The N-Myc-DLL3 cascade is suppressed by the ubiquitin ligase Huwe1 to inhibit proliferation and promote neurogenesis in the developing brain

Intersection between lung cancer and neuroscience: Opportunities and challenges

Lung cancer, which has the highest morbidity and mortality rates worldwide, involves intricate interactions with the nervous system. Research indicates that the nervous system not only plays a role in the origin of lung cancer, but also engages in complex interactions with cancer cells through neurons, neurotransmitters, and various neuroactive molecules during tumor proliferation, invasion, and metastasis, especially in brain metastases. Cancer and its therapies can remodel the nervous system. Despite advancements in immunotherapy and targeted therapies in recent years, drug resistance of lung cancer cells after treatment limits improvements in patient survival and prognosis. The emergence of neuroscience has created new opportunities for the treatment of lung cancer. However, it also presents challenges. This review emphasizes that a deeper understanding of the interactions between the nervous system and lung cancer, along with the identification of new therapeutic targets, may lead to significant advancements or even a revolution in treatment strategies for patients with lung cancer.

Understanding ubiquitination in neurodevelopment by integrating insights across space and time

Ubiquitination regulates a myriad of eukaryotic signaling cascades by modifying substrate proteins, thereby determining their functions and fates. In this perspective, we discuss current challenges in investigating the ubiquitin system in the developing brain. We foster the concept that ubiquitination pathways are spatiotemporally regulated and tightly intertwined with molecular and cellular transitions during neurogenesis and neural circuit assembly. Focusing on the neurologically highly relevant class of homologous to E6AP C-terminus (HECT) ubiquitin ligases, we propose cross-disciplinary translational approaches bridging state-of-the-art cell biology, proteomics, biochemistry, structural biology and neuroscience to dissect ubiquitination in neurodevelopment and its specific perturbations in brain diseases. We highlight that a comprehensive understanding of ubiquitin signaling in the brain may reveal new horizons in basic neuroscience and clinical applications.

Sox2 interacts with Atoh1 and Huwe1 loci to regulate Atoh1 transcription and stability during hair cell differentiation

Stem cell pluripotency gene Sox2 stimulates expression of proneural basic-helix-loop-helix transcription factor Atoh1. Sox2 is necessary for the development of cochlear hair cells and binds to the Atoh1 3' enhancer to stimulate Atoh1 expression. We show here that Sox2 deletion in late embryogenesis results in the formation of extra hair cells, in contrast to the absence of hair cell development obtained after Sox2 knockout early in gestation. Sox2 overexpression decreased the level of Atoh1 protein despite an increase in Atoh1 mRNA. Sox2 upregulated E3 ubiquitin ligase, Huwe1, by direct binding to the Huwe1 gene. By upregulating its cognate E3 ligase, Sox2 disrupts the positive feedback loop through which Atoh1 protein increases the expression of Atoh1. We conclude that Sox2 initiates expression, while also limiting continued activity of bHLH transcription factor, Atoh1, and this inhibition represents a new mechanism for regulating the activity of this powerful initiator of hair cell development.

A Snapshot of Early Transcriptional Changes Accompanying the Pro-Neural Phenotype Switch by NGN2, ASCL1, SOX2, and MSI1 in Human Fibroblasts: An RNA-Seq Study

Direct pro-neural reprogramming is a conversion of differentiated somatic cells to neural cells without an intermediate pluripotency stage. It is usually achieved via ectopic expression (EE) of certain transcription factors (TFs) or other reprogramming factors (RFs). Determining the transcriptional changes (TCs) caused by particular RFs in a given cell line enables an informed approach to reprogramming initiation. Here, we characterized TCs in the human fibroblast cell line LF1 on the 5th day after EE of the single well-known pro-neural RFs NGN2, ASCL1, SOX2, and MSI1. As assessed by expression analysis of the bona fide neuronal markers nestin and beta-III tubulin, all four RFs initiated pro-neuronal phenotype conversion; analysis by RNA-seq revealed striking differences in the resulting TCs, although some pathways were overlapping. ASCL1 and SOX2 were not sufficient to induce significant pro-neural phenotype switches using our EE system. NGN2 induced TCs indicative of cell phenotype changes towards neural crest cells, neural stem cells, mature neurons, as well as radial glia, astrocytes, and oligodendrocyte precursors and their mature forms. MSI1 mainly induced a switch towards early stem-like cells, such as radial glia.

A cell state-specific metabolic vulnerability to GPX4-dependent ferroptosis in glioblastoma

Glioma cells hijack developmental programs to control cell state. Here, we uncover a glioma cell state-specific metabolic liability that can be therapeutically targeted. To model cell conditions at brain tumor inception, we generated genetically engineered murine gliomas, with deletion of p53 alone (p53) or with constitutively active Notch signaling (N1IC), a pathway critical in controlling astrocyte differentiation during brain development. N1IC tumors harbored quiescent astrocyte-like transformed cell populations while p53 tumors were predominantly comprised of proliferating progenitor-like cell states. Further, N1IC transformed cells exhibited increased mitochondrial lipid peroxidation, high ROS production and depletion of reduced glutathione. This altered mitochondrial phenotype rendered the astrocyte-like, quiescent populations more sensitive to pharmacologic or genetic inhibition of the lipid hydroperoxidase GPX4 and induction of ferroptosis. Treatment of patient-derived early-passage cell lines and glioma slice cultures generated from surgical samples with a GPX4 inhibitor induced selective depletion of quiescent astrocyte-like glioma cell populations with similar metabolic profiles. Collectively, these findings reveal a specific therapeutic vulnerability to ferroptosis linked to mitochondrial redox imbalance in a subpopulation of quiescent astrocyte-like glioma cells resistant to standard forms of treatment.

Small Cell Lung Cancer Neuronal Features and Their Implications for Tumor Progression, Metastasis, and Therapy

Small cell lung cancer (SCLC) is an epithelial neuroendocrine form of lung cancer for which survival rates remain dismal and new therapeutic approaches are greatly needed. Key biological features of SCLC tumors include fast growth and widespread metastasis, as well as rapid resistance to treatment. Similar to pulmonary neuroendocrine cells, SCLC cells have traits of both hormone-producing cells and neurons. In this study, we specifically discuss the neuronal features of SCLC. We consider how neuronal G protein-coupled receptors and other neuronal molecules on the surface of SCLC cells can contribute to the growth of SCLC tumors and serve as therapeutic targets in SCLC. We also review recent evidence for the role of neuronal programs expressed by SCLC cells in the fast proliferation, migration, and metastasis of these cells. We further highlight how these neuronal programs may be particularly relevant for the development of brain metastases and how they can assist SCLC cells to functionally interact with neurons and astrocytes. A greater understanding of the molecular and cellular neuronal features of SCLC is likely to uncover new vulnerabilities in SCLC cells, which may help develop novel therapeutic approaches. More generally, the epithelial-to-neuronal transition observed during tumor progression in SCLC and other cancer types can contribute significantly to tumor development and response to therapy.

Hepatic Huwe1 loss protects mice from non-alcoholic fatty liver disease through lipid metabolic rewiring

Non-alcoholic fatty liver disease (NAFLD) is the most pervasive liver pathology worldwide. Here, we demonstrate that the ubiquitin E3 ligase Huwe1 is vital in NAFLD pathogenesis. Using mass spectrometry and RNA sequencing, we reveal that liver-specific deletion of Huwe1 (Huwe1LKO) in 1-year-old mice (approximately middle age in humans) elicits extensive lipid metabolic reprogramming that involves downregulation of de novo lipogenesis and fatty acid uptake, upregulation of fatty acid β-oxidation, and increased oxidative phosphorylation. ChEA transcription factor prediction analysis inferred these changes result from attenuated PPARɑ, LXR, and RXR activity in Huwe1LKO livers. Consequently, Huwe1LKO mice fed chow diet exhibited significantly reduced hepatic steatosis and superior glucose tolerance compared to wild-type mice. Huwe1LKO also conferred protection from high-fat diet-induced hepatic steatosis by 6-months of age, with increasingly robust differences observed as mice reached middle age. Together, we present evidence that Huwe1 plays a critical role in the development of age- and diet-induced NAFLD.

