Stabilization of LSD1 by deubiquitinating enzyme USP7 promotes glioblastoma cell tumorigenesis and metastasis through suppression of the p53 signaling pathway

Unveiling the Pharmacological Role of Human Deubiquitinating Enzymes in Temozolomide Response of Glioblastoma Cells

Temozolomide (TMZ) stands as the primary chemotherapeutic drug utilized in clinical glioma treatment, particularly for high-grade glioblastoma (GBM). However, the emergence of TMZ resistance in GBM poses a significant hurdle to its clinical efficacy. Our objective was to elucidate the role of deubiquitinating enzymes (DUBs) in GBM cell resistance to TMZ. We employed the broad-spectrum DUBs inhibitor G5 to investigate the function of DUBs in TMZ cytotoxicity against GBM cells. Eighty-two GBM cell lines with specified DUBs knockout were generated and subjected to CCK-8 assays to assess cell proliferation and TMZ resistance. Furthermore, the association between DUBs and TMZ resistance in GBM cells, along with the modulation of autophagic flux, was examined. The pan-DUBs inhibitor G5 demonstrated the ability to induce cell death and enhance TMZ toxicity in GBM cells. Subsequently, we identified potential DUBs involved in regulating GBM cell proliferation and TMZ resistance. The impact of DUBs knockout on TMZ cytotoxicity was found to be associated with their regulation of TMZ-induced autophagy. In summary, our study provides primary insights into the role of DUBs in GBM cell proliferation and TMZ resistance, and contributes to a deeper understanding of the complex function of DUBs genes underlying TMZ resistance in GBM cells.

SPIN: sex-specific and pathway-based interpretable neural network for sexual dimorphism analysis

Sexual dimorphism in prevalence, severity and genetic susceptibility exists for most common diseases. However, most genetic and clinical outcome studies are designed in sex-combined framework considering sex as a covariate. Few sex-specific studies have analyzed males and females separately, which failed to identify gene-by-sex interaction. Here, we propose a novel unified biologically interpretable deep learning-based framework (named SPIN) for sexual dimorphism analysis. We demonstrate that SPIN significantly improved the C-index up to 23.6% in TCGA cancer datasets, and it was further validated using asthma datasets. In addition, SPIN identifies sex-specific and -shared risk loci that are often missed in previous sex-combined/-separate analysis. We also show that SPIN is interpretable for explaining how biological pathways contribute to sexual dimorphism and improve risk prediction in an individual level, which can result in the development of precision medicine tailored to a specific individual's characteristics.

Protein degradation of Lsd1 is mediated by Bre1 yet opposed by Lsd1-interacting lncRNAs during fly follicle development

Tissue development, homeostasis, and repair all require efficient progenitor expansion. Lysine-specific demethylase 1 (Lsd1) maintains plastic epigenetic states to promote progenitor proliferation while overexpressed Lsd1 protein causes oncogenic gene expression in cancer cells. However, the precise regulation of Lsd1 protein expression at the molecular level to drive progenitor differentiation remains unclear. Here, using Drosophila melanogaster oogenesis as our experimental system, we discovered molecular machineries that modify Lsd1 protein stability in vivo. Through genetic and biochemical analyses, an E3 ubiquitin ligase, Bre1, was identified as required for follicle progenitor differentiation, likely by mediating Lsd1 protein degradation. Interestingly, specific Lsd1-interacting long non-coding RNAs (LINRs) were found to antagonize Bre1-mediated Lsd1 protein degradation. The intricate interplay discovered among the Lsd1 complex, LINRs and Bre1 provides insight into how Lsd1 protein stability is fine-tuned to underlie progenitor differentiation in vivo.

Understanding the immunosuppressive microenvironment of glioma: mechanistic insights and clinical perspectives

Glioblastoma (GBM), the predominant and primary malignant intracranial tumor, poses a formidable challenge due to its immunosuppressive microenvironment, thereby confounding conventional therapeutic interventions. Despite the established treatment regimen comprising surgical intervention, radiotherapy, temozolomide administration, and the exploration of emerging modalities such as immunotherapy and integration of medicine and engineering technology therapy, the efficacy of these approaches remains constrained, resulting in suboptimal prognostic outcomes. In recent years, intensive scrutiny of the inhibitory and immunosuppressive milieu within GBM has underscored the significance of cellular constituents of the GBM microenvironment and their interactions with malignant cells and neurons. Novel immune and targeted therapy strategies have emerged, offering promising avenues for advancing GBM treatment. One pivotal mechanism orchestrating immunosuppression in GBM involves the aggregation of myeloid-derived suppressor cells (MDSCs), glioma-associated macrophage/microglia (GAM), and regulatory T cells (Tregs). Among these, MDSCs, though constituting a minority (4-8%) of CD45+ cells in GBM, play a central component in fostering immune evasion and propelling tumor progression, angiogenesis, invasion, and metastasis. MDSCs deploy intricate immunosuppressive mechanisms that adapt to the dynamic tumor microenvironment (TME). Understanding the interplay between GBM and MDSCs provides a compelling basis for therapeutic interventions. This review seeks to elucidate the immune regulatory mechanisms inherent in the GBM microenvironment, explore existing therapeutic targets, and consolidate recent insights into MDSC induction and their contribution to GBM immunosuppression. Additionally, the review comprehensively surveys ongoing clinical trials and potential treatment strategies, envisioning a future where targeting MDSCs could reshape the immune landscape of GBM. Through the synergistic integration of immunotherapy with other therapeutic modalities, this approach can establish a multidisciplinary, multi-target paradigm, ultimately improving the prognosis and quality of life in patients with GBM.

Strategies that regulate LSD1 for novel therapeutics

Histone methylation plays crucial roles in regulating chromatin structure and gene transcription in epigenetic modifications. Lysine-specific demethylase 1 (LSD1), the first identified histone demethylase, is universally overexpressed in various diseases. LSD1 dysregulation is closely associated with cancer, viral infections, and neurodegenerative diseases, etc., making it a promising therapeutic target. Several LSD1 inhibitors and two small-molecule degraders (UM171 and BEA-17) have entered the clinical stage. LSD1 can remove methyl groups from histone 3 at lysine 4 or lysine 9 (H3K4 or H3K9), resulting in either transcription repression or activation. While the roles of LSD1 in transcriptional regulation are well-established, studies have revealed that LSD1 can also be dynamically regulated by other factors. For example, the expression or activity of LSD1 can be regulated by many proteins that form transcriptional corepressor complexes with LSD1. Moreover, some post-transcriptional modifications and cellular metabolites can also regulate LSD1 expression or its demethylase activity. Therefore, in this review, we will systematically summarize how proteins involved in the transcriptional corepressor complex, various post-translational modifications, and metabolites act as regulatory factors for LSD1 activity.

