USP7 interacts with and destabilizes oncoprotein SET

Oncoprotein SE translocation (SET) is frequently overexpressed in different types of tumors and correlated with poor prognosis of cancer patients. Targeting SET has been considered a promising strategy for cancer intervention. However, the mechanisms by which SET is regulated under cellular conditions are largely unknown. Here, by performing a tandem affinity purification-mass spectrometry (TAP-MS), we identify that the ubiquitin-specific protease 7 (USP7) forms a stable protein complex with SET in cancer cells. Further analyses reveal that the acidic domain of SET directly binds USP7 while both catalytic domain and ubiquitin-like (UBL) domains of USP7 are required for SET binding. Knockdown of USP7 has no effect on the mRNA level of SET. However, we surprisingly find that USP7 depletion leads to a dramatic elevation of SET protein levels, suggesting that USP7 plays a key role in destabilizing oncoprotein SET, possibly through an indirect mechanism. To our knowledge, our data report the first deubiquitinase (DUB) that physically associates with oncoprotein SET and imply an unexpected regulatory effect of USP7 on SET stability.

Hao-Fountain syndrome: 32 novel patients reveal new insights into the clinical spectrum

Hao-Fountain syndrome (HAFOUS, OMIM: #616863) is a neurodevelopmental disorder caused by pathogenic variants in the gene USP7 coding for USP7, a protein involved in several crucial cellular homeostatic mechanisms and the recently described MUST complex. The phenotype of HAFOUS is insufficiently understood, yet there is a great need to better understand the spectrum of disease, genotype-phenotype correlations, and disease trajectories. We now present a larger cohort of 32 additional individuals and provide further clinical information about six previously reported individuals. A questionnaire-based study was performed to characterize the phenotype of Hao-Fountain syndrome more clearly, to highlight new traits, and to better distinguish the disease from related neurodevelopmental disorders. In addition to confirming previously described features, we report hyperphagia and increased body weight in a subset of individuals. HAFOUS patients present an increased rate of birth complications, congenital anomalies, and abnormal pain thresholds. Speech impairment emerges as a potential hallmark of Hao-Fountain syndrome. Cognitive testing reports reveal borderline intellectual functioning on average, although some individuals score in the range of intellectual disability. Finally, we created a syndrome-specific severity score. This score neither indicates a sex- nor age-specific difference of clinical severity, yet highlights a more severe outcome when amino acid changes colocalize to the catalytic domain of the USP7 protein.

USP7 as an emerging therapeutic target: A key regulator of protein homeostasis

Maintaining protein balance within a cell is essential for proper cellular function, and disruptions in the ubiquitin-proteasome pathway, which is responsible for degrading and recycling unnecessary or damaged proteins, can lead to various diseases. Deubiquitinating enzymes play a vital role in regulating protein homeostasis by removing ubiquitin chains from substrate proteins, thereby controlling important cellular processes, such as apoptosis and DNA repair. Among these enzymes, ubiquitin-specific protease 7 (USP7) is of particular interest. USP7 is a cysteine protease consisting of a TRAF region, catalytic region, and C-terminal ubiquitin-like (UBL) region, and it interacts with tumor suppressors, transcription factors, and other key proteins involved in cell cycle regulation and epigenetic control. Moreover, USP7 has been implicated in the pathogenesis and progression of various diseases, including cancer, inflammation, neurodegenerative conditions, and viral infections. Overall, characterizing the functions of USP7 is crucial for understanding the pathophysiology of diverse diseases and devising innovative therapeutic strategies. This article reviews the structure and function of USP7 and its complexes, its association with diseases, and its known inhibitors and thus represents a valuable resource for advancing USP7 inhibitor development and promoting potential future treatment options for a wide range of diseases.

Variety in the USP deubiquitinase catalytic mechanism

The ubiquitin-specific protease (USP) family of deubiquitinases (DUBs) controls cellular ubiquitin-dependent signaling events. This generates therapeutic potential, with active-site inhibitors in preclinical and clinical studies. Understanding of the USP active site is primarily guided by USP7 data, where the catalytic triad consists of cysteine, histidine, and a third residue (third critical residue), which polarizes the histidine through a hydrogen bond. A conserved aspartate (fourth critical residue) is directly adjacent to this third critical residue. Although both critical residues accommodate catalysis in USP2, these residues have not been comprehensively investigated in other USPs. Here, we quantitatively investigate their roles in five USPs. Although USP7 relies on the third critical residue for catalysis, this residue is dispensable in USP1, USP15, USP40, and USP48, where the fourth critical residue is vital instead. Furthermore, these residues vary in importance for nucleophilic attack. The diverging catalytic mechanisms of USP1 and USP7 are independent of substrate and retained in cells for USP1. This unexpected variety of catalytic mechanisms in this well-conserved protein family may generate opportunities for selective targeting of individual USPs.

DDX4 enhances antiviral activity of type I interferon by disrupting interaction of USP7/SOCS1 and promoting degradation of SOCS1

DEAD-box helicase (DDX) family members play differential roles in regulating innate antiviral immune response. However, the physiological roles played by DDX4 in antiviral innate immunity remain unclear. In this study, we unveiled that DDX4 acts as a positive regulatory molecule of Type-I interferon (IFN-I)-mediated antiviral activity. Our findings demonstrate that IFN-I upregulates DDX4 protein levels, and subsequently, overexpression of DDX4 enhances the IFN-I-mediated signaling pathway. This creates a positive feedback loop that amplifies the antiviral response. DDX4 was found to bind with deubiquitinase ubiquitin-specific protease 7 (USP7), leading to the disruption of the interaction between USP7 and suppressor of cytokine signaling 1 (SOCS1) and the subsequent degradation of SOCS1. This process enhances the antiviral function of IFN-I. Our findings provide new insights into the regulatory role of DDX4 in the IFN-I response.IMPORTANCEDDX4, identified as a putative RNA helicase that modulates RNA secondary structure through RNA binding, is primarily acknowledged for its role in regulating mRNA translation within the germline. Nevertheless, the extent of DDX4's involvement in the antiviral innate immune response remains largely unexplored. This study presents evidence of a previously unrecognized positive feedback loop between DDX4 and the antiviral response, suggesting that disruption of this loop may serve as a novel mechanism for viral evasion. Furthermore, our findings elucidate a positive regulatory mechanism by which the DDX4/USP7/SOCS1 axis mediates the antiviral activity of Type-I interferon, which provides new insight into strategies for improving the efficacy of IFN-based antiviral therapy.

Deubiquitinase USP7 stabilizes KDM5B and promotes tumor progression and cisplatin resistance in nasopharyngeal carcinoma through the ZBTB16/TOP2A axis

Cisplatin-based chemotherapy improves the control of distant metastases in patients with nasopharyngeal carcinoma (NPC); however, around 30% of patients fail treatment due to acquired drug resistance. Epigenetic regulation is known to contribute to cisplatin resistance; nevertheless, the underlying mechanisms remain poorly understood. Here, we showed that lysine-specific demethylase 5B (KDM5B) was overexpressed and correlates with tumor progression and cisplatin resistance in patients with NPC. We also showed that specific inhibition of KDM5B impaired the progression of NPC and reverses cisplatin resistance, both in vitro and in vivo. Moreover, we found that KDM5B inhibited the expression of ZBTB16 by directly reducing H3K4me3 at the ZBTB16 promoter, which subsequently increased the expression of Topoisomerase II- α (TOP2A) to confer cisplatin resistance in NPC. In addition, we showed that the deubiquitinase USP7 was critical for deubiquitinating and stabilizing KDM5B. More importantly, the deletion of USP7 increased sensitivity to cisplatin by disrupting the stability of KDM5B in NPC cells. Therefore, our findings demonstrated that USP7 stabilized KDM5B and promoted cisplatin resistance through the ZBTB16/TOP2A axis, suggesting that targeting KDM5B may be a promising cisplatin-sensitization strategy in the treatment of NPC.

