The ubiquitin ligase HERC4 mediates c-Maf ubiquitination and delays the growth of multiple myeloma xenografts in nude mice

Inhibiting the Otub1/phosphorylated STAT3 axis for the treatment of non-small cell lung cancer

The transcription factor STAT3 is a promising target for the treatment of non-small cell lung cancer (NSCLC). STAT3 activity is mainly dependent on phosphorylation at tyrosine 705 (pSTAT3-Y705), but the modulation on pSTAT3-Y705 is elusive. By screening a library of deubiquitinases (Dubs), we found that the Otub1 increases STAT3 transcriptional activity. As a Dub, Otub1 binds to pSTAT3-Y705 and specifically abolishes its K48-linked ubiquitination, therefore preventing its degradation and promoting NSCLC cell survival. The Otub1/pSTAT3-Y705 axis could be a potential target for the treatment of NSCLC. To explore this concept, we screen libraries of FDA-approved drugs and natural products based on STAT3-recognition element-driven luciferase assay, from which crizotinib is found to block pSTAT3-Y705 deubiquitination and promotes its degradation. Different from its known action to induce ALK positive NSCLC cell apoptosis, crizotinib suppresses ALK-intact NSCLC cell proliferation and colony formation but not apoptosis. Furthermore, crizotinib also suppresses NSCLC xenograft growth in mice. Taken together, these findings identify Otub1 as the first deubiquitinase of pSTAT3-Y705 and provide that the Otub1/pSTAT3-Y705 axis is a promising target for the treatment of NSCLC.

The Ubiquitin-Conjugating Enzyme E2 O (UBE2O) and Its Therapeutic Potential in Human Leukemias and Solid Tumors

Protein degradation is a biological phenomenon essential for cellular homeostasis and survival. Selective protein degradation is performed by the ubiquitination system which selectively targets proteins that need to be eliminated and leads them to proteasome degradation. In this narrative review, we focus on the ubiquitin-conjugating enzyme E2 O (UBE2O) and highlight the role of UBE2O in many biological and physiological processes. We further discuss UBE2O's implications in various human diseases, particularly in leukemias and solid cancers. Ultimately, our review aims to highlight the potential role of UBE2O as a therapeutic target and offers new perspectives for developing targeted treatments for human cancers.

A targetable PRR11-DHODH axis drives ferroptosis- and temozolomide-resistance in glioblastoma

Temozolomide (TMZ) is a widely utilized chemotherapy treatment for patients with glioblastoma (GBM), although drug resistance constitutes a major therapeutic hurdle. Emerging evidence suggests that ferroptosis-mediated therapy could offer an appropriate alternative treatment option against cancer cells that are resistant to certain drugs. However, recurrent gliomas display robust ferroptosis resistance, although the precise mechanism of resistance remains elusive. In the present work, we report that proline rich protein 11 (PRR11) depletion significantly sensitizes GBM cells to TMZ by inducing ferroptosis. Mechanistically, PRR11 directly binds to and stabilizes dihydroorotate dehydrogenase (DHODH), which leads to glioma ferroptosis-resistant in a DHODH-dependent manner in vivo and in vitro. Furthermore, PRR11 inhibits HERC4 and DHODH binding, by suppressing the recruitment of E3 ubiquitin ligase HERC4 and polyubiquitination degradation of DHODH at the K306 site, which maintains DHODH protein stability. Importantly, downregulated PRR11 increases lipid peroxidation and alters DHODH-mediated mitochondrial morphology, thereby promoting ferroptosis and increasing TMZ chemotherapy sensitivity. In conclusion, our results reveal a mechanism via which PRR11 drives ferroptosis resistance and identifies ferroptosis induction and TMZ as an attractive combined therapeutic strategy for GBM.

Unraveling the Immune Regulatory Functions of USP5: Implications for Disease Therapy

Ubiquitin-specific protease 5 (USP5) belongs to the ubiquitin-specific protease (USP) family, which uniquely recognizes unanchored polyubiquitin chains to maintain the homeostasis of monoubiquitin chains. USP5 participates in a wide range of cellular processes by specifically cleaving isopeptide bonds between ubiquitin and substrate proteins or ubiquitin itself. In the process of immune regulation, USP5 affects important cellular signaling pathways, such as NF-κB, Wnt/β-catenin, and IFN, by regulating ubiquitin-dependent protein degradation. These pathways play important roles in immune regulation and inflammatory responses. In addition, USP5 regulates the activity and function of immunomodulatory signaling pathways via the deubiquitination of key proteins, thereby affecting the activity of immune cells and the regulation of immune responses. In the present review, the structure and function of USP5, its role in immune regulation, and the mechanism by which USP5 affects the development of diseases by regulating immune signaling pathways are comprehensively overviewed. In addition, we also introduce the latest research progress of targeting USP5 in the treatment of related diseases, calling for an interdisciplinary approach to explore the therapeutic potential of targeting USP5 in immune regulation.

Small molecule induced STING degradation facilitated by the HECT ligase HERC4

Stimulator of interferon genes (STING) is a central component of the cytosolic nucleic acids sensing pathway and as such master regulator of the type I interferon response. Due to its critical role in physiology and its' involvement in a variety of diseases, STING has been a focus for drug discovery. Targeted protein degradation (TPD) has emerged as a promising pharmacology for targeting previously considered undruggable proteins by hijacking the cellular ubiquitin proteasome system (UPS) with small molecules. Here, we identify AK59 as a STING degrader leveraging HERC4, a HECT-domain E3 ligase. Additionally, our data reveals that AK59 is effective on the common pathological STING mutations, suggesting a potential clinical application of this mechanism. Thus, these findings introduce HERC4 to the fields of TPD and of compound-induced degradation of STING, suggesting potential therapeutic applications.

Structure-based virtual screening of novel USP5 inhibitors targeting the zinc finger ubiquitin-binding domain

The equilibrium of cellular protein levels is pivotal for maintaining normal physiological functions. USP5 belongs to the deubiquitination enzyme (DUBs) family, controlling protein degradation and preserving cellular protein homeostasis. Aberrant expression of USP5 is implicated in a variety of diseases, including cancer, neurodegenerative diseases, and inflammatory diseases. In this paper, a multi-level virtual screening (VS) approach was employed to target the zinc finger ubiquitin-binding domain (ZnF-UBD) of USP5, leading to the identification of a highly promising candidate compound 0456-0049. Molecular dynamics (MD) simulations were then employed to assess the stability of complex binding and predict hotspot residues in interactions. The results indicated that the candidate stably binds to the ZnF-UBD of USP5 through crucial interactions with residues ARG221, TRP209, GLY220, ASN207, TYR261, TYR259, and MET266. Binding free energy calculations, along with umbrella sampling (US) simulations, underscored a superior binding affinity of the candidate relative to known inhibitors. Moreover, US simulations revealed conformational changes of USP5 during ligand dissociation. These insights provide a valuable foundation for the development of novel inhibitors targeting USP5.

HERC4 modulates ovarian cancer cell proliferation by regulating SMO-elicited hedgehog signaling

BACKGROUND

HERC4 has been reported to have functions in several types of tumors, but its roles in ovarian cancer have not been studied yet.

METHODS

Primary tissues from ovarian cancer patients and cell lines were collected for real-time PCR. Kaplan-Meier Plotter was used to predict the prognosis of ovarian cancer patients. HERC4 was overexpressed in cells by lentivirus, and CCK-8 assay was performed to evaluate cell viability. Real-time PCR and Western blot were carried out to analyze the mRNA and protein expression, respectively. Xenograft tumor models were established to analyze HERC4 function in vivo.

RESULTS

Firstly, we found that HERC4 was significantly downregulated in ovarian cancer. We then found that ovarian cancer patients with high HERC4 expression had significantly higher overall survival and progression-free survival rates compared with patients with low expression. Then, HERC4 was overexpressed in ovarian cancer cells, and we found that overexpression of HERC4 significantly inhibited ovarian cancer cell growth, as well as the expression of the target protein SMO, and the key proteins in the downstream hedgehog signaling pathway. Finally, the xenograft tumor models revealed that overexpression of HERC4 significantly inhibited tumor growth in vivo.