Neddylation-dependent LSD1 destabilization inhibits the stemness and chemoresistance of gastric cancer

Histone lysine-specific demethylase 1 (LSD1) expression has been evaluated in multiple tumors, including gastric cancer (GC). However, the mechanisms underlying LSD1 dysregulation in GC remain largely unclear. In this study, neural precursor cell-expressed developmentally down-regulated protein 8 (NEDD8) was identified to be conjugated to LSD1 at K63 by ubiquitin-conjugating enzyme E2 M (UBE2M), and this neddylated LSD1 could promote LSD1 ubiquitination and degradation, leading to a decrease of GC cell stemness and chemoresistance. Herein, our findings revealed a novel mechanism of LSD1 neddylation and its contribution to decreasing GC cell stemness and chemoresistance. Taken together, our findings may whistle about the future application of neddylation inhibitors.

Pyroptosis in glioma: Current management and future application

Glioma, the predominant form of central nervous system (CNS) malignancies, presents a significant challenge due to its high prevalence and low 5-year survival rate. The efficacy of current treatment methods is limited by the presence of the blood-brain barrier, the immunosuppressive microenvironment, and other factors. Immunotherapy has emerged as a promising approach, as it can overcome the blood-brain barrier. A tumor's immune privilege, which is induced by an immunosuppressive environment, constricts immunotherapy's clinical impact in glioma. Pyroptosis, a programmed cell death mechanism facilitated by gasdermins, plays a significant role in the management of glioma. Its ability to initiate and regulate tumor occurrence, progression, and metastasis is well-established. However, it is crucial to note that uncontrolled or excessive cell death can result in tissue damage, acute inflammation, and cytokine release syndrome, thereby potentially promoting tumor advancement or recurrence. This paper aims to elucidate the molecular pathways involved in pyroptosis and subsequently discuss its induction in cancer therapy. In addition, the current treatment methods of glioma and the use of pyroptosis in these treatments are introduced. It is hoped to provide more ideas for the treatment of glioma.

E3 ligase Trim35 inhibits LSD1 demethylase activity through K63-linked ubiquitination and enhances anti-tumor immunity in NSCLC

Targeting lysine-specific histone demethylase 1A (LSD1) can improve tumor immunogenicity of poorly immunogenic tumors, such as non-small cell lung cancer (NSCLC), with elevated T cell infiltration and sensitize tumors to anti-PD-1 therapy. However, the lack of reliable biomarkers limits utilization of LSD1 inhibitors in cancer therapy. Here, we identify an E3 ligase, Trim35, as an effective biomarker for high activity of LSD1 to predict prognosis of LSD1-targeted therapy as well as immunotherapy. Mechanistically, Trim35 represses LSD1 demethylase activity by mediating K63 ubiquitination at lysine site 422 of LSD1. Suppressed LSD1 activity facilitates ERGIC1 transcription, followed by autophagy inhibition and IFNGR1 stabilization to activate IFN-γ signaling, leading to increased MHC class I expression and immune surveillance of NSCLC cells. Furthermore, combinational use of an LSD1 inhibitor and anti-PD-1 therapy can significantly eradicate poorly immunogenic lung cancer with low Trim35. These findings strongly suggest that Trim35 is a promising biomarker for prediction of immunotherapy outcome in NSCLC.

Post-translational modifications of lysine-specific demethylase 1

Lysine-specific demethylase 1 (LSD1) is crucial for regulating gene expression by catalyzing the demethylation of mono- and di-methylated histone H3 lysine 4 (H3K4) and lysine 9 (H3K9) and non-histone proteins through the amine oxidase activity with FAD+ as a cofactor. It interacts with several protein partners, which potentially contributes to its diverse substrate specificity. Given its pivotal role in numerous physiological and pathological conditions, the function of LSD1 is closely regulated by diverse post-translational modifications (PTMs), including phosphorylation, ubiquitination, methylation, and acetylation. In this review, we aim to provide a comprehensive understanding of the regulation and function of LSD1 following various PTMs. Specifically, we will focus on the impact of PTMs on LSD1 function in physiological and pathological contexts and discuss the potential therapeutic implications of targeting these modifications for the treatment of human diseases.

Deubiquitylating Enzymes in Cancer and Immunity

Deubiquitylating enzymes (DUBs) maintain relative homeostasis of the cellular ubiquitome by removing the post-translational modification ubiquitin moiety from substrates. Numerous DUBs have been demonstrated specificity for cleaving a certain type of ubiquitin linkage or positions within ubiquitin chains. Moreover, several DUBs perform functions through specific protein-protein interactions in a catalytically independent manner, which further expands the versatility and complexity of DUBs' functions. Dysregulation of DUBs disrupts the dynamic equilibrium of ubiquitome and causes various diseases, especially cancer and immune disorders. This review summarizes the Janus-faced roles of DUBs in cancer including proteasomal degradation, DNA repair, apoptosis, and tumor metastasis, as well as in immunity involving innate immune receptor signaling and inflammatory and autoimmune disorders. The prospects and challenges for the clinical development of DUB inhibitors are further discussed. The review provides a comprehensive understanding of the multi-faced roles of DUBs in cancer and immunity.

FBXO24 Suppresses Breast Cancer Tumorigenesis by Targeting LSD1 for Ubiquitination

Lysine-specific demethylase 1 (LSD1), a critical chromatin modulator, functions as an oncogene by demethylation of H3K4me1/2. The stability of LSD1 is governed by a complex and intricate process involving ubiquitination and deubiquitination. Several deubiquitinases preserve LSD1 protein levels. However, the precise mechanism underlying the degradation of LSD1, which could mitigate its oncogenic function, remains unknown. To gain a better understanding of LSD1 degradation, we conducted an unbiased siRNA screening targeting all the human SCF family E3 ligases. Our screening identified FBXO24 as a genuine E3 ligase that ubiquitinates and degrades LSD1. As a result, FBXO24 inhibits LSD1-induced tumorigenesis and functions as a tumor suppressor in breast cancer cells. Moreover, FBXO24 exhibits an inverse correlation with LSD1 and is associated with a favorable prognosis in breast cancer patient samples. Taken together, our study uncovers the significant role of FBXO24 in impeding breast tumor progression by targeting LSD1 for degradation.

IMPLICATIONS

Our study provides comprehensive characterization of the significant role of FBXO24 in impeding breast tumor progression by targeting LSD1 for degradation.

Current and future directions of USP7 interactome in cancer study

The ubiquitin-proteasome system (UPS) is an essential protein quality controller for regulating protein homeostasis and autophagy. Ubiquitination is a protein modification process that involves the binding of one or more ubiquitins to substrates through a series of enzymatic processes. These include ubiquitin-activating enzymes (E1), ubiquitin-conjugating enzymes (E2), and ubiquitin ligases (E3). Conversely, deubiquitination is a reverse process that removes ubiquitin from substrates via deubiquitinating enzymes (DUBs). Dysregulation of ubiquitination-related enzymes can lead to various human diseases, including cancer, through the modulation of protein ubiquitination. The most structurally and functionally studied DUB is the ubiquitin-specific protease 7 (USP7). Both the TRAF and UBL domains of USP7 are known to bind to the [P/A/E]-X-X-S or K-X-X-X-K motif of substrates. USP7 has been shown to be involved in cancer pathogenesis by binding with numerous substrates. Recently, a novel substrate of USP7 was discovered through a systemic analysis of its binding motif. This review summarizes the currently discovered substrates and cellular functions of USP7 in cancer and suggests putative substrates of USP7 through a comprehensive systemic analysis.

