Cellular Depletion of BRD8 Causes p53-Dependent Apoptosis and Induces a DNA Damage Response in Non-Stressed Cells

Targeting bromodomian-containing protein 8 (BRD8): An advanced tool to interrogate BRD8

Epigenetic modifications play crucial roles in physiological processes, including cell differentiation, proliferation, and death. Bromodomain/Brd-containing proteins (BCPs) regulate abnormal gene expression in various diseases by recognizing the lysine-ε-N-acetylated residues (KAc) or by acting as transcriptional co-activators. Small molecule inhibitors targeting BCPs offer an attractive strategy for modulating aberrant gene expression. Besides the extensive research on the bromodomain and extra-terminal (BET) domain family proteins, the non-BET proteins have gained increasing attention. Bromodomain containing protein 8 (BRD8), a reader of KAc and co-activator of nuclear receptors (NRs), plays a key role in various cancers. This review provides a comprehensive analysis of the structure, disease-related functions, and inhibitor development of BRD8. Opportunities and challenges for future studies targeting BRD8 in disease treatment are discussed.

Histone and Histone Acetylation-Related Alterations of Gene Expression in Uninvolved Psoriatic Skin and Their Effects on Cell Proliferation, Differentiation, and Immune Responses

Psoriasis is a chronic immune-mediated skin disease in which the symptom-free, uninvolved skin carries alterations in gene expression, serving as a basis for lesion formation. Histones and histone acetylation-related processes are key regulators of gene expression, controlling cell proliferation and immune responses. Dysregulation of these processes is likely to play an important role in the pathogenesis of psoriasis. To gain a complete overview of these potential alterations, we performed a meta-analysis of a psoriatic uninvolved skin dataset containing differentially expressed transcripts from nearly 300 individuals and screened for histones and histone acetylation-related molecules. We identified altered expression of the replication-dependent histones HIST2H2AA3 and HIST2H4A and the replication-independent histones H2AFY, H2AFZ, and H3F3A/B. Eight histone chaperones were also identified. Among the histone acetyltransferases, ELP3 and KAT5 and members of the ATAC, NSL, and SAGA acetyltransferase complexes are affected in uninvolved skin. Histone deacetylation-related alterations were found to affect eight HDACs and members of the NCOR/SMRT, NURD, SIN3, and SHIP HDAC complexes. In this article, we discuss how histone and histone acetylation-related expression changes may affect proliferation and differentiation, as well as innate, macrophage-mediated, and T cell-mediated pro- and anti-inflammatory responses, which are known to play a central role in the development of psoriasis.

Review of possible mechanisms of radiotherapy resistance in cervical cancer

Radiotherapy is one of the main treatments for cervical cancer. Early cervical cancer is usually considered postoperative radiotherapy alone. Radiotherapy combined with cisplatin is the standard treatment for locally advanced cervical cancer (LACC), but sometimes the disease will relapse within a short time after the end of treatment. Tumor recurrence is usually related to the inherent radiation resistance of the tumor, mainly involving cell proliferation, apoptosis, DNA repair, tumor microenvironment, tumor metabolism, and stem cells. In the past few decades, the mechanism of radiotherapy resistance of cervical cancer has been extensively studied, but due to its complex process, the specific mechanism of radiotherapy resistance of cervical cancer is still not fully understood. In this review, we discuss the current status of radiotherapy resistance in cervical cancer and the possible mechanisms of radiotherapy resistance, and provide favorable therapeutic targets for improving radiotherapy sensitivity. In conclusion, this article describes the importance of understanding the pathway and target of radioresistance for cervical cancer to promote the development of effective radiotherapy sensitizers.

Bromodomain (BrD) Family Members as Regulators of Cancer Stemness-A Comprehensive Review

Epigenetic mechanisms involving DNA methylation and chromatin modifications have emerged as critical facilitators of cancer heterogeneity, substantially affecting cancer development and progression, modulating cell phenotypes, and enhancing or inhibiting cancer cell malignant properties. Not surprisingly, considering the importance of epigenetic regulators in normal stem cell maintenance, many chromatin-related proteins are essential to maintaining the cancer stem cell (CSC)-like state. With increased tumor-initiating capacities and self-renewal potential, CSCs promote tumor growth, provide therapy resistance, spread tumors, and facilitate tumor relapse after treatment. In this review, we characterized the epigenetic mechanisms that regulate the acquisition and maintenance of cancer stemness concerning selected epigenetic factors belonging to the Bromodomain (BrD) family of proteins. An increasing number of BrD proteins reinforce cancer stemness, supporting the maintenance of the cancer stem cell population in vitro and in vivo via the utilization of distinct mechanisms. As bromodomain possesses high druggable potential, specific BrD proteins might become novel therapeutic targets in cancers exhibiting de-differentiated tumor characteristics.