CONCLUSIONS

Overall, these results indicate that overexpression of HERC4 inhibits cell proliferation of ovarian cancer in vitro and in vivo, suggesting that HERC4 may serve as an effective target for the treatment of ovarian cancer.

USP5: Comprehensive insights into structure, function, biological and disease-related implications, and emerging therapeutic opportunities

Ubiquitin specific protease 5 (USP5) is a vital deubiquitinating enzyme that regulates various physiological functions by removing ubiquitin chains from target proteins. This review provides an overview of the structural and functional characteristics of USP5. Additionally, we discuss the role of USP5 in regulating diverse cellular processes, including cell proliferation, apoptosis, DNA double-strand damage, methylation, heat stress, and protein quality control, by targeting different substrates. Furthermore, we describe the involvement of USP5 in several pathological conditions such as tumors, pathological pain, developmental abnormalities, inflammatory diseases, and virus infection. Finally, we introduce newly developed inhibitors of USP5. In conclusion, investigating the novel functions and substrates of USP5, elucidating the underlying mechanisms of USP5-substrate interactions, intensifying the development of inhibitors, and exploring the upstream regulatory mechanisms of USP5 in detail can provide a new theoretical basis for the treatment of various diseases, including cancer, which is a promising research direction with considerable potential. Overall, USP5 plays a critical role in regulating various physiological and pathological processes, and investigating its novel functions and regulatory mechanisms may have significant implications for the development of therapeutic strategies for cancer and other diseases.

USP7 promotes non-small-cell lung cancer cell glycolysis and survival by stabilizing and activating c-Abl

BACKGROUND

Abelson tyrosine kinase (c-Abl) is frequently mutated and highly expressed, and promotes non-small-cell lung cancer (NSCLC) survival, metastasis and tumorigenesis. c-Abl could also be modified through ubiquitination, but the underlying mechanism is not well understood.

METHODS

Mass spectrometry assays were performed to search c-Abl deubiquitination enzymes. The molecular mechanism was determined using Co-IP assays, pull-down assays, Western blotting upon gene knockdown or overexpression. Cell lines and animal models were used to investigate the role of c-Abl and USP7 in NSCLC. EdU staining assay and Transwell assay were performed to evaluate the proliferation and migration ability of NSCLC cells, respectively.

RESULTS

Ubiquitin-specific protease 7 (USP7) is found to upregulate c-Abl via the deubiquitinase screen. USP7 interacts with c-Abl and decreases its K48-linked polyubiquitination, thereby increasing the stability of c-Abl. In addition to the wild-type one, c-Abl mutants can also be deubiquitinated and stabilized by USP7. Moreover, USP7 promotes c-Abl accumulation in cytoplasm by increasing its binding to 14-3-3α/β and activates the oncogenic c-Abl signalling pathway. Furthermore, the USP7/c-Abl axis promotes NSCLC cell glycolysis by direct phosphorylating and stabilizing hexokinase-2 (HK2). Knockdown of USP7 or c-Abl suppresses NSCLC cell glycolysis and reduces lactate production. Further studies revealed that overexpression of USP7 facilitates NSCLC cell growth and metastasis as well as xenograft growth in nude mice, while these activities are suppressed with USP7 or c-Abl being knocked down.

CONCLUSIONS

USP7 is a deubiquitinase of c-Abl and upregulates its oncogenic activity. USP7 promotes NSCLC cell metabolism by activating c-Abl and HK2. Targeting the USP7/c-Abl/HK2 axis might be a potential strategy to the precision therapy of NSCLC.

Inhibition of USP10 induces myeloma cell apoptosis by promoting cyclin D3 degradation

The cell cycle regulator cyclin D3 (CCND3) is highly expressed in multiple myeloma (MM) and it promotes MM cell proliferation. After a certain phase of cell cycle, CCND3 is rapidly degraded, which is essential for the strict control of MM cell cycle progress and proliferation. In the present study, we investigated the molecular mechanisms regulating CCND3 degradation in MM cells. By utilizing affinity purification-coupled tandem mass spectrometry, we identified the deubiquitinase USP10 interacting with CCND3 in human MM OPM2 and KMS11 cell lines. Furthermore, USP10 specifically prevented CCND3 from K48-linked polyubiquitination and proteasomal degradation, therefore enhancing its activity. We demonstrated that the N-terminal domain (aa. 1-205) of USP10 was dispensable for binding to and deubiquitinating CCND3. Although Thr283 was important for CCND3 activity, it was dispensable for CCND3 ubiquitination and stability modulated by USP10. By stabilizing CCND3, USP10 activated the CCND3/CDK4/6 signaling pathway, phosphorylated Rb, and upregulated CDK4, CDK6 and E2F-1 in OPM2 and KMS11 cells. Consistent with these findings, inhibition of USP10 by Spautin-1 resulted in accumulation of CCND3 with K48-linked polyubiquitination and degradation that synergized with Palbociclib, a CDK4/6 inhibitor, to induce MM cell apoptosis. In nude mice bearing myeloma xenografts with OPM2 and KMS11 cells, combined administration of Spautin-l and Palbociclib almost suppressed tumor growth within 30 days. This study thus identifies USP10 as the first deubiquitinase of CCND3 and also finds that targeting the USP10/CCND3/CDK4/6 axis may be a novel modality for the treatment of myeloma.

Proteasomal inhibitors induce myeloma cell pyroptosis via the BAX/GSDME pathway

Proteasomes are overexpressed in multiple myeloma (MM) and proteasomal inhibitors (PIs) have been widely used for the treatment of MM. PIs are reported to induce MM cell apoptosis but impair necroptosis. In the present study, we found that PIs MG132 and bortezomib induce MM cell pyroptosis, a novel type of cell death, in a GSDME-dependent manner. Lack of GSDME totally blocks PI-induced pyroptosis. Interestingly, we found that Caspase-3/6/7/9 are all involved in pyroptosis triggered by PIs because the specific inhibitor of each caspase ablates GSDME activation. PIs markedly reduce mitochondrial membrane potential. Moreover, PIs disrupt the interaction of Bcl-2 and BAX, induce cytochrome c release from mitochondria to cytosol and activate GSDME. Furthermore, we found that overexpression of an N-terminal portion of GSDME suffices to release cytochrome c from mitochondria and to activate Caspase-3/9, suggesting N-GSDME might penetrate the mitochondrial membrane. Consistent with Bcl-2 inhibition, BAX can induce MM cell pyroptosis in a GSDME-dependent manner. In accordance with these findings, inhibition of Bcl-2 synergizes with PIs to induce MM cell pyroptosis. Therefore, the present study indicates that PIs trigger MM cell pyroptosis via the mitochondrial BAX/GSDME pathway and provides a rationale for combined treatment of MM with Bcl-2 and proteasome inhibitors to increase therapeutic efficiency via induction of pyroptosis.

A pan-cancer analysis of the role of USP5 in human cancers

Posttranslational modifications (PTM) such as acetylation, deubiquitination, and phosphorylation of proteins, play important roles in various kinds of cancer progression. Ubiquitin-specific proteinase 5 (USP5), a unique member of deubiquitinating enzymes (DUBs) which recognizes unanchored polyubiquitin specifically, could regulate the stability of many tumorigenesis-associated proteins to influence cancer initiation and progression. However, the diverse biological significance of USP5 in pan-cancer has not been systematically and comprehensively studied. Here, we explored the role of USP5 in pan-cancer using The Cancer Genome Atlas (TCGA) and Genotype-Tissue Expression (GTEx) database, and we also acquired and analyzed data via various software and web platforms such as R, GEPIA2.0, HPA, TISIDB, cBioPortal, UALCAN, TIMER 2.0, CancerSEA and BioGRID. USP5 expression was high in most cancers and differed significantly in different molecular and immune subtypes of cancers. In addition, USP5 had certain diagnostic value in multiple cancers, and high expression of USP5 generally predicted poor prognosis for cancer patients. We also found that the most frequent genetic alterations type of USP5 was mutation, and the DNA methylation level of USP5 decreased in various cancers. Furthermore, USP5 expression correlated with cancer-associated fibroblasts (CAFs), endothelial cells (EC) and genetic markers of immunodulators in cancers. Moreover, the result from single cell sequencing showed that USP5 could regulate several tumor biological behaviors such as apoptosis, DNA damage and metastasis. Gene enrichment analysis indicated "spliceosome" and "RNA splicing" may be the critical mechanism for USP5 to involve in cancer. Taken together, our study elucidates the biological significance of USP5 in the diagnosis, prognosis and immune in human pan-cancer.

