Stabilization of the transcription factors slug and twist by the deubiquitinase dub3 is a key requirement for tumor metastasis

DUB3 is a MAGEA3 deubiquitinase and a potential therapeutic target in hepatocellular carcinoma

Although melanoma-associated antigen A3 and A6 (MAGEA3/6)-specific tumor vaccines have shown antitumor effects in melanoma and non-small cell lung cancer (NSCLC), many cancers do not respond because MAGEA3 can promote cancer without triggering an immune response. Here, we identified DUB3 as the MAGEA3 deubiquitinase. DUB3 interacts with, deubiquitinates and stabilizes MAGEA3. Depletion of DUB3 in hepatocellular carcinoma (HCC) cells results in MAGEA3 degradation and P53-dependent growth inhibition. Moreover, DUB3 knockout attenuates HCC tumorigenesis in vivo, which can be rescued by restoration of MAGEA3. Intriguingly, pharmacological inhibition of DUB3 by palbociclib promotes degradation of MAGEA3 and inhibits tumor growth in preclinical models implanted with parental HCC cells but not with DUB3 knockout HCC cells. In patients with HCC, DUB3 is highly expressed, and its levels positively correlate with MAGEA3 levels. Taken together, DUB3 is a MAGEA3 deubiquitinase, and abrogating DUB3 enzymatic activity by palbociclib is a promising therapeutic strategy for HCC.

Deubiquitylating Enzymes in Cancer and Immunity

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

Proactive and reactive roles of TGF-β in cancer

Cancer cells adapt to varying stress conditions to survive through plasticity. Stem cells exhibit a high degree of plasticity, allowing them to generate more stem cells or differentiate them into specialized cell types to contribute to tissue development, growth, and repair. Cancer cells can also exhibit plasticity and acquire properties that enhance their survival. TGF-β is an unrivaled growth factor exploited by cancer cells to gain plasticity. TGF-β-mediated signaling enables carcinoma cells to alter their epithelial and mesenchymal properties through epithelial-mesenchymal plasticity (EMP). However, TGF-β is a multifunctional cytokine; thus, the signaling by TGF-β can be detrimental or beneficial to cancer cells depending on the cellular context. Those cells that overcome the anti-tumor effect of TGF-β can induce epithelial-mesenchymal transition (EMT) to gain EMP benefits. EMP allows cancer cells to alter their cell properties and the tumor immune microenvironment (TIME), facilitating their survival. Due to the significant roles of TGF-β and EMP in carcinoma progression, it is essential to understand how TGF-β enables EMP and how cancer cells exploit this plasticity. This understanding will guide the development of effective TGF-β-targeting therapies that eliminate cancer cell plasticity.

The ubiquitin-proteasome system in breast cancer

Ubiquitin-proteasome system (UPS) is a selective proteolytic system that is associated with the expression or function of target proteins and participates in various physiological and pathological processes of breast cancer. Inhibitors targeting the 26S proteasome in combination with other drugs have shown promising therapeutic effects in the clinical treatment of breast cancer. Moreover, several inhibitors/stimulators targeting other UPS components are also effective in preclinical studies, but have not yet been applied in the clinical treatment of breast cancer. Therefore, it is vital to comprehensively understand the functions of ubiquitination in breast cancer and to identify potential tumor promoters or tumor suppressors among UPS family members, with the aim of developing more effective and specific inhibitors/stimulators targeting specific components of this system.

Deubiquitinase USP1 influences the dedifferentiation of mouse pancreatic β-cells

Loss of insulin-secreting β-cells in diabetes may be either due to apoptosis or dedifferentiation of β-cell mass. The ubiquitin-proteasome system comprising E3 ligase and deubiquitinases (DUBs) controls several aspects of β-cell functions. In this study, screening for key DUBs identified USP1 to be specifically involved in dedifferentiation process. Inhibition of USP1 either by genetic intervention or small-molecule inhibitor ML323 restored epithelial phenotype of β-cells, but not with inhibition of other DUBs. In absence of dedifferentiation cues, overexpression of USP1 was sufficient to induce dedifferentiation in β-cells; mechanistic insight showed USP1 to mediate its effect via modulating the expression of inhibitor of differentiation (ID) 2. In an in vivo streptozotocin (STZ)-induced dedifferentiation mouse model system, administering ML323 alleviated hyperglycemic state. Overall, this study identifies USP1 to be involved in dedifferentiation of β-cells and its inhibition may have a therapeutic application of reducing β-cell loss during diabetes.

USP13 promotes breast cancer metastasis through FBXL14-induced Twist1 ubiquitination

PURPOSE

Epithelial-to-mesenchymal transition (EMT) is an important cause of high mortality in breast cancer. Twist1 is one of the EMT transcription factors (EMT-TFs) with a noticeably short half-life, which is regulated by proteasome degradation pathways. Recent studies have found that USP13 stabilizes several specific oncogenic proteins. As yet, however, the relationship between Twist1 and USP13 has not been investigated.

