Suppressing UBE2N ameliorates Alzheimer's disease pathology through the clearance of amyloid beta.

INTRODUCTION: Aging is one of the risk factors for the early onset of Alzheimer's disease (AD). We previously discovered that the age-dependent increase in Ubiquitin Conjugating Enzyme E2 N (UBE2N) plays a role in the accumulation of misfolded proteins through K63 ubiquitination, which has been linked to AD pathogenesis. However, the impact of UBE2N on amyloid pathology and clearance has remained unknown. RESULTS: We observed the elevated UBE2N during the amyloid beta (Aß) generation in the brains of 5×FAD, APP/PS1 mice, and patients with AD, in comparison to healthy individuals. UBE2N overexpression exacerbated amyloid deposition in 5×FAD mice and senescent monkeys, whereas knocking down UBE2N via CRISPR/Cas9 reduced Aß generation and cognitive deficiency. Moreover, pharmacological inhibition of UBE2N ameliorated Aß pathology and subsequent transcript defects in 5×FAD mice. DISCUSSION: We have discovered that age-dependent expression of UBE2N is a critical regulator of AD pathology. Our findings suggest that UBE2N could serve as a potential pharmacological target for the advancement of AD therapeutics. HIGHLIGHTS: Ubiquitin Conjugating Enzyme E2 N (UBE2N) level was elevated during amyloid beta (Aß) deposition in AD mouse and patients' brains. UBE2N exacerbated Aß generation in the AD mouse and senescent monkey. Drug inhibition of UBE2N ameliorated Aß pathology and cognitive deficiency.

Novel Isoform DTX3c Associates with UBE2N-UBA1 and Cdc48/p97 as Part of the EphB4 Degradation Complex Regulated by the Autocrine IGF-II/IRA Signal in Malignant Mesothelioma.

EphB4 angiogenic kinase over-expression in Mesothelioma cells relies upon a degradation rescue signal provided by autocrine IGF-II activation of Insulin Receptor A. However, the identity of the molecular machinery involved in EphB4 rapid degradation upon IGF-II signal deprivation are unknown. Using targeted proteomics, protein-protein interaction methods, PCR cloning, and 3D modeling approaches, we identified a novel ubiquitin E3 ligase complex recruited by the EphB4 C tail upon autocrine IGF-II signal deprivation. We show this complex to contain a previously unknown N-Terminal isoform of Deltex3 E3-Ub ligase (referred as "DTX3c"), along with UBA1(E1) and UBE2N(E2) ubiquitin ligases and the ATPase/unfoldase Cdc48/p97. Upon autocrine IGF-II neutralization in cultured MSTO211H (a Malignant Mesothelioma cell line that is highly responsive to the EphB4 degradation rescue IGF-II signal), the inter-molecular interactions between these factors were enhanced and their association with the EphB4 C-tail increased consistently with the previously described EphB4 degradation pattern. The ATPase/unfoldase activity of Cdc48/p97 was required for EphB4 recruitment. As compared to the previously known isoforms DTX3a and DTX3b, a 3D modeling analysis of the DTX3c Nt domain showed a unique 3D folding supporting isoform-specific biological function(s). We shed light on the molecular machinery associated with autocrine IGF-II regulation of oncogenic EphB4 kinase expression in a previously characterized IGF-II+/EphB4+ Mesothelioma cell line. The study provides early evidence for DTX3 Ub-E3 ligase involvement beyond the Notch signaling pathway.

TRIM11 suppresses ferritinophagy and gemcitabine sensitivity through UBE2N/TAX1BP1 signaling in pancreatic ductal adenocarcinoma.

