The Deubiquitinase USP47 Stabilizes MAPK by Counteracting the Function of the N-end Rule ligase POE/UBR4 in Drosophila

The Emerging Role of Ubiquitin-Specific Protease 36 (USP36) in Cancer and Beyond

The balance between ubiquitination and deubiquitination is instrumental in the regulation of protein stability and maintenance of cellular homeostasis. The deubiquitinating enzyme, ubiquitin-specific protease 36 (USP36), a member of the USP family, plays a crucial role in this dynamic equilibrium by hydrolyzing and removing ubiquitin chains from target proteins and facilitating their proteasome-dependent degradation. The multifaceted functions of USP36 have been implicated in various disease processes, including cancer, infections, and inflammation, via the modulation of numerous cellular events, including gene transcription regulation, cell cycle regulation, immune responses, signal transduction, tumor growth, and inflammatory processes. The objective of this review is to provide a comprehensive summary of the current state of research on the roles of USP36 in different pathological conditions. By synthesizing the findings from previous studies, we have aimed to increase our understanding of the mechanisms underlying these diseases and identify potential therapeutic targets for their treatment.

Ubiquitin-specific peptidase 47 (USP47) regulates cutaneous oxidative injury through nicotinamide nucleotide transhydrogenase (NNT)

Human skin is daily exposed to oxidative stresses in the environment such as physical stimulation, chemical pollutants and pathogenic microorganisms, which are likely to cause skin diseases. As important post-translational modifications, protein ubiquitination and deubiquitination play crucial roles in maintaining cellular homeostasis by the proteolytic removal of oxidized proteins. We have previously reported that the expression of ubiquitin-specific protease 47 (USP47), a kind of deubiquitinating enzymes (DUBs), was significantly elevated in response to oxidative stress. However, the role of USP47 in cutaneous oxidative injury remains unclear. Usp47 wild-type (Usp47+/+) mice and Usp47 knockout (Usp47-/-) mice were used to establish two animal models of oxidative skin damage: (1) radiation- and (2) imiquimod (IMQ)-induced skin injury. Loss of Usp47 consistently aggravated mouse skin damage in vivo. Subsequently, we screened 63 upregulated and 170 downregulated proteins between the skin tissues of wild-type and Usp47-/- mice after 35 Gy electron beam radiation using proteomic analysis. Among the dysregulated proteins, nicotinamide nucleotide transhydrogenase (NNT), which has been reported as a significant regulator of oxidative stress and redox homeostasis, was further investigated in detail. Results showed that NNT was regulated by USP47 through direct ubiquitination mediated degradation and involved in the pathogenesis of cutaneous oxidative injury. Knockdown of NNT expression dramatically limited the energy production ability, with elevated mitochondrial reactive oxygen species (ROS) accumulation and increased mitochondrial membrane potential in irradiated HaCaT cells. Taken together, our present findings illustrate the critical role of USP47 in oxidative skin damage by modulating NNT degradation and mitochondrial homeostasis.

KCMF1-like suppresses white spot syndrome virus infection by promoting apoptosis in mud crab (Scylla paramamosain)

Potassium channel modulatory factor 1 (KCMF1), an E3 ubiquitin ligase, plays a vital role in renal tubulogenesis, preeclampsia, and tumor development in mammals. Nevertheless, the function of KCMF1 in invertebrates remains to be investigated. Here, we identified KCMF1-like from Scylla paramamosian, encoding 242 amino acids with two zinc finger domains at the N-terminal. Real-time quantitative PCR analysis revealed that KCMF1-like was expressed in all tested tissues, including hemocytes, brain, mid-intestine, subcuticular epidermis, gills, muscle, heart, and stomach, with higher levels in muscle and mid-intestine. KCMF1-like was up-regulated in the hemocytes of mud crabs challenged with white spot syndrome virus (WSSV). RNA interference (RNAi) was performed to investigate the impact of KCMF1-like on the proliferation of WSSV in mud crabs. Knock-down of KCMF1-like resulted in an increase of the WSSV copy number and an impairment of the hemocytes apoptosis rate in vivo. In addition, KCMF1-like could also affect the mitochondrial membrane potential. Collectively, these results revealed that KCMF1-like might play a crucial role in the defense against virus infection in mud crab. This study contributes a novel insight into the role of KCMF1-like in the antiviral immune defense mechanism in crustaceans.

Ubiquitin specific peptidase 47 contributes to liver regeneration

AIMS

Hepatocytes resume proliferation following liver injuries to compensate for the loss of liver mass. Robust liver regeneration is an intrinsic and pivotal process that facilitates restoration of liver anatomy and function. In the present study we investigated the role of ubiquitin-specific peptidase 47 (USP47) in liver regeneration.

