Impeded Nedd4-1-Mediated Ras Degradation Underlies Ras-Driven Tumorigenesis

HNF4A functions as a hepatocellular carcinoma oncogene or tumor suppressor depending upon the AMPK pathway activity status

Cancer cells frequently undergo energy metabolic stress induced by the increased dynamics of nutrient supply. Hepatocyte nuclear factor 4A (HNF4A) is a master transcription factor (TF) in hepatocytes that regulates metabolism and differentiation. However, the mechanism underlying how HNF4A functions in cancer progression remains unclear due to conflicting results observed in numerous studies. To address the roles of HNF4A in hepatocellular carcinoma (HCC), we investigated the regulatory functions of HNF4A in HCC cells under different glucose supply conditions. We found that HNF4A exhibited tumor-suppressive effects on the proliferation and migration of HCC cells in glucose-sufficient conditions and tumor-promotive effects on HCC cells in glucose-insufficient conditions. Further investigation revealed that this diverse function of HNF4A was dependent upon the AMPK pathway activity. Similarly, the prognosis predicted by HNF4A was also correlated with whether the AMPKa expression levels were low or high in clinical HCC patients. Multiomics approaches consisting of proteomics and ChIP-seq revealed that key HNF4A target genes, including NEDD4 and RPS6KA2, are involved in the diverse function of HNF4A in HCC in response to the AMPK activity status. Specifically, HNF4A could bind to the promoter region of NEDD4 and RPS6KA2, and upregulating their expression. Our study has demonstrated the relationship between and synergism of AMPK and HNF4A in the progression of HCC under diverse nutrient conditions.

Construction of ubiquitination-related risk model for predicting prognosis in lung adenocarcinoma

Lung adenocarcinoma is the most prevalent lung cancer type. Ubiquitination, a critical post-translational modification process that regulates protein degradation and signaling pathways, has been implicated in various cancers, including LUAD. We aimed to explore the associations between ubiquitination and lung adenocarcinoma. TCGA-LUAD cohort served as the training set. Unsupervised clustering, univariate Cox regression, Random Survival Forests, and least absolute shrinkage and selection operator (LASSO) Cox regression were applied to identify ubiquitination-related genes (URGs), then ubiquitination-related risk scores (URRS) were calculated using gene expression and the univariate Cox's coefficient. Comparisons between the high and the low URRS group regarding chemotherapy drug response, immune infiltration level, tumor mutation burden (TMB), tumor neoantigen load (TNB), PD1/L1 expression, and enriched pathways were performed. URRS was calculated based on the expression of DTL, UBE2S, CISH, and STC1. Patients with higher URRS had a worse prognosis (Hazard Ratio [HR] = 0.54, 95% Confidence Interval [CI]: 0.39-0.73, p < 0.001), and the prognosis of the URRS was further confirmed in 6 external validation cohorts (Hazard Ratio [HR] = 0.58, 95% Confidence Interval [CI]: 0.36-0.93, pmax = 0.023). The high URRS group had higher PD1/L1 expression level (p < 0.05), TMB (p < 0.001), TNB (p < 0.001), and TME scores (p < 0.001). The IC50 values of various chemotherapy drugs were lower in the high URRS group. In addition, we found that upregulation of STC1, UBE2S, and DTL was associated with worse, while upregulation of CISH was associated with better prognosis. We also performed a reverse transcription-quantitative polymerase chain reaction (RT-qPCR) for validation. In conclusion, the ubiquitination-based signature might serve as a biomarker to help evaluate the prognosis, biological features, and appropriate treatment for patients with lung adenocarcinoma.

Recent advances in targeted degradation in the RAS pathway

RAS (rat sarcoma) is one of the most frequently mutated gene families in cancer, encoding proteins classified as small GTPases. Mutations in RAS proteins result in abnormal activation of the RAS signaling pathway, a key driver in the initiation and progression of various malignancies. Consequently, targeting RAS proteins and the RAS signaling pathway has become a critical strategy in anticancer therapy. While RAS was historically considered an "undruggable" target, recent breakthroughs have yielded inhibitors specifically targeting KRASG12C and KRASG12D mutations, which have shown clinical efficacy in patients. However, these inhibitors face limitations due to rapid acquired resistance and the toxic effects of combination therapies in clinical settings. Targeted protein degradation (TPD) strategies, such as PROTACs and molecular glues, provide a novel approach by selectively degrading RAS proteins, or their upstream and downstream regulatory factors, to block aberrant signaling pathways. These degraders offer a promising alternative to traditional inhibitors by potentially circumventing resistance and enhancing therapeutic precision. This review discusses recent advancements in RAS pathway degraders, with an emphasis on targeting RAS mutations as well as their upstream regulators and downstream effectors for potential cancer treatments.

K27-linked RORγt ubiquitination by Nedd4 potentiates Th17-mediated autoimmunity

BACKGROUND

The HECT E3 ubiquitin ligase Nedd4 has been shown to positively regulate T cell responses, but its role in T helper (Th) cell differentiation and autoimmunity is unknown. Th17 cells are believed to play a pivotal role in the development and pathogenesis of autoimmune diseases. Nevertheless, the regulation of RORγt activation during Th17 cell differentiation by TCR signaling is yet to be elucidated. These uncharted aspects inspire us to explore the potential role of Nedd4 in Th17-mediated autoimmunity.

METHODS

We evaluated the impact of Nedd4 deficiency on mouse T cell development and differentiation using flow cytometry and siRNA transfection, and subsequently validated these findings in T cells from patients with multiple sclerosis (MS). Furthermore, we investigated the influence of Nedd4 deficiency on Th17-mediated autoimmunity through experimental autoimmune encephalomyelitis (EAE), a mouse model of MS. Subsequently, we elucidated the molecular mechanism underlying the interaction between Nedd4 and RORgt through immunoprecipitation, mass spectrometry analysis, and lentiviral transduction. Additionally, we identified Nedd4 as an E3 ubiquitin ligase for RORγt. Moreover, we characterized the tyrosine residue sites and polyubiquitination patterns involved in RORγt ubiquitination.

RESULTS

In this study, we report that loss of Nedd4 in T cells specifically impairs pathogenic and non-pathogenic Th17 responses, and Th17-mediated EAE development. At the molecular level, Nedd4 binds to the PPLY motif within the ligand binding domain of RORγt, and targets RORγt at K112 for K27-linked polyubiquitination, thus augmenting its activity.

CONCLUSION

Nedd4 is a crucial E3 ubiquitin ligase for RORγt in the regulating Th17 cell development and offers potential therapeutic benefits for treating Th17-mediated autoimmune diseases.

The differential interactomes of the KRAS splice variants identify BIRC6 as a ubiquitin ligase for KRAS4A

Transcripts of the KRAS locus are alternatively spliced to generate two proteins, KRAS4A and KRAS4B, which differ in their membrane-targeting sequences. These splice variants have been conserved for more than 450 million years, suggesting non-overlapping functions driven by differential membrane association. Here, we use proximity labeling to map the differential interactomes of the KRAS splice variants. We find 24 and 10 proteins that interact specifically with KRAS4A or KRAS4B, respectively. The KRAS interacting protein most specific to KRAS4A is BIRC6, a large member of the inhibitor of apoptosis protein family unique in possessing E2/E3 ubiquitin ligase activity. We find that this interaction takes place on the Golgi apparatus and results in the mono- and di-ubiquitination of KRAS4A at lysines 128 and 147. Silencing BIRC6 diminishes GTP loading of and growth stimulation by KRAS4A but not KRAS4B. Thus, BIRC6 is a ubiquitin ligase that inhibits apoptosis and also modifies KRAS4A.

