Specific E3 Ligases Research Articles

Citronellal improves endothelial dysfunction by affecting the stability of the GCH1 protein.

Endothelial dysfunction (ED) serves as the pathological basis for various cardiovascular diseases. Guanosine triphosphate cyclopyrrolone 1 (GCH1) emerges as a pivotal protein in sustaining nitric oxide (NO) production within endothelial cells, yet it undergoes degradation under oxidative stress, contributing to endothelial cell dysfunction. Citronellal (CT), a monoterpenoid, has been shown to ameliorate endothelial dysfunction induced by in atherosclerosis rats. However, whether CT can inhibit the degradation of GCH1 protein is not clear. It has been reported that ubiquitination may play a crucial role in regulating GCH1 protein levels and activities. However, the specific E3 ligase for GCH1 and the molecular mechanism of GCH1 ubiquitination remain unclear. Using data-base exploration analysis, we find that the levels of the E3 ligase Smad-ubiquitination regulatory factor 2 (Smurf2) negatively correlate with those of GCH1 in vascular tissues and HUVECs. We observe that Smurf2 interacts with GCH1 and promotes its degradation via the proteasome pathway. Interestingly, ectopic Smurf2 expression not only decreases GCH1 levels but also reduces cell proliferation and reactive oxygen species (ROS) levels, mostly because of increased GCH1 accumulation. Furthermore, we identify BH 4/eNOS as downstream of GCH1. Taken together, our results indicate that CT can obviously improve vascular endothelial injury in Type 1 diabetes mellitus (T1DM) rats and reverse the expressions of GCH1 and Smurf2 proteins in aorta of T1DM rats. Smurf2 promotes ubiquitination and degradation of GCH1 through proteasome pathway in HUVECs. We conclude that the Smurf2-GCH1 interaction might represent a potential target for improving endothelial injury.

P53 upregulation by USP7-engaging molecular glues

Molecular glues are typically small chemical molecules that act at the interface between a target protein and degradation machinery to trigger ternary complex formation. Identifying molecular glues is challenging. There is a scarcity of target-specific upregulating molecular glues, which are highly anticipated for numerous targets, including P53. P53 is degraded in proteasomes through polyubiquitination by specific E3 ligases, whereas deubiquitinases (DUBs) remove polyubiquitination conjugates to counteract these E3 ligases. Thus, small-molecular glues that enhance P53 anchoring to DUBs may stabilize P53 through deubiquitination. Here, using small-molecule microarray-based technology and unbiased screening, we identified three potential molecular glues that may tether P53 to the DUB, USP7, and elevate the P53 level. Among the molecular glues, bromocriptine (BC) is an FDA-approved drug with the most robust effects. BC was further verified to increase P53 stability via the predicted molecular glue mechanism engaging USP7.Consistent with P53 upregulation in cancer cells, BC was shown to inhibit the proliferation of cancer cells in vitro and suppress tumor growth in a xenograft model. In summary, we established a potential screening platform and identified potential molecular glues upregulating P53. Similar strategies could be applied to the identification of other types of molecular glues that may benefit drug discovery and chemical biology studies.

Abstract 6070: Identification of a molecular glue degrader that engages a cancer-specific E3 ligase

Abstract To date, most successful molecular glues have leveraged ubiquitously expressed E3 ligases, most notably Cereblon in the case of the thalidomide derivatives. However, a number of specific E3 ligases are highly over-expressed in certain tumors. Compounds that engage such tumor-specific E3 ligases might provide a unique opportunity to develop molecular glues with higher therapeutic indexes. One such tumor-specific E3 ligase is FBXO5, a member of the F-box family of E3 ligases. Expression analysis suggests this E3 ligase is highly expressed in a wide array of tumor tissues when compared to the corresponding normal tissue, and that within a given tumor type, higher FBXO5 expression correlates with advanced tumor stage and worse disease-free survival. Here, we describe a small molecule (MW~400 Daltons) that uses FBXO5 to function as a molecular glue degrader. This compound, CL-200, exerts cytotoxicity in the nanomolar range across a number of diverse tumor types. The cytotoxicity of CL-200 is abrogated when FBXO5 is knockdown using siRNA. We have further determined that CL-200 induces the FBXO5-dependent proteasomal degradation of at least two critical neosubstrates. One identified neosubstrate is the p150 isoform of ADAR1, an enzyme that catalyzes the posttranscriptional conversion of adenosine to inosine in double-stranded RNA (dsRNA). Evidence suggests that ADAR1p150 is the isoform that confers oncogenic and immune modulating effects in many tumors. Another neosubstrate targeted by CL-200 is c-myc, a critical transcription factor linked to a wide array of tumors. Of note, both p150 ADAR1 or c-myc have been viewed as difficult-to-drug if not undruggable targets. As such, these data suggests that CL-200 functions as a novel molecular glue degrader that engages the cancer-specific E3 ligase FBXO5 to degrade both p150 ADAR1 and c-myc. Structural alteration of CL-200 suggest that chemical modifications can be made that retain the engagement with FBXO5 while altering the neosubstrate profile. Together, these results demonstrate the possibility of leveraging cancer-specific E3 ligases to develop novel molecular glues. Citation Format: Yuan Liu, Mads Larsen, Bo Lin, Irene A. Cardenal, Jason R. Kennerdell, Toren Finkel, Bill B. Chen. Identification of a molecular glue degrader that engages a cancer-specific E3 ligase [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 6070.

