TRIM21/Ro52 - Roles in Innate Immunity and Autoimmune Disease

Inclusion body myositis, viral infections, and TDP-43: a narrative review

The ubiquitous RNA-processing molecule TDP-43 is involved in neuromuscular diseases such as inclusion body myositis, a late-onset acquired inflammatory myopathy. TDP-43 solubility and function are disrupted in certain viral infections. Certain viruses, high viremia, co-infections, reactivation of latent viruses, and post-acute expansion of cytotoxic T cells may all contribute to inclusion body myositis, mainly in an age-shaped immune landscape. The virally induced senescent, interferon gamma-producing cytotoxic CD8+ T cells with increased inflammatory, and cytotoxic features are involved in the occurrence of inclusion body myositis in most such cases, in a genetically predisposed host. We discuss the putative mechanisms linking inclusion body myositis, TDP-43, and viral infections untangling the links between viruses, interferon, and neuromuscular degeneration could shed a light on the pathogenesis of the inclusion body myositis and other TDP-43-related neuromuscular diseases, with possible therapeutic implications.

TRIM21 silencing inhibits the apoptosis and expedites the osteogenic differentiation of dexamethasone‑induced MC3T3‑E1 cells by activating the Keap1/Nrf2 pathway

Steroid-induced osteonecrosis of the femoral head (ONFH) is a serious complication caused by long-term or excessive use of glucocorticoids. The present study aimed to ascertain the effects of tripartite motif-containing protein 21 (TRIM21) on the process of steroid-induced ONFH and its hidden action mechanism. TRIM21 expression in dexamethasone (Dex)-treated mouse MC3T3-E1 preosteoblast cells was examined using reverse transcription-quantitative PCR and western blotting. The Cell Counting Kit-8 (CCK-8) method and lactate dehydrogenase release assay were used to respectively measure cell viability and injury. Flow cytometry analysis was used to assay cell apoptosis. Caspase 3 activity was evaluated using a specific assay, while alkaline phosphatase and Alizarin red S staining were used to evaluate osteogenesis. 2,7-dichloro-dihydrofluorescein diacetate fluorescence probe was used to estimate reactive oxygen species generation. Specific assay kits were used to appraise oxidative stress levels. In addition, the expression of apoptosis-, osteogenic differentiation- and Kelch-like ECH-associated protein 1 (Keap1)/nuclear factor erythroid 2-related factor 2 (Nrf2) signaling-associated proteins was assessed using western blotting. In Nrf2 inhibitor (ML385)-pretreated MC3T3-E1 cells exposed to Dex, cell apoptosis, osteogenesis and oxidative stress were detected again as aforementioned. Results revealed that TRIM21 expression was raised in Dex-induced MC3T3-E1 cells and TRIM21 deletion improved the viability and osteogenic differentiation, whereas it hampered the oxidative stress and apoptosis in MC3T3-E1 cells with Dex induction. In addition, silencing of TRIM21 activated Keap1/Nrf2 signaling. Moreover, ML385 partially abrogated the effects of TRIM21 depletion on the oxidative stress, apoptosis and osteogenic differentiation in MC3T3-E1 cells exposed to Dex. In conclusion, TRIM21 silencing might activate Keap1/Nrf2 signaling to protect against steroid-induced ONFH.

Beyond bNAbs: Uses, Risks, and Opportunities for Therapeutic Application of Non-Neutralising Antibodies in Viral Infection

The vast majority of antibodies generated against a virus will be non-neutralising. However, this does not denote an absence of protective capacity. Yet, within the field, there is typically a large focus on antibodies capable of directly blocking infection (neutralising antibodies, NAbs) of either specific viral strains or multiple viral strains (broadly-neutralising antibodies, bNAbs). More recently, a focus on non-neutralising antibodies (nNAbs), or neutralisation-independent effects of NAbs, has emerged. These can have additive effects on protection or, in some cases, be a major correlate of protection. As their name suggests, nNAbs do not directly neutralise infection but instead, through their Fc domains, may mediate interaction with other immune effectors to induce clearance of viral particles or virally infected cells. nNAbs may also interrupt viral replication within infected cells. Developing technologies of antibody modification and functionalisation may lead to innovative biologics that harness the activities of nNAbs for antiviral prophylaxis and therapeutics. In this review, we discuss specific examples of nNAb actions in viral infections where they have known importance. We also discuss the potential detrimental effects of such responses. Finally, we explore new technologies for nNAb functionalisation to increase efficacy or introduce favourable characteristics for their therapeutic applications.

