determined the role of BRD4 in FXR function in bile acid (BA) regulation and examined whether the known beneficial effects of OCA are enhanced by inhibiting BRD4 in cholestatic mice. Liver-specific downregulation of BRD4 disrupted BA homeostasis in mice, and FXR-mediated regulation of BA-related genes, including small heterodimer partner and cholesterol 7 alpha-hydroxylase, was BRD4 dependent. In cholestatic mice, JQ1 or OCA treatment ameliorated hepatotoxicity, inflammation, and fibrosis, but surprisingly, was antagonistic in combination. Mechanistically, OCA increased binding of FXR, and the corepressor silencing mediator of retinoid and thyroid hormone receptor (SMRT) decreased NF-κB binding at inflammatory genes and repressed the genes in a BRD4-dependent manner. In patients with PBC, hepatic expression of FXR and BRD4 was significantly reduced. In conclusion, BRD4 is a potentially novel cofactor of FXR for maintaining BA homeostasis and hepatoprotection. Although BRD4 promotes hepatic inflammation and fibrosis in cholestasis, paradoxically, BRD4 is required for the antiinflammatory, antifibrotic actions of OCA-activated FXR. Cotreatment with OCA and JQ1, individually beneficial, may be antagonistic in treatment of liver disease patients with inflammation and fibrosis complications.

BRDT is a novel regulator of eIF4EBP1 in renal cell carcinoma

Among all types of kidney diseases, renal cell carcinoma (RCC) has the highest mortality, recurrence and metastasis rates, which results in high numbers of tumor-associated mortalities in China. Identifying a novel therapeutic target has attracted increasing attention. Bromodomain and extraterminal domain (BET) proteins have the ability to read the epigenome, leading to regulation of gene transcription. As an important member of the BET family, bromodomain testis-specific protein (BRDT) has been well studied; however, the mechanism underlying BRDT in the regulation of RCC has not been fully investigated. Eukaryotic translation initiation factor 4E-binding protein 1 (eIF4EBP1) is a binding partner of eIF4E that is involved in affecting the progression of various cancer types via regulating gene transcription. To identify novel regulators of eIF4EBP1, an immunoprecipitation assay and mass spectrometry analysis was performed in RCC cells. It was revealed that eIF4EBP1 interacted with BRDT, a novel interacting protein. In addition, the present study further demonstrated that BRDT inhibitors PLX51107 and INCB054329 blocked the progression of RCC cells, along with suppressing eIF4EBP1 and c-myc expression. Small interfering (si) RNAs were used to knock down BRDT expression, which suppressed RCC cell proliferation and eIF4EBP1 protein expression. In addition, overexpression of eIF4EBP1 partially abolished the inhibited growth function of PLX51107 but knocking down eIF4EBP1 improved the inhibitory effects of PLX51107. Furthermore, treatment with PLX51107 or knockdown of BRDT expression decreased c-myc expression at both the mRNA and protein levels, and attenuated its promoter activity, as determined by luciferase reporter assays. PLX51107 also significantly altered the interaction between the c-myc promoter with eIF4EBP1 and significantly attenuated the increase of RCC tumors, accompanied by decreased c-myc mRNA and protein levels in vivo. Taken together, these data suggested that blocking of BRDT by PLX51107, INCB054329 or BRDT knockdown suppressed the growth of RCC via decreasing eIF4EBP1, thereby leading to decreased c-myc transcription levels. Considering the regulatory function of BET proteins in gene transcription, the present study suggested that there is a novel mechanism underlying eIF4EBP1 regulation by BRDT, and subsequently decreased c-myc in RCC, and further identified a new approach by regulating eIF4EBP1 or c-myc for enhancing BRDT-targeting RCC therapy.

