Reverse the curse--the role of deubiquitination in cell cycle control

Role of histone modifications in neurogenesis and neurodegenerative disease development

Progressive neuronal dysfunction and death are key features of neurodegenerative diseases; therefore, promoting neurogenesis in neurodegenerative diseases is crucial. With advancements in proteomics and high-throughput sequencing technology, it has been demonstrated that histone post-transcriptional modifications (PTMs) are often altered during neurogenesis when the brain is affected by disease or external stimuli and that the degree of histone modification is closely associated with the development of neurodegenerative diseases. This review aimed to show the regulatory role of histone modifications in neurogenesis and neurodegenerative diseases by discussing the changing patterns and functional significance of histone modifications, including histone methylation, acetylation, ubiquitination, phosphorylation, and lactylation. Finally, we explored the control of neurogenesis and the development of neurodegenerative diseases by artificially modulating histone modifications.

Structural optimization and biological evaluation of ML364 based derivatives as USP2a inhibitors

Ubiquitination is a representative post-translational modification that tags target proteins with ubiquitin to induce protein degradation or modify their functions. Deubiquitinating enzymes (DUBs) play a crucial role in reversing this process by removing ubiquitin from target proteins. Among them, USP2a has emerged as a promising target for cancer therapy due to its oncogenic properties in various cancer types, but its inhibitors have been limited. In this study, our aim was to optimize the structure of ML364, a USP2a inhibitor, and synthesize a series of its derivatives to develop potent USP2a inhibitors. Compound 8v emerged as a potential USP2a inhibitor with lower cytotoxicity compared to ML364. Cellular assays demonstrated that compound 8v effectively reduced the levels of USP2a substrates and attenuated cancer cell growth. We confirmed its direct interaction with the catalytic domain of USP2a and its selective inhibitory activity against USP2a over other USP subfamily proteins (USP7, 8, or 15). In conclusion, compound 8v has been identified as a potent USP2a inhibitor with substantial potential for cancer therapy.

DNMT3a-mediated upregulation of the stress inducible protein sestrin-2 contributes to malignant transformation of human bronchial epithelial cells following nickel exposure

BACKGROUND

Nickel is a confirmed human lung carcinogen. Nonetheless, the molecular mechanisms driving its carcinogenic impact on lung tissue remain poorly defined. In this study, we assessed SESN2 expression and the signaling pathways responsible for cellular transformation in human bronchial epithelial cells (HBECs) as a result of nickel exposure.

METHODS

We employed the Western blotting to determine the induction of SESN2 by nickel. To clarify the signaling pathways leading to cellular transformation following nickel exposure, we applied techniques such as gene knockdown, methylation-specific PCR, and chromatin immunoprecipitation.

RESULT

Exposure to nickel results in the upregulation of SESN2 and the initiation of autophagy in human bronchial epithelial cells (HBECs). This leads to degradation of HUR protein and consequently downregulation of USP28 mRNA, PP2AC protein, β-catenin protein, and diminished VHL transcription, culminating in the accumulation of hypoxia-inducible factor-1α (HIF-1α) and the malignant transformation of these cells. Mechanistic studies revealed that the increased expression of SESN2 is attributed to the demethylation of the SESN2 promoter induced by nickel, a process facilitated by decreased DNA methyl-transferase 3 A (DNMT3a) expression, while The downregulation of VHL transcription is linked to the suppression of the PP2A-C/GSK3β/β-Catenin/C-Myc pathway. Additionally, we discovered that SESN2-mediated autophagy triggers the degradation of HUR protein, which subsequently reduces the stability of USP28 mRNA and inhibits the PP2A-C/GSK3β/β-Catenin pathway and c-Myc transcription in HBECs post nickel exposure.

CONCLUSION

Our results reveal that nickel exposure leads to the downregulation of DNMT3a, resulting in the hypomethylation of the SESN2 promoter and its protein induction. This triggers autophagy-dependent suppression of the HUR/USP28/PP2A/β-Catenin/c-Myc pathway, subsequently leading to reduced VHL transcription, accumulation of HIF-1α protein, and the malignant transformation of human bronchial epithelial cells (HBECs). Our research offers novel insights into the molecular mechanisms that underlie the lung carcinogenic effects of nickel exposure. Specifically, nickel induces aberrant DNA methylation in the SESN2 promoter region through the decrease of DNMT3a levels, which ultimately leads to HIF-1α protein accumulation and the malignant transformation of HBECs. Specifically, nickel initiates DNA-methylation of the SESN2 promoter region by decreasing DNMT3a, ultimately resulting in HIF-1α protein accumulation and malignant transformation of HBECs. This study highlights DNMT3a as a potential prognostic biomarker or therapeutic target to improve clinical outcomes in lung cancer patients.

OTUD3 suppresses the mTORC1 signaling by deubiquitinating KPTN

Background: Ubiquitination and deubiquitination modifications play pivotal roles in eukaryotic life processes, regulating protein dynamics via the ubiquitin-proteasome pathway. Dysregulation can impact disease development, including cancer and neurodegenerative disorders. Increasing evidence highlights their role in tumorigenesis, modulating key proteins. OTUD3, a deubiquitinase, stabilizes PTEN, suppressing tumor growth by inhibiting PI3K-AKT signaling. Yet, further OTUD3 substrates remain underexplored. Methods: We employed the In vivo ubiquitination assay to investigate the ubiquitination role of OTUD3 on KPTN within the cellular context. Additionally, CRISPR/Cas9 editing and Immunofluorescence were utilized to study the impact of OTUD3 on the mTOR signaling pathway in cells. Furthermore, Cell proliferation assay and NMR were employed to explore the effects of OTUD3 on cellular growth and proliferation. Results: OTUD3 serves as a deubiquitinase for KPTN. OTUD3 interacts with KPTN, facilitated by the OTU domain within OTUD3. Further investigations confirmed KPTN's ubiquitination modification, primarily at lysine residue 49. Ubiquitination experiments demonstrated OTUD3's ability to mediate KPTN's deubiquitination without affecting its protein levels. This suggests KPTN's ubiquitination is a function-regulated, non-degradable modification. Under various amino acid starvation or stimulation conditions, overexpressing OTUD3 reduces mTORC1 signaling activation, while knocking out OTUD3 further enhances it. Notably, OTUD3's regulation of mTORC1 signaling relies on its deubiquitinase activity, and this effect is observed even in PTEN KO cells, confirming its independence from PTEN, a reported substrate. OTUD3 also promotes GATOR1's lysosomal localization, a process requiring KPTN's involvement. Ultimately, OTUD3 affects cellular metabolic pool products by downregulating the mTORC1 pathway, significantly inhibiting tumor cell growth and proliferation. Discussion: Our experiments shed light on an alternative perspective regarding the intrinsic functions of OTUD3 in inhibiting tumor development. We propose a novel mechanism involving KPTN-mediated regulation of the mTORC1 signaling pathway, offering fresh insights into the occurrence and progression of tumor diseases driven by related genes. This may inspire new approaches for drug screening and cancer treatment, potentially guiding future therapies for relevant tumors.