Impact of sex differences on the clinical presentation, pathogenesis, treatment and prognosis of Sjögren's syndrome

Sjögren's syndrome is a common chronic autoimmune disease that manifests as dry mouth, dry eyes and systemic complications. There are sex differences in the clinical manifestations between men and women, with the average age of onset being around 55 years and the majority of female patients developing the disease during the menopausal years. Understanding the impact of sex differences on SS may help in the treatment and prognosis of patients. Studies have confirmed that a number of factors are associated with the onset of SS, but the exact mechanisms are not fully understood. Sex hormones (especially oestrogens and androgens) play a very important role, and the balance of sex hormone levels in the body is crucial for maintaining homeostasis in the acinar cells of the lacrimal and salivary glands. In addition, chromosomes play a very important role in the sex differences in SS. The gut microbiota also has some influence on sex differences in SS. In this review, we focus on oestrogens and androgens, which are important in the pathogenesis of SS, and summarize the progress of non-clinical studies. Sex differences may influence differences in individualized treatment regimens and further studies are needed.

The Emerging Role of Deubiquitinases in Radiosensitivity

Radiation therapy is a primary treatment for cancer, but radioresistance remains a significant challenge in improving efficacy and reducing toxicity. Accumulating evidence suggests that deubiquitinases (DUBs) play a crucial role in regulating cell sensitivity to ionizing radiation. Traditional small-molecule DUB inhibitors have demonstrated radiosensitization effects, and novel deubiquitinase-targeting chimeras (DUBTACs) provide a promising strategy for radiosensitizer development by harnessing the ubiquitin-proteasome system. This review highlights the mechanisms by which DUBs regulate radiosensitivity, including DNA damage repair, the cell cycle, cell death, and hypoxia. Progress on DUB inhibitors and DUBTACs is summarized, and their potential radiosensitization effects are discussed. Developing drugs targeting DUBs appears to be a promising alternative approach to overcoming radioresistance, warranting further research into their mechanisms.

Systems genetics of influenza A virus-infected mice identifies TRIM21 as a critical regulator of pulmonary innate immune response

Tripartite motif 21 (TRIM21) is a cytosolic Fc receptor that targets antibody-bound, internalized pathogens for destruction. Apart from this intrinsic defense role, TRIM21 is implicated in autoimmune diseases, inflammation, and autophagy. Whether TRIM21 participates in host interactions with influenza A virus (IAV), however, is unknown. By computational modeling of body weight and lung transcriptome data from the BXD parents (C57BL/6 J (B6) and DBA/2 J (D2)) and 41 BXD mouse strains challenged by IAV, we reveal that a Trim21-associated gene network modulates the early host responses to IAV infection. Trim21 transcripts were significantly upregulated in infected mice of both B6 and D2 backgrounds. Its expression was significantly higher in infected D2 than in infected B6 early after infection and significantly correlated with body weight loss. We identified significant trans-eQTL on chromosome 14 that regulates Trim21 expression. Nr1d2 and Il3ra were among the strongest candidate genes. Pathway analysis found Trim21 to be involved in inflammation and immunity related pathways, such as inflammation signaling pathways (TNF, IL-17, and NF-κB), viral detection signaling pathways (NOD-like and RIG-I-like), influenza, and other respiratory viral infections. Knockdown of TRIM21 in human lung epithelial A549 cells significantly augmented IAV-induced expression of IFNB1, IFNL1, CCL5, CXCL10, and IFN-stimulated genes including DDX58 and IFIH1, among others. Our data suggest that a TRIM21-associated gene network is involved in several aspects of inflammation and viral detection mechanisms during IAV infection. We identify and validate TRIM21 as a critical regulator of innate immune responses to IAV in human lung epithelial cells.

Immune-mediated diseases are associated with a higher risk of ALS incidence: a prospective cohort study from the UK Biobank

Objective

The occurrence of immune-mediated diseases (IMDs) in amyotrophic lateral sclerosis (ALS) patients is widely reported. However, whether IMDs and ALS is a simple coexistence or if there exists causal relationships between the two has been a subject of great interest to researchers.

Methods

A total of 454,444 participants from the prospective cohort of UK Biobank were recruited to investigate the longitudinal association between IMDs and ALS. Previously any IMDs and organ specific IMDs were analyzed in relation to the following incident ALS by Cox-proportional hazard models. Subgroup analyses were performed to explore the covariates of these relationships.

Results

After adjusting for potential covariates, the multivariate analysis showed that any IMDs were associated with an increased risk of ALS incidence (HR:1.42, 95%CI:1.03-1.94). IMDs of the endocrine-system and the intestinal-system were associated with increased risk of ALS incidence (endocrine-system IMDs: HR:3.01, 95%CI:1.49-6.06; intestinal system IMDs: HR:2.07, 95%CI: 1.14-3.77). Subgroup analyses revealed that immune burden, including IMD duration and the severity of inflammation had specific effects on the IMD-ALS association. In participants with IMD duration≥10 years or CRP≥1.3mg/L or females, previous IMDs increased the risk of incident ALS; however, in participants with IMD duration <10 years or CRP<1.3mg/L or males, IMDs had no effect on incident ALS.

Interpretation

Our study provides evidence that previous any IMDs and endocrine-system and the intestinal-system specific IMDs are associated with an increased risk of developing ALS in females, but not in males.