Function, mechanism and drug discovery of ubiquitin and ubiquitin-like modification with multiomics profiling for cancer therapy

Ubiquitin (Ub) and ubiquitin-like (Ubl) pathways are critical post-translational modifications that determine whether functional proteins are degraded or activated/inactivated. To date, >600 associated enzymes have been reported that comprise a hierarchical task network (e.g., E1-E2-E3 cascade enzymatic reaction and deubiquitination) to modulate substrates, including enormous oncoproteins and tumor-suppressive proteins. Several strategies, such as classical biochemical approaches, multiomics, and clinical sample analysis, were combined to elucidate the functional relations between these enzymes and tumors. In this regard, the fundamental advances and follow-on drug discoveries have been crucial in providing vital information concerning contemporary translational efforts to tailor individualized treatment by targeting Ub and Ubl pathways. Correspondingly, emphasizing the current progress of Ub-related pathways as therapeutic targets in cancer is deemed essential. In the present review, we summarize and discuss the functions, clinical significance, and regulatory mechanisms of Ub and Ubl pathways in tumorigenesis as well as the current progress of small-molecular drug discovery. In particular, multiomics analyses were integrated to delineate the complexity of Ub and Ubl modifications for cancer therapy. The present review will provide a focused and up-to-date overview for the researchers to pursue further studies regarding the Ub and Ubl pathways targeted anticancer strategies.

Targeting ubiquitin specific proteases (USPs) in cancer immunotherapy: from basic research to preclinical application

Tumors have evolved in various mechanisms to evade the immune system, hindering the antitumor immune response and facilitating tumor progression. Immunotherapy has become a potential treatment strategy specific to different cancer types by utilizing multifarious molecular mechanisms to enhance the immune response against tumors. Among these mechanisms, the ubiquitin-proteasome system (UPS) is a significant non-lysosomal pathway specific to protein degradation, regulated by deubiquitinating enzymes (DUBs) that counterbalance ubiquitin signaling. Ubiquitin-specific proteases (USPs), the largest DUB family with the strongest variety, play critical roles in modulating immune cell function, regulating immune response, and participating in antigen processing and presentation during tumor progression. According to recent studies, the expressions of some USP family members in tumor cells are involved in tumor immune escape and immune microenvironment. This review explores the potential of targeting USPs as a new approach for cancer immunotherapy, highlighting recent basic and preclinical studies investigating the applications of USP inhibitors. By providing insights into the structure and function of USPs in cancer immunity, this review aims at assisting in developing new therapeutic approaches for enhancing the immunotherapy efficacy.

Modulation of the ubiquitin-proteasome system by phytochemicals: Therapeutic implications in malignancies with an emphasis on brain tumors

Regarding the multimechanistic nature of cancers, current chemo- or radiotherapies often fail to eradicate disease pathology, and frequent relapses or resistance to therapies occur. Brain malignancies, particularly glioblastomas, are difficult-to-treat cancers due to their highly malignant and multidimensional biology. Unfortunately, patients suffering from malignant tumors often experience poor prognoses and short survival periods. Thus far, significant efforts have been conducted to discover novel and more effective modalities. To that end, modulation of the ubiquitin-proteasome system (UPS) has attracted tremendous interest since it affects the homeostasis of proteins critically engaged in various cell functions, for example, cell metabolism, survival, proliferation, and differentiation. With their safe and multimodal actions, phytochemicals are among the promising therapeutic tools capable of turning the operation of various UPS elements. The present review, along with an updated outline of the role of UPS dysregulation in multiple cancers, provided a detailed discussion on the impact of phytochemicals on the UPS function in malignancies, especially brain tumors.

The role of histone H3 lysine demethylases in glioblastoma

Glioblastoma (GBM) is the most aggressive primary brain tumor in adults with an average survival of 15-18 months. Part of its malignancy derives from epigenetic regulation that occurs as the tumor develops and after therapeutic treatment. Specifically, enzymes involved in removing methylations from histone proteins on chromatin, i.e., lysine demethylases (KDMs), have a significant impact on GBM biology and reoccurrence. This knowledge has paved the way to considering KDMs as potential targets for GBM treatment. For example, increases in trimethylation of histone H3 on the lysine 9 residue (H3K9me3) via inhibition of KDM4C and KDM7A has been shown to lead to cell death in Glioblastoma initiating cells. KDM6 has been shown to drive Glioma resistance to receptor tyrosine kinase inhibitors and its inhibition decreases tumor resistance. In addition, increased expression of the histone methyltransferase MLL4 and UTX histone demethylase are associated with prolonged survival in a subset of GBM patients, potentially by regulating histone methylation on the promoter of the mgmt gene. Thus, the complexity of how histone modifiers contribute to glioblastoma pathology and disease progression is yet to be fully understood. To date, most of the current work on histone modifying enzymes in GBM are centered upon histone H3 demethylase enzymes. In this mini-review, we summarize the current knowledge on the role of histone H3 demethylase enzymes in Glioblastoma tumor biology and therapy resistance. The objective of this work is to highlight the current and future potential areas of research for GBM epigenetics therapy.

USP7 - a crucial regulator of cancer hallmarks

Over the course of three decades of study, the deubiquitinase Herpesvirus associated Ubiquitin-Specific Protease/Ubiquitin-Specific Protease 7 (HAUSP/USP7) has gradually come to be recognized as a crucially important molecule in cellular physiology. The fact that USP7 is overexpressed in a number of cancers, including breast, prostate, colorectal, and lung cancers, supports the idea that USP7 is also an important regulator of tumorigenesis. In this review, we discuss USP7's function in relation to the cancer hallmarks described by Hanahan and Weinberg. This post-translational modifier can support increased proliferation, block unfavorable growth signals, stop cell death, and support an unstable cellular genome by manipulating key players in the pertinent signalling circuit. It is interesting to note that USP7 also aids in the stabilization of molecules that support angiogenesis and metastasis. Targeting USP7 has now emerged as a crucial component of USP7 research because pharmacological inhibition of USP7 supports p53-mediated cell cycle arrest and apoptosis. Efficacious USP7 inhibition is currently being investigated in both synthetic and natural compounds, but issues with selectivity and a lack of co-crystal structure have hindered USP7 inhibition from being tested in clinical settings. Moreover, the development of new, more effective USP7 inhibitors and their encouraging implications by numerous groups give us a glimmer of hope for USP7-targeting medications as effective substitutes for hazardous cancer chemotherapeutics.

