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

Deubiquitinase USP4 suppresses antitumor immunity by inhibiting IRF3 activation and tumor cell-intrinsic interferon response in colorectal cancer

Despite the approval of immune checkpoint blockade (ICB) therapy for various tumor types, its effectiveness is limited to only approximately 15% of patients with microsatellite instability-high (MSI-H) or mismatch repair deficiency (dMMR) colorectal cancer (CRC). Approximately 80%-85% of CRC patients have a microsatellite stability (MSS) phenotype, which features a rare T-cell infiltration. Thus, elucidating the mechanisms underlying resistance to ICB in patients with MSS CRC is imperative. In this study, we demonstrate that ubiquitin-specific peptidase 4 (USP4) is upregulated in MSS CRC tumors and negatively regulates the immune response against tumors in CRC. Additionally, USP4 represses the cellular interferon (IFN) response and antigen presentation and impairs PRR signaling-mediated cell death. Mechanistically, USP4 impedes the nuclear localization of interferon regulator Factor 3 (IRF3) by deubiquitinating the K63-polyubiquitin chain of TRAF6 and IRF3. Knockdown of USP4 enhances the infiltration of T cells in CRC tumors and overcomes ICB resistance in an MC38 syngeneic mouse model. Moreover, published datasets revealed that patients showing higher USP4 expression exhibited decreased responsiveness to anti-PD-L1 therapy. These findings highlight an essential role of USP4 in the suppression of antitumor immunity in CRC.

ASB6 as an Independent Prognostic Biomarker for Colorectal Cancer Progression Involves Lymphatic Invasion and Immune Infiltration

Background: ASB6, an E3 ubiquitin ligase, mediates the proteasomal degradation of its substrate proteins via the ubiquitin-proteasome pathway. ASB6 has been reported to play significant roles in several biological processes, including tumor stemness and endoplasmic reticulum stress. However, the underlying role and mechanism of ASB6 in colorectal cancer, particularly its association with immune infiltration levels and its prognostic significance, remain to be fully elucidated. Methods: We identified key prognostic genes in CRC patients through LASSO-penalized Cox regression, Univariate and Multivariate Cox regression analyses. Subsequently, we comprehensively analyzed the prognostic value of hub genes and constructed a prognostic nomogram. Finally, we identified ASB6 interacting proteins through immunoprecipitation-mass spectrometry (IP-MS) and constructed protein-protein interaction (PPI) networks and performed pathway enrichment analysis to explore the potential mechanisms of ASB6. Meanwhile, we evaluated the functions of ASB6 in CRC cells through in vitro cell experiments. Results: We identified ASB6 as a hub gene in CRC. ASB6 was highly expressed in CRC, and patients with high ASB6 expression had worse Disease-Free Interval (DFI), Disease-Specific Survival (DSS), Overall Survival (OS), and Progression-Free Interval (PFI). Correlation analysis showed that ASB6 expression were positively correlated with lymph node invasion and distal metastasis. Overexpression of ASB6 enhanced the migration ability of CRC cells. Multivariate Cox regression analysis revealed that ASB6 was an independent prognostic factor for OS and DSS in CRC. The nomogram model constructed based on multivariate analysis results had good predictive effects, with C-indexes of 0.811 and 0.934 for OS and DSS, respectively. Furthermore, analysis of immune infiltration levels showed that ASB6 expression were positively correlated with M2-type macrophage infiltration levels in CRC, and patients with high levels of both ASB6 and M2-type macrophages had a worse prognosis. Furthermore, pathway enrichment analysis of ASB6 interacting proteins identified by IP-MS suggested that ASB6 may play a crucial role through the response to unfolded protein pathway and protein processing in the endoplasmic reticulum pathway. Conclusions: ASB6 is significantly upregulated in CRC tissues and is a risk factor for prognosis in CRC patients. ASB6 enhances the migration ability of CRC cells. Therefore, ASB6 may be an independent prognostic biomarker and potential therapeutic target for CRC patients.