Chlorogenic acid modulates the ubiquitin-proteasome system in stroke animal model

BACKGROUND

Chlorogenic acid, a phenolic compound, has potent antioxidant and neuroprotective properties. The ubiquitin-proteasome system is an important regulators of neurodevelopment and modulators of neuronal function. This system is associated with neurodevelopment and neurotransmission through degradation and removal of damaged proteins. Activation of the ubiquitin-proteasome system is a critical factor in preventing cell death. We have previously reported a decrease in the activity of the ubiquitin-proteasome system during cerebral ischemia. This study investigated whether chlorogenic acid regulates the ubiquitin-proteasome system in an animal stroke model. In adult rats, middle cerebral artery occlusion (MCAO) surgery was performed to induce focal cerebral ischemia. Chlorogenic acid (30 mg/kg) or normal saline was injected into the abdominal cavity 2 h after MCAO surgery, and cerebral cortex tissues were collected 24 h after MCAO damage.

RESULTS

Chlorogenic acid attenuated neurobehavioral disorders and histopathological changes caused by MCAO damage. We identified the decreases in ubiquitin C-terminal hydrolase L1, ubiquitin thioesterase OTUB1, proteasome subunit α type 1, proteasome subunit α type 3, and proteasome subunit β type 4 expression using a proteomics approach in MCAO animals. The decrease in these proteins was alleviated by chlorogenic acid. In addition, the results of reverse transcription-polymerase chain reaction confirmed these changes. The identified proteins were markedly reduced in MCAO damage, while chlorogenic acid prevented these reductions induced by MCAO. The decrease of ubiquitin-proteasome system proteins in ischemic damage was associated with neuronal apoptosis.

CONCLUSIONS

Our results showed that chlorogenic acid regulates ubiquitin-proteasome system proteins and protects cortical neurons from neuronal damage. These results provide evidence that chlorogenic acid has neuroprotective effects and maintains the ubiquitin-proteasome system in ischemic brain injury.

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.

Genome-Wide Identification and Gene Expression Analysis of the OTU DUB Family in Oryza sativa

Ovarian tumor domain (OTU)-containing deubiquitinating enzymes (DUBs) are an essential DUB to maintain protein stability in plants and play important roles in plant growth development and stress response. However, there is little genome-wide identification and analysis of the OTU gene family in rice. In this study, we identified 20 genes of the OTU family in rice genome, which were classified into four groups based on the phylogenetic analysis. Their gene structures, conserved motifs and domains, chromosomal distribution, and cis elements in promoters were further studied. In addition, OTU gene expression patterns in response to plant hormone treatments, including SA, MeJA, NAA, BL, and ABA, were investigated by RT-qPCR analysis. The results showed that the expression profile of OsOTU genes exhibited plant hormone-specific expression. Expression levels of most of the rice OTU genes were significantly changed in response to rice stripe virus (RSV), rice black-streaked dwarf virus (RBSDV), Southern rice black-streaked dwarf virus (SRBSDV), and Rice stripe mosaic virus (RSMV). These results suggest that the rice OTU genes are involved in diverse hormone signaling pathways and in varied responses to virus infection, providing new insights for further functional study of OsOTU genes.

Ubiquitination regulation of aerobic glycolysis in cancer

Aerobic glycolysis, or the Warburg effect, is regarded as a critical part of metabolic reprogramming and plays a crucial role in the occurrence and development of tumours. Ubiquitination and deubiquitination, essential post-translational modifications, have attracted increasing attention with regards to the regulation of metabolic reprogramming in cancer. However, the mechanism of ubiquitination in glycolysis remains unclear. In this review, we discuss the roles of ubiquitination and deubiquitination in regulating glycolysis, and their involvement in regulating important signalling pathways, enzymes, and transcription factors. Focusing on potential mechanisms may provide novel strategies for cancer treatment.

The Role of E3 Ubiquitin Ligases and Deubiquitinases in Inflammatory Bowel Disease: Friend or Foe?

Inflammatory bowel disease (IBD), which include Crohn’s disease (CD) and ulcerative colitis (UC), exhibits a complex multifactorial pathogenesis involving genetic susceptibility, imbalance of gut microbiota, mucosal immune disorder and environmental factors. Recent studies reported associations between ubiquitination and deubiquitination and the occurrence and development of inflammatory bowel disease. Ubiquitination modification, one of the most important types of post-translational modifications, is a multi-step enzymatic process involved in the regulation of various physiological processes of cells, including cell cycle progression, cell differentiation, apoptosis, and innate and adaptive immune responses. Alterations in ubiquitination and deubiquitination can lead to various diseases, including IBD. Here, we review the role of E3 ubiquitin ligases and deubiquitinases (DUBs) and their mediated ubiquitination and deubiquitination modifications in the pathogenesis of IBD. We highlight the importance of this type of posttranslational modification in the development of inflammation, and provide guidance for the future development of targeted therapeutics in IBD.

Design, synthesis, biological evaluation and structure-activity relationship study of quinazolin-4(3H)-one derivatives as novel USP7 inhibitors

Recent research has indicated that the abnormal expression of the deubiquitinase USP7 induces tumorigenesis via multiple cell pathways, and in particular, the p53-MDM2-USP7 pathway is well understood. USP7 is emerging as a promising target for cancer therapy. However, there are limited reports on USP7 inhibitors. Here we report design, synthesis and biological evaluation of novel quinazolin-4(3H)-one derivatives as potent USP7 inhibitors. Our results indicated that the compounds C9 and C19 exhibited the greatest potency against the USP7 catalytic domain, with IC₅₀ values of 4.86 μM and 1.537 μM, respectively. Ub-AMC assays further confirmed IC₅₀ values of 5.048 μM for C9 and 0.595 μM for C19. MTT assays indicated that gastric cancer MGC-803 cells were more sensitive to these compounds than BGC-823 cells. Flow cytometry analysis revealed that C9 restricted cancer cell growth at the G0/G1 and S phases and inhibited the proliferation and clone formation of MGC-803 cells. Further biochemical experiments indicated that C9 decreased the MDM2 protein level and increased the levels of the tumour suppressors p53 and p21 in a dose-dependent manner. Docking studies predicted that solvent exposure of the side chains of C9 and C19 would uniquely form hydrogen bonds with Met407 of USP7. Additionally, C9 exhibited a remarkable anticancer effect in a zebrafish gastric cancer MGC-803 cell model. Our results demonstrated that quinazolin-4(3H)-one derivatives were suitable as leads for the development of novel USP7 inhibitors and especially for anti-gastric cancer drugs.

Expression, purification and characterization of the second DUSP domain of deubiquitinase USP20/VDU2

Deubiquitinase USP20/VDU2 (VHL-interacting Deubiquitinating Enzyme 2) has been proved to play vital roles in multiple cellular processes by controlling the life-span of substrate proteins including hypoxia-inducible factor HIF1α, β2-adrenergic receptor, and type 2 iodothyronine deiodinase etc. USP20 contains four distinct structural domains, which include the N-terminal zinc-finger ubiquitin binding domain (ZnF-UBP), the catalytic domain (USP domain), and two tandem DUSP domains (DUSP1 and DUSP2). Here in this study, we report the setting up of the production approach for USP20 DUSP2, and the NMR characterization of the produced target protein. With the assistance of GB1 tag and glycerol, both the solubility and stability of USP20 DUSP2 are significantly enhanced. And by using the optimized protein production procedure, monomeric and stable ¹⁵N, ¹³C-labeled USP20 DUSP2 sample for NMR data acquisition was obtained. The secondary structural elements of USP20 DUSP2 were then revealed by the analysis of recorded NMR spectra, and USP20 DUSP2 forms an AB3 fold in solution. The production protocol and NMR characterization results reported in this manuscript could be utilized in the extended structural and functional studies of USP20 DUSP2.

