The Shigella kinase effector OspG modulates host ubiquitin signaling to escape septin-cage entrapment.

Shigella flexneri is a Gram-negative bacterium causing severe bloody dysentery. Its pathogenesis is largely dictated by a plasmid-encoded type III secretion system (T3SS) and its associated effectors. Among these, the effector OspG has been shown to bind to the ubiquitin conjugation machinery (E2~Ub) to activate its kinase activity. However, the cellular targets of OspG remain elusive despite years of extensive efforts. Here we show by unbiased phosphoproteomics that a major target of OspG is CAND1, a regulatory protein controlling the assembly of cullin-RING ubiquitin ligases (CRLs). CAND1 phosphorylation weakens its interaction with cullins, which is expected to impact a large panel of CRL E3s. Indeed, global ubiquitome profiling reveals marked changes in the ubiquitination landscape when OspG is introduced. Notably, OspG promotes ubiquitination of a class of cytoskeletal proteins called septins, thereby inhibiting formation of cage-like structures encircling cytosolic bacteria. Overall, we demonstrate that pathogens have evolved an elaborate strategy to modulate host ubiquitin signaling to evade septin-cage entrapment.

A conserved N-terminal motif of CUL3 contributes to assembly and E3 ligase activity of CRL3KLHL22.

The CUL3-RING E3 ubiquitin ligases (CRL3s) play an essential role in response to extracellular nutrition and stress stimuli. The ubiquitin ligase function of CRL3s is activated through dimerization. However, how and why such a dimeric assembly is required for its ligase activity remains elusive. Here, we report the cryo-EM structure of the dimeric CRL3KLHL22 complex and reveal a conserved N-terminal motif in CUL3 that contributes to the dimerization assembly and the E3 ligase activity of CRL3KLHL22. We show that deletion of the CUL3 N-terminal motif impairs dimeric assembly and the E3 ligase activity of both CRL3KLHL22 and several other CRL3s. In addition, we found that the dynamics of dimeric assembly of CRL3KLHL22 generates a variable ubiquitination zone, potentially facilitating substrate recognition and ubiquitination. These findings demonstrate that a CUL3 N-terminal motif participates in the assembly process and provide insights into the assembly and activation of CRL3s.

MSC-derived small extracellular vesicles mitigate diabetic retinopathy by stabilizing Nrf2 through miR-143-3p-mediated inhibition of neddylation.

Diabetic retinopathy (DR) is a highly hazardous and widespread complication of diabetes mellitus (DM). The accumulated reactive oxygen species (ROS) play a central role in DR development. The aim of this research was to examine the impact and mechanisms of mesenchymal stem cell (MSC)-derived small extracellular vesicles (sEV) on regulating ROS and retinal damage in DR. Intravitreal injection of sEV inhibited Cullin3 neddylation, stabilized Nrf2, decreased ROS, reduced retinal inflammation, suppressed Müller gliosis, and mitigated DR. Based on MSC-sEV miRNA sequencing, bioinformatics software, and dual-luciferase reporter assay, miR-143-3p was identified to be the key effector for MSC-sEV's role in regulating neural precursor cell expressed developmentally down-regulated 8 (NEDD8)-mediated neddylation. sEV were able to be internalized by Müller cells. Compared to advanced glycation end-products (AGEs)-induced Müller cells, sEV coculture decreased Cullin3 neddylation, activated Nrf2 signal pathway to combat ROS-induced inflammation. The barrier function of endothelial cells was impaired when endothelial cells were treated with the supernatant of AGEs-induced Müller cells, but was restored when treated with supernatant of AGEs-induced Müller cells cocultured with sEV. The protective effect of sEV was, however, compromised when miR-143-3p was inhibited in sEV. Moreover, the protective efficacy of sEV was diminished when NEDD8 was overexpressed in Müller cells. These findings showed MSC-sEV delivered miR-143-3p to inhibit Cullin3 neddylation, stabilizing Nrf2 to counteract ROS-induced inflammation and reducing vascular leakage. Our findings suggest that MSC-sEV may be a potential nanotherapeutic agent for DR, and that Cullin3 neddylation could be a new target for DR therapy.

