Therapeutic inhibition of USP7-PTEN network in chronic lymphocytic leukemia: a strategy to overcome TP53 mutated/deleted clones

Multiple omics levels of chronic lymphocytic leukemia

Chronic lymphocytic leukemia (CLL) is a lymphoproliferative malignancy characterized by the proliferation of functionally mature but incompetent B cells. It is the most prevalent type of leukemia in Western populations, accounting for approximately 25% of new leukemia cases. While recent advances, such as ibrutinib and venetoclax treatment have improved patient outlook, aggressive forms of CLL such as Richter transformation still pose a significant challenge. This discrepancy may be due to the heterogeneity of factors contributing to CLL development at multiple -omics levels. However, information on the omics of CLL is fragmented, hindering multi-omics-based research into potential treatment options. To address this, we aggregated and presented a selection of important aspects of various omics levels of the disease in this review. The purpose of the present literature analysis is to portray examples of CLL studies from different omics levels, including genomics, epigenomics, transcriptomics, epitranscriptomics, proteomics, epiproteomics, metabolomics, glycomics and lipidomics, as well as those identified by multi-omics approaches. The review includes the list of 102 CLL-associated genes with relevant genomics information. While single-omics studies yield substantial and useful data, they omit a significant level of complex biological interplay present in the disease. As multi-omics studies integrate several different layers of data, they may be better suited for complex diseases such as CLL and have thus far yielded promising results. Future multi-omics studies may assist clinicians in improved treatment choices based on CLL subtypes as well as allow the identification of novel biomarkers and targets for treatments.

Inhibition of USP7 upregulates USP22 and activates its downstream cancer-related signaling pathways in human cancer cells

Deubiquitinases (DUBs) play important roles in various human cancers and targeting DUBs is considered as a novel anticancer therapeutic strategy. Overexpression of ubiquitin specific protease 7 and 22 (USP7 and USP22) are associated with malignancy, therapy resistance, and poor prognosis in many cancers. Although both DUBs are involved in the regulation of similar genes and signaling pathways, such as histone H2B monoubiquitination (H2Bub1), c-Myc, FOXP3, and p53, the interdependence of USP22 and USP7 expression has never been described. In the study, we found that targeting USP7 via either siRNA-mediated knockdown or pharmaceutical inhibitors dramatically upregulates USP22 in cancer cells. Mechanistically, the elevated USP22 occurs through a transcriptional pathway, possibly due to desuppression of the transcriptional activity of SP1 via promoting its degradation upon USP7 inhibition. Importantly, increased USP22 expression leads to significant activation of downstream signal pathways including H2Bub1 and c-Myc, which may potentially enhance cancer malignancy and counteract the anticancer efficacy of USP7 inhibition. Importantly, targeting USP7 further suppresses the in vitro proliferation of USP22-knockout (USP22-Ko) A549 and H1299 lung cancer cells and induces a stronger activation of p53 tumor suppressor signaling pathway. In addition, USP22-Ko cancer cells are more sensitive to a combination of cisplatin and USP7 inhibitor. USP7 inhibitor treatment further suppresses in vivo angiogenesis and tumor growth and induced more apoptosis in USP22-Ko cancer xenografts. Taken together, our findings demonstrate that USP7 inhibition can dramatically upregulate USP22 in cancer cells; and targeting USP7 and USP22 may represent a more effective approach for targeted cancer therapy, which warrants further study. Video Abstract.

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.

USP15-USP7 Axis and UBE2T Differential Expression May Predict Pathogenesis and Poor Prognosis in De Novo Myelodysplastic Neoplasm

The aim of this study was to evaluate the expression of USP7, USP15, UBE2O, and UBE2T genes in Myelodysplastic neoplasm (MDS) to identify possible targets of ubiquitination and deubiquitination in MDS pathobiology. To achieve this, eight datasets from the Gene Expression Omnibus (GEO) database were integrated, and the expression relationship of these genes was analyzed in 1092 MDS patients and healthy controls. Our results showed that UBE2O, UBE2T, and USP7 were upregulated in MDS patients compared with healthy individuals, but only in mononucleated cells collected from bone marrow samples (p < 0.001). In contrast, only the USP15 gene showed a downregulated expression compared with healthy individuals (p = 0.03). Additionally, the upregulation of UBE2T expression was identified in MDS patients with chromosomal abnormalities compared with patients with normal karyotypes (p = 0.0321), and the downregulation of UBE2T expression was associated with MDS hypoplastic patients (p = 0.033). Finally, the USP7 and USP15 genes were strongly correlated with MDS (r = 0.82; r2 = 0.67; p < 0.0001). These findings suggest that the differential expression of the USP15-USP7 axis and UBE2T may play an important role in controlling genomic instability and the chromosomal abnormalities that are a striking characteristic of MDS.

USP7 - a crucial regulator of cancer hallmarks

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

Recent advances in the pharmacological targeting of ubiquitin-regulating enzymes in cancer

As a post-translational modification that has pivotal roles in protein degradation, ubiquitination ensures that intracellular proteins act in a precise spatial and temporal manner to regulate diversified cellular processes. Perturbation of the ubiquitin system contributes directly to the onset and progression of a wide variety of diseases, including various subtypes of cancer. This highly regulated system has been for years an active research area for drug discovery that is exemplified by several approved drugs. In this review, we will provide an update of the main breakthrough scientific discoveries that have been leading the clinical development of ubiquitin-targeting therapies in the last decade, with a special focus on E1 and E3 modulators. We will further discuss the unique challenges of identifying new potential therapeutic targets within this ubiquitous and highly complex machinery, based on available crystallographic structures, and explore chemical approaches by which these challenges might be met.

