Ubiquitin Protein Ligase E3 Component Research Articles

Multiple E3 ligases act as antiviral factors against SARS-CoV-2 via inducing the ubiquitination and degradation of ORF9b.

Severe acute respiratory syndrome-coronavirus-2 (SARS-CoV-2) open reading frame 9b (ORF9b) antagonizes the antiviral type I and III interferon (IFN) responses and is ubiquitinated and degraded via the ubiquitin-proteasome pathway. However, E3 ubiquitin ligases that mediate the polyubiquitination and degradation of ORF9b remain unknown. In this study, we identified 14 E3 ligases that specifically bind to SARS-CoV-2 ORF9b. Specifically, three E3 ligases, HECT, UBA, and WWE domain-containing E3 ubiquitin protein ligase 1 (HUWE1), ubiquitin protein ligase E3 component n-recognin 4 (UBR4), and UBR5, induced K48-linked polyubiquitination and degradation of ORF9b, thereby attenuating ORF9b-mediated inhibition of the IFN response and SARS-CoV-2 replication. Moreover, each E3 ligase performed this function independent of the other two E3 ligases. Therefore, the three E3 ligases identified in this study as anti-SARS-CoV-2 host factors provide novel molecular insight into the virus-host interaction.IMPORTANCEUbiquitination is an important post-translational modification that regulates multiple biological processes, including viral replication. Identification of E3 ubiquitin ligases that target viral proteins for degradation can provide novel targets for antagonizing viral infections. Here, we identified multiple E3 ligases, including HECT, UBA, and WWE domain-containing E3 ubiquitin protein ligase 1 (HUWE1), ubiquitin protein ligase E3 component n-recognin 4 (UBR4), and UBR5, that ubiquitinated and induced the degradation of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) open reading frame 9b (ORF9b), an interferon (IFN) antagonist, thereby enhancing IFN production and attenuating SARS-CoV-2 replication. Our study provides new possibilities for drug development targeting the interaction between E3 ligases and ORF9b.

A review: targeting UBR5 domains to mediate emerging roles and mechanisms: chance or necessity?

Ubiquitinases are known to catalyze ubiquitin chains on target proteins to regulate various physiological functions like cell proliferation, autophagy, apoptosis, and cell cycle progression. As a member of E3 ligase, ubiquitin protein ligase E3 component n-recognin 5 (UBR5) belongs to the HECT E3 ligase and has been reported to be correlated with various pathophysiological processes. In this review, we give a comprehensive insight into the structure and function of UBR5. We discuss the specific domains of UBR5 and explore their biological functions separately. Furthermore, we describe the involvement of UBR5 in different pathophysiological conditions, including immune response, virus infection, DNA damage response and protein quality control. Moreover, we provide a thorough summary of the important roles and regulatory mechanisms of UBR5 in cancers and other diseases. On the whole, investigating the domains and functions of UBR5, elucidating the underlying mechanisms of UBR5 with various substrates in detail may provide new theoretical basis for the treatment of diseases, including cancers, which could improve future studies to construct novel UBR5-targeted therapy strategies.

VIRMA promotes the progression of head and neck squamous cell carcinoma by regulating UBR5 mRNA and m6A levels.

Head and neck squamous cell carcinoma (HNSCC) is a globally prevalent and lethal cancer form, whose precise mechanisms remain incompletely understood. Increasing evidence suggests that N6-methyladenosine (m6A) plays a crucial role in cancer progression. This study aimed to explore the biological function of m6A modification and vir-like m6A methyltransferase associated (VIRMA) in HNSCC. We conducted an analysis of VIRMA expression in HNSCC cells using The Cancer Genome Atlas (TCGA) database and employed reverse transcription quantitative polymerase chain reaction (RT-qPCR) and western blotting to assess its expression levels in HNSCC cell lines. Additionally, m6A levels in HNSCC cells were quantified, and the correlation between VIRMA expression levels and the clinical and pathological features of other genes was analyzed. Upon knocking down VIRMA levels, we assessed HNSCC cell proliferation, migration, and invasion and validated downstream genes using RT-qPCR and western blot. Our findings suggested that VIRMA, as an m6A-related regulator, may significantly influence HNSCC progression by regulating ubiquitin protein ligase E3 component N-recognin 5 (UBR5) through m6A modification. Therefore, VIRMA may serve as a prognostic biomarker.

