Nedd4 and Nedd4-2: ubiquitin ligases at work in the neuron

Angiotensin-Converting Enzyme 2 Posttranslational Modifications and Implications for Hypertension and SARS-CoV-2: 2023 Lewis K. Dahl Memorial Lecture

ACE2 (angiotensin-converting enzyme 2), a multifunctional transmembrane protein, is well recognized as an important member of the (RAS) renin-angiotensin system with important roles in the regulation of cardiovascular function by opposing the harmful effects of Ang-II (angiotensin II) and AT1R (Ang-II type 1 receptor) activation. More recently, ACE2 was found to be the entry point for the SARS-CoV-2 virus into cells, causing COVID-19. This finding has led to an exponential rise in the number of publications focused on ACE2, albeit these studies often have opposite objectives to the preservation of ACE2 in cardiovascular regulation. However, notwithstanding accumulating data of the role of ACE2 in the generation of angiotensin-(1-7) and SARS-CoV-2 internalization, numerous other putative roles of this enzyme remain less investigated and not yet characterized. Currently, no drug modulating ACE2 function or expression is available in the clinic, and the development of new pharmacological tools should attempt targeting each step of the lifespan of the protein from synthesis to degradation. The present review expands on our presentation during the 2023 Lewis K. Dahl Memorial Lecture Sponsored by the American Heart Association Council on Hypertension. We provide a critical summary of the current knowledge of the mechanisms controlling ACE2 internalization and intracellular trafficking, the mutual regulation with GPCRs (G-protein-coupled receptors) and other proteins, and posttranslational modifications. A major focus is on ubiquitination which has become a critical step in the modulation of ACE2 cellular levels.

Inhibition of SENP5 reduces brain injury in TBI rats by regulating NEDD4L/TCF3 axis

BACKGROUND

The underlying mechanism of SENP5 influences neuronal regeneration and apoptosis in the context of TBI remains largely unexplored.

METHODS

In the present study, PC12 cells treated with scratch for 24 h were regarded as a TBI cell model. The expression of SENP5 in PC12 cells was measured via Quantitative Real-Time PCR (qRT-PCR) and western blot assays. Cell Counting Kit 8 (CCK-8) and Flow cytometry assays were used to evaluate the activity of TBI cells. In addition, we assessed the effect of inhibiting SENP5 in vivo on neurological function deficits and apoptosis in the hippocampal tissues of TBI rats. The relationship between SENP5 and NEDD4L/TCF3 axis was proved via immunoprecipitation (IP) and double luciferase assays.

RESULTS

Following TBI cell modeling, an increase in SENP5 expression has been found. Moreover, TBI modeling resulted in reduced cell viability and increased apoptosis, which was rescue by inhibition of SENP5. In vivo experiments demonstrated that SENP5 inhibition could mitigate TBI-induced brain injury in rats. Specifically, this inhibition led to lower neurological impairment scores, improved neuronal morphology and structure, and decreased neuronal apoptosis. In addition, NEDD4L has been proved to be relevant to the enhanced stability of the transcription factor TCF3, which in turn promoted the expression of SENP5.

CONCLUSIONS

This study reveals that inhibiting SENP5 can alleviate brain injury following TBI. NEDD4L/TCF3 axis can regulate the expression of SENP5 to affect the development of TBI. However, SENP5 regulates downstream targets of TBI and important mechanisms need to be further explored.

Chronic social defeat stress induces the down-regulation of the Nedd4L-GLT-1 ubiquitination pathway in the prefrontal cortex of mice

Stressful life events contribute to the onset of major depressive disorder (MDD). We recently demonstrated abnormalities in ubiquitination in the pathophysiology of MDD. However, the underlying molecular mechanisms remain unclear. We investigated the involvement of the ubiquitination system-mediated glutamatergic dysfunction in social impairment induced by chronic social defeat stress (CSDS). Adult C57BL/6J mice were exposed to aggressor ICR male mice for 10 consecutive days. Social impairment was induced by CSDS in the social interaction test 1 days after the last stress exposure. In terms of brain microdialysis, CSDS reduced depolarization-evoked glutamate release in the prefrontal cortex (PFC), which was reversed by a glutamate transporter 1 (GLT-1) inhibitor. Interestingly, the expression of ubiquitinated, but not total GLT-1, was decreased in the PFC of mice exposed to CSDS. The expression of neural precursor cells expressing developmentally downregulated gene 4-like (Nedd4L: E3 ligase for GLT-1), and ubiquitin-conjugating enzyme E2D2 (Ube2d2: E2 ubiquitin-conjugating enzyme for Nedd4L) was also reduced in CSDS mice. Furthermore, the downregulation of the Nedd4L-GLT-1 ubiquitination pathway decreased SIT ratio, but up-regulation increased it even in non-CSDS mice. Taken together, the decrease in GLT-1 ubiquitination may reduce the release of extracellular glutamate induced by high-potassium stimulation, which may lead to social impairment, while we could not find differences in GLT-1 ubiquitination between susceptible and resistant CSDS mice. In conclusion, GLT-1 ubiquitination could play a crucial role in the pathophysiology of MDD and is an attractive target for the development of novel antidepressants.

METTL3 regulates TFRC ubiquitination and ferroptosis through stabilizing NEDD4L mRNA to impact stroke

BACKGROUND

Stroke is a major medical problem, and novel therapeutic targets are urgently needed. This study investigates the protective role and potential mechanisms of the N6-methyladenosine (m6A) RNA methyltransferase METTL3 against cerebral injury resulting from insufficient cerebral blood flow.

METHODS

In this study, we constructed mouse MCAO models and HT-22 cell OGD/R models to mimic ischemic stroke-induced brain injury and neuronal damage. We generated NEDD4L knockout and METTL3 overexpression models and validated therapeutic effects using infarct volume, brain edema, and neurologic scoring. We performed qRT-PCR, western blotting, and co-immunoprecipitation to assess the influence of NEDD4L on ferroptosis markers and TFRC expression. We verified the effect of NEDD4L on TFRC ubiquitination by detecting half-life and ubiquitination. Finally, we validated the impact of METTL3 on NEDD4L mRNA stability and MCAO outcomes in both in vitro and in vivo experimental models.

RESULT

We find NEDD4L expression is downregulated in MCAO models. Overexpressing METTL3 inhibits the iron carrier protein TFRC by upregulating the E3 ubiquitin ligase NEDD4L, thereby alleviating oxidative damage and ferroptosis to protect the brain from ischemic injury. Mechanistic studies show METTL3 can methylate and stabilize NEDD4L mRNA, enhancing NEDD4L expression. As a downstream effector, NEDD4L ubiquitinates and degrades TFRC, reducing iron accumulation and neuronal ferroptosis.

CONCLUSION

In summary, we uncover the METTL3-NEDD4L-TFRC axis is critical for inhibiting post-ischemic brain injury. Enhancing this pathway may serve as an effective strategy for stroke therapy. This study lays the theoretical foundation for developing m6A-related therapies against ischemic brain damage.