METHODS AND MATERIALS

Proliferation of hepatocytes was evaluated by Ki67 staining in vivo and EdU incorporation in vitro. DNA-protein interaction was evaluated by chromatin immunoprecipitation (ChIP).

RESULTS

USP47 expression was up-regulated in hepatocytes isolated from mice subjected to partial hepatectomy (PHx) or exposed to HGF treatment. Ingenuity pathway analysis revealed E2F1 as a primary regulator of USP47 transcription. Reporter assay and ChIP assay confirmed that E2F1 directly bound to the USP47 promoter and activated USP47 transcription. Consistently, E2F1 knockdown abrogated USP47 induction by HGF. Compared to the wild type littermates, USP47 knockout mice displayed compromised liver regeneration following PHx. In addition, USP47 inhibition by a small-molecule compound impaired liver regeneration in mice. On the contrary, USP47 over-expression enhanced proliferation of hepatocytes in vitro and promoted liver regeneration in mice. Importantly, a positive correlation between USP47 expression and hepatocyte proliferation was identified in patients with acute liver failure (ALF).

SIGNIFICANCE

Our data suggest that USP47, transcriptionally activated by E2F1, plays an essential role in liver regeneration.

Y-Linked Copy Number Polymorphism of Target of Rapamycin Is Associated with Sexual Size Dimorphism in Seed Beetles

The Y chromosome is theorized to facilitate evolution of sexual dimorphism by accumulating sexually antagonistic loci, but empirical support is scarce. Due to the lack of recombination, Y chromosomes are prone to degenerative processes, which poses a constraint on their adaptive potential. Yet, in the seed beetle, Callosobruchus maculatus segregating Y linked variation affects male body size and thereby sexual size dimorphism (SSD). Here, we assemble C. maculatus sex chromosome sequences and identify molecular differences associated with Y-linked SSD variation. The assembled Y chromosome is largely euchromatic and contains over 400 genes, many of which are ampliconic with a mixed autosomal and X chromosome ancestry. Functional annotation suggests that the Y chromosome plays important roles in males beyond primary reproductive functions. Crucially, we find that, besides an autosomal copy of the gene target of rapamycin (TOR), males carry an additional TOR copy on the Y chromosome. TOR is a conserved regulator of growth across taxa, and our results suggest that a Y-linked TOR provides a male specific opportunity to alter body size. A comparison of Y haplotypes associated with male size difference uncovers a copy number variation for TOR, where the haplotype associated with decreased male size, and thereby increased sexual dimorphism, has two additional TOR copies. This suggests that sexual conflict over growth has been mitigated by autosome to Y translocation of TOR followed by gene duplications. Our results reveal that despite of suppressed recombination, the Y chromosome can harbor adaptive potential as a male-limited supergene.

Ferulic acid prevents Diosbulbin B-induced liver injury by inhibiting covalent modifications on proteins

Diosbulbin B (DIOB) has been reported to cause serious liver injury. However, in traditional medicine, DIOB-containing herbs are highly safe in combination with ferulic acid (FA)-containing herbs, suggesting potential neutralizing effect of FA on the toxicity of DIOB. DIOB can be metabolized to generate reactive metabolites (RMs), which can covalently bind to proteins and lead to hepatoxicity. In the present study, the quantitative method was firstly established for investigating the correlation between DIOB RM-protein adducts (DRPAs) and hepatotoxicity. Then, we estimated the detoxication effect of FA in combination with DIOB and revealed the underlying mechanism. Our data indicated that the content of DRPAs positively correlate with the severity of hepatotoxicity. Meanwhile, FA is able to reduce the metabolic rate of DIOB in vitro. Moreover, FA suppressed the production of DRPAs and decreased the serum alanine/aspartate aminotransferase (ALT/AST) levels elevated by DIOB in vivo. Thus, FA can ameliorate DIOB-induced liver injury through reducing the production of DRPAs.

USP47 deubiquitylates Groucho/TLE to promote Wnt-β-catenin signaling

The Wnt-β-catenin signal transduction pathway is essential for embryonic development and adult tissue homeostasis. Wnt signaling converts TCF from a transcriptional repressor to an activator in a process facilitated by the E3 ligase XIAP. XIAP-mediated monoubiquitylation of the transcriptional corepressor Groucho (also known as TLE) decreases its affinity for TCF, thereby allowing the transcriptional coactivator β-catenin to displace it on TCF. Through a genome-scale screen in cultured Drosophila melanogaster cells, we identified the deubiquitylase USP47 as a positive regulator of Wnt signaling. We found that USP47 was required for Wnt signaling during Drosophila and Xenopus laevis development, as well as in human cells, indicating evolutionary conservation. In human cells, knockdown of USP47 inhibited Wnt reporter activity, and USP47 acted downstream of the β-catenin destruction complex. USP47 interacted with TLE3 and XIAP but did not alter their amounts; however, knockdown of USP47 enhanced XIAP-mediated ubiquitylation of TLE3. USP47 inhibited ubiquitylation of TLE3 by XIAP in vitro in a dose-dependent manner, suggesting that USP47 is the deubiquitylase that counteracts the E3 ligase activity of XIAP on TLE. Our data suggest a mechanism by which regulated ubiquitylation and deubiquitylation of TLE enhance the ability of β-catenin to cycle on and off TCF, thereby helping to ensure that the expression of Wnt target genes continues only as long as the upstream signal is present.