Gemcitabine is first-line chemotherapy for pancreatic cancer, however, the development of resistance limits its effectiveness. The tripartite motif-containing 11 (TRIM11) protein plays crucial roles in tumor development and undergoes auto-polyubiquitination to promote interactions in selective autophagy. Therefore, Understanding whether TRIM11 is involved in ferritinophagy and gemcitabine resistance in pancreatic cancer is critical in developing pancreatic cancer therapeutics. TRIM11 expression was validated by Western blot analysis, real-time polymease chain reaction, and immunohistochemical staining. 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide and Colony formation assays were performed to investigate pancreatic ductal adenocarcinomas (PDAC) cell viability. Mouse xenograft model of PDAC cells was established to verify the role of TRIM11 in vivo. Coimmunoprecipitation was used to identify the reciprocal regulation between TRIM11 and UBE2N. In this study, we found that TRIM11 expression were higher in PDAC cells and tissues. TRIM11 overexpression promotes PDAC cell proliferation in vitro and tumor growth in vivo. Decreased expression of TRIM11 in PDAC patients is associated with decreased UBE2N and increased TAX1BP1 expression. Coimmunoprecipitation established that TRIM11 interacts and colocalizes with UBE2N. Mechanistically, TRIM11 promoted gemcitabine resistance and suppressed ferritinophagy through UBE2N-TAX1BP1 signaling. Our findings identify TRIM11 as a key regulator of TAX1BP1 signaling with a crucial role in ferritinophagy and gemcitabine resistance in PDAC.

TRIM5α requires Ube2W to anchor Lys63-linked ubiquitin chains and restrict reverse transcription.

TRIM5α is an antiviral, cytoplasmic, E3 ubiquitin (Ub) ligase that assembles on incoming retroviral capsids and induces their premature dissociation. It inhibits reverse transcription of the viral genome and can also synthesize unanchored polyubiquitin (polyUb) chains to stimulate innate immune responses. Here, we show that TRIM5α employs the E2 Ub-conjugating enzyme Ube2W to anchor the Lys63-linked polyUb chains in a process of TRIM5α auto-ubiquitination. Chain anchoring is initiated, in cells and in vitro, through Ube2W-catalyzed monoubiquitination of TRIM5α. This modification serves as a substrate for the elongation of anchored Lys63-linked polyUb chains, catalyzed by the heterodimeric E2 enzyme Ube2N/Ube2V2. Ube2W targets multiple TRIM5α internal lysines with Ub especially lysines 45 and 50, rather than modifying the N-terminal amino group, which is instead αN-acetylated in cells. E2 depletion or Ub mutation inhibits TRIM5α ubiquitination in cells and restores restricted viral reverse transcription, but not infection. Our data indicate that the stepwise formation of anchored Lys63-linked polyUb is a critical early step in the TRIM5α restriction mechanism and identify the E2 Ub-conjugating cofactors involved.

Spatial UBE2N protein expression indicates genomic instability in colorectal cancers.

BACKGROUND: One major hallmark of colorectal cancers (CRC) is genomic instability with its contribution to tumor heterogeneity and therapy resistance. To facilitate the investigation of intra-sample phenotypes and the de novo identification of tumor sub-populations, imaging mass spectrometry (IMS) provides a powerful technique to elucidate the spatial distribution patterns of peptides and proteins in tissue sections. METHODS: In the present study, we analyzed an in-house compiled tissue microarray (n = 60) comprising CRCs and control tissues by IMS. After obtaining protein profiles through direct analysis of tissue sections, two validation sets were used for immunohistochemical evaluation. RESULTS: A total of 28 m/z values in the mass range 800-3500 Da distinguished euploid from aneuploid CRCs (p < 0.001, ROC AUC values < 0.385 or > 0.635). After liquid chromatograph-mass spectrometry identification, UBE2N could be successfully validated by immunohistochemistry in the initial sample cohort (p = 0.0274, ROC AUC = 0.7937) and in an independent sample set of 90 clinical specimens (p = 0.0070, ROC AUC = 0.6957). CONCLUSIONS: The results showed that FFPE protein expression profiling of surgically resected CRC tissue extracts by MALDI-TOF MS has potential value for improved molecular classification. Particularly, the protein expression of UBE2N was validated in an independent clinical cohort to distinguish euploid from aneuploid CRCs.

Structural insights into the nanomolar affinity of RING E3 ligase ZNRF1 for Ube2N and its functional implications.

