La FAM fatale: USP9X in development and disease

USP9X deubiquitinates TRRAP to promote glioblastoma cell proliferation and migration and M2 macrophage polarization

Glioblastoma (GBM) is the most aggressive form of brain cancer, characterized by rapid growth and invasion into surrounding brain tissue. Ubiquitin-specific protease 9X (USP9X) has emerged as a key regulator in various cancers, but its role in GBM pathogenesis remains unclear. Understanding the molecular mechanisms underlying USP9X modulation of GBM progression could unveil potential therapeutic targets for this deadly disease. The mRNA and protein levels were determined in GBM tissues and/or cells using quantitative real-time polymerase chain reaction (qRT-PCR) and western blotting assays, respectively. Cell migration was evaluated through wound-healing assay, while cell proliferation was measured using colony formation and CCK-8 assays. Flow cytometry analysis was performed to quantify the CD206-positive macrophages to assess M2 polarization. Co-immunoprecipitation (Co-IP) assays were conducted to elucidate the association between USP9X and transformation/transcription domain-associated protein (TRRAP). Cycloheximide (CHX) treatment was used to determine the impact of USP9X on TRRAP protein stabilization. Furthermore, the effect of USP9X depletion on GBM cell malignancy was validated using a xenograft mouse model. We found that USP9X expression was elevated in GBM tissues and cells. Depletion of USP9X suppressed GBM cell migration, proliferation, and M2 macrophage polarization. Mechanistically, USP9X stabilized TRRAP through the deubiquitination pathway in GBM cells, and TRRAP mitigated the effects of USP9X silencing on GBM cell malignant phenotypes and M2 macrophage polarization. Moreover, silencing of USP9X inhibited tumor formation in vivo. Together, USP9X deubiquitinated TRRAP, thereby promoting glioblastoma cell proliferation, migration, and M2 macrophage polarization. These results highlight the potential of targeting the USP9X-TRRAP axis as a therapeutic strategy for GBM.

The Role of Ubiquitination in Osteosarcoma Development and Therapies

The ubiquitin-proteasome system (UPS) maintains intracellular protein homeostasis and cellular function by regulating various biological processes. Ubiquitination, a common post-translational modification, plays a crucial role in the regulation of protein degradation, signal transduction, and other physiological and pathological processes, and is involved in the pathogenesis of various cancers, including osteosarcoma. Osteosarcoma, the most common primary malignant bone tumor, is characterized by high metastatic potential and poor prognosis. It is a refractory bone disease, and the main treatment modalities are surgery combined with chemotherapy. Increasing evidence suggests a close association between UPS abnormalities and the progression of osteosarcoma. Due to the complexity and pleiotropy of the ubiquitination system, each step in the ubiquitination process can be targeted by drugs. In recent years, research and development of inhibitors targeting the ubiquitin system have increased gradually, showing great potential for clinical application. This article reviews the role of the ubiquitination system in the development and treatment of osteosarcoma, as well as research progress, with the hope of improving the therapeutic effects and prognosis of osteosarcoma patients by targeting effective molecules in the ubiquitination system.

Characteristic craniofacial defects associated with a novel USP9X truncation mutation

Germline loss-of-function mutations in USP9X have been reported to cause a wide spectrum of congenital anomalies. Here, we report a Japanese girl with a novel heterozygous nonsense mutation in USP9X who exhibited intellectual disability with characteristic craniofacial abnormalities, including hypotelorism, brachycephaly, hypodontia, micrognathia, severe dental crowding, and an isolated submucous cleft palate. Our findings provide further evidence that disruptions in USP9X contribute to a broad range of congenital craniofacial abnormalities.

Cellular functions, molecular signalings and therapeutic applications: Translational potential of deubiquitylating enzyme USP9X as a drug target in cancer treatment

Protein ubiquitination, one of the most significant post-translational modifications, plays an important role in controlling the proteins activity in diverse cellular processes. The reversible process of protein ubiquitination, known as deubiquitination, has emerged as a critical mechanism for maintaining cellular homeostasis. The deubiquitinases (DUBs), which participate in deubiquitination process are increasingly recognized as potential candidates for drug discovery. Among these DUBs, ubiquitin-specific protease 9× (USP9X), a highly conserved member of the USP family, exhibits versatile functions in various cellular processes, including the regulation of cell cycle, protein endocytosis, apoptosis, cell polarity, immunological microenvironment, and stem cell characteristics. The dysregulation and abnormal activities of USP9X are influenced by intricate cellular signaling pathway crosstalk and upstream non-coding RNAs. The complex expression patterns and controversial clinical significance of USP9X in cancers suggest its potential as a prognostic biomarker. Furthermore, USP9X inhibitors has shown promising antitumor activity and holds the potential to overcome therapeutic resistance in preclinical models. However, a comprehensive summary of the role and molecular functions of USP9X in cancer progression is currently lacking. In this review, we provide a comprehensive delineation of USP9X participation in numerous critical cellular processes, complicated signaling pathways within the tumor microenvironment, and its potential translational applications to combat therapeutic resistance. By systematically summarizing the updated molecular mechanisms of USP9X in cancer biology, this review aims to contribute to the advancement of cancer therapeutics and provide essential insights for specialists and clinicians in the development of improved cancer treatment strategies.

Abrogation of USP9X Is a Potential Strategy to Decrease PEG10 Levels and Impede Tumor Progression in Cutaneous T-Cell Lymphoma

Advanced-stage cutaneous T-cell lymphomas (CTCLs) are notorious for their highly aggressive behavior, resistance to conventional treatments, and poor prognosis, particularly when large-cell transformation occurs. PEG10 has been recently proposed as a potent driver for large-cell transformation in CTCL. However, the targeting of PEG10 continues to present a formidable clinical challenge that has yet to be addressed. In this study, we report an important post-translational regulatory mechanism of PEG10 in CTCL. USP9X, a deubiquitinase, interacted with and deubiquitinated PEG10, thereby stabilizing PEG10. Knockdown of USP9X or pharmacological targeting of USP9X resulted in a prominent downregulation of PEG10 and its downstream pathway in CTCL. Moreover, USP9X inhibition conferred tumor cell growth disadvantage and enhanced apoptosis in vitro, an effect that occurred in part through its regulation on PEG10. Furthermore, we demonstrated that inhibition of USP9X obviously restrained CTCL tumor growth in vivo and that high expression of USP9X is associated with poor survival in patients with CTCL. Collectively, our findings uncover USP9X as a key post-translational regulator in the stabilization of PEG10 and suggest that targeting PEG10 stabilization through USP9X inhibition may represent a promising therapeutic strategy for advanced-stage CTCL.

Dysregulation of deubiquitination in breast cancer

Breast cancer (BC) is a highly frequent malignant tumor that poses a serious threat to women's health and has different molecular subtypes, histological subtypes, and biological features, which act by activating oncogenic factors and suppressing cancer inhibitors. The ubiquitin-proteasome system (UPS) is the main process contributing to protein degradation, and deubiquitinases (DUBs) are reverse enzymes that counteract this process. There is growing evidence that dysregulation of DUBs is involved in the occurrence of BC. Herein, we review recent research findings in BC-associated DUBs, describe their nature, classification, and functions, and discuss the potential mechanisms of DUB-related dysregulation in BC. Furthermore, we present the successful treatment of malignant cancer with DUB inhibitors, as well as analyzing the status of targeting aberrant DUBs in BC.