Cullin-3 proteins be a novel biomarkers and therapeutic targets for hyperchloremia induced by oral poisoning.

Oral poisoning can trigger diverse physiological reactions, determined by the toxic substance involved. One such consequence is hyperchloremia, characterized by an elevated level of chloride in the blood and leads to kidney damage and impairing chloride ion regulation. Here, we conducted a comprehensive genome-wide analysis to investigate genes or proteins linked to hyperchloremia. Our analysis included functional enrichment, protein-protein interactions, gene expression, exploration of molecular pathways, and the identification of potential shared genetic factors contributing to the development of hyperchloremia. Functional enrichment analysis revealed that oral poisoning owing hyperchloremia is associated with 4 proteins e.g. Kelch-like protein 3, Serine/threonine-protein kinase WNK4, Serine/threonine-protein kinase WNK1 and Cullin-3. The protein-protein interaction network revealed Cullin-3 as an exceptional protein, displaying a maximum connection of 18 nodes. Insufficient data from transcriptomic analysis indicates that there are lack of information having direct associations between these proteins and human-related functions to oral poisoning, hyperchloremia, or metabolic acidosis. The metabolic pathway of Cullin-3 protein revealed that the derivative is Sulfonamide which play role in, increasing urine output, and metabolic acidosis resulted in hypertension. Based on molecular docking results analysis it found that Cullin-3 proteins has the lowest binding energies score and being suitable proteins. Moreover, no major variations were observed in unbound Cullin-3 and all three peptide bound complexes shows that all systems remain compact during 50 ns simulations. The results of our study revealed Cullin-3 proteins be a strong foundation for the development of potential drug targets or biomarker for future studies.

Structure and dynamics of a pentameric KCTD5/CUL3/Gßγ E3 ubiquitin ligase complex.

Heterotrimeric G proteins can be regulated by posttranslational modifications, including ubiquitylation. KCTD5, a pentameric substrate receptor protein consisting of an N-terminal BTB domain and a C-terminal domain, engages CUL3 to form the central scaffold of a cullin-RING E3 ligase complex (CRL3KCTD5) that ubiquitylates Gßγ and reduces Gßγ protein levels in cells. The cryo-EM structure of a 5:5:5 KCTD5/CUL3NTD/Gß1γ2 assembly reveals a highly dynamic complex with rotations of over 60° between the KCTD5BTB/CUL3NTD and KCTD5CTD/Gßγ moieties of the structure. CRL3KCTD5 engages the E3 ligase ARIH1 to ubiquitylate Gßγ in an E3-E3 superassembly, and extension of the structure to include full-length CUL3 with RBX1 and an ARIH1~ubiquitin conjugate reveals that some conformational states position the ARIH1~ubiquitin thioester bond to within 10 Å of lysine-23 of Gß and likely represent priming complexes. Most previously described CRL/substrate structures have consisted of monovalent complexes and have involved flexible peptide substrates. The structure of the KCTD5/CUL3NTD/Gßγ complex shows that the oligomerization of a substrate receptor can generate a polyvalent E3 ligase complex and that the internal dynamics of the substrate receptor can position a structured target for ubiquitylation in a CRL3 complex.

Cullin 3 RING E3 ligase inactivation causes NRF2-dependent NADH reductive stress, hepatic lipodystrophy, and systemic insulin resistance.