BRD8 maintains glioblastoma by epigenetic reprogramming of the p53 network

Inhibition of the tumour suppressive function of p53 (encoded by TP53) is paramount for cancer development in humans. However, p53 remains unmutated in the majority of cases of glioblastoma (GBM)-the most common and deadly adult brain malignancy1,2. Thus, how p53-mediated tumour suppression is countered in TP53 wild-type (TP53WT) GBM is unknown. Here we describe a GBM-specific epigenetic mechanism in which the chromatin regulator bromodomain-containing protein 8 (BRD8) maintains H2AZ occupancy at p53 target loci through the EP400 histone acetyltransferase complex. This mechanism causes a repressive chromatin state that prevents transactivation by p53 and sustains proliferation. Notably, targeting the bromodomain of BRD8 displaces H2AZ, enhances chromatin accessibility and engages p53 transactivation. This in turn enforces cell cycle arrest and tumour suppression in TP53WT GBM. In line with these findings, BRD8 is highly expressed with H2AZ in proliferating single cells of patient-derived GBM, and is inversely correlated with CDKN1A, a canonical p53 target that encodes p21 (refs. 3,4). This work identifies BRD8 as a selective epigenetic vulnerability for a malignancy for which treatment has not improved for decades. Moreover, targeting the bromodomain of BRD8 may be a promising therapeutic strategy for patients with TP53WT GBM.

p53 Modulates Radiosensitivity in Head and Neck Cancers-From Classic to Future Horizons

p53, initially considered a tumor suppressor, has been the subject of research related to cancer treatment resistance in the last 30 years. The unfavorable response to multimodal therapy and the higher recurrence rate, despite an aggressive approach, make HNSCC a research topic of interest for improving therapeutic outcomes, even if it is only the sixth most common malignancy worldwide. New advances in molecular biology and genetics include the involvement of miRNA in the control of the p53 pathway, the understanding of mechanisms such as gain/loss of function, and the development of different methods to restore p53 function, especially for HPV-negative cases. The different ratio between mutant p53 status in the primary tumor and distant metastasis originating HNSCC may serve to select the best therapeutic target for activating an abscopal effect by radiotherapy as a "booster" of the immune system. P53 may also be a key player in choosing radiotherapy fractionation regimens. Targeting any pathway involving p53, including tumor metabolism, in particular the Warburg effect, could modulate the radiosensitivity and chemo-sensitivity of head and neck cancers.

Chemoproteomics Enabled Discovery of Selective Probes for NuA4 Factor BRD8

Bromodomain-containing proteins frequently reside in multisubunit chromatin complexes with tissue or cell state-specific compositions. Recent studies have revealed tumor-specific dependencies on the BAF complex bromodomain subunit BRD9 that are a result of recurrent mutations afflicting the structure and composition of associated complex members. To enable the study of ligand engaged complex assemblies, we established a chemoproteomics approach using a functionalized derivative of the BRD9 ligand BI-9564 as an affinity matrix. Unexpectedly, in addition to known interactions with BRD9 and associated BAF complex proteins, we identify a previously unreported interaction with members of the NuA4 complex through the bromodomain-containing subunit BRD8. We apply this finding, alongside a homology-model-guided design, to develop chemical biology approaches for the study of BRD8 inhibition and to arrive at first-in-class selective and cellularly active probes for BRD8. These tools will empower further pharmacological studies of BRD9 and BRD8 within respective BAF and NuA4 complexes.