TLR7 activation of age-associated B cells mediates disease in a mouse model of primary Sjögren's disease

Primary Sjögren's disease (pSD) (also referred to as Sjögren's syndrome) is an autoimmune disease that primarily occurs in women. In addition to exocrine gland dysfunction, pSD patients exhibit B cell hyperactivity. B cell-intrinsic TLR7 activation is integral to the pathogenesis of systemic lupus erythematosus, a disease that shares similarities with pSD. The role of TLR7-mediated B cell activation in pSD, however, remains poorly understood. We hypothesized that age-associated B cells (ABCs) were expanded in pSD and that TLR7-stimulated ABCs exhibited pathogenic features characteristic of disease. Our data revealed that ABC expansion and TLR7 expression were enhanced in a pSD mouse model in a Myd88-dependent manner. Splenocytes from pSD mice showed enhanced sensitivity to TLR7 agonism as compared with those derived from control animals. Sort-purified marginal zone B cells and ABCs from pSD mice showed enhanced inflammatory cytokine secretion and were enriched for antinuclear autoantibodies following TLR7 agonism. Finally, IgG from pSD patient sera showed elevated antinuclear autoantibodies, many of which were secreted preferentially by TLR7-stimulated murine marginal zone B cells and ABCs. These data indicate that pSD B cells are hyperresponsive to TLR7 agonism and that TLR7-activated B cells contribute to pSD through cytokine and autoantibody production. Thus, therapeutics that target TLR7 signaling cascades in B cells may have utility in pSD patients.

Heightened TLR7 signaling primes BCR-activated B cells in chronic graft-versus-host disease for effector functions

ABSTRACT

Chronic graft-versus-host disease (cGVHD) is a debilitating, autoimmune-like syndrome that can occur after allogeneic hematopoietic stem cell transplantation. Constitutively activated B cells contribute to ongoing alloreactivity and autoreactivity in patients with cGVHD. Excessive tissue damage that occurs after transplantation exposes B cells to nucleic acids in the extracellular environment. Recognition of endogenous nucleic acids within B cells can promote pathogenic B-cell activation. Therefore, we hypothesized that cGVHD B cells aberrantly signal through RNA and DNA sensors such as Toll-like receptor 7 (TLR7) and TLR9. We found that B cells from patients and mice with cGVHD had higher expression of TLR7 than non-cGVHD B cells. Using ex vivo assays, we found that B cells from patients with cGVHD also demonstrated increased interleukin-6 production after TLR7 stimulation with R848. Low-dose B-cell receptor (BCR) stimulation augmented B-cell responses to TLR7 activation. TLR7 hyperresponsiveness in cGVHD B cells correlated with increased expression and activation of the downstream transcription factor interferon regulatory factor 5. Because RNA-containing immune complexes can activate B cells through TLR7, we used a protein microarray to identify RNA-containing antigen targets of potential pathological relevance in cGVHD. We found that many of the unique targets of active cGVHD immunoglobulin G (IgG) were nucleic acid-binding proteins. This unbiased assay identified the autoantigen and known cGVHD target Ro-52, and we found that RNA was required for IgG binding to Ro-52. Herein, we find that BCR-activated B cells have aberrant TLR7 signaling responses that promote potential effector responses in cGVHD.

The role of ubiquitination and deubiquitination in PI3K/AKT/mTOR pathway: A potential target for cancer therapy

The PI3K/AKT/mTOR pathway controls key cellular processes, including proliferation and tumor progression, and abnormally high activation of this pathway is a hallmark in human cancers. The post-translational modification, such as Ubiquitination and deubiquitination, fine-tuning the protein level and the activity of members in this pathway play a pivotal role in maintaining normal physiological process. Emerging evidence show that the unbalanced ubiquitination/deubiquitination modification leads to human diseases via PI3K/AKT/mTOR pathway. Therefore, a comprehensive understanding of the ubiquitination/deubiquitination regulation of PI3K/AKT/mTOR pathway may be helpful to uncover the underlying mechanism and improve the potential treatment of cancer via targeting this pathway. Herein, we summarize the latest research progress of ubiquitination and deubiquitination of PI3K/AKT/mTOR pathway, systematically discuss the associated crosstalk between them, as well as focus the clinical transformation via targeting ubiquitination process.

Targeted proteomics in a population-based study identifies serum PECAM-1 and TRIM21 as inflammation markers for periodontitis

OBJECTIVES

Periodontitis (PD) can cause systematic inflammation and is associated with various metabolic processes in the body. However, robust serum markers for these relationships are still lacking. This study aims to identify novel circulating inflammation-related proteins associated with PD using targeted proteomics.

MATERIALS AND METHODS

We used population-based, cross-sectional data from 619 participants of the Polish Longitudinal University Study (Bialystok PLUS). Mean pocket probing depth (mPPD) and proportion of bleeding on probing (pBOP) served as exposure variables. Fifty-two inflammation-related proteins were measured using the Olink Target 96 Cardiovascular III and the Olink Target 96 Immune Response panels. Associations between periodontal measures and proteins were tested using covariate-adjusted linear regression models.