Cullin RING E3 ligases (CRL) have emerged as key regulators of disease-modifying pathways and therapeutic targets. Cullin3 (Cul3)-containing CRL (CRL3) has been implicated in regulating hepatic insulin and oxidative stress signaling. However, CRL3 function in liver pathophysiology is poorly defined. Here, we report that hepatocyte Cul3 knockout results in rapid resolution of steatosis in obese mice. However, the remarkable resistance of hepatocyte Cul3 knockout mice to developing steatosis does not lead to overall metabolic improvement but causes systemic metabolic disturbances. Liver transcriptomics analysis identifies that CRL3 inactivation causes persistent activation of the nuclear factor erythroid 2-related factor 2 (NRF2) antioxidant defense pathway, which also reprograms the lipid transcriptional network to prevent TG storage. Furthermore, global metabolomics reveals that NRF2 activation induces numerous NAD+-consuming aldehyde dehydrogenases to increase the cellular NADH/NAD+ ratio, a redox imbalance termed NADH reductive stress that inhibits the glycolysis-citrate-lipogenesis axis in Cul3 knockout livers. As a result, this NRF2-induced cellular lipid storage defect promotes hepatic ceramide accumulation, elevates circulating fatty acids, and worsens systemic insulin resistance in a vicious cycle. Hepatic lipid accumulation is restored, and liver injury and hyperglycemia are attenuated when NRF2 activation and NADH reductive stress are abolished in hepatocyte Cul3/Nrf2 double-knockout mice. The resistance to hepatic steatosis, hyperglycemia, and NADH reductive stress are observed in hepatocyte Keap1 knockout mice with NRF2 activation. In summary, our study defines a critical role of CRL3 in hepatic metabolic regulation and demonstrates that the CRL3 downstream NRF2 overactivation causes hepatic metabolic maladaptation to obesity and insulin resistance.

Mechanism of Ψ-Pro/C-degron recognition by the CRL2FEM1B ubiquitin ligase.

The E3 ligase-degron interaction determines the specificity of the ubiquitin‒proteasome system. We recently discovered that FEM1B, a substrate receptor of Cullin 2-RING ligase (CRL2), recognizes C-degrons containing a C-terminal proline. By solving several cryo-EM structures of CRL2FEM1B bound to different C-degrons, we elucidate the dimeric assembly of the complex. Furthermore, we reveal distinct dimerization states of unmodified and neddylated CRL2FEM1B to uncover the NEDD8-mediated activation mechanism of CRL2FEM1B. Our research also indicates that, FEM1B utilizes a bipartite mechanism to recognize both the C-terminal proline and an upstream aromatic residue within the substrate. These structural findings, complemented by in vitro ubiquitination and in vivo cell-based assays, demonstrate that CRL2FEM1B-mediated polyubiquitination and subsequent protein turnover depend on both FEM1B-degron interactions and the dimerization state of the E3 ligase complex. Overall, this study deepens our molecular understanding of how Cullin-RING E3 ligase substrate selection mediates protein turnover.

Protein neddylation and its role in health and diseases.

NEDD8 (Neural precursor cell expressed developmentally downregulated protein 8) is an ubiquitin-like protein that is covalently attached to a lysine residue of a protein substrate through a process known as neddylation, catalyzed by the enzyme cascade, namely NEDD8 activating enzyme (E1), NEDD8 conjugating enzyme (E2), and NEDD8 ligase (E3). The substrates of neddylation are categorized into cullins and non-cullin proteins. Neddylation of cullins activates CRLs (cullin RING ligases), the largest family of E3 ligases, whereas neddylation of non-cullin substrates alters their stability and activity, as well as subcellular localization. Significantly, the neddylation pathway and/or many neddylation substrates are abnormally activated or over-expressed in various human diseases, such as metabolic disorders, liver dysfunction, neurodegenerative disorders, and cancers, among others. Thus, targeting neddylation becomes an attractive strategy for the treatment of these diseases. In this review, we first provide a general introduction on the neddylation cascade, its biochemical process and regulation, and the crystal structures of neddylation enzymes in complex with cullin substrates; then discuss how neddylation governs various key biological processes via the modification of cullins and non-cullin substrates. We further review the literature data on dysregulated neddylation in several human diseases, particularly cancer, followed by an outline of current efforts in the discovery of small molecule inhibitors of neddylation as a promising therapeutic approach. Finally, few perspectives were proposed for extensive future investigations.

