The ubiquitin ligase Nedd4-1 is required for heart development and is a suppressor of thrombospondin-1

The E3 ubiquitin ligases regulate inflammation in cardiovascular diseases

Accumulating evidence has illustrated that the E3 ubiquitin ligases critically participate in the development and progression of cardiovascular diseases. Dysregulation of E3 ubiquitin ligases exacerbates cardiovascular diseases. Blockade or activation of E3 ubiquitin ligases mitigates cardiovascular performance. Therefore, in this review, we mainly introduced the critical role and underlying molecular mechanisms of E3 ubiquitin ligase NEDD4 family in governing the initiation and progression of cardiovascular diseases, including ITCH, WWP1, WWP2, Smurf1, Smurf2, Nedd4-1 and Nedd4-2. Moreover, the functions and molecular insights of other E3 ubiquitin ligases, such as F-box proteins, in cardiovascular disease development and malignant progression are described. Furthermore, we illustrate several compounds that alter the expression of E3 ubiquitin ligases to alleviate cardiovascular diseases. Therefore, modulation of E3 ubiquitin ligases could be a novel and promising strategy for improvement of therapeutic efficacy of deteriorative cardiovascular diseases.

Physiological Functions of the Ubiquitin Ligases Nedd4-1 and Nedd4-2

The Nedd4 family of E3 ubiquitin ligases, consisting of a C2-WW(n)-HECT domain architecture, includes the closely related Nedd4/Nedd4-1 and Nedd4L/Nedd4-2, which play critical roles in human physiology and pathophysiology.This review focuses on the regulation of enzymatic activity of these Nedd4 proteins, as well as on their roles in regulating stability and function of membrane and other signaling proteins, such as ion channels, ion transporters, and growth factor receptors. The diseases caused by impairment of such regulation are discussed, as well as opportunities and challenges for targeting these enzymes for therapy.

High glucose environment induces NEDD4 deficiency that impairs angiogenesis and diabetic wound healing

BACKGROUND

Healing of diabetic wounds, characterized by impaired angiogenesis, remains a clinical challenge. E3 ligase have been identified as potential therapeutic targets of wound healing.

OBJECTIVE

We assessed the role of E3 ligase NEDD4 in the context of angiogenesis and diabetic wound healing.

METHODS

The mRNA expression levels of NEDD4, TSP1 and VEGF were determined by real-time PCR. Western blotting was used to evaluate the protein expression of NEDD4, TSP1 and VEGF. The ubiquitination of TSP1 was evaluated by immunoprecipitation. MTT assay, wound healing assay and tube formation assay were performed to assess the proliferation, migration and angiogenic functions of endothelial cells. The epigenetic modification in the promoter of NEDD4 was confirmed using BSP assay and ChIP-qPCR assay. The role of NEDD4 in wound healing was further verified in diabetic mouse model.

RESULTS

NEDD4 promotes proliferation, migration and tube formation of endothelial cells. It binds to and ubiquitinates TSP1, which lead to TSP1 degradation and thus increased VEGF expression. The inhibitory effect of NEDD4 silencing on the angiogenesis ability of endothelial cells can be restored by TSP1 knockdown. NEDD4 is reduced in diabetic patients, which may due to hypermethylation of NEDD4 promoter mediated via DNMT1 under high glucose condition. Furthermore, inhibition of NEDD4 represses wound healing in diabetic mouse model.

CONCLUSION

NEDD4 might promote angiogenesis and wound healing by inhibiting TSP1 via ubiquitination in diabetic patients.

HER3: Toward the Prognostic Significance, Therapeutic Potential, Current Challenges, and Future Therapeutics in Different Types of Cancer

Human epidermal growth factor receptor 3 (HER3) is the only family member of the EGRF/HER family of receptor tyrosine kinases that lacks an active kinase domain (KD), which makes it an obligate binding partner with other receptors for its oncogenic role. When HER3 is activated in a ligand-dependent (NRG1/HRG) or independent manner, it can bind to other receptors (the most potent binding partner is HER2) to regulate many biological functions (growth, survival, nutrient sensing, metabolic regulation, etc.) through the PI3K-AKT-mTOR pathway. HER3 has been found to promote tumorigenesis, tumor growth, and drug resistance in different cancer types, especially breast and non-small cell lung cancer. Given its ubiquitous expression across different solid tumors and role in oncogenesis and drug resistance, there has been a long effort to target HER3. As HER3 cannot be targeted through its KD with small-molecule kinase inhibitors via the conventional method, pharmaceutical companies have used various other approaches, including blocking either the ligand-binding domain or extracellular domain for dimerization with other receptors. The development of treatment options with anti-HER3 monoclonal antibodies, bispecific antibodies, and different combination therapies showed limited clinical efficiency for various reasons. Recent reports showed that the extracellular domain of HER3 is not required for its binding with other receptors, which raises doubt about the efforts and applicability of the development of the HER3-antibodies for treatment. Whereas HER3-directed antibody-drug conjugates showed potentiality for treatment, these drugs are still under clinical trial. The currently understood model for dimerization-induced signaling remains incomplete due to the absence of the crystal structure of HER3 signaling complexes, and many lines of evidence suggest that HER family signaling involves more than the interaction of two members. This review article will significantly expand our knowledge of HER3 signaling and shed light on developing a new generation of drugs that have fewer side effects than the current treatment regimen for these patients.

NEDD4 E3 ubiquitin ligases: promising biomarkers and therapeutic targets for cancer

Accumulating evidence has demonstrated that NEDD4 E3 ubiquitin ligase family plays a pivotal oncogenic role in a variety of malignancies via mediating ubiquitin dependent degradation processes. Moreover, aberrant expression of NEDD4 E3 ubiquitin ligases is often indicative of cancer progression and correlated with poor prognosis. In this review, we are going to address association of expression of NEDD4 E3 ubiquitin ligases with cancers, the signaling pathways and the molecular mechanisms by which the NEDD4 E3 ubiquitin ligases regulate oncogenesis and progression, and the therapies targeting the NEDD4 E3 ubiquitin ligases. This review provides the systematic and comprehensive summary of the latest research status of E3 ubiquitin ligases in the NEDD4 subfamily, and proposes that NEDD4 family E3 ubiquitin ligases are promising anti-cancer drug targets, aiming to provide research direction for clinical targeting of NEDD4 E3 ubiquitin ligase therapy.

Unraveling the Potential Role of NEDD4-like E3 Ligases in Cancer

Cancer is a deadly disease worldwide, with an anticipated 19.3 million new cases and 10.0 million deaths occurring in 2020 according to GLOBOCAN 2020. It is well established that carcinogenesis and cancer development are strongly linked to genetic changes and post-translational modifications (PTMs). An important PTM process, ubiquitination, regulates every aspect of cellular activity, and the crucial enzymes in the ubiquitination process are E3 ubiquitin ligases (E3s) that affect substrate specificity and must therefore be carefully regulated. A surfeit of studies suggests that, among the E3 ubiquitin ligases, neuronal precursor cell-expressed developmentally downregulated 4 (NEDD4)/NEDD4-like E3 ligases show key functions in cellular processes by controlling subsequent protein degradation and substrate ubiquitination. In addition, it was demonstrated that NEDD4 mainly acts as an oncogene in various cancers, but also plays a tumor-suppressive role in some cancers. In this review, to comprehend the proper function of NEDD4 in cancer development, we summarize its function, both its tumor-suppressive and oncogenic role, in multiple types of malignancies. Moreover, we briefly explain the role of NEDD4 in carcinogenesis and progression, including cell survival, cell proliferation, autophagy, cell migration, invasion, metastasis, epithelial-mesenchymal transition (EMT), chemoresistance, and multiple signaling pathways. In addition, we briefly explain the significance of NEDD4 as a possible target for cancer treatment. Therefore, we conclude that targeting NEDD4 as a therapeutic method for treating human tumors could be a practical possibility.