The ubiquitin ligase HERC4 suppresses MafA transcriptional activity triggered by GSK3β in myeloma by atypical K63-linked polyubiquitination

MafA and c-Maf are close members of the Maf transcription factor family and indicators of poor prognosis of multiple myeloma (MM). Our previous study finds that the ubiquitin ligase HERC4 induces c-Maf degradation but stabilizes MafA, and the mechanism is elusive. In the present study we find that HERC4 interacts with MafA and mediates its K63-linked polyubiquitination at K33. Moreover, HERC4 inhibits MafA phosphorylation and its transcriptional activity triggered by glycogen synthase kinase 3β (GSK3β). The K33R MafA variant prevents HERC4 from inhibiting MafA phosphorylation and increases MafA transcriptional activity. Further analyses reveal that MafA can also activate the STAT3 signaling but it is suppressed by HERC4. Lastly, we demonstrate that lithium chloride, a GSK3β inhibitor, can upregulate HERC4 and synergizes dexamethasone, a typical anti-MM drug, in inhibiting MM cell proliferation and xenograft growth in nude mice. These findings thus highlight a novel regulation of MafA oncogenic activity in MM and provide the rationale by targeting HERC4/GSK3β/MafA for the treatment of MM.

Lymphoma-associated mutations in autoreactive memory B cells of patients with Sjögren's syndrome

We recently demonstrated that normal memory B lymphocytes carry a substantial number of de novo mutations in the genome. Here, we performed exome-wide somatic mutation analyses of bona fide autoreactive rheumatoid factor (RF)-expressing memory B cells retrieved from patients with Sjӧgren's syndrome (SS). The amount and repertoire of the de novo exome mutations of RF B cells were found to be essentially different from those detected in healthy donor memory B cells. In contrast to the mutation spectra of normal B cells, which appeared random and non-selected, the mutations of the RF B cells were greater in number and enriched for mutations in genes also found mutated in B-cell non-Hodgkin lymphomas. During the study, one of the SS patients developed a diffuse large B-cell lymphoma (DLBCL) out of an RF clone that was identified 2 years earlier in an inflamed salivary gland biopsy. The successive oncogenic events in the RF precursor clone and the DLBCL were assessed. In conclusion, our findings of enhanced and selected genomic damage in growth-regulating genes in RF memory B cells of SS patients together with the documented transformation of an RF-precursor clone into DLBCL provide unique novel insight into the earliest stages of B-cell derailment and lymphomagenesis. © 2022 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of The Pathological Society of Great Britain and Ireland.

The role and regulation of Maf proteins in cancer

The Maf proteins (Mafs) belong to basic leucine zipper transcription factors and are members of the activator protein-1 (AP-1) superfamily. There are two subgroups of Mafs: large Mafs and small Mafs, which are involved in a wide range of biological processes, such as the cell cycle, proliferation, oxidative stress, and inflammation. Therefore, dysregulation of Mafs can affect cell fate and is closely associated with diverse diseases. Accumulating evidence has established both large and small Mafs as mediators of tumor development. In this review, we first briefly describe the structure and physiological functions of Mafs. Then we summarize the upstream regulatory mechanisms that control the expression and activity of Mafs. Furthermore, we discuss recent studies on the critical role of Mafs in cancer progression, including cancer proliferation, apoptosis, metastasis, tumor/stroma interaction and angiogenesis. We also review the clinical implications of Mafs, namely their potential possibilities and limitations as biomarkers and therapeutic targets in cancer.

Induction of zinc finger protein RNF6 auto-ubiquitination for the treatment of myeloma and chronic myeloid leukemia

The zinc finger ubiquitin ligase RNF6 has been proposed as a potential therapeutic target in several cancers, but understanding its molecular mechanism of degradation has been elusive. In the present study, we find that RNF6 is degraded via auto-ubiquitination in a manner dependent on its Really Interesting New Gene (RING) domain. We determine that when the RING domain is deleted (ΔRING) or the core cysteine residues in the zinc finger are mutated (C632S/C635S), the WT protein, but not the ΔRING or mutant RNF6 protein, undergoes polyubiquitination. We also identify USP7 as a deubiquitinase of RNF6 by tandem mass spectrometry. We show that USP7 interacts with RNF6 and abolishes its K48-linked polyubiquitination, thereby preventing its degradation. In contrast, we found a USP7-specific inhibitor promotes RNF6 polyubiquitination, degradation, and cell death. Furthermore, we demonstrate the anti-leukemic drug Nilotinib and anti-myeloma drug Panobinostat (LBH589) induce RNF6 K48-linked polyubiquitination and degradation in both multiple myeloma (MM) and leukemia cells. In agreement with our hypothesis on the mode of RNF6 degradation, we show these drugs promote RNF6 auto-ubiquitination in an in vitro ubiquitination system without other E3 ligases. Consistently, reexpression of RNF6 ablates drug-induced MM and leukemia cell apoptosis. Therefore, our results reveal that RNF6 is a RING E3 ligase that undergoes auto-ubiquitination, which could be abolished by USP7 and induced by anti-cancer drugs. We propose that chemical induction of RNF6 auto-ubiquitination and degradation could be a novel strategy for the treatment of hematological malignancies including MM and leukemia.

Targeting the oncogenic transcription factor c-Maf for the treatment of multiple myeloma

Multiple myeloma (MM) is a hematologic malignancy derived from clonal expansion of plasma cells within the bone marrow and it may progress to the extramedullary region in late stage of the disease course. c-Maf, an oncogenic zipper leucine transcription factor, is overexpressed in more than 50% MM cell lines and primary species in association with chromosomal translocation, aberrant signaling transduction and modulation of stability. By triggering the transcription of critical genes including CCND2, ITGB7, CCR1, ARK5, c-Maf promotes MM progress, proliferation, survival and chemoresistance. Notably, c-Maf is usually expressed at the embryonic stage to promote cell differentiation but less expressed in healthy adult cells. c-Maf has long been proposed as a promising therapeutic target of MM and a panel of small molecule compounds have been identified to downregulate c-Maf and display potent anti-myeloma activities. In the current article, we take a concise summary on the advances in c-Maf biology, pathophysiology, and targeted drug discovery in the potential treatment of MM.

TRIM25 activates AKT/mTOR by inhibiting PTEN via K63-linked polyubiquitination in non-small cell lung cancer

The PTEN/AKT/mTOR signaling pathway is frequently dysregulated in non-small cell lung cancer (NSCLC), but the mechanisms are not well-understood. The present study found that the ubiquitin ligase TRIM25 is highly expressed in NSCLC tissues and promotes NSCLC cell survival and tumor growth. Mechanistic studies revealed that TRIM25 binds to PTEN and mediates its K63-linked ubiquitination at K266. This modification prevents the plasma membrane translocation of PTEN and reduces its phosphatase activity therefore accumulating PI(3,4,5)P3. TRIM25 thus activates the AKT/mTOR signaling. Moreover, we found that the antibacterial nitroxoline can activate PTEN by reducing its K63-linked polyubiquitination and sensitizes NSCLC to cisplatin-induced apoptosis. This study thus identified a novel modulation on the PTEN signaling pathway by TRIM25 and provides a potential target for NSCLC treatment.

Glaucocalyxin A suppresses multiple myeloma progression in vitro and in vivo through inhibiting the activation of STAT3 signaling pathway

Background

Multiple myeloma (MM) is the most common malignant hematological disease in the people worldwide. Glaucocalyxin A (GLA) is a bioactive ent-kauranoid diterpenoid, that is derived from Rabdosia japonica var. GLA has been demonstrated that it had various pharmacological activities, such as anti-coagulation, anti-bacterial, anti-tumor, anti-inflammation, antioxidant activities. Although GLA has effective anti-tumor properties, its effects on multiple myeloma remain unclear. The aim of this study was to examine the possible anti-cancer effects of GLA and their molecular mechanisms on MM cells in vitro and in vivo.

