HDAC3 functions as a positive regulator in Notch signal transduction

Discovery of novel and potent dual-targeting AXL/HDAC2 inhibitors for colorectal cancer treatment via structure-based pharmacophore modelling, virtual screening, and molecular docking, molecular dynamics simulation studies, and biological evaluation

Colorectal cancer (CRC) is one of the most common cancers worldwide. Nowadays, owing to the complex mechanism of tumorigenesis, simultaneous inhibition of multiple targets is an important anticancer strategy. Recent studies have demonstrated receptor tyrosine kinase AXL (AXL) and histone deacetylase 2 (HDAC2) are closely associated with colorectal cancer. Herein, we identified five hit compounds concurrently targeting AXL and HDAC2 using virtual screening. Inhibitory experiments revealed these hit compounds potently inhibited AXL and HDAC2 in the nanomolar range. Among them, Hit-3 showed the strongest inhibitory effects which were better than that of the positive control groups. Additionally, MD assays showed that Hit-3 could bind stably to the AXL and HDAC2 active pockets. Further MTT assays demonstrated that Hit-3 showed potent anti-proliferative activity. Most importantly, Hit-3 exhibited significant in vivo antitumor efficacy in xenograft models. Collectively, this study is the first discovery of dual-targeting AXL/HDAC2 inhibitors for colorectal cancer treatment.

Minor Spliceosomal 65K/RNPC3 Interacts with ANKRD11 and Mediates HDAC3-Regulated Histone Deacetylation and Transcription

RNA splicing is crucial in the multilayer regulatory networks for gene expression, making functional interactions with DNA- and other RNA-processing machineries in the nucleus. However, these established couplings are all major spliceosome-related; whether the minor spliceosome is involved remains unclear. Here, through affinity purification using Drosophila lysates, an interaction is identified between the minor spliceosomal 65K/RNPC3 and ANKRD11, a cofactor of histone deacetylase 3 (HDAC3). Using a CRISPR/Cas9 system, Deletion strains are constructed and found that both Dm65KΔ/Δ and Dmankrd11Δ/Δ mutants have reduced histone deacetylation at Lys9 of histone H3 (H3K9) and Lys5 of histone H4 (H4K5) in their heads, exhibiting various neural-related defects. The 65K-ANKRD11 interaction is also conserved in human cells, and the HsANKRD11 middle-uncharacterized domain mediates Hs65K association with HDAC3. Cleavage under targets and tagmentation (CUT&Tag) assays revealed that HsANKRD11 is a bridging factor, which facilitates the synergistic common chromatin-binding of HDAC3 and Hs65K. Knockdown (KD) of HsANKRD11 simultaneously decreased their common binding, resulting in reduced deacetylation of nearby H3K9. Ultimately, this study demonstrates that expression changes of many genes caused by HsANKRD11-KD are due to the decreased common chromatin-binding of HDAC3 and Hs65K and subsequently reduced deacetylation of H3K9, illustrating a novel and conserved coupling mechanism that links the histone deacetylation with minor spliceosome for the regulation of gene expression.

Comprehensive genomic features indicative for Notch responsiveness

Transcription factor RBPJ is the central component in Notch signal transduction and directly forms a coactivator complex together with the Notch intracellular domain (NICD). While RBPJ protein levels remain constant in most tissues, dynamic expression of Notch target genes varies depending on the given cell-type and the Notch activity state. To elucidate dynamic RBPJ binding genome-wide, we investigated RBPJ occupancy by ChIP-Seq. Surprisingly, only a small set of the total RBPJ sites show a dynamic binding behavior in response to Notch signaling. Compared to static RBPJ sites, dynamic sites differ in regard to their chromatin state, binding strength and enhancer positioning. Dynamic RBPJ sites are predominantly located distal to transcriptional start sites (TSSs), while most static sites are found in promoter-proximal regions. Importantly, gene responsiveness is preferentially associated with dynamic RBPJ binding sites and this static and dynamic binding behavior is repeatedly observed across different cell types and species. Based on the above findings we used a machine-learning algorithm to predict Notch responsiveness with high confidence in different cellular contexts. Our results strongly support the notion that the combination of binding strength and enhancer positioning are indicative of Notch responsiveness.