BETs that cover the spread from acquired to heritable heart failure

Heart failure (HF) with reduced contractile function is a common and lethal syndrome in which the heart cannot pump blood to adequately meet bodily demands, resulting in high mortality despite the current standard of care. In modern societies, the most common drivers of HF are ischemic heart disease and hypertension. However, in a substantial subset of cases, patients present with dilated and poorly contracting hearts without evidence of common inciting stressors, a syndrome called dilated cardiomyopathy (DCM). Genome sequencing has identified a host of deleterious germline variants in key cardiomyocyte genes as causes of heritable DCM, including mutations in LMNA, which encodes the nuclear lamina-associated protein lamin A/C. In this issue of the JCI, Auguste et al. generate a mouse model of DCM in which they delete Lmna in cardiomyocytes and discover that bromodomain and extraterminal (BET) protein activation is a druggable epigenetic mechanism of disease pathogenesis in this heritable HF syndrome.

LncRNA XIST silencing protects against sepsis-induced acute liver injury via inhibition of BRD4 expression

Sepsis is recognized as the acute systemic inflammatory response to severe infection. It is main cause of multiple organ system dysfunction and even organ failure. Long non-coding RNA X inactivate-specific transcript (XIST) is implicated in multiple inflammatory diseases. The aim of present work was to investigate the precise mechanism of XIST underlying sepsis-induced acute liver injury. Rats were underwent cecal ligation and puncture (CLP) to establish sepsis-induced the animal models of acute liver injury. Hematoxylin and eosin (H&E) staining was performed to observe pathological alterations. Corresponding commercial assay kits were employed to analyze the levels of inflammatory cytokines and oxidative stress. Western blot and reverse transcriptional quantitative PCR (RT-qPCR) were performed to determine the expression of proteins and target genes. Finally, TUNEL and CCK-8 assays were performed to test apoptosis rate and cell viability, respectively. In our study, XIST and BRD4 were highly expressed in serum of patients with sepsis-induced acute liver injury. XIST knockdown ameliorated sepsis-induced acute liver injury and inhibited inflammation, oxidative stress, and cell apoptosis in sepsis-induced acute liver injury rats. Interestingly, XIST knockdown downregulated the expression of BRD4, and BRD4 overexpression abolished the impacts of XIST knockdown on inflammation, oxidative stress, and apoptosis of that LPS-induced Kupffer cells. We conclude that lncRNA XIST silencing protects against sepsis-induced acute liver injury via inhibition of the BRD4 expression. Therefore, XIST may be a biomarker for sepsis diagnosis and treatment.

Domain-selective targeting of BET proteins in cancer and immunological diseases

Cancer and inflammation are strongly interconnected processes. Chronic inflammatory pathologies can be at the heart of tumor development; similarly, tumor-elicited inflammation is a consequence of many cancers. The mechanistic interdependence between cancer and inflammatory pathologies points toward common protein effectors which represent potential shared targets for pharmacological intervention. Epigenetic mechanisms often drive resistance to cancer therapy and immunomodulatory strategies. The bromodomain and extraterminal domain (BET) proteins are epigenetic adapters which play a major role in controlling cell proliferation and the production of inflammatory mediators. A plethora of small molecules aimed at inhibiting BET protein function to treat cancer and inflammatory diseases have populated academic and industry efforts in the last 10 years. In this review, we will discuss recent pharmacological approaches aimed at targeting a single or a subset of the eight bromodomains within the BET family which have the potential to tease apart clinical efficacy and safety signals of BET inhibitors.