Vitamin K-dependent gamma-carboxyglutamic acid protein 1 promotes pancreatic ductal adenocarcinoma progression through stabilizing oncoprotein KRAS and tyrosine kinase receptor EGFR

BACKGROUND

Vitamin K-dependent γ-glutamic acid carboxylation (Gla) proteins are calcium-binding and membrane-associated, participating in coagulation, bone turnover, and cancer biology. The molecular function of transmembrane proline-rich Gla proteins (PRRGs) remains unexplored.

METHODS

Analysis of pancreatic ductal adenocarcinoma (PDAC) datasets, including transcription profiles, clinical data, and tissue microarrays, was conducted to evaluate PRRG1 expression and its clinical relevance. PDAC cell lines with overexpressed, knockdown, and mutated PRRG1 were developed to study biological functions and pathways using RNA-seq, co-immunoprecipitation with mass spectrometry, Western blotting, and immunofluorescence. In vivo xenograft and orthotopic models assessed PRRG1's impact on PDAC progression, with and without warfarin treatment.

RESULTS

PRRG1 was significantly upregulated in PDAC compared to normal pancreas, correlating with poorer patient survival. PRRG1 knockdown reduced PDAC cell proliferation, anchorage-independent growth in vitro, and tumor growth in vivo. PRRG1 localized at the plasma membrane, interacted with the HECT E3 ligase NEDD4 via the C-terminal PPXY motif, and promoted NEDD4 self-ubiquitination, reducing its protein levels. PRRG1 knockdown elevated NEDD4, destabilizing the oncoprotein KRAS and receptor EGFR, and attenuating downstream signaling and macropinocytosis under nutrient deprivation. The vitamin K-dependent Gla modification of PRRG1 was crucial for its membrane localization and pro-tumorigenic effects, and was inhibited by low-dose warfarin, a clinical vitamin K antagonist.

CONCLUSIONS

This study identifies PRRG1 as a key regulator of pro-tumorigenic signaling in PDAC, suggesting the potential of repurposing the anticoagulant warfarin as a therapeutic strategy.

KEY POINTS

PRRG1 is identified as the transmembrane Gla protein mediating PDAC malignancy. PRRG1 recruits and induces self-ubiquitination of membrane-anchoring E3 ligase NEDD4. PRRG1 exerts a protective role toward KRAS and EGFR by inhibiting NEDD4. The anticoagulant warfarin can be utilized to inhibit PRRG1 and PDAC advancement.

USP7 deubiquitinates KRAS and promotes non-small cell lung cancer

RAS oncogenic mutations are pivotal drivers of tumorigenesis. Ubiquitination modulates RAS functions, including activation, stability, and localization. While several E3 ligases regulate RAS ubiquitination, RAS deubiquitination remains less understood. Our study reveals that ubiquitin-specific protease 7 (USP7) directly deubiquitinates KRAS, stabilizing it and promoting the proliferation of non-small cell lung cancer (NSCLC) cells. Mechanistically, USP7 binds KRAS via its TRAF domain and removes the K48-linked polyubiquitin chains from residue K147. In addition, USP7 also stabilizes oncogenic KRAS mutants through deubiquitination. In lung cancer tissues, high USP7 expression is positively correlated with KRAS and is associated with lower patient survival rates. Moreover, USP7 inhibitors suppress NSCLC cell proliferation, particularly in cells resistant to the KRAS-G12C inhibitor AMG510. In conclusion, our findings identify USP7 as a key deubiquitinase regulating RAS stability, and targeting USP7 is a promising strategy to counteract KRAS inhibitor resistance in NSCLC.

Targeted genetic and small molecule disruption of N-Ras CaaX cleavage alters its localization and oncogenic potential

Ras GTPases and other CaaX proteins undergo multiple post-translational modifications at their carboxyl-terminus. These events initiate with prenylation of a cysteine and are followed by endoproteolytic removal of the 'aaX' tripeptide and carboxylmethylation. Some CaaX proteins are only subject to prenylation, however, due to the presence of an uncleavable sequence. In this study, uncleavable sequences were used to stage Ras isoforms in a farnesylated and uncleaved state to address the impact of CaaX proteolysis on protein localization and function. This targeted strategy is more specific than those that chemically inhibit the Rce1 CaaX protease or delete the RCE1 gene because global abrogation of CaaX proteolysis impacts the entire CaaX protein proteome and effects cannot be attributed to any specific CaaX protein of the many concurrently affected. With this targeted strategy, clear mislocalization and reduced activity of farnesylated and uncleaved Ras isoforms was observed. In addition, new peptidomimetics based on cleavable Ras CaaX sequences and the uncleavable CAHQ sequence were synthesized and tested as Rce1 inhibitors using in vitro and cell-based assays. Consistently, these non-hydrolyzable peptidomimetic Rce1 inhibitors recapitulate Ras mislocalization effects when modeled on cleavable but not uncleavable CaaX sequences. These findings indicate that a prenylated and uncleavable CaaX sequence, which can be easily applied to a wide range of mammalian CaaX proteins, can be used to probe the specific impact of CaaX proteolysis on CaaX protein properties under conditions of an otherwise normally processed CaaX protein proteome.

NEDD4 and NEDD4L: Ubiquitin Ligases Closely Related to Digestive Diseases

Protein ubiquitination is an enzymatic cascade reaction and serves as an important protein post-translational modification (PTM) that is involved in the vast majority of cellular life activities. The key enzyme in the ubiquitination process is E3 ubiquitin ligase (E3), which catalyzes the binding of ubiquitin (Ub) to the protein substrate and influences substrate specificity. In recent years, the relationship between the subfamily of neuron-expressed developmental downregulation 4 (NEDD4), which belongs to the E3 ligase system, and digestive diseases has drawn widespread attention. Numerous studies have shown that NEDD4 and NEDD4L of the NEDD4 family can regulate the digestive function, as well as a series of related physiological and pathological processes, by controlling the subsequent degradation of proteins such as PTEN, c-Myc, and P21, along with substrate ubiquitination. In this article, we reviewed the appropriate functions of NEDD4 and NEDD4L in digestive diseases including cell proliferation, invasion, metastasis, chemotherapeutic drug resistance, and multiple signaling pathways, based on the currently available research evidence for the purpose of providing new ideas for the prevention and treatment of digestive diseases.

Inhibition of ADAM9 promotes the selective degradation of KRAS and sensitizes pancreatic cancers to chemotherapy

Kirsten rat sarcoma virus (KRAS) signaling drives pancreatic ductal adenocarcinoma (PDAC) malignancy, which is an unmet clinical need. Here, we identify a disintegrin and metalloproteinase domain (ADAM)9 as a modulator of PDAC progression via stabilization of wild-type and mutant KRAS proteins. Mechanistically, ADAM9 loss increases the interaction of KRAS with plasminogen activator inhibitor 1 (PAI-1), which functions as a selective autophagy receptor in conjunction with light chain 3 (LC3), triggering lysosomal degradation of KRAS. Suppression of ADAM9 by a small-molecule inhibitor restricts disease progression in spontaneous models, and combination with gemcitabine elicits dramatic regression of patient-derived tumors. Our findings provide a promising strategy to target the KRAS signaling cascade and demonstrate a potential modality to enhance sensitivity to chemotherapy in PDAC.