Facial and ocular manifestations of male patients affected by the HUWE1-related intellectual developmental disorder

Turner-type X-linked syndromic intellectual developmental disorder (MRXST) is a rare neurodevelopmental disorder. MRXST is caused by pathogenic variants in the HUWE1 gene on chromosome Xp11.22. The HUWE1 gene encodes a ubiquitin ligase, which has downstream effects on the n-MYC protein and DLL3 Notch ligand, ultimately affecting neuronal differentiation. In addition to intellectual disability and developmental delay, other clinical features such as absent or delayed speech, skeletal abnormalities, abnormalities in hands or feet, seizures, and hypotonia have been described in case reports. Facial dysmorphic features and eye manifestations have been reported in patients with MRXST, but have not been identified as distinctive to this condition. We report two cases of individuals affected by HUWE1-Related Intellectual Developmental Disorder and present a review of literature of male patients affected by this disorder. Based on the literature review and findings in our two patients, it is our observation that patients with MRXST present with distinctive features, which include broad nasal tip, root, or prominent nose (39%), blepharophimosis (27%), epicanthic folds (25%), ear abnormalities (25%), thin upper lip (23%), and deep set eyes (23%). Furthermore, we note that oculofacial abnormalities are seen more frequently in patients with missense variants than patients with duplications in the HUWE1 gene. The findings noted in this paper may help clinicians suspect a diagnosis of MRXST when presented with these distinctive ocular and facial features.

HAPSTR1 localizes HUWE1 to the nucleus to limit stress signaling pathways

HUWE1 is a large, enigmatic HECT-domain ubiquitin ligase implicated in the regulation of diverse pathways, including DNA repair, apoptosis, and differentiation. How HUWE1 engages its structurally diverse substrates and how HUWE1 activity is regulated are unknown. Using unbiased quantitative proteomics, we find that HUWE1 targets substrates in a largely cell-type-specific manner. However, we identify C16orf72/HAPSTR1 as a robust HUWE1 substrate in multiple cell lines. Previously established physical and genetic interactions between HUWE1 and HAPSTR1 suggest that HAPSTR1 positively regulates HUWE1 function. Here, we show that HAPSTR1 is required for HUWE1 nuclear localization and nuclear substrate targeting. Nuclear HUWE1 is required for both cell proliferation and modulation of stress signaling pathways, including p53 and nuclear factor κB (NF-κB)-mediated signaling. Combined, our results define a role for HAPSTR1 in gating critical nuclear HUWE1 functions.

A novel Xp11.22 duplication involving HUWE1 in a male with syndromic intellectual disability and additional neurological findings

Sequence variants and duplications in the HECT, UBA and WWE domain -containing 1 (HUWE1) E3 ubiquitin ligase gene have been associated with X-linked mild to severe intellectual disability (ID), but a solid phenotype pattern among the affected males is still remaining to be established. Here, we report a male patient with sporadic, severe and syndromic ID, carrying a novel and unique 842 kb duplication at Xp11.22, including the dosage-sensitive HUWE1 gene and other fifteen curated RefSeq genes. Expression analysis in the patient and his female relatives confirmed increased HUWE1 mRNA levels, with different X-chromosome inactivation patterns among the female carriers. Our patient differs from those previously described by us and others as he presents encephalomalacia at brain Magnetic Resonance Imaging and diffuse bilaterally and synchronous intercritical irritating paroxysms at electroencephalogram. Overall, our clinical, molecular, and neurological findings sum up the previous data, expanding the phenotype spectrum in Xp11.22 copy gains involving the whole HUWE1 gene in both males and female carriers in light of X-chromosome inactivation patterns.

A cell state specific metabolic vulnerability to GPX4-dependent ferroptosis in glioblastoma

Glioma cells hijack developmental transcriptional programs to control cell state. During neural development, lineage trajectories rely on specialized metabolic pathways. However, the link between tumor cell state and metabolic programs is poorly understood in glioma. Here we uncover a glioma cell state-specific metabolic liability that can be leveraged therapeutically. To model cell state diversity, we generated genetically engineered murine gliomas, induced by deletion of p53 alone (p53) or with constitutively active Notch signaling (N1IC), a pathway critical in controlling cellular fate. N1IC tumors harbored quiescent astrocyte-like transformed cell states while p53 tumors were predominantly comprised of proliferating progenitor-like cell states. N1IC cells exhibit distinct metabolic alterations, with mitochondrial uncoupling and increased ROS production rendering them more sensitive to inhibition of the lipid hydroperoxidase GPX4 and induction of ferroptosis. Importantly, treating patient-derived organotypic slices with a GPX4 inhibitor induced selective depletion of quiescent astrocyte-like glioma cell populations with similar metabolic profiles.

The E3 ubiquitin ligase HUWE1 acts through the N-Myc-DLL1-NOTCH1 signaling axis to suppress glioblastoma progression

BACKGROUND

Elucidation of the post-transcriptional modification has led to novel strategies to treat intractable tumors, especially glioblastoma (GBM). The ubiquitin-proteasome system (UPS) mediates a reversible, stringent and stepwise post-translational modification which is closely associated with malignant processes of GBM. To this end, developing novel therapeutic approaches to target the UPS may contribute to the treatment of this disease. This study aimed to screen the vital and aberrantly regulated component of the UPS in GBM. Based on the molecular identification, functional characterization, and mechanism investigation, we sought to elaborate a novel therapeutic strategy to target this vital factor to combat GBM.

METHODS

We combined glioma datasets and human patient samples to screen and identify aberrantly regulated E3 ubiquitin ligase. Multidimensional database analysis and molecular and functional experiments in vivo and in vitro were used to evaluate the roles of HECT, UBA and WWE domain-containing E3 ubiquitin ligase 1 (HUWE1) in GBM. dCas9 synergistic activation mediator system and recombinant adeno-associated virus (rAAV) were used to endogenously overexpress full-length HUWE1 in vitro and in glioma orthotopic xenografts.

RESULTS

Low expression of HUWE1 was closely associated with worse prognosis of GBM patients. The ubiquitination and subsequent degradation of N-Myc mediated by HUWE1, leading to the inactivation of downstream Delta-like 1 (DLL1)-NOTCH1 signaling pathways, inhibited the proliferation, invasion, and migration of GBM cells in vitro and in vivo. A rAAV dual-vector system for packaging and delivery of dCas9-VP64 was used to augment endogenous HUWE1 expression in vivo and showed an antitumor activity in glioma orthotopic xenografts.

CONCLUSIONS

The E3 ubiquitin ligase HUWE1 acts through the N-Myc-DLL1-NOTCH1 signaling axis to suppress GBM progression. Antitumor activity of rAAV dual-vector delivering dCas9-HUWE1 system uncovers a promising therapeutic strategy for GBM.

Transcription factor network analysis identifies REST/NRSF as an intrinsic regulator of CNS regeneration in mice

The inability of neurons to regenerate long axons within the CNS is a major impediment to improving outcome after spinal cord injury, stroke, and other CNS insults. Recent advances have uncovered an intrinsic program that involves coordinate regulation by multiple transcription factors that can be manipulated to enhance growth in the peripheral nervous system. Here, we use a systems genomics approach to characterize regulatory relationships of regeneration-associated transcription factors, identifying RE1-Silencing Transcription Factor (REST; Neuron-Restrictive Silencer Factor, NRSF) as a predicted upstream suppressor of a pro-regenerative gene program associated with axon regeneration in the CNS. We validate our predictions using multiple paradigms, showing that mature mice bearing cell type-specific deletions of REST or expressing dominant-negative mutant REST show improved regeneration of the corticospinal tract and optic nerve after spinal cord injury and optic nerve crush, which is accompanied by upregulation of regeneration-associated genes in cortical motor neurons and retinal ganglion cells, respectively. These analyses identify a role for REST as an upstream suppressor of the intrinsic regenerative program in the CNS and demonstrate the utility of a systems biology approach involving integrative genomics and bio-informatics to prioritize hypotheses relevant to CNS repair.

