RNF20/40-mediated eEF1BδL monoubiquitylation stimulates transcription of heat shock-responsive genes

RNF20 Regulates Oocyte Meiotic Spindle Assembly by Recruiting TPM3 to Centromeres and Spindle Poles

Previously a ring finger protein 20 (RNF20) is found to be essential for meiotic recombination and mediates H2B ubiquitination during spermatogenesis. However, its role in meiotic division is still unknown. Here, it is shown that RNF20 is localized at both centromeres and spindle poles, and it is required for oocyte acentrosomal spindle organization and female fertility. RNF20-depleted oocytes exhibit severely abnormal spindle and chromosome misalignment caused by defective bipolar organization. Notably, it is found that the function of RNF20 in spindle assembly is not dependent on its E3 ligase activity. Instead, RNF20 regulates spindle assembly by recruiting tropomyosin3 (TPM3) to both centromeres and spindle poles with its coiled-coil motif. The RNF20-TPM3 interaction is essential for acentrosomal meiotic spindle assembly. Together, the studies uncover a novel function for RNF20 in mediating TPM3 recruitment to both centromeres and spindle poles during oocyte spindle assembly.

The ubiquitin codes in cellular stress responses

Ubiquitination/ubiquitylation, one of the most fundamental post-translational modifications, regulates almost every critical cellular process in eukaryotes. Emerging evidence has shown that essential components of numerous biological processes undergo ubiquitination in mammalian cells upon exposure to diverse stresses, from exogenous factors to cellular reactions, causing a dazzling variety of functional consequences. Various forms of ubiquitin signals generated by ubiquitylation events in specific milieus, known as ubiquitin codes, constitute an intrinsic part of myriad cellular stress responses. These ubiquitination events, leading to proteolytic turnover of the substrates or just switch in functionality, initiate, regulate, or supervise multiple cellular stress-associated responses, supporting adaptation, homeostasis recovery, and survival of the stressed cells. In this review, we attempted to summarize the crucial roles of ubiquitination in response to different environmental and intracellular stresses, while discussing how stresses modulate the ubiquitin system. This review also updates the most recent advances in understanding ubiquitination machinery as well as different stress responses and discusses some important questions that may warrant future investigation.

Ubiquitin ligase RNF20 coordinates sequential adipose thermogenesis with brown and beige fat-specific substrates

In mammals, brown adipose tissue (BAT) and inguinal white adipose tissue (iWAT) execute sequential thermogenesis to maintain body temperature during cold stimuli. BAT rapidly generates heat through brown adipocyte activation, and further iWAT gradually stimulates beige fat cell differentiation upon prolonged cold challenges. However, fat depot-specific regulatory mechanisms for thermogenic activation of two fat depots are poorly understood. Here, we demonstrate that E3 ubiquitin ligase RNF20 orchestrates adipose thermogenesis with BAT- and iWAT-specific substrates. Upon cold stimuli, BAT RNF20 is rapidly downregulated, resulting in GABPα protein elevation by controlling protein stability, which stimulates thermogenic gene expression. Accordingly, BAT-specific Rnf20 suppression potentiates BAT thermogenic activity via GABPα upregulation. Moreover, upon prolonged cold stimuli, iWAT RNF20 is gradually upregulated to promote de novo beige adipogenesis. Mechanistically, iWAT RNF20 mediates NCoR1 protein degradation, rather than GABPα, to activate PPARγ. Together, current findings propose fat depot-specific regulatory mechanisms for temporal activation of adipose thermogenesis.

KSHV RTA utilizes the host E3 ubiquitin ligase complex RNF20/40 to drive lytic reactivation

IMPORTANCE

Kaposi's sarcoma-associated herpesvirus (KSHV) is a cancer-causing human herpesvirus that establishes a persistent infection in humans. The lytic viral cycle plays a crucial part in lifelong infection as it is involved in the viral dissemination. The master regulator of the KSHV lytic replication cycle is the viral replication and transcription activator (RTA) protein, which is necessary and sufficient to push the virus from latency into the lytic phase. Thus, the identification of host factors utilized by RTA for controlling the lytic cycle can help to find novel targets that could be used for the development of antiviral therapies against KSHV. Using a proteomics approach, we have identified a novel interaction between RTA and the cellular E3 ubiquitin ligase complex RNF20/40, which we have shown to be necessary for promoting RTA-induced KSHV lytic cycle.