RESULTS

At a false discovery rate of < 0.05, we identified associations of mPPD and pBOP with platelet-endothelial cell adhesion molecule-1 (PECAM-1) and tripartite motif-containing protein 21 (TRIM21).

CONCLUSION

This study revealed novel associations between PD and serum levels of PECAM-1 and TRIM21. Our results suggest that these proteins might be affected by molecular processes that take place in the inflamed periodontium.

CLINICAL RELEVANCE

Novel associations of PECAM-1 and TRIM21 with PD indicate promising serum markers for understanding the disease's pathophysiological processes and call for further biomedical investigations.

Mutual regulation between TRIM21 and TRIM8 via K48-linked ubiquitination

Tripartite motif (TRIM)-containing proteins, one of the largest subfamilies of the RING type E3 ubiquitin ligases, control important biological processes such as cell apoptosis, autophagy, signal transduction, innate immunity and tumorigenesis. So far, the mutual regulation between TRIM family members has rarely been reported. Here, we found for the first time that there was a direct mutual regulation between TRIM21 and TRIM8 in lung and renal cancer cells, mechanistically by activating their proteasome pathway via Lys48 (K48)- linked ubiquitination. Subsequent studies verified that negatively correlated expressions existed in clinical non-small cell lung cancer (NSCLC) and renal cell carcinoma (RCC) tissues, which were closely related to tumor progression. Our findings highlighted a possible homeostasis between TRIM21 and TRIM8 that might possibly affect cell stemness and was expected to provide a new idea for cancer therapy.

Association of anti-Ro52 autoantibody with interstitial lung disease in autoimmune diseases: a systematic review and meta-analysis

OBJECTIVES

Interstitial lung disease (ILD) is an important manifestation of autoimmune diseases that can lead to morbidity and mortality. Although several autoantibodies have been linked with ILD presentation and adverse outcomes, the association of anti-Ro52 antibody with ILD is less studied. Hence, we investigated this association in various autoimmune diseases in the current study.

DESIGN

We designed a systematic review and meta-analysis and did a comprehensive search from inception until 2 January 2023.

DATA SOURCES

A systematic search was conducted in four electronic databases: PubMed, Web of Science, Scopus and Embase.

ELIGIBILITY CRITERIA

Observational studies that reported ILD diagnosis (outcome) and anti-Ro antibody (exposure) status in any autoimmune conditions (population) were included. The association between rapidly progressive ILD (RP-ILD) and anti-Ro52 was studied in idiopathic inflammatory myopathies (IIM).

DATA EXTRACTION AND SYNTHESIS

Collected data included study characteristics and ORs with 95% CIs. Quality assessment was performed using a modified version of the Newcastle-Ottawa Scale for cross-sectional studies. Random effects meta-analysis was used to pool the effect estimates.

RESULTS

A total of 2353 studies were identified, from which 59 articles met the eligibility criteria. Anti-Ro52/SSA positivity was associated with ILD in all autoimmune disease subgroups: IIM (OR=3.08; 95% CI: 2.18 to 4.35; p value<0.001; I2=49%), systemic lupus (OR=2.43; 95% CI: 1.02 to 5.79; p=0.046; I2=71%), Sjogren (OR=1.77; 95% CI: 1.09 to 2.87; p=0.021; I2=73%), systemic sclerosis (OR=1.71; 95% CI: 1.04 to 2.83; p=0.036; I2=43%), mixed connective tissue disease (OR=3.34; 95% CI: 1.82 to 6.13; p<0.001; I2=0%). Additionally, anti-Ro52-positive myopathy patients were more likely to have simultaneous RP-ILD (OR=2.69; 95% CI:1.50 to 4.83; p<0.001; I2=71%).

CONCLUSION

Anti-Ro52/SSA positivity is associated with a higher frequency of ILD diagnosis in various autoimmune diseases. Anti-Ro52/SSA is also linked with a more severe lung involvement (RP-ILD). Future studies can investigate the benefits of screening for anti-Ro52 and its association with ILD development.

PROSPERO REGISTRATION NUMBER

CRD42022381447.

Inflammation-induced TRIM21 represses hepatic steatosis by promoting the ubiquitination of lipogenic regulators

Nonalcoholic steatohepatitis (NASH) is a leading cause for chronic liver diseases. Current therapeutic options are limited due to an incomplete mechanistic understanding of how steatosis transitions to NASH. Here we show that the TRIM21 E3 ubiquitin ligase is induced by the synergistic actions of proinflammatory TNF-α and fatty acids in livers of humans and mice with NASH. TRIM21 ubiquitinates and degrades ChREBP, SREBP1, ACC1, and FASN, key regulators of de novo lipogenesis, and A1CF, an alternative splicing regulator of the high-activity ketohexokinase-C (KHK-C) isoform and rate-limiting enzyme of fructose metabolism. TRIM21-mediated degradation of these lipogenic activators improved steatosis and hyperglycemia as well as fructose and glucose tolerance. Our study identifies TRIM21 as a negative regulator of liver steatosis in NASH and provides mechanistic insights into an immunometabolic crosstalk that limits fatty acid synthesis and fructose metabolism during metabolic stress. Thus, enhancing this natural counteracting force of steatosis through inhibition of key lipogenic activators via TRIM21-mediated ubiquitination may provide a therapeutic opportunity to treat NASH.