The equilibrium of tumor suppression: DUBs as active regulators of PTEN

PTEN is among the most commonly lost or mutated tumor suppressor genes in human cancer. PTEN, a bona fide lipid phosphatase that antagonizes the highly oncogenic PI3K-AKT-mTOR pathway, is considered a major dose-dependent tumor suppressor. Although PTEN function can be compromised by genetic mutations in inherited syndromes and cancers, posttranslational modifications of PTEN may also play key roles in the dynamic regulation of its function. Notably, deregulated ubiquitination and deubiquitination lead to detrimental impacts on PTEN levels and subcellular partitioning, promoting tumorigenesis. While PTEN can be targeted by HECT-type E3 ubiquitin ligases for nuclear import and proteasomal degradation, studies have shown that several deubiquitinating enzymes, including HAUSP/USP7, USP10, USP11, USP13, OTUD3 and Ataxin-3, can remove ubiquitin from ubiquitinated PTEN in cancer-specific contexts and thus reverse ubiquitination-mediated PTEN regulation. Researchers continue to reveal the precise molecular mechanisms by which cancer-specific deubiquitinases of PTEN regulate its roles in the pathobiology of cancer, and new methods of pharmacologically for modulating PTEN deubiquitinases are critical areas of investigation for cancer treatment and prevention. Here, we assess the mechanisms and functions of deubiquitination as a recently appreciated mode of PTEN regulation and review the link between deubiquitinases and PTEN reactivation and its implications for therapeutic strategies.

USP7 targets XIAP for cancer progression: Establishment of a p53-independent therapeutic avenue for glioma

Ubiquitin specific peptidase 7 (USP7) is a deubiquitinating enzyme (DUB) that removes ubiquitin tags from specific target protein substrates in order to alter their degradation rate, sub-cellular localization, interaction, and activity. The induction of apoptosis upon USP7 inhibition is well established in cancer containing wild type p53, which operates through the 'USP7-Mdm2-p53' axis. However, in cancers without functional p53, USP7-dependent apoptosis is induced through many other alternative pathways. Here, we have identified another critical p53 independent path active under USP7 to regulate apoptosis. Proteomics analysis identifies XIAP as a potential target of USP7-dependent deubiquitination. GSEA analysis revealed up-regulation of apoptosis signalling upon USP7 inhibition associated with XIAP down-regulation. Modulation of USP7 expression and activity in multiple cancer cell lines showed that USP7 deubiquitinates XIAP to inhibit apoptosis in a caspase-dependent pathway, and the combinatorial inhibition of USP7 and XIAP induces apoptosis in vitro and in vivo. Immunohistochemical staining revealed that grade-wise accumulation of USP7 correlated with an elevated level of XIAP in glioma tissue. This is the first report on the identification and validation of XIAP as a novel substrate of USP7 and together, they involve in the empowerment of the tumorigenic potential of cancer cells by inhibiting apoptosis.

Degradome-focused RNA interference screens to identify proteases important for breast cancer cell growth

Proteases are known to promote or impair breast cancer progression and metastasis. However, while a small number of the 588 human and 672 murine protease genes have been extensively studied, others were neglected. For an unbiased functional analysis of all genome-encoded proteases, i.e., the degradome, in breast cancer cell growth, we applied an inducible RNA interference library for protease-focused genetic screens. Importantly, these functional screens were performed in two phenotypically different murine breast cancer cell lines, including one stem cell-like cell line that showed phenotypic plasticity under changed nutrient and oxygen availability. Our unbiased genetic screens identified 252 protease genes involved in breast cancer cell growth that were further restricted to 100 hits by a selection process. Many of those hits were supported by literature, but some proteases were novel in their functional link to breast cancer. Interestingly, we discovered that the environmental conditions influence the degree of breast cancer cell dependency on certain proteases. For example, breast cancer stem cell-like cells were less susceptible to depletion of several mitochondrial proteases in hypoxic conditions. From the 100 hits, nine proteases were functionally validated in murine breast cancer cell lines using individual knockdown constructs, highlighting the high reliability of our screens. Specifically, we focused on mitochondrial processing peptidase (MPP) subunits alpha (Pmpca) and beta (Pmpcb) and discovered that MPP depletion led to a disadvantage in cell growth, which was linked to mitochondrial dysfunction.

Backbone and ILV side-chain NMR resonance assignments of the catalytic domain of human deubiquitinating enzyme USP7

Ubiquitin specific protease 7 (USP7) is a deubiquitinating enzyme, which removes ubiquitin tag from numerous protein substrates involved in diverse cellular processes such as cell cycle regulation, apoptosis and DNA damage response. USP7 affects stability, interaction network and cellular localization of its cellular and viral substrates by controlling their ubiquitination status. The large 41 kDa catalytic domain of USP7 harbors the active site of the enzyme. Here we present a nearly complete (93%) NMR resonance assignment of isoleucine, leucine and valine (ILV) side-chains of the USP7 catalytic domain along with a refined nearly complete (93%) assignment of its backbone resonances. The reported ILV methyl group assignment will facilitate further NMR investigations of structure, interactions and conformational dynamics of the USP7 enzyme.

Highlights in USP7 inhibitors for cancer treatment

Ubiquitin-specific protease 7 (USP7) is a member of one of the most largely studied families of deubiquitylating enzymes. It plays a key role modulating the levels of multiple proteins, including tumor suppressors, transcription factors, epigenetic modulators, DNA repair proteins, and regulators of the immune response. The abnormal expression of USP7 is found in various malignant tumors and a high expression signature generally indicates poor tumor prognosis. This suggests USP7 as a promising prognostic and druggable target for cancer therapy. Nonetheless, no approved drugs targeting USP7 have already entered clinical trials. Therefore, the development of potent and selective USP7 inhibitors still requires intensive research and development efforts before the pre-clinical benefits translate into the clinic. This mini review systematically summarizes the role of USP7 as a drug target for cancer therapeutics, as well as the scaffolds, activities, and binding modes of some of the most representative small molecule USP7 inhibitors reported in the scientific literature. To wind up, development challenges and potential combination therapies using USP7 inhibitors for less tractable tumors are also disclosed.