The HECT family of E3 ubiquitin ligases and PTEN

Members of the HECT family of E3 ubiquitin ligases have emerged as prominent regulators of PTEN function, subcellular localization and levels. In turn this unfolding regulatory network is allowing for the identification of genes directly involved in both tumorigenesis at large and cancer susceptibility syndromes. While the complexity of this regulatory network is still being unraveled, these new findings are paving the way for novel therapeutic modalities for cancer prevention and therapy as well as for other diseases. Here we will review the signal transduction and therapeutic implications of the cross-talk between HECT family members and PTEN.

The NEDD4 ubiquitin E3 ligase: a snapshot view of its functional activity and regulation

Due to its fundamental role in all eukaryotic cells, a deeper understanding of the molecular mechanisms underlying ubiquitination is of central importance. Being responsible for chain specificity and substrate recognition, E3 ligases are the selective elements of the ubiquitination process. In this review, we discuss different cellular pathways regulated by one of the first identified E3 ligase, NEDD4, focusing on its pathophysiological role, its known targets and modulators. In addition, we highlight small molecule inhibitors that act on NEDD4 and discuss new strategies to effectively target this E3 enzyme.

Loss of NEDD4 causes complete XY gonadal sex reversal in mice

Gonadogenesis is the process wherein two morphologically distinct organs, the testis and the ovary, arise from a common precursor. In mammals, maleness is driven by the expression of Sry. SRY subsequently upregulates the related family member Sox9 which is responsible for initiating testis differentiation while repressing factors critical to ovarian development such as FOXL2 and β-catenin. Here, we report a hitherto uncharacterised role for the ubiquitin-protein ligase NEDD4 in this process. XY Nedd4-deficient mice exhibit complete male-to-female gonadal sex reversal shown by the ectopic upregulation of Foxl2 expression at the time of gonadal sex determination as well as insufficient upregulation of Sox9. This sex reversal extends to germ cells with ectopic expression of SYCP3 in XY Nedd4-/- germ cells and significantly higher Sycp3 transcripts in XY and XX Nedd4-deficient mice when compared to both XY and XX controls. Further, Nedd4-/- mice exhibit reduced gonadal precursor cell formation and gonadal size as a result of reduced proliferation within the developing gonad as well as reduced Nr5a1 expression. Together, these results establish an essential role for NEDD4 in XY gonadal sex determination and development and suggest a potential role for NEDD4 in orchestrating these cell fate decisions through the suppression of the female pathway to ensure proper testis differentiation.

In the balance: how do thrombospondins contribute to the cellular pathophysiology of cardiovascular disease?

Thrombospondins (TSPs) are multidomain, secreted proteins that associate with cell surfaces and extracellular matrix. In mammals, there is a large body of data on functional roles of various TSP family members in cardiovascular disease (CVD), including stroke, cardiac remodeling and fibrosis, atherosclerosis, and aortic aneurysms. Coding single nucleotide polymorphisms (SNPs) of TSP1 or TSP4 are also associated with increased risk of several forms of CVD. Whereas interactions and functional effects of TSPs on a variety of cell types have been studied extensively, the molecular and cellular basis for the differential effects of the SNPs remains under investigation. Here, we provide an integrative review on TSPs, their roles in CVD and cardiovascular cell physiology, and known properties and mechanisms of TSP SNPs relevant to CVD. In considering recent expansions to knowledge of the fundamental cellular roles and mechanisms of TSPs, as well as the effects of wild-type and variant TSPs on cells of the cardiovascular system, we aim to highlight knowledge gaps and areas for future research or of translational potential.

The Role of HECT-Type E3 Ligase in the Development of Cardiac Disease

Despite advances in medicine, cardiac disease remains an increasing health problem associated with a high mortality rate. Maladaptive cardiac remodeling, such as cardiac hypertrophy and fibrosis, is a risk factor for heart failure; therefore, it is critical to identify new therapeutic targets. Failing heart is reported to be associated with hyper-ubiquitylation and impairment of the ubiquitin–proteasome system, indicating an importance of ubiquitylation in the development of cardiac disease. Ubiquitylation is a post-translational modification that plays a pivotal role in protein function and degradation. In 1995, homologous to E6AP C-terminus (HECT) type E3 ligases were discovered. E3 ligases are key enzymes in ubiquitylation and are classified into three families: really interesting new genes (RING), HECT, and RING-between-RINGs (RBRs). Moreover, 28 HECT-type E3 ligases have been identified in human beings. It is well conserved in evolution and is characterized by the direct attachment of ubiquitin to substrates. HECT-type E3 ligase is reported to be involved in a wide range of human diseases and health. The role of HECT-type E3 ligases in the development of cardiac diseases has been uncovered in the last decade. There are only a few review articles summarizing recent advancements regarding HECT-type E3 ligase in the field of cardiac disease. This study focused on cardiac remodeling and described the role of HECT-type E3 ligases in the development of cardiac disease. Moreover, this study revealed that the current knowledge could be exploited for the development of new clinical therapies.

Obestatin signalling counteracts glucocorticoid-induced skeletal muscle atrophy via NEDD4/KLF15 axis

BACKGROUND

A therapeutic approach for the treatment of glucocorticoid-induced skeletal muscle atrophy should be based on the knowledge of the molecular mechanisms determining the unbalance between anabolic and catabolic processes and how to re-establish this balance. Here, we investigated whether the obestatin/GPR39 system, an autocrine signalling system acting on myogenesis and with anabolic effects on the skeletal muscle, could protect against chronic glucocorticoid-induced muscle atrophy.

METHODS

In this study, we used an in vivo model of muscle atrophy induced by the synthetic glucocorticoid dexamethasone to examine the liaison molecules that define the interaction between the glucocorticoid receptor and the obestatin/GPR39 systems. The findings were extended to in vitro effects on human atrophy using human KM155C25 myotubes.

RESULTS

KLF15 and FoxO transcription factors were identified as direct targets of obestatin signalling in the control of proteostasis in skeletal muscle. The KLF15-triggered gene expression program, including atrogenes and FoxOs, was regulated via KLF15 ubiquitination by the E3 ubiquitin ligase NEDD4. Additionally, a specific pattern of FoxO post-translational modification, including FoxO4 phosphorylation by Akt pathway, was critical in the regulation of the ubiquitin-proteasome system. The functional cooperativity between Akt and NEDD4 in the regulation of FoxO and KLF15 provides integrated cues to counteract muscle proteostasis and re-establish protein synthesis.

