RNF39 mediates K48-linked ubiquitination of DDX3X and inhibits RLR-dependent antiviral immunity

ITPR1-AS1 promotes small cell lung cancer metastasis by facilitating P21HRAS splicing and stabilizing DDX3X to activate the cRaf-MEK-ERK cascade

The mechanisms underlying the involvement of long non-coding RNAs (lncRNAs) in the metastasis of small cell lung cancer (SCLC) remain largely unknown. Here, we identified that the lncRNA ITPR1-AS1 was upregulated in SCLC and lymph node metastasis tissues and positively correlated with SCLC malignant features. The overexpression of ITPR1-AS1 in SCLC was an independent risk factor for the overall survival of patients with SCLC. Our data confirmed that ITPR1-AS1 induces SCLC cell metastasis both in vitro and in vivo. Mechanistically, ITPR1-AS1 acts as a scaffold to enhance the interaction between SRC-associated in mitosis 68 kDa and heterogeneous nuclear ribonucleoprotein A1, which facilitates the alternative splicing of the H-Ras proto-oncogene (HRAS) pre-mRNA (P21HRAS). Moreover, we observed that ITPR1-AS1 could associate in a complex with and maintain the stability of DEAD-box polypeptide 3 (DDX3X), which inhibited the latter's ubiquitination and degradation. Our data provide evidence that ITPR1-AS1 activates the cRaf-MEK-ERK cascade by upregulating P21HRAS production and stabilizing DDX3X, to promote SCLC metastasis.

Posttranslational ISGylation of NLRP3 by HERC enzymes facilitates inflammasome activation in models of inflammation

The NOD-, LRR-, and pyrin domain-containing protein 3 (NLRP3) inflammasome is a crucial component of the innate immune system that initiates inflammatory responses. Posttranslational modifications (PTMs) of NLRP3, including ubiquitination and phosphorylation, control inflammasome activation and determine the intensity of inflammation. However, the role of other PTMs in controlling NLRP3 inflammasome activation remains unclear. This study found that TLR priming induced NLRP3 ISGylation (a type of PTM in which ISG15 covalently binds to the target protein) to stabilize the NLRP3 protein. Viral infection, represented by SARS-COV-2 infection, and type I IFNs induced expression of ISG15 and the predominant E3 ISGylation ligases HECT domain- and RCC1-like domain-containing proteins (HERCs; HERC5 in humans and HERC6 in mice). HERCs promoted NLRP3 ISGylation and inhibited K48-linked ubiquitination and proteasomal degradation, resulting in the enhancement of NLRP3 inflammasome activation. Concordantly, Herc6 deficiency ameliorated NLRP3-dependent inflammation as well as hyperinflammation caused by viral infection. The results illustrate the mechanism by which type I IFNs responses control inflammasome activation and viral infection-induced aberrant NLRP3 activation. This work identifies ISGylation as a PTM of NLRP3, revealing a priming target that modulates NLRP3-dependent immunopathology.

Causality between depression and ankylosing spondylitis in a European population: Results from a Mendelian randomization analysis

The aim of this study was to explore the application of Mendelian randomization (MR) Egger and inverse variance weighted (IVW) in a causal effect on depression and ankylosing spondylitis (AS). Instrumental variables (IVs) were determined using genome-wide association studies. The 2-sample MR analysis was conducted by MR Egger to test the causal effect between depression and AS. The pleiotropy of potential instrumental variables was evaluated. The results of MR Egger and IVW were further compared. A total of 3 single nucleotide polymorphisms as the construct IVs were included. IVW results showed a significant causal effect between depression and AS (P < .001). Depression could promote the risk of AS (odds ratio = 1.060, 95% confidence interval: 1.026-1.094). However, the MR Egger showed no causal effect (P = .311). Heterogeneity statistics suggested that no heterogeneity was existed (P > .05). It was also suggested that there was no horizontal pleiotropy in IVs (MR Egger intercept: -0.0004, P = .471). Reverse MR analysis suggested that there was no causal effect between AS and depression (P > .05). Gene expression quantitative trait locus (QTLs) suggested that rs2517601 and RNF39 were positively correlated (beta = 1.066, P < .001). Depression may be one of the causes of AS by MR analysis in a European population. We can estimate the causal effect based on IVW when horizontal pleiotropy is very tiny.

Down-regulation of WWP2 aggravates Type 2 diabetes mellitus-induced vascular endothelial injury through modulating ubiquitination and degradation of DDX3X

BACKGROUND

Endothelial injury caused by Type 2 diabetes mellitus (T2DM) is considered as a mainstay in the pathophysiology of diabetic vascular complications (DVCs). However, the molecular mechanism of T2DM-induced endothelial injury remains largely unknown. Here, we found that endothelial WW domain-containing E3 ubiquitin protein ligase 2 (WWP2) act as a novel regulator for T2DM-induced vascular endothelial injury through modulating ubiquitination and degradation of DEAD-box helicase 3 X-linked (DDX3X).