Deoxyribonuclease 1-like 3 inhibits colorectal malignancy through antagonizing NEDD4-triggered CDKN1A ubiquitination

Deoxyribonuclease 1-like 3 (DNASE1L3) has been shown to play nonnegligible roles in several types of carcinomas. Nevertheless, the biological function, clinical relevance, and influence of DNASE1L3 in colorectal cancer (CRC) remain obscure. Immunohistochemistry was adopted to examine DNASE1L3 and CDKN1A expression in CRC tissue, and the clinical significance of DNASE1L3 was assessed. Cell counting kit-8, colony formation, and transwell assays were employed for assessing tumor proliferation and migration. The mechanisms underlying the impact of DNASE1L3 were explored via western blot analysis, co-immunoprecipitation, and ubiquitination assay. It was observed that DNASE1L3 was downregulated in CRC tissues and was tightly associated with patient prognosis. DNASE1L3 impaired CRC cell proliferation and migration through elevating CDKN1A via suppressing CDKN1A ubiquitination. Meanwhile, DNASE1L3 was positively related to CDKN1A. In mechanism, DNASE1L3 and CDKN1A interacted with the E3 ubiquitin ligase NEDD4. Moreover, DNASE1L3 was competitively bound to NEDD4, thus repressing NEDD4-mediated CDKN1A ubiquitination and degradation. These discoveries implied the potential mechanisms of DNASE1L3 during tumorigenesis, suggesting that DNASE1L3 may serve as a new potential therapeutic agent for CRC.

E3 ubiquitin ligases in lung cancer: Emerging insights and therapeutic opportunities

Aim In this review, we have attempted to provide the readers with an updated account of the role of a family of proteins known as E3 ligases in different aspects of lung cancer progression, along with insights into the deregulation of expression of these proteins during lung cancer. A detailed account of the therapeutic strategies involving E3 ligases that have been developed or currently under development has also been provided in this review. MATERIALS AND METHODS: The review article employs extensive literature search, along with differential gene expression analysis of lung cancer associated E3 ligases using the DESeq2 package in R, and the Gene Expression Profiling Interactive Analysis (GEPIA) database (http://gepia.cancer-pku.cn/). Protein expression analysis of CPTAC lung cancer samples was carried out using the UALCAN webtool (https://ualcan.path.uab.edu/index.html). Assessment of patient overall survival (OS) in response to high and low expression of selected E3 ligases was performed using the online Kaplan-Meier plotter (https://kmplot.com/analysis/index.php?p=background). KEY FINDINGS: SIGNIFICANCE: The review provides an in-depth understanding of the role of E3 ligases in lung cancer progression and an up-to-date account of the different therapeutic strategies targeting oncogenic E3 ligases for improved lung cancer management.

Oncogenic KRAS mutation confers chemoresistance by upregulating SIRT1 in non-small cell lung cancer

Kirsten rat sarcoma viral oncogene homologue (KRAS) is a frequent oncogenic driver of solid tumors, including non-small cell lung cancer (NSCLC). The treatment and outcomes of KRAS-mutant cancers have not been dramatically revolutionized by direct KRAS-targeted therapies because of the lack of deep binding pockets for specific small molecule inhibitors. Here, we demonstrated that the mRNA and protein levels of the class III histone deacetylase SIRT1 were upregulated by the KRASMut-Raf-MEK-c-Myc axis in KRASMut lung cancer cells and in lung tumors of a mouse model with spontaneous KrasG12D expression. KRASMut-induced SIRT1 bound to KRASMut and stably deacetylated KRASMut at lysine 104, which increased KRASMut activity. SIRT1 knockdown (K/D) or the SIRT1H363Y mutation increased KRASMut acetylation, which decreased KRASMut activity and sensitized tumors to the anticancer effects of cisplatin and erlotinib. Furthermore, in KrasG12D/+;Sirt1co/co mice, treatment with cisplatin and erlotinib robustly reduced the tumor burden and increased survival rates compared with those in spontaneous LSL-KrasG12D/+;Sirt1+/+ mice and mice in each single-drug treatment group. Then, we identified p300 as a KRASMut acetyltransferase that reinforced KRASMut lysine 104 acetylation and robustly decreased KRASMut activity. KRASMut lysine 104 acetylation by p300 and deacetylation by SIRT1 were confirmed by LC‒MS/MS. Consistent with this finding, the SIRT1 inhibitor EX527 suppressed KRASMut activity, which synergistically abolished cell proliferation and colony formation, as well as the tumor burden in KRASMut mice, when combined with cisplatin or erlotinib. Our data reveal a novel pathway critical for the regulation of KRASMut lung cancer progression and provide important evidence for the potential application of SIRT1 inhibitors and p300 activators for the combination treatment of KRASMut lung cancer 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.

The Ubiquitin-Proteasome System in Tumor Metabolism

Metabolic reprogramming, which is considered a hallmark of cancer, can maintain the homeostasis of the tumor environment and promote the proliferation, survival, and metastasis of cancer cells. For instance, increased glucose uptake and high glucose consumption, known as the "Warburg effect," play an essential part in tumor metabolic reprogramming. In addition, fatty acids are harnessed to satisfy the increased requirement for the phospholipid components of biological membranes and energy. Moreover, the anabolism/catabolism of amino acids, such as glutamine, cystine, and serine, provides nitrogen donors for biosynthesis processes, development of the tumor inflammatory environment, and signal transduction. The ubiquitin-proteasome system (UPS) has been widely reported to be involved in various cellular biological activities. A potential role of UPS in the metabolic regulation of tumor cells has also been reported, but the specific regulatory mechanism has not been elucidated. Here, we review the role of ubiquitination and deubiquitination modification on major metabolic enzymes and important signaling pathways in tumor metabolism to inspire new strategies for the clinical treatment of cancer.

Epitranscriptic regulation of HRAS by N6-methyladenosine drives tumor progression

Overexpression of Ras, in addition to the oncogenic mutations, occurs in various human cancers. However, the mechanisms for epitranscriptic regulation of RAS in tumorigenesis remain unclear. Here, we report that the widespread N6-methyladenosine (m6A) modification of HRAS, but not KRAS and NRAS, is higher in cancer tissues compared with the adjacent tissues, which results in the increased expression of H-Ras protein, thus promoting cancer cell proliferation and metastasis. Mechanistically, three m6A modification sites of HRAS 3' UTR, which is regulated by FTO and bound by YTHDF1, but not YTHDF2 nor YTHDF3, promote its protein expression by the enhanced translational elongation. In addition, targeting HRAS m6A modification decreases cancer proliferation and metastasis. Clinically, up-regulated H-Ras expression correlates with down-regulated FTO and up-regulated YTHDF1 expression in various cancers. Collectively, our study reveals a linking between specific m6A modification sites of HRAS and tumor progression, which provides a new strategy to target oncogenic Ras signaling.

