Ubiquitin-specific protease 7 is a drug-able target that promotes hepatocellular carcinoma and chemoresistance

Drug resistance mechanisms and treatment strategies mediated by Ubiquitin-Specific Proteases (USPs) in cancers: new directions and therapeutic options

Drug resistance represents a significant obstacle in cancer treatment, underscoring the need for the discovery of novel therapeutic targets. Ubiquitin-specific proteases (USPs), a subclass of deubiquitinating enzymes, play a pivotal role in protein deubiquitination. As scientific research advances, USPs have been recognized as key regulators of drug resistance across a spectrum of treatment modalities, including chemotherapy, targeted therapy, immunotherapy, and radiotherapy. This comprehensive review examines the complex relationship between USPs and drug resistance mechanisms, focusing on specific treatment strategies and highlighting the influence of USPs on DNA damage repair, apoptosis, characteristics of cancer stem cells, immune evasion, and other crucial biological functions. Additionally, the review highlights the potential clinical significance of USP inhibitors as a means to counter drug resistance in cancer treatment. By inhibiting particular USP, cancer cells can become more susceptible to a variety of anti-cancer drugs. The integration of USP inhibitors with current anti-cancer therapies offers a promising strategy to circumvent drug resistance. Therefore, this review emphasizes the importance of USPs as viable therapeutic targets and offers insight into fruitful directions for future research and drug development. Targeting USPs presents an effective method to combat drug resistance across various cancer types, leading to enhanced treatment strategies and better patient outcomes.

Oxyberberine sensitizes liver cancer cells to sorafenib via inhibiting NOTCH1-USP7-c-Myc pathway

BACKGROUND

Sorafenib is the first-line therapy for patients with advanced-stage HCC, but its clinical cure rate is unsatisfactory due to adverse reactions and drug resistance. Novel alternative strategies to overcome sorafenib resistance are urgently needed. Oxyberberine (OBB), a major metabolite of berberine in vivo, exhibits potential antitumor potency in various human malignancies, including liver cancer. However, it remains unknown whether and how OBB sensitizes liver cancer cells to sorafenib.

METHODS

Cell viability, trypan blue staining and flow cytometry assays were employed to determine the synergistic effect of OBB and sorafenib on killing HCC cells. PCR, western blot, co-immunoprecipitation and RNA interference assays were used to decipher the mechanism by which OBB sensitizes sorafenib. HCC xenograft models and clinical HCC samples were utilized to consolidate our findings.

RESULTS

We found for the first time that OBB sensitized liver cancer cells to sorafenib, enhancing its inhibitory effect on cell growth and induction of apoptosis in vitro. Interestingly, we observed that OBB enhanced the sensitivity of HCC cells to sorafenib by reducing ubiquitin-specific peptidase 7 (USP7) expression, a well-known tumor-promoting gene. Mechanistically, OBB inhibited notch homolog 1-mediated USP7 transcription, leading to the downregulation of V-Myc avian myelocytomatosis viral oncogene homolog (c-Myc), which synergized with sorafenib to suppress liver cancer. Furthermore, animal results showed that cotreatment with OBB and sorafenib significantly inhibited the tumor growth of liver cancer xenografts in mice.

CONCLUSIONS

These results indicate that OBB enhances the sensitivity of liver cancer cells to sorafenib through inhibiting notch homolog 1-USP7-c-Myc signaling pathway, which potentially provides a novel therapeutic strategy for liver cancer to improve the effectiveness of sorafenib.