Genome-wide study of longitudinal brain imaging measures of multiple sclerosis progression across six clinical trials

While the genetics of MS risk susceptibility are well-described, and recent progress has been made on the genetics of disease severity, the genetics of disease progression remain elusive. We therefore investigated the genetic determinants of MS progression on longitudinal brain MRI: change in brain volume (BV) and change in T2 lesion volume (T2LV), reflecting progressive tissue loss and increasing disease burden, respectively. We performed genome-wide association studies of change in BV (N = 3401) and change in T2LV (N = 3513) across six randomized clinical trials from Biogen and Roche/Genentech: ADVANCE, ASCEND, DECIDE, OPERA I & II, and ORATORIO. Analyses were adjusted for randomized treatment arm, age, sex, and ancestry. Results were pooled in a meta-analysis, and were evaluated for enrichment of MS risk variants. Variant colocalization and cell-specific expression analyses were performed using published cohorts. The strongest peaks were in PTPRD (rs77321193-C/A, p = 3.9 × 10-7) for BV change, and NEDD4L (rs11398377-GC/G, p = 9.3 × 10-8) for T2LV change. Evidence of colocalization was observed for NEDD4L, and both genes showed increased expression in neuronal and/or glial populations. No association between MS risk variants and MRI outcomes was observed. In this unique, precompetitive industry partnership, we report putative regions of interest in the neurodevelopmental gene PTPRD, and the ubiquitin ligase gene NEDD4L. These findings are distinct from known MS risk genetics, indicating an added role for genetic progression analyses and informing drug discovery.

Associations of genetic variations in NEDD4L with salt sensitivity, blood pressure changes and hypertension incidence in Chinese adults

Neural precursor cell expressed developmentally downregulated 4-like (NEDD4L), a member of the E3 ubiquitin-protein ligases, encoded by NEDD4L gene, was found to be involved in in salt sensitivity by regulating sodium reabsorption in salt-sensitive rats. The authors aimed to explore the associations of NEDD4L genetic variants with salt sensitivity, blood pressure (BP) changes and hypertension incidence in Chinese adults. Participants from 124 families in Northern China in the Baoji Salt-Sensitive Study Cohort in 2004, who received the chronic salt intake intervention, including a 7-day low-salt diet (3.0 g/day) and a 7-day high-salt diet (18 g/day), were analyzed. Besides, the development of hypertension over 14 years was evaluated. NEDD4L single nucleotide polymorphism (SNP) rs74408486 was shown to be significantly associated with systolic BP (SBP), diastolic BP (DBP) and mean arterial pressure (MAP) responses to low-salt diet, while SNPs rs292449 and rs2288775 were significantly associated with pulse pressure (PP) response to high-salt diet. In addition, SNP rs4149605, rs73450471, and rs482805 were significantly associated with the longitudinal changes in SBP, DBP, MAP, or PP at 14 years of follow-up. SNP rs292449 was significantly associated with hypertension incidence over the 14-year follow-up. Finally, this gene-based analysis found that NEDD4L was significantly associated with longitudinal BP changes and the incidence of hypertension over the 14-year follow-up. This study indicated that gene polymorphism in NEDD4L serve an important function in salt sensitivity, longitudinal BP change and development of hypertension in the Chinese population.

Genome-wide analysis of genes encoding core components of the ubiquitin system during cerebral cortex development

Ubiquitination involves three types of enzymes (E1, E2, and E3) that sequentially attach ubiquitin (Ub) to target proteins. This posttranslational modification controls key cellular processes, such as the degradation, endocytosis, subcellular localization and activity of proteins. Ubiquitination, which can be reversed by deubiquitinating enzymes (DUBs), plays important roles during brain development. Furthermore, deregulation of the Ub system is linked to the pathogenesis of various diseases, including neurodegenerative disorders. We used a publicly available RNA-seq database to perform an extensive genome-wide gene expression analysis of the core components of the ubiquitination machinery, covering Ub genes as well as E1, E2, E3 and DUB genes. The ubiquitination network was governed by only Uba1 and Ube2m, the predominant E1 and E2 genes, respectively; their expression was positively regulated during cortical formation. The principal genes encoding HECT (homologous to the E6-AP carboxyl terminus), RBR (RING-in-between-RING), and RING (really interesting new gene) E3 Ub ligases were also highly regulated. Pja1, Dtx3 (RING ligases) and Stub1 (U-box RING) were the most highly expressed E3 Ub ligase genes and displayed distinct developmental expression patterns. Moreover, more than 80 DUB genes were expressed during corticogenesis, with two prominent genes, Uch-l1 and Usp22, showing highly upregulated expression. Several components of the Ub system overexpressed in cancers were also highly expressed in the cerebral cortex under conditions not related to tumour formation or progression. Altogether, this work provides an in-depth overview of transcriptomic changes during embryonic formation of the cerebral cortex. The data also offer new insight into the characterization of the Ub system and may contribute to a better understanding of its involvement in the pathogenesis of neurodevelopmental disorders.

CFDP1 promotes hepatocellular carcinoma progression through activating NEDD4/PTEN/PI3K/AKT signaling pathway

BACKGROUND AND AIMS

It is being increasingly reported that the Cranio Facial Development Protein 1 (CFDP1) plays a significant role in the onset and progression of tumors. Nonetheless, the underlying mechanisms associated with CFDP1 that contribute to hepatocellular carcinoma (HCC) and the specific biological role of CFDP1 remain vague.

METHODS

The Gene Expression Omnibus (GEO) database was analyzed to obtain the gene expression profiles as well as the matching clinical data of HCC patients. The gene co-expression network was developed by means of weighted gene co-expression network analysis (WGCNA) to screen for possible biomarkers that could be used for the purpose of predicting prognosis. The Cancer Genome Atlas (TCGA) and Gene Expression Profile Interaction Analysis (GEPIA) databases were used to assess the relationship between survival and expression. In addition, we identified the underlying mechanism associated with CFDP1 by analyzing the KEGG pathway database, applying the GSEA and GeneCards analysis method. We performed a sequence of experiments (in vivo and in vitro) for the purpose of investigating the specific function of CFDP1 in liver cancer.

RESULTS

The obtained results revealed high expression of CFDP1 in HCC tissues and cell lines. A positive correlation between the overexpression of CFDP1 and the adverse clinicopathological features was observed. Moreover, we observed that the low recurrence-free survival and overall survival were associated with CFDP1 overexpression. In addition, GeneCards and GSEA analysis showed that CFDP1 may interact with NEDD4 and participate in PTEN regulation. Meanwhile, CFDP1 can promote the malignant development of liver cancer in vivo and in vitro. The western blotting technique was also employed so as to examine the samples, and the findings demonstrated that CFDP1 enhanced the malignancy of HCC via the NEDD4-mediated PTEN/PI3K/AKT pathway.

CONCLUSION

We highlighted that CFDP1 played an oncogenic role in HCC and was identified as a possible clinical prognostic factor and a potential novel therapeutic target for HCC.

The Role of NEDD4 E3 Ubiquitin–Protein Ligases in Parkinson’s Disease

Parkinson’s disease (PD) is a debilitating neurodegenerative disease that causes a great clinical burden. However, its exact molecular pathologies are not fully understood. Whilst there are a number of avenues for research into slowing, halting, or reversing PD, one central idea is to enhance the clearance of the proposed aetiological protein, oligomeric α-synuclein. Oligomeric α-synuclein is the main constituent protein in Lewy bodies and neurites and is considered neurotoxic. Multiple E3 ubiquitin-protein ligases, including the NEDD4 (neural precursor cell expressed developmentally downregulated protein 4) family, parkin, SIAH (mammalian homologues of Drosophila seven in absentia), CHIP (carboxy-terminus of Hsc70 interacting protein), and SCFFXBL5 SCF ubiquitin ligase assembled by the S-phase kinase-associated protein (SKP1), cullin-1 (Cul1), a zinc-binding RING finger protein, and the F-box domain/Leucine-rich repeat protein 5-containing protein FBXL5), have been shown to be able to ubiquitinate α-synuclein, influencing its subsequent degradation via the proteasome or lysosome. Here, we explore the link between NEDD4 ligases and PD, which is not only via α-synuclein but further strengthened by several additional substrates and interaction partners. Some members of the NEDD4 family of ligases are thought to crosstalk even with PD-related genes and proteins found to be mutated in familial forms of PD. Mutations in NEDD4 family genes have not been observed in PD patients, most likely because of their essential survival function during development. Following further in vivo studies, it has been thought that NEDD4 ligases may be viable therapeutic targets in PD. NEDD4 family members could clear toxic proteins, enhancing cell survival and slowing disease progression, or might diminish beneficial proteins, reducing cell survival and accelerating disease progression. Here, we review studies to date on the expression and function of NEDD4 ubiquitin ligases in the brain and their possible impact on PD pathology.