CRL4DCAF13 E3 ubiquitin ligase targets MeCP2 for degradation to prevent DNA hypermethylation and ensure normal transcription in growing oocytes.

The DNA methylation is gradually acquired during oogenesis, a process sustained by successful follicle development. However, the functional roles of methyl-CpG-binding protein 2 (MeCP2), an epigenetic regulator displaying specifical binding with methylated DNA, remains unknown in oogenesis. In this study, we found MeCP2 protein was highly expressed in primordial and primary follicle, but was almost undetectable in secondary follicles. However, in aged ovary, MeCP2 protein is significantly increased in both oocyte and granulosa cells. Overexpression of MeCP2 in growing oocyte caused transcription dysregulation, DNA hypermethylation, and genome instability, ultimately leading to follicle growth arrest and apoptosis. MeCP2 is targeted by DCAF13, a substrate recognition adaptor of the Cullin 4-RING (CRL4) E3 ligase, and polyubiquitinated for degradation in both cells and oocytes. Dcaf13-null oocyte exhibited an accumulation of MeCP2 protein, and the partial rescue of follicle growth arrest induced by Dcaf13 deletion was observed following MeCP2 knockdown. The RNA-seq results revealed that large amounts of genes were regulated by the DCAF13-MeCP2 axis in growing oocytes. Our study demonstrated that CRL4DCAF13 E3 ubiquitin ligase targets MeCP2 for degradation to ensure normal DNA methylome and transcription in growing oocytes. Moreover, in aged ovarian follicles, deceased DCAF13 and DDB1 protein were observed, indicating a potential novel mechanism that regulates ovary aging.

Dynamic role of CUL4B in radiation-induced intestinal injury-regeneration.

CUL4B, a crucial scaffolding protein in the largest E3 ubiquitin ligase complex CRL4B, is involved in a broad range of physiological and pathological processes. While previous research has shown that CUL4B participates in maintaining intestinal homeostasis and function, its involvement in facilitating intestinal recovery following ionizing radiation (IR) damage has not been fully elucidated. Here, we utilized in vivo and in vitro models to decipher the role of CUL4B in intestinal repair after IR-injury. Our findings demonstrated that prior to radiation exposure, CUL4B inhibited the ubiquitination modification of PSME3, which led to the accumulation of PSME3 and subsequent negative regulation of p53-mediated apoptosis. In contrast, after radiation, CUL4B dissociated from PSME3 and translocated into the nucleus at phosphorylated histones H2A (γH2AX) foci, thereby impeding DNA damage repair and augmenting p53-mediated apoptosis through inhibition of BRCA1 phosphorylation and RAD51. Our study elucidated the dynamic role of CUL4B in the repair of radiation-induced intestinal damage and uncovered novel molecular mechanisms underlying the repair process, suggesting a potential therapeutic strategy of intestinal damage after radiation therapy for cancers.

Hyperthermia and cisplatin combination therapy promotes caspase-8 accumulation and activation to enhance apoptosis and pyroptosis in cancer cells.

BACKGROUND: Hyperthermia can play a synergistic role with chemotherapy in combination therapy. Although the association between caspase activation, apoptosis, and pyroptosis have been published for both cisplatin (CDDP) and hyperthermia therapies independently, the interactions between these molecular pathways in combination therapy are unknown. The present study aimed to investigate the possible interactions between caspase 8 activation, apoptosis, and pyroptosis in combination therapy. METHODS: Cells were treated with CDDP (15 µg/ml), followed by hyperthermia at optimized temperature (42.5 °C) in water-bath. After combination therapy, cell viability was analyzed by CCK-8, and cell death was analyzed by Annexin-V-FITC/PI and caspases activation. Immuno-staining and co-immuno-precipitation were used to examine the interaction between p62 and caspase-8. Pyroptosis was investigated by western blotting and transmission electron microscopy. E3 ligase Cullin 3 was knockdown by siRNA. In addition, caspase-8 activation was modulated by CRISPR-Cas9 gene-editing or pharmacological inhibition. RESULTS: Combination therapy promoted K63-linked polyubiquitination of caspase-8 and cellular accumulation of caspase-8. In turn, polyubiquitinated caspase-8 interacted with p62 and led to the activation of caspase-3. Knockdown of the E3 ligase Cullin 3 by siRNA reduced caspase-8 polyubiquitination and activation. In addition, combination therapy induced release of the pore-forming N-terminus from gasdermins and promoted pyroptosis along with caspase-8 accumulation and activation. Knockdown of caspase-8 by CRISPR/Cas9 based gene editing reduced the sensitivity of tumor cells to apoptosis and pyroptosis. CONCLUSIONS: Our study presented a novel mechanism in which hyperthermia synergized with chemotherapy in promoting apoptosis and pyroptosis in a caspase-8 dependent manner.