Emerging roles of deubiquitinating enzymes in actin cytoskeleton and tumor metastasis

BACKGROUND

Metastasis accounts for the majority of cancer-related deaths. Actin dynamics and actin-based cell migration and invasion are important factors in cancer metastasis. Metastasis is characterized by actin polymerization and depolymerization, which are precisely regulated by molecular changes involving a plethora of actin regulators, including actin-binding proteins (ABPs) and signalling pathways, that enable cancer cell dissemination from the primary tumour. Research on deubiquitinating enzymes (DUBs) has revealed their vital roles in actin dynamics and actin-based migration and invasion during cancer metastasis.

CONCLUSION

Here, we review how DUBs drive tumour metastasis by participating in actin rearrangement and actin-based migration and invasion. We summarize the well-characterized and essential actin cytoskeleton signalling molecules related to DUBs, including Rho GTPases, Src kinases, and ABPs such as cofilin and cortactin. Other DUBs that modulate actin-based migration signalling pathways are also discussed. Finally, we discuss and address therapeutic opportunities and ongoing challenges related to DUBs with respect to actin dynamics.

Circulating exosomal miR-16-5p and let-7e-5p are associated with bladder fibrosis of diabetic cystopathy

Diabetic cystopathy (DCP) is a prevalent etiology of bladder dysfunction in individuals with longstanding diabetes, frequently leading to bladder interstitial fibrosis. Research investigating the initial pathological alterations of DCP is notably scarce. To comprehend the development of fibrosis and find effective biomarkers for its diagnosis, we prepared streptozotocin-induced long-term diabetic SD rats exhibiting a type 1 diabetes phenotype and bladder fibrosis in histology detection. After observing myofibroblast differentiation from rats' primary bladder fibroblasts with immunofluorescence, we isolated fibroblasts derived exosomes and performed exosomal miRNA sequencing. The co-differentially expressed miRNAs (DEMis) (miR-16-5p and let-7e-5p) were screened through a joint analysis of diabetic rats and long-term patients' plasma data (GES97123) downloaded from the GEO database. Then two co-DEMis were validated by quantitative PCR on exosomes derived from diabetic rats' plasma. Following with a series of analysis, including target mRNAs and transcription factors (TFs) prediction, hubgenes identification, protein-protein interaction (PPI) network construction and gene enrichment analysis, a miRNA-mediated genetic regulatory network consisting of two miRNAs, nine TFs, and thirty target mRNAs were identified in relation to fibrotic processes. Thus, circulating exosomal miR-16-5p and let-7e-5p are associated with bladder fibrosis of DCP, and the crucial genes in regulatory network might hold immense significance in studying the pathogenesis and molecular mechanisms of fibrosis, which deserves further exploration.

The Role of Ubiquitin-Proteasome System and Mitophagy in the Pathogenesis of Parkinson's Disease

Parkinson's disease (PD) is a common neurodegenerative disease that is mainly in middle-aged people and elderly people, and the pathogenesis of PD is complex and diverse. The ubiquitin-proteasome system (UPS) is a master regulator of neural development and the maintenance of brain structure and function. Dysfunction of components and substrates of this UPS has been linked to neurodegenerative diseases such as Parkinson's disease and Alzheimer's disease. Moreover, UPS can regulate α-synuclein misfolding and aggregation, mitophagy, neuroinflammation and oxidative stress to affect the development of PD. In the present study, we review the role of several related E3 ubiquitin ligases and deubiquitinating enzymes (DUBs) on the pathogenesis of PD such as Parkin, CHIP, USP8, etc. On this basis, we summarize the connections and differences of different E3 ubiquitin ligases in the pathogenesis, and elaborate on the regulatory progress of different DUBs on the pathogenesis of PD. Therefore, we can better understand their relationships and provide feasible and valuable therapeutic clues for UPS-related PD treatment research.

The deubiquitinase USP9X regulates RIT1 protein abundance and oncogenic phenotypes

RIT1 is a rare and understudied oncogene in lung cancer. Despite structural similarity to other RAS GTPase proteins such as KRAS, oncogenic RIT1 activity does not appear to be tightly regulated by nucleotide exchange or hydrolysis. Instead, there is a growing understanding that the protein abundance of RIT1 is important for its regulation and function. We previously identified the deubiquitinase USP9X as a RIT1 dependency in RIT1-mutant cells. Here, we demonstrate that both wild-type and mutant forms of RIT1 are substrates of USP9X. Depletion of USP9X leads to decreased RIT1 protein stability and abundance and resensitizes cells to EGFR tyrosine kinase inhibitors. Our work expands upon the current understanding of RIT1 protein regulation and presents USP9X as a key regulator of RIT1-driven oncogenic phenotypes.

Roles of USP9X in cellular functions and tumorigenesis (Review)

Ubiquitin-specific peptidase 9X (USP9X) is involved in certain human diseases, including malignancies, atherosclerosis and certain diseases of the nervous system. USP9X promotes the deubiquitination and stabilization of diverse substrates, thereby exerting a versatile range of effects on pathological and physiological processes. USP9X serves vital roles in the processes of cell survival, invasion and migration in various types of cancer. The present review aims to highlight the current knowledge of USP9X in terms of its structure and the possible mediatory mechanisms involved in certain types of cancer, providing a thorough introduction to its biological functions in carcinogenesis and further outlining its oncogenic or suppressive properties in a diverse range of cancer types. Finally, several perspectives regarding USP9X-targeted pharmacological therapeutics in cancer development are discussed.

The TDRD3-USP9X complex and MIB1 regulate TOP3B homeostasis and prevent deleterious TOP3B cleavage complexes

TOP3B is stabilized by TDRD3. Hypothesizing that TDRD3 recruits a deubiquitinase, we find that TOP3B interacts with USP9X via TDRD3. Inactivation of USP9X destabilizes TOP3B, and depletion of both TDRD3 and USP9X does not promote further TOP3B ubiquitylation. Additionally, we observe that MIB1 mediates the ubiquitylation and proteasomal degradation of TOP3B by directly interacting with TOP3B independently of TDRD3. Combined depletion of USP9X, TDRD3 and MIB1 causes no additional increase in TOP3B levels compared to MIB1 knockdown alone indicating that the TDRD3-USP9X complex works downstream of MIB1. To comprehend why cells degrade TOP3B in the absence of TDRD3, we measured TOP3Bccs. Lack of TDRD3 increases TOP3Bccs in DNA and RNA, and induced R-loops, γH2AX and growth defect. Biochemical experiments confirm that TDRD3 increases the turnover of TOP3B. Our work provides molecular insights into the mechanisms by which TDRD3 protect cells from deleterious TOP3Bccs which are otherwise removed by TRIM41.