CONCLUSIONS

The effective control of FoxO activity in response to glucocorticoid is critical to counteract muscle-related pathologies. These results highlight the potential of the obestatin/GPR39 system to fine-tune the effects of glucocorticoids on skeletal muscle wasting.

Cardiac ECM: Its Epigenetic Regulation and Role in Heart Development and Repair

The extracellular matrix (ECM) is the non-cellular component in the cardiac microenvironment, and serves essential structural and regulatory roles in establishing and maintaining tissue architecture and cellular function. The patterns of molecular and biochemical ECM alterations in developing and adult hearts depend on the underlying injury type. In addition to exploring how the ECM regulates heart structure and function in heart development and repair, this review conducts an inclusive discussion of recent developments in the role, function, and epigenetic guidelines of the ECM. Moreover, it contributes to the development of new therapeutics for cardiovascular disease.

Phosphorylation Modifications Regulating Cardiac Protein Quality Control Mechanisms

Many forms of cardiac disease, including heart failure, present with inadequate protein quality control (PQC). Pathological conditions often involve impaired removal of terminally misfolded proteins. This results in the formation of large protein aggregates, which further reduce cellular viability and cardiac function. Cardiomyocytes have an intricately collaborative PQC system to minimize cellular proteotoxicity. Increased expression of chaperones or enhanced clearance of misfolded proteins either by the proteasome or lysosome has been demonstrated to attenuate disease pathogenesis, whereas reduced PQC exacerbates pathogenesis. Recent studies have revealed that phosphorylation of key proteins has a potent regulatory role, both promoting and hindering the PQC machinery. This review highlights the recent advances in phosphorylations regulating PQC, the impact in cardiac pathology, and the therapeutic opportunities presented by harnessing these modifications.

E3 Ubiquitin ligase NEDD4 family‑regulatory network in cardiovascular disease

Protein ubiquitination represents a critical modification occurring after translation. E3 ligase catalyzes the covalent binding of ubiquitin to the protein substrate, which could be degraded. Ubiquitination as an important protein post-translational modification is closely related to cardiovascular disease. The NEDD4 family, belonging to HECT class of E3 ubiquitin ligases can recognize different substrate proteins, including PTEN, ENaC, Nav1.5, SMAD2, PARP1, Septin4, ALK1, SERCA2a, TGFβR3 and so on, via the WW domain to catalyze ubiquitination, thus participating in multiple cardiovascular-related disease such as hypertension, arrhythmia, myocardial infarction, heart failure, cardiotoxicity, cardiac hypertrophy, myocardial fibrosis, cardiac remodeling, atherosclerosis, pulmonary hypertension and heart valve disease. However, there is currently no review comprehensively clarifying the important role of NEDD4 family proteins in the cardiovascular system. Therefore, the present review summarized recent studies about NEDD4 family members in cardiovascular disease, providing novel insights into the prevention and treatment of cardiovascular disease. In addition, assessing transgenic animals and performing gene silencing would further identify the ubiquitination targets of NEDD4. NEDD4 quantification in clinical samples would also constitute an important method for determining NEDD4 significance in cardiovascular disease.

NEDD4 E3 ligase: Functions and mechanism in human cancer

A growing amount of evidence indicates that the neuronally expressed developmentally downregulated 4 (NEDD4, also known as NEDD4-1) E3 ligase plays a critical role in a variety of cellular processes via the ubiquitination-mediated degradation of multiple substrates. The abnormal regulation of NEDD4 protein has been implicated in cancer development and progression. In this review article, we briefly delineate the downstream substrates and upstream regulators of NEDD4, which are involved in carcinogenesis. Moreover, we succinctly elucidate the functions of NEDD4 protein in tumorigenesis and progression, including cell proliferation, apoptosis, cell cycle, migration, invasion, epithelial mesenchymal transition (EMT), cancer stem cells, and drug resistance. The findings regarding NEDD4 functions are further supported by knockout mouse models and human tumor tissue studies. This review could provide a promising and optimum anticancer therapeutic strategy via targeting the NEDD4 protein.

Regulation of the p53 Family Proteins by the Ubiquitin Proteasomal Pathway

The tumor suppressor p53 and its homologues, p63 and p73, play a pivotal role in the regulation of the DNA damage response, cellular homeostasis, development, aging, and metabolism. A number of mouse studies have shown that a genetic defect in the p53 family could lead to spontaneous tumor development, embryonic lethality, or severe tissue abnormality, indicating that the activity of the p53 family must be tightly regulated to maintain normal cellular functions. While the p53 family members are regulated at the level of gene expression as well as post-translational modification, they are also controlled at the level of protein stability through the ubiquitin proteasomal pathway. Over the last 20 years, many ubiquitin E3 ligases have been discovered that directly promote protein degradation of p53, p63, and p73 in vitro and in vivo. Here, we provide an overview of such E3 ligases and discuss their roles and functions.

Ubiquitin Ligases Involved in the Regulation of Wnt, TGF-β, and Notch Signaling Pathways and Their Roles in Mouse Development and Homeostasis

The Wnt, TGF-β, and Notch signaling pathways are essential for the regulation of cellular polarity, differentiation, proliferation, and migration. Differential activation and mutual crosstalk of these pathways during animal development are crucial instructive forces in the initiation of the body axis and the development of organs and tissues. Due to the ability to initiate cell proliferation, these pathways are vulnerable to somatic mutations selectively producing cells, which ultimately slip through cellular and organismal checkpoints and develop into cancer. The architecture of the Wnt, TGF-β, and Notch signaling pathways is simple. The transmembrane receptor, activated by the extracellular stimulus, induces nuclear translocation of the transcription factor, which subsequently changes the expression of target genes. Nevertheless, these pathways are regulated by a myriad of factors involved in various feedback mechanisms or crosstalk. The most prominent group of regulators is the ubiquitin-proteasome system (UPS). To open the door to UPS-based therapeutic manipulations, a thorough understanding of these regulations at a molecular level and rigorous confirmation in vivo are required. In this quest, mouse models are exceptional and, thanks to the progress in genetic engineering, also an accessible tool. Here, we reviewed the current understanding of how the UPS regulates the Wnt, TGF-β, and Notch pathways and we summarized the knowledge gained from related mouse models.

E3-ubiquitin ligase NEDD4 enhances bone formation by removing TGFβ1-induced pSMAD1 in immature osteoblast

Neural precursor cell expressed developmentally downregulated protein 4 (NEDD4) is an E3 ubiquitin ligase that regulates animal growth and development. To investigate the role of NEDD4 in skeletogenesis in vivo, we established immature osteoblast-specific 2.3-kb Collagen Type I Alpha 1 chain (Col1α1) promoter-driven Nedd4 transgenic (Nedd4-TG, Col1α1-Nedd4^Tg/+) mice and conditional knockout (Nedd4-cKO, Col1α1-Cre;Nedd4^fl/fl) mice. The Nedd4-TG mice displayed enhanced bone mass accrual and upregulated gene expression of osteogenic markers in bone. In addition, bone formation was decreased in the Nedd4-cKO mice compared to that in their littermates. The proliferation of primary osteoblasts isolated from calvaria and the number and surface area of tibial osteoblasts were higher in the Nedd4-TG mice than those in their littermates. Throughout the osteoblast differentiation, the expression of Nedd4 and Tgfb1 were high at early stage of osteoblast maturation, but decreased at the later stage when Bmp2 expression level is high. TGFβ1 signaling was consolidated by degradation of pSMAD1, which was transiently induced by TGFβ1, in NEDD4-overexpressing osteoblasts. Furthermore, pERK1/2 signaling was enhanced in osteoblast from TG mice than those in their littermates. These results suggest that NEDD4 enhances osteoblast proliferation by removing pSMAD1 activated by TGFβ1, and potentiating pSMAD2 and pERK1/2 pathways at early stage of bone formation.