METHODS

Co-Immunoprecipitation, GST-pulldown, Western blot, qRT-PCR and immunofluorescence assays were used to investigate the role of USP13 in de-ubiquitination of Twist1. Chromatin immunoprecipitation and Luciferase reporter assays were used to investigate the role of Twist1 in inhibiting USP13 reporter transcription. Scratch wound healing, cell migration and invasion assays, and a mouse lung metastases assay were used to investigate the roles of USP13 and Twist1 in promoting breast cancer metastasis.

RESULTS

We found that Twist1 can be de-ubiquitinated by USP13. In addition, we found that the protein levels of Twist1 dose-dependently increased with USP13 overexpression, while USP13 knockdown resulted in a decreased expression of endogenous Twist1. We also found that USP13 can directly interact with Twist1 and specifically cleave the K48-linked polyubiquitin chains of Twist1 induced by FBXL14. We found that the effect of USP13 in promoting the migration and invasion capacities of breast cancer cells can at least partly be achieved through its regulation of Twist1, while Twist1 can inhibit the transcriptional activity of USP13.

CONCLUSIONS

Our data indicate that an interplay between Twist1 and USP13 can form a negative physiological feedback loop. Our findings show that USP13 may play an essential role in breast cancer metastasis by regulating Twist1 and, as such, provide a potential target for the clinical treatment of breast cancer.

Renal Cell Carcinoma as a Metabolic Disease: An Update on Main Pathways, Potential Biomarkers, and Therapeutic Targets

Clear cell renal cell carcinoma (ccRCC) is the most frequent histological kidney cancer subtype. Over the last decade, significant progress has been made in identifying the genetic and metabolic alterations driving ccRCC development. In particular, an integrated approach using transcriptomics, metabolomics, and lipidomics has led to a better understanding of ccRCC as a metabolic disease. The metabolic profiling of this cancer could help define and predict its behavior in terms of aggressiveness, prognosis, and therapeutic responsiveness, and would be an innovative strategy for choosing the optimal therapy for a specific patient. This review article describes the current state-of-the-art in research on ccRCC metabolic pathways and potential therapeutic applications. In addition, the clinical implication of pharmacometabolomic intervention is analyzed, which represents a new field for novel stage-related and patient-tailored strategies according to the specific susceptibility to new classes of drugs.

Ubiquitination and deubiquitination in the regulation of epithelial-mesenchymal transition in cancer: Shifting gears at the molecular level

The process of conversion of non-motile epithelial cells to their motile mesenchymal counterparts is known as epithelial-mesenchymal transition (EMT), which is a fundamental event during embryonic development, tissue repair, and for the maintenance of stemness. However, this crucial process is hijacked in cancer and becomes the means by which cancer cells acquire further malignant properties such as increased invasiveness, acquisition of stem cell-like properties, increased chemoresistance, and immune evasion ability. The switch from epithelial to mesenchymal phenotype is mediated by a wide variety of effector molecules such as transcription factors, epigenetic modifiers, post-transcriptional and post-translational modifiers. Ubiquitination and de-ubiquitination are two post-translational processes that are fundamental to the ubiquitin-proteasome system (UPS) of the cell, and the shift in equilibrium between these two processes during cancer dictates the suppression or activation of different intracellular processes, including EMT. Here, we discuss the complex and dynamic relationship between components of the UPS and EMT in cancer.

Atractylodin Induces Apoptosis and Inhibits the Migration of A549 Lung Cancer Cells by Regulating ROS-Mediated Signaling Pathways

Atractylodin (ATR) has anticancer effects on some tumor cells by inducing apoptosis, but its mechanism in lung cancer remains unclear. This study investigates the inhibitory effect of ATR on A549 lung cancer cells. Cell viability was detected by the Cell Counting Kit-8 assay, and results showed that ATR could significantly inhibit the proliferation of A549 cells. Apoptosis was detected by Annexin V-FITC/PI staining, and apoptosis rate and mitochondrial membrane potential were detected by flow cytometry. Results showed that the effect of ATR on the apoptosis of A549 cells was negatively correlated with the change in mitochondrial membrane potential. Western blot analysis showed that ATR regulated apoptosis induced by mitogen-activated protein kinase, signal transducer and activator of transcription 3, and nuclear factor kappa B signaling pathways. Analyses of reactive oxygen species (ROS), cell cycle, and cell migration showed that ATR induced intracellular ROS accumulation as an initiation signal to induce cell cycle arrest regulated by the AKT signaling pathway and cell migration inhibition regulated by the Wnt signaling pathway. Results showed that ATR can inhibit cell proliferation, induce cell apoptosis, induce cell cycle arrest, and inhibit the migration of A549 cells (p < 0.05 was considered statistically significant, * p < 0.05, ** p < 0.01 and *** p < 0.001).