The role of NEDD4 related HECT-type E3 ubiquitin ligases in defective autophagy in cancer cells: molecular mechanisms and therapeutic perspectives

The homologous to the E6-AP carboxyl terminus (HECT)-type E3 ubiquitin ligases are the selective executers in the protein ubiquitination, playing a vital role in modulation of the protein function and stability. Evidence shows the regulatory role of HECT-type E3 ligases in various steps of the autophagic process. Autophagy is an intracellular digestive and recycling process that controls the cellular hemostasis. Defective autophagy is involved in tumorigenesis and has been detected in various types of cancer cells. A growing body of findings indicates that HECT-type E3 ligases, in particular members of the neural precursor cell expressed developmentally downregulated protein 4 (NEDD4) including NEDD4-1, NEDD4-L, SMURFs, WWPs, and ITCH, play critical roles in dysregulation or dysfunction of autophagy in cancer cells. The present review focuses on NEDD4 E3 ligases involved in defective autophagy in cancer cells and discusses their autophagic function in different cancer cells as well as substrates and the signaling pathways in which they participate, conferring a basis for the cancer treatment through the modulating of these E3 ligases.

Specific Disruption of Ras2 CAAX Proteolysis Alters Its Localization and Function

Many CAAX proteins, such as Ras GTPase, undergo a series of posttranslational modifications at their carboxyl terminus (i.e., cysteine prenylation, endoproteolysis of AAX, and carboxylmethylation). Some CAAX proteins, however, undergo prenylation-only modification, such as Saccharomyces cerevisiae Hsp40 Ydj1. We previously observed that altering the CAAX motif of Ydj1 from prenylation-only to canonical resulted in altered Ydj1 function and localization. Here, we investigated the effects of a reciprocal change that altered the well-characterized canonical CAAX motif of S. cerevisiae Ras2 to prenylation-only. We observed that the type of CAAX motif impacted Ras2 protein levels, localization, and function. Moreover, we observed that using a prenylation-only sequence to stage hyperactive Ras2-G19V as a farnesylated and nonproteolyzed intermediate resulted in a different phenotype relative to staging by a genetic RCE1 deletion strategy that simultaneously affected many CAAX proteins. These findings suggested that a prenylation-only CAAX motif is useful for probing the specific impact of CAAX proteolysis on Ras2 under conditions where other CAAX proteins are normally modified. We propose that our strategy could be easily applied to a wide range of CAAX proteins for examining the specific impact of CAAX proteolysis on their functions. IMPORTANCE CAAX proteins are subject to multiple posttranslational modifications: cysteine prenylation, CAAX proteolysis, and carboxylmethylation. For investigations of CAAX proteolysis, this study took the novel approach of using a proteolysis-resistant CAAX sequence to stage Saccharomyces cerevisiae Ras2 GTPase in a farnesylated and nonproteolyzed state. Our approach specifically limited the effects of disrupting CAAX proteolysis to Ras2. This represented an improvement over previous methods where CAAX proteolysis was inhibited by gene knockout, small interfering RNA knockdown, or biochemical inhibition of the Rce1 CAAX protease, which can lead to pleiotropic and unclear attribution of effects due to the action of Rce1 on multiple CAAX proteins. Our approach yielded results that demonstrated specific impacts of CAAX proteolysis on the function, localization, and other properties of Ras2, highlighting the utility of this approach for investigating the impact of CAAX proteolysis in other protein contexts.

E3 Ubiquitin Ligase NEDD4 Affects Estrogen Receptor α Expression and the Prognosis of Patients with Hormone Receptor-Positive Breast Cancer

Neural precursor cell-expressed developmentally downregulated 4-1 (NEDD4) is an E3 ligase that leads to the degradation of proteins, including estrogen receptor α. We evaluated whether the expression level of NEDD4 affected the outcome of breast cancer patients. We performed a retrospective cohort study enrolling 143 patients with hormone receptor-positive, human epidermal growth factor receptor 2-negative early breast cancer. Of the 66 patients with high NEDD4 mRNA levels (high NEDD4 group) and 77 patients with low NEDD4 mRNA levels (low NEDD4 group), 98.4% and 96.1%, respectively, of the patients had received neoadjuvant/adjuvant hormone therapy. Disease-free survival and overall survival were significantly longer in the low NEDD4 group than in the high NEDD4 group (p = 0.048 and p = 0.022, respectively). Western blotting revealed a high expression of estrogen receptor α in the NEDD4-knockdown culture cells. The proliferation of NEDD4-knockdown cells treated with tamoxifen or estradiol deprivation was suppressed, compared with that of NEDD4-expressing cells. Knockdown of NEDD4 in breast cancer cells induced the accumulation of estrogen receptor α and increased sensitivity to hormone therapy. In summary, this mechanism may lead to a better prognosis in hormone receptor-positive breast cancer patients with a low expression of NEDD4.

Progress in Anticancer Drug Development Targeting Ubiquitination-Related Factors

Ubiquitination is extensively involved in critical signaling pathways through monitoring protein stability, subcellular localization, and activity. Dysregulation of this process results in severe diseases including malignant cancers. To develop drugs targeting ubiquitination-related factors is a hotspot in research to realize better therapy of human diseases. Ubiquitination comprises three successive reactions mediated by Ub-activating enzyme E1, Ub-conjugating enzyme E2, and Ub ligase E3. As expected, multiple ubiquitination enzymes have been highlighted as targets for anticancer drug development due to their dominant effect on tumorigenesis and cancer progression. In this review, we discuss recent progresses in anticancer drug development targeting enzymatic machinery components.

The Four Homeostasis Knights: In Balance upon Post-Translational Modifications

A cancer outcome is a multifactorial event that comes from both exogenous injuries and an endogenous predisposing background. The healthy state is guaranteed by the fine-tuning of genes controlling cell proliferation, differentiation, and development, whose alteration induces cellular behavioral changes finally leading to cancer. The function of proteins in cells and tissues is controlled at both the transcriptional and translational level, and the mechanism allowing them to carry out their functions is not only a matter of level. A major challenge to the cell is to guarantee that proteins are made, folded, assembled and delivered to function properly, like and even more than other proteins when referring to oncogenes and onco-suppressors products. Over genetic, epigenetic, transcriptional, and translational control, protein synthesis depends on additional steps of regulation. Post-translational modifications are reversible and dynamic processes that allow the cell to rapidly modulate protein amounts and function. Among them, ubiquitination and ubiquitin-like modifications modulate the stability and control the activity of most of the proteins that manage cell cycle, immune responses, apoptosis, and senescence. The crosstalk between ubiquitination and ubiquitin-like modifications and post-translational modifications is a keystone to quickly update the activation state of many proteins responsible for the orchestration of cell metabolism. In this light, the correct activity of post-translational machinery is essential to prevent the development of cancer. Here we summarize the main post-translational modifications engaged in controlling the activity of the principal oncogenes and tumor suppressors genes involved in the development of most human cancers.

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.

Ubiquitin-related lncRNAs: The new tool for prognosis prediction in prostate cancer

Objective

To establish a ubiquitin-related long noncoding ribonucleic acids (lncRNAs) prognosis prediction model for prostate cancer (Pca).

Methods

Data were acquired through The Cancer Genome Atlas (TCGA) database. Ubiquitin-related differentially expressed genes (DEGs) and lncRNAs in Pca were filtered out. UBE2S was selected as the representative gene and validated in vitro. Progression-free survival (PFS) predictive signature was established with ubiquitin-related lncRNAs screened by Cox regression analyses and internally validated. A nomogram was constructed to assess the prognosis of Pca patients. Gene enrichment analysis was performed to explore functional differences based on risk stratification. Between different risk groups, immune status and drug sensitivity were contrasted.

