RNF20 promotes the polyubiquitination and proteasome-dependent degradation of AP-2α protein

Adipocyte Rnf20 ablation increases the fast-twitch fibers of skeletal muscle via lysophosphatidylcholine 16:0

Both adipose tissue and skeletal muscle are highly dynamic tissues and interact at the metabolic and hormonal levels in response to internal and external stress, and they coordinate in maintaining whole-body metabolic homeostasis. In our previous study, we revealed that adipocyte-specific Rnf20 knockout mice (ASKO mice) exhibited lower fat mass but higher lean mass, providing a good model for investigating the adipose-muscle crosstalk and exploring the effect of the adipocyte Rnf20 gene on the physiology and metabolism of skeletal muscle. Here, we confirmed that ASKO mice exhibited the significantly increased body weight and gastrocnemius muscle weight. Fiber-type switching in the soleus muscle of ASKO mice was observed, as evidenced by the increased number of fast-twitch fibers and decreased number of slow-twitch fibers. Serum metabolites with significant alteration in abundance were identified by metabolomic analysis and the elevated lysophosphatidylcholine 16:0 [LysoPC (16:0)] was observed in ASKO mice. In addition, lipidome analysis of gonadal white adipose tissue revealed a significant increase in LysoPCs and LysoPC (16:0) in ASKO mice. Furthermore, knockdown of Rnf20 gene in 3T3-L1 cells significantly increased the secretion of LysoPC, suggesting that LysoPC might be a critical metabolite in the adipose-muscle crosstalk of ASKO mice. Furthermore, in vitro study demonstrated that LysoPC (16:0) could induce the expression of fast-twitch muscle fibers related genes in differentiated C2C12 cells, indicating its potential role in adipose-muscle crosstalk. Taken together, these findings not only expand our understanding of the biological functions of Rnf20 gene in systemic lipid metabolism, but also provide insight into adipose tissue dysfunction-induced physiological alterations in skeletal muscle.

Linc-ROR drive adriamycin resistance by targeting AP-2α/Wnt/β-catenin axis in hepatocellular carcinoma

Adriamycin is widely used as a chemotherapeutic strategy for advanced hepatocellular carcinoma (HCC). However, the clinical response was disappointing because of the acquired drug resistance with long-term usage. Revealing the underlying mechanism could provide promising therapeutics for the drug-resistant patients. The recently identified linc-ROR (long intergenic non-protein-coding RNA, regulator of reprogramming) has been found to be an oncogene in various cancers, and it also demonstrated to mediate drug resistance and metastasis. We thereby wonder whether this lincRNA could mediate adriamycin chemoresistance in HCC. In this study, linc-ROR was found to be upregulated in adriamycin-resistant HCC cells. And its overexpression accelerated epithelial-mesenchymal transition (EMT) program and adriamycin resistance. Conversely, its silence suppressed EMT and made HCC cells sensitize to adriamycin in vitro and in vivo. Further investigation revealed that linc-ROR physically interacted with AP-2α, mediated its stability by a post-translational modification manner, and sequentially activated Wnt/β-catenin pathway. Furthermore, linc-ROR expression was positively associated with β-catenin expression in human clinical specimens. Taken together, linc-ROR promoted tumorigenesis and adriamycin resistance in HCC via a linc-ROR/AP-2α/Wnt/β-catenin axis, which could be developed as a potential therapeutic target for the adriamycin-resistant patients.

Endoplasmic reticulum stress impairs the immune regulation property of macrophages in asthmatic patients

The current study aims to characterize the counteraction of M2 cells in response to Endoplasmic reticulum (ER) stress. ER stress was detected in bronchoalveolar lavage fluids (BALF) Mϕs, which was at unresolved state in asthma patients. A positive correlation was detected between ER stress in Mϕs and lung functions/allergic mediators/Th2 cytokines in BALF or specific IgE in the serum. Levels of immune regulatory mediator in the BALF were negatively correlated to ER stress in BALF Mϕs. The ER stress state influenced the immune regulatory property of BALF Mϕ. Exposure to environmental pollutant, 3-metheyl-4-nitrophenol, exacerbated ER stress in Mϕ, which affected the Mϕ phenotyping. Exacerbation of ER stress suppressed the expression of IL-10 and programmed cell death protein-1 (PD-1) in Mϕs by increasing the expression of the ring finger protein 20 (Rnf20). Conditional inhibition of Rnf20 in Mϕs attenuated experimental airway allergy.