DNA methylation episignature, extension of the clinical features, and comparative epigenomic profiling of Hao-Fountain syndrome caused by variants in USP7

PURPOSE

Hao-Fountain syndrome (HAFOUS) is a neurodevelopmental disorder caused by pathogenic variants in USP7. HAFOUS is characterized by developmental delay, intellectual disability, speech delay, behavioral abnormalities, autism spectrum disorder, seizures, hypogonadism, and mild dysmorphic features. We investigated the phenotype of 18 participants with HAFOUS and performed DNA methylation (DNAm) analysis, aiming to generate a diagnostic biomarker. Furthermore, we performed comparative analysis with known episignatures to gain more insight into the molecular pathophysiology of HAFOUS.

METHODS

We assessed genomic DNAm profiles of 18 individuals with pathogenic variants and variants of uncertain significance (VUS) in USP7 to map and validate a specific episignature. The comparison between the USP7 cohort and 56 rare genetic disorders with earlier reported DNAm episignatures was performed with statistical and functional correlation.

RESULTS

We mapped a sensitive and specific DNAm episignature for pathogenic variants in USP7 and utilized this to reclassify the VUS. Comparative epigenomic analysis showed evidence of HAFOUS similarity to a number of other rare genetic episignature disorders.

CONCLUSION

We discovered a sensitive and specific DNAm episignature as a robust diagnostic biomarker for HAFOUS that enables VUS reclassification in USP7. We also expand the phenotypic spectrum of 9 new and 5 previously reported individuals with HAFOUS.

Williams-Beuren syndrome in pediatric T-cell acute lymphoblastic leukemia: A rare case report and review of literature

BACKGROUND

Williams-Beuren syndrome (WBS) is a rare genetic disorder caused by hemizygous microdeletion of contiguous genes on chromosome 7q11.23. Although the phenotype features extensive heterogeneity in severity and performance, WBS is not considered to be a predisposing factor for cancer development. Currently, hematologic cancers, mainly Burkitt lymphoma, are rarely reported in patients with WBS. Here in, we report a unique case of T-cell acute lymphoblastic leukemia in a male child with WBS.

METHODS

This retrospective study analyzed the clinical data of this case receiving chemotherapy were analyzed. This is a retrospective study.

RESULTS

The patient, who exhibited a typical WBS phenotype and presented with hemorrhagic spots. Chromosomal genome-wide chip analysis (CMA) revealed abnormalities on chromosomes 7 and 9. The fusion gene STIL-TAL1 and mutations in BCL11B, NOTCH1, and USP7 have also been found and all been associated with the occurrence of T-cell leukemia. The patient responded well to the chemotherapy.

CONCLUSION

To the best of our knowledge, this is the first reported case of WBS in T-cell acute lymphoblastic leukemia. We want to emphasize that the occurrence of leukemia in this patient might be related to the loss of 7q11.23 and microdeletion of 9p21.3 (including 3 TSGs), but the relationship between WBS and malignancy remains unclear. Further studies are required to clarify the relationship between WBS and malignancy.

Ubiquitination-specific protease 7 enhances stemness of hepatocellular carcinoma by stabilizing basic transcription factor 3

This study aims to explore the molecular regulation mechanism of ubiquitination-specific protease 7 (USP7) in facilitating the stemness properties of hepatocellular carcinoma (HCC). Gain-of-function and loss-of-function assays were conducted in SK-Hep1 and HepG2 cells transfected with USP7 overexpression/knockdown plasmids and USP7 inhibitor P22077. The proliferation, migration, invasion, and self-renewal capacity of hepatocellular carcinoma cells were detected by CCK-8, colony formation, Transwell, scratch, and tumor sphere formation, respectively. MS was performed to identify the potential substrate of USP7 following P22077 treatment. Co-IP assay was used to verify the interaction between USP7 and basic transcription factor 3 (BTF3) in HCC cells. The overexpression of USP7 could promote the proliferation, migration, invasion, and colony formation capacity of SK-Hep1 and HepG2 cells. Additionally, ectopic UPS7 enhanced the epithelial-mesenchymal transition (EMT) and stem-like characteristics of the HCC cells. In contrast, USP7 depletion by knockdown of USP7 or administrating inhibitor P22077 significantly inhibited these malignant phenotypes of SK-Hep1 and HepG2 cells. Following MS analysis, BTF3 was identified as a potential substrate for USP7. USP7 could interact with BTF3 and upregulate its protein level, while USP7 depletion significantly upregulated the ubiquitination levels. Overexpression of BTF3 partially rescue the inhibitory effects of USP7 depletion on the malignant phenotypes and stemness properties of SK-Hep1 and HepG2 cells. USP7 can promote the stemness and malignant phenotype of HCC by stabilizing BTF3.

Non-canonical regulation of the reactivation of an oncogenic herpesvirus by the OTUD4-USP7 deubiquitinases

Deubiquitinases (DUBs) remove ubiquitin from substrates and play crucial roles in diverse biological processes. However, our understanding of deubiquitination in viral replication remains limited. Employing an oncogenic human herpesvirus Kaposi's sarcoma-associated herpesvirus (KSHV) to probe the role of protein deubiquitination, we found that Ovarian tumor family deubiquitinase 4 (OTUD4) promotes KSHV reactivation. OTUD4 interacts with the replication and transcription activator (K-RTA), a key transcription factor that controls KSHV reactivation, and enhances K-RTA stability by promoting its deubiquitination. Notably, the DUB activity of OTUD4 is not required for K-RTA stabilization; instead, OTUD4 functions as an adaptor protein to recruit another DUB, USP7, to deubiquitinate K-RTA and facilitate KSHV lytic reactivation. Our study has revealed a novel mechanism whereby KSHV hijacks OTUD4-USP7 deubiquitinases to promote lytic reactivation, which could be potentially harnessed for the development of new antiviral therapies.

SP1-activated USP27X-AS1 promotes hepatocellular carcinoma progression via USP7-mediated AKT stabilisation

BACKGROUND

Hepatocellular carcinoma (HCC) continues to pose a significant threat to patient survival. Emerging evidence underscores the pivotal involvement of long non-coding RNAs (lncRNAs) in the cancer process. Nevertheless, our understanding of the roles and processes of lncRNAs in HCC remains limited.

METHODS

The expression level of USP27X-AS1 was assessed in an HCC patient cohort through a combination of bioinformatics analysis and qRT-PCR. Subsequent biological experiments were conducted to delve into the functional aspects of USP27X-AS1. Additional molecular biology techniques, including RNA pulldown and RNA immunoprecipitation (RIP), were employed to elucidate the potential mechanisms involving USP27X-AS1 in HCC. Finally, CUT-RUN assay and other investigations were carried out to determine the factors contributing to the heightened expression of USP27X-AS1 in HCC.

RESULTS

High expression of the novel oncogene USP27X-AS1 predicted poor prognosis in HCC patients. Further investigation confirmed that USP27X-AS1 promoted the proliferation and metastasis of HCC by enabling USP7 to interact with AKT, which reduced level of AKT poly-ubiquitylation and enhanced AKT protein stability, which improves protein stabilisation of AKT and promotes the progression of HCC. Moreover, we also revealed that SP1 binds to USP27X-AS1 promoter to activate its transcription.

CONCLUSIONS

Novel oncogenic lncRNA USP27X-AS1 promoted HCC progression via recruiting USP7 to deubiquitinate AKT. SP1 transcriptionally activated USP27X-AS1 expression. These findings shed light on HCC and pointed to USP27X-AS1 as a potential predictive biomarker and treatment target for the malignancy.