BET Epigenetic Reader Proteins in Cardiovascular Transcriptional Programs

Epigenetic mechanisms involve the placing (writing) or removal (erasing) of histone modifications that allow heterochromatin to transition to the open, activated euchromatin state necessary for transcription. A third, less studied epigenetic pathway involves the reading of these specific histone marks once placed. The BETs (bromodomain and extraterminal-containing protein family), which includes BRD2, BRD3, and BRD4 and the testis-restricted BRDT, are epigenetic reader proteins that bind to specific acetylated lysine residues on histone tails where they facilitate the assembly of transcription complexes including transcription factors and transcriptional machinery like RNA Polymerase II. As reviewed here, considerable recent data establishes BETs as novel determinants of induced transcriptional programs in vascular cells, like endothelial cells and vascular smooth muscle cells, cardiac myocytes and inflammatory cells, like monocyte/macrophages, cellular settings where these epigenetic reader proteins couple proximal stimuli to chromatin, acting at super-enhancer regulatory regions to direct gene expression. BET inhibition, including the use of specific chemical BET inhibitors like JQ-1, has many reported effects in vivo in the cardiovascular setting, like decreasing atherosclerosis, angiogenesis, intimal hyperplasia, pulmonary arterial hypertension, and cardiac hypertrophy. At the same time, data in endothelial cells, adipocytes, and elsewhere suggest BETs also help regulate gene expression under basal conditions. Studies in the cardiovascular setting have highlighted BET action as a means of controlling gene expression in differentiation, cell identity, and cell state transitions, whether physiological or pathological, adaptive, or maladaptive. While distinct BET inhibitors are being pursued as therapies in oncology, a large prospective clinical cardiovascular outcome study investigating the BET inhibitor RVX-208 (now called apabetalone) has already been completed. Independent of this specific agent and this one trial or the numerous unanswered questions that remain, BETs have emerged as novel epigenetic players involved in the execution of coordinated transcriptional programs in cardiovascular health and disease.

BRD4 inhibition exerts anti-viral activity through DNA damage-dependent innate immune responses

Chromatin dynamics regulated by epigenetic modification is crucial in genome stability and gene expression. Various epigenetic mechanisms have been identified in the pathogenesis of human diseases. Here, we examined the effects of ten epigenetic agents on pseudorabies virus (PRV) infection by using GFP-reporter assays. Inhibitors of bromodomain protein 4 (BRD4), which receives much more attention in cancer than viral infection, was found to exhibit substantial anti-viral activity against PRV as well as a range of DNA and RNA viruses. We further demonstrated that BRD4 inhibition boosted a robust innate immune response. BRD4 inhibition also de-compacted chromatin structure and induced the DNA damage response, thereby triggering the activation of cGAS-mediated innate immunity and increasing host resistance to viral infection both in vitro and in vivo. Mechanistically, the inhibitory effect of BRD4 inhibition on viral infection was mainly attributed to the attenuation of viral attachment. Our findings reveal a unique mechanism through which BRD4 inhibition restrains viral infection and points to its potent therapeutic value for viral infectious diseases.

BRD4 has been well investigated in tumorigenesis for its contribution to chromatin remodeling and gene transcription. BRD4 inhibitors are used as promising chemotherapeutic drugs for cancer therapy. Here, we show a unique mechanism through which BRD4 inhibition broadly inhibits attachment of DNA and RNA viruses through DNA damage-dependent antiviral innate immune activation via the cGAS-STING pathway, in both cell culture and an animal model. STING-associated innate immune signaling has been considered to be a new possibility for cancer therapy, and STING agonists have been tested in early clinical trials. Our data identify BRD4 inhibitors as a potent therapy not only for viral infection but also for cancer immunotherapy.

Bromodomain and extra-terminal domain (BET) proteins regulate melanocyte differentiation

BACKGROUND

Pharmacologic inhibition of bromodomain and extra-terminal (BET) proteins is currently being explored as a new therapeutic approach in cancer. Some studies have also implicated BET proteins as regulators of cell identity and differentiation through their interactions with lineage-specific factors. However, the role of BET proteins has not yet been investigated in melanocyte differentiation. Melanocyte inducing transcription factor (MITF) is the master regulator of melanocyte differentiation, essential for pigmentation and melanocyte survival. In this study, we tested the hypothesis that BET proteins regulate melanocyte differentiation through interactions with MITF.

RESULTS

Here we show that chemical inhibition of BET proteins prevents differentiation of unpigmented melanoblasts into pigmented melanocytes and results in de-pigmentation of differentiated melanocytes. BET inhibition also slowed cell growth, without causing cell death, increasing the number of cells in G1. Transcriptional profiling revealed that BET inhibition resulted in decreased expression of pigment-specific genes, including many MITF targets. The expression of pigment-specific genes was also down-regulated in melanoma cells, but to a lesser extent. We found that RNAi depletion of the BET family members, bromodomain-containing protein 4 (BRD4) and bromodomain-containing protein 2 (BRD2) inhibited expression of two melanin synthesis enzymes, TYR and TYRP1. Both BRD4 and BRD2 were detected on melanocyte promoters surrounding MITF-binding sites, were associated with open chromatin structure, and promoted MITF binding to these sites. Furthermore, BRD4 and BRD2 physically interacted with MITF.