The giant E3 ligase HUWE1 is linked to tumorigenesis, spermatogenesis, intellectual disability, and inflammatory diseases

E3 ubiquitin ligases determine the substrate specificity and catalyze the ubiquitination of lysine residues. HUWE1 is a catalytic HECT domain-containing giant E3 ligase that contains a substrate-binding ring structure, and mediates the ubiquitination of more than 40 diverse substrates. HUWE1 serves as a central node in cellular stress responses, cell growth and death, signal transduction, etc. The expanding atlas of HUWE1 substrates presents a major challenge for the potential therapeutic application of HUWE1 in a particular disease. In addition, HUWE1 has been demonstrated to play contradictory roles in certain aspects of tumor progression in either an oncogenic or a tumor-suppressive manner. We recently defined novel roles of HUWE1 in promoting the activation of multiple inflammasomes. Inflammasome activation-mediated immune responses might lead to multifunctional effects on tumor therapy, inflammation, and autoimmune diseases. In this review, we summarize the known substrates and pleiotropic functions of HUWE1 in different types of cells and models, including its involvement in development, cancer, neuronal disorder and infectious disease. We also discuss the advances in cryo-EM-structural analysis for a functional-mechanistic understanding of HUWE1 in modulating the multitudinous diverse substrates, and introduce the possibility of revisiting the comprehensive roles of HUWE1 in multiple aspects within one microenvironment, which will shed light on the potential therapeutic application of targeting giant E3 ligases like HUWE1.

E3 Ubiquitin ligases and cerebral cortex development in health and disease

Cerebral cortex development involves the sequential progression of biological steps driven by molecular pathways whose tight regulation often relies on ubiquitination. Ubiquitination is a post-translational modification involved in all aspects of cellular homeostasis through the attachment of a ubiquitin moiety on proteins. Over the past years, an increasing amount of research has highlighted the crucial role played by ubiquitin ligases in every step of cortical development and whose impairment often leads to various neurodevelopmental disorders. In this review, we focus on the key contributions of E3 ubiquitin ligases for the progression of the different steps of corticogenesis, as well as the pathological consequences of their mutations, often resulting in malformations of cortical development. Finally, we discuss some promising targeted treatment strategies for these diseases based on recent advances in the field. This article is protected by copyright. All rights reserved.

ZNF117 regulates glioblastoma stem cell differentiation towards oligodendroglial lineage

Glioblastoma (GBM) is a deadly disease without effective treatment. Because glioblastoma stem cells (GSCs) contribute to tumor resistance and recurrence, improved treatment of GBM can be achieved by eliminating GSCs through inducing their differentiation. Prior efforts have been focused on studying GSC differentiation towards the astroglial lineage. However, regulation of GSC differentiation towards the neuronal and oligodendroglial lineages is largely unknown. To identify genes that control GSC differentiation to all three lineages, we performed an image-based genome-wide RNAi screen, in combination with single-cell RNA sequencing, and identified ZNF117 as a major regulator of GSC differentiation. Using patient-derived GSC cultures, we show that ZNF117 controls GSC differentiation towards the oligodendroglial lineage via the Notch pathway. We demonstrate that ZNF117 is a promising target for GSC differentiation therapy through targeted delivery of CRISPR/Cas9 gene-editing nanoparticles. Our study suggests a direction to improve GBM treatment through differentiation of GSCs towards various lineages.

Elevated DLL3 in stomach cancer by tumor-associated macrophages enhances cancer-cell proliferation and cytokine secretion of macrophages

Background

The notch signal pathway is important in the development of both tumor-associated macrophages (TAMs) and stomach cancer, but how Notch signaling affects TAMs in stomach cancer is barely understood.

Methods

The expressions of Notch1, Notch2, Notch3, Notch4, hes family bHLH transcription factor 1 (Hes1), and delta-like canonical Notch ligand 3 (DLL3) were detected by Western blot and the expressions of interleukin (IL)-10, IL-12, and IL1-β were detected using enzyme-linked immunosorbent assay after the co-culture of macrophages and stomach-cancer cells. The proliferation and migration of cancer cells were detected using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay and scratch assay, respectively, and the cell cycle was detected using Annexin V/propidium iodide assay. The protein interactions with DLL3 were detected using co-immunoprecipitation and mass spectrometry.

Results

The co-culture of macrophages and stomach-cancer cells MKN45 and BGC823 could enhance cell proliferation accompanied by the activation of Notch1/Notch2 signaling and upregulation of DLL3. Notch signaling gamma-secretase inhibitor (DAPT) blocked this process. The overexpression of DLL3 in stomach-cancer cells could promote the proliferation of cancer cells, enhance the activation of Notch1/Notch2 signaling, induce the expression of IL-33, lead to the degradation of galectin-3–binding protein (LG3BP) and heat shock cognate 71 kDa protein (HSPA8), and result in elevated IL-1β, IL-12, and IL-10 secretion by macrophages. Higher expression of DLL3 or IL-33 could lead to a lower survival rate based on University of California, Santa Cruz Xena Functional Genomics Explorer and The Cancer Genome Atlas data set.

Conclusions

This is evidence that DLL3 regulates macrophages in stomach cancer, suggesting that DLL3 may be a novel and potential target for stomach-cancer therapy.

O-GlcNAc transferase OGT-1 and the ubiquitin ligase EEL-1 modulate seizure susceptibility in C. elegans

Neurodevelopmental disorders such as epilepsy and autism have been linked to an imbalance of excitation and inhibition (E/I) in the central nervous system. The simplicity and tractability of C. elegans allows our electroconvulsive seizure (ES) assay to be used as a behavioral readout of the locomotor circuit and neuronal function. C. elegans possess conserved nervous system features such as gamma-aminobutyric acid (GABA) and GABA receptors in inhibitory neurotransmission, and acetylcholine (Ach) and acetylcholine receptors in excitatory neurotransmission. Our previously published data has shown that decreasing inhibition in the motor circuit, via GABAergic manipulation, will extend the time of locomotor recovery following electroshock. Similarly, mutations in a HECT E3 ubiquitin ligase called EEL-1 leads to impaired GABAergic transmission, E/I imbalance and altered sensitivity to electroshock. Mutations in the human ortholog of EEL-1, called HUWE1, are associated with both syndromic and non-syndromic intellectual disability. Both EEL-1 and its previously established binding protein, OGT-1, are expressed in GABAergic motor neurons, localize to GABAergic presynaptic terminals, and function in parallel to regulate GABA neuron function. In this study, we tested behavioral responses to electroshock in wildtype, ogt-1, eel-1 and ogt-1; eel-1 double mutants. Both ogt-1 and eel-1 null mutants have decreased inhibitory GABAergic neuron function and increased electroshock sensitivity. Consistent with EEL-1 and OGT-1 functioning in parallel pathways, ogt-1; eel-1 double mutants showed enhanced electroshock susceptibility. Expression of OGT-1 in the C. elegans nervous system rescued enhanced electroshock defects in ogt-1; eel-1 double mutants. Application of a GABA agonist, Baclofen, decreased electroshock susceptibility in all animals. Our C. elegans electroconvulsive seizure assay was the first to model a human X-linked Intellectual Disability (XLID) associated with epilepsy and suggests a potential novel role for the OGT-1/EEL-1 complex in seizure susceptibility.

Low-density-lipoprotein-receptor-related protein 1 mediates Notch pathway activation

The Notch signaling pathway controls cell growth, differentiation, and fate decisions, and its dysregulation has been linked to various human genetic disorders and cancers. To comprehensively understand the global organization of the Notch pathway and identify potential drug targets for Notch-related diseases, we established a protein interaction landscape for the human Notch pathway. By combining and analyzing genetic and phenotypic data with bioinformatics analysis, we greatly expanded this pathway and identified many key regulators, including low-density-lipoprotein-receptor-related protein 1 (LRP1). We demonstrated that LRP1 mediates the ubiquitination chain linkage switching of Delta ligands, which further affects ligand recycling, membrane localization, and stability. LRP1 inhibition led to Notch signaling inhibition and decreased tumorigenesis in leukemia models. Our study provides a glimpse into the Notch pathway interaction network and uncovers LRP1 as one critical regulator of the Notch pathway, as well as a possible therapeutic target for Notch-related cancers.