USP9X deubiquitinates and stabilizes CDC123 to promote breast carcinogenesis through regulating cell cycle

Cell division cycle 123 (CDC123) has been implicated in a variety of human diseases. However, it remains unclear whether CDC123 plays a role in tumorigenesis and how its abundance is regulated. In this study, we found that CDC123 was highly expressed in breast cancer cells, and its high expression was positively correlated with a poor prognosis. Knowndown of CDC123 impaired the proliferation of breast cancer cells. Mechanistically, we identified a deubiquitinase, ubiquitin-specific peptidase 9, X-linked (USP9X), that could physically interact with and deubiquitinate K48-linked ubiquitinated CDC123 at the K308 site. Therefore, the expression of CDC123 was positively correlated with USP9X in breast cancer cells. In addition, we found that deletion of either USP9X or CDC123 led to altered expression of cell cycle-related genes and resulted in the accumulation of cells population in the G0/G1 phase, thereby suppressing cell proliferation. Treatment with the deubiquitinase inhibitor of USP9X, WP1130 (Degrasyn, a small molecule compound that USP9X deubiquitinase inhibitor), also led to the accumulation of breast cancer cells in the G0/G1 phase, but this effect could be rescued by overexpression of CDC123. Furthermore, our study revealed that the USP9X/CDC123 axis promotes the occurrence and development of breast cancer through regulating the cell cycle, and suggests that it may be a potential target for breast cancer intervention. In conclusion, our study demonstrates that USP9X is a key regulator of CDC123, providing a novel pathway for the maintenance of CDC123 abundance in cells, and supports USP9X/CDC123 as a potential target for breast cancer intervention through regulating the cell cycle.

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.

Identification of USP9X as a leukemia susceptibility gene

We recently reported that children with multiple birth defects have a significantly higher risk of childhood cancer. We performed whole-genome sequencing on a cohort of probands from this study with birth defects and cancer and their parents. Structural variant analysis identified a novel 5 kb de novo heterozygous inframe deletion overlapping the catalytic domain of USP9X in a female proband with multiple birth defects, developmental delay, and B-cell acute lymphoblastic leukemia (B-ALL). Her phenotype was consistent with female-restricted X-linked syndromic intellectual developmental disorder-99 (MRXS99F). Genotype-phenotype analysis including previously reported female probands (n = 42) demonstrated that MRXS99F probands with B-ALL (n = 3) clustered with subjects with loss-of-function (LoF) USP9X variants and multiple anomalies. The cumulative incidence of B-ALL among these female probands (7.1%) was significantly higher than an age- and sex-matched cohort (0.003%) from the Surveillance, Epidemiology, and End Results database (P < .0001, log-rank test). There are no reports of LoF variants in males. Males with hypomorphic missense variants have neurodevelopmental disorders without birth defects or leukemia risk. In contrast, in sporadic B-ALL, somatic LoF USP9X mutations occur in both males and females, and expression levels are comparable in leukemia samples from both sexes (P = .54), with the highest expressors being female patients with extra copies of the X-chromosome. Overall, we describe USP9X as a novel female-specific leukemia predisposition gene associated with multiple congenital, neurodevelopmental anomalies, and B-ALL risk. In contrast, USP9X serves as a tumor suppressor in sporadic pediatric B-ALL in both sexes, with low expression associated with poorer survival in patients with high-risk B-ALL.

Aicardi Syndrome Is a Genetically Heterogeneous Disorder

Aicardi Syndrome (AIC) is a rare neurodevelopmental disorder recognized by the classical triad of agenesis of the corpus callosum, chorioretinal lacunae and infantile epileptic spasms syndrome. The diagnostic criteria of AIC were revised in 2005 to include additional phenotypes that are frequently observed in this patient group. AIC has been traditionally considered as X-linked and male lethal because it almost exclusively affects females. Despite numerous genetic and genomic investigations on AIC, a unifying X-linked cause has not been identified. Here, we performed exome and genome sequencing of 10 females with AIC or suspected AIC based on current criteria. We identified a unique de novo variant, each in different genes: KMT2B, SLF1, SMARCB1, SZT2 and WNT8B, in five of these females. Notably, genomic analyses of coding and non-coding single nucleotide variants, short tandem repeats and structural variation highlighted a distinct lack of X-linked candidate genes. We assessed the likely pathogenicity of our candidate autosomal variants using the TOPflash assay for WNT8B and morpholino knockdown in zebrafish (Danio rerio) embryos for other candidates. We show expression of Wnt8b and Slf1 are restricted to clinically relevant cortical tissues during mouse development. Our findings suggest that AIC is genetically heterogeneous with implicated genes converging on molecular pathways central to cortical development.

Protein Levels of Anti-Apoptotic Mcl-1 and the Deubiquitinase USP9x Are Cooperatively Upregulated during Prostate Cancer Progression and Limit Response of Prostate Cancer Cells to Radiotherapy

BACKGROUND

Radiotherapy constitutes an important therapeutic option for prostate cancer. However, prostate cancer cells often acquire resistance during cancer progression, limiting the cytotoxic effects of radiotherapy. Among factors regulating sensitivity to radiotherapy are members of the Bcl-2 protein family, known to regulate apoptosis at the mitochondrial level. Here, we analyzed the role of anti-apoptotic Mcl-1 and USP9x, a deubiquitinase stabilizing Mcl-1 protein levels, in prostate cancer progression and response to radiotherapy.

METHODS

Changes in Mcl-1 and USP9x levels during prostate cancer progression were determined by immunohistochemistry. Neutralization of Mcl-1 and USP9x was achieved by siRNA-mediated knockdown. We analyzed Mcl-1 stability after translational inhibition by cycloheximide. Cell death was determined by flow cytometry using an exclusion assay of mitochondrial membrane potential-sensitive dye. Changes in the clonogenic potential were examined by colony formation assay.

RESULTS

Protein levels of Mcl-1 and USP9x increased during prostate cancer progression, and high protein levels correlated with advanced prostate cancer stages. The stability of Mcl-1 reflected Mcl-1 protein levels in LNCaP and PC3 prostate cancer cells. Moreover, radiotherapy itself affected Mcl-1 protein turnover in prostate cancer cells. Particularly in LNCaP cells, the knockdown of USP9x expression reduced Mcl-1 protein levels and increased sensitivity to radiotherapy.

CONCLUSION

Posttranslational regulation of protein stability was often responsible for high protein levels of Mcl-1. Moreover, we demonstrated that deubiquitinase USP9x as a factor regulating Mcl-1 levels in prostate cancer cells, thus limiting cytotoxic response to radiotherapy.

Novel Variant in the USP9X Gene Is Associated with Congenital Heart Disease in a Male Patient: A Case Report and Literature Review

Introduction

The X-chromosomal USP9X gene encodes a deubiquitylating enzyme involved in protein turnover and TGF-β signaling during fetal and neuronal development. USP9X variants in females are primarily associated with complete loss-of-function (LOF) alleles, leading to neurodevelopmental delay and intellectual disability, as well as a wide range of congenital anomalies. In contrast, USP9X missense variants in males often result in partial rather than complete LOF, specifically affecting neuronal migration and development. USP9X variants in males are associated with intellectual disability, behavioral disorders, global developmental delay, speech delay, and structural CNS defects. Facial dysmorphisms are found in almost all patients.

Case Presentation

We report the case of an Italian boy presenting dysmorphism, intellectual disability, structural brain anomalies, and congenital heart disease. Using next-generation sequencing analysis, we identified a hemizygous de novo variant in the USP9X gene (c.5470A>G, p.Met1824Val) that was never reported in the literature.