ER Stress-Activated HSF1 Governs Cancer Cell Resistance to USP7 Inhibitor-Based Chemotherapy through the PERK Pathway

Ubiquitin-specific protease 7 inhibitors (USP7i) are considered a novel class of anticancer drugs. Cancer cells occasionally become insensitive to anticancer drugs, known as chemoresistance, by acquiring multidrug resistance, resulting in poor clinical outcomes in patients with cancer. However, the chemoresistance of cancer cells to USP7i (P22077 and P5091) and mechanisms to overcome it have not yet been investigated. In the present study, we generated human cancer cells with acquired resistance to USP7i-induced cell death. Gene expression profiling showed that heat stress response (HSR)- and unfolded protein response (UPR)-related genes were largely upregulated in USP7i-resistant cancer cells. Biochemical studies showed that USP7i induced the phosphorylation and activation of heat shock transcription factor 1 (HSF1), mediated by the endoplasmic reticulum (ER) stress protein kinase R-like ER kinase (PERK) signaling pathway. Inhibition of HSF1 and PERK significantly sensitized cancer cells to USP7i-induced cytotoxicity. Our study demonstrated that the ER stress-PERK axis is responsible for chemoresistance to USP7i, and inhibiting PERK is a potential strategy for improving the anticancer efficacy of USP7i.

USP3 inhibition is Active Against Chemo-resistant Hepatocellular Carcinoma Anchorage-independent Growth via Suppressing Wnt/β-catenin

BACKGROUND

USPs are a family of enzymes that regulate protein degradation, and their dysregulation has been implicated in the development and progression of cancer.

AIMS

This study aimed to determine whether ubiquitin-specific proteases 3 (USP3) could be a potential target for therapy in hepatocellular carcinoma (HCC), particularly in resistant HCC. This study systematically investigated the role of USP3 in HCC, with a focus on chemo-resistant HCC cells.

METHODS

The level of USP3 from clinical samples was measured using an ELISA assay. Cell proliferation, apoptosis, migration, and anchorage-independent colony formation assays were performed. Transfection was performed to knock down USP3 expression and measure β-catenin activity, and real-time PCR was used to measure levels of MYC and CYCLIN D1 genes.

RESULTS

USP3 protein was upregulated in HCC tissues, but its upregulation was not associated with clinicopathology. USP3 knockdown had a similar inhibitory effect on growth in both sensitive and resistant HCC cells, did not affect migration, and induced apoptosis in sensitive but not resistant HCC cells. Furthermore, USP3 knockdown was more effective in suppressing anchorage-independent colony formation in chemoresistant HCC cells compared to their chemo-sensitive counterparts. Pearson correlation coefficient analysis revealed a strong positive correlation between USP3 and CTNNB1, and consistently, USP3 knockdown reduced the levels and activities of β-catenin in HCC cells. Using a Wnt activator (lithium) in rescue studies significantly reversed the inhibitory effects of USP3 knockdown.

CONCLUSION

The findings suggest that inhibiting USP3 is an effective strategy against cancer stem cells and chemo-resistant HCC cells.

Diagnostic and Prognostic Value of Protein Post-translational Modifications in Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is a common malignant tumor with high incidence and cancer mortality worldwide. Post-translational modifications (PTMs) of proteins have a great impact on protein function. Almost all proteins can undergo PTMs, including phosphorylation, acetylation, methylation, glycosylation, ubiquitination, and so on. Many studies have shown that PTMs are related to the occurrence and development of cancers. The findings provide novel therapeutic targets for cancers, such as glypican-3 and mucin-1. Other clinical implications are also found in the studies of PTMs. Diagnostic or prognostic value, and response to therapy have been identified. In HCC, it has been shown that glycosylated alpha-fetoprotein (AFP) has a higher detection rate for early liver cancer than conventional AFP. In this review, we mainly focused on the diagnostic and prognostic value of PTM, in order to provide new insights into the clinical implication of PTM in HCC.