Emerging roles of deubiquitinating enzymes in actin cytoskeleton and tumor metastasis

BACKGROUND

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

CONCLUSION

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

Potential markers of cancer stem-like cells in ESCC: a review of the current knowledge

In patients with esophageal squamous cell carcinoma (ESCC), the incidence and mortality rate of ESCC in our country are also higher than those in the rest of the world. Despite advances in the treatment department method, patient survival rates have not obviously improved, which often leads to treatment obstruction and cancer repeat. ESCC has special cells called cancer stem-like cells (CSLCs) with self-renewal and differentiation ability, which reflect the development process and prognosis of cancer. In this review, we evaluated CSLCs, which are identified from the expression of cell surface markers in ESCC. By inciting EMTs to participate in tumor migration and invasion, stem cells promote tumor redifferentiation. Some factors can inhibit the migration and invasion of ESCC via the EMT-related pathway. We here summarize the research progress on the surface markers of CSLCs, EMT pathway, and the microenvironment in the process of tumor growth. Thus, these data may be more valuable for clinical applications.

USP4 promotes the proliferation, migration, and invasion of esophageal squamous cell carcinoma by targeting TAK1

Ubiquitin-specific protease 4 (USP4) represents a potential oncogene involved in various human cancers. Nevertheless, the biological roles and precise mechanism of USP4 in esophageal squamous cell carcinoma (ESCC) progression are not understood. Here, USP4 expression was found to be markedly upregulated in ESCC tumor tissues and cells. Loss- and gain-of-function assays suggested that USP4 silencing inhibited ESCC cell proliferation, migration, and invasion, while USP4 overexpression promoted these behaviors. Consistently, USP4 silencing repressed tumor growth and metastasis in an ESCC nude mouse model in vivo. As a target molecule of USP4, transforming growth factor-β-activated kinase 1 (TAK1) also showed high expression in ESCC. Moreover, we observed that USP4 specifically interacted with TAK1 and stabilized TAK1 protein levels via deubiquitination in ESCC cells. Importantly, USP4 promotes ESCC proliferation, migration, and invasion via the MEK/ERK signaling pathway and can be inhibited by U0126. Neutral red (NR), an inhibitor of USP4 can suppress ESCC progression in vitro and in vivo. Overall, this study revealed that USP4/TAK1 plays crucial roles in ESCC progression by modulating proliferation, migration, and invasion, and USP4 might be a potential therapeutic target in ESCC.

USP32 deubiquitinase: cellular functions, regulatory mechanisms, and potential as a cancer therapy target

An essential protein regulatory system in cells is the ubiquitin-proteasome pathway. The substrate is modified by the ubiquitin ligase system (E1-E2-E3) in this pathway, which is a dynamic protein bidirectional modification regulation system. Deubiquitinating enzymes (DUBs) are tasked with specifically hydrolyzing ubiquitin molecules from ubiquitin-linked proteins or precursor proteins and inversely regulating protein degradation, which in turn affects protein function. The ubiquitin-specific peptidase 32 (USP32) protein level is associated with cell cycle progression, proliferation, migration, invasion, and other cellular biological processes. It is an important member of the ubiquitin-specific protease family. It is thought that USP32, a unique enzyme that controls the ubiquitin process, is closely linked to the onset and progression of many cancers, including small cell lung cancer, gastric cancer, breast cancer, epithelial ovarian cancer, glioblastoma, gastrointestinal stromal tumor, acute myeloid leukemia, and pancreatic adenocarcinoma. In this review, we focus on the multiple mechanisms of USP32 in various tumor types and show that USP32 controls the stability of many distinct proteins. Therefore, USP32 is a key and promising therapeutic target for tumor therapy, which could provide important new insights and avenues for antitumor drug development. The therapeutic importance of USP32 in cancer treatment remains to be further proven. In conclusion, there are many options for the future direction of USP32 research.