USP7 reduces the level of nuclear DICER, impairing DNA damage response and promoting cancer progression

Endoribonuclease DICER is an RNase III enzyme that mainly processes microRNAs in the cytoplasm but also participates in nuclear functions such as chromatin remodelling, epigenetic modification and DNA damage repair. The expression of nuclear DICER is low in most human cancers, suggesting a tight regulation mechanism that is not well understood. Here, we found that ubiquitin carboxyl-terminal hydrolase 7 (USP7), a deubiquitinase, bounded to DICER and reduced its nuclear protein level by promoting its ubiquitination and degradation through MDM2, a newly identified E3 ubiquitin-protein ligase for DICER. This USP7-MDM2-DICER axis impaired histone γ-H2AX signalling and the recruitment of DNA damage response (DDR) factors, possibly by influencing the processing of small DDR noncoding RNAs. We also showed that this negative regulation of DICER by USP7 via MDM2 was relevant to human tumours using cellular and clinical data. Our findings revealed a new way to understand the role of DICER in malignant tumour development and may offer new insights into the diagnosis, treatment and prognosis of cancers.

USP7 promotes non-small-cell lung cancer cell glycolysis and survival by stabilizing and activating c-Abl

BACKGROUND

Abelson tyrosine kinase (c-Abl) is frequently mutated and highly expressed, and promotes non-small-cell lung cancer (NSCLC) survival, metastasis and tumorigenesis. c-Abl could also be modified through ubiquitination, but the underlying mechanism is not well understood.

METHODS

Mass spectrometry assays were performed to search c-Abl deubiquitination enzymes. The molecular mechanism was determined using Co-IP assays, pull-down assays, Western blotting upon gene knockdown or overexpression. Cell lines and animal models were used to investigate the role of c-Abl and USP7 in NSCLC. EdU staining assay and Transwell assay were performed to evaluate the proliferation and migration ability of NSCLC cells, respectively.

RESULTS

Ubiquitin-specific protease 7 (USP7) is found to upregulate c-Abl via the deubiquitinase screen. USP7 interacts with c-Abl and decreases its K48-linked polyubiquitination, thereby increasing the stability of c-Abl. In addition to the wild-type one, c-Abl mutants can also be deubiquitinated and stabilized by USP7. Moreover, USP7 promotes c-Abl accumulation in cytoplasm by increasing its binding to 14-3-3α/β and activates the oncogenic c-Abl signalling pathway. Furthermore, the USP7/c-Abl axis promotes NSCLC cell glycolysis by direct phosphorylating and stabilizing hexokinase-2 (HK2). Knockdown of USP7 or c-Abl suppresses NSCLC cell glycolysis and reduces lactate production. Further studies revealed that overexpression of USP7 facilitates NSCLC cell growth and metastasis as well as xenograft growth in nude mice, while these activities are suppressed with USP7 or c-Abl being knocked down.

CONCLUSIONS

USP7 is a deubiquitinase of c-Abl and upregulates its oncogenic activity. USP7 promotes NSCLC cell metabolism by activating c-Abl and HK2. Targeting the USP7/c-Abl/HK2 axis might be a potential strategy to the precision therapy of NSCLC.

USP7-mediated JUND suppresses RCAN2 transcription and elevates NFATC1 to enhance stem cell property in colorectal cancer

Cancer stem cells (CSCs) encompass a subset of highly aggressive tumor cells that are involved in tumor initiation and progression. This study investigates the function of regulator of calcineurin 2 (RCAN2) in the stem cell property in colorectal cancer (CRC). By analyzing four GEO datasets, we obtained RCAN2 as a stemness-related gene in CRC. RCAN2 was poorly expressed in CRC tissues and cells, especially in CSCs. RCAN2 restoration reduced calcineurin activity and promoted phosphorylation and degradation of nuclear factor of activated T cells 1 (NFATC1) protein, leading to reduced stemness of CSCs. JunD proto-oncogene (JUND), whose protein level was increased in CRC samples and CRC stem cells, bound to RCAN2 and suppressed its transcription. The abundant ubiquitin specific peptidase 7 (USP7) in CSCs enhanced JUND protein stability through deubiquitination modification. Lentivirus-mediated knockdown of USP7 or JUND also blocked the calcineurin-NFATC1 signaling and reduced the protein levels of stemness-related proteins. Moreover, the USP7 knockdown weakened the colony/sphere formation ability as well as the tumorigenicity of CSCs, and it reduced the CSC content in xenograft tumors. However, further restoration of JUND rescued the stemness of the CSCs. Overall, this study demonstrates that USP7-mediated JUND suppresses RCAN2 transcription and activates NFATC1 to enhance stem cell property in CRC. 1. RCAN2 is poorly expressed in CRC tissues and cells and especially in CSCs. 2. RCAN2 reduces stemness of CSCs by blocking calcineurin-NFATC1 signal transduction. 3. JUND binds to RCAN2 promoter to suppresses RCAN2 transcription. 4. USP7 enhances JUND protein stability via deubiquitination modification. 5. Downregulation of USP7 or JUND restores RCAN2 level and suppresses stemness of CSCs.

AML with complex karyotype: extreme genomic complexity revealed by combined long-read sequencing and Hi-C technology

Acute myeloid leukemia with complex karyotype (CK-AML) is associated with poor prognosis, which is only in part explained by underlying TP53 mutations. Especially in the presence of complex chromosomal rearrangements, such as chromothripsis, the outcome of CK-AML is dismal. However, this degree of complexity of genomic rearrangements contributes to the leukemogenic phenotype and treatment resistance of CK-AML remains largely unknown. Applying an integrative workflow for the detection of structural variants (SVs) based on Oxford Nanopore (ONT) genomic DNA long-read sequencing (gDNA-LRS) and high-throughput chromosome confirmation capture (Hi-C) in a well-defined cohort of CK-AML identified regions with an extreme density of SVs. These rearrangements consisted to a large degree of focal amplifications enriched in the proximity of mammalian-wide interspersed repeat elements, which often result in oncogenic fusion transcripts, such as USP7::MVD, or the deregulation of oncogenic driver genes as confirmed by RNA-seq and ONT direct complementary DNA sequencing. We termed this novel phenomenon chromocataclysm. Thus, our integrative SV detection workflow combing gDNA-LRS and Hi-C enables to unravel complex genomic rearrangements at a very high resolution in regions hard to analyze by conventional sequencing technology, thereby providing an important tool to identify novel important drivers underlying cancer with complex karyotypic changes.

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.

Extracellular vesicles from bone marrow mesenchymal stem cells alleviate osteoporosis in mice through USP7-mediated YAP1 protein stability and the Wnt/β-catenin pathway

Mesenchymal stem cells (MSCs) and their derived extracellular vesicles (EVs) have emerged as promising tools for promoting bone regeneration. This study investigates the functions of EVs derived from bone marrow-derived MSCs (BMSCs) in osteoporosis (OP) and the molecular mechanism. EVs were isolated from primary BMSCs in mice. A mouse model with OP was induced by ovariectomy. Treatment with EVs restored bone mass and strength, attenuated trabecular bone loss and cartilage damage, and increased osteogenesis while suppressing osteoclastogenesis in ovariectomized mice. In vitro, the EVs treatment improved the osteogenic differentiation of MC-3T3 while inhibiting osteoclastic differentiation of RAW264.7 cells. Microarray analysis revealed a significant upregulation of ubiquitin specific peptidase 7 (USP7) expression in mouse bone tissues following EV treatment. USP7 was found to interact with Yes1 associated transcriptional regulator (YAP1) and stabilize YAP1 protein through deubiquitination modification. YAP1-related genes were enriched in the Wnt/β-catenin signaling, and overexpression of YAP1 promoted the nuclear translocation of β-catenin. Functional experiments underscored the critical role of maintaining USP7, YAP1, and β-catenin levels in the pro-osteogenic and anti-osteoclastogenic properties of the BMSC-EVs. In conclusion, this study demonstrates that USP7, delivered by BMSC-derived EVs, stabilizes YAP1 protein, thereby ameliorating bone formation in OP through the Wnt/β-catenin activation.