Conclusion

We provide an overview of the available literature on USP9X variants in males, in order to further expand the genotypic and phenotypic landscape of male-restricted X-linked mental retardation syndrome. Our findings confirm the involvement of USP9X variants in neuronal development and corroborate the possible association between the novel USP9X variant and congenital heart malformation.

KSHV Viral Protein Kinase Interacts with USP9X to Modulate the Viral Lifecycle

Kaposi's sarcoma-associated herpesvirus (KSHV) is the etiological agent of Kaposi sarcoma (KS), the plasmablastic form of multicentric Castleman's disease, and primary effusion lymphoma. In sub-Saharan Africa, KS is the most common HIV-related malignancy and one of the most common childhood cancers. Immunosuppressed patients, including HIV-infected patients, are more prone to KSHV-associated disease. KSHV encodes a viral protein kinase (vPK) that is expressed from ORF36. KSHV vPK contributes to the optimal production of infectious viral progeny and upregulation of protein synthesis. To elucidate the interactions of vPK with cellular proteins in KSHV-infected cells, we used a bottom-up proteomics approach and identified host protein ubiquitin-specific peptidase 9X-linked (USP9X) as a potential interactor of vPK. Subsequently, we validated this interaction using a co-immunoprecipitation assay. We report that both the ubiquitin-like and the catalytic domains of USP9X are important for association with vPK. To uncover the biological relevance of the USP9X/vPK interaction, we investigated whether the knockdown of USP9X would modulate viral reactivation. Our data suggest that depletion of USP9X inhibits both viral reactivation and the production of infectious virions. Understanding how USP9X influences the reactivation of KSHV will provide insights into how cellular deubiquitinases regulate viral kinase activity and how viruses co-opt cellular deubiquitinases to propagate infection. Hence, characterizing the roles of USP9X and vPK during KSHV infection constitutes a first step toward identifying a potentially critical interaction that could be targeted by future therapeutics. IMPORTANCE Kaposi's sarcoma-associated herpesvirus (KSHV) is the etiological agent of Kaposi sarcoma (KS), the plasmablastic form of multicentric Castleman's disease, and primary effusion lymphoma. In sub-Saharan Africa, KS is the most common HIV-related malignancy. KSHV encodes a viral protein kinase (vPK) that aids viral replication. To elucidate the interactions of vPK with cellular proteins in KSHV-infected cells, we used an affinity purification approach and identified host protein ubiquitin-specific peptidase 9X-linked (USP9X) as a potential interactor of vPK. Depletion of USP9X inhibits both viral reactivation and the production of infectious virions. Overall, our data suggest a proviral role for USP9X.

Role of Deubiquitinases in Parkinson's Disease-Therapeutic Perspectives

Parkinson's disease (PD) is a neurodegenerative disorder that has been associated with mitochondrial dysfunction, oxidative stress, and defects in mitophagy as well as α-synuclein-positive inclusions, termed Lewy bodies (LBs), which are a common pathological hallmark in PD. Mitophagy is a process that maintains cellular health by eliminating dysfunctional mitochondria, and it is triggered by ubiquitination of mitochondrial-associated proteins-e.g., through the PINK1/Parkin pathway-which results in engulfment by the autophagosome and degradation in lysosomes. Deubiquitinating enzymes (DUBs) can regulate this process at several levels by deubiquitinating mitochondrial substrates and other targets in the mitophagic pathway, such as Parkin. Moreover, DUBs can affect α-synuclein aggregation through regulation of degradative pathways, deubiquitination of α-synuclein itself, and/or via co-localization with α-synuclein in inclusions. DUBs with a known association to PD are described in this paper, along with their function. Of interest, DUBs could be useful as novel therapeutic targets against PD through regulation of PD-associated defects.

USP9X promotes lipopolysaccharide-stimulated acute lung injury by deubiquitination of NLRP3

Alveolar epithelial cells (AECs) function as a vital defense barrier avoiding the invasion of exogenous agents and preserving the functional and structural integrity of lung tissues, while damage/breakdown of this airway epithelial barrier is frequently associated with the pathogenesis of acute lung injury (ALI). NOD-like receptor family, pyrindomain-containing 3 (NLRP3) inflammasome activation-associated pyroptosis is involved in the development of ALI. Yet, how the activity of NLRP3 inflammasome is regulated in the context of ALI remains unknown. Herein we hypothesized that USP9X, an important deubiquitinase, participates in modulating the activation of NLRP3 inflammasome, thereby affecting the phenotypes in a lipopolysaccharide (LPS)-stimulated AEC model. Human pulmonary AECs were subjected to LPS/adenosine triphosphate (ATP) treatment to induce NLRP3 inflammasome activation and cell pyroptosis. Knockdown and overexpression of USP9X were applied to validate the function of USP9X. Inhibitors of proteinase and protein synthesis, as well as approach of co-immunoprecipitation coupled with Western blot, were utilized to explore the molecular mechanism. LPS/ATP challenge resulted in pronouncedly increased pyroptosis of AECs, activation of NLRP3 inflammasome and release of interleukin (IL)-1β and IL-18 cytokines, while downregulation of USP9X could reverse these alterations. USP9X was found to have marked impact on NLRP3 protein instead of mRNA level. Furthermore, increased ubiquitination of NLRP3 was observed upon downregulating USP9X. Additionally, the inhibitory effect of USP9X downregulation was reversed by NLRP3 overexpression, while the promoting impact of USP9X overexpression was dampened by NLRP3 inhibitor in terms of cell pyroptosis and cytokine secretion. USP9X modulated the activity of NLRP3 inflammasome and pyroptosis of AECs via its deubiquitination function.

Periventricular heterotopia in a male child with USP9X missense variant

The ubiquitin-specific protease USP9X has been found to play a role in multiple aspects of neural development including processes of neuronal migrations. In males, hemizygous partial loss of function variants in USP9X lead to a clinical phenotype primarily characterized by intellectual disability, hypotonia, speech and language impairment, behavioral disturbances accompanied by additional clinical features with variable expressivity. Structural brain abnormalities are reported in all cases where neuro-imaging was performed. The most common radiological features described include hypoplasia/agenesis of the corpus callosum, widened ventricles, white matter disturbances, and cerebellar hypoplasia. Here we report a child harboring a missense variant in USP9X presenting with the classical neurodevelopmental phenotype and a previously unreported radiological picture of periventricular heterotopia. This case expands the phenotypic landscape of this emergent condition and supports the critical role of USP9X in neuronal migration processes.

USP9X-mediated NRP1 deubiquitination promotes liver fibrosis by activating hepatic stellate cells

Liver fibrosis is a complex fibrotic process that develops early in the course of cirrhosis and is caused by chronic liver damage. The activation of hepatic stellate cells is primarily responsible for the fibrosis process. Studies show that NRP1 influences HSC motility and migration. However, whether NRP1 regulates HSC activation remains unknown. C57BL/6 male mice (6-8 weeks old) were intraperitoneally injected with 10% CCl₄ in olive oil (5 μl/g body weight) every three days for four weeks to create an animal model of liver fibrosis. Control mice received olive oil (5 μl/g body weight). Different assays such as immunohistochemistry, immunostaining, Western blotting, qRT-PCR, immunoprecipitation, immunoprecipitation, and GST pull-down assays, and in vivo and in vitro ubiquitination assays were conducted. We found that NRP1 expression was significantly elevated both in mouse and human fibrotic livers, mainly in activated HSCs at the fibrotic foci. NRP1 promoted HSC activation via the cytokine TGF-β1, VEGFA, and PDGF-BB. Moreover, USP9X was found to be a critical deubiquitinating enzyme for the stability and high activity of NRP1 and NRP1 deubiquitination mediated by USP9X enhanced HSC activation and liver fibrosis. NRP1 deubiquitination mediated by USP9X enhances HSC activation, implying that targeting NRP1 or USP9X potentiates novel options in the treatment of liver fibrosis.