DUB3/KLF4 combats tumor growth and chemoresistance in hepatocellular carcinoma

This study aimed to investigate the role of deubiquitinating enzyme 3 (DUB3) in the regulation of Krüppel-like factor 4 (KLF4) expression in hepatocellular carcinoma (HCC). Gain- and loss-of-function assay, luciferase reporter assay, co-immunoprecipitation, and intracellular and extracellular deubiquitination assays were conducted in vitro. A tumor xenograft mouse model was established. The expression of DUB3 and KLF4 was examined in HCC patient specimens. The results showed that DUB3 upregulated KLF4 expression by deubiquitinating and stabilizing KLF4 protein in HCC cells through binding with KLF4. DUB3 inhibited HCC cell proliferation in vitro and tumor growth in vivo while enhancing the chemosensitivity of HCC cells in a KLF4-dependent manner. Furthermore, KLF4 promoted DUB3 transcription by binding to the DUB3 promoter. In HCC patients, DUB3 expression positively correlated with KLF4 expression in HCC tissues. Low DUB3 expression predicted worse overall survival and recurrence in HCC patients. In conclusion, this study revealed a positive DUB3/KLF4 feedback loop that inhibits tumor growth and chemoresistance in HCC. These results suggest that DUB3/KLF4 activation might be a potential therapeutic approach for HCC treatment.

Post-Translational Modifications of BRD4: Therapeutic Targets for Tumor

Bromodomain-containing protein 4 (BRD4), a member of the bromodomain and extraterminal (BET) family, is considered to be a major driver of cancer cell growth and a new target for cancer therapy. Over 30 targeted inhibitors currently in preclinical and clinical trials have significant inhibitory effects on various tumors, including acute myelogenous leukemia (AML), diffuse large B cell lymphoma, prostate cancer, breast cancer and so on. However, resistance frequently occurs, revealing the limitations of BET inhibitor (BETi) therapy and the complexity of the BRD4 expression mechanism and action pathway. Current studies believe that when the internal and external environmental conditions of cells change, tumor cells can directly modify proteins by posttranslational modifications (PTMs) without changing the original DNA sequence to change their functions, and epigenetic modifications can also be activated to form new heritable phenotypes in response to various environmental stresses. In fact, research is constantly being supplemented with regards to that the regulatory role of BRD4 in tumors is closely related to PTMs. At present, the PTMs of BRD4 mainly include ubiquitination and phosphorylation; the former mainly regulates the stability of the BRD4 protein and mediates BETi resistance, while the latter is related to the biological functions of BRD4, such as transcriptional regulation, cofactor recruitment, chromatin binding and so on. At the same time, other PTMs, such as hydroxylation, acetylation and methylation, also play various roles in BRD4 regulation. The diversity, complexity and reversibility of posttranslational modifications affect the structure, stability and biological function of the BRD4 protein and participate in the occurrence and development of tumors by regulating the expression of tumor-related genes and even become the core and undeniable mechanism. Therefore, targeting BRD4-related modification sites or enzymes may be an effective strategy for cancer prevention and treatment. This review summarizes the role of different BRD4 modification types, elucidates the pathogenesis in the corresponding cancers, provides a theoretical reference for identifying new targets and effective combination therapy strategies, and discusses the opportunities, barriers, and limitations of PTM-based therapies for future cancer treatment.

Transcriptional and post-transcriptional control of epithelial-mesenchymal plasticity: why so many regulators?

The dynamic transition between epithelial-like and mesenchymal-like cell states has been a focus for extensive investigation for decades, reflective of the importance of Epithelial-Mesenchymal Transition (EMT) through development, in the adult, and the contributing role EMT has to pathologies including metastasis and fibrosis. Not surprisingly, regulation of the complex genetic networks that underlie EMT have been attributed to multiple transcription factors and microRNAs. What is surprising, however, are the sheer number of different regulators (hundreds of transcription factors and microRNAs) for which critical roles have been described. This review seeks not to collate these studies, but to provide a perspective on the fundamental question of whether it is really feasible that so many regulators play important roles and if so, what does this tell us about EMT and more generally, the genetic machinery that controls complex biological processes.

SETD8 stabilized by USP17 epigenetically activates SREBP1 pathway to drive lipogenesis and oncogenesis of ccRCC

Recently, epigenetic modifications, including DNA methylation, histone modification and noncoding RNA (ncRNA)-associated gene silencing, have received increasing attention from the scientific community. Many studies have demonstrated that epigenetic regulation can render dynamic alterations in the transcriptional potential of a cell, which then affects the cell's biological function. The initiation and development of clear cell renal cell carcinoma (ccRCC), the most common subtype of renal cell cancer (RCC), is also closely related to genomic alterations by epigenetic modification. For ccRCC, lipid accumulation is one of the most typical characteristics. In other words, dysregulation of lipid uptake and synthesis occurs in ccRCC, which inversely promotes cancer proliferation and progression. However, the link among epigenetic alterations, lipid biosynthesis and renal cancer progression remains unclear. SETD8 is a histone methyltransferase and plays pivotal roles in cell cycle regulation and oncogenesis of various cancers, but its role in RCC is not well understood. In this study, we discovered that SETD8 was significantly overexpressed in RCC tumors, which was positively related to lipid storage and correlated with advanced tumor grade and stage and poor patient prognosis. Depletion of SETD8 by siRNAs or inhibitor UNC0379 diminished fatty acid (FA) de novo synthesis, cell proliferation and metastasis in ccRCC cells. Mechanistically, SETD8, which was posttranslationally stabilized by USP17, could transcriptionally modulate sterol regulatory element-binding protein 1 (SREBP1), a key transcription factor in fatty acid biosynthesis and lipogenesis, by monomethylating the 20th lysine of the H4 histone, elevating lipid biosynthesis and accumulation in RCC and further promoting cancer progression and metastasis. Taken together, the USP17/SETD8/SREBP1 signaling pathway plays a pivotal role in promoting RCC progression. SETD8 might be a novel biomarker and potential therapeutic target for treating RCC.