Hypoxia-induced SKA3 promoted cholangiocarcinoma progression and chemoresistance by enhancing fatty acid synthesis via the regulation of PAR-dependent HIF-1a deubiquitylation

BACKGROUND

Spindle and kinetochore-associated complex subunit 3 (SKA3) plays an important role in cell proliferation by regulating the separation of chromosomes and their division into daughter cells. Previous studies demonstrated that SKA3 was strongly implicated in tumor development and progression. However, the roles of SKA3 in cholangiocarcinoma (CCA) and the underlying mechanisms remain unclear.

METHODS

Next-generation sequencing (NGS) was performed with paired CCA tissues and normal adjacent tissues (NATs). SKA3 was chose to be the target gene because of its remarkably upregulation and unknown function in cholangiocarcinoma in TCGA datasets, GSE107943 datasets and our sequencing results. RT-PCR and immunohistochemistry staining were used to detect the expression of SKA3 in paired CCA tissues and normal adjacent tissues. The SKA3 knockdown and overexpression cell line were constructed by small interfering RNA and lentivirus vector transfection. The effect of SKA3 on the proliferation of cholangiocarcinoma under hypoxic conditions was detected by experiments in vitro and in vivo. RNA-seq was used to find out the differentially expressed pathways in cholangiocarcinoma proliferation under hypoxia regulated by SKA3. IP/MS analysis and Western blot assays were used to explore the specific mechanism of SKA3 in regulating the expression of HIF-1a under hypoxia.

RESULTS

SKA3 was up-regulated in NGS, TCGA and GSE107943 databases and was associated with poor prognosis. Functional experiments in vitro and in vivo showed that hypoxia-induced SKA3 promoted cholangiocarcinoma cell proliferation. RNA-sequencing was performed and verified that SKA3 enhanced fatty acid synthesis by up-regulating the expression of key fatty acid synthase, thus promoting cholangiocarcinoma cell proliferation under hypoxic conditions. Further studies indicated that under hypoxic conditions, SKA3 recruited PARP1 to bind to HIF-1a, thus enhancing the poly ADP-ribosylation (PARylation) of HIF-1a. This PARylation enhanced the binding between HIF-1a and USP7, which triggered the deubiquitylation of HIF-1a under hypoxic conditions. Additionally, PARP1 and HIF-1a were upregulated in CCA and promoted CCA cell proliferation. SKA3 promoted CCA cell proliferation and fatty acid synthesis via the PARP1/HIF-1a axis under hypoxic conditions. High SKA3 and HIF-1a expression levels were associated with poor prognosis after surgery.

CONCLUSION

Hypoxia-induced SKA3 promoted CCA progression by enhancing fatty acid synthesis via the regulation of PARylation-dependent HIF-1a deubiquitylation. Furthermore, increased SKA3 level enhanced chemotherapy-resistance to gemcitabine-based regimen under hypoxic conditions. SKA3 and HIF-1a could be potential oncogenes and significant biomarkers for the analysis of CCA patient prognosis.

Structural and functional characterization of USP47 reveals a hot spot for inhibitor design

USP47 is widely involved in tumor development, metastasis, and other processes while performing a more regulatory role in inflammatory responses, myocardial infarction, and neuronal development. In this study, we investigate the functional and biochemical properties of USP47, whereby depleting USP47 inhibited cancer cell growth in a p53-dependent manner-a phenomenon that enhances during the simultaneous knockdown of USP7. Full-length USP47 shows higher deubiquitinase activity than the catalytic domain. The crystal structures of the catalytic domain, in its free and ubiquitin-bound states, reveal that the misaligned catalytic triads, ultimately, become aligned upon ubiquitin-binding, similar to USP7, thereby becoming ready for catalysis. Yet, the composition and lengths of BL1, BL2, and BL3 of USP47 differ from those for USP7, and they contribute to the observed selectivity. Our study provides molecular details of USP47 regulation, substrate recognition, and the hotspots for drug discovery by targeting USP47.

USP7 Inhibition Suppresses Neuroblastoma Growth via Induction of p53-Mediated Apoptosis and EZH2 and N-Myc Downregulation

Neuroblastoma (NB) is a pediatric malignancy originating from neural crest cells of the sympathetic nervous system that accounts for 15% of all pediatric cancer deaths. Despite advances in treatment, high-risk NB remains difficult to cure, highlighting the need for novel therapeutic approaches. Ubiquitin-specific protease 7 (USP7) is a deubiquitinase that plays a critical role in tumor suppression and DNA repair, and USP7 overexpression has been associated with tumor aggressiveness in a variety of tumors, including NB. Therefore, USP7 is a potential therapeutic target for NB. The tumor suppressor p53 is a known target of USP7, and therefore reactivation of the p53 pathway may be an effective therapeutic strategy for NB treatment. We hypothesized that inhibition of USP7 would be effective against NB tumor growth. Using a novel USP7 inhibitor, Almac4, we have demonstrated significant antitumor activity, with significant decreases in both cell proliferation and cell viability in TP53 wild-type NB cell lines. USP7 inhibition in NB cells activated the p53 pathway via USP7 and MDM2 degradation, leading to reduced p53 ubiquitination and increased p53 expression in all sensitive NB cells. In addition, USP7 inhibition led to decreased N-myc protein levels in both MYCN-amplified and -nonamplified NB cell lines, but no correlation was observed between MYCN amplification and treatment response. USP7 inhibition induced apoptosis in all TP53 wild-type NB cell lines. USP7 inhibition also induced EZH2 ubiquitination and degradation. Lastly, the combination of USP7 and MDM2 inhibition showed enhanced efficacy. Our data suggests that USP7 inhibition may be a promising therapeutic strategy for children with high-risk and relapsed NB.

MLF2 Negatively Regulates P53 and Promotes Colorectal Carcinogenesis

Inactivation of the p53 pathway is linked to a variety of human cancers. As a critical component of the p53 pathway, ubiquitin-specific protease 7 (USP7) acts as a deubiquitinase for both p53 and its ubiquitin E3 ligase mouse double minute 2 homolog. Here, myeloid leukemia factor 2 (MLF2) is reported as a new negative regulator of p53. MLF2 interacts with both p53 and USP7. Via these interactions, MLF2 inhibits the binding of USP7 to p53 and antagonizes USP7-mediated deubiquitination of p53, thereby leading to p53 destabilization. Functionally, MLF2 plays an oncogenic role in colorectal cancer, at least partially, via the negative regulation of p53. Clinically, MLF2 is elevated in colorectal cancer and its high expression is associated with poor prognosis in patients with colorectal cancer. In wild-type-p53-containing colorectal cancer, MLF2 and p53 expressions are inversely correlated. These findings establish MLF2 as an important suppressor of p53 function. The study also reveals a critical role for the MLF2-p53 axis in promoting colorectal carcinogenesis.

Elastic network models and molecular dynamic simulations reveal the molecular basis of allosteric regulation in ubiquitin-specific protease 7 (USP7)

Ubiquitin-specific protease 7 (USP7) is one of the most abundant deubiquitinases and plays an important role in various malignant tumors. However, the molecular mechanisms underlying USP7's structures, dynamics, and biological significance are yet to be investigated. In this study, we constructed the full-length models of USP7 in both the extended and compact state, and applied elastic network models (ENM), molecular dynamics (MD) simulations, perturbation response scanning (PRS) analysis, residue interaction networks as well as allosteric pocket prediction to investigate allosteric dynamics in USP7. Our analysis of intrinsic and conformational dynamics revealed that the structural transition between the two states is characterized by global clamp motions, during which the catalytic domain (CD) and UBL4-5 domain exhibit strong negative correlations. The PRS analysis, combined with the analysis of disease mutations and post-translational modifications (PTMs) further highlighted the allosteric potential of the two domains. The residue interaction network based on MD simulations captured an allosteric communication path which starts at CD domain and ends at UBL4-5 domain. Moreover, we identified a pocket at the TRAF-CD interface as a high-potential allosteric site for USP7. Overall, our studies not only provide molecular insights into the conformational changes of USP7, but also aid in the design of allosteric modulators that target USP7.