METHODS

Single-cell transcriptome analysis was used to evaluate WWP2 expression in vascular endothelial cells of T2DM patients and healthy controls. Endothelial-specific Wwp2 knockout mice were used to investigate the effect of WWP2 on T2DM-induced vascular endothelial injury. In vitro loss- and gain-of-function studies were performed to assess the function of WWP2 on cell proliferation and apoptosis of human umbilical vein endothelial cells. The substrate protein of WWP2 was verified using mass spectrometry, coimmunoprecipitation assays and immunofluorescence assays. The mechanism of WWP2 regulation on substrate protein was investigated by pulse-chase assay and ubiquitination assay.

RESULTS

The expression of WWP2 was significantly down-regulated in vascular endothelial cells during T2DM. Endothelial-specific Wwp2 knockout in mice significantly aggravated T2DM-induced vascular endothelial injury and vascular remodeling after endothelial injury. Our in vitro experiments showed that WWP2 protected against endothelial injury by promoting cell proliferation and inhibiting apoptosis in ECs. Mechanically, we found that WWP2 is down-regulated in high glucose and palmitic acid (HG/PA)-induced ECs due to c-Jun N-terminal kinase (JNK) activation, and uncovered that WWP2 suppresses HG/PA-induced endothelial injury by catalyzing K63-linked polyubiquitination of DDX3X and targeting it for proteasomal degradation.

CONCLUSION

Our studies revealed the key role of endothelial WWP2 and the fundamental importance of the JNK-WWP2-DDX3X regulatory axis in T2DM-induced vascular endothelial injury, suggesting that WWP2 may serve as a new therapeutic target for DVCs.

Nanoparticle-Mediated STING Activation for Cancer Immunotherapy

As the first line of host defense against pathogenic infections, innate immunity plays a key role in antitumor immunotherapy. The cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) (cGAS-STING) pathway has attracted much attention because of the secretion of various proinflammatory cytokines and chemokines. Many STING agonists have been identified and applied into preclinical or clinical trials for cancer immunotherapy. However, the fast excretion, low bioavailability, nonspecificity, and adverse effects of the small molecule STING agonists limit their therapeutic efficacy and in vivo application. Nanodelivery systems with appropriate size, charge, and surface modification are capable of addressing these dilemmas. In this review, the mechanism of the cGAS-STING pathway is discussed and the STING agonists, focusing on nanoparticle-mediated STING therapy and combined therapy for cancers, are summarized. Finally, the future direction and challenges of nano-STING therapy are expounded, emphasizing the pivotal scientific problems and technical bottlenecks and hoping to provide general guidance for its clinical application.

The E3 Ligase TRIM4 Facilitates SET Ubiquitin-Mediated Degradation to Enhance ER-α Action in Breast Cancer

Estrogen receptor alpha (ER-α) action is critical for hormone-dependent breast cancer, and ER-α dysregulation can lead to the emergence of resistance to endocrine therapy. Here, it is found that TRIM4 is downregulated in tamoxifen (TAM)-resistant breast cancer cells, while the loss of TRIM4 is associated with an unfavorable prognosis. In vitro and in vivo experiments confirm that TRIM4 increased ER-α expression and the sensitivity of breast cancer cells to TAM. Mechanistically, TRIM4 is found to target SET, and TRIM4-SET interactions are mediated by the RING and B-box domains of TRIM4 and the carboxyl terminus of SET. Moreover, it is determined that TRIM4 catalyzed the K48-linked polyubiquitination of SET (K150 and K172), promoting its proteasomal degradation and disassociation from p53 and PP2A. Once released, p53 and PP2A are able to further promote ESR1 gene transcription and enhance mRNA stability. Moreover, univariate and multivariate Cox proportional hazards regression analyses confirm that TRIM4 expression is an independent predictor of overall survival and recurrence-free survival outcomes in patients with ER-α positive breast cancer. Taken together, the data highlights a previously undiscovered mechanism and suggest that TRIM4 is a valuable biomarker that can be analyzed to predict response to endocrine therapy in breast cancer patients.

The DEAD-box helicase DDX3x ameliorates non-alcoholic fatty liver disease via mTORC1 signalling pathway

BACKGROUND & AIMS

The DEAD (Asp-Glu-Ala-Asp)-box helicase family member DDX3x has been proven to involve in hepatic lipid disruption during HCV infection. However, the role of DDX3x in non-alcoholic fatty liver disease (NAFLD), in which lipid homeostasis is severely disrupted, remains unclear. Here, we aimed to illustrate the potential role of DDX3x in NAFLD.

METHODS

DDX3x protein levels were evaluated in NAFLD patients and NAFLD models via immunohistochemistry or western blotting. In vivo ubiquitin assay was performed to identify the ubiquitination levels of DDX3x in the progression of steatosis. DDX3x protein levels in mice livers were manipulated by adeno-associated virus-containing DDX3x short hairpin RNA or DDX3x overexpression plasmid. Hepatic or serum triglyceride and total cholesterol were evaluated and hepatic steatosis was confirmed by haematoxylin and eosin staining and oil red o staining. Western blotting was performed to identify the underlying mechanisms of DDX3x involving in the progression of NAFLD.