The role of the deubiquitinating enzyme DUB3/USP17 in cancer: a narrative review

The balance between ubiquitination and deubiquitination is critical for the degradation, transport, localization, and activity of proteins. Deubiquitinating enzymes (DUBs) greatly contribute to the balance of ubiquitination and deubiquitination, and they have been widely studied due to their fundamental role in cancer. DUB3/ubiquitin-specific protease 17 (USP17) is a type of DUB that has attracted much attention in cancer research. In this review, we summarize the biological functions and regulatory mechanisms of USP17 in central nervous system, head and neck, thoracic, breast, gastrointestinal, genitourinary, and gynecologic cancers as well as bone and soft tissue sarcomas, and we provide new insights into how USP17 can be used in the management of cancer.

The Role of the IL-6 Cytokine Family in Epithelial-Mesenchymal Plasticity in Cancer Progression

Epithelial–mesenchymal plasticity (EMP) plays critical roles during embryonic development, wound repair, fibrosis, inflammation and cancer. During cancer progression, EMP results in heterogeneous and dynamic populations of cells with mixed epithelial and mesenchymal characteristics, which are required for local invasion and metastatic dissemination. Cancer development is associated with an inflammatory microenvironment characterized by the accumulation of multiple immune cells and pro-inflammatory mediators, such as cytokines and chemokines. Cytokines from the interleukin 6 (IL-6) family play fundamental roles in mediating tumour-promoting inflammation within the tumour microenvironment, and have been associated with chronic inflammation, autoimmunity, infectious diseases and cancer, where some members often act as diagnostic or prognostic biomarkers. All IL-6 family members signal through the Janus kinase (JAK)–signal transducer and activator of transcription (STAT) pathway and are able to activate a wide array of signalling pathways and transcription factors. In general, IL-6 cytokines activate EMP processes, fostering the acquisition of mesenchymal features in cancer cells. However, this effect may be highly context dependent. This review will summarise all the relevant literature related to all members of the IL-6 family and EMP, although it is mainly focused on IL-6 and oncostatin M (OSM), the family members that have been more extensively studied.

Inhibitory role of ATF3 in gastric cancer progression through regulating cell EMT and stemness

BACKGROUND

Gastric cancer (GC) is one of the most common cancers and the third leading cause of cancer related mortality worldwide. The 5-year survival rate is rather low owing to advanced unresectable and distant metastasis. The EMT has been widely implicated in the stemness, metastatic dormancy, and chemoresistance of different solid tumors. Given the fact that activating transcription factor-3 (ATF3) is a member of the ATF/CREB family of transcription factors and its role in regulation of GC recurrence and metastasis remain poorly understood, the aim of the present study was to investigate its potential impact in epithelial-mesenchymal transition (EMT) and cancer stem cell (CSC) properties and GC aggression.

METHODS

To elucidate the potential role of ATF3 in gastric cancer, we utilized SGC-7901 and MGC-803 gastric cancer cell lines as research models and constructed stable cell lines overexpressing ATF3. We conducted a series of assays including cell proliferation, colony formation, cell migration, tumorsphere formation, and invasion to investigate the functional roles of ATF3 in stemness of gastric cancer. The possible effect of ATF3 on epithelial-mesenchymal transition (EMT) was assessed through flow cytometry and qRT-PCR. In vivo functional effect of upregulation of ATF3 on tumor growth was examined in a mouse xenograft model.

RESULTS

We found that overexpression of ATF3 inhibited cell proliferation, colony formation, cell migration and invasion. In addition, up-regulation of ATF3 attenuated tumorsphere formation, cell stemness, and potentially decreased expression of EMT markers. Moreover, ATF3 overexpression inhibited tumorigenesis in mouse xenograft model.

CONCLUSION

Our data suggest a suppressive role of ATF3 in gastric cancer development. Our findings will provide a potential therapeutic strategy and novel drug target for gastric cancer.