Modular network mechanism of CCN1-associated resistance to HSV-1-derived oncolytic immunovirotherapies for glioblastomas

Glioblastomas (GBMs) are the most common and lethal primary brain malignancy in adults. Oncolytic virus (OV) immunotherapies selectively kill GBM cells in a manner that elicits antitumor immunity. Cellular communication network factor 1 (CCN1), a protein found in most GBM microenvironments, expression predicts resistance to OVs, particularly herpes simplex virus type 1 (HSV-1). This study aims to understand how extracellular CCN1 alters the GBM intracellular state to confer OV resistance. Protein-protein interaction network information flow analyses of LN229 human GBM transcriptomes identified 39 novel nodes and 12 binary edges dominating flow in CCN1high cells versus controls. Virus response programs, notably against HSV-1, and cytokine-mediated signaling pathways are highly enriched. Our results suggest that CCN1high states exploit IDH1 and TP53, and increase dependency on RPL6, HUWE1, and COPS5. To validate, we reproduce our findings in 65 other GBM cell line (CCLE) and 174 clinical GBM patient sample (TCGA) datasets. We conclude through our generalized network modeling and system level analysis that CCN1 signals via several innate immune pathways in GBM to inhibit HSV-1 OVs before transduction. Interventions disrupting this network may overcome immunovirotherapy resistance.

Transcriptome-Wide Identification of G-to-A RNA Editing in Chronic Social Defeat Stress Mouse Models

Emerging evidence suggests that RNA editing is associated with stress, neurological diseases, and psychiatric disorders. However, the role of G-to-A RNA editing in chronic social defeat stress (CSDS) remains unclear. We herein identified G-to-A RNA editing and its changes in the ventral tegmental area (VTA), a key region of the brain reward system, in CSDS mouse models under emotional stress (ES) and physiological stress (PS) conditions. Our results revealed 3812 high-confidence G-to-A editing events. Among them, 56 events were significantly downregulated while 23 significantly upregulated in CSDS compared to controls. Moreover, divergent editing patterns were observed between CSDS mice under ES and PS conditions, with 42 and 21 events significantly upregulated in PS and ES, respectively. Interestingly, differential RNA editing was enriched in genes with multiple editing events. Genes differentially edited in CSDS included those genetically associated with mental or neurodevelopmental disorders, especially mood disorders, such as FAT atypical cadherin 1 and solute carrier family 6 member 1. Notably, changes of G-to-A RNA editing were also implicated in ionotropic glutamate receptors, a group of well-known targets of adenosine-to-inosine RNA editing. Such results demonstrate dynamic G-to-A RNA editing changes in the brain of CSDS mouse models, underlining its role as a potential molecular mechanism of CSDS and stress-related diseases.

Increased p53 signaling impairs neural differentiation in HUWE1-promoted intellectual disabilities

Essential E3 ubiquitin ligase HUWE1 (HECT, UBA, and WWE domain containing 1) regulates key factors, such as p53. Although mutations in HUWE1 cause heterogenous neurodevelopmental X-linked intellectual disabilities (XLIDs), the disease mechanisms common to these syndromes remain unknown. In this work, we identify p53 signaling as the central process altered in HUWE1-promoted XLID syndromes. By focusing on Juberg-Marsidi syndrome (JMS), one of the severest XLIDs, we show that increased p53 signaling results from p53 accumulation caused by HUWE1 p.G4310R destabilization. This further alters cell-cycle progression and proliferation in JMS cells. Modeling of JMS neurodevelopment reveals majorly impaired neural differentiation accompanied by increased p53 signaling. The neural differentiation defects can be successfully rescued by reducing p53 levels and restoring the expression of p53 target genes, in particular CDKN1A/p21. In summary, our findings suggest that increased p53 signaling underlies HUWE1-promoted syndromes and impairs XLID JMS neural differentiation.

Reduced Granule Cell Proliferation and Molecular Dysregulation in the Cerebellum of Lysosomal Acid Phosphatase 2 (ACP2) Mutant Mice

Lysosomal acid phosphatase 2 (Acp2) mutant mice (naked-ataxia, nax) have a severe cerebellar cortex defect with a striking reduction in the number of granule cells. Using a combination of in vivo and in vitro immunohistochemistry, Western blotting, BrdU assays, and RT-qPCR, we show downregulation of MYCN and dysregulation of the SHH signaling pathway in the nax cerebellum. MYCN protein expression is significantly reduced at P10, but not at the peak of proliferation at around P6 when the number of granule cells is strikingly reduced in the nax cerebellum. Despite the significant role of the SHH-MycN pathway in granule cell proliferation, our study suggests that a broader molecular pathway and additional mechanisms regulating granule cell development during the clonal expansion period are impaired in the nax cerebellum. In particular, our results indicate that downregulation of the protein synthesis machinery may contribute to the reduced number of granule cells in the nax cerebellum.

HUWE1 mediates inflammasome activation and promotes host defense against bacterial infection

The mechanism by which inflammasome activation is modulated remains unclear. In this study, we identified an AIM2-interacting protein, the E3 ubiquitin ligase HUWE1, which was also found to interact with NLRP3 and NLRC4 through the HIN domain of AIM2 and the NACHT domains of NLRP3 and NLRC4. The BH3 domain of HUWE1 was important for its interaction with NLRP3, AIM2, and NLRC4. Caspase-1 maturation, IL-1β release, and pyroptosis were reduced in Huwe1-deficient bone marrow-derived macrophages (BMDMs) compared with WT BMDMs in response to stimuli to induce NLRP3, NLRC4, and AIM2 inflammasome activation. Furthermore, the activation of NLRP3, NLRC4, and AIM2 inflammasomes in both mouse and human cells was remarkably reduced by treatment with the HUWE1 inhibitor BI8622. HUWE1 mediated the K27-linked polyubiquitination of AIM2, NLRP3, and NLRC4, which led to inflammasome assembly, ASC speck formation, and sustained caspase-1 activation. Huwe1-deficient mice had an increased bacterial burden and decreased caspase-1 activation and IL-1β production upon Salmonella, Francisella, or Acinetobacter baumannii infection. Our study provides insights into the mechanisms of inflammasome activation as well as a potential therapeutic target against bacterial infection.

Usp11 controls cortical neurogenesis and neuronal migration through Sox11 stabilization

The role of protein stabilization in cortical development remains poorly understood. A recessive mutation in the USP11 gene is found in a rare neurodevelopmental disorder with intellectual disability, but its pathogenicity and molecular mechanism are unknown. Here, we show that mouse Usp11 is expressed highly in embryonic cerebral cortex, and Usp11 deficiency impairs layer 6 neuron production, delays late-born neuronal migration, and disturbs cognition and anxiety behaviors. Mechanistically, these functions are mediated by a previously unidentified Usp11 substrate, Sox11. Usp11 ablation compromises Sox11 protein accumulation in the developing cortex, despite the induction of Sox11 mRNA. The disease-associated Usp11 mutant fails to stabilize Sox11 and is unable to support cortical neurogenesis and neuronal migration. Our findings define a critical function of Usp11 in cortical development and highlight the importance of orchestrating protein stabilization mechanisms into transcription regulatory programs for a robust induction of cell fate determinants during early brain development.

The role of E3 ubiquitin ligases in the development and progression of glioblastoma

Despite recent advances in our understanding of the disease, glioblastoma (GB) continues to have limited treatment options and carries a dismal prognosis for patients. Efforts to stratify this heterogeneous malignancy using molecular classifiers identified frequent alterations in targetable proteins belonging to several pathways including the receptor tyrosine kinase (RTK) and mitogen-activated protein kinase (MAPK) signalling pathways. However, these findings have failed to improve clinical outcomes for patients. In almost all cases, GB becomes refractory to standard-of-care therapy, and recent evidence suggests that disease recurrence may be associated with a subpopulation of cells known as glioma stem cells (GSCs). Therefore, there remains a significant unmet need for novel therapeutic strategies. E3 ubiquitin ligases are a family of >700 proteins that conjugate ubiquitin to target proteins, resulting in an array of cellular responses, including DNA repair, pro-survival signalling and protein degradation. Ubiquitin modifications on target proteins are diverse, ranging from mono-ubiquitination through to the formation of polyubiquitin chains and mixed chains. The specificity in substrate tagging and chain elongation is dictated by E3 ubiquitin ligases, which have essential regulatory roles in multiple aspects of brain cancer pathogenesis. In this review, we begin by briefly summarising the histological and molecular classification of GB. We comprehensively describe the roles of E3 ubiquitin ligases in RTK and MAPK, as well as other, commonly altered, oncogenic and tumour suppressive signalling pathways in GB. We also describe the role of E3 ligases in maintaining glioma stem cell populations and their function in promoting resistance to ionizing radiation (IR) and chemotherapy. Finally, we consider how our knowledge of E3 ligase biology may be used for future therapeutic interventions in GB, including the use of blood-brain barrier permeable proteolysis targeting chimeras (PROTACs).