Molecular diagnosis and novel genes and phenotypes in a pediatric thoracic insufficiency cohort

Thoracic insufficiency syndromes are a genetically and phenotypically heterogeneous group of disorders characterized by congenital abnormalities or progressive deformation of the chest wall and/or vertebrae that result in restrictive lung disease and compromised respiratory capacity. We performed whole exome sequencing on a cohort of 42 children with thoracic insufficiency to elucidate the underlying molecular etiologies of syndromic and non-syndromic thoracic insufficiency and predict extra-skeletal manifestations and disease progression. Molecular diagnosis was established in 24/42 probands (57%), with 18/24 (75%) probands having definitive diagnoses as defined by laboratory and clinical criteria and 6/24 (25%) probands having strong candidate genes. Gene identified in cohort patients most commonly encoded components of the primary cilium, connective tissue, and extracellular matrix. A novel association between KIF7 and USP9X variants and thoracic insufficiency was identified. We report and expand the genetic and phenotypic spectrum of a cohort of children with thoracic insufficiency, reinforce the prevalence of extra-skeletal manifestations in thoracic insufficiency syndromes, and expand the phenotype of KIF7 and USP9X-related disease to include thoracic insufficiency.

Protein Kinases and Cross-talk between Post-translational Modifications in the Regulation of Drug Transporters

Drug transporters are modulators for drug absorption, distribution, and excretion. Key drug transporters including P-glycoprotein and breast cancer resistance protein of the ABC superfamily; organic anion transporting polypeptide 1B1 and 1B3, organic anion transporter 1 and 3, and organic cation transporter 2, as well as multidrug and toxin extrusion 1 and 2 of the SLC superfamily have been recommended by regulatory agencies to be investigated and evaluated in drug-drug interaction (DDI) studies due to their important roles in determining the efficacy, toxicity and DDI of various drugs. Drug transporters are subjected to multiple levels of control and post-translational modifications (PTMs) provide rapid and versatile ways of regulation. Under pathologic and/or pharmacological conditions, PTMs may be altered in the cellular system, leading to functional changes of transporter proteins. Phosphorylation is by far the most actively investigated form of PTMs in the regulation of transporters. Further, studies in recent years also found that protein kinases coordinate with other PTMs for the dynamic control of these membrane proteins. Here we summarized the regulation of major drug transporters by protein kinases and their cross-talking with other PTMs that may generate a complex regulatory network for fine-tuning the function of these important drug processing modulators. SIGNIFICANCE STATEMENT: Kinases regulate drug transporters in versatile manners; Kinase regulation cross-talks with other PTMs, forming a complex network for transporter regulation; Pathological and/or pharmacological conditions may alter PTMs and affect transporter function with different molecular mechanisms.

Recent advances in esophageal squamous cell precancerous conditions: A review

Esophageal squamous cell carcinoma (ESCC) is a common cancer in many developing countries in Asia and Africa, with a 5-year survival rate of approximately 20%. Most cases are diagnosed at an advanced age when there is no effective treatment strategy. Esophageal precancerous conditions have a much better prognosis, with a 5-year survival rate of over 90% by endoscopic diagnosis and treatment. Nevertheless, limitations, contraindications, and lymph node metastasis incompetency of endoscopy. Thus, the diagnosis and treatment of esophageal precancerous lesions remain a significant challenge. Biomarker investigations provide opportunities for target detection and therapy. Additionally, drug development is ongoing. Changes in lifestyle habits, such as diet balance, smoking and alcohol cessation, are beneficial for the prognosis of esophageal precancerous lesions. Collectively, multiple and sequential diagnoses and treatments are essential for curing esophageal precancerous lesions and reducing the incidence and mortality of ESCC.

The intricate interplay between HIFs, ROS, and the ubiquitin system in the tumor hypoxic microenvironment

Alterations in protein ubiquitination and hypoxia-inducible factor (HIF) signaling both contribute to tumorigenesis and tumor progression. Ubiquitination is a dynamic process that is coordinately regulated by E3 ligases and deubiquitinases (DUBs), which have emerged as attractive therapeutic targets. HIF expression and transcriptional activity are usually increased in tumors, leading to poor clinical outcomes. Reactive oxygen species (ROS) are upregulated in tumors and have multiple effects on HIF signaling and the ubiquitin system. A growing body of evidence has shown that multiple E3 ligases and UBDs function synergistically to control the expression and activity of HIF, thereby allowing cancer cells to cope with the hypoxic microenvironment. Conversely, several E3 ligases and DUBs are regulated by hypoxia and/or HIF signaling. Hypoxia also induces ROS production, which in turn modulates the stability or activity of HIF, E3 ligases, and DUBs. Understanding the complex networks between E3 ligase, DUBs, ROS, and HIF will provide insights into the fundamental mechanism of the cellular response to hypoxia and help identify novel molecular targets for cancer treatment. We review the current knowledge on the comprehensive relationship between E3 ligase, DUBs, ROS, and HIF signaling, with a particular focus on the use of E3 ligase or DUB inhibitors in cancer.

Research Progress for Targeting Deubiquitinases in Gastric Cancers

Gastric cancers (GCs) are malignant tumors with a high incidence that threaten global public health. Despite advances in GC diagnosis and treatment, the prognosis remains poor. Therefore, the mechanisms underlying GC progression need to be identified to develop prognostic biomarkers and therapeutic targets. Ubiquitination, a post-translational modification that regulates the stability, activity, localization, and interactions of target proteins, can be reversed by deubiquitinases (DUBs), which can remove ubiquitin monomers or polymers from modified proteins. The dysfunction of DUBs has been closely linked to tumorigenesis in various cancer types, and targeting certain DUBs may provide a potential option for cancer therapy. Multiple DUBs have been demonstrated to function as oncogenes or tumor suppressors in GC. In this review, we summarize the DUBs involved in GC and their associated upstream regulation and downstream mechanisms and present the benefits of targeting DUBs for GC treatment, which could provide new insights for GC diagnosis and therapy.