RING (Really Interesting New Gene) domains in ubiquitin RING E3 ligases exclusively engage ubiquitin (Ub)-loaded E2s to facilitate ubiquitination of their substrates. Despite such specificity, all RINGs characterized till date bind unloaded E2s with dissociation constants (Kds) in the micromolar to the sub-millimolar range. Here, we show that the RING domain of E3 ligase ZNRF1, an essential E3 ligase implicated in diverse cellular pathways, binds Ube2N with a Kd of ∼50 nM. This high-affinity interaction is exclusive for Ube2N as ZNRF1 interacts with Ube2D2 with a Kd of ∼1 µM, alike few other E3s. The crystal structure of ZNRF1 C-terminal domain in complex with Ube2N coupled with mutational analyses reveals the molecular basis of this unusual affinity. We further demonstrate that the ubiquitination efficiency of ZNRF1 : E2 pairs correlates with their affinity. Intriguingly, as a consequence of its high E2 affinity, an excess of ZNRF1 inhibits Ube2N-mediated ubiquitination at concentrations ≥500 nM instead of showing enhanced ubiquitination. This suggests a novel mode of activity regulation of E3 ligases and emphasizes the importance of E3-E2 balance for the optimum activity. Based on our results, we propose that overexpression-based functional analyses on E3 ligases such as ZNRF1 must be approached with caution as enhanced cellular levels might result in aberrant modification activity.

Sequential ubiquitination and deubiquitination enzymes synchronize the dual sensor and effector functions of TRIM21.

Tripartite motif (TRIM) 21 is a cytosolic antibody receptor that neutralizes antibody-coated viruses that penetrate the cell and simultaneously activates innate immunity. Here we show that the conjugation of TRIM21 with K63-linked ubiquitin (Ub-(63)Ub) catalyzed by the sequential activity of nonredundant E2 Ub enzymes is required for its dual antiviral functions. TRIM21 is first labeled with monoubiquitin (monoUb) by the E2 Ube2W. The monoUb is a substrate for the heterodimeric E2 Ube2N/Ube2V2, resulting in TRIM21-anchored Ub-(63)Ub. Depletion of either E2 abolishes Ub-(63)Ub and Ub-(48)Ub conjugation of TRIM21, NF-κB signaling, and virus neutralization. The formation of TRIM21-Ub-(63)Ub precedes proteasome recruitment, and we identify an essential role for the 19S-resident and degradation-coupled deubiquitinase Poh1 in TRIM21 neutralization, signaling, and cytokine induction. This study elucidates a complex mechanism of step-wise ubiquitination and deubiquitination activities that allows contemporaneous innate immune signaling and neutralization by TRIM21.

UBE2N promotes cell viability and glycolysis by promoting Axin1 ubiquitination in prostate cancer cells.

BACKGROUND: Ubiquitin-conjugating enzyme E2 N (UBE2N) is recognized in the progression of some cancers; however, little research has been conducted to describe its role in prostate cancer. The purpose of this paper is to explore the function and mechanism of UBE2N in prostate cancer cells. METHODS: UBE2N expression was detected in Cancer Genome Atlas Prostate Adenocarcinoma (TCGA-PRAD) data, prostate cancer tissue microarrays, and prostate cancer cell lines, respectively. UBE2N knockdown or overexpression was used to analyze its role in cell viability and glycolysis of prostate cancer cells and tumor growth. XAV939 or Axin1 overexpression was co-treated with UBE2N overexpression to detect the involvement of the Wnt/ß-catenin signaling and Axin1 in the UBE2N function. UBE2N interacting with Axin1 was analyzed by co-immunoprecipitation assay. RESULTS: UBE2N was upregulated in prostate cancer and the UBE2N-high expression correlated with the poor prognosis of prostate cancer. UBE2N knockdown inhibited cell viability and glycolysis in prostate cancer cells and restricted tumor formation in tumor-bearing mice. Wnt/ß-catenin inhibition and Axin1 overexpression reversed the promoting viability and glycolysis function of UBE2N. UBE2N promoted Axin1 ubiquitination and decreased Axin1 protein level.

TAF15 inhibits p53 nucleus translocation and promotes HCC cell 5-FU resistance via post-transcriptional regulation of UBE2N.