CONCLUSION

These findings indicate a requirement for BET proteins in the regulation of pigmentation and melanocyte differentiation. We identified changes in pigmentation specific gene expression that occur upon BET inhibition in melanoblasts, melanocytes, and melanoma cells.

Association of survival and genomic mutation signature with immunotherapy in patients with hepatocellular carcinoma

Background

Current guidelines lack recommendations for the use of immunotherapy and immune-related biomarkers for hepatocellular carcinoma (HCC). We aim to provide reliable evidence of the association of survival with HCC immunotherapy and to demonstrate that genomic mutation signature could be an effective biomarker to predict immunotherapy efficacy of HCC patients.

Methods

We conducted a meta-analysis of 17 randomized trials with 2055 patients and an individual patient-level analysis of 31 patients. Trial data were identified in PubMed, EMBASE and Cochrane Central library, and individual patient data were obtained from the cBioPortal database. Overall survival (OS) and progression-free survival (PFS) were assessed with the hazard ratio (HR) and 95% CI. This study is registered with PROSPERO, number CRD42018083991.

Results

The meta-analysis showed that compared to conventional therapy, immunotherapy resulted in prolonged OS (HR =0.65, P<0.0001, high quality) and PFS (HR =0.81, P<0.0001, high quality); the benefits were observed for cellular immunotherapy, tumor vaccine, and cytokine immunotherapy. Findings were robust to subgroup and trial sequential analyses. In the individual patient-level analysis of patients treated with immune checkpoint inhibitor, mutations in TERT, CTNNB1, BRD4, or MLL, and co-mutations in TP53 and TERT or BRD4 were associated with significantly worse survival. These oncogenes were used to develop a novel integrated mutation risk score, which exhibited better utility in predicting survival than the tumor mutation burden (TMB). Patients with low- versus high- mutation risk score had longer OS (HR =0.18, P=0.02) and PFS (HR =0.33, P=0.018). A nomogram comprising the mutation risk score and essential clinical factors further improved the predictive accuracy (AUC =0.840 for both 1- and 2-year OS).

Conclusions

Immunotherapy showed longer OS and PFS than conventional therapy among HCC patients, especially patients with a low mutation risk score. The nomogram based on genomic and clinical characteristics is effective in predicting survival of HCC patients undergoing immune checkpoint inhibitor.

Epigenetic modifiers as new immunomodulatory therapies in solid tumours

Background

Immune therapies have revolutionized cancer treatment over the last few years by allowing improvements in overall survival. However, the majority of patients is still primary or secondary resistant to such therapies, and enhancing sensitivity to immune therapies is therefore crucial to improve patient outcome. Several recent lines of evidence suggest that epigenetic modifiers have intrinsic immunomodulatory properties, which could be of therapeutic interest.

Material and methods

We reviewed preclinical evidence and clinical studies which describe or exploit immunomodulatory properties of epigenetic agents. Experimental approaches, clinical applicability and corresponding ongoing clinical trials are described.

Results

Several epigenetic modifiers, such as histone deacetylase inhibitors, DNA methyl transferase inhibitors, bromodomain inhibitors, lysine-specific histone demethylase 1 inhibitors and enhancer of zeste homolog 2 inhibitors, display intrinsic immunomodulatory properties. The latter can be achieved through the action of these drugs either on cancer cells (e.g. presentation and generation of neoantigens, induction of immunogenic cell death, modulation of cytokine secretion), on immune cells (e.g. linage, differentiation, activation status and antitumor capability), or on components of the microenvironment (e.g. regulatory T cells and macrophages). Several promising combinations, notably with immune checkpoint blockers or adoptive T-cell therapy, can be envisioned. Dedicated clinically relevant approaches for patient selection and trial design will be required to optimally develop such combinations.