Targeting the USP7/RRM2 axis drives senescence and sensitizes melanoma cells to HDAC/LSD1 inhibitors

Deubiquitinating enzymes are key regulators of the ubiquitin-proteasome system and cell cycle, and their dysfunction leads to tumorigenesis. Our in vivo drop-out screens in patient-derived xenograft models identify USP7 as a regulator of melanoma. We show that USP7 downregulation induces cellular senescence, arresting melanoma growth in vivo and proliferation in vitro in BRAF- and NRAS-mutant melanoma. We provide a comprehensive understanding of targets and networks affected by USP7 depletion by performing a global transcriptomic and proteomics analysis. We show that RRM2 is a USP7 target and is regulated by USP7 during S phase of the cell cycle. Ectopic expression of RRM2 in USP7-depleted cells rescues the senescent phenotype. Pharmacological inhibition of USP7 by P5091 phenocopies the shUSP7-induced senescent phenotype. We show that the bifunctional histone deacetylase (HDAC)/LSD1 inhibitor domatinostat has an additive antitumor effect, eliminating P5091-induced senescent cells, paving the way to a therapeutic combination for individuals with melanoma.

A state-of-the-art review on LSD1 and its inhibitors in breast cancer: Molecular mechanisms and therapeutic significance

Breast cancer (BC) is a kind of malignant cancer in women, and it has become the most diagnosed cancer worldwide since 2020. Histone methylation is a common biological epigenetic modification mediating varieties of physiological and pathological processes. Lysine-specific demethylase 1 (LSD1), a first identified histone demethylase, mediates the removal of methyl groups from histones H3K4me1/2 and H3K9me1/2 and plays a crucial role in varieties of cancer progression. It is also specifically amplified in breast cancer and contributes to BC tumorigenesis and drug resistance via both demethylase and non-demethylase manners. This review will provide insight into the overview structure of LSD1, summarize its action mechanisms in BC, describe the therapeutic potential of LSD1 inhibitors in BC, and prospect the current opportunities and challenges of targeting LSD1 for BC therapy.

Proteomic analysis reveals USP7 as a novel regulator of palmitic acid-induced hepatocellular carcinoma cell death

Nutrient surplus and consequent free fatty acid accumulation in the liver cause hepatosteatosis. The exposure of free fatty acids to cultured hepatocyte and hepatocellular carcinoma cell lines induces cellular stress, organelle adaptation, and subsequent cell death. Despite many studies, the mechanism associated with lipotoxicity and subsequent cell death still remains poorly understood. Here, we have used the proteomics approach to circumvent the mechanism for lipotoxicity using hepatocellular carcinoma cells as a model. Our quantitative proteomics data revealed that ectopic lipids accumulation in cells severely affects the ubiquitin-proteasomal system. The palmitic acid (PA) partially lowered the expression of deubiquitinating enzyme USP7 which subsequently destabilizes p53 and promotes mitotic entry of cells. Our global phosphoproteomics analysis also provides strong evidence of an altered cell cycle checkpoint proteins' expression that abrogates early G2/M checkpoints recovery with damaged DNA and induced mitotic catastrophe leading to hepatocyte death. We observe that palmitic acid prefers apoptosis-inducing factor (AIF) mediated cell death by depolarizing mitochondria and translocating AIF to the nucleus. In summary, the present study provides evidence of PA-induced hepatocellular death mediated by deubiquitinase USP7 downregulation and subsequent mitotic catastrophe.

4,5-Dimethoxycanthin-6-one is a novel LSD1 inhibitor that inhibits proliferation of glioblastoma cells and induces apoptosis and pyroptosis

Background

Glioblastoma is one of the most common fatal intracranial malignancies. Lysine-specific demethylase 1 (LSD1) reportedly has therapeutic effects on a variety of tumors. This study explored the therapeutic effect of LSD1 inhibition on glioblastoma cell lines and the possible underlying mechanisms.

Methods

The MTT assay was utilized to screen for the sensitivity of U87, U251 and T98G cells to 4, 5-dimethoxycarrageenin-6-one. qRT-PCR and western blot were used to measure the proliferation, apoptosis, and pyroptosis signaling pathway expression to observe the effect of LSD1 inhibition on U251 and T98G cells. Flow cytometry, immunofluorescence, immunohistochemistry, wound scratch, clone formation, and TUNEL assay were used to analyze the effects of 4, 5-dimethoxycanthin-6-one on glioblastoma cells. The effect of 4, 5-dimethoxycanthin-6-one was examined in vivo in BALB/c nude mice injected with U251 cells. HE staining was used to detect the histopathology of the tumor.

Results

LSD1 specifically catalyzes the demethylation of monomethylated and demethylated histone H3 lysine at position 4 (h3k4me1, h3k4me2, h3k4me3) and lysine at position 9 (h3k9me1). This regulated the transcriptional activity of proliferation, apoptosis, and pyroptosis signaling pathway genes. In vitro, the proliferation of glioblastoma cells was decreased in the 4, 5-dimethoxycanthin-6-one group. The expression of Caspase1 in glioblastoma cells treated with 4, 5-dimethoxycanthin-6-one increased, and the number of apoptotic cells increased. The tumor volume of mice injected with 4, 5-dimethoxycanthin-6-one decreased significantly.

Conclusion

4, 5-Dimethoxycanthin-6-one could act as a novel inhibitor of LSD1 to regulate glioblastoma, which could inhibit the proliferation of U251 and T98G cells and induce their apoptosis and pyroptosis. It is a potential drug for the treatment of glioblastoma.

The USP7 protein interaction network and its roles in tumorigenesis

Ubiquitin-specific protease (USP7), also known as Herpesvirus-associated ubiquitin-specific protease (HAUSP), is a deubiquitinase. There has been significant recent attention on USP7 following the discovery that USP7 is a key regulator of the p53-MDM2 pathway. The USP7 protein is 130 kDa in size and has multiple domains which bind to a diverse set of proteins. These interactions mediate key developmental and homeostatic processes including the cell cycle, immune response, and modulation of transcription factor and epigenetic regulator activity and localization. USP7 also promotes carcinogenesis through aberrant activation of the Wnt signalling pathway and stabilization of HIF-1α. These findings have shown that USP7 may induce tumour progression and be a therapeutic target. Together with interest in developing USP7 as a target, several studies have defined new protein interactions and the regulatory networks within which USP7 functions. In this review, we focus on the protein interactions of USP7 that are most important for its cancer-associated roles.

The role of ubiquitin-specific peptidases in glioma progression

The balance between ubiquitination and deubiquitination is crucial for protein stability, function and location under physiological conditions. Dysregulation of E1/E2/E3 ligases or deubiquitinases (DUBs) results in malfunction of the ubiquitin system and is involved in many diseases. Increasing reports have indicated that ubiquitin-specific peptidases (USPs) play a part in the progression of many kinds of cancers and could be good targets for anticancer treatment. Glioma is the most common malignant tumor in the central nervous system. Clinical treatment for high-grade glioma is unsatisfactory thus far. Multiple USPs are dysregulated in glioma and have the potential to be therapeutic targets. In this review, we collected studies on the roles of USPs in glioma progression and summarized the mechanisms of USPs in glioma tumorigenesis, malignancy and chemoradiotherapy resistance.