USP7 substrates identified by proteomics analysis reveal the specificity of USP7

Deubiquitylating enzymes (DUBs) remove ubiquitin chains from proteins and regulate protein stability and function. USP7 is one of the most extensively studied DUBs, since USP7 has several well-known substrates important for cancer progression, such as MDM2, N-MYC, and PTEN. Thus, USP7 is a promising drug target. However, systematic identification of USP7 substrates has not yet been performed. In this study, we carried out proteome profiling with label-free quantification in control and single/double-KO cells of USP7and its closest homolog, USP47 Our proteome profiling for the first time revealed the proteome changes caused by USP7 and/or USP47 depletion. Combining protein profiling, transcriptome analysis, and tandem affinity purification of USP7-associated proteins, we compiled a list of 20 high-confidence USP7 substrates that includes known and novel USP7 substrates. We experimentally validated MGA and PHIP as new substrates of USP7. We further showed that MGA deletion reduced cell proliferation, similar to what was observed in cells with USP7 deletion. In conclusion, our proteome-wide analysis uncovered potential USP7 substrates, providing a resource for further functional studies.

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

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

Hes1 Controls Proliferation and Apoptosis in Chronic Lymphoblastic Leukemia Cells by Modulating PTEN Expression

Hairy and enhancer of split homolog-1 (HES1), regulated by the Notch, has been reported to play important roles in the immune response and cancers, such as leukemia. In this study, we aim to explore the effect of HES1-mediated Notch1 signaling pathway in chronic lymphocytic leukemia (CLL). Reverse transcription quantitative polymerase chain reaction and Western blot assay were conducted to determine the expression of HES1, Notch1, and PTEN in B lymphocytes of peripheral blood samples of 60 CLL patients. We used lentivirus-mediated overexpression or silencing of HES1 and the Notch1 signaling pathway inhibitor, MW167, to detect the interaction among HES1, Notch1, and PTEN in CLL MEC1 and HG3 cells. MTT assay and flow cytometry were employed for detection of biological behaviors of CLL cells. HES1 and Notch1 showed high expression, but PTEN displayed low expression in B lymphocytes of peripheral blood samples of patients with CLL in association with poor prognosis. HES1 bound to the promoter region of PTEN and reduced PTEN expression. Overexpression of HES1 activated the Notch1 signaling pathway, thus promoting the proliferation of CLL cells, increasing the proportion of cells arrested at the S phase and limiting the apoptosis of CLL cells. Collectively, HES1 can promote activation of the Notch1 signaling pathway to cause PTEN transcription inhibition and the subsequent expression reduction, thereby promoting the proliferation and inhibiting the apoptosis of CLL cells.

Ubiquitin-Specific Peptidase 7: A Novel Deubiquitinase That Regulates Protein Homeostasis and Cancers

Ubiquitin-Specific Peptidase 7 (USP7), or herpes virus-associated protease (HAUSP), is the largest family of the deubiquitinating enzymes (DUBs). Recent studies have shown that USP7 plays a vital role in regulating various physiological and pathological processes. Dysregulation of these processes mediated by USP7 may contribute to many diseases, such as cancers. Moreover, USP7 with aberrant expression levels and abnormal activity are found in cancers. Therefore, given the association between USP7 and cancers, targeting USP7 could be considered as an attractive and potential therapeutic approach in cancer treatment. This review describes the functions of USP7 and the regulatory mechanisms of its expression and activity, aiming to emphasize the necessity of research on USP7, and provide a better understanding of USP7-related biological processes and cancer.

Elastin MIcrofibriL INterfacer1 (EMILIN-1) is an alternative prosurvival VLA-4 ligand in chronic lymphocytic leukemia

CD49d, the α4 chain of the VLA-4 integrin, is a negative prognosticator in chronic lymphocytic leukemia (CLL) with a key role in CLL cell-microenvironment interactions mainly occurring via its ligands VCAM-1 and fibronectin. In the present study, we focused on EMILIN-1 (Elastin-MIcrofibriL-INterfacer-1), an alternative VLA-4 ligand whose role has been so far reported only in non-hematological settings, by investigating: i) the distribution of EMILIN-1 in CLL-involved tissues; ii) the capability of EMILIN-1 to operate, via its globular C1q (gC1q) domain, as additional adhesion ligand in CLL; iii) the functional meaning of EMILIN-1 gC1q/VLA-4 interactions in CLL. EMILIN-1 is widely present in the CLL-involved areas of bone marrow biopsies (BMBs) without difference between CD49d negative and positive cases, displaying at least three different expression patterns: "fibrillar", "dot-like" and "mixed". The lack in CLL-BMB of neutrophil elastase, whose proteolytic activity degrades EMILIN-1 and impairs EMILIN-1 function, suggests full functional EMILIN-1 in CLL independently of its expression pattern. Functionally, EMILIN-1 gC1q domain promotes adhesion of CLL cells through specific interaction with VLA-4, and releases pro-survival signals for CLL cells, as demonstrated by enhanced ERK and AKT phosphorylation and impairment of in-vitro-induced apoptosis. EMILIN-1/VLA-4 interaction can efficiently contribute to the maintenance of the neoplastic clone in CLL.

Targeting the p53 Pathway in CLL: State of the Art and Future Perspectives

The p53 pathway is a desirable therapeutic target, owing to its critical role in the maintenance of genome integrity. This is exemplified in chronic lymphocytic leukemia (CLL), one of the most common adult hematologic malignancies, in which functional loss of p53 arising from genomic aberrations are frequently associated with clonal evolution, disease progression, and therapeutic resistance, even in the contemporary era of CLL targeted therapy and immunotherapy. Targeting the 'undruggable' p53 pathway therefore arguably represents the holy grail of cancer research. In recent years, several strategies have been proposed to exploit p53 pathway defects for cancer treatment. Such strategies include upregulating wild-type p53, restoring tumor suppressive function in mutant p53, inducing synthetic lethality by targeting collateral genome maintenance pathways, and harnessing the immunogenicity of p53 pathway aberrations. In this review, we will examine the biological and clinical implications of p53 pathway defects, as well as our progress towards development of therapeutic approaches targeting the p53 pathway, specifically within the context of CLL. We will appraise the opportunities and pitfalls associated with these therapeutic strategies, and evaluate their place amongst the array of new biological therapies for CLL.