NAP1L1 regulates BIRC2 ubiquitination modification via E3 ubiquitin ligase UBR4 and hence determines hepatocellular carcinoma progression

We have previously shown that nucleosome assembly protein 1-like 1 (NAP1L1) plays an important role in the abnormal proliferation of hepatocellular carcinoma (HCC) cells. However, the effects of NAP1L1 on the malignant behaviour of HCC cells, including cell migration, invasion and apoptosis, remain unclear. Baculoviral IAP repeat-containing 2 (BIRC2) plays a key role in initiating the abnormal proliferation, apoptotic escape and multidrug resistance of HCC cells; however, the mechanisms through which its stability is regulated in HCC remain elusive. Here, we found that knockdown of NAP1L1 inhibited the proliferation of HCC cells and activated apoptotic pathways but did not remarkably affect the migratory and invasive abilities of HCC cells. In addition, knockdown of NAP1L1 did not alter the expression of BIRC2 at the transcriptional level but substantially reduced its expression at the translational level, suggesting that NAP1L1 is involved in the post-translational modification (such as ubiquitination) of BIRC2. Furthermore, BIRC2 was highly expressed in human HCC tissues and promoted the proliferation and apoptotic escape of HCC cells. Co-immunoprecipitation (Co-IP) assay and mass spectrometry revealed that NAP1L1 and BIRC2 did not bind to each other; however, ubiquitin protein ligase E3 component n-recognin 4 (UBR4) was identified as an intermediate molecule associating NAP1L1 with BIRC2. Knockdown of NAP1L1 promoted the ubiquitin-mediated degradation of BIRC2 through the ubiquitin–protein junction of UBR4, which in turn inhibited the proliferation and apoptotic escape of HCC cells and exerted anti-tumour effects. In conclusion, this study reveals a novel mechanism through which NAP1L1 regulates the ubiquitination of BIRC2 through UBR4, thereby determining the progression of HCC. Based on this mechanism, suppression of NAP1L1 may inhibit tumour progression in patients with HCC with high protein expression of NAP1L1 or BIRC2.

UBR5 promotes antiviral immunity by disengaging the transcriptional brake on RIG-I like receptors

The Retinoic acid-Inducible Gene I (RIG-I) like receptors (RLRs) are the major viral RNA sensors essential for the initiation of antiviral immune responses. RLRs are subjected to stringent transcriptional and posttranslational regulations, of which ubiquitination is one of the most important. However, the role of ubiquitination in RLR transcription is unknown. Here, we screen 375 definite ubiquitin ligase knockout cell lines and identify Ubiquitin Protein Ligase E3 Component N-Recognin 5 (UBR5) as a positive regulator of RLR transcription. UBR5 deficiency reduces antiviral immune responses to RNA viruses, while increases viral replication in primary cells and mice. Ubr5 knockout mice are more susceptible to lethal RNA virus infection than wild type littermates. Mechanistically, UBR5 mediates the Lysine 63-linked ubiquitination of Tripartite Motif Protein 28 (TRIM28), an epigenetic repressor of RLRs. This modification prevents intramolecular SUMOylation of TRIM28, thus disengages the TRIM28-imposed brake on RLR transcription. In sum, UBR5 enables rapid upregulation of RLR expression to boost antiviral immune responses by ubiquitinating and de-SUMOylating TRIM28.

LncRNA OIP5-AS1 Targets the miR-140-5p/UBR5 Cascade to Promote the Development of Gastric Cancer.