HAUSP Is a Key Epigenetic Regulator of the Chromatin Effector Proteins

HAUSP (herpes virus-associated ubiquitin-specific protease), also known as Ubiquitin Specific Protease 7, plays critical roles in cellular processes, such as chromatin biology and epigenetics, through the regulation of different signaling pathways. HAUSP is a main partner of the “Epigenetic Code Replication Machinery,” ECREM, a large protein complex that includes several epigenetic players, such as the ubiquitin-like containing plant homeodomain (PHD) and an interesting new gene (RING), finger domains 1 (UHRF1), as well as DNA methyltransferase 1 (DNMT1), histone deacetylase 1 (HDAC1), histone methyltransferase G9a, and histone acetyltransferase TIP60. Due to its deubiquitinase activity and its ability to team up through direct interactions with several epigenetic regulators, mainly UHRF1, DNMT1, TIP60, the histone lysine methyltransferase EZH2, and the lysine-specific histone demethylase LSD1, HAUSP positions itself at the top of the regulatory hierarchies involved in epigenetic silencing of tumor suppressor genes in cancer. This review highlights the increasing role of HAUSP as an epigenetic master regulator that governs a set of epigenetic players involved in both the maintenance of DNA methylation and histone post-translational modifications.

Histone modifications and their role in epigenetics of cancer

Epigenetic regulations play a crucial role in the expression of various genes that are important in the normal cell function. Any alteration in these epigenetic mechanisms can lead to the modification of histone and DNA resulting in the silencing or enhanced expression of some genes causing various diseases. Acetylation, methylation, ribosylation or phosphorylation of histone proteins modifies its interaction with the DNA, consequently changing the ratio of heterochromatin and euchromatin. Terminal lysine residues of histone proteins serve as potential targets of such epigenetic modifications. The current review focuses on the histone modifications, their contributing factors, role of these modifications on metabolism leading to cancer and methylation of histone in cancer affects the DNA repair mechanisms.

Prognostic role of USP7 expression in cancer patients: A systematic review and meta-analysis

BACKGROUND

Numerous studies have examined the prognostic value of ubiquitin-specific protease 7 (USP7) in cancer, but the results remain controversial. Differences in assessment assays (mRNA/protein) used could be a potential confounding factor. Thus, we extracted studies that measured the protein expression and performed a meta-analysis to assess the prognostic role of USP7 expression in cancer and to identify clinicopathological features associated with USP7 expression.

METHODS

PubMed, Scopus, Web of Science Core Collection, Wiley Online Library, and Google Scholar were searched from inception to July 2020. Pooled hazard ratios were calculated to evaluate the association between USP7 expression and overall survival (OS). In addition, pooled odds ratios were calculated to identify clinicopathological features associated with USP7 expression.

RESULTS

Eight studies in China were included in our meta-analysis, which had a total of 1192 patients and assessed five types of cancer. The pooled results revealed that a high expression of USP7 was associated with poor OS, especially in epithelial ovarian cancer (EOC). Moreover, USP7 expression was increased in patients with tumour-node-metastasis (TNM) stages III-IV, poor pathological grade, and positive lymph node metastasis. For patients with EOC, a high USP7 expression positively correlated with lymph node metastasis.

CONCLUSION

A high USP7 expression may promote cancer progression and predict unfavourable prognosis of cancer patients, especially those with EOC. Our findings suggest that USP7 inhibitors might be promising therapeutics for cancer patients with such characteristics.

Pharmacological inhibition of USP7 suppresses growth and metastasis of melanoma cells in vitro and in vivo

Melanoma is a highly aggressive type of skin cancer. The development of diverse resistance mechanisms and severe adverse effects significantly limit the efficiency of current therapeutic approaches. Identification of the new therapeutic targets involved in the pathogenesis will benefit the development of novel therapeutic strategies. The deubiquitinase ubiquitin–specific protease‐7, a potential target for cancer treatment, is deregulated in types of cancer, but its role in melanoma is still unclear. We investigated the role and the inhibitor P22077 of ubiquitin‐specific protease‐7 in melanoma treatment. We found that ubiquitin‐specific protease‐7 was overexpressed and correlated with poor prognosis in melanoma. Further, pharmacological inhibition of ubiquitin‐specific protease‐7 by P22077 can effectively inhibit proliferation, and induce cell cycle arrest and apoptosis via ROS accumulation–induced DNA damage in melanoma cells. Inhibition of ubiquitin‐specific protease‐7 by P22077 also inhibits melanoma tumour growth in vivo. Moreover, inhibition of ubiquitin‐specific protease‐7 prevented migration and invasion of melanoma cells in vitro and in vivo by decreasing the Wnt/β‐catenin signalling pathway. Taken together, our study revealed that ubiquitin‐specific protease‐7 acted as an oncogene involved in melanoma cell proliferation and metastasis. Therefore, ubiquitin‐specific protease‐7 may serve as potential candidates for the treatment of melanoma.

OTUD7B Deubiquitinates LSD1 to Govern Its Binding Partner Specificity, Homeostasis, and Breast Cancer Metastasis

Genomic amplification of OTUD7B is frequently found across human cancers. But its role in tumorigenesis is poorly understood. Lysine-specific demethylase 1 (LSD1) is known to execute epigenetic regulation by forming corepressor complex with CoREST/histone deacetylases (HDACs). However, the molecular mechanisms by which cells maintain LSD1/CoREST complex integrity are unknown. Here, it is reported that LSD1 protein undergoes K63-linked polyubiquitination. OTUD7B is responsible for LSD1 deubiquitination at K226/277 residues, resulting in dynamic control of LSD1 binding partner specificity and cellular homeostasis. OTUD7B deficiency increases K63-linked ubiquitination of LSD1, which disrupts LSD1/CoREST complex formation and targets LSD1 for p62-mediated proteolysis. Consequently, OTUD7B deficiency impairs genome-wide LSD1 occupancy and enhances the methylation of H3K4/H3K9, therefore profoundly impacting global gene expression and abrogating breast cancer metastasis. Moreover, physiological fluctuation of OTUD7B modulates cell cycle-dependent LSD1 oscillation, ensuring the G1/S transition. Both OTUD7B and LSD1 proteins are overpresented in high-grade or metastatic human breast cancer, while dysregulation of either protein is associated with poor survival and metastasis. Thus, OTUD7B plays a unique partner-switching role in maintaining the integrity of LSD1/CoREST corepressor complex, LSD1 turnover, and breast cancer metastasis.

An Update of Lysine Specific Demethylase 1 Inhibitor: A Patent Review (2016-2020)

BACKGROUND

As a FAD (Flavin Adenine Dinucleotide) - dependent histone demethylase discovered in 2004, LSD1 (lysine specific demethylase 1) was reported to be overexpressed in diverse tumors, regulating target genes transcription associated with cancer development. Hence, LSD1 targeted inhibitors may represent a new insight in anticancer drug discovery. For these reasons, researchers in both the pharmaceutical industry and academia have been actively pursuing LSD1 inhibitors in the quest for new anti-cancer drugs.