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

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

Deubiquitinases in hematological malignancies

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

USP7 promotes hepatoblastoma progression through activation of PI3K/AKT signaling pathway

BACKGROUND

Hepatoblastoma (HB) is an embryonic solid tumor and the most common primary malignant liver tumor in children. HB usually occurs in infants and children. Although treatment diversity is increasing, some patients still have very poor prognosis. Many studies have investigated USP7 inhibitors for tumors. Using database information, we found that USP7 is highly expressed in HB.

METHODS

Lentivirus-mediated USP7 knockdown and overexpression was performed in HB cell lines HepG2 and Huh6. CCK8 and transwell assays were used to determine cell viability and metastasis. Flow cytometry was used to study cell cycle and apoptosis. Levels of proteins were detected using western blots.

RESULTS

Downregulation of USP7 resulted in significant decrease in cell proliferation, clonal formation, and cell migration and invasion. With overexpression of USP7, cellular malignant behavior increased. Cell cycle assays showed that USP7 knockdown inhibited G1 to S phase transition in the cell cycle. Upregulation of USP7 promoted the transition. Animal experiments showed USP7 facilitated tumor growth in vivo. Western blots indicated that USP7 may affect HB tumorigenesis through the PI3K/AKT signaling pathway. Furthermore, USP7 inhibitor P5091 inhibited HB development and PI3K/AKT pathway.

CONCLUSION

USP7 upregulation contributed to HB genesis and development through the PI3K/AKT signaling pathway. USP7 could be a potential target for future HB treatment.

CARD11 is a novel target of miR-181b that is upregulated in chronic lymphocytic leukemia

Aim: To investigate the targets of miR-181b in patients with chronic lymphocytic leukemia (CLL). Materials & methods: The bioinformatic softwares were used to indicate the key target genes associated with miR-181b, and the results were verified in CLL patient samples and 293T cells. Results: CARD11 is a potential target gene of miR-181b, an inverse relationship was revealed between the expression of CARD11 and miR-181b in 104 CLL patients, and it was confirmed in vitro with luciferase assays and western blotting. Kaplan-Meier analysis showed that CLL patients with high CARD11 expression demonstrated poor survival. Conclusion: CARD11 is a novel target of miR-181b that is upregulated, which could be a poor prognostic indicator for CLL patients.

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.

The USP7-TRIM27 axis mediates non-canonical PRC1.1 function and is a druggable target in leukemia

In an attempt to unravel functionality of the non-canonical PRC1.1 Polycomb complex in human leukemogenesis, we show that USP7 and TRIM27 are integral components of PRC1.1. USP7 interactome analyses show that PRC1.1 is the predominant Polycomb complex co-precipitating with USP7. USP7 inhibition results in PRC1.1 disassembly and loss of chromatin binding, coinciding with reduced H2AK119ub and H3K27ac levels and diminished gene transcription of active PRC1.1-controlled loci, whereas H2AK119ub marks are also lost at PRC1 loci. TRIM27 and USP7 are reciprocally required for incorporation into PRC1.1, and TRIM27 knockdown partially rescues USP7 inhibitor sensitivity. USP7 inhibitors effectively impair proliferation in AML cells in vitro, also independent of the USP7-MDM2-TP53 axis, and MLL-AF9-induced leukemia is delayed in vivo in human leukemia xenografts. We propose a model where USP7 counteracts TRIM27 E3 ligase activity, thereby maintaining PRC1.1 integrity and function. Moreover, USP7 inhibition may be a promising new strategy to treat AML patients.

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We identify USP7 and TRIM27 as integral components of non-canonical PRC1.1

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USP7 inhibition results in PRC1.1 disassembly and loss of chromatin binding

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TRIM27 and USP7 are reciprocally required for incorporation into PRC1.1

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USP7 inhibitors effectively impair AML proliferation, also independent of TP53

Integrative network analysis reveals USP7 haploinsufficiency inhibits E-protein activity in pediatric T-lineage acute lymphoblastic leukemia (T-ALL)

USP7, which encodes a deubiquitylating enzyme, is among the most frequently mutated genes in pediatric T-ALL, with somatic heterozygous loss-of-function mutations (haploinsufficiency) predominantly affecting the subgroup that has aberrant TAL1 oncogene activation. Network analysis of > 200 T-ALL transcriptomes linked USP7 haploinsufficiency with decreased activities of E-proteins. E-proteins are also negatively regulated by TAL1, leading to concerted down-regulation of E-protein target genes involved in T-cell development. In T-ALL cell lines, we showed the physical interaction of USP7 with E-proteins and TAL1 by mass spectrometry and ChIP-seq. Haploinsufficient but not complete CRISPR knock-out of USP7 showed accelerated cell growth and validated transcriptional down-regulation of E-protein targets. Our study unveiled the synergistic effect of USP7 haploinsufficiency with aberrant TAL1 activation on T-ALL, implicating USP7 as a haploinsufficient tumor suppressor in T-ALL. Our findings caution against a universal oncogene designation for USP7 while emphasizing the dosage-dependent consequences of USP7 inhibitors currently under development as potential cancer therapeutics.

Ubiquitin-specific protease 7 as a potential therapeutic target in dogs with hematopoietic malignancies

Background

Ubiquitin‐specific protease 7 (USP7) belongs to the group of deubiquitinating enzymes (DUBs), which remove ubiquitin which controls various cellular processes such as chromosome segregation, DNA repair, gene expression, protein localization, kinase activity, protein degradation, cell cycle progression, and apoptosis. It is critical for several important functions in the cell, and therefore dysregulation of USP7 can contribute to tumorigenesis.

Objectives

Alterations in the USP7 protein have been identified in various malignancies of humans. Our aim was to examine whether USP7 could be a potential therapeutic target in hematopoietic cancers of dogs.

Methods

The expression level of USP7 in lymphocytes from healthy dogs and canine lymphoma cells was determined, and the effect of USP7 inhibition on the vital functions of canine cancer cells was examined.

Results

We showed that USP7 was overexpressed in lymphomas in dogs. The USP7 inhibitor P5091 has selective cytotoxic activity in canine lymphoma and leukemia cell lines. Our results indicate that inhibition of USP7 leads to a disruption of cell cycle progression, and triggers DNA damage and apoptosis. The observed proapoptotic effect of the USP7 inhibitor most likely is not dependent on the p53 pathway.