Disruption of cyclin D1 degradation leads to the development of mantle cell lymphoma

Cyclin D1 has been recognized as an oncogene due to its abnormal upregulation in different types of cancers. Here, we demonstrated that cyclin D1 is SUMOylated, and we identified Itch as a specific E3 ligase recognizing SUMOylated cyclin D1 and mediating SUMO-induced ubiquitination and proteasome degradation of cyclin D1. We generated cyclin D1 mutant mice with mutations in the SUMOylation site, phosphorylation site, or both sites of cyclin D1, and found that double mutant mice developed a Mantle cell lymphoma (MCL)-like phenotype. We showed that arsenic trioxide (ATO) enhances cyclin D1 SUMOylation-mediated degradation through inhibition of cyclin D1 deSUMOylation enzymes, leading to MCL cell apoptosis. Treatment of severe combined immunodeficiency (SCID) mice grafted with MCL cells with ATO resulted in a significant reduction in tumor growth. In this study, we provide novel insights into the mechanisms of MCL tumor development and cyclin D1 regulation and discover a new strategy for MCL treatment.

Abstract B140: Elucidating the novel mechanism of action of VVD-065, an allosteric molecular glue for the KEAP1-CUL3 E3-ligase complex that promotes NRF2 degradation in NRF2-activated cancers

Abstract Nuclear factor erythroid 2-related factor 2 (NRF2) is a transcription factor that plays a crucial role in various NRF2-dependent cancers. The protein levels of NRF2 are tightly controlled by a specific E3 ligase complex composed of Kelch-like ECH Associated Protein 1 (KEAP1), Cullin 3 (CUL3), and RING-box protein 1 (RBX1). Under normal conditions, KEAP1 acts as an oxidative sensor and facilitates the ubiquitination and subsequent degradation of NRF2. However, during oxidative or electrophilic stress, KEAP1 can be inactivated through covalent modification of sensor cysteine residues, allowing NRF2 levels to increase and regulate NRF2-dependent genes. In this study, we have elucidated a novel mechanism-of-action for a first-in-class NRF2 inhibitor, VVD-065. Through biochemical and biophysical investigations, we have discovered that VVD-065 functions by covalently interacting with KEAP1 at a sensor cysteine residue, but surprisingly this interaction results in an enhanced affinity between KEAP1 and CUL3, and an increased capacity for Keap1 mediated NRF2 degradation. High-resolution co-crystal structures have revealed that binding of VVD-065 allosterically induces a conformational change that mimics the conformation of KEAP1 when in complex with CUL3. By targeting the KEAP1-CUL3 interaction and promoting the degradation of NRF2, VVD-065 offers a means to modulate NRF2 levels in NRF2-dependent cancers. The unprecedented mechanism of action exhibited by VVD-065 has been confirmed through in vitro and in vivo studies, paving the way for the development of a clinically relevant Keap1 activator. Citation Format: Aaron Snead, Steffen Bernard, Kenneth Hee, Eileen Tran, Sarah Jacinto, Nil Roy, Tine Wyseure, Jonathan Pollock, Gabe Simon, Todd Kinsella, David Weinstein, Matt Patricelli. Elucidating the novel mechanism of action of VVD-065, an allosteric molecular glue for the KEAP1-CUL3 E3-ligase complex that promotes NRF2 degradation in NRF2-activated cancers [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2023 Oct 11-15; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2023;22(12 Suppl):Abstract nr B140.