Methods

To evaluate the role of GLA on the proliferation of MM cells in vitro and in vivo, we used MTT method to detect the role of GLA on the proliferation of MM cells. Cell apoptosis and cell cycle assay were evaluated by flow cytometry. Protein expressions in GLA-treated and untreated MM cells were evaluated by western blot analyses. MM xenograft nude mice model was used to investigate the role of GLA on the proliferation of MM cells in vivo. IHC assay was used to examine the role of GLA on the MM xenograft model in vivo.

Results

In the present study, we firstly reported the potent anti-myeloma activity of GLA on MM cells. We found that GLA could induce apoptosis in vitro and in vivo. GLA could inhibit the phosphorylation of the signal transducer and activator of transcription 3 (STAT3) and downregulate interleukin IL-6 induced STAT3 phosphorylation in MM. Overexpression of STAT3 could significantly prevent apoptosis induced by GLA; while knockdown of STAT3 enhanced it. Moreover, GLA could inhibit cell proliferation by inducing the cell cycle arrest. GLA reduced the expression of cell cycle-related proteins CCNB1, CCND1, CCND2, and CCND3 and increased the expression of p21 in MM cell lines. In addition, in the MM xenograft nude mice model, GLA exhibited very good anti-myeloma activity. Administration of GLA almost completely inhibited tumor growth within 19 days without physical toxicity. And the IHC results showed GLA significantly inhibited cell proliferation and interfered STAT3 pathway on MM xenograft model tumor tissues.

Conclusions

Taken together, our present research indicated that GLA inhibits the MM cell proliferation, induces MM cell apoptosis and cell cycle arrest through blocking the activation of STAT3 pathway. Thus, GLA may be a potential therapeutic candidate for MM patients in the future.

Deubiquitinase USP5 promotes non-small cell lung cancer cell proliferation by stabilizing cyclin D1

Background

Cyclin D1 (CCND1) is overexpressed in non-small cell lung cancer (NSCLC) and contributes to its tumorigenesis and progression. Accumulating evidence shows that ubiquitin-specific protease 5 (USP5), an important member of the USP family, acts as a tumor promoter by deubiquitinating and stabilizing oncoproteins. However, neither the mechanism for dysregulated turnover of CCND1 protein nor the association of CCND1 with USP5 in NSCLC is well understood.

Methods

The association of USP5 with CCND1 in human NSCLC cells and clinical tissues was determined by immunoprecipitation/immunoblotting, immunohistochemistry (IHC), and The Cancer Genome Atlas database analyses. The effect of USP5 knockdown or overexpression on NSCLC cell proliferation in vitro was assessed by Cell Counting Kit-8, flow cytometry-based cell cycle, and colony formation assays. The effect of the USP5 inhibitor EOAI3402143 (G9) on NSCLC proliferation in vitro was analyzed by CCK-8 assay. The effect of G9 on NSCLC xenograft tumor growth was also examined in vivo, using athymic BALB/c nude mice.

Results

USP5 physically bound to CCND1 and decreased its polyubiquitination level, thereby stabilizing CCND1 protein. This USP5-CCND1 axis promoted NSCLC cell proliferation and colony formation. Further, knockdown of USP5 led to CCND1 degradation and cell cycle arrest in NSCLC cells. Importantly, this tumor-suppressive effect elicited by USP5 knockdown in NSCLC cells was validated in vitro and in vivo through chemical inhibition of USP5 activity using G9. Consistently, G9 downregulated the protein levels of CCND1 in NSCLC cells and xenograft tumor tissues. Also, the expression level of USP5 was positively associated with the protein level of CCND1 in human clinical NSCLC tissues.

Conclusions

This study has provided the first evidence that CCND1 is a novel substrate of USP5. The USP5-CCND1 axis could be a potential target for the treatment of NSCLC.

Deubiquitinases in hematological malignancies

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

The deubiquitinase USP10 restores PTEN activity and inhibits non-small cell lung cancer cell proliferation

The phosphatase and tensin homolog deleted on chromosome 10 (PTEN) protein is a key player in tumorigenesis of non–small cell lung cancer (NSCLC) and was recently found to be inactivated by tripartite motif containing 25 (TRIM25)–mediated K63-linked polyubiquitination. However, the deubiquitinase (Dub) coordinate TRIM25 in PTEN ubiquitination is still elusive. In the present study, we found that this K63-linked polyubiquitination could be ablated by the ubiquitin-specific protease 10 (USP10) in a screen against a panel of Dubs. We found using coimmununoprecipitation/immunoblotting that USP10 interacted with PTEN and reduced the K63-linked polyubiquitination of PTEN mediated by TRIM25 in NSCLC cells. Moreover, USP10, but not its inactive C424A deubiquitinating mutant or other Dubs, abolished PTEN from K63-linked polyubiquitination mediated by TRIM25. In contrast to TRIM25, USP10 restored PTEN phosphatase activity and reduced the production of the secondary messenger phosphatidylinositol-3,4,5-trisphosphate, thereby inhibiting AKT/mammalian target of rapamycin progrowth signaling transduction in NSCLC cells. Moreover, USP10 was downregulated in NSCLC cell lines and primary tissues, whereas TRIM25 was upregulated. Consistent with its molecular activity, re-expression of USP10 suppressed NSCLC cell proliferation and migration, whereas knockout of USP10 promoted NSCLC cell proliferation and migration. In conclusion, the present study demonstrates that USP10 coordinates TRIM25 to modulate PTEN activity. Specifically, USP10 activates PTEN by preventing its K63-linked polyubiquitination mediated by TRIM25 and suppresses the AKT/mammalian target of rapamycin signaling pathway, thereby inhibiting NSCLC proliferation, indicating that it may be a potential drug target for cancer treatment.

Post-Translational Modifications in Transcription Factors that Determine T Helper Cell Differentiation

CD4+ T helper (Th) cells play a crucial role in the modulation of innate and adaptive immune responses through the differentiation of Th precursor cells into several subsets, including Th1, Th2, Th17, and regulatory T (Treg) cells. Effector Th and Treg cells are distinguished by the production of signature cytokines and are important for eliminating intracellular and extracellular pathogens and maintaining immune homeostasis. Stimulation of naïve Th cells by T cell receptor and specific cytokines activates master transcription factors and induces lineage specification during the differentiation of Th cells. The master transcription factors directly activate the transcription of signature cytokine genes and also undergo post-translational modifications to fine-tune cytokine production and maintain immune balance through cross-regulation with each other. This review highlights the post-translational modifications of master transcription factors that control the differentiation of effector Th and Treg cells and provides additional insights on the immune regulation mediated by protein arginine-modifying enzymes in effector Th cells.

The Role of AP-1 Transcription Factors in Plasma Cell Biology and Multiple Myeloma Pathophysiology

Multiple myeloma (MM) is an incurable hematologic malignancy characterized by the clonal expansion of malignant plasma cells within the bone marrow. Activator Protein-1 (AP-1) transcription factors (TFs), comprised of the JUN, FOS, ATF and MAF multigene families, are implicated in a plethora of physiologic processes and tumorigenesis including plasma cell differentiation and MM pathogenesis. Depending on the genetic background, the tumor stage, and cues of the tumor microenvironment, specific dimeric AP-1 complexes are formed. For example, AP-1 complexes containing Fra-1, Fra-2 and B-ATF play central roles in the transcriptional control of B cell development and plasma cell differentiation, while dysregulation of AP-1 family members c-Maf, c-Jun, and JunB is associated with MM cell proliferation, survival, drug resistance, bone marrow angiogenesis, and bone disease. The present review article summarizes our up-to-date knowledge on the role of AP-1 family members in plasma cell differentiation and MM pathophysiology. Moreover, it discusses novel, rationally derived approaches to therapeutically target AP-1 TFs, including protein-protein and protein-DNA binding inhibitors, epigenetic modifiers and natural products.