RNA-binding proteins potentially regulate the alternative splicing of apoptotic genes during knee osteoarthritis progression.

BACKGROUND: Alternative splicing (AS) is a principal mode of genetic regulation and one of the most widely used mechanisms to generate structurally and functionally distinct mRNA and protein variants. Dysregulation of AS may result in aberrant transcription and protein products, leading to the emergence of human diseases. Although considered important for regulating gene expression, genome-wide AS dysregulation, underlying mechanisms, and clinical relevance in knee osteoarthritis (OA) remain unelucidated. Therefore, in this study, we elucidated and validated AS events and their regulatory mechanisms during OA progression. RESULTS: In this study, we identified differentially expressed genes between human OA and healthy meniscus samples. Among them, the OA-associated genes were primarily enriched in biological pathways such as extracellular matrix organization and ossification. The predominant OA-associated regulated AS (RAS) events were found to be involved in apoptosis during OA development. The expression of the apoptosis-related gene BCL2L13, XAF1, and NF2 were significantly different between OA and healthy meniscus samples. The construction of a covariation network of RNA-binding proteins (RBPs) and RAS genes revealed that differentially expressed RBP genes LAMA2 and CUL4B may regulate the apoptotic genes XAF1 and BCL2L13 to undergo AS events during OA progression. Finally, RT-qPCR revealed that CUL4B expression was significantly higher in OA meniscus samples than in normal controls and that the AS ratio of XAF1 was significantly different between control and OA samples; these findings were consistent with their expected expression and regulatory relationships. CONCLUSIONS: Differentially expressed RBPs may regulate the AS of apoptotic genes during knee OA progression. XAF1 and its regulator, CUL4B, may serve as novel biomarkers and potential therapeutic targets for this disease.

Icariin ameliorates osteoporosis in ovariectomized rats by targeting Cullin 3/Nrf2/OH pathway for osteoclast inhibition.

Osteoporosis, characterized by low bone mass and bone microarchitecture breakdown, has become a growing public health problem. The increase in oxidative stress could lead to an imbalance between osteoblasts-mediated osteogenesis and osteoclast-mediated bone resorption, which gives rise to osteoporosis. Nrf2 is a master transcription factor that regulates oxidative stress and has recently been reported to take part in the development of osteoporosis. Icariin, a leading active flavonoid in herbal Epimedium pubescens, has significant antioxidant activity in and is widely applied for treating bone diseases. In this study, we aimed to explore the effect of icariin on osteoclastogenesis and its potential mechanism from the perspective of oxidative stress inhibition, using ovariectomized (OVX) rats and RANKL-induced RAW264.7 cells. Our results demonstrated that icariin-treated OVX rats exhibited higher bone density, fewer tartrate-resistant acid phosphatase (TRAP)-positive osteoclasts, and lower ROS levels in bone tissues than vehicle-treated OVX rats. Also, icariin suppressed osteoclast differentiation and inhibited the expression of osteoclastogenesis-related genes, such as NFATc1, Ctsk, Trap, and c-Fos, in RANKL-induced RAW264.7 cells. Icariin also reduced intracellular ROS levels by increasing the expression of nuclear Nrf2 and HO-1. Further mechanistic studies showed icariin inhibited Cullin 3 expression and could delay Nrf2 degradation by reducing the ubiquitination of endogenous Nrf2 in RANKL-stimulated RAW264.7 cells, and these effects were markedly reversed by cullin three overexpression. These findings suggest icariin alleviated osteoporosis by suppressing osteoclastogenesis via targeting the Cullin 3/Nrf2/OH signaling pathway. Our study implied that icariin may be a potential candidate to treat osteoporosis.