Conclusion

In an era where immune therapies are becoming a treatment backbone in many tumour types, epigenetic modifiers could play a crucial role in modulating tumours' immunogenicity and sensitivity to immune agents. Optimal trial design, including window of opportunity trials, will be key in the success of this approach, and clinical evaluation is ongoing.

Transcription modulation by CDK9 regulates inflammatory genes and RIPK3-MLKL-mediated necroptosis in periodontitis progression

Cyclin-dependent kinase 9 (CDK9), one crucial molecule in promoting the transition from transcription pausing to elongation, is a critical modulator of cell survival and death. However, the pathological function of CDK9 in bacterial inflammatory diseases has never been explored. CDK9 inhibition or knock-down attenuated Porphyromonas gingivalis-triggered inflammatory gene expression. Gene-expression microarray analysis of monocytes revealed that knock-down of CDK9 not only affected inflammatory responses, but also impacted cell death network, especially the receptor-interacting protein kinase 3 (RIPK3)-mixed lineage kinase domain-like (MLKL)-mediated necroptosis after P. gingivalis infection. Inhibition of CDK9 significantly decreased necroptosis with downregulation of both MLKL and phosphorylated MLKL. By regulating caspase-8 and cellular FLICE inhibitory protein (cFLIP), key molecules in regulating cell survival and death, CDK9 affected not only the classic RIPK1-RIPK3-mediated necroptosis, but also the alternate TIR-domain-containing adapter-inducing interferon-β-RIPK3-mediated necroptosis. CDK9 inhibition dampened pro-inflammatory gene production in the acute infection process in the subcutaneous chamber model in vivo. Moreover, CDK9 inhibition contributed to the decreased periodontal bone loss and inflammatory response induced by P. gingivalis in the periodontal micro-environment. In conclusion, by modulating the RIPK3-MLKL-mediated necroptosis, CDK9 inhibition provided a novel mechanism to impact the progress of bacterial infection in the periodontal milieu.

Validation of the epigenetic reader bromodomain-containing protein 4 (BRD4) as a therapeutic target for treatment of airway remodeling

Structural remodeling is central to the initiation and progression of many chronic lung diseases, representing an important unmet need. We examine the evidence supporting bromodomain-containing protein 4 (BRD4) as a validated biological target for treatment of airway remodeling. In epithelial cells and fibroblasts, BRD4 serves as a scaffold for chromatin remodeling complexes in active super-enhancers. In response to inflammatory stimuli, BRD4 is repositioned to innate and mesenchymal genes activating their production. Proof-of-concept studies show promising benefit of selective BRD4 inhibitors in disrupting epithelial mesenchymal transition and myofibroblast transition in diverse models of lung injury. Recent identification of biomarkers of BRD4 provides a basis for further drug development for application in viral-induced airway inflammation, COPD and interstitial lung diseases.

Phosphorylation and Signal Transduction Pathways in Translational Control

Protein synthesis, including the translation of specific messenger RNAs (mRNAs), is regulated by extracellular stimuli such as hormones and by the levels of certain nutrients within cells. This control involves several well-understood signaling pathways and protein kinases, which regulate the phosphorylation of proteins that control the translational machinery. These pathways include the mechanistic target of rapamycin complex 1 (mTORC1), its downstream effectors, and the mitogen-activated protein (MAP) kinase (extracellular ligand-regulated kinase [ERK]) signaling pathway. This review describes the regulatory mechanisms that control translation initiation and elongation factors, in particular the effects of phosphorylation on their interactions or activities. It also discusses current knowledge concerning the impact of these control systems on the translation of specific mRNAs or subsets of mRNAs, both in physiological processes and in diseases such as cancer.