Ro52/TRIM21 - From host defense to autoimmunity

Ro52 (TRIM21) belongs to the ubiquitin ligase family. This protein plays a crucial role in many immunological processes, including antibody-dependent intracellular neutralization, synergy with the complement system, antiviral response, death mediation, oxidative stress response, and protein ubiquitination. Abnormal expression of TRIM21 can break immunological tolerance and lead to the production of autoantibodies against TRIM21. Antibodies against TRIM21 are detected in various autoimmune diseases, including Sjögren's syndrome (SS), systemic lupus erythematosus (SLE), or myositis. However, anti-TRIM21 presence is not limited to autoimmune connective tissue disorders. It was observed in patients with malignancies, various cancerous processes, infectious diseases, and idiopathic interstitial pneumonia. The occurrence of TRIM21 autoantibodies is also associated with clinical features, such as the prevalence of interstitial lung diseases and cardiac or haematological involvement in connective tissue disorders. The purpose of this review was to summarize current knowledge of the immunological functions of TRIM21 and analyze the clinical implications of anti-TRIM21 antibodies in the disease course.

TRIM21 of Micropterus salmoides exerts antiviral roles against largemouth bass ulcer syndrome virus

Tripartite motif 21 (TRIM21), a member of the TRIM family, plays an important role in apoptosis, autophagy and ubiquitination in human, and has been proven to play antiviral roles in different organisms. In this study, the TRIM21 gene of Micropterus salmoides (MsTRIM21) was cloned, and it encoded 376 amino acids, which showed 89.3% similarity with Micropterus dolomieu and 38.3% with homo sapiens. Bioinformatics analysis revealed MsTRIM21 contained four domains: C4HC3-type RING-variant (RINGv), coiled coil, PRY and SPRY. The high expression level of MsTRIM21 could be detected in liver, stomach and muscle of healthy Micropterus salmoides, and it was significantly upregulated in head kidney, muscle, gill and brain and significantly down-regulated in the stomach of Micropterus salmoides infected with largemouth bass ulcer syndrome virus (LBUSV). The overexpression of MsTRIM21 could significantly inhibit the viral replication in vitro, evidenced by the reduction of CPE severity and the downregulation of the viral gene transcription. In addition, the overexpression of MsTRIM21 could significantly increase the expression level of interferon regulatory factor (IRF) 3, IRF7, myxovirus resistance 1 (Mx1), interferon stimulated gene 15 (ISG15), double-stranded RNA-activated protein kinase (PKR) and tumor necrosis factor α (TNF-α) in vitro, indicating the enhancement of innate immune response and inflammatory response, which may directly affect the replication of LBUSV. Thus, these results provide new lights on the roles of fish TRIM21 in innate immune response against iridovirus.

STAT1 suppresses the transcriptional activity of TRIM21 in gastric cancer

PURPOSE

Tripartite motif-containing protein 21 (TRIM21) has E3 ubiquitin ligase activity and is involved in the regulation of various biological processes in vivo. TRIM21 has been found to have strong associations with various cancers. However, its role in gastric cancer is unclear.

METHODS

The TCGA database was screened to obtain TRIM21 using WGCNA and PPI analyses. The TCGA database was used to evaluate the correlation of TRIM21 expression with patients' clinical characteristics, prognosis, functional enrichment and immune cell infiltration. The role of TRIM21 in cell proliferation, apoptosis and invasion was verified by in vivo and in vitro assays. The UCSC and JASPAR databases were used to evaluate the regulatory role of STAT1 on TRIM21 transcription. Finally, dual-luciferase reporter assay was used to confirm the regulation of TRIM21 transcriptional activity by STAT1.

RESULTS

As a key gene, high expression of TRIM21 inhibited the gastric cancer growth and was significantly enriched in apoptosis, cell proliferation, and JAK/STAT signaling pathways. TRIM21 expression was positively correlated with a variety of TICs, including T cells, NK cells, and DCs. In vivo assays, TRIM21 inhibited functions in gastric cancer cell lines, including inhibition of proliferation and migration, and promotion of apoptosis. Database analysis and dual-luciferase reporter assay showed that STAT1 inhibited the transcriptional activity of TRIM21. In vivo assays confirmed that TRIM21 inhibited tumor growth, and STAT1 expression was negatively correlated with STAT1.

CONCLUSION

TRIM21 is a tumor-suppressive gene in gastric cancer, and its transcriptional activity is inhibited by STAT1.