Regulation of apoptosis by ubiquitination in liver cancer

Apoptosis is a programmed cell death process critical to cell development and tissue homeostasis in multicellular organisms. Defective apoptosis is a crucial step in the malignant transformation of cells, including hepatocellular carcinoma (HCC), where the apoptosis rate is higher than in normal liver tissues. Ubiquitination, a post-translational modification process, plays a precise role in regulating the formation and function of different death-signaling complexes, including those involved in apoptosis. Aberrant expression of E3 ubiquitin ligases (E3s) in liver cancer (LC), such as cellular inhibitors of apoptosis proteins (cIAPs), X chromosome-linked IAP (XIAP), and linear ubiquitin chain assembly complex (LUBAC), can contribute to HCC development by promoting cell survival and inhibiting apoptosis. Therefore, the review introduces the main apoptosis pathways and the regulation of proteins in these pathways by E3s and deubiquitinating enzymes (DUBs). It summarizes the abnormal expression of these regulators in HCC and their effects on cancer inhibition or promotion. Understanding the role of ubiquitination in apoptosis and LC can provide insights into potential targets for therapeutic intervention.

Ubiquitin-specific protease 7 (USP7): an emerging drug target for cancer treatment

INTRODUCTION

Ubiquitin-specific protease 7 (USP7) also known as herpesvirus-associated ubiquitin-specific protease (HAUSP) is a well-characterized cysteine protease that belongs to the largest subfamily of deubiquitinating enzymes (DUBs). It is involved in multiple signaling pathways, some of them dysregulated in malignant tumors. USP7 inhibition can lead to cell growth arrest and apoptosis through inhibition of tumor promoters and stabilization of tumor suppressors, making it a promising druggable target for cancer therapy.

AREAS COVERED

This review covers the structure of USP7, its function in multiple signaling pathways and relevance in cancer, as well as recent advances and future perspectives in the development of USP7 inhibitors for cancer therapy.

EXPERT OPINION

Literature reports display the multiple antitumor activities of USP7 inhibitors, both in vitro and in vivo. Nonetheless, none have entered clinical trials so far, highlighting the need to delve into a deeper understanding of USP7 binding sites and the development of more accurate compound screening methods. Despite these challenges, further development of USP7 inhibitors is promising as a valuable new approach for cancer treatment, including the ability to address chemoresistance.

Targeting and regulation of autophagy in hepatocellular carcinoma: revisiting the molecular interactions and mechanisms for new therapy approaches

Autophagy is an evolutionarily conserved process that plays a role in regulating homeostasis under physiological conditions. However, dysregulation of autophagy is observed in the development of human diseases, especially cancer. Autophagy has reciprocal functions in cancer and may be responsible for either survival or death. Hepatocellular carcinoma (HCC) is one of the most lethal and common malignancies of the liver, and smoking, infection, and alcohol consumption can lead to its development. Genetic mutations and alterations in molecular processes can exacerbate the progression of HCC. The function of autophagy in HCC is controversial and may be both tumor suppressive and tumor promoting. Activation of autophagy may affect apoptosis in HCC and is a regulator of proliferation and glucose metabolism. Induction of autophagy may promote tumor metastasis via induction of EMT. In addition, autophagy is a regulator of stem cell formation in HCC, and pro-survival autophagy leads to cancer cell resistance to chemotherapy and radiotherapy. Targeting autophagy impairs growth and metastasis in HCC and improves tumor cell response to therapy. Of note, a large number of signaling pathways such as STAT3, Wnt, miRNAs, lncRNAs, and circRNAs regulate autophagy in HCC. Moreover, regulation of autophagy (induction or inhibition) by antitumor agents could be suggested for effective treatment of HCC. In this paper, we comprehensively review the role and mechanisms of autophagy in HCC and discuss the potential benefit of targeting this process in the treatment of the cancer. Video Abstract.

TRIM27-USP7 complex promotes tumour progression via STAT3 activation in human hepatocellular carcinoma

BACKGROUND & AIMS

TRIM27 is stabilized by binding to USP7 and mediates tumour progression in several cancers; however, the roles of TRIM27-USP7 complex on STAT3 activation in HCC are unknown.

METHODS

Regulations and functions of TRIM27 for activating STAT3 in HCC were assessed using 207 HCC samples or HCC cells.