USP33 promotes nonalcoholic fatty acid disease-associated fibrosis in gerbils via the c-myc signaling

Nonalcoholic fatty acid disease (NAFLD) is a common complication of obesity associated with liver fibrosis. The underlying molecular mechanisms involved in the progression from normal to fibrosis remain unclear. Liver tissues from the liver fibrosis model identified the USP33 gene as a key gene in NAFLD-associated fibrosis. USP33 knockdown inhibited hepatic stellate cell activation and glycolysis in gerbils with NAFLD-associated fibrosis. Conversely, overexpression of USP33 caused a contrast function on hepatic stellate cell activation and glycolysis activation, which was inhibited by c-Myc inhibitor 10058-F4. The copy number of short-chain fatty acids-producing bacterium Alistipes sp. AL-1, Mucispirillum schaedleri, Helicobacter hepaticus in the feces, and the total bile acid level in serum were higher in gerbils with NAFLD-associated fibrosis. Bile acid promoted USP33 expression and inhibiting its receptor reversed hepatic stellate cell activation in gerbils with NAFLD-associated fibrosis. These results suggest that the expression of USP33, an important deubiquitinating enzyme, is increased in NAFLD fibrosis. These data also point to hepatic stellate cells as a key cell type that may respond to liver fibrosis via USP33-induced cell activation and glycolysis.

USP51 promotes non-small cell lung carcinoma cell stemness by deubiquitinating TWIST1

BACKGROUND

USP51 is a deubiquitinase (DUB), that is involved in diverse cellular processes. Accumulating evidence has demonstrated that USP51 contributes to cancer development. However, its impact on non-small cell lung carcinoma (NSCLC) cell malignancy is largely unknown.

METHODS

In this study, we performed bioinformatics analysis on a dataset from The Cancer Genome Atlas to determine the association between USP51 and cell stemness marker expression in NSCLC patients. RT‒qPCR, Western blotting, and flow cytometry were performed to examine the effects of USP51 depletion on stemness marker expression. Colony formation and tumor sphere formation assays were used to assess the stemness of NSCLC cells. A cycloheximide chase time-course assay and a polyubiquitination assay were carried out to analyze the effects of USP51 on the TWIST1 protein level. TWIST1 was overexpressed in USP51 knockdown NSCLC cells to determine whether TWIST1 is required. The effect of USP51 on the in vivo growth of NSCLC cells was tested through subcutaneous injections in mice.

RESULTS

We found that USP51 deubiquitinates TWIST1, which is significantly upregulated in the tissues of patients with NSCLC and is closely associated with poor prognosis. USP51 expression was positively correlated with the expression of stemness marker CD44, SOX2, NANOG, and OCT4 in NSCLC patients. USP51 depletion attenuated mRNA, protein, and cell surface expression of stemness markers and the stemness of NSCLC cells. Ectopic USP51 expression potentiated the stability of the TWIST1 protein by attenuating its polyubiquitination. In addition, TWIST1 re-expression in NSCLC cells reversed the inhibitory effect of USP51 knockdown on cell stemness. Furthermore, the in vivo results confirmed the suppressive effect of USP51 depletion on NSCLC cell growth.

CONCLUSIONS

Our results show that USP51 maintains the stemness of NSCLC cells by deubiquitinating TWIST1. Knocking it down reduces both cell stemness and growth of NSCLC cells.

Ubiquitin-proteasome system as a target for anticancer treatment-an update

As the ubiquitin-proteasome system (UPS) regulates almost every biological process, the dysregulation or aberrant expression of the UPS components causes many pathological disorders, including cancers. To find a novel target for anticancer therapy, the UPS has been an active area of research since the FDA's first approval of a proteasome inhibitor bortezomib in 2003 for treating multiple myeloma (MM). Here, we summarize newly described UPS components, including E3 ubiquitin ligases, deubiquitinases (DUBs), and immunoproteasome, whose malfunction leads to tumorigenesis and whose inhibitors have been investigated in clinical trials as anticancer therapy since 2020. We explain the mechanism and effects of several inhibitors in depth to better comprehend the advantages of targeting UPS components for cancer treatment. In addition, we describe attempts to overcome resistance and limited efficacy of some launched proteasome inhibitors, as well as an emerging PROTAC-based tool targeting UPS components for anticancer therapy.