OBJECTIVES

This review summaries patents about LSD1 inhibitors in recent 5 years in hope of providing a reference for LSD1 researchers to develop new modulators of LSD1 with higher potency and fewer adverse effects.

METHODS

This review collects LSD1 inhibitors disclosed in patents since 2016. The primary ways of patent searching are Espacenet®, Google Patents, and CNKI.

RESULTS

This review covers dozens of patents related to LSD1 inhibitors in recent five years. The compound structures are mainly divided into TCP (Tranylcypromine) derivatives, imidazole derivatives, pyrimidine derivatives, and other natural products and peptides. Meanwhile, the compounds that have entered the clinical phase are also described.

CONCLUSION

Most of the compounds in these patents have been subjected to activity analysis with LSD1 and multi-cell lines, showing good antitumor activity in vitro and in vivo. These patents exhibited the structural diversity of LSD1 inhibitors and the potential of natural products as novel LSD1 inhibitors.

The Role of the Ubiquitin Proteasome System in Glioma: Analysis Emphasizing the Main Molecular Players and Therapeutic Strategies Identified in Glioblastoma Multiforme

Gliomas constitute the most frequent tumors of the brain. High-grade gliomas are characterized by a poor prognosis caused by a set of attributes making treatment difficult, such as heterogeneity and cell infiltration. Additionally, there is a subgroup of glioma cells with properties similar to those of stem cells responsible for tumor recurrence after treatment. Since proteasomal degradation regulates multiple cellular processes, any mutation causing disturbances in the function or expression of its elements can lead to various disorders such as cancer. Several studies have focused on protein degradation modulation as a mechanism of glioma control. The ubiquitin proteasome system is the main mechanism of cellular proteolysis that regulates different events, intervening in pathological processes with exacerbating or suppressive effects on diseases. This review analyzes the role of proteasomal degradation in gliomas, emphasizing the elements of this system that modulate different cellular mechanisms in tumors and discussing the potential of distinct compounds controlling brain tumorigenesis through the proteasomal pathway.

LncRNA HAS2-AS1 Promotes Glioblastoma Proliferation by Sponging miR-137

GBM (Glioblastoma multiform) is the most malignant tumor type of the central nervous system and has poor diagnostic and clinical outcomes. LncRNAs (Long non-coding RNAs) have been reported to participate in multiple biological and pathological processes, but their underlying mechanism remains poorly understood. Here, we aimed to explore the role of the lncRNA HAS2-AS1 (HAS2 antisense RNA 1) in GBM. GSE103227 was analyzed, and qRT-PCR was performed to measure the expression of HAS2-AS1 in GBM. FISH (Fluorescence in situ hybridization) was performed to verify the localization of HAS2-AS1. The interaction between HAS2-AS1 and miR-137 (microRNA-137) was predicted by LncBook and miRcode followed by dual-luciferase reporter assays, and the relationships among HAS2-AS1, miR-137 and LSD1 (lysine-specific demethylase 1) were assessed by WB (western blot) and qRT-PCR. Colony formation and CCK-8 (cell counting kit-8) assays were performed as functional tests. In vivo, nude mice were used to confirm the function of HAS2-AS1. HAS2-AS1 expression was upregulated in GBM cell lines, and HAS2-AS1 was localized mainly in the cytoplasm. In vitro, high HAS2-AS1 expression promoted proliferation, and knockdown of HAS2-AS1 significantly inhibited proliferation. Furthermore, HAS2-AS1 functioned as a ceRNA (competing endogenous RNA) of miR-137, leading to the disinhibition of its downstream target LSD1. The miR-137 level was downregulated by HAS2-AS1 overexpression and upregulated by HAS2-AS1 knockdown. In a subsequent study, LSD1 expression was negatively regulated by miR-137, while miR-137 reversed the LSD1 expression levels caused by HAS2-AS1. These results were further supported by the nude mouse tumorigenesis experiment; compared with xenografts with high HAS2-AS1 expression, the group with low levels of HAS2-AS1 exhibited suppressed proliferation and better survival. We conclude that lncRNA HAS2-AS1 promotes proliferation by functioning as a miR-137 decoy to increase LSD1 levels and thus might be a possible biomarker for GBM.

Potential new targets and drugs related to histone modifications in glioma treatment

Glioma accounts for 40-50% of craniocerebral tumors, whose outcome rarely improves after standard treatment. The development of new therapeutic targets for glioma treatment has important clinical significance. With the deepening of research on gliomas, recent researchers have found that the occurrence and development of gliomas is closely associated with histone modifications, including methylation, acetylation, phosphorylation, and ubiquitination. Additionally, evidence has confirmed the close relationship between histone modifications and temozolomide (TMZ) resistance. Therefore, histone modification-related proteins have been widely recognized as new therapeutic targets for glioma treatment. In this review, we summarize the potential histone modification-associated targets and related drugs for glioma treatment. We have further clarified how histone modifications regulate the pathogenesis of gliomas and the mechanism of drug action, providing novel insights for the current clinical glioma treatment. Herein, we have also highlighted the limitations of current clinical therapies and have suggested future research directions and expected advances in potential areas of disease prognosis. Due to the complicated glioma pathogenesis, in the present review, we have acknowledged the limitations of histone modification applications in the related clinical treatment.

Deubiquitinating enzyme USP41 promotes lung cancer cell proliferation and migration

Background

To reveal the function of deubiquitylating enzyme USP41 in lung adenocarcinoma.

Methods

The relationship between USP41 and lung cancer was determined by analyzing data from The Cancer Genome Atlas (TCGA). A549 and H1299 cell lines were transfected with short hairpin RNA against USP41 (shUSP41 group) or negative control (shCon group). Western blotting was used to verify the transfection efficacy and marker expression. Cell proliferation and apoptosis were analyzed by EdU assay, MTT assay, and flow cytometry after USP41 knockdown. Transwell assay was used to determine the effect of USP41 downregulation on cell migration.

Results

Analysis of lung cancer data from TCGA database indicated a higher level of USP41 expression in lung cancer tumor tissue compared with that in noncancerous tissue, and USP41 overexpression was correlated with poor overall survival of lung cancer patients (p < 0.01). The outcomes of the EdU, MTT, and flow cytometry assays indicated decreased cell proliferation and enhanced apoptosis in shUSP41‐transfected cells. Transwell assay further demonstrated that USP41 knockdown increased the migration rate of A549 and H1299 cells.

Conclusions

In our study, USP41 was overexpressed in lung cancer tissue and associated with poor prognosis of lung cancer. USP41 knockdown inhibits cell proliferation and migration and induces cell apoptosis of lung cancer.