RESULTS

TRIM27 expression was increased in some cases of HCC. High TRIM27 expression was an independent predictor for poor prognosis in HCC after surgery. It was correlated with the expression of EpCAM, vimentin, MMP-9, and activation of STAT3 in HCC. TRIM27 expression was correlated with USP7 expression, and HCC with high TRIM27 expression together with high USP7 expression showed enhanced STAT3 activation, resulting in poorer prognosis. p-JAK1 expression was correlated with STAT3 activation in HCC with high TRIM27 expression. In vitro, USP7 knockdown decreased TRIM27 expression, suggesting that USP7 was essential for TRIM27 stabilization. Knocking down of TRIM27 or USP7 suppressed STAT3 activation and overexpression of TRIM27 accelerated STAT3 activation; therefore, the formation of TRIM27-USP7 complex was needed for STAT3 activation, which led to aggressive tumour proliferation and invasion by enhancing EMT and CSC-like property. Binding of JAK1 to TRIM27-USP7 complex was confirmed in vitro. Deletion of TRIM27-USP7 complex by USP7 inhibitor significantly inhibited tumour cell invasion by suppressing STAT3 activation.

CONCLUSIONS

TRIM27 is stabilized by binding to USP7 and is related to aggressive tumour progression in HCC via STAT3 activation, resulting in poor prognosis after operation. Therefore, TRIM27-USP7 complex is a useful prognostic predictor and a promising therapeutic target for HCC.

MF-094 nanodelivery inhibits oral squamous cell carcinoma by targeting USP30

BACKGROUND

Oral squamous cell carcinoma (OSCC) is a common head and neck cancer, and the incidence of OSCC is increasing. As the mortality of OSCC keeps increasing, it is crucial to clarify its pathogenesis and develop new therapeutic strategies.

METHODS

Confocal laser scanning microscopy was used to evaluate the uptake of nanoparticles (NPs). The potential functions of USP30 were evaluated by cell counting kit (CCK)-8, flow cytometry, biochemical assay, coimmunoprecipitation, qRT-PCR, and immunoblotting. The antitumor effect of NP-loaded USP30 inhibitor MF-094 was evaluated in vitro and in vivo.

RESULTS

In this study, increased USP30 expression was found in OSCC specimens and cell lines through qRT-PCR and immunoblotting. CCK-8, flow cytometry, and biochemical assay revealed that the deubiquitylated catalytic activity of USP30 contributed to cell viability and glutamine consumption of OSCC. Subsequently, USP30 inhibitor MF-094 was loaded in ZIF-8-PDA and PEGTK to fabricate ZIF-8-PDA-PEGTK nanoparticles, which exhibited excellent inhibition of cell viability and glutamine consumption of OSCC, both in vitro and in vivo.

CONCLUSION

The results indicated the clinical significance of USP30 and showed that nanocomposites provide a targeted drug delivery system for treating OSCC.

Research Progress of DUB Enzyme in Hepatocellular Carcinoma

According to GLOBOCAN 2021 cancer incidence and mortality statistics compiled by the International Agency for Research on Cancer, hepatocellular carcinoma (HCC) is the most common malignancy in the human liver and one of the leading causes of cancer death worldwide. Although there have been great advances in the treatment of HCC, such as regofenib, sorafenib, and lomvatinib, which have been developed and approved for the clinical treatment of advanced or metastatic HCC. However, they only prolong survival by a few months, and patients with advanced liver cancer are susceptible to tumor invasion metastasis and drug resistance. Ubiquitination modification is a type of post-translational modification of proteins. It can affect the physiological activity of cells by regulating the localization, stability and activity of proteins, such as: gene transcription, DNA damage signaling and other pathways. The reversible process of ubiquitination is called de-ubiquitination: it is the process of re-releasing ubiquitinated substrates with the participation of de-ubiquitinases (DUBs) and other active substances. There is growing evidence that many dysregulations of DUBs are associated with tumorigenesis. Although dysregulation of deuquitinase function is often found in HCC and other cancers, The mechanisms of action of many DUBs in HCC have not been elucidated. In this review, we focused on several deubiquitinases (DUBs) associated with hepatocellular carcinoma, including their structure, function, and relationship to hepatocellular carcinoma. hepatocellular carcinoma was highlighted, as well as the latest research reports. Among them, we focus on the USP family and OTU family which are more studied in the HCC. In addition, we discussed the prospects and significance of targeting DUBs as a new strategy for the treatment of hepatocellular carcinoma. It also briefly summarizes the research progress of some DUB-related small molecule inhibitors and their clinical application significance as a treatment for HCC in the future.