NEDD4-1 protects against ischaemia/reperfusion-induced cardiomyocyte apoptosis via the PI3K/Akt pathway

Activation of the Akt pathway has been shown to protect the heart from ischaemia/reperfusion (I/R) injury. NEDD4-1 has been shown to positively regulate nuclear trafficking of the activated form of Akt. However, the role of NEDD4-1 in cardiac I/R injury remains to be elucidated. In the present study, Lentiviral vectors were constructed to overexpress or knockdown NEDD4-1 in H9c2 cardiomyocytes subjected to I/R injury or ischemic preconditioning (IPC). The results indicated that NEDD4-1 levels were decreased after I/R and increased after IPC in rat heart tissue and in H9c2 cardiomyocytes. Overexpression of NEDD4-1 activated the Akt pathway and regulated apoptosis-related proteins in H9c2 cardiomyocytes, attenuating SI/R-induced cell apoptosis and caspase 3/7 activities. Furthermore, in vivo overexpression of NEDD4-1 attenuated myocardial apoptosis following myocardial I/R. Our results demonstrated that NEDD4-1 protects the myocardium from I/R induced apoptosis by activating PI3K/Akt signaling.

Monocytes and Macrophages in Heart Valves: Uninvited Guests or Critical Performers?

Monocytes and macrophages are critical components of the myeloid niche of the innate immune system. In addition to traditional roles as phagocytes, this subsection of innate immunity has been implicated in its ability to regulate tissue homeostasis and inflammation across diverse physiological systems. Recent emergence of discriminatory features within the monocyte/macrophage niche within the last 5 years has helped to clarify specific function(s) of the subpopulations of these cells. It is becoming increasingly aware that these cells are likely implicated in valve development and disease. This review seeks to use current literature and opinions to show the diverse roles and potential contributions of this niche throughout valvulogenic processes, adult homeostatic function, valve disease mechanisms, and tissue engineering approaches.

Feedback regulation of RTK signaling in development

Precise regulation of the amplitude and duration of receptor tyrosine kinase (RTK) signaling is critical for the execution of cellular programs and behaviors. Understanding these control mechanisms has important implications for the field of developmental biology, and in recent years, the question of how augmentation or attenuation of RTK signaling via feedback loops modulates development has become of increasing interest. RTK feedback regulation is also important for human disease research; for example, germline mutations in genes that encode RTK signaling pathway components cause numerous human congenital syndromes, and somatic alterations contribute to the pathogenesis of diseases such as cancers. In this review, we survey regulators of RTK signaling that tune receptor activity and intracellular transduction cascades, with a focus on the roles of these genes in the developing embryo. We detail the diverse inhibitory mechanisms utilized by negative feedback regulators that, when lost or perturbed, lead to aberrant increases in RTK signaling. We also discuss recent biochemical and genetic insights into positive regulators of RTK signaling and how these proteins function in tandem with negative regulators to guide embryonic development.

High-Throughput Screening of HECT E3 Ubiquitin Ligases Using UbFluor

HECT E3 ubiquitin ligases are responsible for many human disease phenotypes and are promising drug targets; however, screening assays for HECT E3 inhibitors are inherently complex, requiring upstream E1 and E2 enzymes as well as ubiquitin, ATP, and detection reagents. Intermediate ubiquitin thioesters and a complex mixture of polyubiquitin products provide further opportunities for off-target inhibition and increase the complexity of the assay. UbFluor is a novel ubiquitin thioester that bypasses the E1 and E2 enzymes and undergoes direct transthiolation with HECT E3 ligases. The release of fluorophore upon transthiolation allows fluorescence polarization detection of HECT E3 activity. In the presence of inhibitors, HECT E3 activity is ablated, and thus no reaction and no change in FP are observed. This assay has been adapted for high-throughput screening of small molecules against HECT E3 ligases, and its utility has been proven in the discovery of HECT E3 ligase inhibitors. © 2017 by John Wiley & Sons, Inc.

Large-Scale Quantitative Proteomics Identifies the Ubiquitin Ligase Nedd4-1 as an Essential Regulator of Liver Regeneration

The liver is the only organ in mammals that fully regenerates even after major injury. To identify orchestrators of this regenerative response, we performed quantitative large-scale proteomics analysis of cytoplasmic and nuclear fractions from normal versus regenerating mouse liver. Proteins of the ubiquitin-proteasome pathway were rapidly upregulated after two-third hepatectomy, with the ubiquitin ligase Nedd4-1 being a top hit. In vivo knockdown of Nedd4-1 in hepatocytes through nanoparticle-mediated delivery of small interfering RNA caused severe liver damage and inhibition of cell proliferation after hepatectomy, resulting in liver failure. Mechanistically, we demonstrate that Nedd4-1 is required for efficient internalization of major growth factor receptors involved in liver regeneration and their downstream mitogenic signaling. These results highlight the power of large-scale proteomics to identify key players in liver regeneration and the importance of posttranslational regulation of growth factor signaling in this process. Finally, they identify an essential function of Nedd4-1 in tissue repair.

Thrombospondins: A Role in Cardiovascular Disease

Thrombospondins (TSPs) represent extracellular matrix (ECM) proteins belonging to the TSP family that comprises five members. All TSPs have a complex multidomain structure that permits the interaction with various partners including other ECM proteins, cytokines, receptors, growth factors, etc. Among TSPs, TSP1, TSP2, and TSP4 are the most studied and functionally tested. TSP1 possesses anti-angiogenic activity and is able to activate transforming growth factor (TGF)-β, a potent profibrotic and anti-inflammatory factor. Both TSP2 and TSP4 are implicated in the control of ECM composition in hypertrophic hearts. TSP1, TSP2, and TSP4 also influence cardiac remodeling by affecting collagen production, activity of matrix metalloproteinases and TGF-β signaling, myofibroblast differentiation, cardiomyocyte apoptosis, and stretch-mediated enhancement of myocardial contraction. The development and evaluation of TSP-deficient animal models provided an option to assess the contribution of TSPs to cardiovascular pathology such as (myocardial infarction) MI, cardiac hypertrophy, heart failure, atherosclerosis, and aortic valve stenosis. Targeting of TSPs has a significant therapeutic value for treatment of cardiovascular disease. The activation of cardiac TSP signaling in stress and pressure overload may be therefore beneficial.