KCMF1 regulates autophagy and ion channels' function in renal cell carcinoma: a future therapeutic target

INTRODUCTION

In RCC, systematic procedures such as surgery, chemo-radiation therapy, and application of target-based inhibitors increase the risk of several comorbidities such as chronic kidney disease, hemorrhage, and cardiac arrest that may increase the mortality rate. Even though immune-based checkpoint inhibitor therapies have an overall good response rate, it is restricted to only 30-40% of patients. Hence, an in-depth study of tumor pathophysiology in RCC is needed to identify the new therapeutic target. In RCC, persisted hypoxia is an essential phenomenon for tumor growth and progression. KCMF1 is a newly identified ubiquitin ligase whose domain interacts with destabilized proteins and reprogrammed the ubiquitin coding for lysosome-mediated degradation and autophagy under hypoxic conditions/oxidative stress and maintaining cellular homeostasis. But in RCC, the functional role of KCMF1 remains undefined to date.

METHOD

We determined KCMF1 and its associated proteins RAD6 and UBR4 expression and their co-localization using confocal microscopy in tumor and non-tumor tissues samples. Further, immunofluorescence staining was performed to determine autophagy (LC3B, p62), hypoxia-inducible factor (HIF-1A) and ion channel markers (Kv1.3, KCNN4) in RCC patients (n-10). Inductively coupled plasma mass spectrophotometry (ICPMS) was performed to estimate the concentration of potassium (K⁺), sodium (Na⁺) and Zinc (zn²⁺) in tumor and non-tumor cells of RCC patients (n-20). Lastly, images were analyzed using ZEN3.1, and ImageJ software.

RESULT AND CONCLUSION

We observed a discrepancy in the formation of ubiquitin ligase, autophagosome via KCMF1, and ionic concentration in tumor cells, which might be one of the possible factors for cancer evolution. KCMF1-associated ubiquitin ligase system could be considered as a novel therapeutic target for RCC in the future.

Ubiquitin-specific protease 47 regulates intestinal inflammation through deubiquitination of TRAF6 in epithelial cells

Deubiquitinates (DUBs) alter the stabilities, localizations or activities of substrates by removing their ubiquitin conjugates, which are closely related to the development of inflammatory response. Here, we show that ubiquitin-specific protease 47 (USP47) prevents inflammation development in inflammatory bowel disease (IBD). Compared with wild-type mice, Usp47 knockout mice are more susceptible to dextran sodium sulfate (DSS)-induced acute and chronic colitis with higher inflammatory cytokines expression and severe intestinal tissue damage. Chimeric mouse experiments suggest that non-hematopoietic cells mainly contribute to the phenotype. And, DSS-induced colitis of the Usp47 knockout mice depends on commensal bacteria. Mechanistically, down-regulation of USP47 aggravates the activation of NF-κB signaling pathway by increasing the K63-linked poly-ubiquitination of tumor necrosis factor receptor-associated factor 6 (TRAF6) in intestinal epithelial cells. Furthermore, the expression of USP47, negatively correlated with the degree of inflammation, is lower at colonic inflammatory lesions than that non-inflammatory sites from the intestine from ulcerative colitis (UC) and Crohn's disease (CD) patients. These data, taken together, indicate that USP47 regulates intestinal inflammation through de-ubiquitination of K63-linked poly-ubiquitination TRAF6 in intestinal epithelial cells.

LncRNA ZNF883-Mediated NLRP3 Inflammasome Activation and Epilepsy Development Involve USP47 Upregulation