USP9x promotes CD8 + T-cell dysfunction in association with autophagy inhibition in septic liver injury

Sepsis is a life-threatening condition manifested by concurrent inflammation and immunosuppression. Ubiquitin-specific peptidase 9, X-linked (USP9x), is a USP domain-containing deubiquitinase which is required in T-cell development. In the present study, we investigate whether USP9x plays a role in hepatic CD8 ⁺ T-cell dysfunction in septic mice. We find that CD8 ⁺ T cells are decreased in the blood of septic patients with liver injury compared with those without liver injury, the CD4/CD8 ratio is increased, and the levels of cytolytic factors, granzyme B and perforin are downregulated. The number of hepatic CD8 ⁺ T cells and USP9x expression are both increased 24 h after cecal ligation and puncture-induced sepsis in a mouse model, a pattern similar to liver injury. The mechanism involves promotion of CD8 ⁺ T-cell dysfunction by USP9x associated with suppression of cell cytolytic activity via autophagy inhibition, which is reversed by the USP9x inhibitor WP1130. In the in vivo studies, autophagy is significantly increased in hepatic CD8 ⁺ T cells of septic mice with conditional knockout of mammalian target of rapamycin. This study shows that USP9x has the potential to be used as a therapeutic target in septic liver injury.

The DUB Club: Deubiquitinating Enzymes and Neurodevelopmental Disorders

Protein ubiquitination is a widespread, multifunctional, posttranslational protein modification, best known for its ability to direct protein degradation via the ubiquitin proteasome system (UPS). Ubiquitination is also reversible, and the human genome encodes over 90 deubiquitinating enzymes (DUBs), many of which appear to target specific subsets of ubiquitinated proteins. This review focuses on the roles of DUBs in neurodevelopmental disorders (NDDs). We present the current genetic evidence connecting 12 DUBs to a range of NDDs and the functional studies implicating at least 19 additional DUBs as candidate NDD genes. We highlight how the study of DUBs in NDDs offers critical insights into the role of protein degradation during brain development. Because one of the major known functions of a DUB is to antagonize the UPS, loss of function of DUB genes has been shown to culminate in loss of abundance of its protein substrates. The identification and study of NDD DUB substrates in the developing brain is revealing that they regulate networks of proteins that themselves are encoded by NDD genes. We describe the new technologies that are enabling the full resolution of DUB protein networks in the developing brain, with the view that this knowledge can direct the development of new therapeutic paradigms. The fact that the abundance of many NDD proteins is regulated by the UPS presents an exciting opportunity to combat NDDs caused by haploinsufficiency, because the loss of abundance of NDD proteins can be potentially rectified by antagonizing their UPS-based degradation.

Exome sequencing revealed USP9X and COL2A1 mutations in a large family with multiple epiphyseal dysplasia

Diagnosis of rare skeletal diseases is based primarily on clinical phenotype and radiographic analysis. Genetic etiology of these heterogeneous diseases remains largely unknown. Here, we report the identification of two genomic mutations using exome sequencing from patients with multiple epiphyseal dysplasia (MED) of an unusual family in autosomal dominant and X-linked inheritance. A dominant mutation (c.2224G > A; p.Gly687Ser) in the known causal COL2A1 gene was identified in three patients with MED, deformed femoral heads and vertebral dysplasia. Furthermore, a hemizygous mutation (c.2830G > A; p.Ala944Thr) in the USP9X gene was identified in the fourth patient with short stature, MED, deformed femoral head, thoracic and lumbar platyspondyly, right ankle condyle dysplasia, and subchondral sclerosis. This is the first identification of an X-linked candidate causative gene in a patient with MED, suggesting a new clinical entity. Our findings shed a new light on the role of USP9X in MED-associated disorders.

Treating ARID1A mutated cancers by harnessing synthetic lethality and DNA damage response

Chromatin remodeling is an essential cellular process for organizing chromatin structure into either open or close configuration at specific chromatin locations by orchestrating and modifying histone complexes. This task is responsible for fundamental cell physiology including transcription, DNA replication, methylation, and damage repair. Aberrations in this activity have emerged as epigenomic mechanisms in cancer development that increase tumor clonal fitness and adaptability amidst various selection pressures. Inactivating mutations in AT-rich interaction domain 1A (ARID1A), a gene encoding a large nuclear protein member belonging to the SWI/SNF chromatin remodeling complex, result in its loss of expression. ARID1A is the most commonly mutated chromatin remodeler gene, exhibiting the highest mutation frequency in endometrium-related uterine and ovarian carcinomas. As a tumor suppressor gene, ARID1A is essential for regulating cell cycle, facilitating DNA damage repair, and controlling expression of genes that are essential for maintaining cellular differentiation and homeostasis in non-transformed cells. Thus, ARID1A deficiency due to somatic mutations propels tumor progression and dissemination. The recent success of PARP inhibitors in treating homologous recombination DNA repair-deficient tumors has engendered keen interest in developing synthetic lethality-based therapeutic strategies for ARID1A-mutated neoplasms. In this review, we summarize recent advances in understanding the biology of ARID1A in cancer development, with special emphasis on its roles in DNA damage repair. We also discuss strategies to harness synthetic lethal mechanisms for future therapeutics against ARID1A-mutated cancers.

USP9X Increased Tumor Angiogenesis in Mantle Cell Lymphoma by Upregulation of CCND1-Mediated SOX11

Mantle cell lymphoma (MCL) is an aggressive lymphoid malignancy with a poor prognosis. Ubiquitin-specific peptidase 9, X-linked (USP9X), has been associated with multiple physiological pathways and regulates various cellular activities. In this study, we explored the role of USP9X in MCL in vitro and in vivo. USP9X was verified to be increased in peripheral blood mononuclear cells (PBMCs) of MCL patients and MCL cells. Moreover, CCND1 and SOX11 were also upregulated in PBMCs of MCL patients. The positive correlation between USP9X and CCND1, USP9X and SOX11, and CCND1 and SOX11 were identified. Further, USP9X overexpression and knockdown were performed in MCL cells. We proved that USP9X overexpression promoted proliferation and cell cycle and suppressed cell apoptosis in MCL cells. Upregulation of angiogenesis and cell migration were induced by USP9X overexpression in MCL cells. However, the USP9X knockdown showed opposite effects. In addition, USP9X was discovered to decrease Cyclin D1 (CCND1)-mediated SOX11 expression in MCL cells. We demonstrated that SOX11 overexpression reversed USP9X knockdown-mediated angiogenesis in MCL cells. Besides, tumor formation was inhibited by USP9X knockdown in mice in vivo. In conclusion, these results revealed that USP9X promoted tumor angiogenesis in MCL via increasing CCND1-mediated SOX11.

On the Study of Deubiquitinases: Using the Right Tools for the Job

Deubiquitinases (DUBs) have been the subject of intense scrutiny in recent years. Many of their diverse enzymatic mechanisms are well characterized in vitro; however, our understanding of these enzymes at the cellular level lags due to the lack of quality tool reagents. DUBs play a role in seemingly every biological process and are central to many human pathologies, thus rendering them very desirable and challenging therapeutic targets. This review aims to provide researchers entering the field of ubiquitination with knowledge of the pharmacological modulators and tool molecules available to study DUBs. A focus is placed on small molecule inhibitors, ubiquitin variants (UbVs), and activity-based probes (ABPs). Leveraging these tools to uncover DUB biology at the cellular level is of particular importance and may lead to significant breakthroughs. Despite significant drug discovery efforts, only approximately 15 chemical probe-quality small molecule inhibitors have been reported, hitting just 6 of about 100 DUB targets. UbV technology is a promising approach to rapidly expand the library of known DUB inhibitors and may be used as a combinatorial platform for structure-guided drug design.