RNF4 and USP7 cooperate in ubiquitin-regulated steps of DNA replication

DNA replication requires precise regulation achieved through post-translational modifications, including ubiquitination and SUMOylation. These modifications are linked by the SUMO-targeted E3 ubiquitin ligases (STUbLs). Ring finger protein 4 (RNF4), one of only two mammalian STUbLs, participates in double-strand break repair and resolving DNA-protein cross-links. However, its role in DNA replication has been poorly understood. Using CRISPR/Cas9 genetic screens, we discovered an unexpected dependency of RNF4 mutants on ubiquitin specific peptidase 7 (USP7) for survival in TP53-null retinal pigment epithelial cells. TP53-/-/RNF4-/-/USP7-/- triple knockout (TKO) cells displayed defects in DNA replication that cause genomic instability. These defects were exacerbated by the proteasome inhibitor bortezomib, which limited the nuclear ubiquitin pool. A shortage of free ubiquitin suppressed the ataxia telangiectasia and Rad3-related (ATR)-mediated checkpoint response, leading to increased cell death. In conclusion, RNF4 and USP7 work cooperatively to sustain a functional level of nuclear ubiquitin to maintain the integrity of the genome.

USP7 imparts partial EMT state in colorectal cancer by stabilizing the RNA helicase DDX3X and augmenting Wnt/β-catenin signaling

Epithelial mesenchymal transition (EMT) is a fundamental and highly regulated process that is normally observed during embryonic development and tissue repair but is deregulated during advanced cancer. Classically, through the process of EMT, cancer cells gradually transition from a predominantly epithelial phenotype to a more invasive mesenchymal phenotype. Increasing studies have, however, brought into light the existence of unique intermediary states in EMT, often referred to as partial EMT states. Through our studies we have found the deubiquitinase USP7 to be strongly associated with the development of such a partial EMT state in colon cancer cells, characterized by the acquisition of mesenchymal characteristics but without the reduction in epithelial markers. We found USP7 to be overexpressed in colon adenocarcinomas and to be closely associated with advancing tumor stage. We found that functional inhibition or knockdown of USP7 is associated with a marked reduction in mesenchymal markers and in overall migration potential of cancer cells. Starting off with a proteomics-based approach we were able to identify and later on verify the DEAD box RNA helicase DDX3X to be an interacting partner of USP7. We then went on to show that USP7, through the stabilization of DDX3X, augments Wnt/β-catenin signaling, which has previously been shown to be greatly associated with colorectal cancer cell invasiveness. Our results indicate USP7 as a novel key player in establishing a partial mesenchymal phenotype in colorectal cancer.

USP7 inactivation suppresses APC-mutant intestinal hyperproliferation and tumor development

Adenomatous polyposis coli (APC) mutation is the hallmark of colorectal cancer (CRC), resulting in constitutive WNT activation. Despite decades of research, targeting WNT signaling in cancer remains challenging due to its on-target toxicity. We have previously shown that the deubiquitinating enzyme USP7 is a tumor-specific WNT activator in APC-truncated cells by deubiquitinating and stabilizing β-catenin, but its role in gut tumorigenesis is unknown. Here, we show in vivo that deletion of Usp7 in Apc-truncated mice inhibits crypt hyperproliferation and intestinal tumor development. Loss of Usp7 prolongs the survival of the sporadic intestinal tumor model. Genetic deletion, but not pharmacological inhibition, of Usp7 in Apc+/- intestine induces colitis and enteritis. USP7 inhibitor treatment suppresses growth of patient-derived cancer organoids carrying APC truncations in vitro and in xenografts. Our findings provide direct evidence that USP7 inhibition may offer a safe and efficacious tumor-specific therapy for both sporadic and germline APC-mutated CRC.

Ubiquitin-Specific Proteases (USPs) and Metabolic Disorders

Ubiquitination and deubiquitination are reversible processes that modify the characteristics of target proteins, including stability, intracellular localization, and enzymatic activity. Ubiquitin-specific proteases (USPs) constitute the largest deubiquitinating enzyme family. To date, accumulating evidence indicates that several USPs positively and negatively affect metabolic diseases. USP22 in pancreatic β-cells, USP2 in adipose tissue macrophages, USP9X, 20, and 33 in myocytes, USP4, 7, 10, and 18 in hepatocytes, and USP2 in hypothalamus improve hyperglycemia, whereas USP19 in adipocytes, USP21 in myocytes, and USP2, 14, and 20 in hepatocytes promote hyperglycemia. In contrast, USP1, 5, 9X, 14, 15, 22, 36, and 48 modulate the progression of diabetic nephropathy, neuropathy, and/or retinopathy. USP4, 10, and 18 in hepatocytes ameliorates non-alcoholic fatty liver disease (NAFLD), while hepatic USP2, 11, 14, 19, and 20 exacerbate it. The roles of USP7 and 22 in hepatic disorders are controversial. USP9X, 14, 17, and 20 in vascular cells are postulated to be determinants of atherosclerosis. Moreover, mutations in the Usp8 and Usp48 loci in pituitary tumors cause Cushing syndrome. This review summarizes the current knowledge about the modulatory roles of USPs in energy metabolic disorders.

USP7 mediates TRAF4 deubiquitination to facilitate the malignant phenotype of ovarian cancer via the RSK4/PI3K/AKT axis

BACKGROUND

Ubiquitin-specific peptidase 7 (USP7) is upregulated in multiple human cancers, including ovarian cancer; however, its functional role in the latter remains largely unknown.

METHODS

We conducted quantitative real-time PCR to detect the expression of USP7, TRAF4, and RSK4 in ovarian cancer cell lines. In addition, Western blotting served to determine USP7, TRAF4, RSK4, PI3K, and AKT (protein kinase B,PKB) protein levels and USP7 expression in the tissues was detected by immunohistochemical staining. The 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide assay was used to evaluate cell viability, transwell assays to evaluate cell migration and invasion, and co-immunoprecipitation to evaluate TRAF4 ubiquitination.

RESULTS

The results showed USP7 and TRAF4 upregulation, and RSK4 downregulation in ovarian cancer cell lines. Knocking down USP7 suppressed viability, migration, and invasion of ovarian cancer cells; TRAF4 knockdown and RSK4 overexpression had similar effects in ovarian cancer cells. TRAF4 is deubiquitinated and stabilized by USP7, whereas RSK4 is negatively regulated by TRAF4. A mouse xenograft model confirmed that knocking down USP7 suppressed ovarian tumor growth by regulating the TRAF4/RSK4/PI3K/AKT axis.

CONCLUSION

Knocking down USP7 decreased the proliferation, migration, and invasion of ovarian cancer cells and suppressed ovarian tumor growth in mice. Mechanistically, USP7 increased TRAF4 ubiquitination, promoting its degradation and leading to RSK4 upregulation.