Conclusions and Clinical Importance

Our results suggest that USP7 could be explored as a potential therapeutic target in dogs with lymphoma. The effectiveness of USP7 inhibition in malignant cells is predicted to be independent of their p53 status.

The Synergism between DHODH Inhibitors and Dipyridamole Leads to Metabolic Lethality in Acute Myeloid Leukemia

Dihydroorotate Dehydrogenase (DHODH) is a key enzyme of the de novo pyrimidine biosynthesis, whose inhibition can induce differentiation and apoptosis in acute myeloid leukemia (AML). DHODH inhibitors had shown promising in vitro and in vivo activity on solid tumors, but their effectiveness was not confirmed in clinical trials, probably because cancer cells exploited the pyrimidine salvage pathway to survive. Here, we investigated the antileukemic activity of MEDS433, the DHODH inhibitor developed by our group, against AML. Learning from previous failures, we mimicked human conditions (performing experiments in the presence of physiological uridine plasma levels) and looked for synergic combinations to boost apoptosis, including classical antileukemic drugs and dipyridamole, a blocker of the pyrimidine salvage pathway. MEDS433 induced apoptosis in multiple AML cell lines, not only as a consequence of differentiation, but also directly. Its combination with antileukemic agents further increased the apoptotic rate, but when experiments were performed in the presence of physiological uridine concentrations, results were less impressive. Conversely, the combination of MEDS433 with dipyridamole induced metabolic lethality and differentiation in all AML cell lines; this extraordinary synergism was confirmed on AML primary cells with different genetic backgrounds and was unaffected by physiological uridine concentrations, predicting in human activity.

Non-Coding RNAs: The "Dark Side Matter" of the CLL Universe

For many years in the field of onco-hematology much attention has been given to mutations in protein-coding genes or to genetic alterations, including large chromosomal losses or rearrangements. Despite this, biological and clinical needs in this sector remain unmet. Therefore, it is not surprising that recent studies have shifted from coded to non-coded matter. The discovery of non-coding RNAs (ncRNAs) has influenced several aspects related to the treatment of cancer. In particular, in chronic lymphocytic leukemia (CLL) the knowledge of ncRNAs and their contextualization have led to the identification of new biomarkers used to follow the course of the disease, to the anticipation of mechanisms that support resistance and relapse, and to the selection of novel targeted treatment regimens. In this review, we will summarize the main ncRNAs discovered in CLL and the molecular mechanisms by which they are affected and how they influence the development and the progression of the disease.

Therapeutic Options for Patients with TP53 Deficient Chronic Lymphocytic Leukemia: Narrative Review

Chronic lymphocytic leukemia (CLL), which is the most common type of leukemia in western countries in adults, is characterized by heterogeneity in clinical course, prognosis and response to the treatment. Although, in recent years a number of factors with probable prognostic value in CLL have been identified (eg NOTCH1, SF3B1 and BIRC-3 mutations, or evaluation of microRNA expression), TP53 aberrations are still the most important single factors of poor prognosis. It was found that approximately 30% of all TP53 defects are mutations lacking 17p13 deletion, whereas sole 17p13 deletion with the absence of TP53 mutation consists of 10% of all TP53 defects. The detection of del(17)(p13) and/or TP53 mutation is not a criterion itself for starting antileukemic therapy, but it is associated with an aggressive course of the disease and poor response to the standard chemoimmunotherapy. Treatment of patients with CLL harbouring TP53-deficiency requires drugs that promote cell death independently of TP53. Novel and smarter therapies revolutionize the treatment of del(17p) and/or aberrant TP53 CLL, but development of alternative therapeutic approaches still remains an issue of critical importance.

Deubiquitinase USP7 contributes to the pathogenicity of spinal and bulbar muscular atrophy

Polyglutamine (polyQ) diseases are devastating, slowly progressing neurodegenerative conditions caused by expansion of polyQ-encoding CAG repeats within the coding regions of distinct, unrelated genes. In spinal and bulbar muscular atrophy (SBMA), polyQ expansion within the androgen receptor (AR) causes progressive neuromuscular toxicity, the molecular basis of which is unclear. Using quantitative proteomics, we identified changes in the AR interactome caused by polyQ expansion. We found that the deubiquitinase USP7 preferentially interacts with polyQ-expanded AR and that lowering USP7 levels reduced mutant AR aggregation and cytotoxicity in cell models of SBMA. Moreover, USP7 knockdown suppressed disease phenotypes in SBMA and spinocerebellar ataxia type 3 (SCA3) fly models, and monoallelic knockout of Usp7 ameliorated several motor deficiencies in transgenic SBMA mice. USP7 overexpression resulted in reduced AR ubiquitination, indicating the direct action of USP7 on AR. Using quantitative proteomics, we identified the ubiquitinated lysine residues on mutant AR that are regulated by USP7. Finally, we found that USP7 also differentially interacts with mutant Huntingtin (HTT) protein in striatum and frontal cortex of a knockin mouse model of Huntington's disease. Taken together, our findings reveal a critical role for USP7 in the pathophysiology of SBMA and suggest a similar role in SCA3 and Huntington's disease.

[Expression of ubiquitin-specific protease 7 in lung tissue of preterm rats after hyperoxia exposure]

OBJECTIVE

To study the expression and significance of ubiquitin-specific protease 7 (USP7) and the key factors of the Wnt signaling pathway in the lung tissue of preterm rats after hyperoxia exposure.

METHODS

A total of 180 preterm neonatal Wistar rats were randomly divided into an air control group, an air intervention group, a hyperoxia control group, and a hyperoxia intervention group, with 45 rats in each group. Lung injury was induced by hyperoxia exposure in the hyperoxia groups. The preterm rats in the intervention groups were given intraperitoneal injection of the USP7 specific inhibitor P5091 (5 mg/kg) every day. The animals were sacrificed on days 3, 5, and 9 of the experiment to collect lung tissue specimens. Hematoxylin-eosin staining was used to observe the pathological changes of lung tissue. RT-PCR and Western blot were used to measure the mRNA and protein expression levels of USP7 and the key factors of the Wnt signaling pathway β-catenin and α-smooth muscle actin (α-SMA) in lung tissue.