E3 ubiquitin ligase TRIM21 targets TIF1γ to regulate β-catenin signaling in glioblastoma

Background: Elucidation of the mechanism of ubiquitation has led to novel ways to treat glioblastoma (GBM). A tripartite motif (TRIM) protein mediates a reversible, stringent ubiquitation which is closely related to glioma malignancy. This study intends to screen the most vital and abnormal regulating component of the tripartite motif protein and to explore its underlying mechanisms. Methods: TRIM21 is identified as an important oncogene that accelerates the progression of glioma cell through database in a multidimensional way and this is confirmed in human samples and cells. Tandem Mass Tags (TMT) and MS analysis are performed to discover the substrates of TRIM21.The underlying mechanisms are further investigated by CO-IP, luciferase reporter assays and gain and loss of function assays. In vivo treatment with siRNA is applied to evaluate the therapeutic significance of TRIM21. Result: We screened a panel of TRIM proteins and identified TRIM21, a E3 ubiquitin-protein ligase and autoantigen, as well as a prognostic biomarker for GBM. Functionally, high expression of wild-type TRIM21 accelerates tumor progression in vitro and in vivo, whereas TRIM21 mutants, including one with a critical RING-finger deletion, do not. Mechanistically, TRIM21 stimulates K63-linked ubiquitination and subcellular translocation of active β-catenin from the cytoplasm to the nucleus. Moreover, TRIM21 forms a complex with the β-catenin upstream regulator, TIF1γ, in the nucleus and accelerated its degradation by inducing K48-linked ubiquitination at K5 site, consequently increasing further nuclear β-catenin presence. Endogenous TRIM21 levels are found to be inversely correlated with TIF1γ but positively correlated with β-catenin in glioma tissue microarray experiments. Furthermore, direct injection of TRIM21 small interfering RNA (siRNA) into U87 cell-derived tumors (in vivo treatment with siRNA) is proved to inhibit tumor growth in nude mice. Conclusion: This work suggests that TRIM21/TIF1γ/β-catenin axis is involved in the progression of human GBM. TRIM21 is a promising therapeutic and prognostic biomarker for glioma with hyperactive β-catenin.

Validation of an indirect ELISA assay for assessment of autoantibodies against full-length TRIM21 and its individual domains

Anti-SSA-autoantibodies are common in patients with rheumatologic disease, especially Sjögren's syndrome, systemic lupus erythematosus and rheumatoid arthritis. They consist of both autoantibodies towards Ro60 and Ro52, the latter also known as TRIM21. TRIM21 is an intracellular protein consisting of four domains; PRY/SPRY, Coiled-Coil, B-box and RING. The aim of this study was to establish an indirect ELISA detecting autoantibodies towards both the full-length TRIM21 protein and its four domains. We expressed the five constructs, created, and validated indirect ELISA protocols for each target using plasma from anti-SSA positive patients and healthy controls. Our findings were validated to the clinically used standards. We measured significantly higher levels of autoantibodies towards our full-length TRIM21, and the PRY/SPRY, Coiled-Coil and RING domains in patients compared to healthy controls. No significant difference in the level of autoantibodies were detected against the B-box domain. Our setups had a signal to noise ratio in the range of 30 to 184, and an OD between 2 and 3. Readings did not decline using NaCl of 500 mM as wash, affirming the high binding affinity of the autoantibodies measured. Our protocols allow us to further study the different autoantibodies of anti-SSA positive patients. This creates the possibility to stratify our patients into subgroups regarding autoantibody profile and specific pheno- or endotype.

The Toll-like Receptor 7-Mediated Ro52 Antigen-Presenting Pathway in the Salivary Gland Epithelial Cells of Sjögren's Syndrome

OBJECTIVE

To investigate whether stimulation with toll-like receptor (TLR) 7 leads to pathways that proceed to tripartite motif-containing protein 21 (TRIM21) or Ro52/SS-A antigen presentation through major histocompatibility complex (MHC) class I in salivary gland epithelial cells (SGECs) from Sjögren's syndrome (SS) patients.

DESIGN AND METHODS

Cultured SGECs from SS patients were stimulated with TLR7 agonist, loxoribine, and interferon-β. Cell lysates immunoprecipitated by anti-MHC class I antibody were analyzed by Western blotting. The immunofluorescence of salivary gland tissue from SS and non-SS subjects and cultured TLR7-stimulated SGECs was examined.

RESULTS

Significantly increased MHC class I expression was observed in SS patients' ducts versus non-SS ducts; no significant difference was detected for ubiquitin. Upregulated MHC class I in the cell membrane and cytoplasm and augmented Ro52 expression were observed in SGECs stimulated with TLR7. The formation of peptide-loading complex (PLC), including tapasin, calreticulin, transporter associated with antigen processing 1, and endoplasmic reticulum-resident protein 57 in labial salivary glands (LSGs) from SS patients, was dominantly observed and colocalized with MHC class I, which was confirmed in TLR7-stimulated SGEC samples.

CONCLUSION

These findings suggest that the TLR7 stimulation of SS patients' SGECs advances the process toward the antigen presentation of TRIM21/Ro52-SS-A via MHC class I.