Gastric cancer (GC) is a malignant tumor with the highest incidence among all kinds of malignant tumors in China. Long noncoding RNAs (LncRNAs) have been reported to act as microRNA (miRNAs) sponges and thus play key roles in biological processes and pathogenesis. Thus, this study aimed to investigate the functional effects and the regulatory mechanism of lncRNA opa interacting protein 5-antisense 1 (OIP5-AS1) in gastric cancer cells. The expression of OIP5-AS1, miR-140-5p, Ubiquitin protein ligase E3 component n-recognin 5 (UBR5) was detected using quantitative real-time polymerase chain reaction (qRT-PCR). Cell proliferation, apoptosis, migration, and invasion were assessed using Cell-Counting Kit-8 (CCK-8), Flow cytometry, and Transwell assays. UBR5 protein level was detected by Western blot. Binding between miR-140-5p and OIP5-AS1 or UBR5 was predicted by Starbasev2.0 and TargetScan, and verified using Dual-luciferase reporter assays and RNA pull-down assay. A xenograft mice model was used to evaluate the effects of OIP5-AS1 on tumor growth in vivo. OIP5-AS1 was upregulated in GC cancer and cells. OIP5-AS1 knockdown inhibited cell proliferation, migration, invasion, but induced cell apoptosis in GC. In mechanism, OIP5-AS1 might serve as a sponge for miR-140-5p to enhance UBR5 expression. Moreover, overexpression of miR-140-5p or UBR5 partly reversed the effects of OIP5-AS1 depletion on the progression of GC cells. Furthermore, OIP5-AS1 depletion also suppressed tumor growth in vivo. OIP5-AS1 silencing might suppress proliferation, migration, invasion, and induced apoptosis in GC cells by regulating the miR-140-5p/UBR5 axis.

Circ-UBR4 regulates the proliferation, migration, inflammation, and apoptosis in ox-LDL-induced vascular smooth muscle cells via miR-515-5p/IGF2 axis.

The aim of our study is to disclose the role and underlying molecular mechanisms of circular RNA ubiquitin protein ligase E3 component n-recognin 4 (circ-UBR4) in atherosclerosis (AS). Our data showed that circ-UBR4 expression was upregulated in AS patients and oxidized low-density lipoprotein (ox-LDL)-induced vascular smooth muscle cells (VSMCs) compared with healthy volunteer and untreated VSMCs. In addition, ox-LDL stimulated proliferation, migration, and inflammation but decreased apoptosis in VSMCs, which were overturned by the inhibition of circ-UBR4. miR-515-5p was sponged by circ-UBR4, and its inhibitor reversed the inhibitory effect of circ-UBR4 knockdown on proliferation, migration, and inflammation in ox-LDL-induced VSMCs. Insulin-like growth factor2 (IGF2) was a functional target of miR-515-5p, and overexpression of IGF2 reversed the suppressive effect of miR-515-5p on ox-LDL-stimulated VSMCs proliferation, migration, and inflammation. Collectively, circ-UBR4 knockdown decreased proliferation, migration, and inflammation but stimulated apoptosis in ox-LDL-induced VSMCs by targeting the miR-515-5p/IGF2 axis.

Upregulation of UBR1 m6A methylation by METTL14 inhibits autophagy in spinal cord injury.