Complex Presentation of Hao-Fountain Syndrome Solved by Exome Sequencing Highlighting Co-Occurring Genomic Variants

Objective: The co-occurrence of pathogenic variants has emerged as a relatively common finding underlying complex phenotypes. Here, we used whole-exome sequencing (WES) to solve an unclassified multisystem clinical presentation. Patients and Methods: A 20-year-old woman affected by moderate intellectual disability (ID), dysmorphic features, hypertrichosis, scoliosis, recurrent bronchitis, and pneumonia with bronchiectasis, colelithiasis, chronic severe constipation, and a family history suggestive of autosomal dominant recurrence of polycystic kidney disease was analyzed by WES to identify the genomic events underlying the condition. Results: Four co-occurring genomic events fully explaining the proband’s clinical features were identified. A de novo truncating USP7 variant was disclosed as the cause of Hao–Fountain syndrome, a disorder characterized by syndromic ID and distinctive behavior. Compound heterozygosity for a major cystic fibrosis-causing variant and the modulator allele, IVS8-5T, in CFTR explained the recurrent upper and lower respiratory way infections, bronchiectasis, cholelithiasis, and chronic constipation. Finally, a truncating PKD2 variant co-segregating with polycystic kidney disease in the family allowed presymptomatic disease diagnosis. Conclusions: The co-occurring variants in USP7 and CFTR variants explained the multisystem disorder of the patient. The comprehensive dissection of the phenotype and early diagnosis of autosomal dominant polycystic kidney disease allowed us to manage the CFTR-related disorder symptoms and monitor renal function and other complications associated with PKD2 haploinsufficiency, addressing proper care and surveillance.

Organ defects of the Usp7 mutant mouse strain indicate the essential role of K63-polyubiquitinated Usp7 in organ formation

BACKGROUND

K63-linked polyubiquitination of proteins have nonproteolytic functions and regulate the activity of many signal transduction pathways. USP7, a HIF1α deubiquitinase, undergoes K63-linked polyubiquitination under hypoxia. K63-polyubiquitinated USP7 serves as a scaffold to anchor HIF1α, CREBBP, the mediator complex, and the super elongation complex to enhance HIF1α-induced gene transcription. However, the physiological role of K63-polyubiquitinated USP7 remains unknown.

METHODS

Using a Usp7^K444R point mutation knock-in mouse strain, we performed immunohistochemistry and standard molecular biological methods to examine the organ defects of liver and kidney in this knock-in mouse strain. Mechanistic studies were performed by using deubiquitination, immunoprecipitation, and quantitative immunoprecipitations (qChIP) assays.

RESULTS

We observed multiple organ defects, including decreased liver and muscle weight, decreased tibia/fibula length, liver glycogen storage defect, and polycystic kidneys. The underlying mechanisms include the regulation of protein stability and/or modulation of transcriptional activation of several key factors, leading to decreased protein levels of Prr5l, Hnf4α, Cebpα, and Hnf1β. Repression of these crucial factors leads to the organ defects described above.

CONCLUSIONS

K63-polyubiquitinated Usp7 plays an essential role in the development of multiple organs and illustrates the importance of the process of K63-linked polyubiquitination in regulating critical protein functions.

Insights into Conformational Dynamics and Allostery in DNMT1-H3Ub/USP7 Interactions

DNA methyltransferases (DNMTs) including DNMT1 are a conserved family of cytosine methylases that play crucial roles in epigenetic regulation. The versatile functions of DNMT1 rely on allosteric networks between its different interacting partners, emerging as novel therapeutic targets. In this work, based on the modeling structures of DNMT1-ubiquitylated H3 (H3Ub)/ubiquitin specific peptidase 7 (USP7) complexes, we have used a combination of elastic network models, molecular dynamics simulations, structural residue perturbation, network modeling, and pocket pathway analysis to examine their molecular mechanisms of allosteric regulation. The comparative intrinsic and conformational dynamics analysis of three DNMT1 systems has highlighted the pivotal role of the RFTS domain as the dynamics hub in both intra- and inter-molecular interactions. The site perturbation and network modeling approaches have revealed the different and more complex allosteric interaction landscape in both DNMT1 complexes, involving the events caused by mutational hotspots and post-translation modification sites through protein-protein interactions (PPIs). Furthermore, communication pathway analysis and pocket detection have provided new mechanistic insights into molecular mechanisms underlying quaternary structures of DNMT1 complexes, suggesting potential targeting pockets for PPI-based allosteric drug design.

The miRNA-15b/USP7/KDM6B axis engages in the initiation of osteoporosis by modulating osteoblast differentiation and autophagy

Osteoporosis is a metabolic disease that results from oxidative stress or inflammation in renal disorders. microRNAs (miRNAs) are recently implicated to participate in osteoporosis, but the mechanism remains largely unexplored. Herein, we aimed to explore the potential role of miR-15b in osteoblast differentiation and autophagy in osteoporosis. We established osteoporosis models through ovariectomy and determined that miR-15b was highly expressed whereas USP7 and KDM6B were poorly expressed in tissue of osteoporosis mice. Treatment of silenced miR-15b resulted in the elevation of decreased bone mineral density (BMD), the maximum elastic stress and the maximum load of osteoporosis mice. In osteoblasts, miR-15 overexpression decreased proliferation but suppressed the cell differentiation and autophagy, accompanied with decreased expression of USP7. Mechanistically, miR-15 bound and inhibited USP7 expression, while overexpression of USP7 promoted autophagy of osteoblasts. USP7, importantly, strengthened the stability of KDM6B and promoted KDM6B expression. MG132 protease inhibitor increased KDM6B and USP7 expression in osteoblasts. Silencing of KDM6B reversed the promoting effect on autophagy and proliferation induced by overexpression of USP7. Taken altogether, miR-15b inhibits osteoblast differentiation and autophagy to aggravate osteoporosis by targeting USP7 to regulate KDM6B expression.

DNA Polymerase ι Interacts with Both the TRAF-like and UBL1-2 Domains of USP7

Reversible protein ubiquitination is an essential signaling mechanism within eukaryotes. Deubiquitinating enzymes are critical to this process, as they mediate removal of ubiquitin from substrate proteins. Ubiquitin-specific protease 7 (USP7) is a prominent deubiquitinating enzyme, with an extensive network of interacting partners and established roles in cell cycle activation, immune responses and DNA replication. Characterized USP7 substrates primarily interact with one of two major binding sites outside the catalytic domain. These are located on the USP7 N-terminal TRAF-like (TRAF) domain and the first and second UBL domains (UBL1-2) within the C-terminal tail. Here, we report that DNA polymerase iota (Pol ι) is a novel USP7 substrate that interacts with both TRAF and UBL1-2. Through the use of biophysical approaches and mutational analysis, we characterize both interfaces and demonstrate that bipartite binding to both USP7 domains is required for efficient Pol ι deubiquitination. Together, these data establish a new bipartite mode of USP7 substrate binding.

Ubiquitin-specific protease 7 promotes ferroptosis via activation of the p53/TfR1 pathway in the rat hearts after ischemia/reperfusion

Iron overload triggers the ferroptosis in the heart following ischemia/reperfusion (I/R) and transferrin receptor 1 (TfR1) charges the cellular iron uptake. Bioinformatics analysis shows that the three molecules of ubiquitin-specific protease 7 (USP7), p53 and TfR1 form a unique pathway of USP7/p53/TfR1. This study aims to explore whether USP7/p53/TfR1 pathway promotes ferroptosis in rat hearts suffered I/R and the underlying mechanisms. The SD rat hearts were subjected to 1 h-ischemia plus 3 h-reperfusion, showing myocardial injury (increase in creatine kinase release, infarct size, myocardial fiber loss and disarray) and up-regulation of USP7, p53 and TfR1 concomitant with an increase of ferroptosis (reflecting by accumulation of iron and lipid peroxidation while decrease of glutathione peroxidase activity). Inhibition of USP7 activated p53 via suppressing deubiquitination, which led to down-regulation of TfR1, accompanied by the decreased ferroptosis and myocardial I/R injury. Next, H9c2 cells underwent hypoxia/reoxygenation (H/R) in vitro to mimic the myocardial I/R model in vivo. Consistent with the results in vivo, inhibition or knockdown of USP7 reduced the H/R injury (decrease of LDH release and necrosis) and enhanced the ubiquitination of p53 along with the decreased levels of p53 and TfR1 as well as the attenuated ferroptosis (manifesting as the decreased iron content and lipid peroxidation while the increased GPX activity). Knockdown of TfR1 inhibited H/R-induced ferroptosis without p53 deubiquitination. Based on these observations, we conclude that a novel pathway of USP7/p53/TfR1 has been identified in the I/R-treated rat hearts, where up-regulation of USP7promotes ferrptosis via activation of the p53/TfR1 pathway.