Regulation of PKR-dependent RNA translation inhibition by TRIM21 upon virus infection or other stress

The host always employs various ways to defend against viral infection and spread. However, viruses have evolved their own effective strategies, such as inhibition of RNA translation of the antiviral effectors, to destroy the host's defense barriers. Protein synthesis, commonly controlled by the α-subunit of eukaryotic translation initiation factor 2 (eIF2α), is a basic cellular biological process among all species. In response to viral infection, in addition to inducing the transcription of antiviral cytokines by innate immunity, infected cells also inhibit the RNA translation of antiviral factors by activating the protein kinase R (PKR)-eIF2α signaling pathway. Regulation of innate immunity has been well studied; however, regulation of the PKR-eIF2α signaling pathway remains unclear. In this study, we found that the E3 ligase TRIM21 negatively regulates the PKR-eIF2α signaling pathway. Mechanistically, TRIM21 interacts with the PKR phosphatase PP1α and promotes K6-linked polyubiquitination of PP1α. Ubiquitinated PP1α augments its interaction with PKR, causing PKR dephosphorylation and subsequent translational inhibition release. Furthermore, TRIM21 can constitutively restrict viral infection by reversing PKR-dependent translational inhibition of various previously known and unknown antiviral factors. Our study highlights a previously undiscovered role of TRIM21 in regulating translation, which will provide new insights into the host antiviral response and novel targets for the treatment of translation-associated diseases in the clinic.

TRIM21 ameliorates hepatic glucose and lipid metabolic disorders in type 2 diabetes mellitus by ubiquitination of PEPCK1 and FASN

Hepatic glucose and lipid metabolism disorders promote the development and progression of type 2 diabetes mellitus (T2DM), yet the underlying mechanisms are not fully understood. Here, we identify tripartite motif-containing protein 21 (TRIM21), a class IV TRIM family member, as a pivotal regulator of hepatic metabolism in T2DM for the first time. Bioinformatic analysis suggests that TRIM21 expression is significantly reduced in T2DM patients. Intriguingly, in a mouse model of obese diabetes, TRIM21 expression is predominantly reduced in the liver rather than in other metabolic organs. It is further demonstrated that hepatic overexpression of TRIM21 significantly ameliorates glucose intolerance, insulin resistance, hepatic steatosis, and dyslipidemia in obese diabetic mice. In contrast, the knockdown of TRIM21 promotes glucose intolerance, insulin resistance, and triglyceride accumulation. Mechanistically, both phosphoenolpyruvate carboxykinase 1 (PEPCK1) and fatty acid synthase (FASN) are the hepatic targets of TRIM21. We revealed that TRIM21 promotes the degradation of PEPCK1 and FASN through a direct protein-protein interaction mediated K48-linked ubiquitination. Notably, overexpression of PEPCK1 and FASN essentially abolished the beneficial effects achieved by TRIM21 overexpression in obese diabetic mice. Overall, our data demonstrate that TRIM21 is a novel regulator of hepatic metabolic disorder, and suggest TRIM21 as a promising therapeutic target for T2DM.

Characteristic of molecular subtypes based on PANoptosis-related genes and experimental verification of hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is a type of liver cancer that originates from liver cells. It is one of the most common types of liver cancer and a leading cause of cancer-related death worldwide. Early detection and treatment can improve the HCC prognosis. Therefore, it is necessary to further improve HCC markers and risk stratification. PANoptosome is a cytoplasmic polymer protein complex that regulates a proinflammatory programmed cell death pathway called "PANoptosis". The role of PANoptosis in HCC remains unclear. In this study, the molecular changes of PANoptosis related genes (PAN-RGs) in HCC were systematically evaluated. We characterized the heterogeneity of HCC by using consensus clustering to identify two distinct subtypes. The two subtypes showed different survival rate, biological function, chemotherapy drug sensitivity and immune microenvironment. After identification of PAN-RG differential expression genes (DEGs), a prognostic model was established by Cox regression analysis using minimum absolute contraction and selection operator (LASSO), and its prognostic value was verified by Cox regression analysis, Kaplan-Meier curve and receiver operating characteristic (ROC) curve. Our own specimens were also used to further validate the prognostic significance and possible clinical value of the selected targets. Subsequently, we conducted a preliminary discussion on the reasons for the influence of the model on the prognosis through TME analysis, drug resistance analysis, TMB analysis and other studies. This study provides a new idea for individualized and precise treatment of HCC.

Interferon and autoantigens: intersection in autoimmunity

Interferon (IFN) is a key component of the innate immune response. For reasons that remain incompletely understood, the IFN system is upregulated in several rheumatic diseases, particularly those that feature autoantibody production, such as SLE, Sjögren's syndrome, myositis and systemic sclerosis. Interestingly, many of the autoantigens targeted in these diseases are components of the IFN system, representing IFN-stimulated genes (ISGs), pattern recognition receptors (PRRs), and modulators of the IFN response. In this review, we describe features of these IFN-linked proteins that may underlie their status as autoantigens. Note is also made of anti-IFN autoantibodies that have been described in immunodeficiency states.