Deubiquitinase Inhibitor b-AP15 Attenuated LPS-Induced Inflammation via Inhibiting ERK1/2, JNK, and NF-Kappa B

b-AP15 is a deubiquitinase (DUB) inhibitor of 19S proteasomes, which in turn targets ubiquitin C-terminal hydrolase 5 (UCHL5) and ubiquitin-specific peptidase 14 (USP14). Nuclear factor kappa B (NF-κB) is closely linked to cellular response in macrophages when the organism is in the state of microbial infection, and it acts as a vital part in the mechanism of inflammatory reaction. However, the molecular mechanism by which DUB inhibitors, especially b-AP15, regulates inflammation remains poorly understood. This study aimed to investigate the relationship between b-AP15 and inflammation. The results showed that b-AP15 treatment significantly reduced the amounts of inflammatory indicators, such as tumor necrosis factor alpha (TNF-α) and interleukin 6 (IL-6) in lipopolysaccharide (LPS)-stimulated THP-1 and macrophages. Meanwhile, similar results were obtained from in vivo experiments. In addition, b-AP15 also significantly improved the survival rate of sepsis mouse via high-density LPS mediation. Furthermore, b-AP15 also inhibited the ERK1/2 and JNK phosphorylation, increased IκBα levels, and inhibited NF-κB p65 by removing them from the cytoplasm into the nucleus. All these findings suggested that b-AP15 has anti-inflammatory action and acts as a potential neoteric target drug for treating microbial infection.

Structural and functional studies of USP20 ZnF-UBP domain by NMR

Deubiquitinase USP20/VDU2 has been demonstrated to play important roles in multiple cellular processes by controlling the life span of substrate proteins including hypoxia-inducible factor HIF1α, and so forth. USP20 contains four distinct structural domains including the N-terminal zinc-finger ubiquitin binding domain (ZnF-UBP), the catalytic domain (USP domain), and two tandem DUSP domains, and none of the structures for these four domains has been solved. Meanwhile, except for the ZnF-UBP domain, the biological functions for USP20's catalytic domain and tandem DUSP domains have been at least partially clarified. Here in this study, we determined the solution structure of USP20 ZnF-UBP domain and investigated its binding properties with mono-ubiquitin and poly-ubiquitin (K48-linked di-ubiquitin) by using NMR and molecular modeling techniques. USP20's ZnF-UBP domain forms a spherically shaped fold consisting of a central β-sheet with either one α-helix or two α-helices packed on each side of the sheet. However, although having formed a canonical core structure essential for ubiquitin recognition, USP20 ZnF-UBP presents weak ubiquitin binding capacity. The structural basis for understanding USP20 ZnF-UBP's ubiquitin binding capacity was revealed by NMR data-driven docking. Although the electrostatic interactions between D264 of USP5 (E87 in USP20 ZnF-UBP) and R74 of ubiquitin are kept, the loss of the extensive interactions formed between ubiquitin's di-glycine motif and the conserved and non-conserved residues of USP20 ZnF-UBP domain (W41, E55, and Y84) causes a significant decrease in its binding affinity to ubiquitin. Our findings indicate that USP20 ZnF-UBP domain might have a physiological role unrelated to its ubiquitin binding capacity.

Ubiquitin specific peptidase 5 regulates colorectal cancer cell growth by stabilizing Tu translation elongation factor

Ubiquitin specific peptidase 5 (USP5) is a ubiquitous expressed deubiquitinating enzyme (DUB). It has been shown involved in DNA repair, apoptosis, inflammation, and tumor cell growth. However, the function and molecular mechanism of USP5 in colorectal cancer (CRC) are still unclear. In the present study, we asked how it affected the growth of colorectal cancer cells.

Methods: A shRNA-based high-content screening was performed to identify DUBs affecting the growth of CRC cells. CCK-8 assay and xenografts were used to assess CRC cell growth, survival and tumorigenesis. RT-qPCR, immunoblotting and immunohistochemistry were carried out to quantitate USP5 expression in CRC tissues and cell lines. Immunoprecipitation and mass spectrometry analysis were performed to identify USP5-interacting proteins. Cycloheximide chase was performed to assess Tu translation elongation factor (TUFM) stability. Dual luciferase reporter assay was utilized for USP5 promoter analysis.

Results: We found that USP5 was highly expressed in a group of primary CRC tissues, and the increased USP5 was correlated with clinical stages and shorter overall survival. While USP5 knockdown effectively inhibited CRC cell growth, overexpressed USP5 promoted the growth of CRC cells and made them more resistant to doxorubicin (DOX). TUFM was discovered as a substrate of USP5. USP5 deubiquitinated TUFM and increased its level in CRC cells. Enforced expression of TUFM was able to alleviate the growth inhibition induced by USP5 knockdown. Further analyses showed that EBF transcription factor 1 (EBF1) was a major regulator for USP5 transcription, and DOX inhibited EBF1-USP5-TUFM axis in CRC cells.

Conclusions: USP5 was required for CRC cells and promoted their growth and resistance to chemotherapeutics. TUFM was a USP5 deubiquitinating substrate that mediated the cellular effects of USP5. The transcription of USP5 was regulated by EBF1. Thus, targeting EBF1-USP5-TUFM axis is a potential novel strategy for CRC treatment.

Identification of a USP9X Substrate NFX1-123 by SILAC-Based Quantitative Proteomics

The deubiquitinase USP9X is involved in multiple diseases including neurodegeneration, epilepsy, and various types of tumors by targeting different substrates. In the present study, we aimed to explore the potential substrates of USP9X and performed SILAC-based quantitative proteomics to compare these substrates in USP9X-knockdown and wild-type HeLa cells. We consequently carried out Flag-NFX1-123 tag affinity-based mass spectrometry and confirmed that the X-box binding nuclear factor NFX1-123 interacted with USP9X. Moreover, immunoprecipitation assays verified a direct interaction between USP9X and NFX1-123. Further experiments confirmed that NFX1-123 could be modified by ubiquitination and that USP9X stabilized NFX1-123 via efficient deubiquitination of NFX1-123. Knockdown of USP9X resulted in decreased NFX1-123 protein levels compared with their unchanged corresponding mRNA levels in different cell lines. In summary, we found that NFX1-123 was a bona fide substrate of the deubiquitinase USP9X and that it could be degraded by the ubiquitin-proteasome system. The present study provided new insight into understanding the biological function of USP9X by targeting its substrate NFX1-123.

A new gold(I) complex-Au(PPh3)PT is a deubiquitinase inhibitor and inhibits tumor growth

Background

Ubiquitin-proteasome system (UPS) is integral to cell survival by maintaining protein homeostasis, and its dysfunction has been linked to cancer and several other human diseases. Through counteracting ubiquitination, deubiquitinases (DUBs) can either positively or negatively regulate UPS function, thereby representing attractive targets of cancer therapies. Previous studies have shown that metal complexes can inhibit tumor growth through targeting the UPS; however, novel metal complexes with higher specificity for cancer therapy are still lacking.

Methods

We synthesized a new gold(I) complex, Au(PPh₃)PT. The inhibitory activity of Au(PPh₃)PT on the UPS and the growth of multiple cancer cell types were tested in vitro, ex vivo, and in vivo. Furthermore, we compared the efficacy of Au(PPh₃)PT with other metal compounds in inhibition of UPS function and tumor growth.