E3 ubiquitin ligase Nedd4-2 exerts neuroprotective effects during endoplasmic reticulum stress

The neural precursor cell expressed developmentally down-regulated protein 4-like (Nedd4-2) is an E3 ubiquitin ligase critical for neurodevelopment and homeostasis of neural circuit excitability. While dysregulation of Nedd4-2 has been linked to elevated seizure susceptibility through impaired ubiquitination of multiple direct substrates, it remains largely unclear whether Nedd4-2 interconnects other cellular pathways that affect neuronal activity and seizure susceptibility. Here, we first showed that Nedd4-2 associates with the endoplasmic reticulum (ER) and regulates the expression of multiple ER-resident proteins. Furthermore, utilizing Nedd4-2 conditional knockout mice, we showed that Nedd4-2 is required for the maintenance of spontaneous neural activity and excitatory synapses following the induction of ER stress. When analyzing activation of the canonical pathways of ER stress response, we found that Nedd4-2 is required for phosphorylation of eIF2α. While phosphorylation of eIF2α has been shown to reduce seizure susceptibility, attempts to facilitate phosphorylation of eIF2α in Nedd4-2 conditional knockout mice failed to produce such a beneficial function, suggesting a role for Nedd4-2 in integrating the ER stress response to modulate seizure susceptibility. Altogether, our study demonstrates neuroprotective functions of Nedd4-2 during ER stress in neurons and could provide insight into neurological diseases in which the expression or activity of Nedd4-2 is impaired.

MEKK5 Interacts with and Negatively Regulates the E3 Ubiquitin Ligase NEDD4 for Mediating Lung Cancer Cell Migration

Our previous studies have shown that the HECT E3 ubiquitin ligase NEDD4 and kinase MEKK5 both play an essential role in lung cancer migration. A report predicts that MEKK5 may be ubiquitinated by NEDD4; however, interaction of MEKK5 with NEDD4 and ubiquitination of MEKK5 by NEDD4 have not been characterized. In this report, we show that NEDD4 interacts with MEKK5 through a conserved WW3 domain by the co-immunoprecipitation and the GST-pulldown assays. The ubiquitination assay indicates that MEKK5 is not a ubiquitination substrate of NEDD4, but negatively regulates NEDD4-mediated ubiquitination. Furthermore, overexpression of MEKK5 significantly reduced the NEDD4-promoted lung cancer cell migration. Taken together, our studies have defined an inhibitory role of MEKK5 in regulation of NEDD4-mediated ubiquitination.

Pan-cancer Analysis of NEDD4L and Its Tumor Suppressor Effects in Clear Cell Renal Cell Carcinoma

The expression level of NEDD4L, an E3 ubiquitin ligase, has changed significantly in human cancers. In this study, we aimed to study the expression of NEDD4L in pan-carcinoma and its function in malignant tumors. We analyzed the gene expression level of NEDD4L in pan-cancer from The Cancer Genome Atlas (TCGA) microarray data set, the correlation between gene expression and overall survival, disease-specific survival, and tumor immune microenvironment changes. NEDD4L expression changes in half of the cancer types. Low expression of NEDD4L gene predicts poor overall survival and disease-specific survival (DSS) in renal clear cell carcinoma (KIRC) and renal chromophobe cell carcinoma (KIRP). NEDD4L is negatively related to interstitial cell infiltration and immune cell infiltration in most common cancers. Furthermore, the low expression of NEDD4L was verified in our clear cell renal cell carcinoma (ccRCC) clinical tissues. In ccRCC cells, NEDD4L overexpression significantly reduced cell proliferation and migration. In the functional analysis, we proved that NEDD4L could inhibit ERBB3 and MAPK signaling pathways. When cells are deficient in nutrition, NEDD4L promoted the degradation of the autophagy regulatory protein ULK1. Our study provides novel insights into the role of NEDD4L in pan-cancer. NEDD4L may play a tumor suppressor effect in ccRCC, through tumor immune regulation and ubiquitination of key intracellular kinases.

Unbiased proteomic screening identifies a novel role for the E3 ubiquitin ligase Nedd4-2 in translational suppression during ER stress

Endoplasmic reticulum (ER) stress occurs when protein folding or maturation is disrupted. A malfunction in the ER stress response can lead to cell death and has been observed in many neurological diseases. However, how the ER stress response is regulated in neuronal cells remains largely unclear. Here, we studied an E3 ubiquitin ligase named neural precursor cell expressed developmentally down-regulated protein 4-like (Nedd4-2). Nedd4-2 is highly expressed in the brain and has a high affinity toward ubiquitinating membrane-bound proteins. We first utilized unbiased proteomic profiling with ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) of isolated membrane fractions from mouse whole brains to identify novel targets of Nedd4-2. Through this screen, we found that the expression and ubiquitination of ribosomal proteins are regulated by Nedd4-2 and we confirmed an association between Nedd4-2 and ribosomes through ribosome sedimentation and polysome profiling. Further, we utilized immunoprecipitation and western blotting to show that induction of ER stress promotes an association between Nedd4-2 and ribosomal proteins, which is mediated through dephosphorylation of Nedd4-2 at serine-342. This increased interaction between Nedd4-2 and ribosomal proteins in turn mediates ER stress-associated translational suppression. In summary, the results of this study demonstrate a novel regulatory mechanism underlying the ER stress response and a novel function of Nedd4-2 in translational control. Our findings may shed light on neurological diseases in which the ER stress response or the function of Nedd4-2 is dysregulated.

Novel loci for childhood body mass index and shared heritability with adult cardiometabolic traits

The genetic background of childhood body mass index (BMI), and the extent to which the well-known associations of childhood BMI with adult diseases are explained by shared genetic factors, are largely unknown. We performed a genome-wide association study meta-analysis of BMI in 61,111 children aged between 2 and 10 years. Twenty-five independent loci reached genome-wide significance in the combined discovery and replication analyses. Two of these, located near NEDD4L and SLC45A3, have not previously been reported in relation to either childhood or adult BMI. Positive genetic correlations of childhood BMI with birth weight and adult BMI, waist-to-hip ratio, diastolic blood pressure and type 2 diabetes were detected (Rg ranging from 0.11 to 0.76, P-values <0.002). A negative genetic correlation of childhood BMI with age at menarche was observed. Our results suggest that the biological processes underlying childhood BMI largely, but not completely, overlap with those underlying adult BMI. The well-known observational associations of BMI in childhood with cardio-metabolic diseases in adulthood may reflect partial genetic overlap, but in light of previous evidence, it is also likely that they are explained through phenotypic continuity of BMI from childhood into adulthood.