Microplitis bicoloratus bracovirus modulates innate immune suppression through the eIF4E-eIF4A axis in the insect Spodoptera litura

Eukaryotic initiation factor 4E (eIF4E) is regulated during the innate immune response. However, its translational regulation under innate immune suppression remains largely unexplored. Microplitis bicoloratus bracovirus (MbBV), a symbiotic virus harbored by the parasitoid wasp, Microplitis bicoloratus, suppresses innate immunity in parasitized Spodoptera litura. Here, we generated eIF4E dsRNA and used it to silence the eIF4E gene of S. litura, resulting in a hallmark immunosuppressive phenotype characterized by increased apoptosis of hemocytes and retardation of head capsule width development. In response to natural parasitism, loss of eIF4E function was associated with similar immunosuppression, and we detected no significant differences between the response to parasitism and treatment with eIF4E RNAi. Under MbBV infection, eIF4E overexpression significantly suppressed MbBV-induced increase in apoptosis and suppressed apoptosis to the same extent as co-expression of both eIF4E and eIF4A. There were no significant differences between MbBV-infected and uninfected larvae in which eIF4E was overexpressed. More importantly, in the eIF4E RNAi strain, eIF4A RNAi did not increase apoptosis. Collectively, our results indicate that eIF4E plays a nodal role in the MbBV-suppressed innate immune response via the eIF4E-eIF4A axis.

BET Bromodomain Inhibitors Suppress Inflammatory Activation of Gingival Fibroblasts and Epithelial Cells From Periodontitis Patients

BET bromodomain proteins are important epigenetic regulators of gene expression that bind acetylated histone tails and regulate the formation of acetylation-dependent chromatin complexes. BET inhibitors suppress inflammatory responses in multiple cell types and animal models, and protect against bone loss in experimental periodontitis in mice. Here, we analyzed the role of BET proteins in inflammatory activation of gingival fibroblasts (GFs) and gingival epithelial cells (GECs). We show that the BET inhibitors I-BET151 and JQ1 significantly reduced expression and/or production of distinct, but overlapping, profiles of cytokine-inducible mediators of inflammation and bone resorption in GFs from healthy donors (IL6, IL8, IL1B, CCL2, CCL5, COX2, and MMP3) and the GEC line TIGK (IL6, IL8, IL1B, CXCL10, MMP9) without affecting cell viability. Activation of mitogen-activated protein kinase and nuclear factor-κB pathways was unaffected by I-BET151, as was the histone acetylation status, and new protein synthesis was not required for the anti-inflammatory effects of BET inhibition. I-BET151 and JQ1 also suppressed expression of inflammatory cytokines, chemokines, and osteoclastogenic mediators in GFs and TIGKs infected with the key periodontal pathogen Porphyromonas gingivalis. Notably, P. gingivalis internalization and intracellular survival in GFs and TIGKs remained unaffected by BET inhibitors. Finally, inhibition of BET proteins significantly reduced P. gingivalis-induced inflammatory mediator expression in GECs and GFs from patients with periodontitis. Our results demonstrate that BET inhibitors may block the excessive inflammatory mediator production by resident cells of the gingival tissue and identify the BET family of epigenetic reader proteins as a potential therapeutic target in the treatment of periodontal disease.

BRD4 directs hematopoietic stem cell development and modulates macrophage inflammatory responses

BRD4 is a BET family protein that binds acetylated histones and regulates transcription. BET/BRD4 inhibitors block blood cancer growth and inflammation and serve as a new therapeutic strategy. However, the biological role of BRD4 in normal hematopoiesis and inflammation is not fully understood. Analysis of Brd4 conditional knockout (KO) mice showed that BRD4 is required for hematopoietic stem cell expansion and progenitor development. Nevertheless, BRD4 played limited roles in macrophage development and inflammatory response to LPS ChIP-seq analysis showed that despite its limited importance, BRD4 broadly occupied the macrophage genome and participated in super-enhancer (SE) formation. Although BRD4 is critical for SE formation in cancer, BRD4 was not required for macrophage SEs, as KO macrophages created alternate, BRD4-less SEs that compensated BRD4 loss. This and additional mechanisms led to the retention of inflammatory responses in macrophages. Our results illustrate a context-dependent role of BRD4 and plasticity of epigenetic regulation.