Oncogenic mutations of KRAS modulate its turnover by the CUL3/LZTR1 E3 ligase complex.

KRAS is a proto-oncogene encoding a small GTPase. Mutations contribute to ∼30% of human solid tumours, including lung adenocarcinoma, pancreatic, and colorectal carcinomas. Most KRAS activating mutations interfere with GTP hydrolysis, essential for its role as a molecular switch, leading to alterations in their molecular environment and oncogenic signalling. However, the precise signalling cascades these mutations affect are poorly understood. Here, APEX2 proximity labelling was used to profile the molecular environment of WT, G12D, G13D, and Q61H-activating KRAS mutants under starvation and stimulation conditions. Through quantitative proteomics, we demonstrate the presence of known KRAS interactors, including ARAF and LZTR1, which are differentially captured by WT and KRAS mutants. Notably, the KRAS mutations G12D, G13D, and Q61H abrogate their association with LZTR1, thereby affecting turnover. Elucidating the implications of LZTR1-mediated regulation of KRAS protein levels in cancer may offer insights into therapeutic strategies targeting KRAS-driven malignancies.

Targeting kelch-like (KLHL) proteins: achievements, challenges and perspectives.

Kelch-like proteins (KLHLs) are a large family of BTB-containing proteins. KLHLs function as the substrate adaptor of Cullin 3-RING ligases (CRL3) to recognize substrates. KLHLs play pivotal roles in regulating various physiological and pathological processes by modulating the ubiquitination of their respective substrates. Mounting evidence indicates that mutations or abnormal expression of KLHLs are associated with various human diseases. Targeting KLHLs is a viable strategy for deciphering the KLHLs-related pathways and devising therapies for associated diseases. Here, we comprehensively review the known KLHLs inhibitors to date and the brilliant ideas underlying their development.

Inhibition of glycogen synthase kinase-3 enhances NRF2 protein stability, nuclear localisation and target gene transcription in pancreatic beta cells.

Accumulation of reactive oxygen species (i.e., oxidative stress) is a leading cause of beta cell dysfunction and apoptosis in diabetes. NRF2 (NF-E2 p45-related factor-2) regulates the adaptation to oxidative stress, and its activity is negatively regulated by the redox-sensitive CUL3 (cullin-3) ubiquitin ligase substrate adaptor KEAP1 (Kelch-like ECH-associated protein-1). Additionally, NRF2 is repressed by the insulin-regulated Glycogen Synthase Kinase-3 (GSK3). We have demonstrated that phosphorylation of NRF2 by GSK3 enhances ß-TrCP (beta-transducin repeat-containing protein) binding and ubiquitylation by CUL1 (cullin-1), resulting in increased proteasomal degradation of NRF2. Thus, we hypothesise that inhibition of GSK3 activity or ß-TrCP binding upregulates NRF2 and so protects beta cells against oxidative stress. We have found that treating the pancreatic beta cell line INS-1 832/13 with the KEAP1 inhibitor TBE31 significantly enhanced NRF2 protein levels. The presence of the GSK3 inhibitor CT99021 or the ß-TrCP-NRF2 protein-protein interaction inhibitor PHAR, along with TBE31, resulted in prolonged NRF2 stability and enhanced nuclear localisation (P < 0.05). TBE31-mediated induction of NRF2-target genes encoding NAD(P)H quinone oxidoreductase 1 (Nqo1), glutamate-cysteine ligase modifier (Gclm) subunit and heme oxygenase (Hmox1) was significantly enhanced by the presence of CT99021 or PHAR (P < 0.05) in both INS-1 832/13 and in isolated mouse islets. Identical results were obtained using structurally distinct GSK3 inhibitors and inhibition of KEAP1 with sulforaphane. In summary, we demonstrate that GSK3 and ß-TrCP/CUL1 regulate the proteasomal degradation of NRF2, enhancing the impact of KEAP1 regulation, and so contributes to the redox status of pancreatic beta cells. Inhibition of GSK3, or ß-TrCP/CUL1 binding to NRF2 may represent a strategy to protect beta cells from oxidative stress.