The goal of this study was to characterize the mechanisms of long noncoding RNA (lncRNA) ZNF883 regulating NOD-like receptor 3 (NLRP3) inflammasome activation in epilepsy (EP). Rat and cellular EP models were established using pilocarpine and magnesium-free extracellular fluid, respectively, to detect the differential expression of ZNF883, microRNA (miR)-138-5p, ubiquitin-specific peptidase 47 (USP47), and NLRP3. The pathology of the hippocampal neurons was examined by whole-cell patch clamping. The expression of ZNF883, miR-138-5p, and USP47 was modified in epileptic neurons, and the EP rats were injected with sh-ZNF883. Then, alterations in ZNF883, miR-138-5p, and USP47 levels were measured. The histopathology of the hippocampus was detected, along with the detection of IL-6, IL-1β, TNF-α, and NLRP3. Neuronal apoptosis in the rat and cellular EP models was determined. The relationship among ZNF883, miR-138-5p, and USP47 as well as the regulation of NLRP3 ubiquitination by USP47 was determined. ZNF883, USP47, and NLRP3 were increasingly expressed and miR-138-5p was downregulated in epileptic neurons and rats, concurrent with aggravated inflammation and apoptosis. ZNF883 overexpression in epileptic neurons elevated USP47 expression. ZNF883 targeted miR-138-5p and miR-138-5p negatively regulated USP47. In epileptic neurons, inhibiting miR-138-5p or overexpressing USP47 partially reversed the ZNF883 silencing-induced inhibition on NLRP3 inflammasome activation, neuronal apoptosis, and epileptiform activity. ZNF883 silencing in EP rats decreased USP47 and NLRP3, increased miR-138-5p, and inhibited inflammation and apoptosis. USP47 reversed the ubiquitination of NLRP3. ZNF883 inhibits NLRP3 ubiquitination and promotes EP through upregulating USP47 by sponging miR-138-5p.

Ubiquitin specific peptidase 47 promotes proliferation of lung squamous cell carcinoma

BACKGROUND

Ubiquitin specific peptidase 47 (USP47) is a kind of deubiquitinase, which has been reported to play oncogenic roles in several malignancies including colorectal cancer and breast cancer.

OBJECTIVE

Here we aimed to investigate the clinical significance of USP47 in lung squamous cell carcinoma (LUSC).

METHODS

We retrospectively enrolled a cohort of LUSC patients who underwent surgical resection in our hospital (n = 280) and conducted immunohistochemistry staining for their tumor tissues targeting USP47. The correlations between USP47 expression and clinicopathological characteristics were evaluated by Chi-square test. Univariate and multivariate analyses were conducted to assess the prognostic predictive role of USP47 in LUSC. Cell lines and mice models were utilized to explore the tumor-related functions of USP47 in vitro and in vivo, respectively.

RESULTS

Among the 280 cases, there were 127 cases classified as high-USP47 expression and 153 cases with low-USP47 expression. Statistical analyses revealed that higher USP47 expression was independently correlated with larger tumor size, advanced T stage, and unfavorable prognosis. Knockdown of USP47 by shRNA resulted in impaired proliferation of LUSC cell lines and reduced nucleus beta-catenin level. Furthermore, xenograft assays demonstrated that silencing USP47 can inhibit LUSC tumor growth in vivo.

CONCLUSION

Our research established a novel tumor-promoting effect and prognostic predictive role of USP47 in LUSC, thereby providing evidence for further therapeutic development.

Ubiquitin-specific protease 47 is associated with vascular calcification in chronic kidney disease by regulating osteogenic transdifferentiation of vascular smooth muscle cells

Chronic kidney disease (CKD) has recently become a serious health and social concern. Vascular calcification, a common complication of CKD, is a risk factor that increases the incidence and mortality of cardiovascular events in patients with CKD. However, there are currently no effective therapeutic targets that can facilitate treatment with fewer side effects for vascular calcification in CKD. To identify potential therapeutic targets, we performed label-free quantification (LFQ) analyses of protein samples from rat aortic vascular smooth muscle cells (RASMCs) after high-phosphorus treatment by nano-UPLC-MS/MS. We determined that ubiquitin-specific protease 47 (USP47) may be associated with CKD vascular calcification by regulating the osteogenic transdifferentiation of the vascular smooth muscle cell (VSMC) phenotype, thus suggesting a novel and potentially effective therapeutic target for CKD vascular calcification. USP47 knockdown significantly reduced the expression of β-transducin repeat-containing protein (BTRC), serine/threonine-protein kinase akt-1 (AKT1), Klotho, fibroblast growth factor (FGF23), and matrix Gla protein (MGP) in RASMCs after high-phosphorus treatment. Consistent with the results of protein-protein interaction (PPI) analyses, USP47 may be involved in regulating osteogenic transdifferentiation markers, such as runt-related transcription factor 2 (RUNX2), Klotho, FGF23, and MGP through the BTRC/AKT1 pathway upon CKD vascular calcification. These data indicate that USP47 may be associated with vascular calcification in CKD by regulating osteogenic differentiation of VSMCs. USP47 may regulate osteogenic transdifferentiation in VSMCs upon CKD vascular calcification through a process involving the BTRC/AKT1 pathway. This study identified a novel potential therapeutic target for the treatment of vascular calcification in CKD.