A review of deubiquitinases and thier roles in tumorigenesis and development

Ubiquitin is a small protein that can be added onto target protein for inducing target degradation, thereby modulating the activity and stability of protein. Relatively, deubiquitinases (DUBs), a class catalase that can remove ubiquitin from substrate protein, provide a positive regulation of the protein amount at transcription level, post-translational modification, protein interaction, etc. The reversible and dynamic ubiquitination-deubiquitination process plays an essential role in maintaining protein homeostasis, which is critical to almost all the biological processes. Therefore, the metabolic dysregulation of deubiquitinases often lead to serious consequences, including the growth and metastasis of tumors. Accordingly, deubiquitinases can be served as key drug targets for the treatment of tumors. The small molecule inhibitors targeting deubiquitinases has become one of the hot spots of anti-tumor drug research areas. This review concentrated on the function and mechanism of deubiquitinase system in the proliferation, apoptosis, metastasis and autophagy of tumor cells. The research status of small molecule inhibitors of specific deubiquitinases in tumor treatment is introduced, aiming to provide reference for the development of clinical targeted drugs.

Suppression of Cancer Cell Stemness and Drug Resistance via MYC Destabilization by Deubiquitinase USP45 Inhibition with a Natural Small Molecule

Cancer stem cells (CSCs) play significant roles in cancer development, drug resistance and cancer recurrence. In cancer treatments based on the CSC characteristics and inducing factors, MYC is a promising target for therapeutic molecules. Although it has been regarded as an undrugable target, its stability tightly regulated by the ubiquitin-proteasome system offers a new direction for molecule targeting and cancer treatment. Herein we report our discoveries in this research area, and we have found that deubiquitinase USP45 can directly bind with MYC, resulting in its deubiquitination and stabilization. Further, USP45 overexpressing can upregulate MYC, and this overexpressing can significantly enhance cancer development, cancer cell stemness and drug resistance. Interestingly, without enhancing cancer development, MYC silencing with shRNA can only suppress USP45-induced stemness and drug resistance. Moreover, we have identified that USP45 can be specifically bound and inhibited by a natural small molecule (α-mangostin), in turn significantly suppressing USP45-induced stemness and drug resistance. Since USP45 is significantly expressed in cervical tumors, we have discovered that the combination of α-mangostin and doxorubicin can significantly inhibit USP45-induced cervical tumorigenesis in an animal model. In general, on the basis of our USP45 discoveries on its MYC deubiquitination and α-mangostin inhibition, suppressing USP45 has opened a new window for suppressing cancer development, stemness and drug resistance.

The deubiquitinating enzyme MINDY2 promotes pancreatic cancer proliferation and metastasis by stabilizing ACTN4 expression and activating the PI3K/AKT/mTOR signaling pathway

The pathogenic mechanisms of pancreatic cancer (PC) are still not fully understood. Ubiquitination modifications have a crucial role in tumorigenesis and progression. Yet, the role of MINDY2, a member of the motif interacting with Ub-containing novel DUB family (MINDY), as a newly identified deubiquitinating enzyme, in PC is still unclear. In this study, we found that MINDY2 expression is elevated in PC tissue (clinical samples) and was associated with poor prognosis. We also found that MINDY2 is associated with pro-carcinogenic factors such as epithelial-mesenchymal transition (EMT), inflammatory response, and angiogenesis; the ROC curve suggested that MINDY2 has a high diagnostic value in PC. Immunological correlation analysis suggested that MINDY2 is deeply involved in immune cell infiltration in PC and is associated with immune checkpoint-related genes. In vivo and in vitro experiments further suggested that elevated MINDY2 promotes PC proliferation, invasive metastasis, and EMT. Meanwhile, actinin alpha 4 (ACTN4) was identified as a MINDY2-interacting protein by mass spectrometry and other experiments, and ACTN4 protein levels were significantly correlated with MINDY2 expression. The ubiquitination assay confirmed that MINDY2 stabilizes the ACTN4 protein level by deubiquitination. The pro-oncogenic effect of MINDY2 was significantly inhibited by silencing ACTN4. Bioinformatics Analysis and Western blot experiments further confirmed that MINDY2 stabilizes ACTN4 through deubiquitination and thus activates the PI3K/AKT/mTOR signaling pathway. In conclusion, we identified the oncogenic role and mechanism of MINDY2 in PC, suggesting that MINDY2 is a viable candidate gene for PC and may be a therapeutic target and critical prognostic indicator.