Neglected PTM in Animal Adipogenesis: E3-mediated Ubiquitination

Ubiquitination is a widespread post-transcriptional modification (PTM) that occurs during protein degradation in eukaryotes and participates in almost all physiological and pathological processes, including animal adipogenesis. Ubiquitination is a cascade reaction regulated by the activating enzyme E1, conjugating enzyme E2, and ligase E3. Several recent studies have reported that E3 ligases play important regulatory roles in adipogenesis. However, as a key influencing factor for the recognition and connection between the substrate and ubiquitin during ubiquitination, its regulatory role in adipogenesis has not received adequate attention. In this review, we summarize the E3s' regulation and modification targets in animal adipogenesis, explain the regulatory mechanisms in lipogenic-related pathways, and further analyze the existing positive results to provide research directions of guiding significance for further studies on the regulatory mechanisms of E3s in animal adipogenesis.

ER stress modulates the immune regulatory ability in gut M2 cells of patients with ulcerative colitis

This study aims to characterize the impaired immune regulatory function of Mφ obtained from UC patient colon lavage fluid (CLF). Mφs were the largest proportion (21.3 4.0%) of the CLF-derived cellular components. Less abundant and weaker immune suppressive function were observed in M2 Mφs (M2 cells) of the ulcerative colitis (UC) group. High levels of endoplasmic reticulum (ER) stress associated molecules were detected in UC M2 cells. The spliced X box binding protein-1 (XBP1) gene was negatively correlated with programmed death ligand-1 (PD-L1) in UC M2 cells. XBP1 promoted the expression of ring-finger protein 20 (Rnf20) in M2 cells. Rnf20 reduced PD-L1 abundance in UC M2 cells and impaired the immune suppressive ability. Inhibition of Rnf20 restored the immune regulating capacity of M2 cells and suppressed experimental colitis.

RNF20 affects porcine adipocyte differentiation via regulation of mitotic clonal expansion

Objectives

RNF20 is recognized as a main E3 ligase for monoubiquitination of histone H2B at lysine 120 (H2Bub). The critical role of RNF20 and H2Bub in various molecular events, such as DNA replication, RNA transcription, and DNA damage response, has been widely investigated and documented. However, its role in porcine adipogenesis remains unknown. In this study, we aimed to clarify the effect of RNF20 on porcine preadipocyte differentiation.

Materials and Methods

Backfat tissues from fat‐type pigs (Bama and Meishan) and lean‐type pigs (Yorkshire and Landrace) were collected to detect the expression level of RNF20. Preadipocytes were isolated from Bama piglets and induced to differentiation. Small interfering RNAs were applied to deplete RNF20. Oil Red O staining, quantitative real‐time PCR, RNA‐seq, Western blot analysis, and EdU assays were performed to study the regulatory mechanism of RNF20 during adipogenesis.

Results

We found that the expression levels of RNF20 and H2Bub were significantly higher in backfat tissues from fat‐type pigs than in those from lean‐type pigs. Consistently, the significantly induced expression of RNF20 and H2Bub was also observed in porcine differentiated adipocytes. In addition, knockdown of RNF20 greatly inhibited porcine adipogenesis, as evidenced by dramatically decreased lipid droplet formation and lower expression levels of adipogenic transcription masters in RNF20 knockdown cells. Mechanistically, the depletion of RNF20 decreases the cell proliferation and the level of p‐C/EBPβ via the Ras‐Raf‐MEK1/2‐ERK1/2 cascade pathway at the mitotic clonal expansion phase and therefore suppresses cell differentiation.

Conclusions

Our results demonstrate that RNF20 is required for porcine preadipocyte differentiation.