RESULTS

The air groups had normal morphology and structure of lung tissue; on days 3 and 5, the hyperoxia control group showed obvious alveolar compression and disordered structure, with obvious inflammatory cells, erythrocyte diapedesis, and interstitial edema. On day 9, the hyperoxia control group showed alveolar structural disorder and obvious thickening of the alveolar septa. Compared with the hyperoxia control group at the corresponding time points, the hyperoxia intervention group had significantly alleviated disordered structure, inflammatory cell infiltration, and bleeding in lung tissue. At each time point, the hyperoxia groups had a significantly lower radial alveolar count (RAC) than the corresponding air groups (P < 0.05), and the hyperoxia intervention group had a significantly higher RAC than the hyperoxia control group (P < 0.05). On days 3, 5, and 9 of the experiment, the hyperoxia groups had significantly higher mRNA expression of USP7 and β-catenin and protein expression of USP7, β-catenin, and α-SMA than the corresponding air groups (P < 0.05). Compared with the hyperoxia control group, the hyperoxia intervention group had significant reductions in the mRNA expression of β-catenin and the protein expression of β-catenin and α-SMA (P < 0.05), while there were no significant differences in the mRNA and protein expression of USP7 between the hyperoxia intervention and hyperoxia control groups (P > 0.05). There were no significant differences in the mRNA expression of USP7 and β-catenin and the protein expression of USP7, β-catenin, and α-SMA between the air intervention and air control groups (P > 0.05).

CONCLUSIONS

Hyperoxia exposure can activate the Wnt/β-catenin signaling pathway, and USP7 may participate in hyperoxic lung injury through the Wnt/β-catenin signaling pathway. The USP7 specific inhibitor P5091 may accelerate the degradation of β-catenin by enhancing its ubiquitination, reduce lung epithelial-mesenchymal transition, and thus exert a certain protective effect against hyperoxic lung injury.

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

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

The emerging nature of Ubiquitin-specific protease 7 (USP7): a new target in cancer therapy

Human ubiquitin-specific protease 7 (USP7) is a deubiquitinating enzyme that removes the ubiquitin (Ub) protein and spares substrates from degradation. Given its regulation of proteins involved in several cellular processes, abnormal expression and activity of USP7 are associated with several types of disease, including cancer. In this review, we summarize the developments in our understanding of USP7 over the past 5 years, focusing on its role in related cancers. Furthermore, we discuss clinical studies of USP7, including in vivo and pharmacological studies, as well as the development of USP7 inhibitors. A comprehensive understanding of USP7 will expand our knowledge of the structure and function of USP7-mediated signaling and shed light on drug discovery for different diseases in which USP7 is implicated.

Ubiquitin-specific protease 7 downregulation suppresses breast cancer in vitro

Because breast cancer is complicated at the pathological, histological, clinical, and molecular levels, identification of new genetic targets against carcinogenic pathways is required to generate clinically relevant treatment options. In the current study, ubiquitin-specific protease 7 (USP7), which regulates various cellular pathways including Mdm2, p53, and NF–κB, was selected as a potential gene editing strategy for breast cancer in vitro. Anticancer activity of USP7 gene suppression has been evaluated through cell proliferation, gene expression, cell cycle, sphere dissemination, and cell migration analysis. Here, siRNA and shRNA strategies and an allosteric small-molecule inhibitor of USP7 were used to define potential anticancer activity against MCF7 and T47D human breast cancer cell lines. Both blockage of deubiquitination by p5091 and knockdown of USP7 reduced cell proliferation, cell migration, colony formation, and sphere dissemination for both MCF7 and T47D breast cancer cell lines. Restriction of USP7 activity strongly enhanced apoptotic gene expression and reduced metastatic ability of breast cancer cell lines. This study describes one potential molecular target for the suppression of breast cancer proliferation and metastasis. Identification of USP7 as a promising gene editing candidate might open up the possibility of new molecular drug research in targeting the ubiquitination pathway in cancer.

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.

Inhibition of ubiquitin-specific protease 7 sensitizes acute myeloid leukemia to chemotherapy

Resistance of acute myeloid leukemia (AML) to therapeutic agents is frequent. Consequently, the mechanisms leading to this resistance must be understood and addressed. In this paper, we demonstrate that inhibition of deubiquitinylase USP7 significantly reduces cell proliferation in vitro and in vivo, blocks DNA replication progression and increases cell death in AML. Transcriptomic dataset analyses reveal that a USP7 gene signature is highly enriched in cells from AML patients at relapse, as well as in residual blasts from patient-derived xenograft (PDX) models treated with clinically relevant doses of cytarabine, which indicates a relationship between USP7 expression and resistance to therapy. Accordingly, single-cell analysis of AML patient samples at relapse versus at diagnosis showed that a gene signature of the pre-existing subpopulation responsible for relapse is enriched in transcriptomes of patients with a high USP7 level. Furthermore, we found that USP7 interacts and modulates CHK1 protein levels and functions in AML. Finally, we demonstrated that USP7 inhibition acts in synergy with cytarabine to kill AML cell lines and primary cells of patients with high USP7 levels. Altogether, these data demonstrate that USP7 is both a marker of resistance to chemotherapy and a potential therapeutic target in overcoming resistance to treatment.

Tumor Suppressors in Chronic Lymphocytic Leukemia: From Lost Partners to Active Targets

Tumor suppressors play an important role in cancer pathogenesis and in the modulation of resistance to treatments. Loss of function of the proteins encoded by tumor suppressors, through genomic inactivation of the gene, disable all the controls that balance growth, survival, and apoptosis, promoting cancer transformation. Parallel to genetic impairments, tumor suppressor products may also be functionally inactivated in the absence of mutations/deletions upon post-transcriptional and post-translational modifications. Because restoring tumor suppressor functions remains the most effective and selective approach to induce apoptosis in cancer, the dissection of mechanisms of tumor suppressor inactivation is advisable in order to further augment targeted strategies. This review will summarize the role of tumor suppressors in chronic lymphocytic leukemia and attempt to describe how tumor suppressors can represent new hopes in our arsenal against chronic lymphocytic leukemia (CLL).