Homeostatic Roles of the Proteostasis Network in Dendrites

Cellular protein homeostasis, or proteostasis, is indispensable to the survival and function of all cells. Distinct from other cell types, neurons are long-lived, exhibiting architecturally complex and diverse multipolar projection morphologies that can span great distances. These properties present unique demands on proteostatic machinery to dynamically regulate the neuronal proteome in both space and time. Proteostasis is regulated by a distributed network of cellular processes, the proteostasis network (PN), which ensures precise control of protein synthesis, native conformational folding and maintenance, and protein turnover and degradation, collectively safeguarding proteome integrity both under homeostatic conditions and in the contexts of cellular stress, aging, and disease. Dendrites are equipped with distributed cellular machinery for protein synthesis and turnover, including dendritically trafficked ribosomes, chaperones, and autophagosomes. The PN can be subdivided into an adaptive network of three major functional pathways that synergistically govern protein quality control through the action of (1) protein synthesis machinery; (2) maintenance mechanisms including molecular chaperones involved in protein folding; and (3) degradative pathways (e.g., Ubiquitin-Proteasome System (UPS), endolysosomal pathway, and autophagy. Perturbations in any of the three arms of proteostasis can have dramatic effects on neurons, especially on their dendrites, which require tightly controlled homeostasis for proper development and maintenance. Moreover, the critical importance of the PN as a cell surveillance system against protein dyshomeostasis has been highlighted by extensive work demonstrating that the aggregation and/or failure to clear aggregated proteins figures centrally in many neurological disorders. While these studies demonstrate the relevance of derangements in proteostasis to human neurological disease, here we mainly review recent literature on homeostatic developmental roles the PN machinery plays in the establishment, maintenance, and plasticity of stable and dynamic dendritic arbors. Beyond basic housekeeping functions, we consider roles of PN machinery in protein quality control mechanisms linked to dendritic plasticity (e.g., dendritic spine remodeling during LTP); cell-type specificity; dendritic morphogenesis; and dendritic pruning.

Partners of wild type Grb7 and a mutant lacking its calmodulin-binding domain

Growth factor receptor bound protein 7 (Grb7) is a mammalian adaptor protein participating in signaling pathways implicated in cell migration, metastatic invasion, cell proliferation and tumor-associated angiogenesis. We expressed tagged versions of wild type Grb7 and the mutant Grb7Δ, lacking its calmodulin-binding domain (CaM-BD), in human embryonic kidney (HEK) 293 cells and rat glioma C6 cells to identify novel binding partners using shot-gun proteomics. Among the new identified proteins, we validated the ubiquitin-ligase Nedd4 (neural precursor cell expressed developmentally down-regulated protein 4), the heat-shock protein Hsc70/HSPA8 (heat shock cognate protein 70) and the cell cycle regulatory protein caprin-1 (cytoplasmic activation/proliferation-associated protein 1) in rat glioma C6 cells. Our results suggest a role of Grb7 in pathways where these proteins are implicated. These include protein trafficking and degradation, stress-response, chaperone-mediated autophagy, apoptosis and cell proliferation.

Pulsed SILAM Reveals In Vivo Dynamics of Murine Brain Protein Translation

Identification of proteins that are synthesized de novo in response to specific microenvironmental cues is critical for understanding molecular mechanisms that underpin vital physiological processes and pathologies. Here, we report that a brief period of SILAM (Stable Isotope Labeling of Mammals) diet enables the determination of biological functions corresponding to actively translating proteins in the mouse brain. Our results demonstrate that the synapse, dendrite, and myelin sheath are highly active neuronal structures that display rapid protein synthesis, producing key mediators of chemical signaling as well as nutrient sensing, lipid metabolism, and amyloid precursor protein processing/stability. Together, these findings confirm that protein metabolic activity varies significantly between brain functional units in vivo. Our data indicate that pulsed SILAM approaches can unravel complex protein expression dynamics in the murine brain and identify active synthetic pathways and associated functions that are likely impaired in neurodegenerative diseases.

Association between polymorphism of the NEDD4 gene and cognitive dysfunction of schizophrenia patients in Chinese Han population

BACKGROUND

Schizophrenia is a complex psychiatric disorder with unknown etiology. A number of recent studies have shown that the polymorphism of the neural precursor cell expressed developmentally down-regulated 4 (NEDD4) gene is associated with a variety of neuropsychiatric disorders, such as schizophrenia, and may also be associated with cognitive dysfunction in these diseases.

METHODS

A case-control study was carried out, the alleles and genotypes distributions of five loci (rs3088077, rs2303579, rs7162435, rs11550869, rs62043855) of the NEDD4 gene from 296 schizophrenia patients and 320 healthy controls were detected by using Taqman single-nucleotide polymorphism (SNP) genotyping technology. The clinical data of case and control group members were collected by self-made questionnaire and the psychotic symptoms of case group members were assessed by the Positive and Negative Syndrome Scale (PANSS). The Matrics Consensus Cognitive Battery (MCCB) was used to test the cognitive function of case group members.

RESULTS

The alleles and genotypes frequency of two loci (rs3088077, rs2303579) between case and control group showed significant differences (P <  0.05). There was no significant difference in MCCB scores of patients with different genotypes at rs3088077, rs11550869 and rs7162435 loci in case group. The study of rs2303579 locus showed that, patients' scores with CT genotype were significantly lower than those with CC and TT genotypes (P <  0.05) in the test of Wechsler Memory Scale-Third Edition (WMS-III): Spatial Span, the scores of patients with TT genotype were significantly higher than those with CT genotype (P < 0.05) in the test of Hopkins Verbal Learning Test-Revised (HVLT-R). The study of rs62043855 locus showed that patients with TG genotype had significantly lower scores than those with GG genotype (P < 0.05) in the test of Neuropsychological Assessment Battery (NAB): Mazes.

CONCLUSIONS

Our study showed that in schizophrenia patients of Chinese Han population, the polymorphisms of rs3088077 and rs2303579 loci were related to the pathogenesis of schizophrenia, while the polymorphisms of rs2303579 and rs62043855 loci were associated with cognitive dysfunction.

IGF-1-enhanced miR-513a-5p signaling desensitizes glioma cells to temozolomide by targeting the NEDD4L-inhibited Wnt/β-catenin pathway

Temozolomide (TMZ) is a first-line alkylating agent for glioblastoma multiforme (GBM). Clarifying the mechanisms inducing TMZ insensitivity may be helpful in improving its therapeutic effectiveness against GBM. Insulin-like growth factor (IGF)-1 signaling and micro (mi)RNAs are relevant in mediating GBM progression. However, their roles in desensitizing GBM cells to TMZ are still unclear. We aimed to identify IGF-1-mediated miRNA regulatory networks that elicit TMZ insensitivity for GBM. IGF-1 treatment attenuated TMZ cytotoxicity via WNT/β-catenin signaling, but did not influence glioma cell growth. By miRNA array analyses, 93 upregulated and 148 downregulated miRNAs were identified in IGF-1-treated glioma cells. miR-513a-5p from the miR-513a-2 gene locus was upregulated by IGF-1-mediated phosphoinositide 3-kinase (PI3K) signaling. Its elevated levels were also observed in gliomas versus normal cells, in array data of The Cancer Genome Atlas (TCGA), and the GSE61710, GSE37366, and GSE41032 datasets. In addition, lower levels of neural precursor cell-expressed developmentally downregulated 4-like (NEDD4L), an E3 ubiquitin protein ligase that inhibits WNT signaling, were found in gliomas by analyzing cells, arrays, and RNA sequencing data of TCGA glioma patients. Furthermore, a negative correlation was identified between miR-513a-5p and NEDD4L in glioma. NEDD4L was also validated as a direct target gene of miR-513a-5p, and it was reduced by IGF-1 treatment. Overexpression of NEDD4L inhibited glioma cell viability and reversed IGF-1-repressed TMZ cytotoxicity. In contrast, miR-513a-5p significantly affected NEDD4L-inhibited WNT signaling and reduced TMZ cytotoxicity. These findings demonstrate a distinct role of IGF-1 signaling through miR-513a-5p-inhibited NEDD4L networks in influencing GBM's drug sensitivity to TMZ.