Chemotherapy resistance is an important factor responsible for the low 5-year survival rate of hepatocellular carcinoma (HCC) patients. Ubiquitin-conjugating enzyme E2N (UBE2N) is a cancer-associated ubiquitin-conjugating enzyme that is expressed in HCC tissues, and its high expression is associated with a poor prognosis. This study explored the role played by UBE2N in development of 5-fluorouracil (5-FU) resistance in HCC cells. Three HCC cell lines (HepG2 [p53 wild type], Huh7 [p53 point mutant type], Hep3B [p53 non-expression type]), and one normal liver cell line (MIHA) were used in our present study. The IC50 value of 5-FU was determined using a cell counting kit-8 (CCK-8) assay. Cell viability was assessed by colony formation assays. TUNEL assays and flow cytometry were used to analyze cell apoptosis. RNA pull-down and RNA immunoprecipitation (RIP) assays were performed to confirm the binding relationship between UBE2N mRNA and TAF15 protein. Our results showed that TAF15 and UBE2N were highly expressed in HCC cells. UBE2N inhibited the translocation of p53 protein into the cell nucleus to increase 5-FU resistance, as reflected by an increased IC50 value, an increase in cell viability, and a reduction in cell apoptosis. Overexpression of p53 reduced 5-FU resistance, but that effect could be reversed by UBE2N overexpression. TAF15 protein bound to and stabilized UBE2N mRNA, thereby inhibiting p53 translocation into the nucleus and promoting 5-FU resistance in HCC cells. Collectively, our present study identified a novel mechanism by which TAF15/UBE2N regulates p53 distribution to increase 5-FU resistance. Our results also suggest potential therapeutic strategies for treating HCC.

UBE2N Is Essential for Maintenance of Skin Homeostasis and Suppression of Inflammation.

UBE2N, a Lys63 ubiquitin-conjugating enzyme, plays critical roles in embryogenesis and immune system development and function. However, its roles in adult epithelial tissue homeostasis and pathogenesis are unclear. We generated conditional mouse models that deleted Ube2n in skin cells in a temporally and spatially controlled manner. We found that Ube2n knockout in the adult skin keratinocytes induced a range of inflammatory skin defects characteristic of psoriatic and actinic keratosis. These included inflammation, epidermal and dermal thickening, parakeratosis, and increased immune cell infiltration as well as signs of edema and blistering. Single-cell transcriptomic analyses and RT-qPCR showed that Ube2n-knockout keratinocytes expressed elevated myeloid cell chemoattractants such as Cxcl1 and Cxcl2 and decreased the homeostatic T lymphocyte chemoattractant Ccl27a. Consistently, the infiltrating immune cells were predominantly myeloid-derived cells, including neutrophils and M1-like macrophages, which expressed high levels of inflammatory cytokines such as Il1ß and Il24. Pharmacological blockade of the IL-1 receptor associated kinases (IRAK1/4) alleviated inflammation, epidermal and dermal thickening, and immune infiltration of the Ube2n-mutant skin. Together, these findings highlight a key role of keratinocyte UBE2N in maintenance of epidermal homeostasis and skin immunity and identify IRAK1/4 as potential therapeutic target for inflammatory skin disorders.

Validating the temporal performance of genetic biomarkers in an animal model of recurrence/ non-recurrence myocardial infarction persuades by bioinformatics tools.