Objective: Gene Expression Omnibus database shows significantly downregulated expression of ubiquitin protein ligase E3 component N-recognin 1 (UBR1) in spinal cord injury (SCI). In this study, we investigated the mechanism of action of UBR1 in SCI.Methods: Following the establishment of SCI models in rats and PC12 cells, Basso-Beattie-Bresnahan score and H&E and Nissl staining were used to evaluate SCI. The localization of NeuN/LC3 and the expression of LC3II/I, Beclin-1, and p62 were detected to assess autophagy. The expression of Bax, Bcl-2, and cleaved caspase-3 was detected and TdT-mediated dUTP-biotin nick end-labelling staining was employed to determine the changes in apoptosis. The N(6)-methyladenosine (m6A) modification level of UBR1 was analyzed by methylated RNA immunoprecipitation, and the binding of METTL14 and UBR1 mRNA was analysed by photoactivatable ribonucleoside-enhanced crosslinking and immunoprecipitation.Results: UBR1 was poorly expressed, and METTL14 was highly expressed in rat and cell models of SCI. UBR1 overexpression or METTL14 knockdown enhanced motor function in rats with SCI. Moreover, this modification increased Nissl bodies and autophagy and inhibited apoptosis in the spinal cord of SCI rats. METTL14 silencing reduced the m6A modification level of UBR1 and enhanced UBR1 expression. Importantly, UBR1 knockdown nullified METTL14 knockdown -induced autophagy promotion and apoptosis reduction.Conclusion: The METTL14-catalyzed m6A methylation of UBR1 promoted apoptosis and inhibited autophagy in SCI.

Clinical manifestation of Johanson-Blizzard syndrome in patient with nucleotide variants in UBR1 gene

Introduction. Johanson-Blizzard syndrome (JBS) is a very rare genetic disorder caused by a mutation of the ubiquitin protein ligase E3 component N-recognin 1 (UBR1) gene. Clinical diagnosis is based on the pathognomonic combination of congenital exocrine pancreatic insufficiency and characteristic signs of facial dysmorphology (nasal wing hypoplasia/aplasia and oligodontia of permanent teeth). Diagnosis is confirmed by genetic screening of the UBR1 gene. The aim of this case report was to emphasize that nucleotide variants in the UBR1 gene, described as benign or unclassified, should still be considered a genetic cause of the clinical characteristics in patients with JBS. Case report. We present an 8-month-old child, with clinical features of JBS, who was admitted to our hospital due to poor weight gain and loose stools. Upon admission, signs of protein-energy malnutrition, facial dysmorphology, and other anomalies were observed. The child had hypotonia and convergent strabismus. A laboratory examination confirmed exocrine pancreatic insufficiency and hypothyroidism. Genetic testing confirmed two single nucleotide variants in the UBR1 gene ? chromosome 15q15.2: NM_174916.3:c.4700+12A>G (intron 42) and NM_174916.3 UBR1:c.862-18C>T (intron 07). A pancreatic enzyme replacement therapy with liposoluble vitamin supplementation and adequate nutrition was conducted. Conclusion. Recognizing the clinical features of JBS and confirming it with genetic analysis is essential, especially in patients with idiopathic pancreatic insufficiency. Even when genetic confirmation is not possible, adequate treatment is necessary for normal growth and development of the child.

UBR7 inhibits HCC tumorigenesis by targeting Keap1/Nrf2/Bach1/HK2 and glycolysis

BackgroundGlycolysis metabolism is an attractive target for cancer therapy. Reprogramming metabolic pathways could improve the ability of metabolic inhibitors to suppress cancers with limited treatment options. The ubiquitin–proteasome system facilitates the turnover of most intracellular proteins with E3 ligase conferring the target selection and specificity. Ubiquitin protein ligase E3 component N-recognin 7 (UBR7), among the least studied E3 ligases, recognizes its substrate through a plant homeodomain (PHD) finger. Here, we bring into focus on its suppressive role in glycolysis and HCC tumorigenesis, dependent on its E3 ubiquitin ligase activity toward monoubiquitination of histone H2B at lysine 120 (H2BK120ub).MethodsIn this study, we carried out high-throughput RNAi screening to identify epigenetic candidates in regulating lactic acid and investigated its possible roles in HCC progression.ResultsUBR7 loss promotes HCC tumorigenesis both in vitro and in vivo. UBR7 inhibits glycolysis by indirectly suppressing HK2 expression, a downstream target of Nrf2/Bach1 axis. Mechanically, UBR7 regulates H2BK120ub to bind to Keap1 promoter through H2BK120ub monoubiquitination, thereby modulating Keap1 expression and downstream Nrf2/Bach1/HK2 signaling. Pharmaceutical and genetic inhibition of glycolytic enzymes attenuate the promoting effect of UBR7 deficiency on tumor growth. In addition, methyltransferase ALKBH5, downregulated in HCC, regulated UBR7 expression in an m6A-dependent manner.ConclusionsThese results collectively establish UBR7 as a critical negative regulator of aerobic glycolysis and HCC tumorigenesis through regulation of the Keap1/Nrf2/Bach1/HK2 axis, providing a potential clinical and therapeutic target for the HCC treatment.