USP53 plays an antitumor role in hepatocellular carcinoma through deubiquitination of cytochrome c

Despite of advances in treatment options, hepatocellular carcinoma (HCC) remains nearly incurable and has been recognized as the third leading cause of cancer-related deaths worldwide. As a deubiquitinating enzyme, the antitumor effect of ubiquitin-specific peptidase 53 (USP53) has been demonstrated on few malignancies. In this study, we investigated the potential antitumor role of USP53 in HCC. The results showed that USP53 was downregulated in HCC tissues as well as in HCC cell lines using both in silico data as well as patient samples. Furthermore, the ectopic expression of USP53 inhibited the proliferation, migration and invasion, and induced the apoptosis of HCC cells. Co-immunoprecipitation (CO-IP) assay and mass spectrometry (MS) combined with the gene set enrichment analysis (GSEA) identified cytochrome c (CYCS) as an interacting partner of USP53. USP53 overexpression increased the stability of CYCS in HCC cells following cycloheximide treatment. Finally, the overexpression of CYCS compensated for the decreased apoptotic rates in cells with USP53 knocked down, suggesting that USP53 induced the apoptosis in HCC cells through the deubiquitination of CYCS. To summarize, we identified USP53 as a tumor suppressor as well as a therapeutic target in HCC, providing novel insights into its pivotal role in cell apoptosis.

The emerging role of deubiquitylating enzymes as therapeutic targets in cancer metabolism

Cancer cells must rewire cellular metabolism to satisfy the unbridled proliferation, and metabolic reprogramming provides not only the advantage for cancer cell proliferation but also new targets for cancer treatment. However, the plasticity of the metabolic pathways makes them very difficult to target. Deubiquitylating enzymes (DUBs) are proteases that cleave ubiquitin from the substrate proteins and process ubiquitin precursors. While the molecular mechanisms are not fully understood, many DUBs have been shown to be involved in tumorigenesis and progression via controlling the dysregulated cancer metabolism, and consequently recognized as potential drug targets for cancer treatment. In this article, we summarized the significant progress in understanding the key roles of DUBs in cancer cell metabolic rewiring and the opportunities for the application of DUBs inhibitors in cancer treatment, intending to provide potential implications for both research purpose and clinical applications.

Identification of the Potential Prognosis Biomarkers in Hepatocellular Carcinoma: An Analysis Based on WGCNA and PPI

Aim

This study was done to determine biomarkers for the prognostic prediction of hepatocellular carcinoma (HCC).

Materials and Methods

In the Gene Expression Omnibus, the gene expression profiles of HCC were downloaded. Biomarkers were identified by weighted gene co-expression network analysis and protein–protein interaction network analysis.

Results

There were 24 modules, which were characterized by the high correlation with HCC. Meanwhile, through enrichment analysis, differentially expressed genes were largely participated in the ubiquitination and autophagy processes. Moreover, PRC1, TOP2A and CKAP2L may be the hub genes involved in HCC tumorigenesis, and their biomarker roles were further demonstrated via Gene Expression Profiling Interactive Analysis (GEPIA) and Oncomine databases. In addition, the levels of PRC1, TOP2A and CKAP2L were obviously up-regulated in the sera of HCC patients.