With a global towering prevalence of index acute myocardial infarction (nonrecurrent MI, NR-MI), a high incidence of recurrent MI (R-MI) has emerged in recent decades. Despite the extensive occurrence, the promising predictors of R-MI have been elusive within the cohort of survivors. This study investigates and validates the involvement of distinct gene expressions in R-MI and NR-MI. Bioinformatics tools were used to identify DEGs from the GEO dataset, functional annotation, pathway enrichment analysis, and the PPI network analysis to find hub genes. The validation of proposed genes was conceded by qRT-PCR and Western Blot analysis in experimentally induced NR-MI and R-MI models on a temporal basis. The temporal findings based on RT-PCR consequences reveal a significant and constant upregulation of the UBE2N in the NR-MI model out of the proposed three DEGs (UBE2N, UBB, and TMEM189), while no expression was reported in the R-MI model. Additionally, the proteomics study proposed five DEGs (IL2RB, NKG7, GZMH, CXCR6, and GZMK) for the R-MI model since IL2RB was spotted for significant and persistent downregulation with different time points. Further, Western Blot analysis validated these target genes' expressions temporally. I/R-induced NR-MI and R-MI models were confirmed by the biochemical parameters (CKMB, LDH, cTnI, serum nitrite/nitrate concentration, and inflammatory cytokines) and histological assessments of myocardial tissue. These results underscore the importance of understanding genetic mechanisms underlying MI and highlight the potential of UBE2N and IL2RB as biomarkers for non-recurrent and recurrent MI, respectively.

Integrative experimental validation of concomitant miRNAs and transcription factors with differentially expressed genes in acute myocardial infarction.

Identification of concomitant miRNAs and transcription factors (TFs) with differential expression (DEGs) in MI is crucial for understanding holistic gene regulation, identifying key regulators, and precision in biomarker and therapeutic target discovery. We performed a comprehensive analysis using Affymetrix microarray data, advanced bioinformatic tools, and experimental validation to explore potential biomarkers associated with human pathology. The search strategy includes the identification of the GSE83500 dataset, comprising gene expression profiles from aortic wall punch biopsies of MI and non-MI patients, which were used in the present study. The analysis identified nine distinct genes exhibiting DEGs within the realm of MI. miRNA-gene/TF and TF-gene/miRNA regulatory relations were mapped to retrieve interacting hub genes to acquire an MI miRNA-TF co-regulatory network. Furthermore, an animal model of I/R-induced MI confirmed the involved gene based on quantitative RT-PCR and Western blot analysis. The consequences of the bioinformatic tool substantiate the inference regarding the presence of three key hub genes (UBE2N, TMEM106B, and CXADR), a central miRNA (hsa-miR-124-3p), and sixteen TFs. Animal studies support the involvement of predicted genes in the I/R-induced myocardial infarction assessed by RT-PCR and Western blotting. Thus, the final consequences suggest the involvement of promising molecular pathways regulated by TF (p53/NF-κB1), miRNA (hsa-miR-124-3p), and hub gene (UBE2N), which may play a key role in the pathogenesis of MI.

SP1 transcriptionally regulates UBE2N expression to promote lung adenocarcinoma progression.

Lung adenocarcinoma (LUAD) is the main cause of cancer-related death worldwide. Understanding the mechanisms of LUAD progression may provide insights into targeted therapy approaches for this malignancy. Ubiquitin-conjugating enzyme 2 N (UBE2N) has been demonstrated to play key roles in the progression of various cancers. However, the functions and mechanisms underlying UBE2N expression in LUAD are still unclear. In this study, we found that UBE2N is highly expressed in LUAD and patients with high UBE2N expression in their tumors have poor clinical outcomes. Moreover, we showed that UBE2N interference significantly inhibited LUAD progression in vitro and in vivo. At the molecular level, we demonstrated that the UBE2N is a bona fide target of transcription factor SP1. SP1 directly bound to the promoter of UBE2N and upregulated its expression in LUAD cells, which in turn contributed to the progression of LUAD. Furthermore, we found that there is a strong positive correlation between the expression of SP1 and UBE2N in LUAD samples. Importantly, LUAD patients with concomitantly high expression of SP1 and UBE2N were significantly associated with poor clinical outcomes. In conclusion, our study demonstrated that the SP1-UBE2N signaling axis might play a key role in the malignant progression of LUAD, which provides new targets and strategies for the treatment of LUAD.

ALDOC promotes non-small cell lung cancer through affecting MYC-mediated UBE2N transcription and regulating Wnt/ß-catenin pathway.