Knockdown of lncRNA ANRIL suppresses the production of inflammatory cytokines and mucin 5AC in nasal epithelial cells via the miR-15a-5p/JAK2 axis

The incidence of allergic rhinitis (AR) is increasing worldwide. Human nasal epithelial cells (HNECs) are the key cells in the occurrence of AR. Antisense non-coding RNA in the INK4 locus (ANRIL) was discovered to be involved in the progression of AR. However, the mechanism by which ANRIL mediates the progression of AR remains to be determined. The present study aimed to further explore the mechanism by which ANRIL regulates AR. Thereby, HNECs were treated with IL-13 to mimic AR in vitro. The mRNA expression levels of ANRIL, microRNA (miR)-15a-5p, JAK2, mucin 5AC (MUC5AC), granulocyte-macrophage colony-stimulating factor (GM-CSF) and eotaxin-1, and protein expression levels of JAK2, STAT3 and phosphorylated-STAT3 in HNECs were analyzed using reverse transcription-quantitative PCR and western blotting, respectively. ELISAs were used to detect the secretory levels of inflammatory cytokines and mucin in cell supernatants. In addition, a dual luciferase reporter assay was used to confirm the downstream target of ANRIL and the target gene of miR-15a-5p. The results revealed that the secretory levels of eotaxin-1, GM-CSF and MUC5AC were significantly upregulated by IL-13 in the supernatant of HNECs. The expression levels of ANRIL and JAK2 were also upregulated in IL-13-induced HNECs, while the expression levels of miR-15a-5p were downregulated. In addition, ANRIL was identified to bind to miR-15a-5p. The IL-13-induced upregulation of eotaxin-1, GM-CSF and MUC5AC mRNA expression and secretory levels was significantly inhibited by the genetic knockdown of ANRIL, while the miR-15a-5p inhibitor effectively reversed this effect. JAK2 was also discovered to be directly targeted by miR-15a-5p. The overexpression of JAK2 significantly suppressed the therapeutic effect of miR-15a-5p mimics on IL-13-induced inflammation in vitro. In conclusion, the findings of the present study suggested that the genetic knockdown of ANRIL may suppress the production of inflammatory cytokines and mucin in IL-13-treated HNECs via regulation of the miR-15a-5p/JAK2 axis. Thus, ANRIL may serve as a novel target for AR treatment.

USP7 promotes proliferation of papillary thyroid carcinoma cells through TBX3-mediated p57KIP2 repression

Ubiquitin-specific protease 7 (USP7/HAUSP) is known to regulate multiple cellular phenomena, including cell cycle progression and proliferation, and is involved in binding and stabilizing specific target proteins through deubiquitylation. However, the detailed role of USP7 in papillary thyroid carcinoma (PTC) remains to be investigated. In this study, our results showed that USP7 was upregulated in PTC tissues compared with adjacent nontumour tissues. Consistently, a series of gain/loss functional assays in vivo and in vitro demonstrated the role of USP7 in promoting PTC cell proliferation. Furthermore, we showed that there was a negative correlation between USP7 and the CDK inhibitor p57^KIP2 expression in PTC tissues and that USP7 facilitated PTC cell proliferation by inhibiting p57^KIP2. Mechanistically, USP7 inhibited p57^KIP2 expression by modulating TBX3, directly binding to TBX3, and decreasing its ubiquitination and degradation. Our findings demonstrated that USP7 played a critical oncogenic role in PTC tumorigenesis, suggesting that USP7 might act as a prognostic and therapeutic target for PTC progression.

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.

The Effect of Dysfunctional Ubiquitin Enzymes in the Pathogenesis of Most Common Diseases

Ubiquitination is a multi-step enzymatic process that involves the marking of a substrate protein by bonding a ubiquitin and protein for proteolytic degradation mainly via the ubiquitin–proteasome system (UPS). The process is regulated by three main types of enzymes, namely ubiquitin-activating enzymes (E1), ubiquitin-conjugating enzymes (E2), and ubiquitin ligases (E3). Under physiological conditions, ubiquitination is highly reversible reaction, and deubiquitinases or deubiquitinating enzymes (DUBs) can reverse the effect of E3 ligases by the removal of ubiquitin from substrate proteins, thus maintaining the protein quality control and homeostasis in the cell. The dysfunction or dysregulation of these multi-step reactions is closely related to pathogenic conditions; therefore, understanding the role of ubiquitination in diseases is highly valuable for therapeutic approaches. In this review, we first provide an overview of the molecular mechanism of ubiquitination and UPS; then, we attempt to summarize the most common diseases affecting the dysfunction or dysregulation of these mechanisms.

USP7 Is a Master Regulator of Genome Stability

Genetic alterations, including DNA mutations and chromosomal abnormalities, are primary drivers of tumor formation and cancer progression. These alterations can endow cells with a selective growth advantage, enabling cancers to evade cell death, proliferation limits, and immune checkpoints, to metastasize throughout the body. Genetic alterations occur due to failures of the genome stability pathways. In many cancers, the rate of alteration is further accelerated by the deregulation of these processes. The deubiquitinating enzyme ubiquitin specific protease 7 (USP7) has recently emerged as a key regulator of ubiquitination in the genome stability pathways. USP7 is also deregulated in many cancer types, where deviances in USP7 protein levels are correlated with cancer progression. In this work, we review the increasingly evident role of USP7 in maintaining genome stability, the links between USP7 deregulation and cancer progression, as well as the rationale of targeting USP7 in cancer therapy.

Critical Roles of Deubiquitinating Enzymes in the Nervous System and Neurodegenerative Disorders

Post-translational modifications play major roles in the stability, function, and localization of target proteins involved in the nervous system. The ubiquitin-proteasome pathway uses small ubiquitin molecules to degrade neuronal proteins. Deubiquitinating enzymes (DUBs) reverse this degradation and thereby control neuronal cell fate, synaptic plasticity,axonal growth, and proper function of the nervous system.Moreover, mutations or downregulation of certain DUBshave been found in several neurodegenerative diseases, as well as gliomas and neuroblastomas. Based on emerging findings, DUBs represent an important target for therapeutic intervention in various neurological disorders. Here, we summarize advances in our understanding of the roles of DUBs related to neurobiology.

USP7 inhibition inhibits proliferation and induces megakaryocytic differentiation in MDS cells by upregulating gelsolin

Myelodysplastic syndrome (MDS), a largely incurable hematological malignancy, is driven by complex genetic and epigenetic alterations from an aberrant clone of hematopoietic stem/progenitor cells (HSPCs). Ubiquitin-specific protease 7 (USP7) has been demonstrated to have an important oncogenic role in the development of several cancer types, but its role in MDS is unknown. Here, we demonstrate that USP7 expression is elevated in MDS cell lines and patient samples. The USP7-selective small-molecule inhibitors P5091 and P22077 inhibited cell proliferation and induced megakaryocytic differentiation in both cell lines and primary cells. Furthermore, pharmacological inhibition of USP7 markedly suppressed the growth of MDS cell lines in xenograft mouse models. To explore the mechanisms underlying the observed phenotypic changes, we employed RNA-seq to compare the differences in genes after USP7 inhibitor treatment and found that gelsolin (GSN) expression was increased significantly after USP7 inhibitor treatment. Furthermore, knockdown of GSN attenuated the proliferation inhibition, apoptosis induction and megakaryocyte differentiation induced by USP7 inhibitors in MDS cells. Collectively, our findings identify previously unknown roles of USP7 and suggest that the USP7/GSN axis may be a potential therapeutic target in MDS.