Inhibition of USP7 activity selectively eliminates senescent cells in part via restoration of p53 activity

The accumulation of senescent cells (SnCs) is a causal factor of various age‐related diseases as well as some of the side effects of chemotherapy. Pharmacological elimination of SnCs (senolysis) has the potential to be developed into novel therapeutic strategies to treat these diseases and pathological conditions. Here we show that ubiquitin‐specific peptidase 7 (USP7) is a novel target for senolysis because inhibition of USP7 with an inhibitor or genetic depletion of USP7 by RNA interference induces apoptosis selectively in SnCs. The senolytic activity of USP7 inhibitors is likely attributable in part to the promotion of the human homolog of mouse double minute 2 (MDM2) ubiquitination and degradation by the ubiquitin–proteasome system. This degradation increases the levels of p53, which in turn induces the pro‐apoptotic proteins PUMA, NOXA, and FAS and inhibits the interaction of BCL‐XL and BAK to selectively induce apoptosis in SnCs. Further, we show that treatment with a USP7 inhibitor can effectively eliminate SnCs and suppress the senescence‐associated secretory phenotype (SASP) induced by doxorubicin in mice. These findings suggest that small molecule USP7 inhibitors are novel senolytics that can be exploited to reduce chemotherapy‐induced toxicities and treat age‐related diseases.

Inhibition of bromodomain and extra-terminal proteins increases sensitivity to venetoclax in chronic lymphocytic leukaemia

The development of drugs able to target BTK, PI3k‐delta and BCL2 has dramatically improved chronic lymphocytic leukaemia (CLL) therapies. However, drug resistance to these therapies has already been reported due to non‐recurrent changes in oncogenic pathways and genes expression signatures. In this study, we investigated the cooperative role of the BCL2 inhibitor venetoclax and the BRD4 inhibitor JQ1. In particular, we found that JQ1 shows additional activity with venetoclax, in CLL cell lines and in ex vivo isolated primary CD19⁺ lymphocytes, arguing in favour of combination strategies. Lastly, JQ1 is also effective in venetoclax‐resistant CLL cell lines. Together, our findings indicated that the BET inhibitor JQ1 could be a promising therapy in CLL, both as first‐line therapy in combination with venetoclax and as second‐line therapy, after the emergence of venetoclax‐resistant clones.

Strategies For Targeting Chronic Myeloid Leukaemia Stem Cells

Chronic Myeloid Leukaemia is a myeloproliferative disorder driven by the t(9;22) chromosomal translocation coding for the chimeric protein BCR-ABL. CML treatment represents the paradigm of molecular therapy of cancer. Since the development of the tyrosine kinase inhibitor of the BCR-ABL kinase, the clinical approach to CML has dramatically changed, with a stunning improvement in the quality of life and response rates of patients. However, it remains clear that tyrosine kinase inhibitors (TKIs) are unable to target the most immature cellular component of CML, the CML stem cell. This review summarizes new insights into the mechanisms of resistance to TKIs.

USP7: Novel Drug Target in Cancer Therapy

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

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.

Nuclear deubiquitination in the spotlight: the multifaceted nature of USP7 biology in disease

Ubiquitination is a versatile and tightly regulated post-translational protein modification with many distinct outcomes affecting protein stability, localization, interactions, and activity. Ubiquitin chain linkages anchored on substrates can be further modified by additional post-translational modifications, including phosphorylation and SUMOylation. Deubiquitinases (DUBs) reverse these ubiquitin marks with matched levels of precision. Over hundred known DUBs regulate a wide variety of cellular events. In this review, we focus on ubiquitin-specific protease 7 (USP7, also known as herpesvirus-associated ubiquitin-specific protease, or HAUSP) as one of the best studied, disease-associated DUBs. By highlighting the functions of USP7, particularly in the nucleus, and the emergence of the newest generation of USP7 inhibitors, we illustrate the importance of individual DUBs in the nucleus, and the therapeutic prospects of DUB targeting in human disease.

Increase in the nuclear localization of PTEN by the Toxoplasma GRA16 protein and subsequent induction of p53-dependent apoptosis and anticancer effect

This study investigated the efficacy of Toxoplasma GRA16, which binds to herpes virus‐associated ubiquitin‐specific protease (HAUSP), in anticancer treatment, and whether the expression of GRA16 in genetically modified hepatocellular carcinoma (HCC) cells (GRA16‐p53‐wild HepG2 and GRA16‐p53‐null Hep3B) regulates PTEN because alterations in phosphatase and tensin homologue (PTEN) and p53 are vital in liver carcinogenesis and the abnormal p53 gene appears in HCC. For this purpose, we established the GRA16 cell lines using the pBABE retrovirus system, assessed the detailed mechanism of PTEN regulation in vitro and established the anticancer effect in xenograft mice. Our study showed that cell proliferation, antiapoptotic factors, p‐AKT/AKT ratio, cell migration and invasive activity were decreased in GRA16‐stable HepG2 cells. Conversely, the apoptotic factors PTEN and p53 and apoptotic cells were elevated in GRA16‐stable HepG2 cells but not in Hep3B cells. The change in MDM2 was inconspicuous in both HepG2 and Hep3B; however, the PTEN level was remarkably elevated in HepG2 but not in Hep3B. HAUSP‐bound GRA16 preferentially increased p53 stabilization by the nuclear localization of PTEN rather than MDM2‐dependent mechanisms. These molecular changes appeared to correlate with the decreased tumour mass in GRA16‐stable‐HepG2 cell‐xenograft nude mice. This study establishes that GRA16 is a HAUSP inhibitor that targets the nuclear localization of PTEN and induces the anticancer effect in a p53‐dependent manner. The efficacy of GRA16 could be newly highlighted in HCC treatment in a p53‐dependent manner.