Findings

Here we report that (i) a new gold(I) complex-pyrithione, i.e., Au(PPh₃)PT, induced apoptosis in two lung cancer cell lines A549 and NCI-H1299; (ii) Au(PPh₃)PT severely impaired UPS proteolytic function; (iii) Au(PPh₃)PT selectively inhibited 19S proteasome-associated DUBs (UCHL5 and USP14) and other non-proteasomal DUBs with minimal effects on the function of 20S proteasome; (iv) Au(PPh₃)PT induced apoptosis in cancer cells from acute myeloid leukemia patients; (v) Au(PPh₃)PT effectively suppressed the growth of lung adenocarcinoma xenografts in nude mice; and (vi) Au (PPh₃)PT elicited less cytotoxicity in normal cells than several other metal compounds.

Interpretation

Together, this study discovers a new gold(I) complex to be an effective inhibitor of the DUBs and a potential anti-cancer drug.

Fund

The National High Technology Research and Development Program of China, the project of Guangdong Province Natural Science Foundation, the projects from Foundation for Higher Education of Guangdong, the project from Guangzhou Medical University for Doctor Scientists, the Medical Scientific Research Foundation of Guangdong Province, and the Guangzhou Key Medical Discipline Construction Project Fund.

A novel USP9X substrate TTK contributes to tumorigenesis in non-small-cell lung cancer

The X-linked deubiquitinase, USP9X, is implicated in multiple cancers by targeting various substrates. Increased expression of USP9X is observed in non-small-cell lung cancer (NSCLC) and is correlated with poor prognosis. However, the molecular mechanism for USP9X regulation of tumor cell survival and tumorigenesis in NSCLC is less defined.

Methods: In this study, chemical labeling, quantitative proteomic screening was applied to analyze A549 cells with or without USP9X RNA interference. Functional in vitro and in vivo experiments were performed to confirm the oncogenic effects of USP9X in NSCLC and to investigate the underlying mechanisms.

Results: The resulting data suggested that dual specificity protein kinase TTK is a potential substrate of USP9X. Further experimental evidences confirmed that USP9X stabilized TTK via direct interaction and efficient deubiquitination of TTK on K48 ubiquitin chain. Moreover, knockdown of USP9X or TTK inhibited cell proliferation, migration and tumorigenesis, and the immunohistochemical analysis of clinical NSCLC samples showed that the protein expression levels of USP9X and TTK were significantly elevated and positively correlated in tumor tissues.

Conclusions: In summary, our data demonstrated that the USP9X-TTK axis may play a critical role in NSCLC, and could be considered as a potential therapeutic target.

Ubiquitin-specific peptidase 5 and ovarian tumor deubiquitinase 6A are differentially expressed in p53+/+ and p53-/- HCT116 cells

Most proteins undergo ubiquitination, a process by which ubiquitin proteins bind to their substrate proteins; by contrast, deubiquitination is a process that reverses ubiquitination. Deubiquitinating enzymes (DUBs) function to remove ubiquitin proteins from the protein targets and serve an essential role in regulating DNA repair, protein degradation, apoptosis and immune responses. Abnormal regulation of DUBs may affect a number of cellular processes and may lead to a variety of human diseases, including cancer. Therefore, it is important to identify abnormally expressed DUBs to identify DUB-related diseases and biological mechanisms. The present study aimed to develop a multiplex polymerase chain reaction screening platform comprising primers for various DUB genes. This assay was used to identify p53-related DUBs in HCT116 p53+/+ and p53-/- cells. The results demonstrated that ubiquitin-specific peptidase 5 (USP5) and ovarian tumor deubiquitinase 6A (OTUD6A) were differentially expressed in p53+/+ and p53-/- HCT116 cells. Based on the data obtained through DUB screening, the protein expression levels of USP5 and OTUD6A were examined by western blotting, which confirmed that both of these DUBs were also expressed differentially in p53+/+ and p53-/- HCT116 cells. In conclusion, results from the DUB screening performed by the present study revealed that the expression of USP5 and OTUD6A may be affected by p53, and this method may be useful for the rapid and cost-effective identification of possible biomarkers.

Delineating Crosstalk Mechanisms of the Ubiquitin Proteasome System That Regulate Apoptosis

Regulatory functions of the ubiquitin-proteasome system (UPS) are exercised mainly by the ubiquitin ligases and deubiquitinating enzymes. Degradation of apoptotic proteins by UPS is central to the maintenance of cell health, and deregulation of this process is associated with several diseases including tumors, neurodegenerative disorders, diabetes, and inflammation. Therefore, it is the view that interrogating protein turnover in cells can offer a strategy for delineating disease-causing mechanistic perturbations and facilitate identification of drug targets. In this review, we are summarizing an overview to elucidate the updated knowledge on the molecular interplay between the apoptosis and UPS pathways. We have condensed around 100 enzymes of UPS machinery from the literature that ubiquitinates or deubiquitinates the apoptotic proteins and regulates the cell fate. We have also provided a detailed insight into how the UPS proteins are able to fine-tune the intrinsic, extrinsic, and p53-mediated apoptotic pathways to regulate cell survival or cell death. This review provides a comprehensive overview of the potential of UPS players as a drug target for cancer and other human disorders.

BRCA1 mutation spectrum, functions, and therapeutic strategies: The story so far

BRCA1 gene mutations account for about 25-28% of hereditary Breast Cancer as BRCA1 is included in the category of high penetrance genes. Except for few commonmutations, there is a heterogenous spectrum of BRCA1 mutations in various ethnic groups. 185AGdel and 5382ins Care the most common BRCA1 alterations (founder mutations) which have been identified in most of the population. This review has been compiled with an aim to consolidate the information on genetic variants reported in BRCA1 found in various ethnic groups, their functional implications if known; involvement of BRCA1 in various cellular pathways/processes and potential BRCA1 targeted therapies. The pathological variations of BRCA1 vary among different ethical groups. A systematic search in PubMed and Google scholar for the literature on BRCA1 gene was carried out to figure out structure and function of BRCA1 gene. BRCA1 is a large protein having 1863 amino acids with multiple functional domains and interacts with multiple proteins to carry out various crucial cellular processes. BRCA1 plays a major role in maintaining genome integrity, transcription regulation, chromatin remodeling, cell cycle checkpoint control, DNA damage repair, chromosomal segregation, and apoptosis. Studies investigating the phenotypic response of mutant BRCA1 protein and comparing it to wildtype BRCA1 protein are clinically important as they are involved in homologous recombination and other repair mechanisms. These studies may help in developing more targetted therapies, detecting novel interacting partners, identification of new signaling pathways that BRCA1 is a part of or downstream target genes that BRCA1 affects.

APC/CFZR-1 Controls SAS-5 Levels To Regulate Centrosome Duplication in Caenorhabditis elegans

As the primary microtubule-organizing center, centrosomes play a key role in establishing mitotic bipolar spindles that secure correct transmission of genomic content. For the fidelity of cell division, centrosome number must be strictly controlled by duplicating only once per cell cycle. Proper levels of centrosome proteins are shown to be critical for normal centrosome number and function. Overexpressing core centrosome factors leads to extra centrosomes, while depleting these factors results in centrosome duplication failure. In this regard, protein turnover by the ubiquitin-proteasome system provides a vital mechanism for the regulation of centrosome protein levels. Here, we report that FZR-1, the Caenorhabditis elegans homolog of Cdh1/Hct1/Fzr, a coactivator of the anaphase promoting complex/cyclosome (APC/C), an E3 ubiquitin ligase, functions as a negative regulator of centrosome duplication in the C. elegans embryo. During mitotic cell division in the early embryo, FZR-1 is associated with centrosomes and enriched at nuclei. Loss of fzr-1 function restores centrosome duplication and embryonic viability to the hypomorphic zyg-1(it25) mutant, in part, through elevated levels of SAS-5 at centrosomes. Our data suggest that the APC/C^FZR-1 regulates SAS-5 levels by directly recognizing the conserved KEN-box motif, contributing to proper centrosome duplication. Together, our work shows that FZR-1 plays a conserved role in regulating centrosome duplication in C. elegans.