Combination of Inhibitors of USP7 and PLK1 has a Strong Synergism against Paclitaxel Resistance

USP7 is a promising target for the development of cancer treatments because of its high expression and the critical functions of its substrates in carcinogenesis of several different carcinomas. Here, we demonstrated the effectiveness of targeting USP7 in advanced malignant cells showing high levels of USP7, especially in taxane-resistant cancer. USP7 knockdown effectively induced cell death in several cancer cells of lung, prostate, and cervix. Depletion of USP7 induced multiple spindle pole formation in mitosis, and, consequently, resulted in mitotic catastrophe. When USP7 was blocked in the paclitaxel-resistant lung cancer NCI-H460TXR cells, which has resistance to mitotic catastrophe, NCI-H460TXR cells underwent apoptosis effectively. Furthermore, combination treatment with the mitotic kinase PLK1 inhibitor volasertib and the USP7 inhibitor P22077 showed a strong synergism through down-regulation of MDR1/ABCB1 in paclitaxel-resistant lung cancer. Therefore, we suggest USP7 is a promising target for cancer therapy, and combination therapy with inhibitors of PLK1 and USP7 may be valuable for treating paclitaxel-resistant cancers, because of their strong synergism.

Deubiquitinase USP7-mediated MCL-1 up-regulation enhances Arsenic and Benzo(a)pyrene co-exposure-induced Cancer Stem Cell-like property and Tumorigenesis

Rationale: MCL-1 is up-regulated in cancer and a target for cancer treatment. How MCL-1 is up-regulated and whether MCL-1 up-regulation plays a role in tumorigenic process is not well-known. Arsenic and benzo(a)pyrene (BaP) are well-recognized lung carcinogens and we recently reported that arsenic and BaP co-exposure acts synergistically in inducing cancer stem cell (CSC)-like property and lung tumorigenesis. This study was performed to further investigate the underlying mechanism focusing on the role of MCL-1. Methods: The spheroid formation assay and nude mouse tumorigenesis assay were used to determine the CSC-like property and tumorigenicity of arsenic plus BaP co-exposure-transformed human bronchial epithelial BEAS-2B cells, respectively. Biochemical, pharmacological and genetic approaches were used to manipulate gene expressions, dissect signaling pathways and determine protein-protein interactions. Both loss-of-function and gain-of-function approaches were used to validate the role of MCL-1 in arsenic plus BaP co-exposure-enhanced CSC-like property and tumorigenicity. Results: Arsenic plus BaP co-exposure-transformed cells express significantly higher protein levels of MCL-1 than the passage-matched control, arsenic or BaP exposure alone-transformed cells. Knocking down MCL-1 levels in arsenic plus BaP co-exposure-transformed cells significantly reduced their apoptosis resistance, CSC-like property and tumorigenicity in mice. Mechanistic studies revealed that arsenic plus BaP co-exposure up-regulates MCL-1 protein levels by synergistically activating the PI3K/Akt/mTOR pathway to increase the level of a deubiquitinase USP7, which in turn reduces the level of MCL-1 protein ubiquitination and prevents its subsequent proteasome degradation. Conclusions: The deubiquitinase USP7-mediated MCL-1 up-regulation enhances arsenic and BaP co-exposure-induced CSC-like property and tumorigenesis, providing the first evidence demonstrating that USP7 stabilizes MCL-1 protein during the tumorigenic process.

CAF secreted miR-522 suppresses ferroptosis and promotes acquired chemo-resistance in gastric cancer

BACKGROUND

Ferroptosis is a novel mode of non-apoptotic cell death induced by build-up of toxic lipid peroxides (lipid-ROS) in an iron dependent manner. Cancer-associated fibroblasts (CAFs) support tumor progression and drug resistance by secreting various bioactive substances, including exosomes. Yet, the role of CAFs in regulating lipid metabolism as well as ferroptosis of cancer cells is still unexplored and remains enigmatic.

METHODS

Ferroptosis-related genes in gastric cancer (GC) were screened by using mass spectrum; exosomes were isolated by ultra-centrifugation and CAF secreted miRNAs were determined by RT-qPCR. Erastin was used to induce ferroptosis, and ferroptosis levels were evaluated by measuring lipid-ROS, cell viability and mitochondrial membrane potential.

RESULTS

Here, we provide clinical evidence to show that arachidonate lipoxygenase 15 (ALOX15) is closely related with lipid-ROS production in gastric cancer, and that exosome-miR-522 serves as a potential inhibitor of ALOX15. By using primary stromal cells and cancer cells, we prove that exosome-miR-522 is mainly derived from CAFs in tumor microenvironment. Moreover, heterogeneous nuclear ribonucleoprotein A1 (hnRNPA1) was found to mediate miR-522 packing into exosomes, and ubiquitin-specific protease 7 (USP7) stabilizes hnRNPA1 through de-ubiquitination. Importantly, cisplatin and paclitaxel promote miR-522 secretion from CAFs by activating USP7/hnRNPA1 axis, leading to ALOX15 suppression and decreased lipid-ROS accumulation in cancer cells, and ultimately result in decreased chemo-sensitivity.

CONCLUSIONS

The present study demonstrates that CAFs secrete exosomal miR-522 to inhibit ferroptosis in cancer cells by targeting ALOX15 and blocking lipid-ROS accumulation. The intercellular pathway, comprising USP7, hnRNPA1, exo-miR-522 and ALOX15, reveals new mechanism of acquired chemo-resistance in GC.

USP7-Dependent Regulation of TRAF Activation and Signaling by a Viral Interferon Regulatory Factor Homologue

Human herpesvirus 8 (HHV-8) encodes four viral interferon regulatory factors (vIRFs 1 to 4), all of which are expressed during lytic replication and inhibit a variety of antiviral signaling pathways. Viral IRFs 1, 2, and 3 are also expressed during latency in primary effusion lymphoma (PEL) cells, and vIRF-1 and vIRF-3 have been reported to promote PEL cell viability. Viral IRFs 1, 3, and 4 are known to interact with ubiquitin-specific protease 7 (USP7); interactions of vIRF-1 and vIRF-3 with USP7 promote PEL cell viability and regulate productive replication. Here, we report that vIRF-2 also targets USP7, utilizing a PSTS motif matching the USP7 N-terminal domain-binding A/PxxS consensus, but uniquely requires catalytic domain residues for intracellular interaction. In functional and mechanistic analyses, tumor necrosis factor receptor-associated factor (TRAF)-mediated signaling and associated polyubiquitination of TRAFs 3 and 6, specifically, were regulated negatively by USP7 and positively by vIRF-2-USP7 interaction, the latter competing for USP7-TRAF association. Using depletion, depletion-complementation, and targeted mutagenesis approaches, vIRF-2 was determined to promote latent PEL cell viability, likely independently of USP7 interaction, while lytic replication was inhibited by vIRF-2, in part or in whole via USP7 interaction. Together, our data identify a new molecular determinant of USP7 recognition, TRAF3/6-specific targeting by the deubiquitinase, associated activation of these TRAFs by vIRF-2, and activities of vIRF-2 and vIRF-2-USP7 interaction in HHV-8 latent and lytic biology.IMPORTANCE Human herpesvirus 8-encoded IRF homologues were the first to be identified in a virus. Through inhibitory interactions with cellular IRFs and other mediators of antiviral signaling, the vIRFs are believed to be essential for productive replication and also for latency in particular cell types. The deubiquitinase USP7 is a regulator of key cellular pathways, modulates HHV-8 latent and lytic infection, and is targeted by vIRFs 1, 3, and 4. Here, we report that vIRF-2 also interacts with USP7, via a means distinguishable from USP7 interactions with other vIRFs and other proteins, that this interaction modulates antiviral signaling via disruption of USP7 interactions with innate immune signaling proteins TRAF3 and TRAF6, and that vIRF-2 targeting of USP7 regulates HHV-8 productive replication. The presented data are the first to identify vIRF-2 targeting of USP7 and its role in HHV-8 biology, expanding our understanding of the repertoire and importance of virus-host interactions.