The Bromodomain Containing 8 (BRD8) transcriptional network in human lung epithelial cells

Mechanisms regulating gene expression in the airway epithelium underlie its response to the environment. A network of transcription factors (TFs) and architectural proteins, modulate chromatin accessibility and recruit activating or repressive signals. Bromodomain-containing proteins function as TFs or by engaging methyltransferase or acetyltransferase activity to induce chromatin modifications. Here we investigate the role of Bromodomain Containing 8 (BRD8) in coordinating lung epithelial function. Sites of BRD8 occupancy genome-wide were mapped in human lung epithelial cell lines (Calu-3 and 16HBE14o^-). CCCTC-Binding Factor (CTCF) was identified as a predicted co-factor of BRD8, based upon motif over-representation under BRD8 ChIP-seq peaks. Following siRNA-mediated depletion of BRD8, differentially expressed genes with nearby peaks of BRD8 occupancy were subject to gene ontology process enrichment analysis. BRD8 targets are enriched for genes involved in the innate immune response and the cell cycle. Depletion of BRD8 increased the secretion of the antimicrobial peptide beta-defensin 1 and multiple chemokines, and reduced cell proliferation.

Machine Learning for Building Immune Genetic Model in Hepatocellular Carcinoma Patients

BACKGROUND

Hepatocellular carcinoma (HCC) is the leading liver cancer with special immune microenvironment, which played vital roles in tumor relapse and poor drug responses. In this study, we aimed to explore the prognostic immune signatures in HCC and tried to construct an immune-risk model for patient evaluation.

METHODS

RNA sequencing profiles of HCC patients were collected from the cancer genome Atlas (TCGA), international cancer genome consortium (ICGC), and gene expression omnibus (GEO) databases (GSE14520). Differentially expressed immune genes, derived from ImmPort database and MSigDB signaling pathway lists, between tumor and normal tissues were analyzed with Limma package in R environment. Univariate Cox regression was performed to find survival-related immune genes in TCGA dataset, and in further random forest algorithm analysis, significantly changed immune genes were used to generate a multivariate Cox model to calculate the corresponding immune-risk score. The model was examined in the other two datasets with recipient operation curve (ROC) and survival analysis. Risk effects of immune-risk score and clinical characteristics of patients were individually evaluated, and significant factors were then used to generate a nomogram.

RESULTS

There were 52 downregulated and 259 upregulated immune genes between tumor and relatively normal tissues, and the final immune-risk model (based on SPP1, BRD8, NDRG1, KITLG, HSPA4, TRAF3, ITGAV and MAP4K2) can better differentiate patients into high and low immune-risk subpopulations, in which high score patients showed worse outcomes after resection (p < 0.05). The differentially enriched pathways between the two groups were mainly about cell proliferation and cytokine production, and calculated immune-risk score was also highly correlated with immune infiltration levels. The nomogram, constructed with immune-risk score and tumor stages, showed high accuracy and clinical benefits in prediction of 1-, 3- and 5-year overall survival, which is useful in clinical practice.

CONCLUSION

The immune-risk model, based on expression of SPP1, BRD8, NDRG1, KITLG, HSPA4, TRAF3, ITGAV, and MAP4K2, can better differentiate patients into high and low immune-risk groups. Combined nomogram, using immune-risk score and tumor stages, could make accurate prediction of 1-, 3- and 5-year survival in HCC patients.

BRD8, which is negatively regulated by miR-876-3p, promotes the proliferation and apoptosis resistance of hepatocellular carcinoma cells via KAT5