Ablation of an Ovarian Tumor Family Deubiquitinase Exposes the Underlying Regulation Governing the Plasticity of Cell Cycle Progression in Toxoplasma gondii

The Toxoplasma genome encodes the capacity for distinct architectures underlying cell cycle progression in a life cycle stage-dependent manner. Replication in intermediate hosts occurs by endodyogeny, whereas a hybrid of schizogony and endopolygeny occurs in the gut of the definitive feline host. Here, we characterize the consequence of the loss of a cell cycle-regulated ovarian tumor (OTU family) deubiquitinase, OTUD3A of Toxoplasma gondii (TgOTUD3A; TGGT1_258780), in T. gondii tachyzoites. Rather than the mutation being detrimental, mutant parasites exhibited a fitness advantage, outcompeting the wild type. This phenotype was due to roughly one-third of TgOTUD3A-knockout (TgOTUD3A-KO) tachyzoites exhibiting deviations from endodyogeny by employing replication strategies that produced 3, 4, or 5 viable progeny within a gravid mother instead of the usual 2. We established the mechanistic basis underlying these altered replication strategies to be a dysregulation of centrosome duplication, causing a transient loss of stoichiometry between the inner and outer cores that resulted in a failure to terminate S phase at the attainment of 2N ploidy and/or the decoupling of mitosis and cytokinesis. The resulting dysregulation manifested as deviations in the normal transitions from S phase to mitosis (S/M) (endopolygeny-like) or M phase to cytokinesis (M/C) (schizogony-like). Notably, these imbalances are corrected prior to cytokinesis, resulting in the generation of normal progeny. Our findings suggest that decisions regarding the utilization of specific cell cycle architectures are controlled by a ubiquitin-mediated mechanism that is dependent on the absolute threshold levels of an as-yet-unknown target(s). Analysis of the TgOTUD3A-KO mutant provides new insights into mechanisms underlying the plasticity of apicomplexan cell cycle architecture.

Replication by Toxoplasma gondii can occur by 3 distinct cell cycle architectures. Endodyogeny is used by asexual stages, while a hybrid of schizogony and endopolygeny is used by merozoites in the definitive feline host. Here, we establish that the disruption of an ovarian-tumor (OTU) family deubiquitinase, TgOTUD3A, in tachyzoites results in dysregulation of the mechanism controlling the selection of replication strategy in a subset of parasites. The mechanistic basis for these altered cell cycles lies in the unique biology of the bipartite centrosome that is associated with the transient loss of stoichiometry between the inner and outer centrosome cores in the TgOTUD3A-KO mutant. This highlights the importance of ubiquitin-mediated regulation in the transition from the nuclear to the budding phases of the cell cycle and provides new mechanistic insights into the regulation of the organization of the apicomplexan cell cycle.

Ubiquitin levels: the next target against gynecological cancers?

Ubiquitylation is a tightly regulated process that is essential for appropriate cell survival and function, and the ubiquitin pathway has shown promise as a therapeutic target for several forms of cancer. In this issue of the JCI, Kedves and colleagues report the identification of a subset of gynecological cancers with repressed expression of the polyubiquitin gene UBB, which renders these cancer cells sensitive to further decreases in ubiquitin production by inhibition of the polyubiquitin gene UBC. Moreover, inducible depletion of UBC in mice harboring tumors with low UBB levels dramatically decreased tumor burden and prolonged survival. Together, the results of this study indicate that there is a synthetic lethal relationship between UBB and UBC that has potential to be exploited as a therapeutic strategy to fight these devastating cancers.

Do Low Serum UCH-L1 and TDP-43 Levels Indicate Disturbed Ubiquitin-Proteosome System in Autism Spectrum Disorder?

INTRODUCTION

The mechanism of ubiquitination-related abnormalities causing neural development problems is still unclear. We examined the association between autism and serum transactive response DNA-binding protein-43 (TDP-43) and ubiquitin c-terminal hydrolase-L1 (UCH-L1) levels, both of which are members of the ubiquitin-proteosome system.

METHODS

We measured serum levels of TDP-43 and UCH-L1 in 24 children with autism and 24 healthy children. Childhood Autism Rating Scale (CARS) was used to assess symptom severity at admission.

RESULTS

The mean serum TDP-43 and UCH-L1 levels in children with autism spectrum disorder (ASD) were found to decrease compared to healthy controls (p<0.001, 506.21±780.97 ng/L and 1245.80±996.76 ng/L, respectively; 3.08±5.44 ng/mL and 8.64±6.67 ng/mL, respectively). A positive correlation between serum TDP-43 levels and UCH-L1 levels was found in the ASD group (r=0.947, n=24, p<0.001). The CARS score of children with ASD was 48.91 points (standard deviation [SD]: 5.82).

CONCLUSION

Low serum levels of UCH-L1 and TDP-43 may reflect disturbed ubiquitination in autism.

Structural and Functional Investigations of the N-Terminal Ubiquitin Binding Region of Usp25

Ubiquitin-specific protease 25 (Usp25) is a deubiquitinase that is involved in multiple biological processes. The N-terminal ubiquitin-binding region (UBR) of Usp25 contains one ubiquitin-associated domain, one small ubiquitin-like modifier (SUMO)-interacting motif and two ubiquitin-interacting motifs. Previous studies suggest that the covalent sumoylation in the UBR of Usp25 impairs its enzymatic activity. Here, we raise the hypothesis that non-covalent binding of SUMO, a prerequisite for efficient sumoylation, will impair Usp25's catalytic activity as well. To test our hypothesis and elucidate the underlying molecular mechanism, we investigated the structure and function of the Usp25 N-terminal UBR. The solution structure of Usp25_1-146 is obtained, and the key residues responsible for recognition of ubiquitin and SUMO2 are identified. Our data suggest inhibition of Usp25's catalytic activity upon the non-covalent binding of SUMO2 to the Usp25 SUMO-interacting motif. We also find that SUMO2 can competitively block the interaction between the Usp25 UBR and its ubiquitin substrates. Based on our findings, we have proposed a working model to depict the regulatory role of the Usp25 UBR in the functional display of the enzyme.

Deubiquitylating enzymes in receptor endocytosis and trafficking

In recent times, our knowledge of the roles ubiquitin plays in multiple cellular processes has expanded exponentially, with one example being the role of ubiquitin in receptor endocytosis and trafficking. This has prompted a multitude of studies examining how the different machinery involved in the addition and removal of ubiquitin can influence this process. Multiple deubiquitylating enzymes (DUBs) have been implicated either in facilitating receptor endocytosis and lysosomal degradation or in rescuing receptor levels by preventing endocytosis and/or promoting recycling to the plasma membrane. In this review, we will discuss in detail what is currently known about the role of DUBs in regulating the endocytosis of various transmembrane receptors and ion channels. We will also expand upon the role DUBs play in receptor sorting at the multivesicular body to determine whether a receptor is recycled or trafficked to the lysosome for degradation. Finally, we will briefly discuss how the DUBs implicated in these processes may contribute to the pathogenesis of a range of diseases, and thus the potential these have as therapeutic targets.