Buffalo colostrum peptide mitigates Parkinson's disease pathophysiology through Cullin-3 inhibition.

Colostrum/Milk is a chief repertoire of antioxidant peptides. Nuclear factor-erythroid 2 related factor 2 (Nrf2) is a viable target for Parkinson's Disease (PD), as this pathway deduced to be impaired in PD. Cullin-3 is one of the crucial E3 ligase responsible for its regulation. The present study screened peptide libraries of buffalo colostrum & milk peptides for Cullin-3 inhibition, thus ensuing activation of Nrf2 to alleviate the molecular etiopathology in PD using the C. elegans as a model. The structure was modelled, binding sites analyzed and peptide-interactions analyzed by docking. Among the 55 sequences (≤1 kDa), the peptide SFVSEVPEL having the highest dock score (-16.919) was synthesized and evaluated for its effects on oxidative stress markers, antioxidant enzymes, neurochemical marker and Nrf2/Skn-1 levels. The lead peptide alleviated the oxidative pathophysiology and behavioural deficits associated with PD in C. elegans.

Regulation of the water channel aquaporin-2 by cullin E3 ubiquitin ligases.

Aquaporin 2 (AQP2) is a vasopressin (VP)-regulated water channel in the renal collecting duct. Phosphorylation and ubiquitylation of AQP2 play an essential role in controlling the cellular abundance of AQP2 and its accumulation on the plasma membrane in response to VP. Cullin-RING ubiquitin ligases (CRLs) are multisubunit E3 ligases involved in ubiquitylation and degradation of their target proteins, eight of which are expressed in the collecting duct. Here, we used an established cell model of the collecting duct (mpkCCD14 cells) to study the role of cullins in modulating AQP2. Western blotting identified Cul-1 to Cul-5 in mpkCCD14 cells. Treatment of cells for 4 h with a pan-cullin inhibitor (MLN4924) decreased AQP2 abundance, prevented a VP-induced reduction in AQP2 Ser261 phosphorylation, and attenuated VP-induced plasma membrane accumulation of AQP2 relative to the vehicle. AQP2 ubiquitylation levels were significantly higher after MLN4924 treatment compared with controls, and they remained higher despite VP treatment. Cullin inhibition increased ERK1/2 activity, a kinase that regulates AQP2 Ser261 phosphorylation, and VP-induced reductions in ERK1/2 phosphorylation were absent during MLN4924 treatment. Furthermore, the greater Ser261 phosphorylation and reduction in AQP2 abundance during MLN4924 treatment were attenuated during ERK1/2 inhibition. MLN4924 increased intracellular calcium levels via calcium release-activated calcium channels, inhibition of which abolished MLN4924 effects on Ser261 phosphorylation and AQP2 abundance. In conclusion, CRLs play a vital role in mediating some of the effects of VP to increase AQP2 plasma membrane accumulation and AQP2 abundance. Whether modulation of cullin activity can contribute to body water homeostasis requires further studies.NEW & NOTEWORTHY Aquaporin 2 (AQP2) is essential for body water homeostasis and is regulated by the antidiuretic hormone vasopressin. The posttranslational modification ubiquitylation is a key regulator of AQP2 abundance and plasma membrane localization. Here we demonstrate that cullin-RING E3 ligases play a vital role in mediating some of the effects of vasopressin to increase AQP2 abundance and plasma membrane accumulation. The results suggest that manipulating cullin activity could be a novel strategy to alter kidney water handling.