FBXL2 promotes E47 protein instability to inhibit breast cancer stemness and paclitaxel resistance

Triple-negative breast cancer (TNBC) is the most aggressive subtype of breast cancer with a high risk of metastasis and recurrence. Although chemotherapy has greatly improved the clinical outcome of TNBC patients, acquired drug resistance remains a huge challenge for TNBC treatment. Breast cancer stem cells (BCSCs) play a critical role in breast cancer development, metastasis, recurrence, and chemotherapy resistance. Thus, it is of great importance to decipher the underlying molecular mechanism of BCSCs regulation for TNBC drug resistance. In this study, we demonstrate that the F-box protein FBXL2 is a critical negative regulator of BCSCs stemness and that downregulation of FBXL2 plays a causal role in TNBC drug resistance. We show that expression levels of FBXL2 significantly influence CD44^high/CD24^low subpopulation and the mammosphere formation ability of TNBC cells. Ectopic expression of FBXL2 inhibits initiation of TNBC and overcomes paclitaxel resistance in vivo. In addition, activation of FBXL2 by nebivolol, a clinically used small-molecule inhibitor of the beta-1 receptor, markedly overcomes BCSCs-induced paclitaxel resistance. Mechanistically, we show that FBXL2 targets transcriptional factor E47 for polyubiquitin- and proteasome-mediated degradation, resulting in inhibition of BCSC stemness. Clinical analyses indicate that low expression of FBXL2 correlates with high expression of E47 as well as with high stemness features, and is associated with poor clinical outcomes of breast cancer patients. Taken together, these results highlight that the FBXL2-E47 axis plays a critical role in the regulation of BCSC stemness and paclitaxel resistance. Thus, targeting FBXL2 might be a potential therapeutic strategy for drug-resistant TNBC.

MIR99AHG inhibits EMT in pulmonary fibrosis via the miR-136-5p/USP4/ACE2 axis

Background

Long non-coding RNAs (lncRNAs) are closely related to the occurrence and development of cancer. Abnormally expressed lncRNA can be used as a diagnostic marker for cancer. In this study, we aim to investigate the clinical significance of MIR99AHG expression in lung adenocarcinoma (LUAD), and its biological roles in LUAD progression.

Methods

The relative expression of MIR99AHG in LUAD tissues and cell lines was analyzed using public databases and RT-qPCR. The biological functions of MIR99AHG were investigated using a loss-of-function approach. The effect of MIR99AHG on lung fibrosis was assessed by scratch assay, invasion assay and lung fibrosis rat model. FISH, luciferase reporter assay and immunofluorescence were performed to elucidate the underlying molecular mechanisms.

Results

LncRNA MIR99AHG expression level was downregulated in LUAD tissues and cell lines. Low MIR99AHG levels were associated with poorer patient overall survival. Functional analysis showed that MIR99AHG is associated with the LUAD malignant phenotype in vitro and in vivo. Further mechanistic studies showed that, MIR99AHG functions as a competitive endogenous RNA (ceRNA) to antagonize miR-136-5p-mediated ubiquitin specific protease 4 (USP4) degradation, thereby unregulated the expression of angiotensin-converting enzyme 2 (ACE2), a downstream target gene of USP4, which in turn affected alveolar type II epithelial cell fibrosis and epithelial–mesenchymal transition (EMT). In summary, the MIR99AHG/miR-136-5p/USP4/ACE2 signalling axis regulates lung fibrosis and EMT, thus inhibiting LUAD progression.