Monogenic causes of pigmentary mosaicism

Pigmentary mosaicism of the Ito type, also known as hypomelanosis of Ito, is a neurocutaneous syndrome considered to be predominantly caused by somatic chromosomal mosaicism. However, a few monogenic causes of pigmentary mosaicism have been recently reported. Eleven unrelated individuals with pigmentary mosaicism (mostly hypopigmented skin) were recruited for this study. Skin punch biopsies of the probands and trio-based blood samples (from probands and both biological parents) were collected, and genomic DNA was extracted and analyzed by exome sequencing. In all patients, plausible monogenic causes were detected with somatic and germline variants identified in five and six patients, respectively. Among the somatic variants, four patients had MTOR variant (36%) and another had an RHOA variant. De novo germline variants in USP9X, TFE3, and KCNQ5 were detected in two, one, and one patients, respectively. A maternally inherited PHF6 variant was detected in one patient with hyperpigmented skin. Compound heterozygous GTF3C5 variants were highlighted as strong candidates in the remaining patient. Exome sequencing, using patients' blood and skin samples is highly recommended as the first choice for detecting causative genetic variants of pigmentary mosaicism.

Deubiquitinating enzyme USP9X regulates metastasis and chemoresistance in triple-negative breast cancer by stabilizing Snail1

Breast cancer is one of the most common malignancies in women worldwide. Triple-negative breast cancer (TNBC) is a highly aggressive and metastatic subtype that has the characteristics of easy recurrence, poor prognosis as well as lack of targeted therapeutics. Snail1, a key factor regulating epithelial-mesenchymal transition (EMT) process, contributing to metastasis and chemoresistance in human cancers. However, the molecular mechanism of Snail1 stabilization in cancers is not fully understood. Here, we demonstrate that the deubiquitinating enzyme USP9X deubiquitinates and stabilizes Snail1, thereby promoting metastasis and chemoresistance. The depletion and pharmacological inhibition of USP9X by WP1130, an inhibitor of USP9X, downregulate endogenous Snail1 protein, inhibit cell migration, invasion, metastasis, and increase cellular sensitivity to cisplatin and paclitaxel both in vitro and in vivo, whereas the reconstitution of Snail1 in cells with USP9X depletion at least partially reverses these phenotypes. Overall, our study establishes the USP9X-Snail1 axis as an important regulatory mechanism of breast cancer metastasis and chemoresistance and provides a rationale for potential therapeutic interventions in the treatment of TNBC.

Exome and RNA-Seq analyses of an incomplete penetrance variant in USP9X in female-specific syndromic intellectual disability

Pathogenic variants in USP9X, on X chromosome, have been implicated in syndromic intellectual disability (ID) in both males and females with distinct craniofacial features. We report a truncating variant, c.885_889delAAAAG, p.(Lys296Serfs*4), in the USP9X gene with incomplete penetrance in two nontwin female siblings with phenotypic resemblance to female-specific syndromic ID (MIM 300969, also known as MRX99F). To investigate the possible genetic etiology of the reduced penetrance, X-inactivation, RNA-Seq, and full quad exome analyses were attempted, but failed to identify a promising candidate modifier. While the penetrance of pathogenic variants in USP9X in female appears to be high (95%) and the variants frequently occur de novo, incomplete penetrance should be considered.

Reciprocal Xp11.4p11.3 microdeletion/microduplication spanning USP9X, DDX3X, and CASK genes in two patients with syndromic intellectual disability

Only a few patients with deletions or duplications at Xp11.4, bridging USP9X, DDX3X, and CASK genes, have been described so far. Here, we report on a female harboring a de novo Xp11.4p11.3 deletion and a male with an overlapping duplication inherited from an unaffected mother, presenting with syndromic intellectual disability. We discuss the role of USP9X, DDX3X, and CASK genes in human development and describe the effects of Xp11.4 deletion and duplications in female and male patients, respectively.

Circ-USP9X Inhibition Reduces Oxidized Low-density Lipoprotein-induced Endothelial Cell Injury via the microRNA 599/Chloride Intracellular Channel 4 Axis

ABSTRACT

Atherosclerosis (AS) is the common pathological basis of cardiovascular disease. Circular RNA circ-USP9X (hsa_circ_0090231) has been discovered to be upregulated in oxidized low-density lipoprotein (ox-LDL)-induced human umbilical vein endothelial cells (HUVECs), but the role of circ-USP9X in ox-LDL-induced endothelial cell injury is indistinct. The purpose of the research was to investigate the role and regulatory mechanism of circ-USP9X in ox-LDL--induced endothelial cell injury. Expression of circ-USP9X was examined by quantitative real-time polymerase chain reaction. Loss-of-function experiments were performed to assess the impacts of circ-USP9X inhibition on viability, cell cycle progression, apoptosis, and tube formation, inflammation, and oxidative stress of ox-LDL-induced HUVEC. The regulatory mechanism of circ-USP9X predicted by bioinformatics analysis and verified by dual-luciferase reporter or RNA immunoprecipitation assays. We observed that circ-USP9X was upregulated in AS patients' serum and ox-LDL-induced HUVEC. Inhibition of circ-USP9X elevated viability, promoted cell cycle progression and angiopoiesis, and decreased apoptosis, inflammation, and oxidative stress of ox-LDL-induced HUVEC. Mechanically, circ-USP9X regulated chloride intracellular channel 4 (CLIC4) messenger RNA expression by sponging microRNA (miR)-599. Furthermore, miR-599 inhibitor overturned circ-USP9X silencing-mediated influence on ox-LDL-induced HUVEC injury. Also, CLIC4 overexpression reversed miR-599 elevation-mediated effect on ox-LDL-induced HUVEC injury. In conclusion, circ-USP9X silencing decreased ox-LDL-induced endothelial cell injury via the miR-599/CLIC4 axis, which offered a novel molecular mechanism to comprehend the pathology of AS.

Therapeutic inhibition of USP9x-mediated Notch signaling in triple-negative breast cancer

Triple-negative breast cancer (TNBC) is a breast cancer subtype that lacks targeted treatment options. The activation of the Notch developmental signaling pathway, which is a feature of TNBC, results in the secretion of proinflammatory cytokines and the recruitment of protumoral macrophages to the tumor microenvironment. While the Notch pathway is an obvious therapeutic target, its activity is ubiquitous, and predictably, anti-Notch therapies are burdened with significant on-target side effects. Previously, we discovered that, under conditions of cellular stress commonly found in the tumor microenvironment, the deubiquitinase USP9x forms a multiprotein complex with the pseudokinase tribbles homolog 3 (TRB3) that together activate the Notch pathway. Herein, we provide preclinical studies that support the potential of therapeutic USP9x inhibition to deactivate Notch. Using a murine TNBC model, we show that USP9x knockdown abrogates Notch activation, reducing the production of the proinflammatory cytokines, C-C motif chemokine ligand 2 (CCL2) and interleukin-1 beta (IL-1β). Concomitant with these molecular changes, a reduction in tumor inflammation, the augmentation of antitumor immune response, and the suppression of tumor growth were observed. The pharmacological inhibition of USP9x using G9, a partially selective, small-molecule USP9x inhibitor, reduced Notch activity, remodeled the tumor immune landscape, and reduced tumor growth without associated toxicity. Proving the role of Notch, the ectopic expression of the activated Notch1 intracellular domain rescued G9-induced effects. This work supports the potential of USP9x inhibition to target Notch in metabolically vulnerable tissues like TNBC, while sparing normal Notch-dependent tissues.