Regulation of Mitogen-Activated Protein Kinase Signaling Pathways by the Ubiquitin-Proteasome System and Its Pharmacological Potential

Mitogen-activated protein kinase (MAPK) cascades are evolutionarily conserved signaling pathways that play essential roles in transducing extracellular environmental signals into diverse cellular responses to maintain homeostasis. These pathways are classically organized into an architecture of three sequentially acting protein kinases: a MAPK kinase kinase that phosphorylates and activates a MAPK kinase, which in turn phosphorylates and activates the effector MAPK. The activity of MAPKs is tightly regulated by phosphorylation of their activation loop, which can be modulated by positive and negative feedback mechanisms to control the amplitude and duration of the signal. The signaling outcomes of MAPK pathways are further regulated by interactions of MAPKs with scaffolding and regulatory proteins. Accumulating evidence indicates that, in addition to these mechanisms, MAPK signaling is commonly regulated by ubiquitin-proteasome system (UPS)-mediated control of the stability and abundance of MAPK pathway components. Notably, the biologic activity of some MAPKs appears to be regulated mainly at the level of protein turnover. Recent studies have started to explore the potential of targeted protein degradation as a powerful strategy to investigate the biologic functions of individual MAPK pathway components and as a new therapeutic approach to overcome resistance to current small-molecule kinase inhibitors. Here, we comprehensively review the mechanisms, physiologic importance, and pharmacological potential of UPS-mediated protein degradation in the control of MAPK signaling. SIGNIFICANCE STATEMENT: Accumulating evidence highlights the importance of targeted protein degradation by the ubiquitin-proteasome system in regulating and fine-tuning the signaling output of mitogen-activated protein kinase (MAPK) pathways. Manipulating protein levels of MAPK cascade components may provide a novel approach for the development of selective pharmacological tools and therapeutics.

USP47-Mediated Deubiquitination and Stabilization of TCEA3 Attenuates Pyroptosis and Apoptosis of Colorectal Cancer Cells Induced by Chemotherapeutic Doxorubicin

The ubiquitin–proteasome system regulates a variety of cellular processes including growth, differentiation and apoptosis. While E1, E2, and E3 are responsible for the conjugation of ubiquitin to substrates, deubiquitinating enzymes (DUBs) reverse the process to remove ubiquitin and edit ubiquitin chains, which have profound effects on substrates’ degradation, localization, and activities. In the present study, we found that the deubiquitinating enzyme USP47 was markedly decreased in primary colorectal cancers (CRC). Its reduced expression was associated with shorter disease-free survival of CRC patients. In cultured CRC cells, knockdown of USP47 increased pyroptosis and apoptosis induced by chemotherapeutic doxorubicin. We found that USP47 was able to bind with transcription elongation factor a3 (TCEA3) and regulated its deubiquitination and intracellular level. While ectopic expression of USP47 increased cellular TCEA3 and resistance to doxorubicin, the effect was markedly attenuated by TCEA3 knockdown. Further analysis showed that the level of pro-apoptotic Bax was regulated by TCEA3. These results indicated that the USP47-TCEA3 axis modulates cell pyroptosis and apoptosis and may serve as a target for therapeutic intervention in CRC.

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.

RACK1 modulates polyglutamine-induced neurodegeneration by promoting ERK degradation in Drosophila

Polyglutamine diseases are neurodegenerative diseases caused by the expansion of polyglutamine (polyQ) tracts within different proteins. Although multiple pathways have been found to modulate aggregation of the expanded polyQ proteins, the mechanisms by which polyQ tracts induced neuronal cell death remain unknown. We conducted a genome-wide genetic screen to identify genes that suppress polyQ-induced neurodegeneration when mutated. Loss of the scaffold protein RACK1 alleviated cell death associated with the expression of polyQ tracts alone, as well as in models of Machado-Joseph disease (MJD) and Huntington's disease (HD), without affecting proteostasis of polyQ proteins. A genome-wide RNAi screen for modifiers of this rack1 suppression phenotype revealed that knockdown of the E3 ubiquitin ligase, POE (Purity of essence), further suppressed polyQ-induced cell death, resulting in nearly wild-type looking eyes. Biochemical analyses demonstrated that RACK1 interacts with POE and ERK to promote ERK degradation. These results suggest that RACK1 plays a key role in polyQ pathogenesis by promoting POE-dependent degradation of ERK, and implicate RACK1/POE/ERK as potent drug targets for treatment of polyQ diseases.

Trauma-induced regulation of VHP-1 modulates the cellular response to mechanical stress

Mechanical stimuli initiate adaptive signal transduction pathways, yet exceeding the cellular capacity to withstand physical stress results in death. The molecular mechanisms underlying trauma-induced degeneration remain unclear. In the nematode C. elegans, we have developed a method to study cellular degeneration in response to mechanical stress caused by blunt force trauma. Herein, we report that physical injury activates the c-Jun kinase, KGB-1, which modulates response elements through the AP-1 transcriptional complex. Among these, we have identified a dual-specificity MAPK phosphatase, VHP-1, as a stress-inducible modulator of neurodegeneration. VHP-1 regulates the transcriptional response to mechanical stress and is itself attenuated by KGB-1-mediated inactivation of a deubiquitinase, MATH-33, and proteasomal degradation. Together, we describe an uncharacterized stress response pathway in C. elegans and identify transcriptional and post-translational components comprising a feedback loop on Jun kinase and phosphatase activity.