Conclusion

PRC1, TOP2A and CKAP2L may serve as biomarkers for the prognostic prediction of HCC patients.

Novel oncogenes and tumor suppressor genes in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is a very deadly disease. HCC initiation and progression involve multiple genetic events, including the activation of proto-oncogenes and disruption of the function of specific tumor suppressor genes. Activation of oncogenes stimulates cell growth and survival, while loss-of-function mutations of tumor suppressor genes result in unrestrained cell growth. In this review, we summarize the new findings that identified novel proto-oncogenes and tumor suppressors in HCC over the past five years. These findings may inspire the development of novel therapeutic strategies to improve the outcome of HCC patients.

Morin Acts as a USP7 Inhibitor to Hold Back the Migration of Rheumatoid Arthritis Fibroblast-Like Synoviocytes in a "Prickle1-mTORC2" Dependent Manner

INTRODUCTION

The aim of this study is to investigate the effect and detailed mechanisms of morin, an anti-arthritis compound widely distributed in foods of plant origin, on the pathological migration of fibroblast-like synoviocytes (FLS).

METHODS AND RESULTS

The migration of FLS collected from arthritis rats and MH7A cells is induced by platelet-derived growth factor, and an arthritis model in rats is established by Freund's complete adjuvant. The results show that morin remarkably restrains FLS migration but slightly affects FLS apoptosis and proliferation. Moreover, in the progression of FLS migration, focal adhesion (FA) turnover is inhibited by morin via lowering the activation of Paxillin and focal adhesion kinase (FAK) and internalization of integrin β1. Morin disrupts the formation of mTOR complex 2 (mTORC2) and the activation of AKT (S473) and PKCα (S657), and MHY1485 reverses morin-limited FLS migration. Of note, the protein stability of Prickle1, a binding factor of Rictor, is reduced by morin, and MG132 but not Baf A1 shows a repressive effect. Finally, the target protein is identified as ubiquitin-specific protease 7 (USP7) but not USP9X. USP7 overexpressing plasmid weakens morin-affected protein and ubiquitination of Prickle1, and mechanisms are confirmed in vivo by using an overexpressing plasmid and inhibitor.

CONCLUSION

Morin restricts FLS migration and arthritis by intervening in "USP7-Prickle1-mTORC2" signaling and FA turnover.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSION

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

Deubiquitinating Enzymes Orchestrate the Cancer Stem Cell-Immunosuppressive Niche Dialogue: New Perspectives and Therapeutic Potential

Cancer stem cells (CSCs) are sparks for igniting tumor recurrence and the instigators of low response to immunotherapy and drug resistance. As one of the important components of tumor microenvironment, the tumor associated immune microenvironment (TAIM) is driving force for the heterogeneity, plasticity and evolution of CSCs. CSCs create the inhibitory TAIM (ITAIM) mainly through four stemness-related signals (SRSs), including Notch-nuclear factor-κB axis, Hedgehog, Wnt and signal transducer and activator of transcription. Ubiquitination and deubiquitination in proteins related to the specific stemness of the CSCs have a profound impact on the regulation of ITAIM. In regulating the balance between ubiquitination and deubiquitination, it is crucial for deubiquitinating enzymes (DUBs) to cleave ubiquitin chains from substrates. Ubiquitin-specific peptidases (USPs) comprise the largest family of DUBs. Growing evidence suggests that they play novel functions in contribution of ITAIM, including regulating tumor immunogenicity, activating stem cell factors, upregulating the SRSs, stabilizing anti-inflammatory receptors, and regulating anti-inflammatory cytokines. These overactive or abnormal signaling may dampen antitumor immune responses. The inhibition of USPs could play a regulatory role in SRSs and reversing ITAIM, and also have great potential in improving immune killing ability against tumor cells, including CSCs. In this review, we focus on the USPs involved in CSCs signaling pathways and regulating ITAIM, which are promising therapeutic targets in antitumor therapy.