Arginine methylation-dependent LSD1 stability promotes invasion and metastasis of breast cancer

Histone lysine demethylase 1 (LSD1), the first identified histone demethylase, is overexpressed in multiple tumor types, including breast cancer. However, the mechanisms that cause LSD1 dysregulation in breast cancer remain largely unclear. Here, we report that protein arginine methyltransferase 4 (PRMT4 or CARM1) dimethylates LSD1 at R838, which promotes the binding of the deubiquitinase USP7, resulting in the deubiquitination and stabilization of LSD1. Moreover, CARM1- and USP7-dependent LSD1 stabilization plays a key role in repressing E-cadherin and activating vimentin transcription through promoter H3K4me2 and H3K9me2 demethylation, respectively, which promotes invasion and metastasis of breast cancer cells. Consistently, LSD1 arginine methylation levels correlate with tumor grade in human malignant breast carcinoma samples. Our findings unveil a unique mechanism controlling LSD1 stability by arginine methylation, also highlighting the role of the CARM1-USP7-LSD1 axis in breast cancer progression.

USP7: Novel Drug Target in Cancer Therapy

Ubiquitin specific protease 7 (USP7) is one of the deubiquitinating enzymes (DUB) that erases ubiquitin and protects substrate protein from degradation. Full activity of USP7 requires the C-terminal Ub-like domains fold back onto the catalytic domain, allowing the remodeling of the active site to a catalytically competent state by the C-terminal peptide. Until now, numerous proteins have been identified as substrates of USP7, which play a key role in cell cycle, DNA repair, chromatin remodeling, and epigenetic regulation. Aberrant activation or overexpression of USP7 may promote oncogenesis and viral disease, making it a target for therapeutic intervention. Currently, several synthetic small molecules have been identified as inhibitors of USP7, and applied in the treatment of diverse diseases. Hence, USP7 may be a promising therapeutic target for the treatment of cancer.

Developmental origins and oncogenic pathways in malignant brain tumors

Brain tumors such as adult glioblastomas and pediatric high-grade gliomas or medulloblastomas are among the leading causes of cancer-related deaths, exhibiting poor prognoses with little improvement in outcomes in the past several decades. These tumors are heterogeneous and can be initiated from various neural cell types, contributing to therapy resistance. How such heterogeneity arises is linked to the tumor cell of origin and their genetic alterations. Brain tumorigenesis and progression recapitulate key features associated with normal neurogenesis; however, the underlying mechanisms are quite dysregulated as tumor cells grow and divide in an uncontrolled manner. Recent comprehensive genomic, transcriptomic, and epigenomic studies at single-cell resolution have shed new light onto diverse tumor-driving events, cellular heterogeneity, and cells of origin in different brain tumors. Primary and secondary glioblastomas develop through different genetic alterations and pathways, such as EGFR amplification and IDH1/2 or TP53 mutation, respectively. Mutations such as histone H3K27M impacting epigenetic modifications define a distinct group of pediatric high-grade gliomas such as diffuse intrinsic pontine glioma. The identification of distinct genetic, epigenomic profiles and cellular heterogeneity has led to new classifications of adult and pediatric brain tumor subtypes, affording insights into molecular and lineage-specific vulnerabilities for treatment stratification. This review discusses our current understanding of tumor cells of origin, heterogeneity, recurring genetic and epigenetic alterations, oncogenic drivers and signaling pathways for adult glioblastomas, pediatric high-grade gliomas, and medulloblastomas, the genetically heterogeneous groups of malignant brain tumors. This article is categorized under: Gene Expression and Transcriptional Hierarchies > Gene Networks and Genomics Adult Stem Cells, Tissue Renewal, and Regeneration > Stem Cell Differentiation and Reversion Signaling Pathways > Cell Fate Signaling.

USP7 Regulates Cytokinesis through FBXO38 and KIF20B

The ubiquitin specific protease 7 (USP7 or HAUSP) is known to regulate a variety of cellular processes by binding and deubiquitylating specific target proteins. To gain a more comprehensive understanding of its interactions and functions, we used affinity purification coupled to mass spectrometry to profile USP7 interactions. This revealed a novel interaction with FBXO38, a poorly characterized F-box protein. We showed that USP7 stabilizes FBXO38 dependent on its catalytic activity by protecting FBXO38 from proteasomal degradation. We used a BioID approach to profile the protein interactions (and putative functions) of FBXO38, revealing an interaction with KIF20B, a Kinesin-6 protein required for efficient cytokinesis. FBXO38 was shown to function independently from an SCF complex to stabilize KIF20B. Consequently, depletion of either FBXO38 or USP7 led to dramatic decreases in KIF20B levels and KIF20B at the midbody, which were manifested in cytokinetic defects. Furthermore, cytokinetic defects associated with USP7 silencing were rescued by restoring FBXO38 or KIF20B. The results indicate a novel mechanism of regulating cytokinesis through USP7 and FBXO38.

USP7: Structure, substrate specificity, and inhibition

Turnover of cellular proteins is regulated by Ubiquitin Proteasome System (UPS). Components of this pathway, including the proteasome, ubiquitinating enzymes and deubiquitinating enzymes, are highly specialized and tightly regulated. In this mini-review we focus on the de-ubiquitinating enzyme USP7, and summarize latest advances in understanding its structure, substrate specificity and relevance to human cancers. There is increasing interest in UPS components as targets for cancer therapy and here we also overview the recent progress in the development of small molecule inhibitors that target USP7.

The deubiquitinase USP38 affects cellular functions through interacting with LSD1

Background

Deubiquitination is a posttranslational protein modification prevalent in mammalian cells. Deubiquitinases regulate the functions of the target protein by removing its ubiquitin chain. In this study, the effects of the deubiquitinase USP38’s functions on the LSD1 protein and on cell physiology were investigated.

Materials and methods

Western blotting, real-time quantitative PCR, immunoprecipitation, denaturing immunoprecipitation and luciferase reporter assays were used to analyze the protein stability, protein interactions and changes in the ubiquitin chain. Cell proliferation assays, colony formation assays, drug treatments and western blotting were used to explore the functions of USP38 in cells.

Results

The deubiquitinase USP38 stabilizes protein LSD1 in cells by binding LSD1 and cleaving its ubiquitin chain to prevent the degradation of LSD1 by the intracellular proteasome. USP38 enhances the ability of LSD1 to activate signaling pathways and hence promotes cellular abilities of proliferation and colony formation through interacting with LSD1. Furthermore, USP38 enhances the drug tolerance of human colon cancer cells.

Conclusions

USP38 is an LSD1-specific deubiquitinase that affects cellular physiology through interacting with LSD1.