The landscape of alterations affecting epigenetic regulators in T-cell acute lymphoblastic leukemia: Roles in leukemogenesis and therapeutic opportunities

T-cell acute lymphoblastic leukemia (T-ALL) is an aggressive malignancy accounting for 10%-15% of pediatric and 20%-25% of adult ALL cases. Epigenetic irregularities in T-ALL include alterations in both DNA methylation and the post-translational modifications on histones which together play a critical role in the initiation and development of T-ALL. Characterizing the oncogenic mutations that result in these epigenetic changes combined with the reversibility of epigenetic modifications represents an opportunity for the development of epigenetic therapies. Oncogenic mutations and deregulated expression of DNA methyltransferases (DNMTs), Ten-Eleven Translocation dioxygenases (TETs), Histone acetyltransferases (HATs) and members of Polycomb Repressor Complex 2 (PRC2) have all been identified in T-ALL. This review focuses on the current understanding of how these mutations lead to epigenetic changes in T-ALL, their association with disease pathogenesis and the current efforts to exploit these clinically through the development of epigenetic therapies in T-ALL treatment.

Current treatment strategies targeting histone deacetylase inhibitors in acute lymphocytic leukemia: a systematic review

Acute lymphocytic leukemia is a hematological malignancy that primarily affects children. Long-term chemotherapy is effective, but always causes different toxic side effects. With the application of a chemotherapy-free treatment strategy, we intend to demonstrate the most recent results of using one type of epigenetic drug, histone deacetylase inhibitors, in ALL and to provide preclinical evidence for further clinical trials. In this review, we found that panobinostat (LBH589) showed positive outcomes as a monotherapy, whereas vorinostat (SAHA) was a better choice for combinatorial use. Preclinical research has identified chidamide as a potential agent for investigation in more clinical trials in the future. In conclusion, histone deacetylase inhibitors play a significant role in the chemotherapy-free landscape in cancer treatment, particularly in acute lymphocytic leukemia.

Pancreatic Neuroendocrine Tumors: Signaling Pathways and Epigenetic Regulation

Pancreatic neuroendocrine tumors (PNETs) are characterized by dysregulated signaling pathways that are crucial for tumor formation and progression. The efficacy of traditional therapies is limited, particularly in the treatment of PNETs at an advanced stage. Epigenetic alterations profoundly impact the activity of signaling pathways in cancer development, offering potential opportunities for drug development. There is currently a lack of extensive research on epigenetic regulation in PNETs. To fill this gap, we first summarize major signaling events that are involved in PNET development. Then, we discuss the epigenetic regulation of these signaling pathways in the context of both PNETs and commonly occurring-and therefore more extensively studied-malignancies. Finally, we will offer a perspective on the future research direction of the PNET epigenome and its potential applications in patient care.

A TLR4/TRAF6-dependent signaling pathway mediates NCoR coactivator complex formation for inflammatory gene activation

The nuclear receptor corepressor (NCoR) forms a complex with histone deacetylase 3 (HDAC3) that mediates repressive functions of unliganded nuclear receptors and other transcriptional repressors by deacetylation of histone substrates. Recent studies provide evidence that NCoR/HDAC3 complexes can also exert coactivator functions in brown adipocytes by deacetylating and activating PPARγ coactivator 1α (PGC1α) and that signaling via receptor activator of nuclear factor kappa-B (RANK) promotes the formation of a stable NCoR/HDAC3/PGC1β complex that coactivates nuclear factor kappa-B (NFκB)- and activator protein 1 (AP-1)-dependent genes required for osteoclast differentiation. Here, we demonstrate that activation of Toll-like receptor (TLR) 4, but not TLR3, the interleukin 4 (IL4) receptor nor the Type I interferon receptor, also promotes assembly of an NCoR/HDAC3/PGC1β coactivator complex. Receptor-specific utilization of TNF receptor-associated factor 6 (TRAF6) and downstream activation of extracellular signal-regulated kinase 1 (ERK1) and TANK-binding kinase 1 (TBK1) accounts for the common ability of RANK and TLR4 to drive assembly of an NCoR/HDAC3/PGC1β complex in macrophages. ERK1, the p65 component of NFκB, and the p300 histone acetyltransferase (HAT) are also components of the induced complex and are associated with local histone acetylation and transcriptional activation of TLR4-dependent enhancers and promoters. These observations identify a TLR4/TRAF6-dependent signaling pathway that converts NCoR from a corepressor of nuclear receptors to a coactivator of NFκB and AP-1 that may be relevant to functions of NCoR in other developmental and homeostatic processes.