Suppression of USP7 induces BCR-ABL degradation and chronic myelogenous leukemia cell apoptosis

Chronic myelogenous leukemia (CML) is a clonal malignancy of hematopoietic stem cells featured with the fusion protein kinase BCR-ABL. To elicit the mechanism underlying BCR-ABL stability, we perform a screen against a panel of deubiquitinating enzymes (DUBs) and find that the ubiquitin-specific protease 7 (USP7) drastically stabilizes the BCR-ABL fusion protein. Further studies show that USP7 interacts with BCR-ABL and blocks its polyubiquitination and degradation. Moreover, USP7 knockdown triggers BCR-ABL degradation and suppresses its downstream signaling transduction. In line with this finding, genetic or chemical inhibition of USP7 leads to BCR-ABL protein degradation, suppresses BCR/ABL signaling, and induces CML cell apoptosis. Furthermore, we find the antimalarial artesunate (ART) significantly inhibits USP7/BCR-ABL interaction, thereby promoting BCR-ABL degradation and inducing CML cell death. This study thus identifies USP7 as a putative Dub of BCR-ABL and provides a rationale in targeting USP7/BCR-ABL for the treatment of CML.

Role of ARK5 in cancer and other diseases (Review)

Malignant tumors are often exposed to hypoxic and glucose-starved microenvironments. AMP-activated protein kinase (AMPK) is an energy sensor that is stimulated during energy-deficient conditions and protects cells from hypoxic injury by regulating metabolism. AMPK-related protein kinase 5 (ARK5) is a member of the catalytic sub-unit of the AMPK family and has an important role in energy regulation and hypoxia. ARK5 is regulated by Akt and liver kinase B1 and is associated with numerous tumor-related molecules to exert the negative effects of tumors. Studies have revealed ARK5 overexpression in cases of tumor invasion and metastasis and a positive association with the degree of cancer cell malignancy, which is regarded as a key element in determining cancer prognosis. Furthermore, ARK5 downregulation improves drug sensitivity through the epithelial-mesenchymal transition pathway, indicating that it may be a potential therapeutic target. In other non-cancer conditions, ARK5 has various roles in neurodegenerative diseases (Alzheimer's and Huntington's disease), renal disorders (diabetic nephropathy and renal fibrosis) and physiological processes (striated muscle generation). In the present review, the upstream and downstream molecular pathways of ARK5 in cancer and other diseases are described and potential therapeutic strategies are discussed.

Targeting RFWD2 as an Effective Strategy to Inhibit Cellular Proliferation and Overcome Drug Resistance to Proteasome Inhibitor in Multiple Myeloma

The potential to overcome resistance to proteasome inhibitors is greatly related with ubiquitin-proteasome system during multiple myeloma (MM) treatment process. The constitutive photomorphogenic 1 (RFWD2), referred to an E3 ubiquitin ligase, has been identified as an oncogene in multiple cancers, yet important questions on the role of RFWD2 in MM biology and treatment remain unclear. Here we demonstrated that MM patients with elevated RFWD2 expression achieved adverse outcome and drug resistance by analyzing gene expression profiling. Moreover, we proved that RFWD2 participated in the process of cell cycle, cell growth and death in MM by mass spectrometry analysis. In vitro study indicated that inducible knockdown of RFWD2 hindered cellular growth and triggered apoptosis in MM cells. Mechanism study revealed that RFWD2 controlled MM cellular proliferation via regulating the degradation of P27 rather than P53. Further exploration unveiled that RFWD2 meditated P27 ubiquitination via interacting with RCHY1, which served as an E3 ubiquitin ligase of P27. Finally, in vivo study illustrated that blocking RFWD2 in BTZ-resistant MM cells overcame the drug resistance in a myeloma xenograft mouse model. Taken together, these findings provide compelling evidence for prompting that targeting RFWD2 may be an effective strategy to inhibit cellular proliferation and overcome drug resistance to proteasome inhibitor in MM.

Targeting the Otub1/c-Maf axis for the treatment of multiple myeloma

The oncogenic transcription factor c-Maf has been proposed as an ideal therapeutic target for multiple myeloma (MM), but how to achieve it is still elusive. In the present study, we found the Otub1/c-Maf axis could be a potential target. Otub1, an OTU family deubiquitinase, was found to interact with c-Maf by mass spectrometry. Otub1 abrogates c-Maf K48-linked polyubiquitination, thus preventing its degradation and enhancing its transcriptional activity. Specifically, this deubiquitinating activity depends on its Lys71 and the N terminus but is independent of UBE2O, a known E2 of c-Maf. Otub1 promotes MM cell survival and MM tumor growth. In contrast, silence of Otub1 leads to c-Maf degradation and c-Maf-expressing MM cell apoptosis. Therefore, the Otub1/c-Maf axis could be a therapeutic target of MM. In order to explore this concept, we performed a c-Maf recognition element-driven luciferase-based screen against US Food and Drug Administration-approved drugs and natural products, from which the generic cardiac glycoside lanatoside C (LanC) is found to prevent c-Maf deubiquitination and induces its degradation by disrupting the interaction of Otub1 and c-Maf. Consequently, LanC inhibits c-Maf transcriptional activity, induces c-Maf-expressing MM cell apoptosis, and suppresses MM growth and prolongs overall survival of model mice, but without apparent toxicity. Therefore, the present study identifies Otub1 as a novel deubiquitinase of c-Maf and establishes that the Otub1/c-Maf axis is a potential therapeutic target for MM.

Inhibition of the Otub1/c-Maf axis by the herbal acevaltrate induces myeloma cell apoptosis

BACKGROUND

The oncogenic transcript factor c-Maf is stabilized by the deubiquitinase Otub1 and promotes myeloma cell proliferation and confers to chemoresistance. Inhibition of the Otub1/c-Maf axis is a promising therapeutic target, but there are no inhibitors reported on this specific axis.

METHODS

A luciferase assay was applied to screen potential inhibitors of Otub1/c-Maf. Annexin V staining/flow cytometry was applied to evaluate cell apoptosis. Immunoprecipitation was applied to examine protein ubiquitination and interaction. Xenograft models in nude mice were used to evaluate anti-myeloma activity of AVT.

RESULTS

Acevaltrate (AVT), isolated from Valeriana glechomifolia, was identified based on a bioactive screen against the Otub1/c-Maf/luciferase system. AVT disrupts the interaction of Otub1/c-Maf thus inhibiting Otub1 activity and leading to c-Maf polyubiquitination and subsequent degradation in proteasomes. Consistently, AVT inhibits c-Maf transcriptional activity and downregulates the expression of its target genes key for myeloma growth and survival. Moreover, AVT displays potent anti-myeloma activity by triggering myeloma cell apoptosis in vitro and impairing myeloma xenograft growth in vivo but presents no marked toxicity.

CONCLUSIONS

The natural product AVT inhibits the Otub1/c-Maf axis and displays potent anti-myeloma activity. Given its great safety and efficacy, AVT could be further developed for MM treatment. Video Abstract.

MAFG-AS1 promotes tumor progression via regulation of the HuR/PTBP1 axis in bladder urothelial carcinoma

Long noncoding RNAs (lncRNAs) play a crucial role in progression of bladder urothelial carcinoma (BUC). However, the molecular mechanisms behind this role have not been elucidated yet. Here, we found that the lncRNA MAFG-AS1, which is highly expressed in BUC, is correlated with aggressive characteristics and poor prognosis of BUC. We demonstrate that MAFG-AS1 can promote BUC proliferation, invasion, metastasis, and epithelial-mesenchymal transition in vitro and in vivo. Mechanistically, MAFG-AS1 direct binding to Hu antigen R (HuR) could recruit ubiquitin-specific proteinase 5 (USP5) to prevent HuR from degrading by ubiquitination. We further demonstrate that overexpression of MAFG-AS1 can upregulate the expression of polypyrimidine tract-binding protein 1 (PTBP1) through promoting its stability mediated by bound HuR. In conclusion, these findings indicate that MAFG-AS1 promotes the progression of BUC via regulation of the HUR/PTBP1 axis. Targeting MAFG-AS1 may provide a novel strategy for individualized therapy and a potential biomarker for prognosis of BUC.