Nedd4 Deficiency in Vascular Smooth Muscle Promotes Vascular Calcification by Stabilizing pSmad1

The nonosseous calcification process such as atherosclerosis is one of the major complications in several types of metabolic diseases. In a previous study, we uncovered that aberrant activity of transforming growth factor β (TGF-β) signaling pathway could contribute to the vascular smooth muscle cells' (VSMCs) calcification process. Also, we identified NEDD4 E3 ligase as a key suppressor of bone morphogenetic protein (BMP)/Smad pathway via a polyubiquitination-dependent selective degradation of C-terminal phosphorylated Smad1 (pSmad1) activated by TGF-β. Here, we further validated and confirmed the role of Nedd4 in in vivo vascular calcification progression. First, Nedd4 deletion in SM22α-positive mouse tissues (Nedd4^fl/fl ;SM22α-Cre) showed deformed aortic structures with disarranged elastin fibers at 24 weeks after birth. Second, vitamin D-induced aorta vascular calcification rate in Nedd4^fl/fl ;SM22α-Cre mice was significantly higher than their wild-type littermates. Nedd4^fl/fl ;SM22α-Cre mice showed a development of vascular calcification even at very low-level injection of vitamin D, but this was not exhibited in wild-type littermates. Third, we confirmed that TGF-β1-induced pSmad1 levels were elevated in Nedd4-deficient primary VSMCs isolated from Nedd4^fl/fl ;SM22α-Cre mice. Fourth, we further found that Nedd4^fl/fl ;SM22α-Cre mVSMCs gained mesenchymal cell properties toward osteoblast-like differentiation by a stable isotope labeling in cell culture (SILAC)-based proteomics analysis. Finally, epigenetic analysis revealed that methylation levels of human NEDD4 gene promoter were significantly increased in atherosclerosis patients. Collectively, abnormal expression or dysfunction of Nedd4 E3 ligase could be involved in vascular calcification of VSMCs by activating bone-forming signals during atherosclerosis progression. © 2016 American Society for Bone and Mineral Research.

Rare copy number variants in patients with congenital conotruncal heart defects

BACKGROUND

Previous studies using different cardiac phenotypes, technologies and designs suggest a burden of large, rare or de novo copy number variants (CNVs) in subjects with congenital heart defects. We sought to identify disease-related CNVs, candidate genes, and functional pathways in a large number of cases with conotruncal and related defects that carried no known genetic syndrome.

METHODS

Cases and control samples were divided into two cohorts and genotyped to assess each subject's CNV content. Analyses were performed to ascertain differences in overall CNV prevalence and to identify enrichment of specific genes and functional pathways in conotruncal cases relative to healthy controls.

RESULTS

Only findings present in both cohorts are presented. From 973 total conotruncal cases, a burden of rare CNVs was detected in both cohorts. Candidate genes from rare CNVs found in both cohorts were identified based on their association with cardiac development or disease, and/or their reported disruption in published studies. Functional and pathway analyses revealed significant enrichment of terms involved in either heart or early embryonic development.

CONCLUSION

Our study tested one of the largest cohorts specifically with cardiac conotruncal and related defects. These results confirm and extend previous findings that CNVs contribute to disease risk for congenital heart defects in general and conotruncal defects in particular. As disease heterogeneity renders identification of single recurrent genes or loci difficult, functional pathway and gene regulation network analyses appear to be more informative. Birth Defects Research 109:271-295, 2017. © 2017 Wiley Periodicals, Inc.

Copy number variation of E3 ubiquitin ligase genes in peripheral blood leukocyte and colorectal cancer

Given that E3 ubiquitin ligases (E3) regulate specific protein degradation in many cancer-related biological processes. E3 copy number variation (CNV) may affect the development and prognosis of colorectal cancer (CRC). Therefore, we detected CNVs of five E3 genes in 518 CRC patients and 518 age, gender and residence matched controls in China, and estimated the association between E3 gene CNVs and CRC risk and prognosis. We also estimated their interactions with environmental factors and CRC risk. We find a significant association between the CNVs of MDM2 and CRC risk (amp v.s. wt: odds ratio = 14.37, 95% confidence interval: 1.27, 163.74, P = 0.032), while SKP2 CNVs may significantly decrease CRC risk (del v.s. wt: odds ratio = 0.32, 95% confidence interval: 0.10, 1.00, P = 0.050). However, we find no significant association between the CNVs of other genes and CRC risk. The only significant gene-environment interaction effects are between SKP2 CNVs and consumption of fish and/or fruit (P = 0.014 and P = 0.035) and between FBXW7 CNVs and pork intake (P = 0.040). Finally, we find marginally significant association between β-TRCP CNVs and CRC prognosis (amp v.s. wt, hazard ratio = 0.42, 95% confidence interval: 0.19, 0.97, P = 0.050).

Intestinal knockout of Nedd4 enhances growth of Apcmin tumors

Nedd4 (Nedd4-1) is an E3 ubiquitin ligase that belongs to the HECT family and comprises a C2-WW(n)-HECT domain architecture. Although it has been reported to regulate growth factor receptors and cellular signaling, its role in cancer development has been controversial, with some studies proposing that it promotes cancer while others suggest it inhibits tumor growth. Here, we tested the effect of Nedd4 on intestinal tumor formation and growth using Nedd4-knockout mice (Nedd4 floxed (fl) mice crossed to villin-Cre mice). Although we find that knockout of Nedd4 on its own does not cause tumor growth, its knockout in the context of Apc^+/min-derived colorectal tumors leads to augmentation of tumor growth, suggesting that Nedd4 normally suppresses intestinal WNT signaling and growth of colonic tumors. WNT signaling microarray, immunoblotting and immunohistochemistry analyses of tumors derived from the Villin-Cre;Nedd4^fl/fl;Apc^+/min colons demonstrated elevated expression of the WNT upstream effectors LEF1 (full length) and YY1 in these tumors relative to control (Apc^+/min alone) tumors. Together, these results suggest that Nedd4 suppresses colonic WNT signaling and tumor growth, at least in part, by suppressing the transcription factors LEF1 and YY1.

Cardiomyocyte-specific overexpression of the ubiquitin ligase Wwp1 contributes to reduction in Connexin 43 and arrhythmogenesis

Gap junctions (GJ) are intercellular channels composed of connexin subunits that play a critical role in a diverse number of cellular processes in all tissue types. In the heart, GJs mediate electrical coupling between cardiomyocytes and display mislocalization and/or downregulation in cardiac disease (a process known as GJ remodeling), producing an arrhythmogenic substrate. The main constituent of GJs in the ventricular myocardium is Connexin 43 (Cx43), an integral membrane protein that is rapidly turned over and shows decreased expression or function with age. We hypothesized that Wwp1, an ubiquitin ligase whose expression in known to increase in aging-related pathologies, may regulate Cx43 in vivo by targeting it for ubiquitylation and degradation and yield tissue-specific Cx43 loss of function phenotypes. When Wwp1 was globally overexpressed in mice under the control of a β-actin promoter, the highest induction of Wwp1 expression was observed in the heart which was associated with a 90% reduction in cardiac Cx43 protein levels, left ventricular hypertrophy (LVH), and the development of lethal ventricular arrhythmias around 8weeks of age. This phenotype was completely penetrant in two independent founder lines. Cardiomyocyte-specific overexpression of Wwp1 confirmed that this phenotype was cell autonomous and delineated Cx43-dependent and -independent roles for Wwp1 in arrhythmogenesis and LVH, respectively. Using a cell-based system, it was determined that Wwp1 co-immunoprecipitates with and ubiquitylates Cx43, causing a decrease in the steady state levels of Cx43 protein. These findings offer new mechanistic insights into the regulation of Cx43 which may be exploitable in various gap junctionopathies.