E2F7 Transcriptionally Inhibits MicroRNA-199b Expression to Promote USP47, Thereby Enhancing Colon Cancer Tumor Stem Cell Activity and Promoting the Occurrence of Colon Cancer

microRNAs (miRNAs) can modulate the expression level of genes in a post-transcription manner, which are closely related to growth and metastasis of colon cancer. Herein, we aimed to explore how miR-199b influences colon cancer and to characterize its underlying molecular mechanism associating with E2F transcription factor 7 (E2F7). Assays of RT-qPCR, Western blot, and immunohistochemistry were utilized to detect the expression of E2F7 in the tissue samples collected from 30 patients diagnosed with colon cancer. Flow analysis was utilized to detect the ratio of ALDH1⁺ and CD133⁺ colon cancer stem cells. The interaction between E2F7, miR-199b, USP47, and MAPK was identified by ChIP-Seq analysis, luciferase reporter, RNA pull-down, co-immunoprecipitation, as well as glutathione-S-transferase (GST) pull-down experiments. Based on the gain- and loss-of-function approaches, the cellular functions of colon cancer cells by the E2F7-regulated miR-199b/USP47/MAPK axis were assessed. It was identified that E2F7 are expressed highly in the collected colon cancer tissues. E2F7 silencing reduced the production of ALDH1⁺ and CD133⁺ colon cancer stem cells and antagonized the effects of 5-fluorouracil (5-FU) treatment. Besides, the silencing of E2F7 was observed to suppress the oxidative stress, proliferation, migration, as well as invasion of ALDH1⁺ cells in vitro and tumorigenesis of colon cancer cells in vivo. Our findings reveal the pro-oncogenic effect of E2F7 on colon cancer development, highlighting E2F7 as a novel target for therapeutic strategy for colon cancer.

Targeting USP47 overcomes tyrosine kinase inhibitor resistance and eradicates leukemia stem/progenitor cells in chronic myelogenous leukemia

Identifying novel drug targets to overcome resistance to tyrosine kinase inhibitors (TKIs) and eradicating leukemia stem/progenitor cells are required for the treatment of chronic myelogenous leukemia (CML). Here, we show that ubiquitin-specific peptidase 47 (USP47) is a potential target to overcome TKI resistance. Functional analysis shows that USP47 knockdown represses proliferation of CML cells sensitive or resistant to imatinib in vitro and in vivo. The knockout of Usp47 significantly inhibits BCR-ABL and BCR-ABLT315I-induced CML in mice with the reduction of Lin-Sca1+c-Kit+ CML stem/progenitor cells. Mechanistic studies show that stabilizing Y-box binding protein 1 contributes to USP47-mediated DNA damage repair in CML cells. Inhibiting USP47 by P22077 exerts cytotoxicity to CML cells with or without TKI resistance in vitro and in vivo. Moreover, P22077 eliminates leukemia stem/progenitor cells in CML mice. Together, targeting USP47 is a promising strategy to overcome TKI resistance and eradicate leukemia stem/progenitor cells in CML.

UBR E3 ligases and the PDIA3 protease control degradation of unfolded antibody heavy chain by ERAD

Accumulation of unfolded antibody chains in the ER triggers ER stress that may lead to reduced productivity in therapeutic antibody manufacturing processes. We identified UBR4 and UBR5 as ubiquitin E3 ligases involved in HC ER-associated degradation. Knockdown of UBR4 and UBR5 resulted in intracellular accumulation, enhanced secretion, and reduced ubiquitination of HC. In concert with these E3 ligases, PDIA3 was shown to cleave ubiquitinated HC molecules to accelerate HC dislocation. Interestingly, UBR5, and to a lesser degree UBR4, were down-regulated as cellular demand for antibody expression increased in CHO cells during the production phase, or in plasma B cells. Reducing UBR4/UBR5 expression before the production phase increased antibody productivity in CHO cells, possibly by redirecting antibody molecules from degradation to secretion. Altogether we have characterized a novel proteolysis/proteasome-dependent pathway involved in degradation of unfolded antibody HC. Proteins characterized in this pathway may be novel targets for CHO cell engineering.