RNF2 regulates Wnt/ß-catenin signaling via TCF7L1 destabilization

The Wnt signaling pathway is a crucial regulator of various biological processes, such as development and cancer. The downstream transcription factors in this pathway play a vital role in determining the threshold for signaling induction and the length of the response, which vary depending on the biological context. Among the four transcription factors involved in canonical Wnt/ß-catenin signaling, TCF7L1 is known to possess an inhibitory function; however, the underlying regulatory mechanism remains unclear. In this study, we identified the E3 ligase, RNF2, as a novel positive regulator of the Wnt pathway. Here, we demonstrate that RNF2 promotes the degradation of TCF7L1 through its ubiquitination upon activation of Wnt signaling. Loss-of-function studies have shown that RNF2 consistently destabilizes nuclear TCF7L1 and is required for proper Wnt target gene transcription in response to Wnt activation. Furthermore, our results revealed that RNF2 controls the threshold, persistence, and termination of Wnt signaling by regulating TCF7L1. Overall, our study sheds light on the previously unknown degradation mechanism of TCF7L1 by a specific E3 ligase, RNF2, and provides new insights into the variability in cellular responses to Wnt activation.

Novel approaches to determine the functional role of cardiomyocyte specific E3 ligase, Pellino-1 following myocardial infarction

ObjectivesUbiquitination plays a vital role in controlling vascular inflammation, cellular protein quality control, and minimizing misfolded protein toxicity. Pellino-1 (Peli1), a type of E3 ubiquitin ligase, has emerged as a critical regulator of the innate immune response; however, its role in the repair and regeneration of ischemic myocardium remains to be elucidated. MethodsMice (8-12 weeks old, male and females) were divided into (i) Wild type (ii) cardiomyocyte-specific Peli1 overexpressed (AMPEL1Tg/+), (iii) cardiomyocyte-specific Peli1 knockout (CP1KO) and were subjected to sham and left anterior descending artery ligation. The tissues were collected at various time points after surgery for Western blot, and immunohistochemical analyses. Echocardiography is performed 30 days after myocardial infarction. Cardiomyocytes isolated from wild-type, Peli1 overexpressed and knockout mice were used to study the interaction between cardiomyocytes and endothelial cells in vitro under oxidative stress and cells were used for Western blot, flow cytometric analysis, and scratch assay. ResultsWe observed faster wound closure and increased expression of angiogenic factors with MCECs treated with conditioned media obtained from the AMPEL1Tg/+ cardiomyocytes compared to CPIKO and WT cardiomyocytes. Again, AMPEL1Tg/+MI mice showed preserved systolic function and reduced fibrosis compared to the CPIKOMI and WTMI groups. Capillary and arteriolar density were found to be increased in AMPEL1Tg/+MI compared to CP1KOMI. Increased survival and angiogenic factors such as p-Akt, p-MK2, p-IkBα, VEGF, cIAP2, and Bcl2 were observed in AMPEL1Tg/+ compared to CP1KO and WT mice subjected to MI. ConclusionThe present study uncovers the crucial role of cardiac Peli1 as a regulator of the repair and regeneration of ischemic myocardium by using multiple genetically engineered mouse models.

Abstract P2112: Mechanism Of Bag3's Degradation Of Tgfbr2 In Cardiac Fibroblasts

BAG3 levels are diminished in patients with heart failure and several mutations have been identified to cause dilated cardiomyopathy with cardiac fibrosis. BAG3’s four binding domains are critical to its function to facilitate proteostasis. BAG3’s role has been extensively studied in CMs, where it aids sarcomere protein turnover through chaperone-assisted selective autophagy, through BAG3’s complex with HSP70, HSPB8, and E3 ligase CHIP. However, BAG3 is ubiquitously expressed and its role in non-myocytes has been overlooked. Cardiac fibroblasts are responsible for the excessive matrix deposition leading to fibrosis, mostly through TGF-beta signaling. Previously, we have shown the importance of BAG3 in cardiac fibroblasts through its role in TGF-beta signaling and identified BAG3 to facilitate the degradation of the type II TGF-beta receptor (TGFBR2). As BAG3 does not have inherent E3 activity, this study aimed to identify the specific E3 ligase of TGFBR2 and the binding domains of BAG3 that are crucial to this interaction to gain insight into the effects of the clinical mutations of BAG3. Immunoprecipitation (IP) of endogenous BAG3 in cardiac fibroblasts revealed five E3 ligases as high-confidence interactors of BAG3. To find the specific E3 ligase of TGFBR2, we performed an IP of a V5-tagged TGFBR2 and identified HSP70, HSPB8 and CHIP as binding partners. To delineate the critical domains of BAG3 that impact the TGFBR2 degradation, we overexpressed 3x-FLAG-tagged BAG3 proteins lacking each domain respectively (WW, IPV, PxxP, and BAG) and show that the BAG domain is imperative in TGFBR2 degradation. This has clinical implications for the common DCM-causing E455K mutation in the BAG domain. The ubiquitination of TGFBR2 was decreased upon overexpression of a BAG3 plasmid containing the E455K mutation. Lastly, the drug JG-98, which disrupts the binding of HSP70 to BAG3, was used to show the importance of the HSP70-BAG3 axis in the degradation of TGFBR2. In conclusion, we have uncovered the molecular mechanism of TGFBR2 degradation in cardiac fibroblasts mediated by the BAG3-HSP70-HSPB8 complex, with clinical implications for the loss of BAG3 and several common DCM-causing mutations in the development of cardiac fibrosis.