RNF20/RNF40 ameliorates streptozotocin-induced type 1 diabetes by activating vitamin D receptors in vivo

BACKGROUND

Type 1 diabetes is one of the chronic autoimmune diseases. Its features include the immune-triggered pancreatic beta-cells destruction. Ubiquitin ligases RNF20 and RNF40 have been discovered to participate into beta cells gene expression, insulin secretion, and expression of vitamin D receptors (VDRs). However, no reports about the role of RNF20/RNF40 in type 1 diabetes are known till now. The aim of this study was to clarify the role of RNF20/RNF40 in type 1 diabetes and explore the mechanism.

METHODS

In this study, streptozotocin (STZ)-induced mice type 1 diabetes model was used. The protein expressions of genes were examined through Western blot analysis. Fasting blood glucose was detected through glucose meter. The plasma insulin was tested through the commercial kit. Hematoxylin and eosin staining was utilized to observe pathological changes of pancreatic tissues. Immunofluorescence assay was performed to evaluate the level of insulin. The levels of pro-inflammatory cytokines in serum were assessed by enzyme-linked-immunosorbent serologic assay. The cell apoptosis was measured through terminal deoxynucleotidyl transferase dUTP nick end labelling assay.

RESULTS

STZ was used to stimulate mice model for type 1 diabetes. At first, both RNF20 and RNF40 expressions were down-regulated in STZ-mediated type 1 diabetes. Additionally, RNF20/RNF40 improved hyperglycemia in STZ-stimulated mice. Moreover, RNF20/RNF40 relieved pancreatic tissue injury in STZ-induced mice. Further experiments found that RNF20/RNF40 rescued the strengthened inflammation mediated by STZ treatment. The cell apoptosis was enhanced in the pancreatic tissues of STZ-triggered mice, but this effect was weakened by overexpression of RNF20/RNF40. Besides, the VDR expression was positively regulated by RNF20/RNF40. Finally, VDR knockdown reversed improved hyperglycemia, inflammation, and cell apoptosis stimulated by overexpression of RNF20/RNF40.

CONCLUSION

Our findings proved that RNF20/RNF40 activated VDR to relieve type 1 diabetes. This work might highlight the functioning of RNF20/RNF40 in the treatment of type 1 diabetes.

The RPA-RNF20-SNF2H cascade promotes proper chromosome segregation and homologous recombination repair

The human tumor suppressor Ring finger protein 20 (RNF20)-mediated histone H2B monoubiquitination (H2Bub) is essential for proper chromosome segregation and DNA repair. However, what is the precise function and mechanism of RNF20-H2Bub in chromosome segregation and how this pathway is activated to preserve genome stability remain unknown. Here, we show that the single-strand DNA-binding factor Replication protein A (RPA) interacts with RNF20 mainly in the S and G2/M phases and recruits RNF20 to mitotic centromeres in a centromeric R-loop-dependent manner. In parallel, RPA recruits RNF20 to chromosomal breaks upon DNA damage. Disruption of the RPA-RNF20 interaction or depletion of RNF20 increases mitotic lagging chromosomes and chromosome bridges and impairs BRCA1 and RAD51 loading and homologous recombination repair, leading to elevated chromosome breaks, genome instability, and sensitivities to DNA-damaging agents. Mechanistically, the RPA-RNF20 pathway promotes local H2Bub, H3K4 dimethylation, and subsequent SNF2H recruitment, ensuring proper Aurora B kinase activation at centromeres and efficient loading of repair proteins at DNA breaks. Thus, the RPA-RNF20-SNF2H cascade plays a broad role in preserving genome stability by coupling H2Bub to chromosome segregation and DNA repair.