Targeting Ubiquitin-Specific Protease 7 (USP7) in Cancer: A New Insight to Overcome Drug Resistance

Chemoresistance is one of the leading causes for the failure of tumor treatment. Hence, it is necessary to study further and understand the potential mechanisms of tumor resistance to design and develop novel anti-tumor drugs. Post-translational modifications are critical for proteins’ function under physiological and pathological conditions, among which ubiquitination is the most common one. The protein degradation process mediated by the ubiquitin-proteasome system is the most well-known function of ubiquitination modification. However, ubiquitination also participates in the regulation of many other biological processes, such as protein trafficking and protein-protein interaction. A group of proteins named deubiquitinases can hydrolyze the isopeptide bond and disassemble the ubiquitin-protein conjugates, thus preventing substrate proteins form degradation or other outcomes. Ubiquitin-specific protease 7 (USP7) is one of the most extensively studied deubiquitinases. USP7 exhibits a high expression signature in various malignant tumors, and increased USP7 expression often indicates the poor tumor prognosis, suggesting that USP7 is a marker of tumor prognosis and a potential drug target for anti-tumor therapy. In this review, we first discussed the structure and function of USP7. Further, we summarized the underlying mechanisms by which tumor cells develop resistance to anti-tumor therapies, provided theoretical support for targeting USP7 to overcome drug resistance, and some inspiration for the design and development of USP7 inhibitors.

Deubiquitinases: Modulators of Different Types of Regulated Cell Death

The mechanisms and physiological implications of regulated cell death (RCD) have been extensively studied. Among the regulatory mechanisms of RCD, ubiquitination and deubiquitination enable post-translational regulation of signaling by modulating substrate degradation and signal transduction. Deubiquitinases (DUBs) are involved in diverse molecular pathways of RCD. Some DUBs modulate multiple modalities of RCD by regulating various substrates and are powerful regulators of cell fate. However, the therapeutic targeting of DUB is limited, as the physiological consequences of modulating DUBs cannot be predicted. In this review, the mechanisms of DUBs that regulate multiple types of RCD are summarized. This comprehensive summary aims to improve our understanding of the complex DUB/RCD regulatory axis comprising various molecular mechanisms for diverse physiological processes. Additionally, this review will enable the understanding of the advantages of therapeutic targeting of DUBs and developing strategies to overcome the side effects associated with the therapeutic applications of DUB modulators.

Identification and Validation of Ubiquitin-Specific Proteases as a Novel Prognostic Signature for Hepatocellular Carcinoma

Purpose

Ubiquitin-specific proteases (USPs), as a sub-family of deubiquitinating enzymes (DUBs), are responsible for the elimination of ubiquitin-triggered modification. USPs are recently correlated with various malignancies. However, the expression features and clinical significance of USPs have not been systematically investigated in hepatocellular carcinoma (HCC).

Methods

Genomic alterations and expression profiles of USPs were investigated in CbioPortal and The Cancer Genome Atlas (TCGA) Liver hepatocellular carcinoma (LIHC) dataset. Cox regression and least absolute shrinkage and selection operator (LASSO) analyses were conducted to establish a risk signature for HCC prognosis in TCGA LIHC cohort. Subsequently, Kaplan-Meier analysis, receiver operating characteristic (ROC) curves and univariate/multivariate analyses were performed to evaluate the prognostic significance of the risk signature in TCGA LIHC and international cancer genome consortium (ICGC) cohorts. Furthermore, we explored the alterations of the signature genes during hepatocarcinogenesis and HCC progression in GSE89377. In addition, the expression feature of USP39 was further explored in HCC tissues by performing western blotting and immunohistochemistry.