Anti-bacterial and anti-viral nanchangmycin displays anti-myeloma activity by targeting Otub1 and c-Maf

As a deubiqutinase Otub1 stabilizes and promotes the oncogenic activity of the transcription factor c-Maf in multiple myeloma (MM), a malignancy of plasma cells. In the screen for bioactive inhibitors of the Otub1/c-Maf axis for MM treatment, nanchangmycin (Nam), a polyketide antibiotic, was identified to suppress c-Maf activity in the presence of Otub1. By suppressing Otub1, Nam induces c-Maf polyubiquitination and subsequent degradation in proteasomes but does not alter its mRNA level. Consistently, Nam downregulates the expression of CCND2, ARK5, and ITGB7, the downstream genes regulated by c-Maf, and promotes MM cell apoptosis as evidenced by PARP and Caspase-3 cleavage, as well as Annexin V staining. In line with the hypothesis, overexpression of Otub1 partly rescues Nam-induced MM cell apoptosis, and interestingly, when Otub1 is knocked down, Nam-decreased MM cell survival is also partly ablated, suggesting Otub1 is essential for Nam anti-MM activity. Nam also displays potent anti-MM activity synergistically with Doxorubicin or lenalidomide. In the in vivo assays, Nam almost completely suppresses the growth of MM xenografts in nude mice at low dosages but it shows no toxicity. Given its safety and efficacy, Nam has a potential for MM treatment by targeting the Otub1/c-Maf axis.

Upregulation of miR-155 regulates group 2 innate lymphoid cells by targeting c-maf in allergic rhinitis

Group 2 innate lymphoid cells (ILC2s) and Th2 type immune response are critically involved in the pathogenesis of allergic rhinitis (AR), and this pathological process is influenced by microRNAs-mediated post-transcriptional regulation. The present study investigated the adaptation and function of miR-155 in AR patients and mouse model. We found that significantly increased miR-155 expression (1.63 ± 0.12 vs. 0.92 ± 0.11 in human, and 1.68 ± 0.15 vs. 1.06 ± 0.06 in mice) and ILC2s activity in nasal mucosa and serum in AR patients and mice. Administration of miR-155 antagomir significantly reduced the activity of ILC2s in nasal mucosa, suppressed the production of Th2 cytokines in serum and nasal mucosa, and alleviated the airway inflammation and allergic symptoms in AR mice, while miR-155 agomir increased ILC2s activity and production of Th2 cytokines and induced airway inflammation and allergic symptoms in control mice. Meanwhile, the expression of transcriptional factor c-Maf (0.57 ± 0.05 vs. 0.37 ± 0.04) in nasal mucosa in AR mice, which was significantly recovered by miR-155 antagomir (0.56 ± 0.04). Treatment with miR-155 agomir decreased c-Maf expression in nasal mucosa in control mice. This synchronized with the similar pattern in the current observations that miR-155 regulated Th2 cytokine (IL-4, IL-5, IL-9 and IL-13) production, airway inflammation and allergic symptoms in AR mice. Together, upregulation miR-155 suppressed the expression of transcriptional factor c-Maf and was critically involved in the ILC2s activation, which contributed to the airway inflammation and allergic symptoms in AR.

HERC Ubiquitin Ligases in Cancer

HERC proteins are ubiquitin E3 ligases of the HECT family. The HERC subfamily is composed of six members classified by size into large (HERC1 and HERC2) and small (HERC3-HERC6). HERC family ubiquitin ligases regulate important cellular processes, such as neurodevelopment, DNA damage response, cell proliferation, cell migration, and immune responses. Accumulating evidence also shows that this family plays critical roles in cancer. In this review, we provide an integrated view of the role of these ligases in cancer, highlighting their bivalent functions as either oncogenes or tumor suppressors, depending on the tumor type. We include a discussion of both the molecular mechanisms involved and the potential therapeutic strategies.

The E3 ligase HUWE1 inhibition as a therapeutic strategy to target MYC in multiple myeloma

Proteasome inhibitors have provided a significant advance in the treatment of multiple myeloma (MM). Consequently, there is increasing interest in developing strategies to target E3 ligases, de-ubiquitinases, and/or ubiquitin receptors within the ubiquitin proteasome pathway, with an aim to achieve more specificity and reduced side-effects. Previous studies have shown a role for the E3 ligase HUWE1 in modulating c-MYC, an oncogene frequently dysregulated in MM. Here we investigated HUWE1 in MM. We identified elevated expression of HUWE1 in MM compared with normal cells. Small molecule-mediated inhibition of HUWE1 resulted in growth arrest of MM cell lines without significantly effecting the growth of normal bone marrow cells, suggesting a favorable therapeutic index. Studies using a HUWE1 knockdown model showed similar growth inhibition. HUWE1 expression positively correlated with MYC expression in MM bone marrow cells and correspondingly, genetic knockdown and biochemical inhibition of HUWE1 reduced MYC expression in MM cell lines. Proteomic identification of HUWE1 substrates revealed a strong association of HUWE1 with metabolic processes in MM cells. Intracellular glutamine levels are decreased in the absence of HUWE1 and may contribute to MYC degradation. Finally, HUWE1 depletion in combination with lenalidomide resulted in synergistic anti-MM activity in both in vitro and in vivo models. Taken together, our data demonstrate an important role of HUWE1 in MM cell growth and provides preclinical rationale for therapeutic strategies targeting HUWE1 in MM.

Post-Translational Modifications of Transcription Factors Harnessing the Etiology and Pathophysiology in Colonic Diseases

Defects in mucosal immune balance can lead to colonic diseases such as inflammatory bowel diseases and colorectal cancer. With the advancement of understanding for the immunological and molecular basis of colonic disease, therapies targeting transcription factors have become a potential approach for the treatment of colonic disease. To date, the biomedical significance of unique post-translational modifications on transcription factors has been identified, including phosphorylation, methylation, acetylation, ubiquitination, SUMOylation, and O-GlcNAcylation. This review focuses on our current understanding and the emerging evidence of how post-translational regulations modify transcription factors involved in the etiology and pathophysiology of colonic disease as well as the implications of these findings for new therapeutic approaches in these disorders.

Pharmacogenetics of medication-related osteonecrosis of the jaw: a systematic review and meta-analysis

Medication-related osteonecrosis of the jaw (MRONJ) is a severe complication that can develop in patients treated with anti-resorptive drugs. Although the pathogenesis of MRONJ is still unclear, genetic factors have a demonstrated important role. Thus, the aim of this study was to perform a systematic review on the pharmacogenetics of MRONJ. Studies published until March 2019 were retrieved from eight databases and were selected by two independent reviewers. Evidence on several genetic polymorphisms was summarized and a meta-analysis was conducted when possible. Fourteen studies involving 1515 participants were eligible for systematic review. For CYP2C8 rs1934951, no significant difference was observed between the MRONJ and non-MRONJ groups (odds ratio (OR) 2.04, 95% confidence interval (CI) 0.88-4.73, P=0.09). However, a subgroup analysis based on only multiple myeloma status showed a positive association (OR 3.64, 95% CI 1.29-10.30, P=0.01). PPARG rs1152003 was not differently distributed between groups (OR 0.25, 95% CI 0.01-9.92, P=0.46). Also, VEGF rs3025039 was found to be correlated with the occurrence of MRONJ (OR 0.35, 95% CI 0.15-0.82, P=0.02). CYP2C8 rs1934951 (in multiple myeloma patients) and VEGF rs3025039 are associated with the development of MRONJ in patients treated with bisphosphonates. The results are promising and call for new trials with a larger sample to further explore this growing field.

The deubiquitinase USP7 stabilizes Maf proteins to promote myeloma cell survival

The Maf proteins, including c-Maf, MafA, and MafB, are critical transcription factors in myelomagenesis. Previous studies demonstrated that Maf proteins are processed by the ubiquitin-proteasome pathway, but the mechanisms remain elusive. This study applied MS to identify MafB ubiquitination-associated proteins and found that the ubiquitin-specific protease USP7 was present in the MafB interactome. Moreover, USP7 also interacted with c-Maf and MafA and blocked their polyubiquitination and degradation. Consistently, knockdown of USP7 resulted in Maf protein degradation along with increased polyubiquitination levels. The action of USP7 thus promoted Maf transcriptional activity as evidenced by luciferase assays and by the up-regulation of the expression of Maf-modulated genes. Furthermore, USP7 was up-regulated in myeloma cells, and it was negatively associated with the survival of myeloma patients. USP7 promoted myeloma cell survival, and when it was inhibited by its specific inhibitor P5091, myeloma cell lines underwent apoptosis. These results therefore demonstrated that USP7 is a deubiquitinase of Maf proteins and promotes MM cell survival in association with Maf stability. Given the significance of USP7 and Maf proteins in myeloma genesis, targeting the USP7/Maf axle is a potential strategy to the precision therapy of MM.