Conclusion

This study showed that downregulated MIR99AHG leads to the development of pulmonary fibrosis. Therefore, overexpression of MIR99AHG may provide a new approach to preventing LUAD progression.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12967-022-03633-y.

Binding of Vialinin A and p-Terphenyl Derivatives to Ubiquitin-Specific Protease 4 (USP4): A Molecular Docking Study

The para-terphenyl derivative vialinin A (Vi-A), isolated from Thelephora fungi, has been characterized as a potent inhibitor of the ubiquitin-specific protease 4 (USP4). Blockade of USP4 contributes to the anti-inflammatory and anticancer properties of the natural product. We have investigated the interaction of Vi-A with USP4 by molecular modeling, to locate the binding site (around residue V98 within the domain in USP segment) and to identify the binding process and interaction contacts. From this model, a series of 32 p-terphenyl compounds were tested as potential USP4 binders, mainly in the vialinin, terrestrin and telephantin series. We identified 11 compounds presenting a satisfactory USP4 binding capacity, including two fungal products, vialinin B and aurantiotinin A, with a more favorable empirical energy of USP4 interaction (ΔE) than the reference product Vi-A. The rare p-terphenyl aurantiotinin A, isolated from the basidiomycete T. aurantiotincta, emerged as a remarkable USP4 binder. Structure-binding relationships have been identified and discussed, to guide the future design of USP4 inhibitors based on the p-terphenyl skeleton. The docking study should help the identification of other protease inhibitors from fungus.

Deubiquitinases in Cancers: Aspects of Proliferation, Metastasis, and Apoptosis

Simple Summary

This review summarizes the current DUBs findings that correlate with the most common cancers in the world (liver, breast, prostate, colorectal, pancreatic, and lung cancers). The DUBs were further classified by their biological functions in terms of proliferation, metastasis, and apoptosis. The work provides an updated of the current findings, and could be used as a quick guide for researchers to identify target DUBs in cancers.

Abstract

Deubiquitinases (DUBs) deconjugate ubiquitin (UBQ) from ubiquitylated substrates to regulate its activity and stability. They are involved in several cellular functions. In addition to the general biological regulation of normal cells, studies have demonstrated their critical roles in various cancers. In this review, we evaluated and grouped the biological roles of DUBs, including proliferation, metastasis, and apoptosis, in the most common cancers in the world (liver, breast, prostate, colorectal, pancreatic, and lung cancers). The current findings in these cancers are summarized, and the relevant mechanisms and relationship between DUBs and cancers are discussed. In addition to highlighting the importance of DUBs in cancer biology, this study also provides updated information on the roles of DUBs in different types of cancers.

The Deubiquitinase USP13 Maintains Cancer Cell Stemness by Promoting FASN Stability in Small Cell Lung Cancer

USP13 is significantly amplified in over 20% of lung cancer patients and critical for tumor progression. However, the functional role of USP13 in small cell lung cancer (SCLC) remains largely unclear. In this study, we found that the deubiquitinase USP13 is highly expressed in SCLC tumor samples and positively associated with poor prognosis in multiple cohorts. In vitro and in vivo depletion of USP13 inhibited SCLC cancer stem cells (CSCs) properties and tumorigenesis, and this inhibitory effect was rescued by reconstituted expression of wide type (WT) USP13 but not the enzyme-inactive USP13 mutant. Mechanistically, USP13 interacts with fatty acid synthase (FASN) and enhances FASN protein stability. FASN downregulation suppresses USP13-enhanced cell renewal regulator expression, sphere formation ability, and de novo fatty acids biogenesis. Accordingly, we found FASN expression is upregulated in surgical resected SCLC specimens, positively correlated with USP13, and associated with poor prognosis of SCLC patients. More importantly, the small molecule inhibitor of FASN, TVB-2640, significantly inhibits lipogenic phenotype and attenuates self-renewal ability, chemotherapy resistance and USP13-mediated tumorigenesis in SCLC. Thus, our study highlights a critical role of the USP13-FASN-lipogenesis axis in SCLC cancer stemness maintenance and tumor growth, and reveals a potential combination therapy for SCLC patients.