Physiological Functions of Nedd4-2: Lessons from Knockout Mouse Models

Protein modification by ubiquitination plays a key evolutionarily conserved role in regulating membrane proteins. Nedd4-2, a ubiquitin ligase, targets membrane proteins such as ion channels and transporters for ubiquitination. This Nedd4-2-mediated ubiquitination provides a crucial step in controlling the membrane availability of these proteins, thus affecting their signaling and physiological outcomes. In one well-studied example, Nedd4-2 fine-tunes the physiological function of the epithelial sodium channel (ENaC), thus modulating Na⁺ reabsorption by epithelia to maintain whole-body Na⁺ homeostasis. This review summarizes the key signaling pathways regulated by Nedd4-2 and the possible implications of such regulation in various pathologies.

The E3 ubiquitin ligase NEDD4 is translationally upregulated and facilitates pancreatic cancer

Aim

To determine the regulation and function of the neural precursor cell expressed developmentally down regulated protein 4 (NEDD4) in PDAC and to determine its dependency on phosphatase and tensin homolog (PTEN) and PI3K/AKT signaling.

Methods

We investigated the expression of NEDD4 and the tumor suppressor PTEN in normal immortalized human pancreatic duct epithelial cell line and pancreatic adenocarcinoma (PDAC) cell lines. We further evaluated whether RNAi-mediated depletion of NEDD4 can attenuate PDAC cell proliferation and migration. We subsequently determined the crosstalk between NEDD4 expression and the PTEN/PI3K/AKT signaling pathway. Finally, we determined the mechanism behind differential NEDD4 protein expression in pancreatic cancer.

Results

The expression of NEDD4 was heterogeneous in PDAC cells, but was significantly higher compared to normal pancreatic ductal epithelial cells. Analogically, PTEN was decreased in the PDAC cells. A combination of MTT assay, wound healing migration assay, and transwell invasion assays confirmed that depletion of NEDD4 decreased the proliferation and migration ability of PDAC cells. Western blot and immunofluorescence results revealed that NEDD4 could affect PTEN/PI3K/AKT signaling pathway in PDAC cells. Polysomal profiling revealed that higher NEDD4 protein expression in PDAC cells was due to undefined mechanism involving translational activation.

Conclusions

Our results reveal a novel mechanism of upregulation of NEDD4 expression in PDAC. Our findings indicate that NEDD4 potentially plays a critical role in activating the PI3K/AKT signaling pathway by negatively regulating PTEN levels in PDAC cells, which promotes pancreatic cancer cell proliferation and metastasis. Therefore, NEDD4 may be a potential therapeutic target in PDAC.

NEDD4 promotes cell growth and migration via PTEN/PI3K/AKT signaling in hepatocellular carcinoma

The novel E3 ubiquitin-protein ligase neural precursor cell-expressed developmentally downregulated protein 4 (NEDD4) has been implicated as a crucial factor promoting the tumorigenesis of several types of cancer. The present study investigated the oncogenic role of NEDD4 in hepatocellular carcinoma (HCC) by targeted small interfering RNA silencing of the tumor suppressor phosphatase and tensin homolog (PTEN). Using normal hepatocyte and HCC cell lines, the influence of NEDD4 depletion on proliferation and migration as well as on the PTEN/phosphatidylinositol-3-kinase/protein kinase B signaling pathway was assessed. Additionally, the expression of NEDD4 was assessed in HCC specimens from 78 patients. The in vitro immunohistochemistry results indicated that NEDD4 protein expression was higher, but PTEN expression was lower, in HCC cells compared with normal hepatocytes. The results from the MTT assay, wound healing experiment and Transwell assays demonstrated that NEDD4 depletion lead to decreased proliferation and migration ability of HCC cells. Results from western blotting and immunofluorescence demonstrated that silencing of NEDD4 disrupted the PTEN/phosphoinositide 3-kinase (PI3K)/protein kinase B (AKT) signaling pathway in HCC cells. A total of 55 (70.5%) of the HCC specimens stained positive for NEDD4 and expression significantly correlated with tumor size (P=0.047), differentiation degree (P=0.032), vascular invasion (P<0.001), and lymph node metastasis (P=0.005). Thus, NEDD4 appears to perform a critical role in promoting the proliferation and metastasis of HCC via activation of the PTEN/PI3K/AKT signaling pathway; as such, NEDD4 may be a promising target for novel treatments of HCC.

NEDD4 is involved in acquisition of epithelial-mesenchymal transition in cisplatin-resistant nasopharyngeal carcinoma cells

Nasopharyngeal carcinoma (NPC) is a highly invasive head-neck cancer derived from the nasopharyngeal epithelium, mainly prevalent in southern China and Southeast Asia. Radiotherapy and adjuvant cisplatin (DDP) chemotherapy are standard administrations applied in the treatment of NPC. However, resistance to chemotherapeutic drugs has recently become more common, resulting in worse treatment outcome for NPC therapy. To elucidate the underlying molecular basis of drug resistance to DDP in NPC cells, we examined the morphocytology, cell motility and molecular changes in DDP-resistant NPC cells with respect to epithelial-mesenchymal transition (EMT) features. We found that EMT is closely associated with DDP-induced drug resistance in NPC cells, as DDP-resistant cells displayed morphological and molecular markers changes consistent with EMT. Wound healing and Transwell Boyden chamber assays revealed an enhanced migration and invasion potential in DDP-resistant NPC cells. Mechanistically, upregulation of NEDD4 was observed to relate to EMT in DDP-resistant cells. More importantly, depletion of NEDD4 in resistant cells led to a partial reversion of EMT phenotypes to MET characteristics. These data suggest that NEDD4 is largely involved in EMT features and chemoresistance of NPC cancer cells. NEDD4 could be a novel therapeutic target to overcome drug resistance in successful administrations of NPC.

E3 Ubiquitin Ligase Nedd4 Promotes Japanese Encephalitis Virus Replication by Suppressing Autophagy in Human Neuroblastoma Cells

Japanese encephalitis virus (JEV) is a mosquito-borne flavivirus that causes the most prevalent viral encephalitis in Asia. Since JEV is a neurotropic virus, it is important to identify key molecules that mediate JEV infection in neuronal cells and to investigate their underlying mechanisms. In this study, the critical role of Nedd4, an E3 ubiquitin ligase that is highly expressed in the central nervous system, was examined in JEV propagation. In SK-N-SH neuroblastoma cells, Nedd4 was up-regulated in response to JEV infection. Moreover, down-regulation of Nedd4 resulted in a significant decrease in JEV replication without alterations in virus attachment and internalization or in JEV pseudotyped virus infection, suggesting that Nedd4 participates in the replication but not in the entry stage of JEV infection. Further functional analysis showed that Nedd4 attenuated JEV-induced autophagy, which negatively regulates virus replication during infection. These results suggest that Nedd4 facilitates the replication of JEV by suppressing virus-induced autophagy. Taken together, our results indicate that Nedd4 plays a crucial role in JEV infection of neuronal cells, which provides a potential target for the development of novel treatment to combat JEV infection.

Nedd4-2 haploinsufficiency causes hyperactivity and increased sensitivity to inflammatory stimuli

Nedd4-2 (NEDD4L in humans) is a ubiquitin protein ligase best known for its role in regulating ion channel internalization and turnover. Nedd4-2 deletion in mice causes perinatal lethality associated with increased epithelial sodium channel (ENaC) expression in lung and kidney. Abundant data suggest that Nedd4-2 plays a role in neuronal functions and may be linked to epilepsy and dyslexia in humans. We used a mouse model of Nedd4-2 haploinsufficiency to investigate whether an alteration in Nedd4-2 levels of expression affects general nervous system functions. We found that Nedd4-2 heterozygous mice are hyperactive, have increased basal synaptic transmission and have enhanced sensitivity to inflammatory pain. Thus, Nedd4-2 heterozygous mice provide a new genetic model to study inflammatory pain. These data also suggest that in human, SNPs affecting NEDD4L levels may be involved in the development of neuropsychological deficits and peripheral neuropathies and may help unveil the genetic basis of comorbidities.