Targeting UBR5 in hepatocellular carcinoma cells and precise treatment via echinacoside nanodelivery

BackgroundHepatocellular carcinoma (HCC) is among the most common and malignant cancers with no effective therapeutic approaches. Echinacoside (ECH), a phenylethanoid glycoside isolated from Chinese herbal medicine, Cistanche salsa, can inhibit HCC progression; however, poor absorption and low bioavailability limit its biological applications.MethodsTo improve ECH sensitivity to HepG2 cells, we developed a mesoporous silica nanoparticle (MSN)-based drug delivery system to deliver ECH to HepG2 cells via galactose (GAL) and poly(ethylene glycol) diglycidyl ether (PEGDE) conjugation (ECH@Au@MSN-PEGDE-GAL, or ECH@AMPG). Gain- and loss-of-function assays were conducted to assess the effects of UBR5 on HCC cell apoptosis and glycolysis. Moreover, the interactions among intermediate products were also investigated to elucidate the mechanisms by which UBR5 functions.ResultsThe present study showed that ubiquitin protein ligase E3 component N-recognin 5 (UBR5) acted as an oncogene in HCC tissues and that its expression was inhibited by ECH. AMPG showed a high drug loading property and a slow and sustained release pattern over time. Moreover, owing to the valid drug accumulation, ECH@AMPG promoted apoptosis and inhibited glycolysis of HepG2 cells in vitro. In vivo experiments demonstrated that AMPG also enhanced the antitumor effects of ECH in HepG2 cell-bearing mice.ConclusionsOur results indicated the clinical significance of UBR5 as a therapeutic target. On the basis of the nontoxic and high drug-loading capabilities of AMPG, ECH@AMPG presented better effects on HCC cells compared with free ECH, indicating its potential for the chemotherapy of HCC.

Space microgravity improves proliferation of human iPSC-derived cardiomyocytes.

SummaryIn microgravity, cells undergo profound changes in their properties. However, how human cardiac progenitors respond to space microgravity is unknown. In this study, we evaluated the effect of space microgravity on differentiation of human induced pluripotent stem cell (hiPSC)-derived cardiac progenitors compared with 1G cultures on the International Space Station (ISS). Cryopreserved 3D cardiac progenitors were cultured for 3 weeks on the ISS. Compared with 1G cultures, the microgravity cultures had 3-fold larger sphere sizes, 20-fold higher counts of nuclei, and increased expression of proliferation markers. Highly enriched cardiomyocytes generated in space microgravity showed improved Ca2+ handling and increased expression of contraction-associated genes. Short-term exposure (3 days) of cardiac progenitors to space microgravity upregulated genes involved in cell proliferation, survival, cardiac differentiation, and contraction, consistent with improved microgravity cultures at the late stage. These results indicate that space microgravity increased proliferation of hiPSC-cardiomyocytes, which had appropriate structure and function.

Rice OsUBR7 modulates plant height by regulating histone H2B monoubiquitination and cell proliferation