The equilibrium of ubiquitination and deubiquitination at PLK1 regulates sister chromatid separation

PLK1 regulates almost every aspect of mitotic events, including mitotic entry, spindle assembly, chromosome alignment, sister chromatid segregation, metaphase-anaphase transition, cytokinesis, etc. In regulating the chromosome alignment and sister chromatid segregation, PLK1 has to be localized to and removed from kinetochores at the right times, and the underlying mechanism that regulates PLK1 both spatially and temporally only became clearer recently. It has been found that deubiquitination and ubiquitination of PLK1 are responsible for its localization to and dissociation from the kinetochores, respectively. The equilibrium of this ubiquitination and deubiquitination plays an important role in regulating proper chromosome alignment and timely sister chromatid segregation. Here, we summarize and discuss the recent findings in investigating the spatial and temporal regulation of PLK1 during chromosome alignment and sister chromatid segregation.

Proteasome-associated deubiquitinase ubiquitin-specific protease 14 regulates prostate cancer proliferation by deubiquitinating and stabilizing androgen receptor

Androgen receptor (AR) is frequently over-expressed and plays a critical role in the growth and progression of human prostate cancer. The therapy attempting to target AR signalling was established in decades ago but the treatment of prostate cancer is far from being satisfactory. The assignable cause is that our understanding of the mechanism of AR regulation and re-activation remains incomplete. Increasing evidence suggests that deubiquitinases are involved in the regulation of cancer development and progression but the specific underlying mechanism often is not elucidated. In the current study, we have identified ubiquitin-specific protease 14 (USP14) as a novel regulator of AR, inhibiting the degradation of AR via deubiquitinating this oncoprotein in the androgen-responsive prostate cancer cells. We found that (i) USP14 could bind to AR, and additionally, both genetic and pharmacological inhibition of USP14 accelerated the ubiquitination and degradation of AR; (ii) downregulation or inhibition of USP14 suppressed cell proliferation and colony formation of LNcap cells and, conversely, overexpression of USP14 promoted the proliferation; and (iii) reduction or inhibition of USP14 induced G0/G1 phase arrest in LNcap prostate cancer cells. Hence, we conclude that USP14 promotes prostate cancer progression likely through stabilization of AR, suggesting that USP14 could be a promising therapeutic target for prostate cancer.

Two clinical drugs deubiquitinase inhibitor auranofin and aldehyde dehydrogenase inhibitor disulfiram trigger synergistic anti-tumor effects in vitro and in vivo

Inhibition of proteasome-associated deubiquitinases (DUBs) is emerging as a novel strategy for cancer therapy. It was recently reported that auranofin (Aur), a gold (I)-containing compound used clinically to treat rheumatoid arthritis, is a proteasome-associated DUB inhibitor. Disulfiram (DSF), an inhibitor of aldehyde dehydrogenase, is currently in clinical use for treating alcoholism. Recent studies have indicated that DSF can also act as an antitumor agent. We investigated the effect of combining DSF and Aur on apoptosis induction and tumor growth in hepatoma cancer cells. Here we report that (i) the combined treatment of Aur and DSF results in synergistic cytotoxicity to hepatoma cells in vitro and in vivo; (ii) Aur and DSF in combination induces caspase activation, endoplasmic reticulum (ER) stress, and reactive oxygen species (ROS) production; (iii) pan-caspase inhibitor z-VAD-FMK could efficiently block apoptosis but not proteasome inhibition induced by Aur and DSF combined treatment, and ROS is not required for Aur+DSF to induce apoptosis. Collectively, we demonstrate a model of synergism between DSF and proteasome-associated DUB inhibitor Aur in the induction of apoptosis in hepatoma cancer cells, identifying a potential novel anticancer strategy for clinical use in the future.

Ubiquitin-specific protease 14 regulates cell proliferation and apoptosis in oral squamous cell carcinoma

Ubiquitin-specific protease 14, a deubiquitinating enzyme, has been implicated in the tumorigenesis and progression of several cancers, but its role in oral squamous cell carcinoma remains to be elucidated. The aim of this study was to explore the expression pattern and roles of Ubiquitin-specific protease 14 in the occurrence and development of oral squamous cell carcinoma. Interestingly, Ubiquitin-specific protease 14 was overexpressed in oral cancer tissues and cell lines at both mRNA and protein levels. b-AP15, a specific inhibitor of Ubiquitin-specific protease 14, significantly inhibited the growth of cancer cells and increased cell apoptosis in a dose-dependent manner. Moreover, knockdown of Ubiquitin-specific protease 14 by shRNA significantly inhibited the proliferation and migration of cancer cells in vitro. Finally, using a xenograft mouse model of oral squamous cell carcinoma, knockdown of Ubiquitin-specific protease 14 markedly inhibited tumor growth and triggered the cancer cell apoptosis in vivo, supporting previous results. In conclusion, for the first time we have demonstrated the expression pattern of Ubiquitin-specific protease 14 in oral squamous cell carcinoma and verified a relationship with tumor growth and metastasis. These results may highlight new therapeutic strategies for tumor treatment, application of Ubiquitin-specific protease 14 selective inhibitor, such as b-AP15, or knockdown by shRNA. Collectively, Ubiquitin-specific protease 14 could be a potential therapeutic target for oral squamous cell carcinoma patients.

DUBbing Cancer: Deubiquitylating Enzymes Involved in Epigenetics, DNA Damage and the Cell Cycle As Therapeutic Targets

Controlling cell proliferation is one of the hallmarks of cancer. A number of critical checkpoints ascertain progression through the different stages of the cell cycle, which can be aborted when perturbed, for instance by errors in DNA replication and repair. These molecular checkpoints are regulated by a number of proteins that need to be present at the right time and quantity. The ubiquitin system has emerged as a central player controlling the fate and function of such molecules such as cyclins, oncogenes and components of the DNA repair machinery. In particular, proteases that cleave ubiquitin chains, referred to as deubiquitylating enzymes (DUBs), have attracted recent attention due to their accessibility to modulation by small molecules. In this review, we describe recent evidence of the critical role of DUBs in aspects of cell cycle checkpoint control, associated DNA repair mechanisms and regulation of transcription, representing pathways altered in cancer. Therefore, DUBs involved in these processes emerge as potentially critical targets for the treatment of not only hematological, but potentially also solid tumors.

The N-terminal ubiquitin-binding region of ubiquitin-specific protease 28 modulates its deubiquitination function: NMR structural and mechanistic insights

We have characterized the structure and function of the N-terminal UBR of Usp28 in this study. Our findings are helpful for a better understanding of the underlying molecular mechanism in the control of catalytic activity of DUBs.

The Ubp15 deubiquitinase promotes timely entry into S phase in Saccharomyces cerevisiae

The anaphase-promoting complex in partnership with its activator, Cdh1, is an E3 ubiquitin ligase responsible for targeting cell cycle proteins during G1 phase. In the budding yeast Saccharomyces cerevisiae, Cdh1 associates with the deubiquitinating enzyme Ubp15, but the significance of this interaction is unclear. To better understand the physiological role(s) of Ubp15, we examined cell cycle phenotypes of cells lacking Ubp15. We found that ubp15∆ cells exhibited delayed progression from G1 into S phase and increased sensitivity to the DNA synthesis inhibitor hydroxyurea. Both phenotypes of ubp15∆ cells were rescued by additional copies of the S-phase cyclin gene CLB5. Clb5 is an unstable protein targeted for proteasome-mediated degradation by several pathways. We found that during G1 phase, the APC(Cdh1)-mediated degradation of Clb5 was accelerated in ubp15∆ cells. Ubp15 interacted with Clb5 independent of Cdh1 and deubiquitinated Clb5 in a reconstituted system. Thus deubiquitination by Ubp15 counteracts APC activity toward cyclin Clb5 to allow Clb5 accumulation and a timely entry into S phase.