USP17-mediated de-ubiquitination and cancer: Clients cluster around the cell cycle

Eukaryotic cells perform a range of complex processes, some essential for life, others specific to cell type, all of which are governed by post-translational modifications of proteins. Among the repertoire of dynamic protein modifications, ubiquitination is arguably the most arcane and profound due to its complexity. Ubiquitin conjugation consists of three main steps, the last of which involves a multitude of target-specific ubiquitin ligases that conjugate a range of ubiquitination patterns to protein substrates with diverse outcomes. In contrast, ubiquitin removal is catalysed by a relatively small number of de-ubiquitinating enzymes (DUBs), which can also display target specificity and impact decisively on cell function. Here we review the current knowledge of the intriguing ubiquitin-specific protease 17 (USP17) family of DUBs, which are expressed from a highly copy number variable gene that has been implicated in multiple cancers, although available evidence points to conflicting roles in cell proliferation and survival. We show that key USP17 substrates populate two pathways that drive cell cycle progression and that USP17 activity serves to promote one pathway but inhibit the other. We propose that this arrangement enables USP17 to stimulate or inhibit proliferation depending on the mitogenic pathway that predominates in any given cell and may partially explain evidence pointing to both oncogenic and tumour suppressor properties of USP17.

Deubiquitinase USP20 promotes breast cancer metastasis by stabilizing SNAI2

In this study, Li et al. conducted comprehensive gain- and loss-of-function screens using a human DUB cDNA library of 65 genes and an siRNA library of 98 genes, and identified USP20 as a deubiquitinase (DUB) that regulates a metastasis-promoting transcription factor, SNAI2, ubiquitination, and stability.

SNAI2/SLUG, a metastasis-promoting transcription factor, is a labile protein that is degraded through the ubiquitin proteasome degradation system. Here, we conducted comprehensive gain- and loss-of-function screens using a human DUB cDNA library of 65 genes and an siRNA library of 98 genes, and identified USP20 as a deubiquitinase (DUB) that regulates SNAI2 ubiquitination and stability. Further investigation of USP20 demonstrated its function in promoting migration, invasion, and metastasis of breast cancer. USP20 positively correlates with SNAI2 protein level in breast tumor samples, and higher USP20 expression is associated with poor prognosis in ER⁻ breast cancer patients.

Twist-mediated PAR1 induction is required for breast cancer progression and metastasis by inhibiting Hippo pathway

Breast cancer is considered to be the most prevalent cancer in women worldwide, and metastasis is the primary cause of death. Protease-activated receptor 1 (PAR1) is a GPCR family member involved in the invasive and metastatic processes of cancer cells. However, the functions and underlying mechanisms of PAR1 in breast cancer remain unclear. In this study, we found that PAR1 is highly expressed in high invasive breast cancer cells, and predicts poor prognosis in ER-negative and high-grade breast cancer patients. Mechanistically, Twist transcriptionally induces PAR1 expression, leading to inhibition of Hippo pathway and activation of YAP/TAZ; Inhibition of PAR1 suppresses YAP/TAZ-induced epithelial-mesenchymal transition (EMT), invasion, migration, cancer stem cell (CSC)-like properties, tumor growth and metastasis of breast cancer cells in vitro and in vivo. These findings suggest that PAR1 acts as a direct transcriptionally target of Twist, can promote EMT, tumorigenicity and metastasis by controlling the Hippo pathway; this may lead to a potential therapeutic target for treating invasive breast cancer.

The Deubiquitinase USP4 Stabilizes Twist1 Protein to Promote Lung Cancer Cell Stemness

Lung cancer stem cells (CSCs) play a pivotal role in tumor development, drug resistance, metastasis and recurrence of lung cancer. Thus, it is of great importance to study the mechanism by which CSCs are regulated. In this study, we demonstrate that the deubiquitinase USP4 is critically important in promoting lung cancer stemness. Silencing of USP4 leads to reduction of Oct4 and Sox2 expression, decreased CD133+ cell population and inhibition of tumorsphere formation. Conversely, ectopic expression of USP4 significantly enhances lung cancer cell stemness, which is effectively rescued by simultaneous silencing of Twist1. Mechanistically, we identified USP4 as a novel deubiquitinase of Twist1. USP4 binds to, deubiquitinates and stabilizes Twist1 protein. Furthermore, we show that USP4 expression is elevated in human lung cancer specimens and is positively correlated with Twist1 expression. High expression of USP4/Twist1 is associated with poor clinical outcomes of lung cancer patients. Together, this study highlights an important role for USP4 in lung cancer stemness and suggests USP4 as a potential target for lung cancer diagnosis and treatment.

Role of Deubiquitinases in Human Cancers: Potential Targeted Therapy

Deubiquitinases (DUBs) are involved in various cellular functions. They deconjugate ubiquitin (UBQ) from ubiquitylated substrates to regulate their activity and stability. Studies on the roles of deubiquitylation have been conducted in various cancers to identify the carcinogenic roles of DUBs. In this review, we evaluate the biological roles of DUBs in cancer, including proliferation, cell cycle control, apoptosis, the DNA damage response, tumor suppression, oncogenesis, and metastasis. This review mainly focuses on the regulation of different downstream effectors and pathways via biochemical regulation and posttranslational modifications. We summarize the relationship between DUBs and human cancers and discuss the potential of DUBs as therapeutic targets for cancer treatment. This review also provides basic knowledge of DUBs in the development of cancers and highlights the importance of DUBs in cancer biology.