NEDD4 Regulates PAX7 Levels Promoting Activation of the Differentiation Program in Skeletal Muscle Precursors

The transcription factor Pax7 regulates skeletal muscle stem cell (satellite cells) specification and maintenance through various mechanisms, including repressing the activity of the muscle regulatory factor MyoD. Hence, Pax7-to-MyoD protein ratios can determine maintenance of the committed-undifferentiated state or activation of the differentiation program. Pax7 expression decreases sharply in differentiating myoblasts but is maintained in cells (re)acquiring quiescence, yet the mechanisms regulating Pax7 levels based on differentiation status are not well understood. Here we show that Pax7 levels are directly regulated by the ubiquitin-ligase Nedd4. Our results indicate that Nedd4 is expressed in quiescent and activated satellite cells, that Nedd4 and Pax7 physically interact during early muscle differentiation-correlating with Pax7 ubiquitination and decline-and that Nedd4 loss of function prevented this effect. Furthermore, even transient nuclear accumulation of Nedd4 induced a drop in Pax7 levels and precocious muscle differentiation. Consequently, we propose that Nedd4 functions as a novel Pax7 regulator, which activity is temporally and spatially controlled to modulate the Pax7 protein levels and therefore satellite cell fate.

E3 Ubiquitin Ligase NEDD4 Promotes Influenza Virus Infection by Decreasing Levels of the Antiviral Protein IFITM3

Interferon (IFN)-induced transmembrane protein 3 (IFITM3) is a cell-intrinsic factor that limits influenza virus infections. We previously showed that IFITM3 degradation is increased by its ubiquitination, though the ubiquitin ligase responsible for this modification remained elusive. Here, we demonstrate that the E3 ubiquitin ligase NEDD4 ubiquitinates IFITM3 in cells and in vitro. This IFITM3 ubiquitination is dependent upon the presence of a PPxY motif within IFITM3 and the WW domain-containing region of NEDD4. In NEDD4 knockout mouse embryonic fibroblasts, we observed defective IFITM3 ubiquitination and accumulation of high levels of basal IFITM3 as compared to wild type cells. Heightened IFITM3 levels significantly protected NEDD4 knockout cells from infection by influenza A and B viruses. Similarly, knockdown of NEDD4 in human lung cells resulted in an increase in steady state IFITM3 and a decrease in influenza virus infection, demonstrating a conservation of this NEDD4-dependent IFITM3 regulatory mechanism in mouse and human cells. Consistent with the known association of NEDD4 with lysosomes, we demonstrate for the first time that steady state turnover of IFITM3 occurs through the lysosomal degradation pathway. Overall, this work identifies the enzyme NEDD4 as a new therapeutic target for the prevention of influenza virus infections, and introduces a new paradigm for up-regulating cellular levels of IFITM3 independently of IFN or infection.

IFITM3 is critical for limiting the severity of influenza virus infections in humans and mice. Optimal antiviral activity of IFITM3 is achieved when it is present at high levels within cells. Our results indicate that the E3 ubiquitin ligase NEDD4 decreases baseline IFITM3 levels by ubiquitinating IFITM3 and promoting its turnover. Depleting NEDD4 from cells results in IFITM3 accumulation and greater resistance to infection by influenza viruses. Therefore, we have identified NEDD4 as a regulator of IFITM3 levels and as a novel drug target for preventing influenza virus and other IFITM3-sensitive virus infections.

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.

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.

Regulation of ERBB3/HER3 signaling in cancer

ERBB3/HER3 is emerging as a molecular target for various cancers. HER3 is overexpressed and activated in a number of cancer types under the conditions of acquired resistance to other HER family therapeutic interventions such as tyrosine kinase inhibitors and antibody therapies. Regulation of the HER3 expression and signaling involves numerous HER3 interacting proteins. These proteins include PI3K, Shc, and E3 ubiquitin ligases NEDD4 and Nrdp1. Furthermore, recent identification of a number of HER3 oncogenic mutations in colon and gastric cancers elucidate the role of HER3 in cancer development. Despite the strong evidence regarding the role of HER3 in cancer, the current understanding of the regulation of HER3 expression and activation requires additional research. Moreover, the lack of biomarkers for HER3-driven cancer poses a big challenge for the clinical development of HER3 targeting antibodies. Therefore, a better understanding of HER3 regulation should improve the strategies to therapeutically target HER3 for cancer therapy.

Invoking the power of thrombospondins: regulation of thrombospondins expression

Increasing evidence suggests critical functions of thrombospondins (TSPs) in a variety of physiological and pathological processes. With the growing understanding of the importance of these matricellular proteins, the need to understand the mechanisms of regulation of their expression and potential approaches to modulate their levels is also increasing. The regulation of TSP expression is multi-leveled, cell- and tissue-specific, and very precise. However, the knowledge of mechanisms modulating the levels of TSPs is fragmented and incomplete. This review discusses the known mechanisms of regulation of TSP levels and the gaps in our knowledge that prevent us from developing strategies to modulate the expression of these physiologically important proteins.

Ubiquitylation of voltage-gated sodium channels

Ion channel proteins are regulated by different types of posttranslational modifications. The focus of this review is the regulation of voltage-gated sodium channels (Navs) upon their ubiquitylation. The amiloride-sensitive epithelial sodium channel (ENaC) was the first ion channel shown to be regulated upon ubiquitylation. This modification results from the binding of ubiquitin ligase from the Nedd4 family to a protein-protein interaction domain, known as the PY motif, in the ENaC subunits. Many of the Navs have similar PY motifs, which have been demonstrated to be targets of Nedd4-dependent ubiquitylation, tagging them for internalization from the cell surface. The role of Nedd4-dependent regulation of the Nav membrane density in physiology and disease remains poorly understood. Two recent studies have provided evidence that Nedd4-2 is downregulated in dorsal root ganglion (DRG) neurons in both rat and mouse models of nerve injury-induced neuropathic pain. Using two different mouse models, one with a specific knockout of Nedd4-2 in sensory neurons and another where Nedd4-2 was overexpressed with the use of viral vectors, it was demonstrated that the neuropathy-linked neuronal hyperexcitability was the result of Nav1.7 and Nav1.8 overexpression due to Nedd4-2 downregulation. These studies provided the first in vivo evidence of the role of Nedd4-2-dependent regulation of Nav channels in a disease state. This ubiquitylation pathway may be involved in the development of symptoms and diseases linked to Nav-dependent hyperexcitability, such as pain, cardiac arrhythmias, epilepsy, migraine, and myotonias.