Results

Genomic alterations and overexpression of USPs were observed in HCC tissues. The consensus analysis indicated that the USPs-overexpressed sub-Cluster was correlated with aggressive characteristics and poor prognosis. Cox regression with LASSO algorithm identified a risk signature formed by eight USPs for HCC prognosis. High-risk group stratified by the signature score was correlated with advanced tumor stage and poor survival HCC patients in TCGA LIHC cohort. In addition, the 8-USPs based signature could also robustly predict overall survival of HCC patients in ICGC(LIRI-JP) cohort. Furthermore, gene sets enrichment analysis (GSEA) showed that the high-risk score was associated with tumor-related pathways. According to the observation in GSE89377, USP39 expression was dynamically increased with hepatocarcinogenesis and HCC progression. The overexpression of USP39 was further determined in a local HCC cohort and correlated with poor prognosis. The co-concurrence analysis suggested that USP39 might promote HCC by regulating cell-cycle- and proliferation- related genes.

Conclusion

The current study provided a USPs-based signature, highlighting its robust prognostic significance and targeted value for HCC treatment.

USP7 mediates pathological hepatic de novo lipogenesis through promoting stabilization and transcription of ZNF638

Aberrant de novo lipogenesis (DNL) results in excessive hepatic lipid accumulation and liver steatosis, the causative factors of many liver diseases, such as non-alcoholic fatty liver disease (NAFLD), non-alcoholic steatohepatitis (NASH), and hepatocellular carcinoma (HCC). However, the underlying mechanism of DNL dysregulation remains largely unknown. Ubiquitination of proteins in hepatocytes has been shown to be widely involved in lipid metabolism of liver. Here, we revealed that Ubiquitin-specific peptidase 7 (USP7), a deubiquitinase (DUB), played key roles in DNL through regulation of zinc finger protein 638 (ZNF638) in hepatocytes. USP7 has been shown not only to interact with and deubiquitylate ZNF638, but also to facilitate the transcription of ZNF638 via the stabilization of cAMP responsive element binding protein (CREB). USP7/ZNF638 axis selectively increased the cleavage of sterol regulatory element binding protein (SREBP1C) through AKT/mTORC1/S6K signaling, and formed USP7/ZNF638/SREBP1C nuclear complex to regulate lipogenesis-associated enzymes, including acetyl-CoA carboxylase (ACACA), fatty acid synthase (FASN), and Stearoyl-CoA desaturase (SCD). In the mice liver steatosis model induced by fructose, USP7 or ZNF638 abrogation significantly ameliorated disease progression. Furthermore, USP7/ZNF638 axis participated in the progression of lipogenesis-associated HCC. Our results have uncovered a novel mechanism of hepatic DNL, which might be beneficial to the development of new therapeutic targets for hepatic lipogenesis-associated diseases.

USP7 Is a Master Regulator of Genome Stability

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

DUBs Activating the Hedgehog Signaling Pathway: A Promising Therapeutic Target in Cancer

The Hedgehog (HH) pathway governs cell proliferation and patterning during embryonic development and is involved in regeneration, homeostasis and stem cell maintenance in adult tissues. The activity of this signaling is finely modulated at multiple levels and its dysregulation contributes to the onset of several human cancers. Ubiquitylation is a coordinated post-translational modification that controls a wide range of cellular functions and signaling transduction pathways. It is mediated by a sequential enzymatic network, in which ubiquitin ligases (E3) and deubiquitylase (DUBs) proteins are the main actors. The dynamic balance of the activity of these enzymes dictates the abundance and the fate of cellular proteins, thus affecting both physiological and pathological processes. Several E3 ligases regulating the stability and activity of the key components of the HH pathway have been identified. Further, DUBs have emerged as novel players in HH signaling transduction, resulting as attractive and promising drug targets. Here, we review the HH-associated DUBs, discussing the consequences of deubiquitylation on the maintenance of the HH pathway activity and its implication in tumorigenesis. We also report the recent progress in the development of selective inhibitors for the DUBs here reviewed, with potential applications for the treatment of HH-related tumors.