Targeting transcription factors in cancer - from undruggable to reality

Mutated or dysregulated transcription factors represent a unique class of drug targets that mediate aberrant gene expression, including blockade of differentiation and cell death gene expression programmes, hallmark properties of cancers. Transcription factor activity is altered in numerous cancer types via various direct mechanisms including chromosomal translocations, gene amplification or deletion, point mutations and alteration of expression, as well as indirectly through non-coding DNA mutations that affect transcription factor binding. Multiple approaches to target transcription factor activity have been demonstrated, preclinically and, in some cases, clinically, including inhibition of transcription factor-cofactor protein-protein interactions, inhibition of transcription factor-DNA binding and modulation of levels of transcription factor activity by altering levels of ubiquitylation and subsequent proteasome degradation or by inhibition of regulators of transcription factor expression. In addition, several new approaches to targeting transcription factors have recently emerged including modulation of auto-inhibition, proteolysis targeting chimaeras (PROTACs), use of cysteine reactive inhibitors, targeting intrinsically disordered regions of transcription factors and combinations of transcription factor inhibitors with kinase inhibitors to block the development of resistance. These innovations in drug development hold great promise to yield agents with unique properties that are likely to impact future cancer treatment.

The role of DUBs in the post-translational control of cell migration

Cell migration is a multifactorial/multistep process that requires the concerted action of growth and transcriptional factors, motor proteins, extracellular matrix remodeling and proteases. In this review, we focus on the role of transcription factors modulating Epithelial-to-Mesenchymal Transition (EMT-TFs), a fundamental process supporting both physiological and pathological cell migration. These EMT-TFs (Snail1/2, Twist1/2 and Zeb1/2) are labile proteins which should be stabilized to initiate EMT and provide full migratory and invasive properties. We present here a family of enzymes, the deubiquitinases (DUBs) which have a crucial role in counteracting polyubiquitination and proteasomal degradation of EMT-TFs after their induction by TGFβ, inflammatory cytokines and hypoxia. We also describe the DUBs promoting the stabilization of Smads, TGFβ receptors and other key proteins involved in transduction pathways controlling EMT.

The ubiquitin-specific protease USP17 prevents cellular senescence by stabilizing the methyltransferase SET8 and transcriptionally repressing p21

Su(var)3-9, Enhancer-of-zeste, and Trithorax (SET) domain-containing protein 8 (SET8) is the sole enzyme that monomethylates Lys-20 of histone H4 (H4K20). SET8 has been implicated in the regulation of multiple biological processes, such as gene transcription, the cell cycle, and senescence. SET8 quickly undergoes ubiquitination and degradation by several E3 ubiquitin ligases; however, the enzyme that deubiquitinates SET8 has not yet been identified. Here we demonstrated that ubiquitin-specific peptidase 17-like family member (USP17) deubiquitinates and therefore stabilizes the SET8 protein. We observed that USP17 interacts with SET8 and removes polyubiquitin chains from SET8. USP17 knockdown not only decreased SET8 protein levels and H4K20 monomethylation but also increased the levels of the cyclin-dependent kinase inhibitor p21. As a consequence, USP17 knockdown suppressed cell proliferation. We noted that USP17 was down-regulated in replicative senescence and that USP17 inhibition alone was sufficient to trigger cellular senescence. These results reveal a regulatory mechanism whereby USP17 prevents cellular senescence by removing ubiquitin marks from and stabilizing SET8 and transcriptionally repressing p21.

Contribution of Epithelial Plasticity to Therapy Resistance

Therapy resistance is responsible for tumour recurrence and represents one of the major challenges in present oncology. Significant advances have been made in the understanding of the mechanisms underlying resistance to conventional and targeted therapies improving the clinical management of relapsed patients. Unfortunately, in too many cases, resistance reappears leading to a fatal outcome. The recent introduction of immunotherapy regimes has provided an unprecedented success in the treatment of specific cancer types; however, a good percentage of patients do not respond to immune-based treatments or ultimately become resistant. Cellular plasticity, cancer cell stemness and tumour heterogeneity have emerged as important determinants of treatment resistance. Epithelial-to-mesenchymal transition (EMT) is associated with resistance in many different cellular and preclinical models, although little evidence derives directly from clinical samples. The recognition of the presence in tumours of intermediate hybrid epithelial/mesenchymal states as the most likely manifestation of epithelial plasticity and their potential link to stemness and tumour heterogeneity, provide new clues to understanding resistance and could be exploited in the search for anti-resistance strategies. Here, recent evidence linking EMT/epithelial plasticity to resistance against conventional, targeted and immune therapy are summarized. In addition, future perspectives for related clinical approaches are also discussed.