Despite advancements in therapeutic options, the overall prognosis for non-small cell lung cancer (NSCLC) remains poor. Therefore, it is crucial to further explore the etiology and targets for novel treatments to effectively manage NSCLC. In this study, immunohistochemistry was used to analyze the expression of aldolase, fructose-bisphosphate C (ALDOC) protein in tumor tissues and adjacent non-malignant tissues from 79 NSCLC patients. Our findings revealed that ALDOC was overexpressed in NSCLC tissues. ALDOC expression was associated with lymph node metastasis, lymphatic metastasis and pathological stage. In addition, Kaplan-Meier analysis showed that higher ALDOC levels were indicative of a poorer prognosis. Additionally, we observed elevated ALDOC mRNA levels in NSCLC cell lines relative to normal cells. To investigate the functional roles of ALDOC, we infected cells with small interfering RNA against ALDOC, which led to attenuated proliferation and migration, as well as ameliorated apoptosis. Furthermore, through our investigations, we discovered that ubiquitin-conjugating enzyme E2N (UBE2N) acts as a downstream factor of ALDOC. ALDOC promoted NSCLC through affecting MYC-mediated UBE2N transcription and regulating the Wnt pathway. More importantly, we found that downregulation of UBE2N or the use of Wnt pathway inhibitor could reverse the promoting effects of ALDOC elevation on NSCLC development in vitro and in vivo. Based on these findings, our study highlights the potential of ALDOC as a future therapeutic target for NSCLC.

Ube2N is present and functions within listeria Actin-rich structures and lamellipodia: A localization and pharmacological inhibition study.

The actin cytoskeleton forms much of the structure needed for the intracellular motility of an assortment of microbes as well as entire cells. The co-factor to the ubiquitin conjugating enzyme Ube2N (Ube2V1) has been implicated in both cancer cell metastasis and lysine-63 ubiquitylation of ß actin. As this protein complexes with Ube2N, we sought to investigate whether Ube2N itself was involved in actin-based events occurring during the Listeria monocytogenes infections as well as within motile whole cells. Through examination of L. monocytogenes actin clouds, comet tails and membrane protrusions as well as lamellipodia in migrating cells, we show that Ube2N is recruited to actin-rich structures. When pharmacologically inhibited we demonstrate that Ube2N is crucial for the function of actin-rich structures when associated with the plasma membrane.

UBE2N is essential for maintenance of skin homeostasis and suppression of inflammation.

UBE2N, a Lys63-ubiquitin conjugating enzyme, plays critical roles in embryogenesis and immune system development and function. However, its roles in adult epithelial tissue homeostasis and pathogenesis are unclear. We generated conditional mouse models that deleted Ube2n in skin cells in a temporally and spatially controlled manner. We found that Ube2n-knockout (KO) in the adult skin keratinocytes induced a range of inflammatory skin defects characteristic of psoriatic and actinic keratosis. These included eczematous inflammation, epidermal and dermal thickening, parakeratosis, and increased immune cell infiltration, as well as signs of edema and blistering. Single cell transcriptomic analyses and RT-qPCR showed that Ube2n KO keratinocytes expressed elevated myeloid cell chemo-attractants such as Cxcl1 and Cxcl2 and decreased the homeostatic T lymphocyte chemo-attractant, Ccl27a. Consistently, the infiltrating immune cells of Ube2n-KO skin were predominantly myeloid-derived cells including neutrophils and M1-like macrophages that were highly inflammatory, as indicated by expression of Il1ß and Il24. Pharmacological blockade of the IL-1 receptor associated kinases (IRAK1/4) alleviated eczema, epidermal and dermal thickening, and immune infiltration of the Ube2n mutant skin. Together, these findings highlight a key role of keratinocyte-UBE2N in maintenance of epidermal homeostasis and skin immunity and identify IRAK1/4 as potential therapeutic target for inflammatory skin disorders.

CRISPR-Cas9 knockout screen identifies novel treatment targets in childhood high-grade glioma.