Comprehensive analysis of the proximity-dependent nuclear interactome for the oncoprotein NOTCH1 in live cells

Notch signaling plays a critical role in cell fate decisions in all cell types. Furthermore, gain-of-function mutations in NOTCH1 have been uncovered in many human cancers. Disruption of Notch signaling has recently emerged as an attractive disease treatment strategy. However, the nuclear interaction landscape of the oncoprotein NOTCH1 remains largely unexplored. We therefore employed here a proximity-dependent biotin identification approach to identify in vivo protein associations with the nuclear Notch1 intracellular domain in live cells. We identified a large set of previously reported and unreported proteins that associate with NOTCH1, including general transcription and elongation factors, DNA repair and replication factors, coactivators, corepressors, and components of the NuRD and SWI/SNF chromatin remodeling complexes. We also found that Notch1 intracellular domain associates with protein modifiers and components of other signaling pathways that may influence Notch signal transduction and protein stability such as USP7. We further validated the interaction of NOTCH1 with histone deacetylase 1 or GATAD2B using protein network analysis, proximity-based ligation, in vivo cross-linking and coimmunoprecipitation assays in several Notch-addicted cancer cell lines. Through data mining, we also revealed potential drug targets for the inhibition of Notch signaling. Collectively, these results provide a valuable resource to uncover the mechanisms that fine-tune Notch signaling in tumorigenesis and inform therapeutic targets for Notch-addicted tumors.

Hdac1 and Hdac2 positively regulate Notch1 gain-of-function pathogenic signaling in committed osteoblasts of male mice

BACKGROUND

Skeletal development requires precise extrinsic and intrinsic signals to regulate processes that form and maintain bone and cartilage. Notch1 is a highly conserved signaling receptor that regulates cell fate decisions by controlling the duration of transcriptional bursts. Epigenetic molecular events reversibly modify DNA and histone tails by influencing the spatial organization of chromatin and can fine-tune the outcome of a Notch1 transcriptional response. Histone deacetylase 1 and 2 (HDAC1 and HDAC2) are chromatin modifying enzymes that mediate osteoblast differentiation. While an HDAC1-Notch interaction has been studied in vitro and in Drosophila, its role in mammalian skeletal development and disorders is unclear. Osteosclerosis is a bone disorder with an abnormal increase in the number of osteoblasts and excessive bone formation.

METHODS

Here, we tested whether Hdac1/2 contribute to the pathogenesis of osteosclerosis in a murine model of the disease owing to conditionally cre-activated expression of the Notch1 intracellular domain in immature osteoblasts.

RESULTS

Importantly, selective homozygous deletions of Hdac1/2 in osteoblasts partially alleviate osteosclerotic phenotypes (Col2.3kb-Cre; TGRosaN1ICD/+ ; Hdac1flox/flox ; Hdac2flox/flox ) with a 40% decrease in bone volume and a 22% decrease in trabecular thickness in 4 weeks old when compared to male mice with heterozygous deletions of Hdac1/2 (Col2.3 kb-Cre; TGRosaN1ICD/+ ; Hdac1flox/+ ; Hdac2flox/+ ). Osteoblast-specific deletion of Hdac1/2 in male and female mice results in no overt bone phenotype in the absence of the Notch1 gain-of-function (GOF) allele.

CONCLUSIONS

These results provide evidence that Hdac1/2 contribute to Notch1 pathogenic signaling in the mammalian skeleton. Our study on epigenetic regulation of Notch1 GOF-induced osteosclerosis may facilitate further mechanistic studies of skeletal birth defects caused by Notch-related GOF mutations in human patients, such as Adams-Oliver disease, congenital heart disease, and lateral meningocele syndrome.

Endothelial Notch1 signaling in white adipose tissue promotes cancer cachexia

Cachexia is a major cause of morbidity and mortality in individuals with cancer and is characterized by weight loss due to adipose and muscle tissue wasting. Hallmarks of white adipose tissue (WAT) remodeling, which often precedes weight loss, are impaired lipid storage, inflammation and eventually fibrosis. Tissue wasting occurs in response to tumor-secreted factors. Considering that the continuous endothelium in WAT is the first line of contact with circulating factors, we postulated whether the endothelium itself may orchestrate tissue remodeling. Here, we show using human and mouse cancer models that during precachexia, tumors overactivate Notch1 signaling in distant WAT endothelium. Sustained endothelial Notch1 signaling induces a WAT wasting phenotype in male mice through excessive retinoic acid production. Pharmacological blockade of retinoic acid signaling was sufficient to inhibit WAT wasting in a mouse cancer cachexia model. This demonstrates that cancer manipulates the endothelium at distant sites to mediate WAT wasting by altering angiocrine signals.