Nur77 is involved in the regulation of obesity-related lower muscle mass by promoting Pten degradation.

Obesity may impair muscle function and is sometimes associated with lower muscle mass. However, the internal regulatory mechanism is still unclear. Nur77 has been reported to improve obesity phenotype by regulating glucose and lipid metabolism and inhibiting the production of inflammatory factors and reactive oxygen species. Concurrently, Nur77 also plays an important role in muscle differentiation and development. We aimed to investigate the role of Nur77 in obesity-related lower muscle mass. Our in vivo and in vitro experiments illustrated that the reduction of obesity-related Nur77 accelerated the occurrence of lower muscle mass by interfering with the signaling pathways involved in the regulation of myoprotein synthesis and degradation. We further demonstrated that Nur77 activates the PI3K/Akt pathway by promoting Pten degradation, which enhances the phosphorylation of the Akt/mTOR/p70S6K pathway and inhibits the expression of skeletal muscle-specific E3 ligases (MAFbx/MuRF1). Nur77 induces Pten degradation by increasing the transcription of its specific E3 ligase Syvn1. Our study confirms that Nur77 is a key factor in ameliorating obesity-related lower muscle mass, providing a new therapeutic target and theoretical basis for the treatment of obesity-related lower muscle mass.

H2Bub1 loss is an early contributor to clear cell ovarian cancer progression.

Epigenetic aberrations, including posttranslational modifications of core histones, are major contributors to cancer. Here, we define the status of histone H2B monoubiquitylation (H2Bub1) in clear cell ovarian carcinoma (CCOC), low-grade serous carcinoma, and endometrioid carcinomas. We report that clear cell carcinomas exhibited profound loss, with nearly all cases showing low or negative H2Bub1 expression. Moreover, we found that H2Bub1 loss occurred in endometriosis and atypical endometriosis, which are established precursors to CCOCs. To examine whether dysregulation of a specific E3 ligase contributes to the loss of H2Bub1, we explored expression of ring finger protein 40 (RNF40), ARID1A, and UBR7 in the same case cohort. Loss of RNF40 was significantly and profoundly correlated with loss of H2Bub1. Using genome-wide DNA methylation profiles of 230 patients with CCOC, we identified hypermethylation of RNF40 in CCOC as a likely mechanism underlying the loss of H2Bub1. Finally, we demonstrated that H2Bub1 depletion promoted cell proliferation and clonogenicity in an endometriosis cell line. Collectively, our results indicate that H2Bub1 plays a tumor-suppressive role in CCOCs and that its loss contributes to disease progression.

1642-P: Deferoxamine Prevented Dexamethasone-Induced Muscle Atrophy through Inhibition of KLF15 and FOXO3a

Aim/hypothesis: Muscle atrophy is caused by various factors such as aging, a lack of exercise, and diseases. During these events, the balance between protein synthesis and degradation is disrupted and finally muscle mass is decreased. This has been reported to occur via the ubiquitin-proteasome dependent pathway, autophagy, or apoptosis. In this study, we investigated the main mechanisms of dexamethasone-induced muscle atrophy and preventing mechanisms of deferoxamine on DEX-induced muscle atrophy. Method: To measure the effects of DFO on muscle atrophy, C2C12 myotubes were treated with dexamethasone, with or without DFO, then myotubes atrophy was measured by phalloidin staining, RT-PCR, and western blotting. Results: In differentiated C2C12 myotubes, DEX induced muscle atrophy in a time- and dose-dependent manner. DEX induced expressions of muscle-specific ligases, including muscle ring finger 1 and muscle atrophy F box, and activated the ubiquitin-proteasome system leading to muscle atrophy, not autophagy or apoptosis. Interestingly, DFO administration alleviated DEX-induced myotubes atrophy. DFO inhibited DEX-activated expressions of KLF15, not REDD or FOXO3a. DFO dramatically diminished FOXO3a translocation from cytosol to nucleus through the activation of AKT. Finally, expressions of muscle-specific ligases, such as MURF1 and Atrogin-1, were reduced by treatment of DFO, and ubiquitinated myoprotein was also reduced. In addition, mice treated with DEX for 12 days had a significant decrease in grip strength and TA muscle mass. However, treatment with DFO prevented DEX-induced reduction of muscle fiber size, loss of TA muscle, and grip strength. Conclusion: DEX activated muscle specific E3 ligase and induced-muscle atrophy through ubiquitin-proteasome system. DFO ameliorates muscle atrophy by inhibition of E3 ligase expression via KLF15 and FOXO3a in DEX-treated C2C12 myotubes and C57BL6J mice. Disclosure Y.Kim: None. H.Kim: None. D.Kim: None. T.Kim: None. S.An: None. K.Lee: None. N.Lee: None. S.Choi: None. Y.Kim: None. Y.Son: None. S.Choi: None. Y.Y.Kang: None. J.Jeon: None. S.Han: None.