RESULTS

DDX3x protein levels were significantly decreased in NAFLD patients and NAFLD models. DDX3x protein might be degraded via ubiquitin-proteasome system in the progression of steatosis. Knockdown of hepatic DDX3x exacerbated HFD-induced hepatic steatosis in mice, while overexpression of hepatic DDX3x alleviated HFD-induced hepatic steatosis in mice. Further explorative experiments revealed that knockdown of DDX3x could lead to the overactivation of mTORC1 signalling pathway which exacerbates NAFLD.

CONCLUSIONS

DDX3x involved in the progression of NAFLD via affecting the mTORC1 signalling pathway. DDX3x might be a potential target for NAFLD treatment.

Melatonin: Regulation of Viral Phase Separation and Epitranscriptomics in Post-Acute Sequelae of COVID-19

The relentless, protracted evolution of the SARS-CoV-2 virus imposes tremendous pressure on herd immunity and demands versatile adaptations by the human host genome to counter transcriptomic and epitranscriptomic alterations associated with a wide range of short- and long-term manifestations during acute infection and post-acute recovery, respectively. To promote viral replication during active infection and viral persistence, the SARS-CoV-2 envelope protein regulates host cell microenvironment including pH and ion concentrations to maintain a high oxidative environment that supports template switching, causing extensive mitochondrial damage and activation of pro-inflammatory cytokine signaling cascades. Oxidative stress and mitochondrial distress induce dynamic changes to both the host and viral RNA m6A methylome, and can trigger the derepression of long interspersed nuclear element 1 (LINE1), resulting in global hypomethylation, epigenetic changes, and genomic instability. The timely application of melatonin during early infection enhances host innate antiviral immune responses by preventing the formation of "viral factories" by nucleocapsid liquid-liquid phase separation that effectively blockades viral genome transcription and packaging, the disassembly of stress granules, and the sequestration of DEAD-box RNA helicases, including DDX3X, vital to immune signaling. Melatonin prevents membrane depolarization and protects cristae morphology to suppress glycolysis via antioxidant-dependent and -independent mechanisms. By restraining the derepression of LINE1 via multifaceted strategies, and maintaining the balance in m6A RNA modifications, melatonin could be the quintessential ancient molecule that significantly influences the outcome of the constant struggle between virus and host to gain transcriptomic and epitranscriptomic dominance over the host genome during acute infection and PASC.

TRIM25 and DEAD-Box RNA Helicase DDX3X Cooperate to Regulate RIG-I-Mediated Antiviral Immunity

The cytoplasmic retinoic acid-inducible gene-I (RIG-I)-like receptors (RLRs) initiate interferon (IFN) production and antiviral gene expression in response to RNA virus infection. Consequently, RLR signalling is tightly regulated by both host and viral factors. Tripartite motif protein 25 (TRIM25) is an E3 ligase that ubiquitinates multiple substrates within the RLR signalling cascade, playing both ubiquitination-dependent and -independent roles in RIG-I-mediated IFN induction. However, additional regulatory roles are emerging. Here, we show a novel interaction between TRIM25 and another protein in the RLR pathway that is essential for type I IFN induction, DEAD-box helicase 3X (DDX3X). In vitro assays and knockdown studies reveal that TRIM25 ubiquitinates DDX3X at lysine 55 (K55) and that TRIM25 and DDX3X cooperatively enhance IFNB1 induction following RIG-I activation, but the latter is independent of TRIM25's catalytic activity. Furthermore, we found that the influenza A virus non-structural protein 1 (NS1) disrupts the TRIM25:DDX3X interaction, abrogating both TRIM25-mediated ubiquitination of DDX3X and cooperative activation of the IFNB1 promoter. Thus, our results reveal a new interplay between two RLR-host proteins that cooperatively enhance IFN-β production. We also uncover a new and further mechanism by which influenza A virus NS1 suppresses host antiviral defence.

Emerging Roles of MHC Class I Region-Encoded E3 Ubiquitin Ligases in Innate Immunity

The major histocompatibility complex (MHC) class I (MHC-I) region contains a multitude of genes relevant to immune response. Multiple E3 ubiquitin ligase genes, including tripartite motif 10 (TRIM10), TRIM15, TRIM26, TRIM27, TRIM31, TRIM38, TRIM39, TRIM40, and RING finger protein 39 (RNF39), are organized in a tight cluster, and an additional two TRIM genes (namely TRIM38 and TRIM27) telomeric of the cluster within the MHC-I region. The E3 ubiquitin ligases encoded by these genes possess important roles in controlling the intensity of innate immune responses. In this review, we discuss the E3 ubiquitin ligases encoded within the MHC-I region, highlight their regulatory roles in innate immunity, and outline their potential functions in infection, inflammatory and autoimmune diseases.