Glycidamide Promotes the Growth and Migratory Ability of Prostate Cancer Cells by Changing the Protein Expression of Cell Cycle Regulators and Epithelial-to-Mesenchymal Transition (EMT)-Associated Proteins with Prognostic Relevance

Acrylamide (AA) and glycidamide (GA) can be produced in carbohydrate-rich food when heated at a high temperature, which can induce a malignant transformation. It has been demonstrated that GA is more mutagenic than AA. It has been shown that the proliferation rate of some cancer cells are increased by treatment with GA; however, the exact genes that are induced by GA in most cancer cells are not clear. In the present study, we demonstrated that GA promotes the growth of prostate cancer cells through induced protein expression of the cell cycle regulator. In addition, we also found that GA promoted the migratory ability of prostate cancer cells through induced epithelial-to-mesenchymal transition (EMT)-associated protein expression. In order to understand the potential prognostic relevance of GA-mediated regulators of the cell cycle and EMT, we present a three-gene signature to evaluate the prognosis of prostate cancer patients. Further investigations suggested that the three-gene signature (CDK4, TWIST1 and SNAI2) predicted the chances of survival better than any of the three genes alone for the first time. In conclusion, we suggested that the three-gene signature model can act as marker of GA exposure. Hence, this multi-gene panel may serve as a promising outcome predictor and potential therapeutic target in prostate cancer patients.

Protein kinase Cα-mediated phosphorylation of Twist1 at Ser-144 prevents Twist1 ubiquitination and stabilizes it

Twist1 is a basic helix-loop-helix transcription factor that plays a key role in embryonic development, and its expression is down-regulated in adult cells. However, Twist1 is highly expressed during cancer development, conferring a proliferative, migratory, and invasive phenotype to malignant cells. Twist1 expression can be regulated post-translationally by phosphorylation or ubiquitination events. We report in this study a previously unknown and relevant Twist1 phosphorylation site that controls its stability. To identify candidate phosphorylation sites in Twist1, we first conducted an in silico analysis of the Twist1 protein, which yielded several potential sites. Because most of these sites were predicted to be phosphorylated by protein kinase C (PKC), we overexpressed PKCα in several cell lines and found that it phosphorylates Twist1 on Ser-144. Using a combination of immunoblotting, immunoprecipitation, protein overexpression, and CRISPR/Cas9-mediated PKCα knockout experiments, we observed that PKCα-mediated Twist1 phosphorylation at Ser-144 inhibits Twist1 ubiquitination and consequently stabilizes it. These results provide evidence for a direct association between PKCα and Twist1 and yield critical insights into the PKCα/Twist1 signaling axis that governs cancer aggressiveness.

Whole exome sequencing identifies hemizygous deletions in the UGT2B28 and USP17L2 genes in a three‑generation family with endometriosis

Endometriosis is an enigmatic condition with an unknown etiology and a poorly understood pathogenesis. It is considered to appear from the interplay of many genetic and environmental factors, affecting up to 10% of women and represents a major cause of pain and infertility. The familial association of endometriosis, as demonstrated through monozygotic twin and family studies suggests a genetic contribution to the disease, with further case-control and genome-wide association studies (GWAS) detecting various endometriosis risk factors. In a recent study, we described a unique, three-generation family of Cretan origin (Greece) with 7 females with surgically confirmed endometriosis (grandmother, 3 daughters and 3 granddaughters). All the affected members of this family displayed a variety of clinical manifestations and complications. In the present study, to further analyze the genetic variants conferring the risk of developing endometriosis, whole exome sequencing (WES) was performed, using the AmpliSeq technology on the Ion Proton platform. An initial analysis of 64 variants that were detected across the 14 genes previously confirmed to be associated with endometriosis, did not identify any deleterious exonic variants in these genes. However, further analysis revealed 2 hemizygous deletions in the grandmother that segregate in several of her affected offspring. The first deletion was found in the UGT2B28 locus, spanning 7 informative sequence variants across at least 14 kb. The second deletion, located in USP17L2, spans 3 informative variants across at least 2 kb. On the whole, the findings of the presents study implicate 2 additional genes in the pathogenesis of endometriosis, apart from those already identified by GWAS.

Epithelial-Mesenchymal Transition and Metastasis under the Control of Transforming Growth Factor β

Metastasis of tumor cells from primary sites of malignancy to neighboring stromal tissue or distant localities entails in several instances, but not in every case, the epithelial-mesenchymal transition (EMT). EMT weakens the strong adhesion forces between differentiated epithelial cells so that carcinoma cells can achieve solitary or collective motility, which makes the EMT an intuitive mechanism for the initiation of tumor metastasis. EMT initiates after primary oncogenic events lead to secondary secretion of cytokines. The interaction between tumor-secreted cytokines and oncogenic stimuli facilitates EMT progression. A classic case of this mechanism is the cooperation between oncogenic Ras and the transforming growth factor β (TGFβ). The power of TGFβ to mediate EMT during metastasis depends on versatile signaling crosstalk and on the regulation of successive waves of expression of many other cytokines and the progressive remodeling of the extracellular matrix that facilitates motility through basement membranes. Since metastasis involves many organs in the body, whereas EMT affects carcinoma cell differentiation locally, it has frequently been debated whether EMT truly contributes to metastasis. Despite controversies, studies of circulating tumor cells, studies of acquired chemoresistance by metastatic cells, and several (but not all) metastatic animal models, support a link between EMT and metastasis, with TGFβ, often being a common denominator in this link. This article aims at discussing mechanistic cases where TGFβ signaling and EMT facilitate tumor cell dissemination.