Targeting the Ubiquitin System in Glioblastoma

Glioblastoma is the most common primary brain tumor in adults with poor overall outcome and 5-year survival of less than 5%. Treatment has not changed much in the last decade or so, with surgical resection and radio/chemotherapy being the main options. Glioblastoma is highly heterogeneous and frequently becomes treatment-resistant due to the ability of glioblastoma cells to adopt stem cell states facilitating tumor recurrence. Therefore, there is an urgent need for novel therapeutic strategies. The ubiquitin system, in particular E3 ubiquitin ligases and deubiquitinating enzymes, have emerged as a promising source of novel drug targets. In addition to conventional small molecule drug discovery approaches aimed at modulating enzyme activity, several new and exciting strategies are also being explored. Among these, PROteolysis TArgeting Chimeras (PROTACs) aim to harness the endogenous protein turnover machinery to direct therapeutically relevant targets, including previously considered "undruggable" ones, for proteasomal degradation. PROTAC and other strategies targeting the ubiquitin proteasome system offer new therapeutic avenues which will expand the drug development toolboxes for glioblastoma. This review will provide a comprehensive overview of E3 ubiquitin ligases and deubiquitinating enzymes in the context of glioblastoma and their involvement in core signaling pathways including EGFR, TGF-β, p53 and stemness-related pathways. Finally, we offer new insights into how these ubiquitin-dependent mechanisms could be exploited therapeutically for glioblastoma.

Associations between Huwe1 and autophagy in rat cerebral neuron oxygen‑glucose deprivation and reperfusion injury

Autophagy and the ubiquitin proteasome system (UPS) are two major protein degradation pathways involved in brain ischemia. Autophagy can compensate for UPS impairment-induced cellular dysfunction. HECT, UBA and WWE domain containing E3 ubiquitin protein ligase 1 (Huwe1), an E3 ubiquitin ligase, serves critical roles in nervous system plasticity, regeneration and disease. However, the role of Huwe1 in autophagy in brain ischemia/reperfusion (I/R) injury remains unknown. The aim of the present study was to investigate the crosstalk between autophagy and the UPS in brain ischemia. The present study established an oxygen-glucose deprivation and reperfusion (OGD/R) model in rat primary cortex neurons in vitro. Lentiviral interference was used to silence the expression of Huwe1. An autophagy promoter (rapamycin), an autophagy inhibitor (wortmannin) and a JNK pathway inhibitor (SP600125) were also used in the current study. Cellular autophagy-related proteins, including Beclin-1, autophagy related (ATG) 7, ATG5, ATG3 and microtubule associated protein 1 light chain 3 α, and apoptosis-related proteins, such as P53, cleaved caspase 3, Bax and Bcl2, were detected via western blotting and immunocytochemistry. Neuronal apoptosis was evaluated using a TUNEL assay. The results demonstrated that silencing Huwe1 increased the expression levels of autophagy-related proteins at 24 h after OGD/R. Treatment with a JNK inhibitor or cotreatment with Huwe1 shRNA significantly increased autophagy. Rapamycin increased apoptosis under OGD/R conditions. However, treatment with Huwe1 shRNA decreased the number of TUNEL-positive cells at 24 h after OGD/R. Cotreatment with Huwe1 shRNA and wortmannin alleviated neuronal apoptosis under OGD/R conditions compared with cotreatment with DMSO. Collectively, the present results suggested that silencing Huwe1 was accompanied by a compensatory induction of autophagy under OGD/R conditions. Furthermore, the JNK pathway may be a key mediator of the interaction between Huwe1 and autophagy in response to UPS impairment.

Proteogenomics analysis unveils a TFG-RET gene fusion and druggable targets in papillary thyroid carcinomas

Papillary thyroid cancer (PTC) is the most common type of endocrine malignancy. By RNA-seq analysis, we identify a RET rearrangement in the tumour material of a patient who does not harbour any known RAS or BRAF mutations. This new gene fusion involves exons 1–4 from the 5′ end of the Trk fused Gene (TFG) fused to the 3′ end of RET tyrosine kinase leading to a TFG-RET fusion which transforms immortalized human thyroid cells in a kinase-dependent manner. TFG-RET oligomerises in a PB1 domain-dependent manner and oligomerisation of TFG-RET is required for oncogenic transformation. Quantitative proteomic analysis reveals the upregulation of E3 Ubiquitin ligase HUWE1 and DUBs like USP9X and UBP7 in both tumor and metastatic lesions, which is further confirmed in additional patients. Expression of TFG-RET leads to the upregulation of HUWE1 and inhibition of HUWE1 significantly reduces RET-mediated oncogenesis.

Papillary thyroid cancer (PTC) is one of the most common type of endocrine malignancy. Here, the authors use proteogenomic approaches to analyse the primary tumour and lymph node metastases from a PTC patient and report an oncogenic RET fusion, and potential druggable targets from the ubiquitin signaling machinery for treating human PTCs.

Roles of the HUWE1 ubiquitin ligase in nervous system development, function and disease

Huwe1 is a highly conserved member of the HECT E3 ubiquitin ligase family. Here, we explore the growing importance of Huwe1 in nervous system development, function and disease. We discuss extensive progress made in deciphering how Huwe1 regulates neural progenitor proliferation and differentiation, cell migration, and axon development. We highlight recent evidence indicating that Huwe1 regulates inhibitory neurotransmission. In covering these topics, we focus on findings made using both vertebrate and invertebrate in vivo model systems. Finally, we discuss extensive human genetic studies that strongly implicate HUWE1 in intellectual disability, and heighten the importance of continuing to unravel how Huwe1 affects the nervous system.

Combinatorial targeting of MTHFD2 and PAICS in purine synthesis as a novel therapeutic strategy

MYCN-amplified (MNA) neuroblastoma is an aggressive neural crest-derived pediatric cancer. However, MYCN is indispensable for development and transcriptionally regulates extensive network of genes. Integrating anti-MYCN ChIP-seq and gene expression profiles of neuroblastoma patients revealed the metabolic enzymes, MTHFD2 and PAICS, required for one-carbon metabolism and purine biosynthesis were concomitantly upregulated, which were more susceptible to metastatic neuroblastoma. Moreover, we found that MYCN mediated the folate cycle via MTHFD2, which contributed one-carbon unit to enhance purine synthesis, and further regulated nucleotide production by PAICS in response to cancer progression. Dual knockdown of the MYCN-targeted gene pair, MTHFD2 and PAICS, in MNA neuroblastoma cells synergically reduced cell proliferation, colony formation, migration ability, and DNA synthesis. By systematically screening the compound perturbagens, the gene expression levels of MTHFD2 and PAICS were specifically suppressed by anisomycin and apicidin across cell lines, and our co-treatment results also displayed synergistic inhibition of MNA neuroblastoma cell proliferation. Collectively, targeting a combination of MYCN-targeted genes that interrupts the interconnection of metabolic pathways may overcome drug toxicity and improve the efficacy of current therapeutic agents in MNA neuroblastoma.