RNF20 deletion causes inflammation in model of sepsis through the NLRP3 activation

Aim: Sepsis is an extremely complex, threatening and difficult-to-treat disease, which can occur at any age and under any underlying disease. RNF20 regulate NF-kappaB (NF-κB) signaling pathway and the transcription of inflammatory factors of target genes. Therefore, it is of great significance to study the function of RNF20 in the clinical treatment of sepsis and its underlying mechanisms.Methods: C57BL/6 mice were subjected to cecal ligation and puncture (CLP) surgery. THP-1 cells were induced with Lipopolysaccharide for 4 h.Results: RNF20 gene, mRNA expression and protein expression were reduced in patients with sepsis and mice with sepsis. Based on RNF20 deletion (RNF20^-/-) mice, these were found to be increased inflammation reactions in RNF20^-/- mice. However, the RNF20 human protein reduced inflammation reactions in mice with sepsis. In vitro model of sepsis, over-expression of RNF20 inhibited inflammation reactions by inducing Vitamin D Receptor (VDR), while down-regulation of RNF20 promoted inflammation reactions through the suppression of VDR. RNF20 protein was interlinked with VDR protein, and VDR protein was also interlinked with NLRP3. Furthermore, VDR promoted NLRP3 ubiquitination and reduced NLRP3 function in vitro model of sepsis.Conclusion: These studies demonstrate that RNF20 suppressed inflammation reactions in models with sepsis through NLRP3 inflammasome and NLRP3 ubiquitination by activating VDR.

Interfering with the expression of EEF1D gene enhances the sensitivity of ovarian cancer cells to cisplatin

Background

Eukaryotic translation elongation factors 1 δ (EEF1D), has garnered much attention with regards to their role in the drug resistance of cancers. In this paper, we investigated the effects and mechanisms of increasing the sensitivity of ovarian cancer cells to cisplatin or cis-dichlorodiammine platinum (DDP) by knockdown and knockout of EEF1D gene in cellular and animal models.

Methods

The EEF1D gene was knocked-down or -out by siRNA or CRISPR/Cas9 respectively in human ovarian cancer cell SKOV3, DDP-resistant subline SKOV3/DDP, and EEF1D gene in human primary ovarian cancer cell from 5 ovarian cancer patients with progressive disease/stable disease (PD/SD) was transiently knocked down by siRNA interference. The mice model bearing xenografted tumor was established with subcutaneous inoculation of SKOV3/DDP.

Results

The results show that reducing or removing EEF1D gene expression significantly increased the sensitivity of human ovarian cancer cells to DDP in inhibiting viability and inducing apoptosis in vitro and in vivo, and also boosted DDP to inhibit xenografted tumor growth. Interfering with EEF1D gene expression in mice xenografted tumor significantly affected the levels of OPTN, p-Akt, Bcl-2, Bax, cleaved caspase-3 and ERCC1 compared to DDP treated mice alone, and had less effect on PI3K, Akt and caspase-3.

Conclusions

The knocking down or out EEF1D gene expression could enhance the sensitivity of ovarian cancer cells to DDP partially, which may be achieved via inactivating the PI3K/AKT signaling pathway, thus inducing cell apoptosis and decreasing repairment of DNA damage. Our study provides a novel therapeutic strategy for the treatment of ovarian cancer.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12885-022-09699-7.

Localization and Functional Roles of Components of the Translation Apparatus in the Eukaryotic Cell Nucleus

Components of the translation apparatus, including ribosomal proteins, have been found in cell nuclei in various organisms. Components of the translation apparatus are involved in various nuclear processes, particularly those associated with genome integrity control and the nuclear stages of gene expression, such as transcription, mRNA processing, and mRNA export. Components of the translation apparatus control intranuclear trafficking; the nuclear import and export of RNA and proteins; and regulate the activity, stability, and functional recruitment of nuclear proteins. The nuclear translocation of these components is often involved in the cell response to stimulation and stress, in addition to playing critical roles in oncogenesis and viral infection. Many components of the translation apparatus are moonlighting proteins, involved in integral cell stress response and coupling of gene expression subprocesses. Thus, this phenomenon represents a significant interest for both basic and applied molecular biology. Here, we provide an overview of the current data regarding the molecular functions of translation factors and ribosomal proteins in the cell nucleus.