NatB regulates Rb mutant cell death and tumor growth by modulating EGFR/MAPK signaling through the N-end rule pathways

Inactivation of the Rb tumor suppressor causes context-dependent increases in cell proliferation or cell death. In a genetic screen for factors that promoted Rb mutant cell death in Drosophila, we identified Psid, a regulatory subunit of N-terminal acetyltransferase B (NatB). We showed that NatB subunits were required for elevated EGFR/MAPK signaling and Rb mutant cell survival. We showed that NatB regulates the posttranscriptional levels of the highly conserved pathway components Grb2/Drk, MAPK, and PP2AC but not that of the less conserved Sprouty. Interestingly, NatB increased the levels of positive pathway components Grb2/Drk and MAPK while decreased the levels of negative pathway component PP2AC, which were mediated by the distinct N-end rule branch E3 ubiquitin ligases Ubr4 and Cnot4, respectively. These results suggest a novel mechanism by which NatB and N-end rule pathways modulate EGFR/MAPK signaling by inversely regulating the levels of multiple conserved positive and negative pathway components. As inactivation of Psid blocked EGFR signaling-dependent tumor growth, this study raises the possibility that NatB is potentially a novel therapeutic target for cancers dependent on deregulated EGFR/Ras signaling.

Proteomic Analysis of Radiation-Induced Acute Liver Damage in a Rabbit Model

Radiation-induced liver damage (RILD) has become a limitation in radiotherapy for hepatocellular carcinoma. We established a rabbit model of RILD by CyberKnife. Electron microscopy analysis revealed obvious nuclear atrophy and disposition of fat in the nucleus after irradiation. We then utilized a mass spectrometry-based label-free relative quantitative proteomics approach to compare global proteomic changes of rabbit liver in response to radiation. In total, 2365 proteins were identified, including 338 proteins that were significantly dysregulated between irradiated and nonirradiated liver tissues. These differentially expressed proteins included USP47, POLR2A, CSTB, MCFD2, and CSNK2A1. Real-time polymerase chain reaction confirmed that USP47 and CABLES1 transcripts were significantly higher in irradiated liver tissues, whereas MCFD2 and CSNK2A1 expressions were significantly reduced. In Clusters of Orthologous Groups of proteins analysis, differentially expressed proteins were annotated and divided into 24 categories, including posttranslational modification, protein turnover, and chaperones. Kyoto Encyclopedia of Genes and Genomes analysis revealed that the enriched pathways in dysregulated proteins included the vascular endothelial growth factors (VEGF) signaling pathway, the mitogen-activated protein kinase (MAPK) signaling pathway, and the adipocytokine signaling pathway. The identification of proteins and pathways is crucial toward elucidating the radiation response process of the liver, which may facilitate the discovery of novel therapeutic targets.

Differential expression of Öbek controls ploidy in the Drosophila blood-brain barrier

During development, tissue growth is mediated by either cell proliferation or cell growth, coupled with polyploidy. Both strategies are employed by the cell types that make up the Drosophila blood-brain barrier. During larval growth, the perineurial glia proliferate, whereas the subperineurial glia expand enormously and become polyploid. Here, we show that the level of ploidy in the subperineurial glia is controlled by the N-terminal asparagine amidohydrolase homolog Öbek, and high Öbek levels are required to limit replication. In contrast, perineurial glia express moderate levels of Öbek, and increased Öbek expression blocks their proliferation. Interestingly, other dividing cells are not affected by alteration of Öbek expression. In glia, Öbek counteracts fibroblast growth factor and Hippo signaling to differentially affect cell growth and number. We propose a mechanism by which growth signals are integrated differentially in a glia-specific manner through different levels of Öbek protein to adjust cell proliferation versus endoreplication in the blood-brain barrier.

CD99: A Cell Surface Protein with an Oncojanus Role in Tumors

The cell surface molecule CD99 has gained interest because of its involvement in regulating cell differentiation and adhesion/migration of immune and tumor cells. However, the molecule plays an intriguing and dual role in different cell types. In particular, it acts as a requirement for cell malignancy or as an oncosuppressor in tumors. In addition, the gene encodes for two different isoforms, which also act in opposition inside the same cell. This review highlights key studies focusing on the dual role of CD99 and its isoforms and discusses major critical issues, challenges, and strategies for overcoming those challenges. The review specifically underscores the properties that make the molecule an attractive therapeutic target and identifies new relationships and areas of study that may be exploited. The elucidation of the spatial and temporal control of the expression of CD99 in normal and tumor cells is required to obtain a full appreciation of this molecule and its signaling.