A Critical E-box in Barhl1 3' Enhancer Is Essential for Auditory Hair Cell Differentiation

Barhl1, a mouse homologous gene of Drosophila BarH class homeobox genes, is highly expressed within the inner ear and crucial for the long-term maintenance of auditory hair cells that mediate hearing and balance, yet little is known about the molecular events underlying Barhl1 regulation and function in hair cells. In this study, through data mining and in vitro report assay, we firstly identified Barhl1 as a direct target gene of Atoh1 and one E-box (E3) in Barhl1 3’ enhancer is crucial for Atoh1-mediated Barhl1 activation. Then we generated a mouse embryonic stem cell (mESC) line carrying disruptions on this E3 site E-box (CAGCTG) using CRISPR/Cas9 technology and this E3 mutated mESC line is further subjected to an efficient stepwise hair cell differentiation strategy in vitro. Disruptions on this E3 site caused dramatic loss of Barhl1 expression and significantly reduced the number of induced hair cell-like cells, while no affections on the differentiation toward early primitive ectoderm-like cells and otic progenitors. Finally, through RNA-seq profiling and gene ontology (GO) enrichment analysis, we found that this E3 box was indispensable for Barhl1 expression to maintain hair cell development and normal functions. We also compared the transcriptional profiles of induced cells from CDS mutated and E3 mutated mESCs, respectively, and got very consistent results except the Barhl1 transcript itself. These observations indicated that Atoh1-mediated Barhl1 expression could have important roles during auditory hair cell development. In brief, our findings delineate the detail molecular mechanism of Barhl1 expression regulation in auditory hair cell differentiation.

A complex containing the O-GlcNAc transferase OGT-1 and the ubiquitin ligase EEL-1 regulates GABA neuron function

Inhibitory GABAergic transmission is required for proper circuit function in the nervous system. However, our understanding of molecular mechanisms that preferentially influence GABAergic transmission, particularly presynaptic mechanisms, remains limited. We previously reported that the ubiquitin ligase EEL-1 preferentially regulates GABAergic presynaptic transmission. To further explore how EEL-1 functions, here we performed affinity purification proteomics using Caenorhabditis elegans and identified the O-GlcNAc transferase OGT-1 as an EEL-1 binding protein. This observation was intriguing, as we know little about how OGT-1 affects neuron function. Using C. elegans biochemistry, we confirmed that the OGT-1/EEL-1 complex forms in neurons in vivo and showed that the human orthologs, OGT and HUWE1, also bind in cell culture. We observed that, like EEL-1, OGT-1 is expressed in GABAergic motor neurons, localizes to GABAergic presynaptic terminals, and functions cell-autonomously to regulate GABA neuron function. Results with catalytically inactive point mutants indicated that OGT-1 glycosyltransferase activity is dispensable for GABA neuron function. Consistent with OGT-1 and EEL-1 forming a complex, genetic results using automated, behavioral pharmacology assays showed that ogt-1 and eel-1 act in parallel to regulate GABA neuron function. These findings demonstrate that OGT-1 and EEL-1 form a conserved signaling complex and function together to affect GABA neuron function.

Exome sequencing reveals a novel splice site variant in HUWE1 gene in patients with suspected Say-Meyer syndrome

Say-Meyer syndrome is a rare and clinically heterogeneous syndrome characterized by trigonocephaly, short stature, developmental delay and hypotelorism. Nine patients with this syndrome have been reported thus far although no causative gene has yet been identified. Here, we report two siblings with clinical phenotypes of Say-Meyer syndrome with moderate to severe intellectual disability and autism spectrum disorder. Cytogenetics and array-based comparative genomic hybridization did not reveal any chromosome abnormalities or copy number alterations. Exome sequencing of the patients revealed a novel X-linked recessive splice acceptor site variant c.145-2A > G in intron 5 of HUWE1 gene in both affected siblings. RT-PCR and sequencing revealed the use of an alternate cryptic splice acceptor site downstream, which led to deletion of six nucleotides resulting loss of two amino acids p.(Cys49-Glu50del) in HUWE1 protein. Deletion of these two amino acids, which are located in a highly conserved region, is predicted to be deleterious and quite likely to affect the function of HUWE1 protein. This is the first report of a potential candidate gene mutation for Say-Meyer syndrome, which was initially described four decades ago.

Ubiquitination and inhibition of glycine receptor by HUWE1 in spinal cord dorsal horn

Glycine receptors (GlyRs) are pentameric proteins that consist of α (α1-α4) subunits and/or β subunit. In the spinal cord of adult animals, the majority of inhibitory glycinergic neurotransmission is mediated by α1 subunit-containing GlyRs. The reduced glycinergic inhibition (disinhibition) is proposed to increase the excitabilities and spontaneous activities of spinal nociceptive neurons during pathological pain. However, the molecular mechanisms by which peripheral lesions impair GlyRs-α1-mediated synaptic inhibition remain largely unknown. Here we found that activity-dependent ubiquitination of GlyRs-α1 subunit might contribute to glycinergic disinhibition after peripheral inflammation. Our data showed that HUWE1 (HECT, UBA, WWE domain containing 1), an E3 ubiquitin ligase, located at spinal synapses and specifically interacted with GlyRs-α1 subunit. By ubiquitinating GlyRs-α1, HUWE1 reduced the surface expression of GlyRs-α1 through endocytic pathway. In the dorsal horn of Complete Freund's Adjuvant-injected mice, shRNA-mediated knockdown of HUWE1 blunted GlyRs-α1 ubiquitination, potentiated glycinergic synaptic transmission and attenuated inflammatory pain. These data implicated that ubiquitin modification of GlyRs-α1 represented an important way for peripheral inflammation to reduce spinal glycinergic inhibition and that interference with HUWE1 activity generated analgesic action by resuming GlyRs-α1-mediated synaptic transmission.

Silencing Huwe1 reduces apoptosis of cortical neurons exposed to oxygen-glucose deprivation and reperfusion

HECT, UBA and WWE domain-containing 1 (Huwe1), an E3 ubiquitin ligase involved in the ubiquitin-proteasome system, is widely expressed in brain tissue. Huwe1 is involved in the turnover of numerous substrates, including p53, Mcl-1, Cdc6 and N-myc, thereby playing a critical role in apoptosis and neurogenesis. However, the role of Huwe1 in brain ischemia and reperfusion injury remains unclear. Therefore, in this study, we investigated the role of Huwe1 in an in vitro model of ischemia and reperfusion injury. At 3 days in vitro, primary cortical neurons were transduced with a control or shRNA-Huwe1 lentiviral vector to silence expression of Huwe1. At 7 days in vitro, the cells were exposed to oxygen-glucose deprivation for 3 hours and reperfusion for 24 hours. To examine the role of the c-Jun N-terminal kinase (JNK)/p38 pathway, cortical neurons were pretreated with a JNK inhibitor (SP600125) or a p38MAPK inhibitor (SB203508) for 30 minutes at 7 days in vitro, followed by ischemia and reperfusion. Neuronal apoptosis was assessed by TUNEL assay. Protein expression levels of JNK and p38MAPK and of apoptosis-related proteins (p53, Gadd45a, cleaved caspase-3, Bax and Bcl-2) were measured by western blot assay. Immunofluorescence labeling for cleaved caspase-3 was performed. We observed a significant increase in neuronal apoptosis and Huwe1 expression after ischemia and reperfusion. Treatment with the shRNA-Huwe1 lentiviral vector markedly decreased Huwe1 levels, and significantly decreased the number of TUNEL-positive cells after ischemia and reperfusion. The silencing vector also downregulated the pro-apoptotic proteins Bax and cleaved caspase-3, and upregulated the anti-apoptotic proteins Gadd45a and Bcl-2. Silencing Huwe1 also significantly reduced p-JNK levels and increased p-p38 levels. Our findings show that downregulating Huwe1 affects the JNK and p38MAPK signaling pathways as well as the expression of apoptosis-related genes to provide neuroprotection during ischemia and reperfusion. All animal experiments and procedures were approved by the Animal Ethics Committee of Sichuan University, China in January 2018 (approval No. 2018013).