Results

A total of 254 ubiquitin-related genes were screened. UBE2S was shown to promote the proliferation of Pca cells in vitro. The predictive signature was established based on six ubiquitin-related lncRNAs and validated. The prognosis of Pca patients was worse with an increasing risk score. The area under the curve (AUC) of the signature was higher than that of clinicopathological variables (0.806 vs 0.504–0.701). The AUC was 0.811 for 1-year PFS, 0.807 for 3-year PFS, and 0.790 for 5-year PFS. The calibration curves of risk score-based nomogram demonstrated high consistency. By contrasting the expression of immune function, cells, and checkpoints, we found that the signature was closely related to immunity. The high-risk patients were more sensitive to gemcitabine, cisplatin, bortezomib, etc. and resistant to bicalutamide.

Conclusion

The ubiquitin-related lncRNAs can effectively predict the prognosis of Pca and may provide new treatment options for Pca.

Combination of artesunate and WNT974 induces KRAS protein degradation by upregulating E3 ligase ANACP2 and β-TrCP in the ubiquitin–proteasome pathway

Background

KRAS mutation is one of the dominant gene mutations in colorectal cancer (CRC). Up to present, targeting KRAS for CRC treatment remains a clinical challenge. WNT974 (LGK974) is a porcupine inhibitor that interferes Wnt signaling pathway. Artesunate (ART) is a water-soluble semi-synthetic derivative of artemisinin.

Methods

The synergistic effect of ART and WNT974 combination in reducing CRC cell viability was determined by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. RT-PCR was utilized for the mRNA levels of KRAS, CUL7, ANAPC2, UBE2M, RNF123, SYVN1, or β-TrCP. Western blot assay was utilized for the protein levels of NRAS, HRAS, KRAS, ANAPC2, β-TrCP, GSK-3β, p-Akt (Ser473), t-Akt, p-PI3K (Tyr458), t-PI3K, p-mTOR (Ser2448), t-mTOR. Xenograft mouse model assay was performed for the anti-CRC effect of combination of ART and WNT974 in vivo. IHC assay was utilized for the levels of KRAS, β-TrCP, GSK-3β or ANAPC2 in tumor tissues.

Results

Our study shows that the combination of WNT974 and ART exhibits synergistic effect in reducing CRC growth. The combination treatment significantly reduces KRAS protein level and activity in CRC cells. Interestingly, the combination treatment increases E3 ligases ANAPC2 expression. Our data show that overexpression of ANAPC2 significantly reduces KRAS protein levels, which is reversed by MG132. Knockdown of ANAPC2 in CRC abolishes the combination treatment-reduce KRAS expression. Besides, the treatment also increases the expressions of GSK-3β and E3 ligase β-TrCP that is known to degrade GSK-3β-phosphorylated KRAS protein. Knockdown of β-TrCP- and inhibition of GSK-3β abolish the combination treatment-induce KRAS ubiquitination and reduction in expression. Last but not least, combination treatment suppresses PI3K/Akt/m-TOR signaling pathway.

Conclusions

Our data clearly show that the combination treatment significantly enhances KRAS protein degradation via the ubiquitination ubiquitin–proteasome pathway, which is also demonstrated in xenograft mouse model. The study provides strong scientific evidence for the development of the combination of WNT974 and ART as KRAS-targeting therapeutics for CRC treatment.

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.

Ubiquitination-Proteasome System (UPS) and Autophagy Two Main Protein Degradation Machineries in Response to Cell Stress

In response to environmental stimuli, cells make a series of adaptive changes to combat the injury, repair the damage, and increase the tolerance to the stress. However, once the damage is too serious to repair, the cells will undergo apoptosis to protect the overall cells through suicidal behavior. Upon external stimulation, some intracellular proteins turn into unfolded or misfolded protein, exposing their hydrophobic regions to form protein aggregation, which may ultimately produce serious damage to the cells. Ubiquitin plays an important role in the degradation of these unnatural proteins by tagging with ubiquitin chains in the ubiquitin-proteasome or autophagy system. If the two processes fail to eliminate the abnormal protein aggregates, the cells will move to apoptosis and death. Dysregulation of ubiquitin-proteasome system (UPS) and autophagy may result in the development of numerous diseases. This review focuses on the molecular mechanisms of UPS and autophagy in clearance of intracellular protein aggregates, and the relationship between dysregulation of ubiquitin network and diseases.

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.

Ubiquitination and SUMOylation: protein homeostasis control over cancer

Ubiquitination and SUMOylation are two essential components of the ubiquitination proteasome system playing fundamental roles in protein homeostasis maintenance and signal transduction, perturbation of which is associated with tumorigenesis. By comparing the mechanisms of ubiquitination and SUMOylation, assessing their crosstalk, reviewing their differential associations with cancer and identifying unaddressed yet important questions that may lead the field trend, this review sheds light on the similarities and differences of ubiquitination and SUMOylation toward the improved harnessing of both post-translational modification machineries, as well as forecasts novel onco-therapeutic opportunities through cell homeostasis control.

Overexpression of RNF126 is associated with poor prognosis and contributes to the progression of lung adenocarcinoma

Aim: To document the expression and function of RNF126 in lung adenocarcinoma (LAD). Materials & methods: A total of 102 LAD patients were enrolled in this retrospective study. The mRNA and protein levels of RNF126 were tested via RT-qPCR and immunohistochemical staining, respectively. Univariate and multivariate analyses were conducted to exploring the clinical significance of RNF126 in the prognosis. Knockdown and overexpression strategies were used to validate the tumor-related roles of RNF126 both in vitro and in vivo. Results: RNF126 was highly expressed and was an independent predictor of a poor prognosis for LAD patients. We also revealed that RNF126 knockdown suppressed proliferation of LAD cells and xenografts. Conclusion: RNF126 is a potential survival predictor and therapeutic target for LAD.

Post-translational modification of KRAS: potential targets for cancer therapy

Aberrant activation of the RAS superfamily is one of the critical factors in carcinogenesis. Among them, KRAS is the most frequently mutated one which has inspired extensive studies for developing approaches to intervention. Although the cognition toward KRAS remains far from complete, mounting evidence suggests that a variety of post-translational modifications regulate its activation and localization. In this review, we summarize the regulatory mode of post-translational modifications on KRAS including prenylation, post-prenylation, palmitoylation, ubiquitination, phosphorylation, SUMOylation, acetylation, nitrosylation, etc. We also highlight the recent studies targeting these modifications having exhibited potent anti-tumor activities.

K-Ras prenylation as a potential anticancer target

KRAS is one of the most commonly mutated oncogene and a negative predictive factor for a number of targeted therapies. Therefore, the development of targeting strategies against mutant KRAS is urgently needed. One potential strategy involves disruption of K-Ras membrane localization, which is necessary for its proper function. In this review, we summarize the current data about the importance of membrane-anchorage of K-Ras and provide a critical evaluation of this targeting paradigm focusing mainly on prenylation inhibition. Additionally, we performed a RAS mutation-specific analysis of prenylation-related drug sensitivity data from a publicly available database (https://depmap.org/repurposing/) of three classes of prenylation inhibitors: statins, N-bisphosphonates, and farnesyl-transferase inhibitors. We observed significant differences in sensitivity to N-bisphosphonates and farnesyl-transferase inhibitors depending on KRAS mutational status and tissue of origin. These observations emphasize the importance of factors affecting efficacy of prenylation inhibition, like distinct features of different KRAS mutations, tissue-specific mutational patterns, K-Ras turnover, and changes in regulation of prenylation process. Finally, we enlist the factors that might be responsible for the large discrepancy between the outcomes in preclinical and clinical studies including methodological pitfalls, the incomplete understanding of K-Ras protein turnover, and the variation of KRAS dependency in KRAS mutant tumors.