Heat Shock-Induced Dephosphorylation of Eukaryotic Elongation Factor 1BδL by Protein Phosphatase 1

Several variant proteins are produced from EEF1D, including two representative proteins produced via alternative splicing machinery. One protein is the canonical translation eukaryotic elongation factor eEF1Bδ1, and the other is the heat shock-responsive transcription factor eEF1BδL. eEF1Bδ1 is phosphorylated by cyclin-dependent kinase 1 (CDK1), but the machinery controlling eEF1BδL phosphorylation and dephosphorylation has not been clarified. In this study, we found that both proteins were dephosphorylated under heat shock and proteotoxic stress, and this dephosphorylation was inhibited by okadaic acid. Using proteins with mutations at putative phosphorylated residues, we revealed that eEF1Bδ1 and eEF1BδL are phosphorylated at S133 and S499, respectively, and these residues are both CDK1 phosphorylation sites. The eEF1BδL S499A mutant more strongly activated HSPA6 promoter-driven reporter than the wild-type protein and S499D mutant. Furthermore, protein phosphatase 1 (PP1) was co-immunoprecipitated with eEF1Bδ1 and eEF1BδL, and PP1 dephosphorylated both proteins in vitro. Thus, this study clarified the role of phosphorylation/dephosphorylation in the functional regulation of eEF1BδL during heat shock.

Epigenetic modification and a role for the E3 ligase RNF40 in cancer development and metastasis

RNF40 (OMIM: 607700) is a really interesting new gene (RING) finger E3 ubiquitin ligase containing multiple coiled-coil domains and a C-terminal RING finger motif, which engage in protein–DNA and protein–protein interactions. RNF40 encodes a polypeptide of 1001 amino acids with a predicted molecular mass of 113,678 Da. RNF40 and its paralog RNF20 form a stable heterodimer complex that can monoubiquitylate histone H2B at lysine 120 as well as other nonhistone proteins. Cancer is a major public health problem and the second leading cause of death. Through its protein ubiquitylation activity, RNF40 acts as a tumor suppressor or oncogene to play major epigenetic roles in cancer development, progression, and metastasis, highlighting the essential function of RNF40 and the importance of studying it. In this review, we summarize current knowledge about RNF40 gene structure and the role of RNF40 in histone H2B monoubiquitylation, DNA damage repair, apoptosis, cancer development, and metastasis. We also underscore challenges in applying this information to cancer prognosis and prevention and highlight the urgent need for additional investigations of RNF40 as a potential target for cancer therapeutics.

Structures of three ependymin-related proteins suggest their function as a hydrophobic molecule binder

Ependymin was first discovered as a predominant protein in brain extracellular fluid in fish and was suggested to be involved in functions mostly related to learning and memory. Orthologous proteins to ependymin called ependymin-related proteins (EPDRs) have been found to exist in various tissues from sea urchins to humans, yet their functional role remains to be revealed. In this study, the structures of EPDR1 from frog, mouse and human were determined and analyzed. All of the EPDR1s fold into a dimer using a monomeric subunit that is mostly made up of two stacking antiparallel β-sheets with a curvature on one side, resulting in the formation of a deep hydrophobic pocket. All six of the cysteine residues in the monomeric subunit participate in the formation of three intramolecular disulfide bonds. Other interesting features of EPDR1 include two asparagine residues with glycosylation and a Ca2+-binding site. The EPDR1 fold is very similar to the folds of bacterial VioE and LolA/LolB, which also use a similar hydrophobic pocket for their respective functions as a hydrophobic substrate-binding enzyme and a lipoprotein carrier, respectively. A further fatty-acid binding assay using EPDR1 suggests that it indeed binds to fatty acids, presumably via this pocket. Additional interactome analysis of EPDR1 showed that EPDR1 interacts with insulin-like growth factor 2 receptor and flotillin proteins, which are known to be involved in protein and vesicle translocation.