Genome-Wide Association Study of Susceptibility Loci for T-Cell Acute Lymphoblastic Leukemia in Children

BACKGROUND

Acute lymphoblastic leukemia (ALL) is the most common cancer in children and can arise in B or T lymphoid lineages. Although risk loci have been identified for B-ALL, the inherited basis of T-ALL is mostly unknown, with a particular paucity of genome-wide investigation of susceptibility variants in large patient cohorts.

METHODS

We performed a genome-wide association study (GWAS) in 1191 children with T-ALL and 12 178 controls, with independent replication using 117 cases and 5518 controls. The associations were tested using an additive logistic regression model. Top risk variants were tested for effects on enhancer activity using luciferase assay. All statistical tests were two sided.

RESULTS

A novel risk locus in the USP7 gene (rs74010351, odds ratio [OR] = 1.44, 95% confidence interval [CI] = 1.27 to 1.65, P = 4.51 × 10-8) reached genome-wide significance in the discovery cohort, with independent validation (OR = 1.51, 95% CI = 1.03 to 2.22, P = .04). The USP7 risk allele was overrepresented in individuals of African descent, thus contributing to the higher incidence of T-ALL in this race/ethnic group. Genetic changes in USP7 (germline variants or somatic mutations) were observed in 56.4% of T-ALL with TAL1 overexpression, statistically significantly higher than in any other subtypes. Functional analyses suggested this T-ALL risk allele is located in a putative cis-regulatory DNA element with negative effects on USP7 transcription. Finally, comprehensive comparison of 14 susceptibility loci in T- vs B-ALL pointed to distinctive etiology of these leukemias.

CONCLUSIONS

These findings indicate strong associations between inherited genetic variation and T-ALL susceptibility in children and shed new light on the molecular etiology of ALL, particularly commonalities and differences in the biology of the two major subtypes (B- vs T-ALL).

USP7 is a novel Deubiquitinase sustaining PLK1 protein stability and regulating chromosome alignment in mitosis

BACKGROUND

The deubiquitinase USP7 has been identified as an oncogene with key roles in tumorigenesis and therapeutic resistance for a series of cancer types. Recently small molecular inhibitors have been developed to target USP7. However, the anticancer mechanism of USP7 inhibitors is still elusive.

METHODS

Cell viability or clonogenicity was tested by violet crystal assay. Cell apoptosis or cell cycle was analyzed by flow cytometry, and chromosome misalignment was observed by a fluorescent microscopy. The protein interaction of PLK1 and USP7 was detected by tandem affinity purification and high throughput proteomics, and further confirmed by co-immunoprecipitation, GST pull-down and protein co-localization. The correlation between USP7 level of tumor tissues and taxane-resistance was evaluated.

RESULTS

Pharmacological USP7 inhibition by P5091 retarded cell proliferation and induced cell apoptosis. Further studies showed that P5091 induced cell cycle arrest at G2/M phase, and particularly induced chromosome misalignment, indicating the key roles of USP7 in mitosis. USP7 protein was detected in the PLK1-interacted protein complex. USP7 interacts with PLK1 protein through its PBD domain by catalytic activity. USP7 as a deubiquitinase sustained PLK1 protein stability via the C223 site, and inversely, USP7 inhibition by P5091 promoted the protein degradation of PLK1 through the ubiquitination-proteasome pathway. By overexpressing PLK1, USP7 that had been depleted by RNAi ceased to induce chromosome misalignment in mitosis and again supported cell proliferation and cell survival. Both USP7 and PLK1 were overexpressed in taxane-resistant cancer cells, and negatively correlated with the MP scores in tumor tissues. Either USP7 or PLK1 knockdown by RNAi significantly sensitized taxane-resistant cells to taxane cell killing.

CONCLUSION

This is the first report that PLK1 is a novel substrate of USP7 deubiquitinase, and that USP7 sustained the protein stability of PLK1. USP7 inhibition induces cell apoptosis and cell cycle G2/M arrest, and overcomes taxane resistance by inducing the protein degradation of PLK1, resulting in chromosome misalignment in mitosis.

Exosome circRNA secreted from adipocytes promotes the growth of hepatocellular carcinoma by targeting deubiquitination-related USP7

Hepatocellular carcinoma (HCC), the major form of liver cancer, has shown increasing incidence and poor prognosis. Adipose tissue is known to function in energy storage and metabolism regulation by the secretion of adipokines. Circular RNAs (circRNAs), a novel type of noncoding RNA, have recently been recognized as key factors in tumor development, but the role of exosome circRNAs derived from adipose tissues has not been defined yet. Here, adipose-secreted circRNAs were found to regulate deubiquitination in HCC, thus facilitating cell growth. It was observed that exosome circ-deubiquitination (circ-DB) is upregulated in HCC patients with higher body fat ratios. Moreover, in vitro and in vivo studies showed that exo-circ-DB promotes HCC growth and reduces DNA damage via the suppression of miR-34a and the activation of deubiquitination-related USP7. Finally, the results showed that the effects of adipose exosomes on HCC cells can be reversed by knockdown of circ-DB. These results indicate that exosome circRNAs secreted from adipocytes promote tumor growth and reduce DNA damage by suppressing miR-34a and activating the USP7/Cyclin A2 signaling pathway.

Bach1 regulates self-renewal and impedes mesendodermal differentiation of human embryonic stem cells

The transcription factor BTB and CNC homology 1 (Bach1) is expressed in the embryos of mice, but whether Bach1 regulates the self-renewal and early differentiation of human embryonic stem cells (hESCs) is unknown. We report that the deubiquitinase ubiquitin-specific processing protease 7 (Usp7) is a direct target of Bach1, that Bach1 interacts with Nanog, Sox2, and Oct4, and that Bach1 facilitates their deubiquitination and stabilization via the recruitment of Usp7, thereby maintaining stem cell identity and self-renewal. Bach1 also interacts with polycomb repressive complex 2 (PRC2) and represses mesendodermal gene expression by recruiting PRC2 to the genes' promoters. The loss of Bach1 in hESCs promotes differentiation toward the mesendodermal germ layers by reducing the occupancy of EZH2 and H3K27me3 in mesendodermal gene promoters and by activating the Wnt/β-catenin and Nodal/Smad2/3 signaling pathways. Our study shows that Bach1 is a key determinant of pluripotency, self-renewal, and lineage specification in hESCs.

Destabilizing NEK2 overcomes resistance to proteasome inhibition in multiple myeloma

Drug resistance remains the key problem in cancer treatment. It is now accepted that each myeloma patient harbors multiple subclones and subclone dominance may change over time. The coexistence of multiple subclones with high or low chromosomal instability (CIN) signature causes heterogeneity and drug resistance with consequent disease relapse. In this study, using a tandem affinity purification-mass spectrometry (TAP-MS) technique, we found that NEK2, a CIN gene, was bound to the deubiquitinase USP7. Binding to USP7 prevented NEK2 ubiquitination resulting in NEK2 stabilization. Increased NEK2 kinase levels activated the canonical NF-κB signaling pathway through the PP1α/AKT axis. Newly diagnosed myeloma patients with activated NF-κB signaling through increased NEK2 activity had poorer event-free and overall survivals based on multiple independent clinical cohorts. We also found that NEK2 activated heparanase, a secreted enzyme, responsible for bone destruction in an NF-κB-dependent manner. Intriguingly, both NEK2 and USP7 inhibitors showed great efficacy in inhibiting myeloma cell growth and overcoming NEK2-induced and -acquired drug resistance in xenograft myeloma mouse models.