Plant height is an important agronomic trait for lodging resistance and yield. Here, we report a new plant-height-related gene, OsUBR7 in rice (Oryza sativa L.); knockout of OsUBR7 caused fewer cells in internodes, resulting in a semi-dwarf phenotype. OsUBR7 encodes a putative E3 ligase containing a plant homeodomain finger and a ubiquitin protein ligase E3 component N-recognin 7 (UBR7) domain. OsUBR7 interacts with histones and monoubiquitinates H2B (H2Bub1) at lysine148 in coordination with the E2 conjugase OsUBC18. OsUBR7 mediates H2Bub1 at a number of chromatin loci for the normal expression of target genes, including cell-cycle-related and pleiotropic genes, consistent with the observation that cell-cycle progression was suppressed in the osubr7 mutant owing to reductions in H2Bub1 and expression levels at these loci. The genetic divergence of OsUBR7 alleles among japonica and indica cultivars affects their transcriptional activity, and these alleles may have undergone selection during rice domestication. Overall, our results reveal a novel mechanism that mediates H2Bub1 in plants, and UBR7 orthologs could be utilized as an untapped epigenetic resource for crop improvement.

A Novel circUBR4/miR-491-5p/NRP2 ceRNA Network Regulates Oxidized Low-density Lipoprotein-induced Proliferation and Migration in Vascular Smooth Muscle Cells.

Vascular smooth muscle cells (VSMCs) play critical roles in the progression of atherosclerosis. Circular RNA (circRNA) ubiquitin protein ligase E3 component n-recognin 4 (circUBR4) has been shown to regulate VSMC migration and proliferation. In this study, we sought to identify the mechanism in the regulation of circUBR4. CircUBR4, microRNA (miR)-491-5p, and Neuropilin-2 (NRP2) were quantified by quantitative real-time polymerase chain reaction (PCR) and western blot. Cell proliferation was evaluated by Cell Counting Kit-8 and 5-Ethynyl-2'-Deoxyuridine assays. Cell migration was examined by wound-healing and transwell invasion assays. The direct relationship between miR-491-5p and circUBR4 or NRP2 was validated by dual-luciferase reporter and RNA immunoprecipitation assays. Our data indicated that in VSMCs, ox-LDL induced circUBR4 expression. Silencing endogenous circUBR4 attenuated VSMC proliferation and migration induced by ox-LDL. Mechanistically, circUBR4 targeted miR-491-5p by pairing to miR-491-5p. Moreover, miR-491-5p was identified as a downstream mediator of circUBR4 function in ox-LDL-treated VSMCs. NRP2 was a direct target of miR-491-5p, and circUBR4 acted as a competing endogenous RNA for miR-491-5p to regulate NRP2 expression. In addition, NRP2 was a functionally downstream effector of miR-491-5p in regulating ox-LDL-evoked VSMC proliferation and migration. Our findings identify a new competing endogenous RNA network, the circUBR4/miR-491-5p/NRP2 axis, for the regulation of circUBR4 in VSMC migration and proliferation.

Jak2 Inhibitor AG490 Improved Poststroke Central and Peripheral Inflammation and Metabolic Abnormalities in a Rat Model of Ischemic Stroke.

Poststroke hyperglycemia and inflammation have been implicated in the pathogenesis of stroke. Janus Kinase 2 (Jak2), a catalytic signaling component for cytokine receptors such as Interleukin-6 (IL-6), has inflammatory and metabolic properties. This study aimed to investigate the roles of Jak2 in poststroke inflammation and metabolic abnormality in a rat model of permanent cerebral ischemia. Pretreatment with Jak2 inhibitor AG490 ameliorated neurological deficit, brain infarction, edema, oxidative stress, inflammation, caspase-3 activation, and Zonula Occludens-1 (ZO-1) reduction. Moreover, in injured cortical tissues, Tumor Necrosis Factor-α, IL-1β, and IL-6 levels were reduced with concurrent decreased NF-κB p65 phosphorylation, Signal Transducers and Activators of Transcription 3 phosphorylation, Ubiquitin Protein Ligase E3 Component N-Recognin 1 expression, and Matrix Metalloproteinase activity. In the in vitro study on bEnd.3 endothelial cells, AG490 diminished IL-6-induced endothelial barrier disruption by decreasing ZO-1 decline. Metabolically, administration of AG490 lowered fasting glucose, with improvements in glucose intolerance, plasma-free fatty acids, and plasma C Reactive Proteins. In conclusion, AG490 improved the inflammation and oxidative stress of neuronal, hepatic, and muscle tissues of stroke rats as well as impairing insulin signaling in the liver and skeletal muscles. Therefore, Jak2 blockades may have benefits for combating poststroke central and peripheral inflammation, and metabolic abnormalities.