Drosophila HUWE1 Ubiquitin Ligase Regulates Endoreplication and Antagonizes JNK Signaling During Salivary Gland Development

The HECT-type ubiquitin ligase HECT, UBA and WWE Domain Containing 1, (HUWE1) regulates key cancer-related pathways, including the Myc oncogene. It affects cell proliferation, stress and immune signaling, mitochondria homeostasis, and cell death. HUWE1 is evolutionarily conserved from Caenorhabditis elegance to Drosophila melanogaster and Humans. Here, we report that the Drosophila ortholog, dHUWE1 (CG8184), is an essential gene whose loss results in embryonic lethality and whose tissue-specific disruption establishes its regulatory role in larval salivary gland development. dHUWE1 is essential for endoreplication of salivary gland cells and its knockdown results in the inability of these cells to replicate DNA. Remarkably, dHUWE1 is a survival factor that prevents premature activation of JNK signaling, thus preventing the disintegration of the salivary gland, which occurs physiologically during pupal stages. This function of dHUWE1 is general, as its inhibitory effect is observed also during eye development and at the organismal level. Epistatic studies revealed that the loss of dHUWE1 is compensated by dMyc proeitn expression or the loss of dmP53. dHUWE1 is therefore a conserved survival factor that regulates organ formation during Drosophila development.

Ubiquitination by HUWE1 in tumorigenesis and beyond

Ubiquitination modulates a large repertoire of cellular functions and thus, dysregulation of the ubiquitin system results in multiple human diseases, including cancer. Ubiquitination requires an E3 ligase, which is responsible for substrate recognition and conferring specificity to ubiquitination. HUWE1 is a multifaceted HECT domain-containing ubiquitin E3 ligase, which catalyzes both mono-ubiquitination and K6-, K48- and K63-linked poly-ubiquitination of its substrates. Many of the substrates of HUWE1 play a crucial role in maintaining the homeostasis of cellular development. Not surprisingly, dysregulation of HUWE1 is associated with tumorigenesis and metastasis. HUWE1 is frequently overexpressed in solid tumors, but can be downregulated in brain tumors, suggesting that HUWE1 may possess differing cell-specific functions depending on the downstream targets of HUWE1. This review introduces some important discoveries of the HUWE1 substrates, including those controlling proliferation and differentiation, apoptosis, DNA repair, and responses to stress. In addition, we review the signaling pathways HUWE1 participates in and obstacles to the identification of HUWE1 substrates. We also discuss up-to-date potential therapeutic designs using small molecules or ubiquitin variants (UbV) against the HUWE1 activity. These molecular advances provide a translational platform for future bench-to-bed studies. HUWE1 is a critical ubiquitination modulator during the tumor progression and may serve as a possible therapeutic target for cancer treatment.

Huwe1 is a novel mediator of protection of neural progenitor L2.3 cells against oxygen‑glucose deprivation injury

Hypoxic‑ischemic encephalopathy is one of the most notable causes of brain injury in newborns. Cerebral ischemia and reperfusion lead to neuronal damage and neurological disability. In vitro and in vivo analyses have indicated that E3 ubiquitin protein ligase (Huwe1) is important for the process of neurogenesis during brain development; however, the exact biological function and the underlying mechanism of Huwe1 remain controversial. In the present study, neural progenitor cells, L2.3, of which we previously generated from rat E14.5 cortex, were used to investigate the role of Huwe1 and its effects on the downstream N‑Myc‑Delta‑like 3‑Notch1 signaling pathway during oxygen‑glucose deprivation (OGD). To evaluate the role of Huwe1 in L2.3 cells, transduction, cell viability, lactate dehydrogenase, 5‑bromo‑2'deoxyurine incorporation, western blotting and immunocytochemical assays were performed. The results of the present study indicated that Huwe1 rescued L2.3 cells from OGD‑induced insults by inhibiting proliferation and inducing neuronal differentiation. In addition, Huwe1 was suggested to mediate the survival of L2.3 cells by inhibiting the activation of the N‑Myc‑Notch1 signaling pathway. Of note, the effects of Huwe1 on Notch1 signaling were completely abolished by knockdown of N‑Myc, indicating that Huwe1 may require N‑Myc to suppress the activation of the Notch1 signaling in L2.3 cells. The determination of the neuroprotective function of the Huwe1‑N‑Myc‑Notch1 axis may provide insight into novel potential therapeutic targets for the treatment of ischemic stroke.

FOXP1 Promotes Embryonic Neural Stem Cell Differentiation by Repressing Jagged1 Expression

Mutations in FOXP1 have been linked to neurodevelopmental disorders including intellectual disability and autism; however, the underlying molecular mechanisms remain ill-defined. Here, we demonstrate with RNA and chromatin immunoprecipitation sequencing that FOXP1 directly regulates genes controlling neurogenesis. We show that FOXP1 is expressed in embryonic neural stem cells (NSCs), and modulation of FOXP1 expression affects both neuron and astrocyte differentiation. Using a murine model of cortical development, FOXP1-knockdown in utero was found to reduce NSC differentiation and migration during corticogenesis. Furthermore, transplantation of FOXP1-knockdown NSCs in neonatal mice after hypoxia-ischemia challenge demonstrated that FOXP1 is also required for neuronal differentiation and functionality in vivo. FOXP1 was found to repress the expression of Notch pathway genes including the Notch-ligand Jagged1, resulting in inhibition of Notch signaling. Finally, blockade of Jagged1 in FOXP1-knockdown NSCs rescued neuronal differentiation in vitro. Together, these data support a role for FOXP1 in regulating embryonic NSC differentiation by modulating Notch signaling.

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FOXP1 promotes astrocyte and neuronal differentiation of NSCs in vitro

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FOXP1 promotes neuronal differentiation of NSCs in vivo

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FOXP1 transcriptionally regulates pro-neural genes and represses Notch pathway genes

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FOXP1 promotes neuronal differentiation by limiting Jagged1 expression

HUWE1 controls the development of non-small cell lung cancer through down-regulation of p53

Lung cancer is the most frequent cancer type and the leading cause of tumor-associated deaths worldwide. TP53 is an important tumor suppressor gene and is frequently inactivated in lung cancer. E3 ligases targeting p53, such as MDM2, are involved in the development of lung cancer. The E3 ligase HUWE1, which targets many tumor-associated proteins including p53, has been reported to be highly expressed in lung cancer; however, its role in lung tumorigenesis is unclear.

Methods: The expression of HUWE1 and p53 in lung cancer cells was modulated and the phenotypes were assessed by performing soft agar colony forming assays, cell cycle analysis, BrdU incorporation assays, and xenograft tumor growth assays. The effect on tumorigenesis in genetically-engineered mice was also analyzed. The mechanism through which HUWE1 sustained lung cancer cell malignancy was confirmed by western blotting. HUWE1 expression in clinical lung cancer was identified by immunohistochemistry and validated by analyzing lung adenocarcinoma and lung squamous carcinoma samples from the Cancer Genome Atlas (TCGA) database. Finally, we assessed the association between HUWE1 expression and patient outcome using online survival analysis software including survival information from the caBIG, GEO, and TCGA database.

Results: Inactivation of HUWE1 in a human lung cancer cell line inhibited proliferation, colony-forming capacity, and tumorigenicity. Mechanistically, this phenotype was driven by increased p53, which was due to attenuated proteasomal degradation by HUWE1. Up-regulation of p53 inhibited cancer cell malignancy, mainly through the induction of p21 expression and the down-regulation of HIF1α. Huwe1 deletion completely abolished the development of EGFRVIII-induced lung cancer in Huwe1 conditional knockout mice. Furthermore, survival analysis of lung cancer patients showed that increased HUWE1 expression is significantly associated with worse prognosis.

Conclusion: Our data suggest that HUWE1 plays a critical role in lung cancer and that the HUWE1-p53 axis might be a potential target for lung cancer therapy.

Next-Generation Sequencing Reveals Novel Mutations in X-linked Intellectual Disability

Robust diagnostics for many human genetic disorders are much needed in the pursuit of global personalized medicine. Next-generation sequencing now offers new promise for biomarker and diagnostic discovery, in developed as well as resource-limited countries. In this broader global health context, X-linked intellectual disability (XLID) is an inherited genetic disorder that is associated with a range of phenotypes impacting societies in both developed and developing countries. Although intellectual disability arises due to diverse causes, a substantial proportion is caused by genomic alterations. Studies have identified causal XLID genomic alterations in more than 100 protein-coding genes located on the X-chromosome. However, the causes for a substantial number of intellectual disability and associated phenotypes still remain unknown. Identification of causative genes and novel mutations will help in early diagnosis as well as genetic counseling of families. Advent of next-generation sequencing methods has accelerated the discovery of new genes involved in mental health disorders. In this study, we analyzed the exomes of three families from India with nonsyndromic XLID comprising seven affected individuals. The affected individuals had varying degrees of intellectual disability, microcephaly, and delayed motor and language milestones. We identified potential causal variants in three XLID genes, including PAK3 (V294M), CASK (complex structural variant), and MECP2 (P354T). Our findings reported in this study extend the spectrum of mutations and phenotypes associated with XLID, and calls for further studies of intellectual disability and mental health disorders with use of next-generation sequencing technologies.