Recent histone deacetylase inhibitors in cancer therapy

Cancer metastasis increases the complexity of the disease and escalates patient mortality. Traditional chemotherapy has been associated with low efficacy and marked side effects. Studies pivot toward histone deacetylase (HDAC) enzymes and inhibitors because they are critical for chromatin structure, gene regulation, and cellular activities that are linked to metastasis and cancer progression. HDAC inhibitors (HDACi) can alter gene expression patterns and can lead to cell-cycle arrest and apoptosis in neoplastic cells. Several HDACi drugs like vorinostat, romidepsin, panobinostat, and belinostat are approved by the Food and Drug Administration. China and Japan have approved the use of tucidinostat, a new subtype-selective HDACi that inhibits class 1 HDAC1, HDAC2, HDAC3, as well as class 2b HDAC10. These drugs have shown promising results in the treatment of multiple carcinoma including cervical cancer, T-cell lymphoma, brain cancer, and breast cancer. This review highlights the HDACi classes, the mechanism of action of these inhibitors, their preclinical and clinical efficacy, and the latest clinical trials and patents used in cancer therapeutics. Overall, this review focuses on patents and clinical trials data from 2019 onward to give a better viewpoint on current trends in HDACis as chemotherapy agents.

RANK ligand converts the NCoR/HDAC3 co-repressor to a PGC1β- and RNA-dependent co-activator of osteoclast gene expression

The nuclear receptor co-repressor (NCoR) complex mediates transcriptional repression dependent on histone deacetylation by histone deacetylase 3 (HDAC3) as a component of the complex. Unexpectedly, we found that signaling by the receptor activator of nuclear factor κB (RANK) converts the NCoR/HDAC3 co-repressor complex to a co-activator of AP-1 and NF-κB target genes that are required for mouse osteoclast differentiation. Accordingly, the dominant function of NCoR/HDAC3 complexes in response to RANK signaling is to activate, rather than repress, gene expression. Mechanistically, RANK signaling promotes RNA-dependent interaction of the transcriptional co-activator PGC1β with the NCoR/HDAC3 complex, resulting in the activation of PGC1β and inhibition of HDAC3 activity for acetylated histone H3. Non-coding RNAs Dancr and Rnu12, which are associated with altered human bone homeostasis, promote NCoR/HDAC3 complex assembly and are necessary for RANKL-induced osteoclast differentiation in vitro. These findings may be prototypic for signal-dependent functions of NCoR in other biological contexts.

Chidamide: Targeting epigenetic regulation in the treatment of hematological malignancy

Epigenetic alterations frequently participate in the onset of hematological malignancies. Histone deacetylases (HDACs) are essential for regulating gene transcription and various signaling pathways. Targeting HDACs has become a novel treatment option for hematological malignancies. Chidamide is the first oral selective HDAC inhibitor for HDAC1, HDAC2, HDAC3, and HDAC10 and was first approved for the treatment of R/R peripheral T-cell lymphoma by the China Food and Drug Administration in 2014. Chidamide was also approved under the name Hiyasta (HBI-8000) in Japan in 2021. In vitro studies revealed that chidamide could inhibit proliferation and induce apoptosis via cell cycle arrest and the regulation of apoptotic proteins. In clinical studies, chidamide was also efficacious in multiple myeloma, acute leukemia and myelodysplastic syndrome. This review includes reported experimental and clinical data on chidamide monotherapy or chidamide treatment in combination with chemotherapy for various hematological malignancies, offering a rationale for the renewed exploration of this drug.

lncRNA BREA2 promotes metastasis by disrupting the WWP2-mediated ubiquitination of Notch1

Notch has been implicated in human cancers and is a putative therapeutic target. However, the regulation of Notch activation in the nucleus remains largely uncharacterized. Therefore, characterizing the detailed mechanisms governing Notch degradation will identify attractive strategies for treating Notch-activated cancers. Here, we report that the long noncoding RNA (lncRNA) BREA2 drives breast cancer metastasis by stabilizing the Notch1 intracellular domain (NICD1). Moreover, we reveal WW domain containing E3 ubiquitin protein ligase 2 (WWP2) as an E3 ligase for NICD1 at K1821 and a suppressor of breast cancer metastasis. Mechanistically, BREA2 impairs WWP2-NICD1 complex formation and in turn stabilizes NICD1, leading to Notch signaling activation and lung metastasis. BREA2 loss sensitizes breast cancer cells to inhibition of Notch signaling and suppresses the growth of breast cancer patient-derived xenograft tumors, highlighting its therapeutic potential in breast cancer. Taken together, these results reveal the lncRNA BREA2 as a putative regulator of Notch signaling and an oncogenic player driving breast cancer metastasis.