CCDC6 and USP7 expression levels suggest novel treatment options in high-grade urothelial bladder cancer

Background

The muscle invasive form of urothelial bladder cancer (UBC) is a deadly disease. Currently, the therapeutic approach of UBC is mostly based on surgery and standard chemotherapy.

Biomarkers to establish appropriate drugs usage are missing. Deficiency of the tumor suppressor CCDC6 determines PARP-inhibitor sensitivity. The CCDC6 levels are modulated by the deubiquitinase USP7. In this work we scored CCDC6 and USP7 expression levels in primary UBC and we evaluated the expression levels of CCDC6 in correlation with the effects of the PARP-inhibitors combined with the USP7 inhibitor, P5091, in vitro. Since PARP-inhibitors could be enhanced by conventional chemotherapy or DNA damage inducers, we tested the new agent RRx-001, able to induce DNA damage, to prove the benefit of combined treatments in bladder cancer cells.

Methods

The J82, T24, 5637 and KU-19-19 bladder cancer cells were exposed to USP7 inhibitor P5091 in presence of cycloheximide to analyse the CCDC6 stability. Upon the CCDC6 degradation induced by P5091, the cells sensitivity to PARP-inhibitor was evaluated by cell viability assays. The ability of the DNA damage inducer RRx-001 to modulate CCDC6 protein levels and H2AX phosphorylation was detected at immunoblot. The combination of USP7 inhibitor plus RRx-001 enhanced the PARP-inhibitor sensitivity, as evaluated by cell viability assays. The results of the scores and correlation of CCDC6 and USP7 expression levels obtained by UBC primary biopsies staining were used to cluster patients by a K-mean cluster analysis.

Results

P5091 determining CCDC6 degradation promoted bladder cancer cells sensitivity to PARP-inhibitor drugs. RRx-001, by inducing DNA damage, enhanced the effects of the combined treatment. The immunohistochemical staining of both CCDC6 and USP7 proteins allowed to cluster the high grade (G3) UBC patients, on the basis of CCDC6 expression levels.

Conclusions

In high grade UBC the identification of two clusters of patients based on CCDC6 and USP7 expession can possibly indicate the use of PARP-inhibitor drugs, in combination with USP7 inhibitor in addition to the DNA damage inducer RRx-001, that also acts as an immunomodulatory agent, offering novel therapeutic strategy for personalized medicine in bladder cancer patients.

Electronic supplementary material

The online version of this article (10.1186/s13046-019-1087-1) contains supplementary material, which is available to authorized users.

USP7: Structure, substrate specificity, and inhibition

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

USP7 Cooperates with NOTCH1 to Drive the Oncogenic Transcriptional Program in T-Cell Leukemia

PURPOSE

T-cell acute lymphoblastic leukemia (T-ALL) is an aggressive disease, affecting children and adults. Chemotherapy treatments show high response rates but have debilitating effects and carry risk of relapse. Previous work implicated NOTCH1 and other oncogenes. However, direct inhibition of these pathways affects healthy tissues and cancer alike. Our goal in this work has been to identify enzymes active in T-ALL whose activity could be targeted for therapeutic purposes.

EXPERIMENTAL DESIGN

To identify and characterize new NOTCH1 druggable partners in T-ALL, we coupled studies of the NOTCH1 interactome to expression analysis and a series of functional analyses in cell lines, patient samples, and xenograft models.

RESULTS

We demonstrate that ubiquitin-specific protease 7 (USP7) interacts with NOTCH1 and controls leukemia growth by stabilizing the levels of NOTCH1 and JMJD3 histone demethylase. USP7 is highly expressed in T-ALL and is transcriptionally regulated by NOTCH1. In turn, USP7 controls NOTCH1 levels through deubiquitination. USP7 binds oncogenic targets and controls gene expression through stabilization of NOTCH1 and JMJD3 and ultimately H3K27me3 changes. We also show that USP7 and NOTCH1 bind T-ALL superenhancers, and inhibition of USP7 leads to a decrease of the transcriptional levels of NOTCH1 targets and significantly blocks T-ALL cell growth in vitro and in vivo.

CONCLUSIONS

These results provide a new model for USP7 deubiquitinase activity through recruitment to oncogenic chromatin loci and regulation of both oncogenic transcription factors and chromatin marks to promote leukemia. Our studies also show that targeting USP7 inhibition could be a therapeutic strategy in aggressive leukemia.

Targeting USP7 Identifies a Metastasis-Competent State within Bone Marrow-Resident Melanoma CTCs

Systemic metastasis is the major cause of death from melanoma, the most lethal form of skin cancer. Although most patients with melanoma exhibit a substantial gap between onset of primary and metastatic tumors, signaling mechanisms implicated in the period of metastatic latency remain unclear. We hypothesized that melanoma circulating tumor cells (CTC) home to and reside in the bone marrow during the asymptomatic phase of disease progression. Using a strategy to deplete normal cell lineages (Lin-), we isolated CTC-enriched cell populations from the blood of patients with metastatic melanoma, verified by the presence of putative CTCs characterized by melanoma-specific biomarkers and upregulated gene transcripts involved in cell survival and prodevelopment functions. Implantation of Lin- population in NSG mice (CTC-derived xenografts, i.e., CDX), and subsequent transcriptomic analysis of ex vivo bone marrow-resident tumor cells (BMRTC) versus CTC identified protein ubiquitination as a significant regulatory pathway of BMRTC signaling. Selective inhibition of USP7, a key deubiquinating enzyme, arrested BMRTCs in bone marrow locales and decreased systemic micrometastasis. This study provides first-time evidence that the asymptomatic progression of metastatic melanoma can be recapitulated in vivo using patient-isolated CTCs. Furthermore, these results suggest that USP7 inhibitors warrant further investigation as a strategy to prevent progression to overt clinical metastasis.Significance: These findings provide insights into mechanism of melanoma recurrence and propose a novel approach to inhibit systematic metastatic disease by targeting bone marrow-resident tumor cells through pharmacological inhibition of USP7.Graphical Abstract: http://cancerres.aacrjournals.org/content/canres/78/18/5349/F1.large.jpg Cancer Res; 78(18); 5349-62. ©2018 AACR.