Mebendazole elicits potent antimyeloma activity by inhibiting the USP5/c-Maf axis

c-Maf is a critical oncogenic transcription factor that contributes to myelomagenesis. Our previous studies demonstrated that the deubiquitinase USP5 stabilizes c-Maf and promotes myeloma cell proliferation and survival; therefore, the USP5/c-Maf axis could be a potential target for myeloma therapy. As a concept of principle, the present study established a USP5/c-Maf-based luciferase system that was used to screen an FDA-approved drug library. It was found that mebendazole, a typical anthelmintic drug, preferentially induced apoptosis in c-Maf-expressing myeloma cells. Moreover, oral administration of mebendazole delayed the growth of human myeloma xenografts in nude mice but did not show overt toxicity. Further studies showed that the selective antimyeloma activity of mebendazole was associated with the inhibition of the USP5/c-Maf axis. Mebendazole downregulated USP5 expression and disrupted the interaction between USP5 and c-Maf, thus leading to increased levels of c-Maf ubiquitination and subsequent c-Maf degradation. Mebendazole inhibited c-Maf transcriptional activity, as confirmed by both luciferase assays and expression measurements of c-Maf downstream genes. In summary, this study identified mebendazole as a USP5/c-Maf inhibitor that could be developed as a novel antimyeloma agent.

Structure and function of USP5: Insight into physiological and pathophysiological roles

Deubiquitinase (DUB)-mediated cleavage of ubiquitin chains from substrate proteins plays a crucial role in various cellular processes, such as DNA repair and protein stabilization and localization. DUBs can be classified into five families based on their sequence and structural homology, and the majority belong to the ubiquitin-specific proteinase (USP) family. As one of the USPs, ubiquitin-specific proteinase 5 (USP5) is unique in that it can specifically recognize unanchored (not conjugated to target proteins) polyubiquitin and is essential for maintaining homeostasis of the monoubiquitin pool. USP5 has also been implicated in a wide variety of cellular events. In the present review, we focus on USP5 and provide a comprehensive overview of the current knowledge regarding its structure, physiological roles in multiple cellular events, and pathophysiological roles in relevant diseases, especially cancer. Signaling pathways and emerging pharmacological profiles of USP5 are also introduced, which fully embody the therapeutic potential of USP5 for human diseases ranging from cancer to neurological diseases.

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.

Targeted silencing of MYCL1 by RNA interference inhibits migration and invasion of MGC-803 gastric cancer cells

MYCL1 protein expression encoded by a proto-oncogene MYCL1, a member of the MYC family, is correlated with poor prognosis in gastric cancer patients. Nevertheless, the role of MYCL1 in gastric cancer cells remains unknown. In this study, the expression levels of MYCL1 mRNA and protein were downregulated by lentiviral-mediated RNA interference (RNAi) in the MGC-803 gastric cancer cell line. Then, the influence of MYCL1 on the biological behaviour of gastric cancer cells was investigated. Finally, a stable animal model of the MGC-803 human gastric cancer tumour model in nude mice was made successfully. Functionally, silencing of MYCL1 inhibited migration and invasion of the MGC-803 line in vitro and was accompanied with some ultrastructural changes. These results provide some evidences that lentiviral-mediated MYCL1 silencing may be a novel therapeutic strategy for the treatment of gastric cancer. SIGNIFICANCE OF THE STUDY: Gastric cancer is one of the most common malignant tumours worldwide and the second leading cause of cancer-related death in China. Our previous study revealed that expression of MYCL1 in gastric cancer tissue was associated with poor prognosis of patients. However, the potential underlying mechanism is still unclear. In the current study, we displayed the influence of MYCL1 gene on invasion and migration phenotype of gastric cancer cells and provided a possible explanation from the aspect of structural alteration. Our results suggested that downregulation of MYCL1 may be a potential therapeutic strategy for gastric cancer.

Inhibition of the deubiquitinase USP9x induces pre-B cell homeobox 1 (PBX1) degradation and thereby stimulates prostate cancer cell apoptosis

Chemoresistance is a leading obstacle in effective management of advanced prostate cancer (PCa). A better understanding of the molecular mechanisms involved in PCa chemoresistance could improve treatment of patients with PCa. In the present study, using immune histochemical, chemistry, and precipitation assays with cells from individuals with benign or malignant prostate cancer or established PCa cell lines, we found that the oncogenic transcription factor pre-B cell leukemia homeobox-1 (PBX1) promotes PCa cell proliferation and confers to resistance against common anti-cancer drugs such as doxorubicin and cisplatin. We observed that genetic PBX1 knockdown abrogates this resistance, and further experiments revealed that PBX1 stability was modulated by the ubiquitin-proteasomal pathway. To directly probe the impact of this pathway on PBX1 activity, we screened for PBX1-specific deubiquitinases (Dubs) and found that ubiquitin-specific peptidase 9 X-linked (USP9x) interacted with and stabilized the PBX1 protein by attenuating its Lys-48-linked polyubiquitination. Moreover, the USP9x inhibitor WP1130 markedly induced PBX1 degradation and promoted PCa cell apoptosis. The results in this study indicate that PBX1 confers to PCa chemoresistance and identify USP9x as a Dub of PBX1. We concluded that targeting the USP9x/PBX1 axis could be a potential therapeutic strategy for managing advanced prostate cancer.

Thrombopoietin mutation in congenital amegakaryocytic thrombocytopenia treatable with romiplostim

Congenital amegakaryocytic thrombocytopenia (CAMT) is an inherited disorder characterized at birth by thrombocytopenia with reduced megakaryocytes, which evolves into generalized bone marrow aplasia during childhood. Although CAMT is genetically heterogeneous, mutations of MPL, the gene encoding for the receptor of thrombopoietin (THPO), are the only known disease‐causing alterations. We identified a family with three children affected with CAMT caused by a homozygous mutation (p.R119C) of the THPO gene. Functional studies showed that p.R119C affects not only ability of the cytokine to stimulate MPL but also its release, which is consistent with the relatively low serum THPO levels measured in patients. In all the three affected children, treatment with the THPO‐mimetic romiplostim induced trilineage hematological responses, remission of bleeding and infections, and transfusion independence, which were maintained after up to 6.5 years of observation. Recognizing patients with THPO mutations among those with juvenile bone marrow failure is essential to provide them with appropriate substitutive therapy and prevent the use of invasive and unnecessary treatments, such as hematopoietic stem cell transplantation or immunosuppression.

SUMO-defective c-Maf preferentially transactivates Il21 to exacerbate autoimmune diabetes

SUMOylation is involved in the development of several inflammatory diseases, but the physiological significance of SUMO-modulated c-Maf in autoimmune diabetes is not completely understood. Here, we report that an age-dependent attenuation of c-Maf SUMOylation in CD4+ T cells is positively correlated with the IL-21-mediated diabetogenesis in NOD mice. Using 2 strains of T cell-specific transgenic NOD mice overexpressing wild-type c-Maf (Tg-WTc) or SUMOylation site-mutated c-Maf (Tg-KRc), we demonstrated that Tg-KRc mice developed diabetes more rapidly than Tg-WTc mice in a CD4+ T cell-autonomous manner. Moreover, SUMO-defective c-Maf preferentially transactivated Il21 to promote the development of CD4+ T cells with an extrafollicular helper T cell phenotype and expand the numbers of granzyme B-producing effector/memory CD8+ T cells. Furthermore, SUMO-defective c-Maf selectively inhibited recruitment of Daxx/HDAC2 to the Il21 promoter and enhanced histone acetylation mediated by CREB-binding protein (CBP) and p300. Using pharmacological interference with CBP/p300, we illustrated that CBP30 treatment ameliorated c-Maf-mediated/IL-21-based diabetogenesis. Taken together, our results show that the SUMOylation status of c-Maf has a stronger regulatory effect on IL-21 than the level of c-Maf expression, through an epigenetic mechanism. These findings provide new insights into how SUMOylation modulates the pathogenesis of autoimmune diabetes in a T cell-restricted manner and on the basis of a single transcription factor.