The deubiquitylase USP9X controls ribosomal stalling

When a ribosome stalls during translation, it runs the risk of collision with a trailing ribosome. Such an encounter leads to the formation of a stable di-ribosome complex, which needs to be resolved by a dedicated machinery. The initial stalling and the subsequent resolution of di-ribosomal complexes requires activity of Makorin and ZNF598 ubiquitin E3 ligases, respectively, through ubiquitylation of the eS10 and uS10 subunits of the ribosome. We have developed a specific small-molecule inhibitor of the deubiquitylase USP9X. Proteomics analysis, following inhibitor treatment of HCT116 cells, confirms previous reports linking USP9X with centrosome-associated protein stability but also reveals a loss of Makorin 2 and ZNF598. We show that USP9X interacts with both these ubiquitin E3 ligases, regulating their abundance through the control of protein stability. In the absence of USP9X or following chemical inhibition of its catalytic activity, levels of Makorins and ZNF598 are diminished, and the ribosomal quality control pathway is impaired.

The Role of ER Stress-Related Phenomena in the Biology of Malignant Peripheral Nerve Sheath Tumors

Malignant peripheral nerve sheath tumors (MPNST) are rare but one of the most aggressive types of cancer. Currently, there are no effective chemotherapy strategies for these malignancies. The inactivation of the neurofibromatosis type I (NF1) gene, followed by loss of TP53, is an early stage in MPNST carcinogenesis. NF1 is a negative regulator of the Ras proteins family, which are key factors in regulating cell growth, homeostasis and survival. Cell cycle dysregulation induces a stress phenotype, such as proteotoxic stress, metabolic stress, and oxidative stress, which should result in cell death. However, in the case of neoplastic cells, we observe not only the avoidance of apoptosis, but also the impact of stress factors on the treatment effectiveness. This review focuses on the pathomechanisms underlying MPNST cells physiology, and discusses the possible ways to develop a successful treatment based on the molecular background of the disease.

Deubiquitinases in hematological malignancies

Deubiquitinases (DUBs) are enzymes that control the stability, interactions or localization of most cellular proteins by removing their ubiquitin modification. In recent years, some DUBs, such as USP7, USP9X and USP10, have been identified as promising therapeutic targets in hematological malignancies. Importantly, some potent inhibitors targeting the oncogenic DUBs have been developed, showing promising inhibitory efficacy in preclinical models, and some have even undergone clinical trials. Different DUBs perform distinct function in diverse hematological malignancies, such as oncogenic, tumor suppressor or context-dependent effects. Therefore, exploring the biological roles of DUBs and their downstream effectors will provide new insights and therapeutic targets for the occurrence and development of hematological malignancies. We summarize the DUBs involved in different categories of hematological malignancies including leukemia, multiple myeloma and lymphoma. We also present the recent development of DUB inhibitors and their applications in hematological malignancies. Together, we demonstrate DUBs as potential therapeutic drug targets in hematological malignancies.

Molecular mechanisms of the microRNA-132 during tumor progressions

Cancer as one of the leading causes of human deaths has always been one of the main health challenges in the world. Despite recent advances in therapeutic and diagnostic methods, there is still a high mortality rate among cancer patients. Late diagnosis is one of the main reasons for the high ratio of cancer related deaths. Therefore, it is required to introduce novel early detection methods. Various molecular mechanisms are associated with the tumor progression and metastasis. MicroRNAs (miRNAs) are a class of non-coding RNAs (ncRNAs) family that has important functions in regulation of the cellular processes such as cell proliferation, apoptosis, and tumor progression. Moreover, they have higher stability in body fluids compared with mRNAs which can be introduced as non-invasive diagnostic markers in cancer patients. MiR-132 has important functions as tumor suppressor or oncogene in different cancers. In the present review, we have summarized all of the studies which have been reported the role of miR-132 during tumor progressions. We categorized the miR-132 target genes based on their cell and molecular functions. Although, it has been reported that the miR-132 mainly functions as a tumor suppressor, it has also oncogenic functions especially in pancreatic tumors. MiR-132 mainly exerts its roles during tumor progressions by regulation of the transcription factors and signaling pathways. Present review clarifies the tumor specific molecular mechanisms of miR-132 to introduce that as an efficient non-invasive diagnostic marker in various cancers.

CHIP-dependent regulation of the actin cytoskeleton is linked to neuronal cell membrane integrity

CHIP is an E3-ubiquitin ligase that contributes to healthy aging and has been characterized as neuroprotective. To elucidate dominant CHIP-dependent changes in protein steady-state levels in a patient-derived human neuronal model, CHIP function was ablated using gene-editing and an unbiased proteomic analysis conducted to compare knock-out and wild-type isogenic induced pluripotent stem cell (iPSC)-derived cortical neurons. Rather than a broad effect on protein homeostasis, loss of CHIP function impacted on a focused cohort of proteins from actin cytoskeleton signaling and membrane integrity networks. In support of the proteomics, CHIP knockout cells had enhanced sensitivity to induced membrane damage. We conclude that the major readout of CHIP function in cortical neurons derived from iPSC of a patient with elevate α-synuclein, Parkinson's disease and dementia, is the modulation of substrates involved in maintaining cellular "health". Thus, regulation of the actin cytoskeletal and membrane integrity likely contributes to the neuroprotective function(s) of CHIP.

Elevated USP9X drives early-to-late-stage oral tumorigenesis via stabilisation of anti-apoptotic MCL-1 protein and impacts outcome in oral cancers

BACKGROUND

Overexpression of anti-apoptotic MCL-1 protein in oral squamous cell carcinoma (OSCC) is linked to disease progression, therapy resistance and poor outcome. Despite its characteristic short half-life owing to ubiquitin-proteasome-dependent degradation, oral tumours frequently show elevated MCL-1 protein expression. Hence, we investigated the role of deubiquitinase USP9X in stabilising MCL-1 protein and its contribution to oral tumorigenesis.

METHODS

Expression of MCL-1 and USP9X was assessed by immunoblotting and immunohistochemistry in oral cancer cell lines and tissues. The association between MCL-1 and USP9X was confirmed by coimmunoprecipitation and immunofluorescence. Cell death assessment was performed by MTT, flow cytometry and clonogenic assays.

RESULTS

Both USP9X and MCL-1 are significantly elevated in oral premalignant lesions and oral tumours versus normal mucosa. USP9X interacts with and deubiquitinates MCL-1, thereby stabilising it. Pharmacological inhibition of USP9X potently induced cell death in OSCC cells in vitro and in vivo. The elevated expression of USP9X and MCL-1 correlated with poor prognosis in OSCC patients.

CONCLUSION

We demonstrate the oncogenic role of USP9X in driving early-to-late stages of oral tumorigenesis via stabilisation of MCL-1, suggesting its potential as a prognostic biomarker and therapeutic target in oral cancers.

Patent highlights February-March 2021

A snapshot of noteworthy recent developments in the patent literature of relevance to pharmaceutical and medical research and development.