Clinically used antirheumatic agent auranofin is a proteasomal deubiquitinase inhibitor and inhibits tumor growth

Proteasomes are attractive emerging targets for anti-cancer therapies. Auranofin (Aur), a gold-containing compound clinically used to treat rheumatic arthritis, was recently approved by US Food and Drug Administration for Phase II clinical trial to treat cancer but its anti-cancer mechanism is poorly understood. Here we report that (i) Aur shows proteasome-inhibitory effect that is comparable to that of bortezomib/Velcade (Vel); (ii) different from bortezomib, Aur inhibits proteasome-associated deubiquitinases (DUBs) UCHL5 and USP14 rather than the 20S proteasome; (iii) inhibition of the proteasome-associated DUBs is required for Aur-induced cytotoxicity; and (iv) Aur selectively inhibits tumor growth in vivo and induces cytotoxicity in cancer cells from acute myeloid leukemia patients. This study provides important novel insight into understanding the proteasome-inhibiting property of metal-containing compounds. Although several DUB inhibitors were reported, this study uncovers the first drug already used in clinic that can inhibit proteasome-associated DUBs with promising anti-tumor effects.

Role of the deubiquitylating enzyme DmUsp5 in coupling ubiquitin equilibrium to development and apoptosis in Drosophila melanogaster

Protein ubiquitylation is a dynamic process that affects the function and stability of proteins and controls essential cellular processes ranging from cell proliferation to cell death. This process is regulated through the balanced action of E3 ubiquitin ligases and deubiquitylating enzymes (DUB) which conjugate ubiquitins to, and remove them from target proteins, respectively. Our genetic analysis has revealed that the deubiquitylating enzyme DmUsp5 is required for maintenance of the ubiquitin equilibrium, cell survival and normal development in Drosophila. Loss of the DmUsp5 function leads to late larval lethality accompanied by the induction of apoptosis. Detailed analyses at a cellular level demonstrated that DmUsp5 mutants carry multiple abnormalities, including a drop in the free monoubiquitin level, the excessive accumulation of free polyubiquitins, polyubiquitylated proteins and subunits of the 26S proteasome. A shortage in free ubiquitins results in the induction of a ubiquitin stress response previously described only in the unicellular budding yeast. It is characterized by the induction of the proteasome-associated deubiquitylase DmUsp14 and sensitivity to cycloheximide. Removal of DmUsp5 also activates the pro-apoptotic machinery thereby resulting in widespread apoptosis, indicative of an anti-apoptotic role of DmUsp5. Collectively, the pleiotropic effects of a loss of DmUsp5 function can be explained in terms of the existence of a limited pool of free monoubiquitins which makes the ubiquitin-dependent processes mutually interdependent.

WP1130 increases doxorubicin sensitivity in hepatocellular carcinoma cells through usp9x-dependent p53 degradation

Resistance to chemotherapeutic drugs is a major obstacle in hepatocellular carcinoma (HCC) therapy. However, the underlying mechanisms are not well understood. Recent evidence suggests that deubiquitinases (DUB) are key regulators in the mechanisms of cell proliferation, apoptosis and chemoresistance. The present study aimed to investigate whether WP1130, which inhibits activity of deubiquitinases, exerts synergistic cytotoxicity with doxorubicin in HCC and the underlying mechanisms. In the study, we found that Huh7, HepG2, and SNU387 HCC cells with p53 expression displayed enhanced response to the combination therapy compared with p53-deficient HCC cells (Hep3B) in the manner of inhibiting cell proliferation. Downregulation of p53 abolished the synergistic cytotoxicity of doxorubicin and WP1130 on HCC cells. Mechanistically, we found that combined treatment with WP1130 suppressed doxorubicin-mediated upregulation of p53 via promoting its ubiquitin-proteasome dependent degradation, whereas knockdown of DUB usp9x abolished this effect. Taken together, these results demonstrate that combined treatment with WP1130 sensitized HCC cells to doxorubicin via usp9x-depedent p53 degradation.

Measurement of deubiquitinating enzyme activity via a suicidal HA-Ub-VS probe

Deubiquitinating enzymes (DUBs) are a novel "drug-able" target for cervical cancer, and small-molecule inhibitors of DUBs are currently being evaluated as novel chemotherapeutic agents. In this chapter, we describe an enzyme activity assay to assess the selectivity of a putative small-molecule DUB inhibitor toward a subset of DUBs in cancer cell lines.

Ubiquitin specific protease 22 promotes cell proliferation and tumor growth of epithelial ovarian cancer through synergy with transforming growth factor β1

Ubiquitin specific protease 22 (USP22) is an oncogene that is upregulated in many cancer types, and aberrant expression of USP22 correlates with clinical outcome. However, its potential functional impact in epithelial ovarian cancer (EOC) has not been determined. Here, we report that USP22 was upregulated in EOC specimens and EOC cell lines with important functional consequences. A high level of USP22 in EOC tissues was associated with advanced clinical FIGO stage, lymph node metastasis and worse prognosis. Patients with higher USP22 expression had shorter relapse-free and overall survival. Depletion of USP22 suppressed cell proliferation in vitro and tumor growth in vivo. We found that inhibition of USP22 suppressed cell proliferation by inducing G1 phase cell cycle arrest through synergy with oncogenic transforming growth factor-β1 (TGFB1). Our results indicate that USP22 functions as an oncogene in EOC, and thus USP22 may serve as a potential therapeutic target for individualized EOC treatment.

¹H, ¹³C and ¹⁵N backbone and side-chain resonance assignments of the N-terminal ubiquitin-binding domains of USP25

Ubiquitin Specific Protease 25 (USP25), a member of the deubiquitinase family, is involved in several disease-related signal pathways including myogenesis, immunity and protein degradation. It specially catalyzes the hydrolysis of the K48-linked and K63-linked polyubiquitin chains. USP25 contains one ubiquitin-associated domain and two ubiquitin-interacting motifs (UIMs) in its N-terminal region, which interact with ubiquitin and play a role in substrate recognition. Besides, it has been shown that the catalysis activity of USP25 is either impaired by sumoylation or enhanced by ubiquitination within its UIM. To elucidate the structural basis of the cross-regulation of USP25 function by non-covalent binding and covalent modifications of ubiquitin and SUMO2/3, a systematic structural biology study of USP25 is required. Here, we report the (1)H, (13)C and (15)N backbone and side-chain resonance assignments of the N-terminal ubiquitin binding domains (UBDs) of USP25 with BMRB accession number of 19111, which is the first step of the systematic structural biology study of the enzyme.