The HECT Family Ubiquitin Ligase EEL-1 Regulates Neuronal Function and Development

Genetic changes in the HECT ubiquitin ligase HUWE1 are associated with intellectual disability, but it remains unknown whether HUWE1 functions in post-mitotic neurons to affect circuit function. Using genetics, pharmacology, and electrophysiology, we show that EEL-1, the HUWE1 ortholog in C. elegans, preferentially regulates GABAergic presynaptic transmission. Decreasing or increasing EEL-1 function alters GABAergic transmission and the excitatory/inhibitory (E/I) balance in the worm motor circuit, which leads to impaired locomotion and increased sensitivity to electroshock. Furthermore, multiple mutations associated with intellectual disability impair EEL-1 function. Although synaptic transmission defects did not result from abnormal synapse formation, sensitizing genetic backgrounds revealed that EEL-1 functions in the same pathway as the RING family ubiquitin ligase RPM-1 to regulate synapse formation and axon termination. These findings from a simple model circuit provide insight into the molecular mechanisms required to obtain E/I balance and could have implications for the link between HUWE1 and intellectual disability.

Ubiquitin Ligase Huwe1 Modulates Spermatogenesis by Regulating Spermatogonial Differentiation and Entry into Meiosis

Spermatogenesis consists of a series of highly regulated processes that include mitotic proliferation, meiosis and cellular remodeling. Although alterations in gene expression are well known to modulate spermatogenesis, posttranscriptional mechanisms are less well defined. The ubiquitin proteasome system plays a significant role in protein turnover and may be involved in these posttranscriptional mechanisms. We previously identified ubiquitin ligase Huwe1 in the testis and showed that it can ubiquitinate histones. Since modulation of histones is important at many steps in spermatogenesis, we performed a complete characterization of the functions of Huwe1 in this process by examining the effects of its inactivation in the differentiating spermatogonia, spermatocytes and spermatids. Inactivation of Huwe1 in differentiating spermatogonia led to their depletion and formation of fewer pre-leptotene spermatocytes. The cell degeneration was associated with an accumulation of DNA damage response protein γH2AX, impaired downstream signalling and apoptosis. Inactivation of Huwe1 in spermatocytes indicated that Huwe1 is not essential for meiosis and spermiogenesis, but can result in accumulation of γH2AX. Collectively, these results provide a comprehensive survey of the functions of Huwe1 in spermatogenesis and reveal Huwe1’s critical role as a modulator of the DNA damage response pathway in the earliest steps of spermatogonial differentiation.

HUWE1 variants cause dominant X-linked intellectual disability: a clinical study of 21 patients

Whole-gene duplications and missense variants in the HUWE1 gene (NM_031407.6) have been reported in association with intellectual disability (ID). Increased gene dosage has been observed in males with non-syndromic mild to moderate ID with speech delay. Missense variants reported previously appear to be associated with severe ID in males and mild or no ID in obligate carrier females. Here, we report the largest cohort of patients with HUWE1 variants, consisting of 14 females and 7 males, with 15 different missense variants and one splice site variant. Clinical assessment identified common clinical features consisting of moderate to profound ID, delayed or absent speech, short stature with small hands and feet and facial dysmorphism consisting of a broad nasal tip, deep set eyes, epicanthic folds, short palpebral fissures, and a short philtrum. We describe for the first time that females can be severely affected, despite preferential inactivation of the affected X chromosome. Three females with the c.329 G  >  A p.Arg110Gln variant, present with a phenotype of mild ID, specific facial features, scoliosis and craniosynostosis, as reported previously in a single patient. In these females, the X inactivation pattern appeared skewed in favour of the affected transcript. In summary, HUWE1 missense variants may cause syndromic ID in both males and females.

Impaired oxidative stress response characterizes HUWE1-promoted X-linked intellectual disability

Mutations in the HECT, UBA and WWE domain-containing 1 (HUWE1) E3 ubiquitin ligase cause neurodevelopmental disorder X-linked intellectual disability (XLID). HUWE1 regulates essential processes such as genome integrity maintenance. Alterations in the genome integrity and accumulation of mutations have been tightly associated with the onset of neurodevelopmental disorders. Though HUWE1 mutations are clearly implicated in XLID and HUWE1 regulatory functions well explored, currently much is unknown about the molecular basis of HUWE1-promoted XLID. Here we showed that the HUWE1 expression is altered and mutation frequency increased in three different XLID individual (HUWE1 p.R2981H, p.R4187C and HUWE1 duplication) cell lines. The effect was most prominent in HUWE1 p.R4187C XLID cells and was accompanied with decreased DNA repair capacity and hypersensitivity to oxidative stress. Analysis of HUWE1 substrates revealed XLID-specific down-regulation of oxidative stress response DNA polymerase (Pol) λ caused by hyperactive HUWE1 p.R4187C. The subsequent restoration of Polλ levels counteracted the oxidative hypersensitivity. The observed alterations in the genome integrity maintenance may be particularly relevant in the cortical progenitor zones of human brain, as suggested by HUWE1 immunofluorescence analysis of cerebral organoids. These results provide evidence that impairments of the fundamental cellular processes, like genome integrity maintenance, characterize HUWE1-promoted XLID.

Huwe1 Regulates the Establishment and Maintenance of Spermatogonia by Suppressing DNA Damage Response

Spermatogenesis is sustained by a heterogeneous population of spermatogonia that includes the spermatogonial stem cells. However, the mechanisms underlying their establishment from gonocyte embryonic precursors and their maintenance thereafter remain largely unknown. In this study, we report that inactivation of the ubiquitin ligase Huwe1 in male germ cells in mice led to the degeneration of spermatogonia in neonates and resulted in a Sertoli cell-only phenotype in the adult. Huwe1 knockout gonocytes showed a decrease in mitotic re-entry, which inhibited their transition to spermatogonia. Inactivation of Huwe1 in primary spermatogonial culture or the C18-4 cell line resulted in cell degeneration. Degeneration of Huwe1 knockout spermatogonia was associated with an increased level of histone H2AX and an elevated DNA damage response that led to apparent mitotic catastrophe but not apoptosis or senescence. Blocking this increase in H2AX prevented the degeneration of Huwe1-depleted cells. Taken together, these results reveal a previously undefined role of Huwe1 in orchestrating the physiological DNA damage response in the male germline that contributes to the establishment and maintenance of spermatogonia.

The genomic landscape of pediatric and young adult T-lineage acute lymphoblastic leukemia

Genetic alterations that activate NOTCH1 signaling and T cell transcription factors, coupled with inactivation of the INK4/ARF tumor suppressors, are hallmarks of T-lineage acute lymphoblastic leukemia (T-ALL), but detailed genome-wide sequencing of large T-ALL cohorts has not been carried out. Using integrated genomic analysis of 264 T-ALL cases, we identified 106 putative driver genes, half of which had not previously been described in childhood T-ALL (for example, CCND3, CTCF, MYB, SMARCA4, ZFP36L2 and MYCN). We describe new mechanisms of coding and noncoding alteration and identify ten recurrently altered pathways, with associations between mutated genes and pathways, and stage or subtype of T-ALL. For example, NRAS/FLT3 mutations were associated with immature T-ALL, JAK3/STAT5B mutations in HOXA1 deregulated ALL, PTPN2 mutations in TLX1 deregulated T-ALL, and PIK3R1/PTEN mutations in TAL1 deregulated ALL, which suggests that different signaling pathways have distinct roles according to maturational stage. This genomic landscape provides a logical framework for the development of faithful genetic models and new therapeutic approaches.