Loss-of-Function Mutations in TRAF7 and KLF4 Cooperatively Activate RAS-Like GTPase Signaling and Promote Meningioma Development

Meningiomas are the most common benign brain tumors. Mutations of the E3 ubiquitin ligase TRAF7 occur in 25% of meningiomas and commonly cooccur with mutations in KLF4, yet the functional link between TRAF7 and KLF4 mutations remains unclear. By generating an in vitro meningioma model derived from primary meningeal cells, we elucidated the cooperative interactions that promote meningioma development. By integrating TRAF7-driven ubiquitinome and proteome alterations in meningeal cells and the TRAF7 interactome, we identified TRAF7 as a proteostatic regulator of RAS-related small GTPases. Meningioma-associated TRAF7 mutations disrupted either its catalytic activity or its interaction with RAS GTPases. TRAF7 loss in meningeal cells altered actin dynamics and promoted anchorage-independent growth by inducing CDC42 and RAS signaling. TRAF deficiency-driven activation of the RAS/MAPK pathway promoted KLF4-dependent transcription that led to upregulation of the tumor-suppressive Semaphorin pathway, a negative regulator of small GTPases. KLF4 loss of function disrupted this negative feedback loop and enhanced mutant TRAF7-mediated cell transformation. Overall, this study provides new mechanistic insights into meningioma development, which could lead to novel treatment strategies. SIGNIFICANCE: The intricate molecular cross-talk between the ubiquitin ligase TRAF7 and the transcription factor KLF4 provides a first step toward the identification of new therapies for patients with meningioma.

NEDD4 regulates ubiquitination and stability of the cell adhesion molecule IGPR-1 via lysosomal pathway

Background

The cell adhesion molecule IGPR-1 regulates various critical cellular processes including, cell–cell adhesion, mechanosensing and autophagy and plays important roles in angiogenesis and tumor growth; however, the molecular mechanism governing the cell surface levels of IGPR-1 remains unknown.

Results

In the present study, we used an in vitro ubiquitination assay and identified ubiquitin E3 ligase NEDD4 and the ubiquitin conjugating enzyme UbcH6 involved in the ubiquitination of IGPR-1. In vitro GST-pulldown and in vivo co-immunoprecipitation assays demonstrated that NEDD4 binds to IGPR-1. Over-expression of wild-type NEDD4 downregulated IGPR-1 and deletion of WW domains (1–4) of NEDD4 revoked its effects on IGPR-1. Knockdown of NEDD4 increased IGPR-1 levels in A375 melanoma cells. Deletion of 57 amino acids encompassing the polyproline rich (PPR) motifs on the C-terminus of IGPR-1 nullified its binding with NEDD4. Furthermore, we demonstrate that NEDD4 promotes K48- and K63-dependent polyubiquitination of IGPR-1. The NEDD4-mediated polyubiquitination of IGPR-1 stimulates lysosomal-dependent degradation of IGPR-1 as the treatment of cells with the lysosomal inhibitors, bafilomycine or ammonium chloride increased IGPR-1 levels ectopically expressed in HEK-293 cells and in multiple endogenously IGPR-1 expressing human skin melanoma cell lines.

Conclusions

NEDD4 ubiquitin E3 ligase binds to and mediates polyubiquitination of IGPR-1 leading to its lysosomal-dependent degradation. NEDD4 is a key regulator of IGPR-1 expression with implication in the therapeutic targeting of IGPR-1 in human cancers.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12929-021-00731-9.

Cellular microbiology: Bacterial toxin interference drives understanding of eukaryotic cell function

Intimate interactions between the armament of pathogens and their host dictate tissue and host susceptibility to infection also forging specific pathophysiological outcomes. Studying these interactions at the molecular level has provided an invaluable source of knowledge on cellular processes, as ambitioned by the Cellular Microbiology discipline when it emerged in early 90s. Bacterial toxins act on key cell regulators or membranes to produce major diseases and therefore constitute a remarkable toolbox for dissecting basic biological processes. Here, we review selected examples of recent studies on bacterial toxins illustrating how fruitful the discipline of cellular microbiology is in shaping our understanding of eukaryote processes. This ever-renewing discipline unveils new virulence factor biochemical activities shared by eukaryotic enzymes and hidden rules of cell proteome homeostasis, a particularly promising field to interrogate the impact of proteostasis breaching in late onset human diseases. It is integrating new concepts from the physics of soft matter to capture biomechanical determinants forging cells and tissues architecture. The success of this discipline is also grounded by the development of therapeutic tools and new strategies to treat both infectious and noncommunicable human diseases.

Ras sumoylation in cell signaling and transformation

Ras proteins are small GTPases that participate in multiple signal cascades, regulating crucial cellular processes including cell survival, proliferation, and differentiation. Mutations or deregulated activities of Ras are frequently the driving force for oncogenic transformation and tumorigenesis. Posttranslational modifications play a crucial role in mediating the stability, activity, or subcellular localization/trafficking of numerous cellular regulators including Ras proteins. A series of recent studies reveal that Ras proteins are also regulated by sumoylation. All three Ras protein isoforms (HRas, KRas, and NRas) are modified by SUMO3. The conserved lysine42 appears to be the primary site for mediating sumoylation. Expression of KRas^V12/R42 mutants compromised the activation of the Raf/MEK/ERK signaling axis, leading to a reduced rate of cell migration and invasion in vitro in multiple cell lines. Moreover, treatment of transformed pancreatic cells with a SUMO E2 inhibitor blocks cell migration in a concentration-dependent manner, which is associated with a reduced level of both KRas sumoylation and expression of mesenchymal cell markers. Furthermore, mouse xenograft experiments reveal that expression of a SUMO-resistant mutant appears to suppress tumor development in vivo. Combined, these studies indicate that sumoylation functions as an important mechanism in mediating the roles of Ras in cell proliferation, differentiation, and malignant transformation and that the SUMO-modification system of Ras oncoproteins can be explored as a new druggable target for various human malignancies.

Recent Updates on the Significance of KRAS Mutations in Colorectal Cancer Biology

The most commonly mutated isoform of RAS among all cancer subtypes is KRAS. In this review, we focus on the special role of KRAS mutations in colorectal cancer (CRC), aiming to collect recent data on KRAS-driven enhanced cell signalling, in vitro and in vivo research models, and CRC development-related processes such as metastasis and cancer stem cell formation. We attempt to cover the diverse nature of the effects of KRAS mutations on age-related CRC development. As the incidence of CRC is rising in young adults, we have reviewed the driving forces of ageing-dependent CRC.

Ubiquitin-proteasome system (UPS) as a target for anticancer treatment

The ubiquitin-proteasome system (UPS) plays an important role in the cellular processes for protein quality control and homeostasis. Dysregulation of the UPS has been implicated in numerous diseases, including cancer. Indeed, components of UPS are frequently mutated or abnormally expressed in various cancers. Since Bortezomib, a proteasome inhibitor, received FDA approval for the treatment of multiple myeloma and mantle cell lymphoma, increasing numbers of researchers have been seeking drugs targeting the UPS as a cancer therapeutic strategy. Here, we introduce the essential component of UPS, including ubiquitinating enzymes, deubiquitinating enzymes and 26S proteasome, and we summarize their targets and mechanisms that are crucial for tumorigenesis. In addition, we briefly discuss some UPS inhibitors, which are currently in clinical trials as cancer therapeutics.