Rnf20 deficiency in adipocyte impairs adipose tissue development and thermogenesis

RNF20, an E3 ligase critical for monoubiquitination of histone H2B at lysine 120 (H2Bub), has been implicated in the regulation of various cellar processes; however, its physiological roles in adipocytes remain poorly characterized. Here, we report that the adipocyte-specific knockout of Rnf20 (ASKO) in mice led to progressive fat loss, organomegaly and hyperinsulinemia. Despite signs of hyperinsulinemia, normal insulin sensitivity and improved glucose tolerance were observed in the young and aged CD-fed ASKO mice. In addition, high-fat diet-fed ASKO mice developed severe liver steatosis. Moreover, we observed that the ASKO mice were extremely sensitive to a cold environment due to decreased expression levels of brown adipose tissue (BAT) selective genes, including uncoupling protein 1 (Ucp1), and impaired mitochondrial functions. Significantly decreased levels of peroxisome proliferator-activated receptor gamma (Pparγ) were observed in the gonadal white adipose tissues (gWAT) from the ASKO mice, suggesting that Rnf20 regulates adipogenesis, at least in part, through Pparγ. Rosiglitazone-treated ASKO mice exhibited increased fat mass compared to that of the non-treated ASKO mice. Collectively, our results illustrate the critical role of RNF20 in control of white and brown adipose tissue development and physiological function.

Molecular Characterization, Expression Profiling, and SNP Analysis of the Porcine RNF20 Gene

Simple Summary

In this study, we found that RNF20 is ubiquitously expressed in porcine tissues, and the sequence of the RING domain was highly conserved across different species. Eight potential single nucleotide polymorphisms (SNPs) were discovered, and one of them, SNP1 (A-1027G), was confirmed by PCR-restriction fragment length polymorphism (RFLP). Allele frequency differences were also analyzed in four pig breeds. This study provides a preliminary understanding of the porcine RNF20 gene.

Abstract

Fat deposition is considered an economically important trait in pig breeding programs. Ring finger protein 20 (RNF20), an E3 ubiquitin protein ligase, has been shown to be closely involved in adipogenesis in mice, suggesting its conserved role in pigs. In this study, we obtained the exon sequences of the porcine RNF20 gene and characterized its molecular sequence. The porcine RNF20 gene contains 20 exons that encode 975 amino acids, and its RING domain is highly conserved across different species. Western blot analysis revealed that RNF20 was widely expressed, especially in various fat depots, and the level of H2B monoubiquitination (H2Bub) was highly consistent. Eight potential SNPs were detected by sequencing pooled PCR fragments. PCR–RFLP was developed to detect a single nucleotide polymorphism (A-1027G) in exon 1, and the allele frequency differences were examined in four pig breeds. The G allele was predominant in these pigs. Association analysis between (A-1027G) and the backfat thickness of three commercial pig breeds was performed, but no significant association was found. Taken together, these results enabled us to undertake the molecular characterization, expression profiling, and SNP analysis of the porcine RNF20 gene.

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

RNF20/40 E3 ubiquitin ligase-mediated histone H2B monoubiquitylation plays important roles in many cellular processes, including transcriptional regulation. However, the multiple defects observed in RNF20-depleted cells suggest additional ubiquitylation targets of RNF20/40 beyond histone H2B. Here, using biochemically defined assays employing purified factors and cell-based analyses, we demonstrate that RNF20/40, in conjunction with its cognate E2 ubiquitin-conjugating enzyme RAD6, monoubiquitylates lysine 381 of eEF1BδL, a heat shock transcription factor. Notably, monoubiquitylation of eEF1BδL increases eEF1BδL accumulation and potentiates recruitment of p-TEFb to the promoter regions of heat shock-responsive genes, leading to enhanced transcription of these genes. We further demonstrate that cooperative physical interactions among eEF1BδL, RNF20/40, and HSF1 synergistically promote expression of heat shock-responsive genes. In addition to identifying eEF1BδL as a novel ubiquitylation target of RNF20/40 and elucidating its function, we provide a molecular mechanism for the cooperative function of distinct transcription factors in heat shock-responsive gene transcription.

GhHUB2, a ubiquitin ligase, is involved in cotton fiber development via the ubiquitin-26S proteasome pathway