NEDD4 E3 ligase inhibits the activity of the Hippo pathway by targeting LATS1 for degradation

Proper regulation of cell proliferation, cell apoptosis, and cell death are vital for the development and survival of living organisms. Failure or dysfunction of any of these processes can have devastating effects, including cancer. The Hippo pathway, first discovered in Drosophila, has been found to be a major growth-regulatory signaling pathway that controls these crucial processes and has been implicated in cell-progress regulation and organ size determination. Abnormal regulation of this pathway has been found in several cancer types. However, the mechanisms that regulate the pathway and its core members yet have to be elucidated. One of the main core components of this pathway is LATS1, a serine/threonine kinase. Therefore, understanding how LATS1 activity is regulated is expected to shed light on new mechanisms that regulate the Hippo pathway. In the current work, we identified several potential LATS1 regulators and proved that NEDD4 E3 ubiquitin ligase controls LATS1 stability. We demonstrate that NEDD4 directly interacts with LATS1, leading to ubiquitination and decreased levels of LATS1 and, thus, increased YAP localization in the nucleus, which subsequently increases the transcriptional activity of YAP. As such, we show that NEDD4 acts as an additional regulator of the Hippo pathway on the protein level via interactions between WW domain-containing and PPxY motif-containing proteins. These findings might be applied in the development of new therapeutic approaches through the activation of LATS1.

The ubiquitin ligase Nedd4 regulates craniofacial development by promoting cranial neural crest cell survival and stem-cell like properties

The integration of multiple morphogenic signalling pathways and transcription factor networks is essential to mediate neural crest (NC) cell induction, delamination, survival, stem-cell properties, fate choice and differentiation. Although the transcriptional control of NC development is well documented in mammals, the role of post-transcriptional modifications, and in particular ubiquitination, has not been explored. Here we report an essential role for the ubiquitin ligase Nedd4 in cranial NC cell development. Our analysis of Nedd4(-/-) embryos identified profound deficiency of cranial NC cells in the absence of structural defects in the neural tube. Nedd4 is expressed in migrating cranial NC cells and was found to positively regulate expression of the NC transcription factors Sox9, Sox10 and FoxD3. We found that in the absence of these factors, a subset of cranial NC cells undergo apoptosis. In accordance with a lack of cranial NC cells, Nedd4(-/-) embryos have deficiency of the trigeminal ganglia, NC derived bone and malformation of the craniofacial skeleton. Our analyses therefore uncover an essential role for Nedd4 in a subset of cranial NC cells and highlight E3 ubiquitin ligases as a likely point of convergence for multiple NC signalling pathways and transcription factor networks.

Unraveling the genetic basis of aspirin hypersensitivity in asthma beyond arachidonate pathways

Although aspirin-exacerbated respiratory disease (AERD) has attracted a great deal of attention because of its association with severe asthma, it remains widely under-diagnosed in the asthmatic population. Oral aspirin challenge is the best method of diagnosing AERD, but this is a time-consuming procedure with serious complications in some cases. Thus, development of non-invasive methods for easy diagnosis is necessary to prevent unexpected complications of aspirin use in susceptible patients. For the past decade, many studies have attempted to elucidate the genetic variants responsible for risk of AERD. Several approaches have been applied in these genetic studies. To date, a limited number of biologically plausible candidate genes in the arachidonate and immune and inflammatory pathways have been studied. Recently, a genome-wide association study was performed. In this review, the results of these studies are summarized, and their limitations discussed. In addition to the genetic variants, changes in methylation patterns on CpG sites have recently been identified in a target tissue of aspirin hypersensitivity. Finally, perspectives on application of new genomic technologies are introduced; these will aid our understanding of the genetic pathogenesis of aspirin hypersensitivity in asthma.

Role of the ubiquitin proteasome system in the heart

Proper protein turnover is required for cardiac homeostasis and, accordingly, impaired proteasomal function appears to contribute to heart disease. Specific proteasomal degradation mechanisms underlying cardiovascular biology and disease have been identified, and such cellular pathways have been proposed to be targets of clinical relevance. This review summarizes the latest literature regarding the specific E3 ligases involved in heart biology, and the general ways that the proteasome regulates protein quality control in heart disease. The potential for therapeutic intervention in Ubiquitin Proteasome System function in heart disease is discussed.

Structure and dynamics of human Nedd4-1 WW3 in complex with the αENaC PY motif

Nedd4-1 (neuronal precursor cell expressed developmentally downregulated gene 4-1) is an E3 ubiquitin ligase that interacts with and negatively regulates the epithelial Na(+) channel (ENaC). The WW domains of Nedd4-1 bind to the ENaC subunits via recognition of PY motifs. Human Nedd4-1 (hNedd4-1) contains four WW domains with the third domain (WW3*) showing the strongest affinity to the PY motif. To understand the mechanism underlying this binding affinity, we have carried out NMR structural and dynamics analyses of the hNedd4-1 WW3* domain in complex with a peptide comprising the C-terminal tail of the human ENaC α-subunit. The structure reveals that the peptide interacts in a similar manner to other WW domain-ENaC peptide structures. Crucial interactions that likely provide binding affinity are the broad XP groove facilitating additional contacts between the WW3* domain and the peptide, compared to similar complexes, and the large surface area buried (83Å(2)) between R430 (WW3*) and L647' (αENaC). This corroborates the model-free analysis of the (15)N backbone relaxation data, which showed that R430 is the most rigid residue in the domain (S(2)=0.90±0.01). Carr-Purcell-Meiboom-Gill relaxation dispersion analysis identified two different conformational exchange processes on the μs-ms time-scale. One of these processes involves residues located at the peptide binding interface, suggesting conformational exchange may play a role in peptide recognition. Thus, both structural and dynamic features of the complex appear to define the high binding affinity. The results should aid interpretation of biochemical data and modeling interfaces between Nedd4-1 and other interacting proteins.

Mammalian HECT ubiquitin-protein ligases: biological and pathophysiological aspects

Members of the HECT family of E3 ubiquitin-protein ligases are characterized by a C-terminal HECT domain that catalyzes the covalent attachment of ubiquitin to substrate proteins and by N-terminal extensions of variable length and domain architecture that determine the substrate spectrum of a respective HECT E3. Since their discovery in 1995, it has become clear that deregulation of distinct HECT E3s plays an eminent role in human disease or disease-related processes including cancer, cardiovascular and neurological disorders, viral infections, and immune response. Thus, a detailed understanding of the structure-function aspects of HECT E3s as well as the identification and characterization of the substrates and regulators of HECT E3s is critical in developing new approaches in the treatment of respective diseases. In this review, we summarize what is currently known about mammalian HECT E3s, with a focus on their biological functions and roles in pathophysiology.This article is part of a Special Issue entitled: Ubiquitin-Proteasome System. Guest Editors: Thomas Sommer and Dieter H. Wolf.

HECT domain-containing E3 ubiquitin ligase NEDD4L negatively regulates Wnt signaling by targeting dishevelled for proteasomal degradation

Wnt signaling plays a pivotal role in embryogenesis and tissue homeostasis. Dishevelled (Dvl) is a central mediator for both Wnt/β-catenin and Wnt/planar cell polarity pathways. NEDD4L, an E3 ubiquitin ligase, has been shown to regulate ion channel activity, cell signaling, and cell polarity. Here, we report a novel role of NEDD4L in the regulation of Wnt signaling. NEDD4L induces Dvl2 polyubiquitination and targets Dvl2 for proteasomal degradation. Interestingly, the NEDD4L-mediated ubiquitination of Dvl2 is Lys-6, Lys-27, and Lys-29 linked but not typical Lys-48-linked ubiquitination. Consistent with the role of Dvl in both Wnt/β-catenin and Wnt/planar cell polarity signaling, NEDD4L regulates the cellular β-catenin level and Rac1, RhoA, and JNK activities. We have further identified a hierarchical regulation that Wnt5a induces JNK-mediated phosphorylation of NEDD4L, which in turn promotes its ability to degrade Dvl2. Finally, we show that NEDD4L inhibits Dvl2-induced axis duplication in Xenopus embryos. Our work thus demonstrates that NEDD4L is a negative feedback regulator of Wnt signaling.