The role of ubiquitination and deubiquitination in cancer metabolism

Metabolic reprogramming, including enhanced biosynthesis of macromolecules, altered energy metabolism, and maintenance of redox homeostasis, is considered a hallmark of cancer, sustaining cancer cell growth. Multiple signaling pathways, transcription factors and metabolic enzymes participate in the modulation of cancer metabolism and thus, metabolic reprogramming is a highly complex process. Recent studies have observed that ubiquitination and deubiquitination are involved in the regulation of metabolic reprogramming in cancer cells. As one of the most important type of post-translational modifications, ubiquitination is a multistep enzymatic process, involved in diverse cellular biological activities. Dysregulation of ubiquitination and deubiquitination contributes to various disease, including cancer. Here, we discuss the role of ubiquitination and deubiquitination in the regulation of cancer metabolism, which is aimed at highlighting the importance of this post-translational modification in metabolic reprogramming and supporting the development of new therapeutic approaches for cancer treatment.

Biology, pathology, and therapeutic targeting of RAS

RAS was identified as a human oncogene in the early 1980s and subsequently found to be mutated in nearly 30% of all human cancers. More importantly, RAS plays a central role in driving tumor development and maintenance. Despite decades of effort, there remain no FDA approved drugs that directly inhibit RAS. The prevalence of RAS mutations in cancer and the lack of effective anti-RAS therapies stem from RAS' core role in growth factor signaling, unique structural features, and biochemistry. However, recent advances have brought promising new drugs to clinical trials and shone a ray of hope in the field. Here, we will exposit the details of RAS biology that illustrate its key role in cell signaling and shed light on the difficulties in therapeutically targeting RAS. Furthermore, past and current efforts to develop RAS inhibitors will be discussed in depth.

A conserved, N-terminal tyrosine signal directs Ras for inhibition by Rabex-5

Dysregulation of the Ras oncogene in development causes developmental disorders, "Rasopathies," whereas mutational activation or amplification of Ras in differentiated tissues causes cancer. Rabex-5 (also called RabGEF1) inhibits Ras by promoting Ras mono- and di-ubiquitination. We report here that Rabex-5-mediated Ras ubiquitination requires Ras Tyrosine 4 (Y4), a site of known phosphorylation. Ras substitution mutants insensitive to Y4 phosphorylation did not undergo Rabex-5-mediated ubiquitination in cells and exhibited Ras gain-of-function phenotypes in vivo. Ras Y4 phosphomimic substitution increased Rabex-5-mediated ubiquitination in cells. Y4 phosphomimic substitution in oncogenic Ras blocked the morphological phenotypes associated with oncogenic Ras in vivo dependent on the presence of Rabex-5. We developed polyclonal antibodies raised against an N-terminal Ras peptide phosphorylated at Y4. These anti-phospho-Y4 antibodies showed dramatic recognition of recombinant wild-type Ras and RasG12V proteins when incubated with JAK2 or SRC kinases but not of RasY4F or RasY4F,G12V recombinant proteins suggesting that JAK2 and SRC could promote phosphorylation of Ras proteins at Y4 in vitro. Anti-phospho-Y4 antibodies also showed recognition of RasG12V protein, but not wild-type Ras, when incubated with EGFR. A role for JAK2, SRC, and EGFR (kinases with well-known roles to activate signaling through Ras), to promote Ras Y4 phosphorylation could represent a feedback mechanism to limit Ras activation and thus establish Ras homeostasis. Notably, rare variants of Ras at Y4 have been found in cerebellar glioblastomas. Therefore, our work identifies a physiologically relevant Ras ubiquitination signal and highlights a requirement for Y4 for Ras inhibition by Rabex-5 to maintain Ras pathway homeostasis and to prevent tissue transformation.

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.

The NEDD4-1 E3 ubiquitin ligase: A potential molecular target for bortezomib sensitivity in multiple myeloma

E3 ubiquitin ligases primarily determine the substrate specificity of the ubiquitin-proteasome system and play an essential role in the resistance to bortezomib in multiple myeloma (MM). Neural precursor cell-expressed developmentally downregulated gene 4-1 (NEDD4-1, also known as NEDD4) is a founding member of the NEDD4 family of E3 ligases and is involved in the proliferation, migration, invasion and drug sensitivity of cancer cells. In the present study, we investigated the role of NEDD4-1 in MM cells and explored its underlying mechanism. Clinically, low NEDD4-1 expression has been linked to poor prognosis in patients with MM. Functionally, NEDD4-1 knockdown (KD) resulted in bortezomib resistance in MM cells in vitro and in vivo. The overexpression (OE) of NEDD4-1, but not an enzyme-dead NEDD4-1-C867S mutant, had the opposite effect. Furthermore, the overexpression of NEDD4-1 in NEDD4-1 KD cells resensitized the cells to bortezomib in an add-back rescue experiment. Mechanistically, pAkt-Ser473 levels and Akt signaling were elevated and decreased by NEDD4-1 KD and OE, respectively. NEDD4-1 ubiquitinated Akt and targeted pAkt-Ser473 for proteasomal degradation. More importantly, the NEDD4-1 KD-induced upregulation of Akt expression sensitized MM cells to growth inhibition after treatment with an Akt inhibitor. Collectively, our results suggest that high NEDD4-1 levels may be a potential new therapeutic target in MM.

NEDD4 and NEDD4L regulate Wnt signalling and intestinal stem cell priming by degrading LGR5 receptor

The intestinal stem cell (ISC) marker LGR5 is a receptor for R-spondin (RSPO) that functions to potentiate Wnt signalling in the proliferating crypt. It has been recently shown that Wnt plays a priming role for ISC self-renewal by inducing RSPO receptor LGR5 expression. Despite its pivotal role in homeostasis, regeneration and cancer, little is known about the post-translational regulation of LGR5. Here, we show that the HECT-domain E3 ligases NEDD4 and NEDD4L are expressed in the crypt stem cell regions and regulate ISC priming by degrading LGR receptors. Loss of Nedd4 and Nedd4l enhances ISC proliferation, increases sensitivity to RSPO stimulation and accelerates tumour development in Apcmin mice with increased numbers of high-grade adenomas. Mechanistically, we find that both NEDD4 and NEDD4L negatively regulate Wnt/β-catenin signalling by targeting LGR5 receptor and DVL2 for proteasomal and lysosomal degradation. Our findings unveil the previously unreported post-translational control of LGR receptors via NEDD4/NEDD4L to regulate ISC priming. Inactivation of NEDD4 and NEDD4L increases Wnt activation and ISC numbers, which subsequently enhances tumour predisposition and progression.

The ubiquitin system: orchestrating cellular signals in non-small-cell lung cancer

The ubiquitin system, known as a common feature in eukaryotes, participates in multiple cellular processes, such as signal transduction, cell-cycle progression, receptor trafficking and endocytosis, and even the immune response. In lung cancer, evidence has revealed that aberrant events in ubiquitin-mediated processes can cause a variety of pathological outcomes including tumorigenesis and metastasis. Likewise, ubiquitination on the core components contributing to the activity of cell signaling controls bio-signal turnover and cell final destination. Given this, inhibitors targeting the ubiquitin system have been developed for lung cancer therapies and have shown great prospects for clinical application. However, the exact biological effects and physiological role of the drugs used in lung cancer therapies are still not clearly elucidated, which might seriously impede the progress of treatment. In this work, we summarize current research advances in cell signal regulation processes mediated through the ubiquitin system during the development of lung cancer, with the hope of improving the therapeutic effects by means of aiming at efficient targets.