Pro-apoptotic and anti-apoptotic regulation mediated by deubiquitinating enzymes

Although damaged cells can be repaired, cells that are considered unlikely to be repaired are eliminated through apoptosis, a type of predicted cell death found in multicellular organisms. Apoptosis is a structured cell death involving alterations to the cell morphology and internal biochemical changes. This process involves the expansion and cracking of cells, changes in cell membranes, nuclear fragmentation, chromatin condensation, and chromosome cleavage, culminating in the damaged cells being eaten and processed by other cells. The ubiquitin-proteasome system (UPS) is a major cellular pathway that regulates the protein levels through proteasomal degradation. This review proposes that apoptotic proteins are regulated through the UPS and describes a unique direction for cancer treatment by controlling proteasomal degradation of apoptotic proteins, and small molecules targeted to enzymes associated with UPS.

Tight junction protein 1 promotes vasculature remodeling via regulating USP2/TWIST1 in bladder cancer

Bladder cancer (BLCA) is the most common malignant tumor of the urinary system and is characterized by high metastatic rates and poor prognosis. The expression of tight junction protein 1 (TJP1) is associated with bladder cancer invasion; however, the mechanism by which TJP1 affects vasculature remodeling remains unknown. In this study, we found that TJP1 expression correlated with tumor angiogenesis and poor overall survival in clinical samples. Furthermore, TJP1 overexpression promoted tumor angiogenesis in BLCA cells and stimulated recruitment of macrophages to tumors by upregulating CCL2 expression. Mechanistically, TJP1 interacted with TWIST1 and enhanced the transcriptional activity of CCL2. The impairment of tumor angiogenesis caused by knockdown of TJP1 was dramatically rescued by overexpression of TWIST1. Furthermore, TJP1 recruited USP2, which deubiquitinated TWIST1, thereby protecting TWIST1 from proteasome-mediated protein degradation. In conclusion, our results suggest that TJP1 controls angiogenesis in BLCA via TWIST1-dependent regulation of CCL2. We demonstrate that TJP1 functions as a scaffold for the interaction between USP2 and TWIST1 and this may provide potential therapeutic targets in bladder cancer.

Fungal Secondary Metabolites as Inhibitors of the Ubiquitin-Proteasome System

The ubiquitin–proteasome system (UPS) is the major non-lysosomal pathway responsible for regulated degradation of intracellular proteins in eukaryotes. As the principal proteolytic pathway in the cytosol and the nucleus, the UPS serves two main functions: the quality control function (i.e., removal of damaged, misfolded, and functionally incompetent proteins) and a major regulatory function (i.e., targeted degradation of a variety of short-lived regulatory proteins involved in cell cycle control, signal transduction cascades, and regulation of gene expression and metabolic pathways). Aberrations in the UPS are implicated in numerous human pathologies such as cancer, neurodegenerative disorders, autoimmunity, inflammation, or infectious diseases. Therefore, the UPS has become an attractive target for drug discovery and development. For the past two decades, much research has been focused on identifying and developing compounds that target specific components of the UPS. Considerable effort has been devoted to the development of both second-generation proteasome inhibitors and inhibitors of ubiquitinating/deubiquitinating enzymes. With the feature of unique structure and bioactivity, secondary metabolites (natural products) serve as the lead compounds in the development of new therapeutic drugs. This review, for the first time, summarizes fungal secondary metabolites found to act as inhibitors of the UPS components.