Abstract 2520: Blocking muscle wasting via deletion of the muscle specific E3 ligase, MuRF1, impedes pancreatic tumor growth

Abstract Pancreatic cancer-induced muscle atrophy is a debilitating condition that contributes to a deterioration in physical function and reduced quality of life, often complicates or precludes cancer treatment, and strongly predicts early mortality from cancer. A pharmacological therapy for this atrophy does not exist, in part because of an incomplete understanding of the molecular mechanisms which are causative in the condition. We recently identified that Trim63/MuRF1 is elevated in skeletal myonuclei from cachectic mice and people with pancreatic ductal adenocarcinoma (PDAC) compared to non-cancer controls. MuRF1 is an E3 ubiquitin ligase, specific to striated muscle that targets proteins for degradation. Based on this finding, we investigated the requirement of MuRF1 for PDAC-induced muscle atrophy. Murine KPC cells (or saline) were injected orthotopically into the pancreas of WT and MuRF1 KO mice, and tissues harvested at several time points throughout tumor progression. WT KPC mice showed loss of tumor-free body mass and muscle mass by day 12, and reached experimental endpoint on day 16, defined by significant body wasting in combination with a body condition score ≤2. At endpoint, WT KPC mice showed significant muscle wasting (-8-17%), muscle weakness (-32-46%), fat wasting (-71%) and splenomegaly (+100%) and had a mean tumor mass of 1.9 ± 0.5 g. At this same timepoint (day 16), MuRF1 KO KPC mice were completely protected from body, muscle and fat wasting, with KPC tumors in MuRF1 KO mice 84% smaller than in WT mice. We therefore tracked an additional cohort of MuRF1 KO KPC mice until their tumors reached a comparable size to that of WT mice at their endpoint which, on average, was reached on day 32. Despite having comparable tumor mass at this time point, MuRF1 KO mice remained protected from body, muscle and fat wasting, and were spared from muscle weakness. Using ubiquitin proteomics in muscle, we found that MuRF1 was responsible for the ubiquitination of multiple cytoskeletal and contractile proteins—whose proteolytic degradation into amino acids may contribute to myofiber atrophy and help fuel tumor growth. To explore the impact of MuRF1 deletion on tumor metabolism we conducted global metabolomic profiling of KPC tumors from WT mice on day 16, and from MuRF1 KO mice on day 16 and at matched tumor size. Overall, these analyses revealed an accumulation of metabolites in tumors from MuRF1 KO mice, including glucose, amino acids and amino acid derivatives, suggesting that pancreatic tumors in mice spared from muscle wasting may be less metabolically active. In summary, these combined findings demonstrate that MuRF1 is required for KPC-induced skeletal muscle catabolism, whose deletion impinges on normal tumor metabolism and delays tumor growth. Citation Format: Daria Neyroud, Orlando Laitano, Christopher Lopez, David W. Hammers, H Lee Sweeney, Glenn A. Walter, Sarah M. Judge, Andrew R. Judge. Blocking muscle wasting via deletion of the muscle specific E3 ligase, MuRF1, impedes pancreatic tumor growth [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 2520.

AGO4 suppresses tumor growth by modulating autophagy and apoptosis via enhancing TRIM21-mediated ubiquitination of GRP78 in a p53-independent manner.