Molecular characterization of substrate-induced ubiquitin transfer by UBR7-PHD finger, a newly identified histone H2BK120 ubiquitin ligase.

Monoubiquitination of histone H2B at lysine 120 plays a vital role in active transcription and DNA damage response pathways. Ubiquitin protein ligase E3 component N-recognin 7 (UBR7) has been recently identified as an H2BK120 monoubiquitin ligase. However, the molecular details of its ubiquitin transfer mechanism are not well understood. Here, we report that the plant homeodomain (PHD) finger of UBR7 is essential for its association with E2 UbcH6 and consequent ubiquitin transfer to its substrate histone H2B. We also identified the critical region of UbcH6 involved in this function and shown that the residues stretching from 114 to 125 of histone H2B C-terminal tail are sufficient for UBR7/UbcH6-mediated ubiquitin transfer. We also employed antibody-independent mass spectrometry to confirm UBR7-mediated ubiquitination of the H2B C-terminal tail. We demonstrated that the PHD finger of UBR7 forms a dimer and this dimerization is essential for ubiquitination of histone H2B. We mapped the critical residues involved in the dimerization and mutation of these residues that abrogate E3 ligase activity and are associated with cancer. Furthermore, we compared the mode of ubiquitin discharge from UbcH6 mediated by UBR7 and RING finger protein 20 (RNF20) through a thioester hydrolysis assay. Interestingly, binding of substrate H2B to UBR7 induces a conformational change in the PHD finger, which triggers ubiquitin transfer from UbcH6. However, the RNF20 RING finger alone is sufficient to promote the release of ubiquitin from UbcH6. Overall, the mechanism of ubiquitin transfer by the newly identified E3 ubiquitin ligase UBR7 is markedly different from that of RNF20.

Histone acetyltransferase 1 promotes gemcitabine resistance by regulating the PVT1/EZH2 complex in pancreatic cancer

The poor prognosis of pancreatic cancer is primarily due to the development of resistance to therapies, including gemcitabine. The long noncoding RNA PVT1 (lncRNA PVT1) has been shown to interact with enhancer of zeste 2 polycomb repressive complex 2 subunit (EZH2), promoting gemcitabine resistance in pancreatic cancer. In this study, we found histone acetyltransferase 1 (HAT1) enhanced the tolerance of pancreatic cancer cells to gemcitabine and HAT1-mediated resistance mechanisms were regulated by PVT1 and EZH2. Our results showed that the aberrant HAT1 expression promoted gemcitabine resistance, while silencing HAT1 restored gemcitabine sensitivity. Moreover, HAT1 depletion caused a notable increase of gemcitabine sensitivity in gemcitabine-resistant pancreatic cancer cell lines. Further research found that HAT1 increased PVT1 expression to induce gemcitabine resistance, which enhanced the binding of bromodomain containing 4 (BRD4) to the PVT1 promoter, thereby promoting PVT1 transcription. Besides, HAT1 prevented EZH2 degradation by interfering with ubiquitin protein ligase E3 component n-recognin 4 (UBR4) binding to the N-terminal domain of EZH2, thus maintaining EZH2 protein stability to elevate the level of EZH2 protein, which also promoted HAT1-mediated gemcitabine resistance. These results suggested that HAT1 induced gemcitabine resistance of pancreatic cancer cells through regulating PVT1/EZH2 complex. Given this, Chitosan (CS)-tripolyphosphate (TPP)-siHAT1 nanoparticles were developed to block HAT1 expression and improve the antitumor effect of gemcitabine. The results showed that CS-TPP-siHAT1 nanoparticles augmented the antitumor effects of gemcitabine in vitro and in vivo. In conclusion, HAT1-targeted therapy can improve observably gemcitabine sensitivity of pancreatic cancer cells. HAT1 is a promising therapeutic target for pancreatic cancer.