TGFβ-Activated USP27X Deubiquitinase Regulates Cell Migration and Chemoresistance via Stabilization of Snail1

In cancer cells, epithelial-to-mesenchymal transition (EMT) is controlled by Snail1, a transcriptional factor also required for the activation of cancer-associated fibroblasts (CAF). Snail1 is short-lived in normal epithelial cells as a consequence of its coordinated and continuous ubiquitination by several F-box-specific E3 ligases, but its degradation is prevented in cancer cells and in activated fibroblasts. Here, we performed an siRNA screen and identified USP27X as a deubiquitinase that increases Snail1 stability. Expression of USP27X in breast and pancreatic cancer cell lines and tumors positively correlated with Snail1 expression levels. Accordingly, downregulation of USP27X decreased Snail1 protein in several tumor cell lines. USP27X depletion impaired Snail1-dependent cell migration and invasion and metastasis formation and increased cellular sensitivity to cisplatin. USP27X was upregulated by TGFβ during EMT and was required for TGFβ-induced expression of Snail1 and other mesenchymal markers in epithelial cells and CAF. In agreement with this, depletion of USP27X prevented TGFβ-induced EMT and fibroblast activation. Collectively, these results indicate that USP27X is an essential protein controlling Snail1 expression and function and may serve as a target for inhibition of Snail1-dependent tumoral invasion and chemoresistance. SIGNIFICANCE: These findings show that inhibition of USP27X destabilizes Snail1 to impair EMT and renders tumor cells sensitive to chemotherapy, thus opening new strategies for the inhibition of Snail1 expression and its protumoral actions.Graphical Abstract: http://cancerres.aacrjournals.org/content/canres/79/1/33/F1.large.jpg.

Epithelial-mesenchymal-transition-inducing transcription factors: new targets for tackling chemoresistance in cancer?

Chemoresistance remains a major complication of cancer treatments. Recent data provide strong evidence that chemoresistance is linked to epithelial-mesenchymal transition (EMT), a latent developmental process, which is re-activated during cancer progression. EMT involves transcriptional reprogramming and is driven by specific EMT transcription factors (EMT-TFs). In this review, we provide support for the idea that EMT-TFs contribute to the development of resistance against cancer therapy and discuss how EMT-TFs might be targeted to advance novel therapeutic approaches to the treatment of cancer.

Organoids Provide an Important Window on Inflammation in Cancer

Inflammation is a primary driver of cancer initiation and progression. However, the complex and dynamic nature of an inflammatory response make this a very difficult process to study. Organoids are a new model system where complex multicellular structures of primary cells can be grown in a 3D matrix to recapitulate the biology of the parent tissue. This experimental model offers several distinct advantages over alternatives including the ability to be genetically engineered, implanted in vivo and reliably derived from a wide variety of normal and cancerous tissue from patients. Furthermore, long-term organoid cultures reproduce many features of their source tissue, including genetic and epigenetic alterations and drug sensitivity. Perhaps most significantly, cancer organoids can be cocultured in a variety of different systems with a patients’ own immune cells, uniquely permitting the study of autologous cancer-immune cell interactions. Experiments with such systems promise to shed light on the mechanisms governing inflammation-associated cancer while also providing prognostic information on an individual patient’s responsiveness to immunotherapeutic anti-cancer drugs. Thanks to their ability to capture important features of the complex relationship between a cancer and its microenvironment, organoids are poised to become an essential tool for unraveling the mechanisms by which inflammation promotes cancer.

OTUB1 promotes esophageal squamous cell carcinoma metastasis through modulating Snail stability

Snail is a key regulator of epithelial-mesenchymal transition (EMT) and plays an important role in tumor progression and metastasis. Snail is rapidly degraded in the cells and its protein level is critically controlled. Although several E3 ligases regulating Snail degradation have been defined, the deubiquitinases (DUBs) responsible for Snail deubiquitination are less studied. We identified ovarian tumor domain-containing ubiquitin aldehyde binding protein 1 (OTUB1) as a DUB that stabilizes Snail through preventing its ubiquitination and proteasomal degradation. Functionally, OTUB1 facilitates metastasis of esophageal squamous cell carcinoma (ESCC) through promoting Snail protein stability. Moreover, OTUB1 is highly expressed in ESCC and higher expression of OTUB1 predicts poor prognosis. These findings suggest that OTUB1 is an essential regulator of Snail and plays a critical role in facilitating esophageal cancer progression.