Argonaute proteins, which consist of AGO1, AGO2, AGO3 and AGO4, are key players in microRNA-mediated gene silencing. So far, few non-microRNA related biological roles of AGO4 have been reported. Here, we first found that AGO4 had low expression in non-small cell lung cancer (NSCLC) patient tumor tissues and could suppress NSCLC cell proliferation and metastasis. Subsequent studies on the mechanism showed that AGO4 could interact with the tripartite motif-containing protein 21 (TRIM21) and the glucose-regulated protein 78 (GRP78). AGO4 promoted ubiquitination of GRP78 by stabilizing TRIM21, a new specific ubiquitin E3 ligase for promoting K48-linked polyubiquitination of GRP78 confirmed in this paper, which resulted in induced cell apoptosis and inhibited autophagy by activating mTOR signal pathway. Further studies showed that p53 had dominant effects on TRIM21-GRP78 axis by directly increasing the expression of TRIM21 in p53 wild-type cells and AGO4 may alternatively regulate TRIM21-GRP78 axis in p53-deficient cells. We also found that overexpression of AGO4 results in suppression of multiple p53-deficient cell growth both in vivo and vitro. Together, we showed for the first time that the AGO4-TRIM21-GRP78 axis, as a new regulatory pathway, may be a novel potential therapeutic target for p53-deficient tumor treatment.

Circular RNA circPOLR2A promotes clear cell renal cell carcinoma progression by facilitating the UBE3C-induced ubiquitination of PEBP1 and, thereby, activating the ERK signaling pathway

BackgroundIncreasing evidence has demonstrated that circular RNAs (circRNAs) are implicated in cancer progression. However, the aberrant expression and biological functions of circRNAs in clear cell renal cell carcinoma (cRCC) remain largely elusive.MethodDifferentially expressed circRNAs in cRCC were filtered via bioinformatics analysis. Aberrant circPOLR2A expression was validated in cRCC tissues and cell lines via qRT-PCR. Sanger sequencing was used to identify the backsplicing site of circPOLR2A. In vitro and in vivo functional experiments were performed to evaluate the role of circPOLR2A in cRCC malignancy. RNA pull-down, mass spectrometry, RIP, FISH and immunofluorescence assays were used to identify and validate the circPOLR2A-interacting proteins. Ubiquitination modification and interaction between proteins were detected via Co-IP and western blotting. The m6A modification in circPOLR2A was validated by the meRIP assay.ResultsBioinformatics analysis revealed that circPOLR2A was highly expressed in cRCC tissues and metastatic cRCC tissues. CircPOLR2A expression was associated with tumor size and TNM stage in cRCC patients. In vitro and in vivo functional assays revealed that circPOLR2A accelerated cRCC cell proliferation, migration, invasion and angiogenesis, while inhibiting apoptosis. Further mechanistic research suggested that circPOLR2A could interact with UBE3C and PEBP1 proteins, and that UBE3C could act as a specific ubiquitin E3 ligase for the PEBP1 protein. The UBE3C/circPOLR2A/PEBP1 protein-RNA ternary complex enhanced the UBE3C-mediated ubiquitination and degradation of the PEBP1 protein which could inactivate the ERK signaling pathway. Rescue experiments revealed that the PEBP1 protein was the functional downstream target of circPOLR2A. Furthermore, m6A modification in circPOLR2A was confirmed, and the m6A reader YTHDF2 could regulate circPOLR2A expression.ConclusionOur study demonstrated that circPOLR2A modulated the UBE3C-mediated ubiquitination and degradation of the PEBP1 protein, and further activated the ERK pathway during cRCC progression and metastasis. The m6A reader, YTHDF2, regulated circPOLR2A expression in cRCC. Hence, circPOLR2A could be a potential target for the diagnosis and treatment of cRCC.

Long Noncoding RNA H19 Derived from M2 Tumor-Associated Macrophages Promotes Bladder Cell Autophagy via Stabilizing ULK1.

Purpose M2-like tumor-associated macrophages (TAMs) are crucial component of immune infiltration in tumor microenvironment (TME), and exosomes derived from TAMs contributed to the regulation of tumor progression through cellular communication. However, in bladder cancer, the role of exosomal components still remains largely unknown. In the current study, we investigated the role of exosomes derived from M2-like TAMs in the regulation of autophagy in bladder cancer (BC) cells. Methods THP-1 cells were stimulated with IL-4 and IL-13 for the polarization of TAMs, and exosomes were extracted by ultracentrifugation. H19 overexpression plasmid and H19 siRNAs were used in the study. Fluorescent analysis was performed for GFP-LC3 detection. Levels of autophagy and potential target were confirmed by western blot assay and immunoprecipitation. Results We found that TAMs-exosome treatment significantly enhanced autophagy in BC cells, and the expression of lncRNA H19 was greatly upregulated in TAMs-exosome. Silencing of lncRNA H19 in TAMs-exo obviously decreased the levels of LC3-II expression whereas the p62 levels were increased. Mechanistically, silencing of exosomal H19 from TAMs alleviated ULK1 stabilization in BC cells through promoting K48-linked polyubiquitination of ULK1. At last, we found that overexpression of exosomal H19 from TAMs suppressed the interaction between ULK1 and its specific E3 ligase NEDD4L in BC cells. Conclusion We revealed the effect of TAMs-exo-contained lncRNA H19 on regulating autophagy of bladder cancer cells, which indicated that targeting TAMs-H19 is a promising therapeutic strategy for the treatment of BC.