Bromodomain-containing 8 (BRD8), which belongs to the histone acetyl transferase (HAT) complex, functions as a driver in colorectal cancer. However, the role of BRD8 and its related regulatory mechanisms in hepatocellular carcinoma (HCC) remain unexplored. In this study, we found that the level of BRD8 mRNA in HCC was prominently higher than that in nontumor tissues. Furthermore, immunohistochemistry analysis indicated that BRD8 protein expression was upregulated in HCC compared to noncancerous tissues. The positive expression of BRD8 was closely associated with HBV infection, a tumor size ≥5 cm and an advanced TNM stage. Moreover, HCC patients with an elevated expression of BRD8 had an obvious poorer survival rate. Functionally, BRD8 knockdown markedly reduced the proliferation of Hep3B and Huh7 cells. Depletion of BRD8 obviously induced the apoptosis of HCC cells. Conversely, BRD8 overexpression promoted the proliferation and apoptosis resistance of Huh7 cells. Lysine acetyltransferase 5 (KAT5) expression was significantly upregulated in HCC tissues. In addition, BRD8 knockdown obviously reduced the level of KAT5 protein and the mRNA expression of KAT5-induced genes in both Hep3B and Huh7 cells. KAT5 knockdown showed similar effects as BRD8 silencing on HCC cell proliferation and apoptosis. The expression of miR-876-3p was downregulated and inversely correlated with the BRD8 mRNA level in HCC tissues. The expression of BRD8 protein in HCC cells was reduced by the overexpression of miR-876-3p and enhanced by the knockdown of miR-876-3p. A luciferase reporter assay demonstrated that BRD8 was a direct target of miR-876-3p. Notably, in HCC cells, the ectopic expression of miR-876-3p inhibited proliferation and induced apoptosis. In conclusion, BRD8, which was negatively regulated by miR-876-3p, facilitated proliferation and inhibited apoptosis in HCC cells by modulating KAT5.

Hyaluronic Acid-Coated Camptothecin Nanocrystals for Targeted Drug Delivery to Enhance Anticancer Efficacy

Tumor-targeted drug delivery via chemotherapy is very effective on cancer treatment. For potential anticancer agent such as Camptothecin (CPT), high chemotherapeutic efficacy and accurate tumor targeting are equally crucial. Inspired by special CD44 binding capability from hyaluronic acid (HA), in this study, novel HA-coated CPT nanocrystals were successfully prepared by an antisolvent precipitation method for tumor-targeted delivery of hydrophobic drug CPT. These HA-coated CPT nanocrystals demonstrated high drug loading efficiency, improved aqueous dispersion, prolonged circulation, and enhanced stability resulting from their nanoscaled sizes and hydrophilic HA layer. Moreover, as compared to crude CPT and naked CPT nanocrystals, HA-coated CPT nanocrystals displayed dramatically enhanced in vitro anticancer activity, apoptosis-inducing potency against CD44 overexpressed cancer cells, and lower toxic effect toward normal cells due to pH-responsive drug release behavior and specific HA-CD44 mediated endocytosis. Additionally, HA-coated CPT nanocrystals performed fairly better antimigration activity and biocompatibility. The possible molecular mechanism regarding this novel drug formulation might be linked to intrinsic mitochondria-mediated apoptosis by an increase of Bax to Bcl-2 ratio and upregulation of P53. Consequently, HA-coated CPT nanocrystals are expected to be an effective nanoplatform in drug delivery for cancer therapy.

DNA damage response signaling pathways and targets for radiotherapy sensitization in cancer

Radiotherapy is one of the most common countermeasures for treating a wide range of tumors. However, the radioresistance of cancer cells is still a major limitation for radiotherapy applications. Efforts are continuously ongoing to explore sensitizing targets and develop radiosensitizers for improving the outcomes of radiotherapy. DNA double-strand breaks are the most lethal lesions induced by ionizing radiation and can trigger a series of cellular DNA damage responses (DDRs), including those helping cells recover from radiation injuries, such as the activation of DNA damage sensing and early transduction pathways, cell cycle arrest, and DNA repair. Obviously, these protective DDRs confer tumor radioresistance. Targeting DDR signaling pathways has become an attractive strategy for overcoming tumor radioresistance, and some important advances and breakthroughs have already been achieved in recent years. On the basis of comprehensively reviewing the DDR signal pathways, we provide an update on the novel and promising druggable targets emerging from DDR pathways that can be exploited for radiosensitization. We further discuss recent advances identified from preclinical studies, current clinical trials, and clinical application of chemical inhibitors targeting key DDR proteins, including DNA-PKcs (DNA-dependent protein kinase, catalytic subunit), ATM/ATR (ataxia–telangiectasia mutated and Rad3-related), the MRN (MRE11-RAD50-NBS1) complex, the PARP (poly[ADP-ribose] polymerase) family, MDC1, Wee1, LIG4 (ligase IV), CDK1, BRCA1 (BRCA1 C terminal), CHK1, and HIF-1 (hypoxia-inducible factor-1). Challenges for ionizing radiation-induced signal transduction and targeted therapy are also discussed based on recent achievements in the biological field of radiotherapy.

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.