The Rac1 hypervariable region in targeting and signaling: a tail of many stories

Cellular signaling by small GTPases is critically dependent on proper spatio-temporal orchestration of activation and output. In addition to their core G (guanine nucleotide binding)-domain, small GTPases comprise a hypervariable region (HVR) and a lipid anchor that are generally accepted to control subcellullar localization. The HVR encodes in many small GTPases a polybasic region (PBR) that permits charge-mediated association to the inner leaflet of the plasma membrane or to intracellular organelles. Over the past 15-20 years, evidence has accumulated for specific protein-protein interactions, mediated by the HVR, that control both targeting and signaling specificity of small GTPases. Using the RhoGTPase Rac1 as a paradigm we here review a series of protein partners that require the Rac1 HVR for association and that control various aspects of localized Rac1 signaling. Some of these proteins represent Rac1 activators, whereas others mediate Rac1 inactivation and degradation and yet others potentiate Rac1 downstream signaling. Finally, evidence is discussed which shows that the HVR of Rac1 also contributes to effector interactions, co-operating with the N-terminal effector domain. The complexity of localized Rac1 signaling, reviewed here, is most likely exemplary for many other small GTPases as well, representing a challenge to identify and define similar mechanisms controlling the specific signaling induced by small GTPases.

ARID1a-DNA interactions are required for promoter occupancy by SWI/SNF

Every known SWI/SNF chromatin-remodeling complex incorporates an ARID DNA binding domain-containing subunit. Despite being a ubiquitous component of the complex, physiological roles for this domain remain undefined. Here, we show that disruption of ARID1a-DNA binding in mice results in embryonic lethality, with mutant embryos manifesting prominent defects in the heart and extraembryonic vasculature. The DNA binding-defective mutant ARID1a subunit is stably expressed and capable of assembling into a SWI/SNF complex with core catalytic properties, but nucleosome substrate binding and promoter occupancy by ARID1a-containing SWI/SNF complexes (BAF-A) are impaired. Depletion of ARID domain-dependent, BAF-A associations at THROMBOSPONDIN 1 (THBS1) led to the concomitant upregulation of this SWI/SNF target gene. Using a THBS1 promoter-reporter gene, we further show that BAF-A directly regulates THBS1 promoter activity in an ARID domain-dependent manner. Our data not only demonstrate that ARID1a-DNA interactions are physiologically relevant in higher eukaryotes but also indicate that these interactions facilitate SWI/SNF binding to target sites in vivo. These findings support the model wherein cooperative interactions among intrinsic subunit-chromatin interaction domains and sequence-specific transcription factors drive SWI/SNF recruitment.

The ubiquitin ligase Nedd4-1 participates in denervation-induced skeletal muscle atrophy in mice

Skeletal muscle atrophy is a consequence of muscle inactivity resulting from denervation, unloading and immobility. It accompanies many chronic disease states and also occurs as a pathophysiologic consequence of normal aging. In all these conditions, ubiquitin-dependent proteolysis is a key regulator of the loss of muscle mass, and ubiquitin ligases confer specificity to this process by interacting with, and linking ubiquitin moieties to target substrates through protein∶protein interaction domains. Our previous work suggested that the ubiquitin-protein ligase Nedd4-1 is a potential mediator of skeletal muscle atrophy associated with inactivity (denervation, unloading and immobility). Here we generated a novel tool, the Nedd4-1 skeletal muscle-specific knockout mouse (myo^Cre;Nedd4-1^flox/flox) and subjected it to a well validated model of denervation induced skeletal muscle atrophy. The absence of Nedd4-1 resulted in increased weights and cross-sectional area of type II fast twitch fibres of denervated gastrocnemius muscle compared with wild type littermates controls, at seven and fourteen days following tibial nerve transection. These effects are not mediated by the Nedd4-1 substrates MTMR4, FGFR1 and Notch-1. These results demonstrate that Nedd4-1 plays an important role in mediating denervation-induced skeletal muscle atrophy in vivo.

NEDD4 is overexpressed in colorectal cancer and promotes colonic cell growth independently of the PI3K/PTEN/AKT pathway

Ubiquitination controls multiple cellular processes relevant to cancer pathogenesis. Using Gene Set Enrichment Analysis of an mRNA transcriptome dataset, we have identified genes encoding components of the ubiquitin system that are differentially expressed in colorectal cancers as compared to normal colonic mucosa. Among the significantly overexpressed genes was NEDD4 (neural precursor cell-expressed developmentally down-regulated 4), the prototype member of the HECT (homologous to E6AP C-terminus) E3 ubiquitin ligase family. Previous studies have shown that NEDD4 may act as an oncoprotein by inducing ubiquitination and degradation of the tumor suppressor protein PTEN (phosphatase and tensin homolog). To investigate its functional importance in colorectal cancer, HCT-15 and LoVo colon cancer cells were depleted of NEDD4 by small interfering RNA. The depletion resulted in reduced growth and altered cell morphology in both cell lines. However, NEDD4 depletion did not affect the PTEN protein level or PI3K/AKT signaling pathway activation. Moreover, ectopic expression of NEDD4 did not influence the PTEN subcellular localization or protein level. Collectively, these data demonstrate that NEDD4 is overexpressed in colorectal cancers, and suggest that NEDD4 promotes growth of colon cancer cells independently of PTEN and PI3K/AKT signaling.

Phosphorylation of Kif26b promotes its polyubiquitination and subsequent proteasomal degradation during kidney development

Kif26b, a member of the kinesin superfamily proteins (KIFs), is essential for kidney development. Kif26b expression is restricted to the metanephric mesenchyme, and its transcription is regulated by a zinc finger transcriptional regulator Sall1. However, the mechanism(s) by which Kif26b protein is regulated remain unknown. Here, we demonstrate phosphorylation and subsequent polyubiquitination of Kif26b in the developing kidney. We find that Kif26b interacts with an E3 ubiquitin ligase, neural precursor cell expressed developmentally down-regulated protein 4 (Nedd4) in developing kidney. Phosphorylation of Kif26b at Thr-1859 and Ser-1962 by the cyclin-dependent kinases (CDKs) enhances the interaction of Kif26b with Nedd4. Nedd4 polyubiquitinates Kif26b and thereby promotes degradation of Kif26b via the ubiquitin-proteasome pathway. Furthermore, Kif26b lacks ATPase activity but does associate with microtubules. Nocodazole treatment not only disrupts the localization of Kif26b to microtubules but also promotes phosphorylation and polyubiquitination of Kif26b. These results suggest that the function of Kif26b is microtubule-based and that Kif26b degradation in the metanephric mesenchyme via the ubiquitin-proteasome pathway may be important for proper kidney development.