Cotton fibers, which are extremely elongated single cells of epidermal seed trichomes and have highly thickened cell walls, constitute the most important natural textile material worldwide. However, the regulation of fiber development is not well understood. Here, we report that GhHUB2, a functional homolog of AtHUB2, controls fiber elongation and secondary cell wall (SCW) deposition. GhHUB2 is ubiquitously expressed, including within fibers. Overexpression of GhHUB2 in cotton increased fiber length and SCW thickness, while RNAi knockdown of GhHUB2 resulted in shortened fibers and thinner cell walls. We found that GhHUB2 interacted with GhKNL1, a transcriptional repressor predominantly expressed in developing fibers, and that GhHUB2 ubiquitinated and degraded GhKNL1 via the ubiquitin-26S proteasome pathway. GhHUB2 negatively regulated GhKNL1 protein levels and lead to the disinhibition of genes such as GhXTH1, Gh1,3-β-G, GhCesA4, GhAGP4, GhCTL1, and GhCOBL4, thus promoting fiber elongation and enhancing SCW biosynthesis. We found that GhREV-08, a transcription factor that participates in SCW deposition and auxin signaling pathway, was a direct target of GhKNL1. In conclusion, our study uncovers a novel function of HUB2 in plants in addition to its monoubiquitination of H2B. Moreover, we provide evidence for control of the fiber development by the ubiquitin-26S proteasome pathway.

ZSCAN4 is negatively regulated by the ubiquitin-proteasome system and the E3 ubiquitin ligase RNF20

Zscan4 is an early embryonic gene cluster expressed in mouse embryonic stem and induced pluripotent stem cells where it plays critical roles in genomic stability, telomere maintenance, and pluripotency. Zscan4 expression is transient, and characterized by infrequent high expression peaks that are quickly down-regulated, suggesting its expression is tightly controlled. However, little is known about the protein degradation pathway responsible for regulating the human ZSCAN4 protein levels. In this study we determine for the first time the ZSCAN4 protein half-life and degradation pathway, including key factors involved in the process, responsible for the regulation of ZSCAN4 stability. We demonstrate lysine 48 specific polyubiquitination and subsequent proteasome dependent degradation of ZSCAN4, which may explain how this key factor is efficiently cleared from the cells. Importantly, our data indicate an interaction between ZSCAN4 and the E3 ubiquitin ligase RNF20. Moreover, our results show that RNF20 depletion by gene knockdown does not affect ZSCAN4 transcription levels, but instead results in increased ZSCAN4 protein levels. Further, RNF20 depletion stabilizes the ZSCAN4 protein half-life, suggesting that RNF20 negatively regulates ZSCAN4 stability. Due to the significant cellular functions of ZSCAN4, our results have important implications in telomere regulation, stem cell biology, and cancer.

H2B ubiquitination: Conserved molecular mechanism, diverse physiologic functions of the E3 ligase during meiosis

RNF20/Bre1 mediated H2B ubiquitination (H2Bub) has various physiologic functions. Recently, we found that H2Bub participates in meiotic recombination by promoting chromatin relaxation during meiosis. We then analyzed the phylogenetic relationships among the E3 ligase for H2Bub, its E2 Rad6 and their partner WW domain-containing adaptor with a coiled-coil (WAC) or Lge1, and found that the molecular mechanism underlying H2Bub is evolutionarily conserved from yeast to mammals. However, RNF20 has diverse physiologic functions in different organisms, which might be caused by the evolutionary divergency of their domain/motif architectures. In the current extra view, we not only elucidate the evolutionarily conserved molecular mechanism underlying H2Bub, but also discuss the diverse physiologic functions of RNF20 during meiosis.

Characterization of the Human Transcription Elongation Factor Rtf1: Evidence for Nonoverlapping Functions of Rtf1 and the Paf1 Complex

Restores TBP function 1 (Rtf1) is generally considered to be a subunit of the Paf1 complex (PAF1C), a multifunctional protein complex involved in histone modification and transcriptional or posttranscriptional regulation. Rtf1, however, is not stably associated with the PAF1C in most species except Saccharomyces cerevisiae, and its biochemical functions are not well understood. Here, we show that human Rtf1 is a transcription elongation factor that may function independently of the PAF1C. Rtf1 requires "Rtf1 coactivator" activity, which is most likely unrelated to the PAF1C or DSIF, for transcriptional activation in vitro. A mutational study revealed that the Plus3 domain of human Rtf1 is critical for its coactivator-dependent function. Transcriptome sequencing (RNA-seq) and chromatin immunoprecipitation studies in HeLa cells showed that Rtf1 and the PAF1C play distinct roles in regulating the expression of a subset of genes. Moreover, contrary to the finding in S. cerevisiae, the PAF1C was apparently recruited to the genes examined in an Rtf1-independent manner. The present study establishes a role for human Rtf1 as a transcription elongation factor and highlights the similarities and differences between the S. cerevisiae and human Rtf1 proteins.