Identify specific gene pairs for subarachnoid hemorrhage based on wavelet analysis and genetic algorithm

Subarachnoid hemorrhage (SAH) is a fatal stroke caused by bleeding in the brain. SAH can be caused by a ruptured aneurysm or head injury. One-third of patients will survive and recover. One-third will survive with disability; one-third will die. The focus of treatment is to stop bleeding, restore normal blood flow, and prevent vasospasm. Treatment for SAH varies, depending on the bleeding’s underlying cause and the extent of damage to the brain. Treatment may include lifesaving measures, symptom relief, repair of the bleeding vessel, and complication prevention. However, the useful diagnostic biomarkers of SAH are still limited due to the instability of gene marker expression. To overcome this limitation, we developed a new protocol pairing genes and screened significant gene pairs based on the feature selection algorithm. A classifier was constructed with the selected gene pairs and achieved a high performance.

Spotlight on USP4: Structure, Function, and Regulation

The deubiquitinating enzyme (DUB)–mediated cleavage of ubiquitin plays a critical role in balancing protein synthesis and degradation. Ubiquitin-specific protease 4 (USP4), a member of the largest subfamily of cysteine protease DUBs, removes monoubiquitinated and polyubiquitinated chains from its target proteins. USP4 contains a DUSP (domain in USP)–UBL (ubiquitin-like) domain and a UBL-insert catalytic domain, sharing a common domain organization with its paralogs USP11 and USP15. USP4 plays a critical role in multiple cellular and biological processes and is tightly regulated under normal physiological conditions. When its expression or activity is aberrant, USP4 is implicated in the progression of a wide range of pathologies, especially cancers. In this review, we comprehensively summarize the current knowledge of USP4 structure, biological functions, pathological roles, and cellular regulation, highlighting the importance of exploring effective therapeutic interventions to target USP4.

What deubiquitinating enzymes, oncogenes, and tumor suppressors actually do: Are current assumptions supported by patient outcomes?

Context can determine whether a given gene acts as an oncogene or a tumor suppressor. Deubiquitinating enzymes (DUBs) regulate the stability of many components of the pathways dictating cell fate so it would be expected that alterations in the levels or activity of these enzymes may have oncogenic or tumor suppressive consequences. In the current review we survey publications reporting that genes encoding DUBs are oncogenes or tumor suppressors. For many DUBs both claims have been made. For such "double agents," the effects of gain or loss of function will depend on the overall status of a complex of molecular signaling networks subject to extensive crosstalk. As the TGF-β paradox makes clear context is critical in cell fate decisions, and the disconnect between experimental findings and patient survival outcomes can in part be attributed to disparities between culture conditions and the microenvironment in vivo. Convincing claims for oncogene or tumor suppressor roles require the documentation of gene alterations in patient samples; survival curves are alone inadequate.

SOX2-Upregulated microRNA-30e Promotes the Progression of Esophageal Cancer via Regulation of the USP4/SMAD4/CK2 Axis

Esophageal cancer (EC) is a highly aggressive disease, and its progression involves a complex gene regulation network. Transcription factor SOX2 is amplified in various cancers including EC. A pathway involving SOX2 regulation of microRNAs (miRNAs) and their target genes has been previously revealed. This study aims to delineate the ability of SOX2 to influence the EC progression, with the involvement of miR-30e/USP4/SMAD4/CK2 axis. SOX2 expression was first examined in the clinical tissue samples from 30 EC patients. Effects of SOX2 on proliferation, migration, and invasion alongside tumorigenicity of transfected cells were examined by means of gain- and loss-of-function experiments. EC tissues and cells exhibited high expression of SOX2, miR-30e, and CK2 and poor expression of USP4 and SMAD4. Mechanistically, SOX2 was positively correlated with miR-30e and upregulated the expression of miR-30e. miR-30e specifically targeted USP4, which induced deubiquitination of SMAD4 and promoted its expression. Meanwhile, SMAD4 was enriched in the CK2 promoter region and thus inhibited its expression. SOX2 stimulated EC cell proliferative, invasive, and migratory capacities in vitro and tumor growth in vivo by regulating the miR-30e/USP4/SMAD4/CK2 axis. Collectively, our work reveals a novel SOX2-mediated regulatory network in EC that may be a viable target for EC treatment.