Advances of Epigenetic Biomarkers and Epigenome Editing for Early Diagnosis in Breast Cancer

Epigenetic modifications are known to regulate cell phenotype during cancer progression, including breast cancer. Unlike genetic alterations, changes in the epigenome are reversible, thus potentially reversed by epi-drugs. Breast cancer, the most common cause of cancer death worldwide in women, encompasses multiple histopathological and molecular subtypes. Several lines of evidence demonstrated distortion of the epigenetic landscape in breast cancer. Interestingly, mammary cells isolated from breast cancer patients and cultured ex vivo maintained the tumorigenic phenotype and exhibited aberrant epigenetic modifications. Recent studies indicated that the therapeutic efficiency for breast cancer regimens has increased over time, resulting in reduced mortality. Future medical treatment for breast cancer patients, however, will likely depend upon a better understanding of epigenetic modifications. The present review aims to outline different epigenetic mechanisms including DNA methylation, histone modifications, and ncRNAs with their impact on breast cancer, as well as to discuss studies highlighting the central role of epigenetic mechanisms in breast cancer pathogenesis. We propose new research areas that may facilitate locus-specific epigenome editing as breast cancer therapeutics.

HDAC11 Regulates the Proliferation of Bovine Muscle Stem Cells through the Notch Signaling Pathway and Inhibits Muscle Regeneration

Myogenesis is an essential process that can affect the yield and quality of beef. Transcriptional studies have shown that histone deacetylase 11 (HDAC11) was differentially expressed in muscle tissues of 6 and 18 month old Longlin cattle, but its role in the regulation of myogenesis remains unclear. This study aimed to determine the role of HDAC11 in the proliferation and differentiation of bovine muscle stem cells (MuSCs). HDAC11 promoted MuSC proliferation by activating Notch signaling and inhibited myoblast differentiation by reducing MyoD1 transcription. In addition, overexpression of HDAC11 inhibited the repair regeneration process of muscle in mice. HDAC11 was found to be a novel key target for the control of myogenesis, and this is a theoretical basis for the development of HDAC11-specific modulators as a new strategy to regulate myogenesis.

Notch-dependent and -independent functions of transcription factor RBPJ

Signal transduction pathways often involve transcription factors that promote activation of defined target gene sets. The transcription factor RBPJ is the central player in Notch signaling and either forms an activator complex with the Notch intracellular domain (NICD) or a repressor complex with corepressors like KYOT2/FHL1. The balance between these two antagonizing RBPJ-complexes depends on the activation state of the Notch receptor regulated by cell-to-cell interaction, ligand binding and proteolytic cleavage events. Here, we depleted RBPJ in mature T-cells lacking active Notch signaling and performed RNA-Seq, ChIP-Seq and ATAC-seq analyses. RBPJ depletion leads to upregulation of many Notch target genes. Ectopic expression of NICD1 activates several Notch target genes and enhances RBPJ occupancy. Based on gene expression changes and RBPJ occupancy we define four different clusters, either RBPJ- and/or Notch-regulated genes. Importantly, we identify early (Hes1 and Hey1) and late Notch-responsive genes (IL2ra). Similarly, to RBPJ depletion, interfering with transcriptional repression by squelching with cofactor KYOT2/FHL1, leads to upregulation of Notch target genes. Taken together, RBPJ is not only an essential part of the Notch co-activator complex but also functions as a repressor in a Notch-independent manner.

Hydroxylation of the NOTCH1 intracellular domain regulates Notch signaling dynamics

Notch signaling plays a pivotal role in the development and, when dysregulated, it contributes to tumorigenesis. The amplitude and duration of the Notch response depend on the posttranslational modifications (PTMs) of the activated NOTCH receptor - the NOTCH intracellular domain (NICD). In normoxic conditions, the hydroxylase FIH (factor inhibiting HIF) catalyzes the hydroxylation of two asparagine residues of the NICD. Here, we investigate how Notch-dependent gene transcription is regulated by hypoxia in progenitor T cells. We show that the majority of Notch target genes are downregulated upon hypoxia. Using a hydroxyl-specific NOTCH1 antibody we demonstrate that FIH-mediated NICD1 hydroxylation is reduced upon hypoxia or treatment with the hydroxylase inhibitor dimethyloxalylglycine (DMOG). We find that a hydroxylation-resistant NICD1 mutant is functionally impaired and more ubiquitinated. Interestingly, we also observe that the NICD1-deubiquitinating enzyme USP10 is downregulated upon hypoxia. Moreover, the interaction between the hydroxylation-defective NICD1 mutant and USP10 is significantly reduced compared to the NICD1 wild-type counterpart. Together, our data suggest that FIH hydroxylates NICD1 in normoxic conditions, leading to the recruitment of USP10 and subsequent NICD1 deubiquitination and stabilization. In hypoxia, this regulatory loop is disrupted, causing a dampened Notch response.