Hypoxic stress disrupts HGF/Met signaling in human trophoblasts: implications for the pathogenesis of preeclampsia

BackgroundPreeclampsia (PE), a placenta-associated pregnancy complication, is the leading cause of maternal and perinatal morbidity and mortality. Met/Erk signaling is inhibited in the placentas of patients with early-onset preeclampsia (E-PE), but the underlying mechanisms remain elusive. In this study, the expression modes of Met and endocytic vesicles in normal and preeclamptic placentas were compared. Biotinylation internalization/recycling assays were used to measure the endocytosis of Met under hypoxia and normoxia in HTR8/SVneo cells. In addition, the expression level of Cbl, a specific E3 ligase of Met, was measured under hypoxia and normoxia, and the endocytosis of Met was studied by using confocal microscopy.ResultsWe found considerable intracellular accumulation of Met, which was colocalized with caveolin-1 (CAV-1), in trophoblasts from E-PE placentas. Prolonged hypoxic stimulation led to the remarkable augmentation of CAV-1-mediated Met endocytosis in HTR8/SVneo cells. In addition, the expression of Cbl was substantially repressed by sustained hypoxia, disrupting ubiquitin degradation and the subsequent intracellular accumulation of Met in HTR8/SVneo cells. The abnormal degradation of Met hampered the ability of hepatocyte growth factor (HGF) to promote trophoblast cell invasion. In E-PE placentas, aberrant upregulation of CAV-1 and downregulation of Cbl were observed in parallel to the intracellular accumulation of Met.ConclusionsThese findings reveal that prolonged hypoxic stress induces the augmentation of endocytosis and repression of ubiquitin-mediated Met degradation, which leads to the impaired regulation of trophoblast invasion by HGF/Met signaling. These data provide novel evidence for elucidating the pathogenesis of preeclampsia, especially of the early-onset subtype.

ASB2 is a novel E3 ligase of SMAD9 required for cardiogenesis

Cardiogenesis requires the orchestrated spatiotemporal tuning of BMP signalling upon the balance between induction and counter-acting suppression of the differentiation of the cardiac tissue. SMADs are key intracellular transducers and the selective degradation of SMADs by the ubiquitin–proteasome system is pivotal in the spatiotemporal tuning of BMP signalling. However, among three SMADs for BMP signalling, SMAD1/5/9, only the specific E3 ligase of SMAD9 remains poorly investigated. Here, we report for the first time that SMAD9, but not the other SMADs, is ubiquitylated by the E3 ligase ASB2 and targeted for proteasomal degradation. ASB2, as well as Smad9, is conserved among vertebrates. ASB2 expression was specific to the cardiac region from the very early stage of cardiac differentiation in embryogenesis of mouse. Knockdown of Asb2 in zebrafish resulted in a thinned ventricular wall and dilated ventricle, which were rescued by simultaneous knockdown of Smad9. Abundant Smad9 protein leads to dysregulated cardiac differentiation through a mechanism involving Tbx2, and the BMP signal conducted by Smad9 was downregulated under quantitative suppression of Smad9 by Asb2. Our findings demonstrate that ASB2 is the E3 ligase of SMAD9 and plays a pivotal role in cardiogenesis through regulating BMP signalling.

Exploration of Aberrant E3 Ligases Implicated in Alzheimer's Disease and Development of Chemical Tools to Modulate Their Function.