BACKGROUND: Brain tumours are the leading cause of cancer-related death in children, and there is no effective treatment. A growing body of evidence points to deregulated epigenetics as a tumour driver, particularly in paediatric cancers as they have relatively few genomic alterations, and key driver mutations have been identified in histone 3 (H3). Cancer stem cells (CSC) are implicated in tumour development, relapse and therapy resistance and thus particularly important to target. We therefore aimed to identify novel epigenetic treatment targets in CSC derived from H3-mutated high-grade glioma (HGG) through a CRISPR-Cas9 knockout screen. RESULTS: The knockout screen identified more than 100 novel genes essential for the growth of CSC derived from paediatric HGG with H3K27M mutation. We successfully validated 12 of the 13 selected hits by individual knockout in the same two CSC lines, and for the top six hits we included two additional CSC lines derived from H3 wild-type paediatric HGG. Knockout of these genes led to a significant decrease in CSC growth, and altered stem cell and differentiation markers. CONCLUSIONS: The screen robustly identified essential genes known in the literature, but also many novel genes essential for CSC growth in paediatric HGG. Six of the novel genes (UBE2N, CHD4, LSM11, KANSL1, KANSL3 and EED) were validated individually thus demonstrating their importance for CSC growth in H3-mutated and wild-type HGG. These genes should be further studied and evaluated as novel treatment targets in paediatric HGG.

Echinococcus multilocularis infection induces UBE2N suppression via exosomal emu-miR-4989.

Echinococcus multilocularis metacestodes mainly reside in liver in humans and animals, and cause serious damages. UBE2N was herein shown to be downregulated in response to the infection. UBE2N was further shown to be predominantly expressed in the hepatocytes, which was also significantly downregulated during the infection. UBE2N was a target of emu-miR-4989, which was loaded into the exosomes secreted by parasites. These emu-miR-4989-encapsulating exosomes were internalized by hepatocytes, and induced a significant decrease of relative luciferase activity in the cells transfected with the construct containing a wild type of UBE2N 3'-UTR compared to the control (p < 0.05). These results demonstrate that emu-miR-4989 is involved in the UBE2N inhibition in the hepatocytes during E. multilocularis through exosomes.

Cytoplasmic TDP-43 impairs the activity of the ubiquitin-proteasome system.

The cytoplasmic inclusions of nuclear TAR DNA-binding protein 43 (TDP-43) are a pathologic hallmark in amyotrophic lateral sclerosis (ALS), frontotemporal lobar degeneration (FTD), and other neurological disorders. We reported that expressing mutant TDP-43(M337V) in rhesus monkeys can mimic the cytoplasmic mislocalization of mutant TDP-43 seen in patient brains. Here we investigated how cytoplasmic mutant TDP-43 mediates neuropathology. We found that C-terminal TDP-43 fragments are primarily localized in the cytoplasm and that the age-dependent elevated UBE2N promotes the accumulation of cytoplasmic C-terminal TDP-43 via K63 ubiquitination. Immunoprecipitation and mass spectrometry revealed that cytoplasmic mutant TDP-43 interacts with proteasome assembly proteins PSMG2 and PSD13, which might lead to the impairment of the proteasomal activity. Our findings suggest that cytoplasmic TDP-43 may participate in age-dependent accumulation of misfolded proteins in the brain by inhibiting the UPS activity.

Immune regulator LGP2 targets Ubc13/UBE2N to mediate widespread interference with K63 polyubiquitination and NF-κB activation.

Lysine 63-linked polyubiquitin (K63-Ub) chains activate a range of cellular immune and inflammatory signaling pathways, including the mammalian antiviral response. Interferon and antiviral genes are triggered by TRAF family ubiquitin ligases that form K63-Ub chains. LGP2 is a feedback inhibitor of TRAF-mediated K63-Ub that can interfere with diverse immune signaling pathways. Our results demonstrate that LGP2 inhibits K63-Ub by association with and sequestration of the K63-Ub-conjugating enzyme, Ubc13/UBE2N. The LGP2 helicase subdomain, Hel2i, mediates protein interaction that engages and inhibits Ubc13/UBE2N, affecting control over a range of K63-Ub ligase proteins, including TRAF6, TRIM25, and RNF125, all of which are inactivated by LGP2. These findings establish a unifying mechanism for LGP2-mediated negative regulation that can modulate a variety of K63-Ub signaling pathways.