NEDD4 expression is associated with breast cancer progression and is predictive of a poor prognosis

Background

A role for neural precursor cell-expressed developmentally downregulated gene 4 (NEDD4) in tumorigenesis has been suggested. However, information is lacking on its role in breast tumor biology. The purpose of this study was to determine the role of NEDD4 in the promotion of the growth and progression of breast cancer (BC) and to evaluate the clinicopathologic and prognostic significance of NEDD4.

Methods

The impact of NEDD4 expression in BC cell growth was determined by Cell Counting Kit-8 and colony formation assays. Formalin-fixed paraffin-embedded specimens were collected from 133 adjacent normal tissues (ANTs), 445 BC cases composed of pre-invasive ductal carcinoma in situ (DCIS, n = 37), invasive ductal carcinomas (IDC, n = 408, 226 without and 182 with lymph node metastasis), and 116 invaded lymph nodes. The expression of NEDD4 was analyzed by immunohistochemistry. The association between NEDD4 expression and clinicopathological characteristics was analyzed by chi-square test. Survival was evaluated using the Kaplan–Meier method, and curves were compared using a log-rank test. Univariate and multivariate analyses were performed using the Cox regression method.

Results

NEDD4 promoted BC growth in vitro. In clinical retrospective studies, 16.5% of ANTs (22/133) demonstrated positive NEDD4 staining. Strikingly, the proportion of cases showing NEDD4-positive staining increased to 51.4% (19/37) in DCIS, 58.4% (132/226) in IDC without lymph node metastasis, and 73.1% (133/182) in BC with lymph node metastasis (BCLNM). In addition, NEDD4-positive staining was associated with clinical parameters, including tumor size (P = 0.030), nodal status (P = 0.001), estrogen receptor status (P = 0.035), and progesterone receptor status (P = 0.023). Moreover, subset analysis in BCLNM revealed that high NEDD4 expression correlated with an elevated risk of relapse (P = 0.0276). Further, NEDD4 expression was an independent prognostic predictor. Lastly, the rates for 10-year overall survival and disease-free survival were significantly lower in patients with positive NEDD4 staining than those in BC patients with negative NEDD4 staining BC (P = 0.0024 and P = 0.0011, respectively).

Conclusions

NEDD4 expression is elevated in BC and is associated with BC growth. NEDD4 correlated with clinicopathological parameters and predicts a poor prognosis. Thus, NEDD4 is a potential biomarker of poor prognosis and a potential therapeutic target for BC treatment.

The many substrates and functions of NEDD4-1

Tumorigenesis, tumor growth, and prognosis are highly related to gene alterations and post-translational modifications (PTMs). Ubiquitination is a critical PTM that governs practically all aspects of cellular function. An increasing number of studies show that E3 ubiquitin ligases (E3s) are important enzymes in the process of ubiquitination that primarily determine substrate specificity and thus need to be tightly controlled. Among E3s, neural precursor cell expressed developmentally downregulated 4-1 (NEDD4-1) has been shown to play a critical role in modulating the proliferation, migration, and invasion of cancer cells and the sensitivity of cancer cells to anticancer therapies via regulating multiple substrates. This review discusses some significant discoveries on NEDD4-1 substrates and the signaling pathways in which NEDD4-1 participates. In addition, we introduce the latest potential therapeutic strategies that inhibit or activate NEDD4-1 activity using small molecules. NEDD4-1 likely acts as a novel drug target or diagnostic marker in the battle against cancer.

A Propensity Score-adjusted Analysis of the Effects of Ubiquitin E3 Ligase Copy Number Variation in Peripheral Blood Leukocytes on Colorectal Cancer Risk

Background: The ubiquitin ligases E3 (E3s) plays a key role in the specific protein degradation in many carcinogenic biological processes. Colorectal cancer (CRC) development may be affected by the copy number variation (CNV) of E3s. Prior studies may have underestimated the impact of potential confounding factors' effects on the association between gene CNV and CRC risk, and CRC risk predictive model integrating gene CNV patterns is lacking. Our research sought to assess the genes CNVs of MDM2, SKP2, FBXW7, β-TRCP, and NEDD4-1 and CRC risk by using propensity score (PS) adjustment and developing models that integrate CNV patterns for CRC risk predictions.

Methods: This study comprising 1036 participants used traditional regression and different PS techniques to adjust the confounding factors to evaluate the relationships between five gene CNVs and CRC risk, and to establish a CRC risk predictive model. The AUC was applied to evaluate the effect of the model. The categorical net reclassification improvement (NRI) and the integrated discrimination improvement (IDI) were analyzed to evaluate the discriminatory accuracy improvement among the models.

Results: Compared to variable adjustment, the odds ratios (ORs) tended to be conservative and accurate with narrow confidence intervals (CIs) after PS adjustment. After PS adjustment, MDM2 amplification was related to increased CRC risk (Amp-pattern: OR = 8.684, 95% CI: 1.213-62.155, P = 0.031), whereas SKP2 deletion and the (del+amp) genotype were associated with reduced CRC risk (Del-pattern: OR = 0.323, 95% CI: 0.106-0.979, P = 0.046; Var-pattern: OR = 0.339, 95% CI: 0.135-0.854, P = 0.024). The predictive model integrating the gene CNV pattern could correctly reclassify 1.7% of the subjects.

Conclusions: MDM2 amplification and SKP2 CNVs are associated with increased and decreased CRC risk, respectively; abnormal CNV-integrated model is more precise for predicting CRC risk. Further studies are needed to verify these encouraging outcomes.

TIPE2 Suppresses Pseudomonas aeruginosa Keratitis by Inhibiting NF-κB Signaling and the Infiltration of Inflammatory Cells

Background

The role of tumor necrosis factor α (TNF-α) induced protein 8-like-2 (TIPE2) in Pseudomonas aeruginosa (PA) keratitis was explored.

Methods

Eight-week-old TIPE2 knockout (TIPE2−/−) C57BL/6 mice and their wild-type (WT) littermates were used. Corneal disease was graded at 1, 2, and 3 days postinfection, and slit lamp, clinical score, histopathology, and immunostaining were performed in the infected corneas. The corneas were harvested, and messenger ribonucleic acid (mRNA) levels of TNF-α, interleukin-1β (IL-1β), and interleukin-6 (IL-6) were tested. Enzyme-linked immunosorbent assay (ELISA) determined the protein levels, and nuclear factor κ-light-chain-enhancer of activated B cell (NF-κB) signaling molecules were tested by Western blot. In vitro human corneal epithelial cells (HCECs) were used to determine the relationship between TIPE2 and TAK1. The HCECs were treated with TIPE2 short hairpin ribonucleic acid (shRNA) and lipopolysaccharide (LPS) to test the NF-κB signaling molecules by Western blot.

Results

Pseudomonas aeruginosa infection induced a decreased expression of TIPE2 in mouse corneas 2 days postinfection. Compared with the control group, TIPE2-deficient mice were susceptible to infection with PA and showed increased corneal inflammation. Reduced NF-κB signaling and inflammatory cell infiltration were required in the TIPE2-mediated immune modulation.

Conclusions

TIPE2 promoted host resistance to PA infection by suppressing corneal inflammation via regulating TAK1 signaling negatively and inhibiting the infiltration of inflammatory cells.