The Ubiquitin Proteasome System (UPS) is responsible for the degradation of misfolded or aggregated proteins via a multistep ATP-dependent proteolytic mechanism. This process involves a cascade of ubiquitin (Ub) transfer steps from E1 to E2 to E3 ligase. The E3 ligase transfers Ub to a targeted protein that is brought to the proteasome for degradation. The inability of the UPS to remove misfolded or aggregated proteins due to UPS dysfunction is commonly observed in neurodegenerative diseases, such as Alzheimer’s disease (AD). UPS dysfunction in AD drives disease pathology and is associated with the common hallmarks such as amyloid-β (Aβ) accumulation and tau hyperphosphorylation, among others. E3 ligases are key members of the UPS machinery and dysfunction or changes in their expression can propagate other aberrant processes that accelerate AD pathology. The upregulation or downregulation of expression or activity of E3 ligases responsible for these processes results in changes in protein levels of E3 ligase substrates, many of which represent key proteins that propagate AD. A powerful way to better characterize UPS dysfunction in AD and the role of individual E3 ligases is via the use of high-quality chemical tools that bind and modulate specific E3 ligases. Furthermore, through combining gene editing with recent advances in 3D cell culture, in vitro modeling of AD in a dish has become more relevant and possible. These cell-based models of AD allow for study of specific pathways and mechanisms as well as characterization of the role E3 ligases play in driving AD. In this review, we outline the key mechanisms of UPS dysregulation linked to E3 ligases in AD and highlight the currently available chemical modulators. We present several key approaches for E3 ligase ligand discovery being employed with respect to distinct classes of E3 ligases. Where possible, specific examples of the use of cultured neurons to delineate E3 ligase biology have been captured. Finally, utilizing the available ligands for E3 ligases in the design of proteolysis targeting chimeras (PROTACs) to degrade aberrant proteins is a novel strategy for AD, and we explore the prospects of PROTACs as AD therapeutics.

Autophagy Regulates VDAC3 Ubiquitination by FBXW7 to Promote Erastin-Induced Ferroptosis in Acute Lymphoblastic Leukemia.

Background: The discovery of ferroptosis is a major breakthrough in the development of cancer treatments. However, the mechanism by which ferroptosis contributes to acute lymphoblastic leukemia (ALL) is to be clarified. Here, we explored erastin-induced ferroptosis in ALL cells and the impact of autophagic activity on this process. Materials and Methods: Cell viability was evaluated in various ALL cell lines following erastin treatment by the MTS assay, while cell death was evaluated via a trypan blue assay. Immunoblotting and quantitative real-time PCR were used to detect protein and mRNA expression, respectively. The UbiBrowser database was used to predict the E3 ligase of VDAC3, which was confirmed by immunoprecipitation. The role of FBXW7 in erastin-induced ferroptosis in vitro was evaluated via lentiviral-mediated silencing and overexpression. ALL xenograft mice were used to observe the impact of autophagy on erastin-induced ferroptosis. Results: Resistance to erastin-induced ferroptosis was higher in Jurkat and CCRF-CEM cells than in Reh cells. The sensitivity could be modified by the autophagy activator rapamycin (Rapa) and the autophagy inhibitor chloroquine (CQ). Rapa sensitized ALL cells to erastin-induced ferroptosis. In ALL xenograft mice, the combination treatment of Rapa and erastin resulted in longer survival time than those observed with erastin or Rapa treatment alone. VDAC3 was regulated by autophagy post-transcriptionally, mainly via the ubiquitin-proteasome system (UPS). FBXW7 was verified as a specific E3 ligase of VDAC3. FBXW7 knockdown attenuated VDAC3 degradation by suppressing its ubiquitination, thereby increasing the sensitivity of ALL cells to erastin. Conclusion: Autophagy regulated erastin-induced ferroptosis via the FBXW7-VDAC3 axis. Rapa sensitized ALL cells to erastin-induced ferroptosis both in vitro and in vivo. Our findings provide potential therapeutic targets for ALL.

A strategy to assess the cellular activity of E3 ligase components against neo-substrates using electrophilic probes

While there are hundreds of predicted E3 ligases, characterizing their applications for targeted protein degradation has proved challenging. Here, we report a chemical biology approach to evaluate the ability of modified recombinant E3 ligase components to support neo-substrate degradation. Bypassing the need for specific E3 ligase binders, we use maleimide-thiol chemistry for covalent functionalization followed by E3 electroporation (COFFEE) in live cells. We demonstrate that electroporated recombinant von Hippel-Lindau (VHL) protein, covalently functionalized at its ligandable cysteine with JQ1 or dasatinib, induces degradation of BRD4 or tyrosine kinases, respectively. Furthermore, by applying COFFEE to SPSB2, a Cullin-RING ligase 5 receptor, as well as to SKP1, the adaptor protein for Cullin-RING ligase 1F box (SCF) complexes, we validate this method as a powerful approach to define the activity of previously uncharacterized ubiquitin ligase components, and provide further evidence that not only E3 ligase receptors but also adaptors can be directly hijacked for neo-substrate degradation.