Hes1 Controls Proliferation and Apoptosis in Chronic Lymphoblastic Leukemia Cells by Modulating PTEN Expression

Hairy and enhancer of split homolog-1 (HES1), regulated by the Notch, has been reported to play important roles in the immune response and cancers, such as leukemia. In this study, we aim to explore the effect of HES1-mediated Notch1 signaling pathway in chronic lymphocytic leukemia (CLL). Reverse transcription quantitative polymerase chain reaction and Western blot assay were conducted to determine the expression of HES1, Notch1, and PTEN in B lymphocytes of peripheral blood samples of 60 CLL patients. We used lentivirus-mediated overexpression or silencing of HES1 and the Notch1 signaling pathway inhibitor, MW167, to detect the interaction among HES1, Notch1, and PTEN in CLL MEC1 and HG3 cells. MTT assay and flow cytometry were employed for detection of biological behaviors of CLL cells. HES1 and Notch1 showed high expression, but PTEN displayed low expression in B lymphocytes of peripheral blood samples of patients with CLL in association with poor prognosis. HES1 bound to the promoter region of PTEN and reduced PTEN expression. Overexpression of HES1 activated the Notch1 signaling pathway, thus promoting the proliferation of CLL cells, increasing the proportion of cells arrested at the S phase and limiting the apoptosis of CLL cells. Collectively, HES1 can promote activation of the Notch1 signaling pathway to cause PTEN transcription inhibition and the subsequent expression reduction, thereby promoting the proliferation and inhibiting the apoptosis of CLL cells.

HDACs and the epigenetic plasticity of cancer cells: Target the complexity

Cancer cells must adapt to the hostile conditions of the microenvironment in terms of nutrition, space, and immune system attack. Mutations of DNA are the drivers of the tumorigenic process, but mutations must be able to hijack cellular functions to sustain the spread of mutant genomes. Transcriptional control is a key function in this context and is controlled by the rearrangement of the epigenome. Unlike genomic mutations, the epigenome of cancer cells can in principle be reversed. The discovery of the first epigenetic drugs triggered a contaminating enthusiasm. Unfortunately, the complexity of the epigenetic machinery has frustrated this enthusiasm. To develop efficient patient-oriented epigenetic therapies, we need to better understand the nature of this complexity. In this review, we will discuss recent advances in understanding the contribution of HDACs to the maintenance of the transformed state and the rational for their selective targeting.

Upregulation of OATP1A2 in human oesophageal squamous cell carcinoma cells via the HDAC6-GCN5/PCAF-H3K9Ac axis

1. OATP1A2 overexpressed is involved in chemotherapy disposition, indicating its role in tumour development and progression.2. CHIP and siRNA were used to evaluate the status of histone acetylation at the OATP1A2 promoter. The role of OATP1A2 was analysed by gene-set enrichment and overall survival analysis.3. OATP1A2 expression levels in ESCC was notably higher than that in para-cancer tissues. OATP1A2 high expression are associated with bile salt metabolic pathway and poor prognosis. Furthermore, HDAC6 was repressed in ESCC, increasing the levels of H3K9Ac catalysed by GCN5/PCAF at the OATP1A2 promoter region.4. Abnormal histone hyperacetylation mediated by the HDAC6-GCN5/PCAF-H3K9Ac axis resulted in increased OATP1A2 expression in ESCC, and OATP1A2 may serve as a promising prognostic biomarker for ESCC.5. In conclusion, this study indicated that suppression of OATP1A2 would inhibit the progression and prognosis in ESCC.