Ubiquitin-specific Protease 36 (USP36) Controls Neuronal Precursor Cell-expressed Developmentally Down-regulated 4-2 (Nedd4-2) Actions over the Neurotrophin Receptor TrkA and Potassium Voltage-gated Channels 7.2/3 (Kv7.2/3)

Ubiquitination of the TrkA neurotrophin receptor in response to NGF is critical in the regulation of TrkA activation and functions. TrkA is ubiquitinated, among other E3 ubiquitin ligases, by Nedd4-2. To understand mechanistically how TrkA ubiquitination is regulated, we performed a siRNA screening to identify deubiquitinating enzymes and found that USP36 acts as an important regulator of TrkA activation kinetics and ubiquitination. However, USP36 action on TrkA was indirect because it does not deubiquitinate TrkA. Instead, USP36 binds to Nedd4-2 and regulates the association of TrkA and Nedd4-2. In addition, depletion of USP36 increases TrkA·Nedd4-2 complex formation, whereas USP36 expression disrupts the complex, resulting in an enhancement or impairment of Nedd4-2-dependent TrkA ubiquitination, respectively. Moreover, USP36 depletion leads to enhanced total and surface TrkA expression that results in increased NGF-mediated TrkA activation and signaling that augments PC12 cell differentiation. USP36 actions extend beyond TrkA because the presence of USP36 interferes with Nedd4-2-dependent Kv7.2/3 channel regulation. Our results demonstrate that USP36 binds to and regulates the actions of Nedd4-2 over different substrates affecting their expression and functions.

Homeostasis of the astrocytic glutamate transporter GLT-1 is altered in mouse models of Lafora disease

Lafora disease (LD, OMIM 254780) is a fatal rare disorder characterized by epilepsy and neurodegeneration. Although in recent years a lot of information has been gained on the molecular basis of the neurodegeneration that accompanies LD, the molecular basis of epilepsy is poorly understood. Here, we present evidence indicating that the homeostasis of glutamate transporter GLT-1 (EAAT2) is compromised in mouse models of LD. Our results indicate that primary astrocytes from LD mice have reduced capacity of glutamate transport, probably because they present a reduction in the levels of the glutamate transporter at the plasma membrane. On the other hand, the overexpression in cellular models of laforin and malin, the two proteins related to LD, results in an accumulation of GLT-1 (EAAT2) at the plasma membrane and in a severe reduction of the ubiquitination of the transporter. All these results suggest that the laforin/malin complex slows down the endocytic recycling of the GLT-1 (EAAT2) transporter. Since, defects in the function of this transporter lead to excitotoxicity and epilepsy, we suggest that the epilepsy that accompanies LD could be due, at least in part, to deficiencies in the function of the GLT-1 (EAAT2) transporter.

Learning, memory and long-term potentiation are altered in Nedd4 heterozygous mice

The consolidation of short-term memory into long-term memory involves changing protein level and activity for the synaptic plasticity required for long-term potentiation (LTP). AMPA receptor trafficking is a key determinant of LTP and recently ubiquitination by Nedd4 has been shown to play an important role via direct action on the GluA1 subunit, although the physiological relevance of these findings are yet to be determined. We therefore investigated learning and memory in Nedd4(+/-) mice that have a 50% reduction in levels of Nedd4. These mice showed decreased long-term spatial memory as evidenced by significant increases in the time taken to learn the location of and subsequently find a platform in the Morris water maze. In contrast, there were no significant differences between Nedd4(+/+) and Nedd4(+/-) mice in terms of short-term spatial memory in a Y-maze test. Nedd4(+/-) mice also displayed a significant reduction in post-synaptic LTP measured in hippocampal brain slices. Immunofluorescence of Nedd4 in the hippocampus confirmed its expression in hippocampal neurons of the CA1 region. These findings indicate that reducing Nedd4 protein by 50% significantly impairs LTP and long-term memory thereby demonstrating an important role for Nedd4 in these processes.

Novel somatic mutations identified by whole-exome sequencing in muscle-invasive transitional cell carcinoma of the bladder

Transitional cell carcinoma (TCC) is the one of the most commonly observed types of cancer globally. The identification of novel disease-associated genes in TCC has had a significant effect on the diagnosis and treatment of bladder cancer; however, there may be a large number of novel genes that have not been identified. In the present study, the exomes of two individuals who were diagnosed with muscle-invasive TCC (MI-TCC) were sequenced to investigate potential variants. Subsequently, following algorithm and filter analysis, Sanger sequencing was used to validate the results of deep sequencing. Immunohistochemistry (IHC) was employed to observe the differences in HECT, C2 and WW domain-containing E3 ubiquitin protein ligase 1 (HECW1) protein expression between tumor tissues and para-carcinoma tissues. A total of 6 nonsynonymous mutation genes were identified in MI-TCC, identified as copine VII, RNA binding motif protein, X-linked-like 3, acyl-CoA synthetase medium-chain family member 2A, HECW1, zinc finger protein 273 and trichohyalin. Furthermore, 5 cases were identified to possess a HECW1 gene mutation in 61 MI-TCC specimens, and all of these were point mutations located at exon 11 on chromosome 7. The mutation categories of HECW1 had 4 missense mutations and 1 nonsense mutation. IHC revealed that HECW1 protein was expressed at significantly increased levels in MI-TCC compared with normal bladder urothelium (P<0.001). The present study provided a novel approach for investigating genetic changes in the MI-TCC exome, and identified the novel mutant gene HECW1, which may possess a significant role in the pathogenesis of TCC.

NEDD4-mediated HSF1 degradation underlies α-synucleinopathy

Cellular protein homeostasis is achieved by a delicate network of molecular chaperones and various proteolytic processes such as ubiquitin–proteasome system (UPS) to avoid a build-up of misfolded protein aggregates. The latter is a common denominator of neurodegeneration. Neurons are found to be particularly vulnerable to toxic stress from aggregation-prone proteins such as α-synuclein. Induction of heat-shock proteins (HSPs), such as through activated heat shock transcription factor 1 (HSF1) via Hsp90 inhibition, is being investigated as a therapeutic option for proteinopathic diseases. HSF1 is a master stress-protective transcription factor which activates genes encoding protein chaperones (e.g. iHsp70) and anti-apoptotic proteins. However, whether and how HSF1 is dysregulated during neurodegeneration has not been studied. Here, we discover aberrant HSF1 degradation by aggregated α-synuclein (or α-synuclein-induced proteotoxic stress) in transfected neuroblastoma cells. HSF1 dysregulation via α-synuclein was confirmed by in vivo assessment of mouse and in situ studies of human specimens with α-synucleinopathy. We demonstrate that elevated NEDD4 is implicated as the responsible ubiquitin E3 ligase for HSF1 degradation through UPS. Furthermore, pharmacologically induced SIRT1-mediated deacetylation can attenuate aberrant NEDD4-mediated HSF1 degradation. Indeed, we define the acetylation status of the Lys 80 residue located in the DNA-binding domain of HSF1 as a critical factor in modulating HSF1 protein stability in addition to its previously identified role in the transcriptional activity. Together with the finding that preserving HSF1 can alleviate α-synuclein toxicity, this study strongly suggests that aberrant HSF1 degradation is a key neurodegenerative mechanism underlying α-synucleinopathy.