A novel small molecule inhibitor of deubiquitylating enzyme USP14 and UCHL5 induces apoptosis in multiple myeloma and overcomes bortezomib resistance

Proteasome inhibitors have demonstrated that targeting protein degradation is effective therapy in multiple myeloma (MM). Here we show that deubiquitylating enzymes (DUBs) USP14 and UCHL5 are more highly expressed in MM cells than in normal plasma cells. USP14 and UCHL5 short interfering RNA knockdown decreases MM cell viability. A novel 19S regulatory particle inhibitor b-AP15 selectively blocks deubiquitylating activity of USP14 and UCHL5 without inhibiting proteasome activity. b-AP15 decreases viability in MM cell lines and patient MM cells, inhibits proliferation of MM cells even in the presence of bone marrow stroma cells, and overcomes bortezomib resistance. Anti-MM activity of b-AP15 is associated with growth arrest via downregulation of CDC25C, CDC2, and cyclin B1 as well as induction of caspase-dependent apoptosis and activation of unfolded protein response. In vivo studies using distinct human MM xenograft models show that b-AP15 is well tolerated, inhibits tumor growth, and prolongs survival. Combining b-AP15 with suberoylanilide hydroxamic acid, lenalidomide, or dexamethasone induces synergistic anti-MM activity. Our preclinical data showing efficacy of b-AP15 in MM disease models validates targeting DUBs in the ubiquitin proteasomal cascade to overcome proteasome inhibitor resistance and provides the framework for clinical evaluation of USP14/UCHL5 inhibitors to improve patient outcome in MM.

Ubiquitin-specific proteases 25 negatively regulates virus-induced type I interferon signaling

Ubiquitination and deubiquitination have emerged as critical regulatory processes in the virus-triggered type I interferon (IFN) induction pathway. In this study, we carried out a targeted siRNA screen of 54 ubiquitin-specific proteases (USPs) and identified USP25 as a negative regulator of the virus-triggered type I IFN signaling pathway. Overexpression of USP25 inhibited virus-induced activation of IFN-β, interferon regulation factor 3 (IRF3) and nuclear factor-kappa B (NF-κB), as well as the phosphorylation of IRF3 and NF-κB subunit p65. Furthermore, Knockdown of USP25 potentiated virus-induced induction of the IFN-β. In addition, detailed analysis demonstrated that USP25 cleaved lysine 48- and lysine 63-linked polyubiquitin chains in vitro and in vivo, and its deubiquitinating enzyme (DUB) activity, were dependent on a cysteine residue (Cys178) and a histidine residue (His607). USP25 mutants lacking DUB activity lost the ability to block virus-induced type I IFN to some degree. Mechanistically, USP25 deubiquitinated retinoic acid-inducible gene I (RIG-I), tumornecrosis factor (TNF) receptor-associated factor 2 (TRAF2), and TRAF6 to inhibit RIG-I-like receptor-mediated IFN signaling. Our findings suggest that USP25 is a novel DUB negatively regulating virus-induced type I IFN production.

Expression of HAUSP in gliomas correlates with disease progression and survival of patients

The human herpesvirus-associated ubiquitin-specific protease (HAUSP) deubiquitinating enzyme has been shown to regulate many proteins involved in the cell cycle, as well as tumor suppressors and oncogenes. However, the expression pattern of HAUSP in glioma patients is still unclear. The purpose of the present study was to investigate the expression pattern and prognostic significance of HAUSP in patients with glioma. Eighty glioma specimens and 10 normal control samples were obtained. Immunohistochemical assay, quantitative real-time PCR and western blot analysis were carried out to explore the expression of HAUSP. Additionally, the association of HAUSP expression with clinicopathological parameters and the survival of glioma patients were analyzed. Our results showed that HAUSP expression levels were increased from grade I to grade IV in the tumors of the glioma patients. Moreover, the survival rate of patients with HAUSP-positive tumors was lower when compared to that of patients with HAUSP-negative tumors. We further confirmed that high expression of HAUSP was a significant and independent prognostic indicator in glioma by multivariate analysis. Our data provide convincing evidence for the first time that the overexpression of HAUSP at the gene and protein levels is correlated with poor outcome in patients with glioma in China. HAUSP may play an important oncogenic role in glioma progression, and it is a potential diagnostic and therapeutic target.

Deubiquitinases as a signaling target of oxidative stress

Deubiquitinating enzymes (DUBs) constitute a large family of cysteine proteases that have a broad impact on numerous biological and pathological processes, including the regulation of genomic stability. DUBs are often assembled onto multiprotein complexes to assist in their localization and substrate selection, yet it remains unclear how the enzymatic activity of DUBs is modulated by intracellular signals. Herein, we show that bursts of reactive oxygen species (ROS) reversibly inactivate DUBs through the oxidation of the catalytic cysteine residue. Importantly, USP1, a key regulator of genomic stability, is reversibly inactivated upon oxidative stress. This, in part, explains the rapid nature of PCNA monoubiquitination-dependent DNA damage tolerance in response to oxidative DNA damage in replicating cells. We propose that DUBs of the cysteine protease family act as ROS sensors in human cells and that ROS-mediated DUB inactivation is a critical mechanism for fine-tuning stress-activated signaling pathways.

UCHL1 regulates ubiquitination and recycling of the neural cell adhesion molecule NCAM

The neural cell adhesion molecule (NCAM) is involved in neural development and in plasticity in the adult brain. NCAM140 and NCAM180 isoforms are transmembrane proteins with cytoplasmic domains that differ only in an alternatively spliced exon in the NCAM180 isoform. Both isoforms can interact with several extracellular and cytoplasmic molecules mediating NCAM-dependent functions. Most identified intracellular interaction partners bind to both isoforms, NCAM140 and NCAM180. To identify further intracellular interaction partners specifically binding to NCAM180 the cytosolic domain of human NCAM180 was recombinantly expressed and applied onto a protein macroarray containing the protein library from human fetal brain. We identified the ubiquitin C-terminal hydrolase (UCHL1) which has been described as a de-ubiquitinating enzyme as a potential interaction partner of NCAM180. Since NCAM180 and NCAM140 are ubiquitinated, NCAM140 was included in the subsequent experiments. A partial colocalization of both NCAM isoforms and UCHL1 was observed in primary neurons and the B35 neuroblastoma cell line. Overexpression of UCHL1 significantly decreased constitutive ubiquitination of NCAM180 and NCAM140 whereas inhibition of endogenous UCHL1 increased NCAM's ubiquitination. Furthermore, lysosomal localization of NCAM180 and NCAM140 was significantly reduced after overexpression of UCHL1 consistent with a partial colocalization of internalized NCAM with UCHL1. These data indicate that UCHL1 is a novel interaction partner of both NCAM isoforms that regulates their ubiquitination and intracellular trafficking.

Deubiquitinating enzyme BAP1 is involved in the formation and maintenance of the diapause embryos of Artemia

The modification of proteins by ubiquitination and deubiquitination plays an important role in various cellular processes. BRCA1-associated protein-1 (BAP1) is a deubiquitinating enzyme whose function in the control of the cell cycle requires both its deubiquitinating activity and nuclear localization. In the present study, a ubiquitin carboxyl-terminal hydrolase belonging to the BAP1 family was identified and characterized from Artemia parthenogenetica, a member of a family of brine shrimp that, under certain conditions, produce and release diapause embryos in which cell division and turnover of macromolecules are arrested. Western blot analysis and in vitro enzyme activity assay revealed ArBAP1 to be a cytoplasmic protein with typical ubiquitin hydrolase activity. Northern blot analysis revealed that ArBAP1 was abundant in the abdomen of Artemia producing diapause-destined embryos. Furthermore, by in situ hybridization, ArBAP1 was located exclusively in the embryos. In vivo knockdown of ArBAP1 by RNA interference resulted in the formation of embryos with split shells and abortive nauplii. The present findings suggest that ArBAP1, the first reported cytoplasmic BAP1, participates in the formation of diapause embryos and plays an important role in the control of cell cycle arrest in these encysted embryos.