MicroRNA-361-5p slows down gliomas development through regulating UBR5 to elevate ATMIN protein expression

MicroRNA (miR)-361-5p has been studied to suppress gliomas development. Based on that, an insight into the regulatory mechanism of miR-361-5p in gliomas was supplemented from ubiquitin protein ligase E3 component N-recognin 5 (UBR5)-mediated ubiquitination of ataxia-telangiectasia mutated interactor (ATMIN). miR-361-5p, ATMIN, and UBR5 levels were clinically analyzed in gliomas tissues, which were further validated in gliomas cell lines. Loss/gain-of-function method was applied to determine the roles of miR-361-5p and UBR5 in gliomas, as to cell viability, migration, invasion, colony formation ability, and apoptosis in vitro and tumorigenesis in vivo. The relationship between miR-361-5p and UBR5 was verified and the interaction between UBR5 and ATMIN was explored. It was detected that reduced miR-361-5p and ATMIN and enhanced UBR5 levels showed in gliomas. Elevating miR-361-5p was repressive in gliomas progression. UBR5 was directly targeted by miR-361-5p. UBR5 can ubiquitinate ATMIN. miR-361-5p suppressed gliomas by regulating UBR5-mediated ubiquitination of ATMIN. Downregulating UBR5 impeded gliomas tumor growth in vivo. Upregulating miR-361-5p targets UBR5 to promote ATMIN protein expression, thus to recline the malignant phenotype of gliomas cells.

Circ_UBR4 Knockdown Alleviates Oxidized Low-Density Lipoprotein-Provoked Growth and Migration of Human Vascular Smooth Muscle Cells by Acting on the miR-637/FOXO4 Pathway.

Excessive proliferation and migration of human vascular smooth muscle cells (HVSMCs) induced by oxidized low-density lipoprotein (ox-LDL) are important pathological features of atherosclerosis. Emerging evidence indicates that circular RNAs deregulation is involved in this pathological process. The objective of this study was to explore the role of circular RNA ubiquitin protein ligase E3 component n-recognin 4 (circ_UBR4) in ox-LDL-treated HVSMCs. The expression of circ_UBR4, microRNA-637 (miR-637), and forkhead box O4 (FOXO4) mRNA was detected by quantitative real-time PCR. Cell cycle progression was examined by flow cytometry assay. Cell viability was examined by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. Cell migration was examined by transwell assay. The protein levels of proliferating cell nuclear antigen, matrix metalloproteinase 2, and FOXO4 were measured by western blot. The relationship between miR-637 and circ_UBR4 or FOXO4 was confirmed by dual-luciferase reporter assay. The results presented that the expression of circ_UBR4 was increased in atherosclerosis serum samples and ox-LDL-treated HVSMCs. Cell cycle progression, cell proliferation, and cell migration were promoted by ox-LDL, whereas circ_UBR4 knockdown inhibited HVSMCs proliferation and migration. MiR-637 was a target of circ_UBR4, and FOXO4 was a target of miR-637. Circ_UBR4 positively regulated FOXO4 expression by targeting miR-637. Circ_UBR4 knockdown-inhibited HVSMCs proliferation and migration were recovered by miR-637 inhibition, and miR-637 restoration-inhibited HVSMCs proliferation and migration were recovered by FOXO4 overexpression. In conclusion, circ_UBR4 knockdown inhibited ox-LDL-induced excessive proliferation and migration of HVSMCs by regulating FOXO4 via targeting miR-637.

UBR5 inhibits the radiosensitivity of non-small cell lung cancer cells via the activation of the PI3K/AKT pathway

Ubiquitin protein ligase E3 component n-recognin 5 (UBR5) has been identified as an oncogene in diverse cancers; however, whether its expression was associated with radiosensitivities of non-small cell lung cancer...