NEDD4-2 and salt-sensitive hypertension

PURPOSE OF REVIEW

NEDD4-2 is an ubiquitin-protein ligase that was originally identified as an interactor of the epithelial Na+ channel (ENaC); this interaction is defective in Liddle's syndrome, causing elevated ENaC activity and salt-sensitive hypertension. In this review we aim to highlight progress achieved in recent years demonstrating that NEDD4-2 is involved in the control of Na+ transporters that are different from ENaC, but which also play a role in salt-sensitive hypertension.

RECENT FINDINGS

It has been shown that NEDD4-2 interacts with ubiquitylates and negatively regulates the thiazide-sensitive NCC (Na+,Cl- -cotransporter), both in vitro and in vivo in inducible, nephron-specific Nedd4-2 knockout mice. Moreover, evidence has been provided that NEDD4-2 is also involved in the regulation of human NHE3 (Na+,H+-exchanger 3) and NKCC2 (Na+,K+,2Cl- -cotransporter 2).

SUMMARY

The emerging role of NEDD4-2 in the regulation of different Na+ transporters along the nephron and the identification of human polymorphisms in the NEDD4-2 gene (Nedd4L) related to salt-sensitive hypertension makes this ubiquitin-protein ligase an interesting target for the development of antihypertensive drugs.

The E3 ubiquitin ligases, HUWE1 and NEDD4-1, are involved in the post-translational regulation of the ABCG1 and ABCG4 lipid transporters

The ATP-binding cassette transporter ABCG1 has an essential role in cellular cholesterol homeostasis, and dysregulation has been associated with a number of high burden diseases. Previous studies reported that ABCG1 is ubiquitinated and degraded via the ubiquitin proteasome system. However, so far the molecular mechanism, including the identity of any of the rate-limiting ubiquitination enzymes, or E3 ligases, is unknown. Using liquid chromatography mass spectrometry, we identified two HECT domain E3 ligases associated with ABCG1, named HUWE1 (HECT, UBA, and WWE domain containing 1, E3 ubiquitin protein ligase) and NEDD4-1 (Neural precursor cell-expressed developmentally down regulated gene 4), of which the latter is the founding member of the NEDD4 family of ubiquitin ligases. Silencing both HUWE1 and NEDD4-1 in cells overexpressing human ABCG1 significantly increased levels of the ABCG1 monomeric and dimeric protein forms, however ABCA1 protein expression was unaffected. In addition, ligase silencing increased ABCG1-mediated cholesterol export to HDL in cells overexpressing the transporter as well as in THP-1 macrophages. Reciprocally, overexpression of both ligases resulted in a significant reduction in protein levels of both the ABCG1 monomeric and dimeric forms. Like ABCG1, ABCG4 protein levels and cholesterol export activity were significantly increased after silencing both HUWE1 and NEDD4-1 in cells overexpressing this closely related ABC half-transporter. In summary, we have identified for the first time two E3 ligases that are fundamental enzymes in the post-translational regulation of ABCG1 and ABCG4 protein levels and cellular cholesterol export activity.

NEDD4: a promising target for cancer therapy

The Neuronally expressed developmentally downregulated 4 (NEDD4), functioning largely as an E3 ubiquitin ligase, has been demonstrated to play a critical role in the development and progression of human cancers. In this review, to understand the regulatory mechanism(s) of NEDD4 as well as the signaling pathways controlled by NEDD4, we briefly describe the NEDD4 upstream regulators and its downstream ubiquitin substrates. Moreover, we further discuss its oncogenic roles in human malignancies. Therefore, targeting NEDD4 could be a potential therapeutic strategy for treatment of human cancers.

SCF(β-TRCP)-mediated degradation of NEDD4 inhibits tumorigenesis through modulating the PTEN/Akt signaling pathway

The HECT domain-containing ubiquitin E3 ligase NEDD4 is widely expressed in mammalian tissues and plays a crucial role in governing a wide spectrum of cellular processes including cell growth, tissue development and homeostasis. Recent reports have indicated that NEDD4 might facilitate tumorigenesis through targeted degradation of multiple tumor suppressor proteins including PTEN. However, the molecular mechanism by which NEDD4 stability is regulated has not been fully elucidated. Here we report that SCF(β-TRCP) governs NEDD4 protein stability by targeting it for ubiquitination and subsequent degradation in a Casein Kinase-I (CKI) phosphorylation-dependent manner. Specifically, depletion of β-TRCP, or inactivation of CKI, stabilized NEDD4, leading to down-regulation of its ubiquitin target PTEN and subsequent activation of the mTOR/Akt oncogenic pathway. Furthermore, we found that CKIδ-mediated phosphorylation of Ser347 and Ser348 on NEDD4 promoted its interaction with SCF(β-TRCP) for subsequent ubiquitination and degradation. As a result, compared to ectopic expression of wild-type NEDD4, introducing a non-degradable NEDD4 (S347A/S348A-NEDD4) promoted cancer cell growth and migration. Hence, our findings revealed the CKI/SCF(β-TRCP) signaling axis as the upstream negative regulator of NEDD4, and further suggested that enhancing NEDD4 degradation, presumably with CKI or SCF(β-TRCP) agonists, could be a promising strategy for treating human cancers.

NEDD4: The founding member of a family of ubiquitin-protein ligases

Ubiquitination plays a crucial role in regulating proteins post-translationally. The focus of this review is on NEDD4, the founding member of the NEDD4 family of ubiquitin ligases that is evolutionarily conserved in eukaryotes. Many potential substrates of NEDD4 have been identified and NEDD4 has been shown to play a critical role in the regulation of a number of membrane receptors, endocytic machinery components and the tumour suppressor PTEN. In this review we will discuss the diverse pathways in which NEDD4 is involved, and the patho-physiological significance of this important ubiquitin ligase.

Prefrontal cortical and striatal transcriptional responses to the reinforcing effect of repeated methylphenidate treatment in the spontaneously hypertensive rat, animal model of attention-deficit/hyperactivity disorder (ADHD)

Background

Methylphenidate is the most commonly used stimulant drug for the treatment of attention-deficit/hyperactivity disorder (ADHD). Research has found that methylphenidate is a “reinforcer” and that individuals with ADHD also abuse this medication. Nevertheless, the molecular consequences of long-term recreational methylphenidate use or abuse in individuals with ADHD are not yet fully known.

Methods

Spontaneously hypertensive rats (SHR), the most validated and widely used ADHD animal model, were pretreated with methylphenidate (5 mg/kg, i.p.) during their adolescence (post-natal day [PND] 42–48) and tested for subsequent methylphenidate-induced conditioned place preference (CPP) and self-administration. Thereafter, the differentially expressed genes in the prefrontal cortex (PFC) and striatum of representative methylphenidate-treated SHRs, which showed CPP to and self-administration of methylphenidate, were analyzed.

Results

Genome-wide transcriptome profiling analyses revealed 30 differentially expressed genes in the PFC, which include transcripts involved in apoptosis (e.g. S100a9, Angptl4, Nfkbia), transcription (Cebpb, Per3), and neuronal plasticity (Homer1, Jam2, Asap1). In contrast, 306 genes were differentially expressed in the striatum and among them, 252 were downregulated. The main functional categories overrepresented among the downregulated genes include those involved in cell adhesion (e.g. Pcdh10, Ctbbd1, Itgb6), positive regulation of apoptosis (Perp, Taf1, Api5), (Notch3, Nsbp1, Sik1), mitochondrion organization (Prps18c, Letm1, Uqcrc2), and ubiquitin-mediated proteolysis (Nedd4, Usp27x, Ube2d2).