Chidamide inhibits the NOTCH1-MYC signaling axis in T-cell acute lymphoblastic leukemia

T-cell acute lymphoblastic leukemia (T-ALL) is one of the most dangerous hematological malignancies, with high tumor heterogeneity and poor prognosis. More than 60% of T-ALL patients carry NOTCH1 gene mutations, leading to abnormal expression of downstream target genes and aberrant activation of various signaling pathways. We found that chidamide, an HDAC inhibitor, exerts an antitumor effect on T-ALL cell lines and primary cells including an anti-NOTCH1 activity. In particular, chidamide inhibits the NOTCH1-MYC signaling axis by down-regulating the level of the intracellular form of NOTCH1 (NICD1) as well as MYC, partly through their ubiquitination and degradation by the proteasome pathway. We also report here the preliminary results of our clinical trial supporting that a treatment by chidamide reduces minimal residual disease (MRD) in patients and is well tolerated. Our results highlight the effectiveness and safety of chidamide in the treatment of T-ALL patients, including those with NOTCH1 mutations and open the way to a new therapeutic strategy for these patients.

Targeting Notch to Maximize Chemotherapeutic Benefits: Rationale, Advanced Strategies, and Future Perspectives

Simple Summary

The Notch signaling pathway regulates cell proliferation, apoptosis, stem cell self-renewal, and differentiation in a context-dependent fashion both during embryonic development and in adult tissue homeostasis. Consistent with its pleiotropic physiological role, unproper activation of the signaling promotes or counteracts tumor pathogenesis and therapy response in distinct tissues. In the last twenty years, a wide number of studies have highlighted the anti-cancer potential of Notch-modulating agents as single treatment and in combination with the existent therapies. However, most of these strategies have failed in the clinical exploration due to dose-limiting toxicity and low efficacy, encouraging the development of novel agents and the design of more appropriate combinations between Notch signaling inhibitors and chemotherapeutic drugs with improved safety and effectiveness for distinct types of cancer.

Abstract

Notch signaling guides cell fate decisions by affecting proliferation, apoptosis, stem cell self-renewal, and differentiation depending on cell and tissue context. Given its multifaceted function during tissue development, both overactivation and loss of Notch signaling have been linked to tumorigenesis in ways that are either oncogenic or oncosuppressive, but always context-dependent. Notch signaling is critical for several mechanisms of chemoresistance including cancer stem cell maintenance, epithelial-mesenchymal transition, tumor-stroma interaction, and malignant neovascularization that makes its targeting an appealing strategy against tumor growth and recurrence. During the last decades, numerous Notch-interfering agents have been developed, and the abundant preclinical evidence has been transformed in orphan drug approval for few rare diseases. However, the majority of Notch-dependent malignancies remain untargeted, even if the application of Notch inhibitors alone or in combination with common chemotherapeutic drugs is being evaluated in clinical trials. The modest clinical success of current Notch-targeting strategies is mostly due to their limited efficacy and severe on-target toxicity in Notch-controlled healthy tissues. Here, we review the available preclinical and clinical evidence on combinatorial treatment between different Notch signaling inhibitors and existent chemotherapeutic drugs, providing a comprehensive picture of molecular mechanisms explaining the potential or lacking success of these combinations.

SUMOylated non-canonical polycomb PRC1.6 complex as a prerequisite for recruitment of transcription factor RBPJ

BACKGROUND

Notch signaling controls cell fate decisions in many contexts during development and adult stem cell homeostasis and, when dysregulated, leads to carcinogenesis. The central transcription factor RBPJ assembles the Notch coactivator complex in the presence of Notch signaling, and represses Notch target gene expression in its absence.

RESULTS

We identified L3MBTL2 and additional members of the non-canonical polycomb repressive PRC1.6 complex in DNA-bound RBPJ associated complexes and demonstrate that L3MBTL2 directly interacts with RBPJ. Depletion of RBPJ does not affect occupancy of PRC1.6 components at Notch target genes. Conversely, absence of L3MBTL2 reduces RBPJ occupancy at enhancers of Notch target genes. Since L3MBTL2 and additional members of the PRC1.6 are known to be SUMOylated, we investigated whether RBPJ uses SUMO-moieties as contact points. Indeed, we found that RBPJ binds to SUMO2/3 and that this interaction depends on a defined SUMO-interaction motif. Furthermore, we show that pharmacological inhibition of SUMOylation reduces RBPJ occupancy at Notch target genes.

CONCLUSIONS

We propose that the PRC1.6 complex and its conjugated SUMO-modifications provide a favorable environment for binding of RBPJ to Notch target genes.