Plasmodium falciparum contains functional SCF and CRL4 ubiquitin E3 ligases, and CRL4 is critical for cell division and membrane integrity.

Protein ubiquitination is essential for cellular homeostasis and regulation of several processes, including cell division and genome integrity. Ubiquitin E3 ligases determine substrate specificity for ubiquitination, and Cullin-RING E3 ubiquitin ligases (CRLs) make the largest group among the ubiquitin E3 ligases. Although conserved and most studied in model eukaryotes, CRLs remain underappreciated in Plasmodium and related parasites. To investigate the CRLs of human malaria parasite Plasmodium falciparum, we generated parasites expressing tagged P. falciparum cullin-1 (PfCullin-1), cullin-2 (PfCullin-2), Rbx1 (PfRbx1) and Skp1 (PfSkp1). PfCullin-1 and PfCullin-2 were predominantly expressed in erythrocytic trophozoite and schizont stages, with nucleocytoplasmic localization and chromatin association, suggesting their roles in different cellular compartments and DNA-associated processes. Immunoprecipitation, in vitro protein-protein interaction, and ubiquitination assay confirmed the presence of a functional Skp1-Cullin-1-Fbox (PfSCF) complex, comprising of PfCullin-1, PfRbx1, PfSkp1, PfFBXO1, and calcyclin binding protein. Immunoprecipitation, sequence analysis, and ubiquitination assay indicated that PfCullin-2 forms a functional human CRL4-like complex (PfCRL4), consisting of PfRbx1, cleavage and polyadenylation specificity factor subunit_A and WD40 repeat proteins. PfCullin-2 knock-down at the protein level, which would hinder PfCRL4 assembly, significantly decreased asexual and sexual erythrocytic stage development. The protein levels of several pathways, including protein translation and folding, lipid biosynthesis and transport, DNA replication, and protein degradation were significantly altered upon PfCullin-2 depletion, which likely reflects association of PfCRL4 with multiple pathways. PfCullin-2-depleted schizonts had poorly delimited merozoites and internal membraned structures, suggesting a role of PfCRL4 in maintaining membrane integrity. PfCullin-2-depleted parasites had a significantly lower number of nuclei/parasite than the normal parasites, indicating a crucial role of PfCRL4 in cell division. We demonstrate the presence of functional CRLs in P. falciparum, with crucial roles for PfCRL4 in cell division and maintaining membrane integrity.

JunD-miR494-CUL3 axis promotes radioresistance and metastasis by facilitating EMT and restraining PD-L1 degradation in esophageal squamous cell carcinoma.

Therapy resistance and metastatic progression jointly determine the fatal outcome of cancer, therefore, elucidating their crosstalk may provide new opportunities to improve therapeutic efficacy and prevent recurrence and metastasis in esophageal squamous cell carcinoma (ESCC). Here, we have established radioresistant ESCC cells with the remarkable metastatic capacity, and identified miR-494-3p (miR494) as a radioresistant activator. Mechanistically, we demonstrated that cullin 3 (CUL3) is a direct target of miR494, which is transcriptionally regulated by JunD, and highlighted that JunD-miR494-CUL3 axis promotes radioresistance and metastasis by facilitating epithelial-mesenchymal transition (EMT) and restraining programmed cell death 1 ligand 1 (PD-L1) degradation. In clinical specimens, miR494 is significantly up-regulated and positively associated with T stage and lymph node metastasis in ESCC tissues and serum. Notably, patients with higher serum miR494 expression have poor prognosis, and patients with higher CUL3 expression have more conventional dendritic cells (cDCs) and plasmacytoid DCs (pDCs), less cancer-associated fibroblasts (CAF2/4), and tumor endothelial cells (TEC2/3) infiltration than patients with lower CUL3 expression, suggesting that CUL3 may be involved in tumor microenvironment (TME). Overall, miR494 may serve as a potential prognostic predictor and therapeutic target, providing a promising strategy for ESCC treatment.