Conclusion

Together, these changes indicate methylphenidate-induced neurotoxicity, altered synaptic and neuronal plasticity, energy metabolism and ubiquitin-dependent protein degradation in the brains of methylphenidate-treated SHRs, which showed methylphenidate CPP and self-administration. In addition, these findings may also reflect cognitive impairment associated with chronic methylphenidate use as demonstrated in preclinical studies. Future studies are warranted to determine the clinical significance of the present findings with regard to long-term recreational methylphenidate use or abuse in individuals with ADHD.

Overlapping microdeletions involving 15q22.2 narrow the critical region for intellectual disability to NARG2 and RORA

Microdeletions in the 15q22 region have not been well documented. We collected genotype and phenotype data from five patients with microdeletions involving 15q22.2, which were between 0.7 Mb and 6.5 Mb in size; two were of de novo origin and one was of familial origin. Intellectual disability and epilepsy are frequently observed in patients with 15q22.2 deletions. Genotype-phenotype correlation analysis narrowed the critical region for such neurologic symptoms to a genomic region of 654 Kb including the NMDA receptor-regulated 2 gene (NARG2) and the PAR-related orphan receptor A gene (RORA), either of which may be responsible for neurological symptoms commonly observed in patients with deletions in this region. The neighboring regions, including the forkhead box B1 gene (FOXB1), may also be related to the additional neurological features observed in the patients with larger deletions.

Subtle gait abnormalities in Nedd4 heterozygous mice

Nedd4 is a widely expressed ubiquitin ligase that is necessary for normal neuronal development and function. However, largely due to the lethality of Nedd4 homozygous knockout mice, little is known about the physiological roles of Nedd4 in the adult brain. In this study we used Nedd4 heterozygous mice, which are viable and live to maturity, to assess for motor function and gait. Global motor function was not altered in these mice, a result consistent with the low level of Nedd4 expression observed in motor neurons of the spinal cord. However, Nedd4 heterozygous mice showed significant age-dependent changes in gait. The gait abnormalities included an overall extension of gait that was only evident in the 6 month old mice. We also observed distinct expression patterns of Nedd4, with pronounced staining in the Purkinje neurons of the cerebellum that are crucial for normal gait, and lower levels in other motor areas of the CNS. It has been recently shown that Nedd4 directly interacts with GluR1 containing AMPA receptors in an activity dependent manner to modulate receptor levels at the post-synaptic membrane. Using confocal immunohistochemistry, we found that there were subtle changes in GluR1 expression in 6 month old Nedd4 heterozygous mice. There appeared to be a redistribution of GluR1 into larger puncta in the molecular layer and in the membrane of the soma of the Purkinje neurons. This study is the first to show that a 50% reduction in Nedd4 levels is sufficient to produce significant gait defects in 6 month old mice. These defects may arise in part, from altered distribution of GluR1 in cerebellar neurons.

Identification and rescue of α-synuclein toxicity in Parkinson patient-derived neurons

The induced pluripotent stem (iPS) cell field holds promise for in vitro disease modeling. However, identifying innate cellular pathologies, particularly for age-related neurodegenerative diseases, has been challenging. Here, we exploited mutation correction of iPS cells and conserved proteotoxic mechanisms from yeast to humans to discover and reverse phenotypic responses to α-synuclein (αsyn), a key protein involved in Parkinson's disease (PD). We generated cortical neurons from iPS cells of patients harboring αsyn mutations, who are at high risk of developing PD dementia. Genetic modifiers from unbiased screens in a yeast model of αsyn toxicity led to identification of early pathogenic phenotypes in patient neurons. These included nitrosative stress, accumulation of endoplasmic reticulum (ER)-associated degradation substrates, and ER stress. A small molecule identified in a yeast screen (NAB2), and the ubiquitin ligase Nedd4 it affects, reversed pathologic phenotypes in these neurons.

Genetic risk factors in two Utah pedigrees at high risk for suicide

We have used unique population-based data resources to identify 22 high-risk extended pedigrees that show clustering of suicide over twice that expected from demographically adjusted incidence rates. In this initial study of genetic risk factors, we focused on two high-risk pedigrees. In the first of these (pedigree 12), 10/19 (53%) of the related suicides were female, and the average age at death was 30.95. In the second (pedigree 5), 7/51 (14%) of the suicides were female and the average age at death was 36.90. Six decedents in pedigree 12 and nine in pedigree 5 were genotyped with the Illumina HumanExome BeadChip. Genotypes were analyzed using the Variant Annotation, Analysis, and Search program package that computes likelihoods of risk variants using the functional impact of the DNA variation, aggregative scoring of multiple variants across each gene and pedigree structure. We prioritized variants that were: (1) shared across pedigree members, (2) rare in other Utah suicides not related to these pedigrees, (3) < or = 5% in genotyping data from 398 other Utah population controls and (4) < or = 5% frequency in publicly available sequence data from 1358 controls and/or in dbSNP. Results included several membrane protein genes (ANO5, and TMEM141 for pedigree 12 and FAM38A and HRCT1 for pedigree 5). Other genes with known neuronal involvement and/or previous associations with psychiatric conditions were also identified, including NFKB1, CASP9, PLXNB1 and PDE11A in pedigree 12, and THOC1, and AUTS2 in pedigree 5. Although the study is limited to variants included on the HumanExome BeadChip, these findings warrant further exploration, and demonstrate the utility of this high-risk pedigree resource to identify potential genes or gene pathways for future development of targeted interventions.

The Nedd4-binding protein 3 (N4BP3) is crucial for axonal and dendritic branching in developing neurons

Background

Circuit formation in the nervous system essentially relies on the proper development of neurons and their processes. In this context, the ubiquitin ligase Nedd4 is a crucial modulator of axonal and dendritic branching.

Results

Herein we characterize the Nedd4-binding protein 3 (N4BP3), a Fezzin family member, during nerve cell development. In developing rat primary hippocampal neurons, endogenous N4BP3 localizes to neuronal processes, including axons and dendrites. Transient in vitro knockdown of N4BP3 in hippocampal cultures during neuritogenesis results in impaired branching of axons and dendrites. In line with these findings, in vivo knockdown of n4bp3 in Xenopus laevis embryos results in severe alteration of cranial nerve branching.

Conclusions

We introduce N4BP3 as a novel molecular element for the correct branching of neurites in developing neurons and propose a central role for an N4BP3-Nedd4 complex in neurite branching and circuit formation.

Genome-wide scan of healthy human connectome discovers SPON1 gene variant influencing dementia severity

Aberrant connectivity is implicated in many neurological and psychiatric disorders, including Alzheimer's disease and schizophrenia. However, other than a few disease-associated candidate genes, we know little about the degree to which genetics play a role in the brain networks; we know even less about specific genes that influence brain connections. Twin and family-based studies can generate estimates of overall genetic influences on a trait, but genome-wide association scans (GWASs) can screen the genome for specific variants influencing the brain or risk for disease. To identify the heritability of various brain connections, we scanned healthy young adult twins with high-field, high-angular resolution diffusion MRI. We adapted GWASs to screen the brain's connectivity pattern, allowing us to discover genetic variants that affect the human brain's wiring. The association of connectivity with the SPON1 variant at rs2618516 on chromosome 11 (11p15.2) reached connectome-wide, genome-wide significance after stringent statistical corrections were enforced, and it was replicated in an independent subsample. rs2618516 was shown to affect brain structure in an elderly population with varying degrees of dementia. Older people who carried the connectivity variant had significantly milder clinical dementia scores and lower risk of Alzheimer's disease. As a posthoc analysis, we conducted GWASs on several organizational and topological network measures derived from the matrices to discover variants in and around genes associated with autism (MACROD2), development (NEDD4), and mental retardation (UBE2A) significantly associated with connectivity. Connectome-wide, genome-wide screening offers substantial promise to discover genes affecting brain connectivity and risk for brain diseases.