Characterization of Histone Deacetylase Mechanisms in Cancer Development

Over decades of studies, accumulating evidence has suggested that epigenetic dysregulation is a hallmark of tumours. Post-translational modifications of histones are involved in tumour pathogenesis and development mainly by influencing a broad range of physiological processes. Histone deacetylases (HDACs) and histone acetyltransferases (HATs) are pivotal epigenetic modulators that regulate dynamic processes in the acetylation of histones at lysine residues, thereby influencing transcription of oncogenes and tumour suppressor genes. Moreover, HDACs mediate the deacetylation process of many nonhistone proteins and thus orchestrate a host of pathological processes, such as tumour pathogenesis. In this review, we elucidate the functions of HDACs in cancer.

Chromatin Regulator SPEN/SHARP in X Inactivation and Disease

Simple Summary

Carcinogenesis is a multistep process involving not only the activation of oncogenes and disabling tumor suppressor genes, but also epigenetic modulation of gene expression. X chromosome inactivation (XCI) is a paradigm to study heterochromatin formation and maintenance. The double dosage of X chromosomal genes in female mammals is incompatible with early development. XCI is an excellent model system for understanding the establishment of facultative heterochromatin initiated by the expression of a 17,000 nt long non-coding RNA, known as Xinactivespecifictranscript (Xist), on the X chromosome. This review focuses on the molecular mechanisms of how epigenetic modulators act in a step-wise manner to establish facultative heterochromatin, and we put these in the context of cancer biology and disease. An in depth understanding of XCI will allow a better characterization of particular types of cancer and hopefully facilitate the development of novel epigenetic therapies.

Abstract

Enzymes, such as histone methyltransferases and demethylases, histone acetyltransferases and deacetylases, and DNA methyltransferases are known as epigenetic modifiers that are often implicated in tumorigenesis and disease. One of the best-studied chromatin-based mechanism is X chromosome inactivation (XCI), a process that establishes facultative heterochromatin on only one X chromosome in females and establishes the right dosage of gene expression. The specificity factor for this process is the long non-coding RNA Xinactivespecifictranscript (Xist), which is upregulated from one X chromosome in female cells. Subsequently, Xist is bound by the corepressor SHARP/SPEN, recruiting and/or activating histone deacetylases (HDACs), leading to the loss of active chromatin marks such as H3K27ac. In addition, polycomb complexes PRC1 and PRC2 establish wide-spread accumulation of H3K27me3 and H2AK119ub1 chromatin marks. The lack of active marks and establishment of repressive marks set the stage for DNA methyltransferases (DNMTs) to stably silence the X chromosome. Here, we will review the recent advances in understanding the molecular mechanisms of how heterochromatin formation is established and put this into the context of carcinogenesis and disease.

Histone Deacetylase Inhibitors to Overcome Resistance to Targeted and Immuno Therapy in Metastatic Melanoma

Therapies that target oncogenes and immune checkpoint molecules constitute a major group of treatments for metastatic melanoma. A mutation in BRAF (BRAF V600E) affects various signaling pathways, including mitogen activated protein kinase (MAPK) and PI3K/AKT/mammalian target of rapamycin (mTOR) in melanoma. Target-specific agents, such as MAPK inhibitors improve progression-free survival. However, BRAF^V600E mutant melanomas treated with BRAF kinase inhibitors develop resistance. Immune checkpoint molecules, such as programmed death-1 (PD-1) and programmed death ligand-1(PD-L1), induce immune evasion of cancer cells. MAPK inhibitor resistance results from the increased expression of PD-L1. Immune checkpoint inhibitors, such as anti-PD-L1 or anti-PD-1, are main players in immune therapies designed to target metastatic melanoma. However, melanoma patients show low response rate and resistance to these inhibitors develops within 6–8 months of treatment. Epigenetic reprogramming, such as DNA methylaion and histone modification, regulates the expression of genes involved in cellular proliferation, immune checkpoints and the response to anti-cancer drugs. Histone deacetylases (HDACs) remove acetyl groups from histone and non-histone proteins and act as transcriptional repressors. HDACs are often dysregulated in melanomas, and regulate MAPK signaling, cancer progression, and responses to various anti-cancer drugs. HDACs have been shown to regulate the expression of PD-1/PD-L1 and genes involved in immune evasion. These reports make HDACs ideal targets for the development of anti-melanoma therapeutics. We review the mechanisms of resistance to anti-melanoma therapies, including MAPK inhibitors and immune checkpoint inhibitors. We address the effects of HDAC inhibitors on the response to MAPK inhibitors and immune checkpoint inhibitors in melanoma. In addition, we discuss current progress in anti-melanoma therapies involving a combination of HDAC inhibitors, immune checkpoint inhibitors, and MAPK inhibitors.