Interferon-stimulated gene 15 induces cancer cell death by suppressing the NF-κB signaling pathway

Interferon-stimulated gene 15 (ISG15) is an important cytokine that has been reported in carcinogenesis. However, we found that ISG15 and de-ISGylase USP18 were induced by several anti-cancer agents, which was confirmed by both RT-PCR and immunoblotting assays. Further studies demonstrated that ectopic ISG15 and USP18 inhibited proliferation of myeloma, leukemia and cervical cancer cells. More importantly, ISG15 and USP18 induced cancer cell apoptosis. This finding was confirmed in a cervical xenograft model in which cervical cancer growth was suppressed by lentiviral ISG15. In the mechanistic study, ISG15 was found to disrupt the NF-κB signaling pathway by downregulating the expression of IKKβ and p65, phosphorylation of p65 and IκBα. Consistent with this finding, ISG15 suppressed the expression of NF-κB recognition element-driving luciferase and decreased the transcription of XIAP and Mcl-1, two typical genes regulated by NF-κB. Therefore, the present study demonstrated that ISG15 induces cancer cell apoptosis by disrupting the NF-κB signaling pathway. This study highlighted a novel role of ISG15 in tumor suppression.

The transmembrane protein TMEPAI induces myeloma cell apoptosis by promoting degradation of the c-Maf transcription factor

TMEPAI (transmembrane prostate androgen-induced protein, also called prostate transmembrane protein, androgen-induced 1 (PMEPA1)) is a type I transmembrane (TM) protein, but its cellular function is largely unknown. Here, studying factors influencing the stability of c-Maf, a critical transcription factor in multiple myeloma (MM), we found that TMEPAI induced c-Maf degradation. We observed that TMEPAI recruited NEDD4 (neural precursor cell expressed, developmentally down-regulated 4), a WW domain-containing ubiquitin ligase, to c-Maf, leading to its degradation through the proteasomal pathway. Further investigation revealed that TMEPAI interacts with NEDD4 via its conserved PY motifs. Alanine substitution or deletion of these motifs abrogated the TMEPAI complex formation with NEDD4, resulting in failed c-Maf degradation. Functionally, TMEPAI suppressed the transcriptional activity of c-Maf. Of note, increased TMEPAI expression was positively associated with the overall survival of MM patients. Moreover, TMEPAI was down-regulated in MM cells, and re-expression of TMEPAI induced MM cell apoptosis. In conclusion, this study highlights that TMEPAI decreases c-Maf stability by recruiting the ubiquitin ligase NEDD4 to c-Maf for proteasomal degradation. Our findings suggest that the restoration of functional TMEPA1 expression may represent a promising complementary therapeutic strategy for treating patients with MM.

Anthelmintic pyrvinium pamoate blocks Wnt/β-catenin and induces apoptosis in multiple myeloma cells

Multiple myeloma (MM) is a malignancy of the bone marrow. The median survival time of patients with MM is only 5 years, with patients frequently experiencing relapse. Currently, there is no effective therapy for recurrent MM. The results of the present study indicated that pyrvinium pamoate (PP), a US Food and Drug Administration-approved oral anthelmintic drug, exhibited potent antitumor activity in MM cells in vitro. It is demonstrated that PP inhibited MM cell proliferation and mediated apoptosis. Notably, PP markedly promoted the degradation of β-catenin and abrogated its phosphorylation. PP triggered apoptosis in MM cells by inducing the release of cytochrome c and downregulating the expression of myeloid leukemia cell differentiation protein. In addition, PP effectively induced cell death in primary MM cells. In conclusion, PP may be a promising agent for the clinical treatment of MM.

Nitroxoline shows antimyeloma activity by targeting the TRIM25/p53 axle

The aim of this study was to identify the most potent quinoline-based anti-infectives for the treatment of multiple myeloma (MM) and to understand the molecular mechanisms. A small-scale screen against a panel of marketed quinoline-based drugs was performed in MM cell lines. Cell apoptosis was examined by flow cytometry. Anti-MM activity was also evaluated in nude mice. Western blotting was performed to investigate mechanisms. Nitroxoline (NXQ) was the most effective in suppressing MM cell proliferation. NXQ induced more than 40% MM cell apoptosis within 24 h and potentiated anti-MM activities of current major drugs including doxorubicin and lenalidomide. This finding was shown by activation of caspase-3, a major executive apoptotic enzyme, and by inactivation of PARP, a major enzyme in DNA damage repair. NXQ also suppressed prosurvival proteins Bcl-xL and Mcl-1. Moreover, NXQ suppressed the growth of myeloma xenografts in nude mice models. In the mechanistic study, NXQ was found to downregulate TRIM25, a highly expressed ubiquitin ligase in MM. Notably, NXQ upregulated tumor suppressor p53, but not PTEN. Furthermore, overexpression of TRIM25 decreased p53 protein. This study indicated that the long-term use of anti-infective NXQ has potential for MM treatment by targeting the TRIM25/p53 axle.

Inhibition of the deubiquitinase USP5 leads to c-Maf protein degradation and myeloma cell apoptosis

The deubiquitinase USP5 stabilizes c-Maf, a key transcription factor in multiple myeloma (MM), but the mechanisms and significance are unclear. In the present study, USP5 was found to interact with c-Maf and prevented it from degradation by decreasing its polyubiquitination level. Specifically, the 308th and 347th lysine residues in c-Maf were critical for USP5-mediated deubiquitination and stability. There are five key domains in the USP5 protein and subsequent studies revealed that the cryptic ZnF domain and the C-box domain interacted with c-Maf but the UBA1/UBA2 domain partly increased its stability. Notably, MafA and MafB are also members of the c-Maf family, however, USP5 failed to deubiquitinate MafA, suggesting its substrate specificity. In the functional studies, USP5 was found to promoted the transcriptional activity of c-Maf. Consistent with the high level of c-Maf protein in MM cells, USP5 was also highly expressed. When USP5 was knocked down, c-Maf underwent degradation. Interestingly, USP5 silence led to apoptosis of MM cells expressing c-Maf but not MM cells lacking c-Maf, indicating c-Maf is a key factor in USP5-mediated MM cell proliferation and survival. Consistent with this finding, WP1130, an inhibitor of several Dubs including USP5, suppressed the transcriptional activity of c-Maf and induced MM cell apoptosis. When c-Maf was overexpressed, WP1130-induced MM cell apoptosis was abolished. Taken together, these findings suggest that USP5 regulates c-Maf stability and MM cell survival. Targeting the USP5/c-Maf axis could be a potential strategy for MM treatment.

The ubiquitin-conjugating enzyme UBE2O modulates c-Maf stability and induces myeloma cell apoptosis

Background

UBE2O is proposed as a ubiquitin-conjugating enzyme, but its function was largely unknown.

Methods

Mass spectrometry was applied to identify c-Maf ubiquitination-associated proteins. Immunoprecipitation was applied for c-Maf and UBE2O interaction. Immunoblotting was used for Maf protein stability. Luciferase assay was used for c-Maf transcriptional activity. Lentiviral infections were applied for UBE2O function in multiple myeloma (MM) cells. Flow cytometry and nude mice xenografts were applied for MM cell apoptosis and tumor growth assay, respectively.

Results

UBE2O was found to interact with c-Maf, a critical transcription factor in MM, by the affinity purification/tandem mass spectrometry assay and co-immunoprecipitation assays. Subsequent studies showed that UBE2O mediated c-Maf polyubiquitination and degradation. Moreover, UBE2O downregulated the transcriptional activity of c-Maf and the expression of cyclin D2, a typical gene modulated by c-Maf. DNA microarray revealed that UBE2O was expressed in normal bone marrow cells but downregulated in MGUS, smoldering MM and MM cells, which was confirmed by RT-PCR in primary MM cells, suggesting its potential role in myeloma pathophysiology. When UBE2O was restored, c-Maf protein in MM cells was significantly decreased and MM cells underwent apoptosis. Furthermore, the human MM xenograft in nude mice showed that re-expression of UBE2O delayed the growth of myeloma xenografts in nude mice in association with c-Maf downregulation and activation of the apoptotic pathway.

Conclusions

UBE2O mediates c-Maf polyubiquitination and degradation, induces MM cell apoptosis, and suppresses myeloma tumor growth, which provides a novel insight in understanding myelomagenesis and UBE2O biology.