Insights into the ubiquitin-proteasome system of human embryonic stem cells

Human embryonic stem cells (hESCs) exhibit high levels of proteasome activity, an intrinsic characteristic required for their self-renewal, pluripotency and differentiation. However, the mechanisms by which enhanced proteasome activity maintains hESC identity are only partially understood. Besides its essential role for the ability of hESCs to suppress misfolded protein aggregation, we hypothesize that enhanced proteasome activity could also be important to degrade endogenous regulatory factors. Since E3 ubiquitin ligases are responsible for substrate selection, we first define which E3 enzymes are increased in hESCs compared with their differentiated counterparts. Among them, we find HECT-domain E3 ligases such as HERC2 and UBE3A as well as several RING-domain E3s, including UBR7 and RNF181. Systematic characterization of their interactome suggests a link with hESC identity. Moreover, loss of distinct up-regulated E3s triggers significant changes at the transcriptome and proteome level of hESCs. However, these alterations do not dysregulate pluripotency markers and differentiation ability. On the contrary, global proteasome inhibition impairs diverse processes required for hESC identity, including protein synthesis, rRNA maturation, telomere maintenance and glycolytic metabolism. Thus, our data indicate that high proteasome activity is coupled with other determinant biological processes of hESC identity.

Loss of the deubiquitinase USP36 destabilizes the RNA helicase DHX33 and causes preimplantation lethality in mice

Deubiquitinases are proteases with a wide functional diversity that profoundly impact multiple biological processes. Among them, the ubiquitin-specific protease 36 (USP36) has been implicated in the regulation of nucleolar activity. However, its functional relevance in vivo has not yet been fully described. Here, we report the generation of an Usp36-deficient mouse model to examine the function of this enzyme. We show that Usp36 depletion is lethal in preimplantation mouse embryos, where it blocks the transition from morula to blastocyst during embryonic development. USP36 reduces the ubiquitination levels and increases the stability of the DEAH-box RNA helicase DHX33, which is critically involved in ribosomal RNA synthesis and mRNA translation. In agreement with this finding, O-propargyl-puromycin incorporation experiments, Northern blot, and electron microscopy analyses demonstrated the role of USP36 in ribosomal RNA and protein synthesis. Finally, we show that USP36 down-regulation alters cell proliferation in human cancer cells by inducing both apoptosis and cell cycle arrest, and that reducing DHX33 levels through short hairpin RNA interference has the same effect. Collectively, these results support that Usp36 is essential for cell and organism viability because of its role in ribosomal RNA processing and protein synthesis, which is mediated, at least in part, by regulating DHX33 stability.

A screen for E3 ubiquitination ligases that genetically interact with the adaptor protein Cindr during Drosophila eye patterning

Ubiquitination is a crucial post-translational modification that can target proteins for degradation. The E3 ubiquitin ligases are responsible for recognizing substrate proteins for ubiquitination, hence providing specificity to the process of protein degradation. Here, we describe a genetic modifier screen that identified E3 ligases that modified the rough-eye phenotype generated by expression of cindr^RNAi transgenes during Drosophila eye development. In total, we identified 36 E3 ligases, as well as 4 Cullins, that modified the mild cindr^RNA mis-patterning phenotype. This indicates possible roles for these E3s/Cullins in processes that require Cindr function, including cytoskeletal regulation, cell adhesion, cell signaling and cell survival. Three E3 ligases identified in our screen had previously been linked to regulating JNK signaling.

Reliance of Wolbachia on High Rates of Host Proteolysis Revealed by a Genome-Wide RNAi Screen of Drosophila Cells

Wolbachia are gram-negative, obligate, intracellular bacteria carried by a majority of insect species worldwide. Here we use a Wolbachia-infected Drosophila cell line and genome-wide RNA interference (RNAi) screening to identify host factors that influence Wolbachia titer. By screening an RNAi library targeting 15,699 transcribed host genes, we identified 36 candidate genes that dramatically reduced Wolbachia titer and 41 that increased Wolbachia titer. Host gene knockdowns that reduced Wolbachia titer spanned a broad array of biological pathways including genes that influenced mitochondrial function and lipid metabolism. In addition, knockdown of seven genes in the host ubiquitin and proteolysis pathways significantly reduced Wolbachia titer. To test the in vivo relevance of these results, we found that drug and mutant inhibition of proteolysis reduced levels of Wolbachia in the Drosophila oocyte. The presence of Wolbachia in either cell lines or oocytes dramatically alters the distribution and abundance of ubiquitinated proteins. Functional studies revealed that maintenance of Wolbachia titer relies on an intact host Endoplasmic Reticulum (ER)-associated protein degradation pathway (ERAD). Accordingly, electron microscopy studies demonstrated that Wolbachia is intimately associated with the host ER and dramatically alters the morphology of this organelle. Given Wolbachia lack essential amino acid biosynthetic pathways, the reliance of Wolbachia on high rates of host proteolysis via ubiquitination and the ERAD pathways may be a key mechanism for provisioning Wolbachia with amino acids. In addition, the reliance of Wolbachia on the ERAD pathway and disruption of ER morphology suggests a previously unsuspected mechanism for Wolbachia's potent ability to prevent RNA virus replication.