Plasma proteomic profiling reveals KRT19 could be a potential biomarker in patients with anti-MDA5+ dermatomyositis

OBJECTIVE

To investigate the immune response-related protein profiling in plasma of patients with idiopathic inflammatory myopathies (IIMs), especially in anti-MDA5+ dermatomyositis (DM).

METHODS

A total of 166 IIM patients and 107 healthy controls (HCs) were enrolled in our study. Ninety-two plasma immune response-related proteins were detected by Olink proteomics in 36 IIM patients and 25 HCs. The expression of plasma KRT19 was validated in another 130 IIM patients, 82 HCs, and 55 other rheumatic diseases.

RESULTS

A total of 46 differentially expressed proteins were detected, including 12 upregulated proteins and 34 downregulated proteins in IIM patients compared with HCs. Pathway analysis revealed lactoferrin danger signal response pathway, TLR4 signaling and tolerance, infection, and IL-10 signaling pathway were activated. The immune response-related protein profiling significantly altered in anti-MDA5+ DM patients, with LAMP3, HSD11B1, and KRT19 significantly increased, while SH2D1A, ITGA11, TRIM21, CD28, ITGB6, and HEXIM1 tremendously decreased. In addition, KRT19 was significantly increased in IIM patients, especially in anti-MDA5+ DM patients with the diagnostic value of a significant area under the ROC curve of 0.881.

CONCLUSION

Immune response-related proteins are significantly altered in patients with anti-MDA5+ DM patients. KRT19 could be a potential biomarker for anti-MDA5+ DM patients. Key Points • What is already known on this topic? Anti-MDA5+ DM is a distinctive subtype of IIM. Plasma immune response-related proteins panel needs to be investigated. • What this study adds? Plasma protein profiling of immune response-related proteins significantly altered in patients with idiopathic inflammatory myopathies (IIM), especially in anti-MDA5+ DM patients. • How this study might affect research, practice, or policy? KRT19 could be a potential biomarker in patients with anti-MDA5+ dermatomyositis.

The E3 Ubiquitin Ligase TRIM21 Regulates Basal Levels of PDGFRβ

Activation of platelet-derived growth factor (PDGF) receptors α and β (PDGFRα and PDGFRβ) at the cell surface by binding of PDGF isoforms leads to internalization of receptors, which affects the amplitude and kinetics of signaling. Ubiquitination of PDGF receptors in response to ligand stimulation is mediated by the Casitas b-lineage lymphoma (Cbl) family of ubiquitin ligases, promoting internalization and serving as a sorting signal for vesicular trafficking of receptors. We report here that another E3 ligase, i.e., tripartite motif-containing protein 21 (TRIM21), contributes to the ubiquitination of PDGFRβ in human primary fibroblasts AG1523 and the osteosarcoma cell line U2OS and regulates basal levels of PDGFRβ. We found that siRNA-mediated depletion of TRIM21 led to decreased ubiquitination of PDGFRβ in response to PDGF-BB stimulation, while internalization from the cell surface and the rate of ligand-induced degradation of the receptor were not affected. Moreover, induction of TRIM21 decreased the levels of PDGFRβ in serum-starved cells, and even more in growing cells, in the absence of PDGF stimulation. Consistently, siRNA knockdown of TRIM21 caused accumulation of the total amount of PDGFRβ, both in the cytoplasm and on the cell surface, without affecting mRNA levels of the receptor. We conclude that TRIM21 acts post-translationally and maintains basal levels of PDGFRβ, thus suggesting that ubiquitination of PDGFRβ by TRIM21 may direct a portion of receptor for degradation in growing cells in a ligand-independent manner.

TRIM21 Expression as a Prognostic Biomarker for Progression-Free Survival in HNSCC

Patients with head and neck squamous cell carcinoma (HNSCC) continue to have a rather poor prognosis. Treatment-related comorbidities have negative impacts on their quality of life. TRIM21 is a cytosolic E3 ubiquitin ligase that was initially described as an autoantigen in autoimmune diseases and later associated with the intracellular antiviral response. Here, we investigated the role of TRIM21 as a biomarker candidate for HNSCC in predicting tumor progression and patient survival. We analyzed TRIM21 expression and its association with clinical-pathological parameters in our HNSCC cohort using immunohistochemistry. Our HNSCC cohort included samples from 419 patients consisting of primary tumors (n = 337), lymph node metastases (n = 156), recurrent tumors (n = 54) and distant metastases (n = 16). We found that cytoplasmic TRIM21 expression was associated with the infiltration of immune cells into primary tumors. In addition, TRIM21 expression was significantly higher in primary tumors than in lymph node metastases, and increased TRIM21 expression was correlated with shorter progression-free survival in HNSCC patients. These results suggest that TRIM21 could be a new biomarker for progression-free survival.

Sex/gender-related differences in inflammaging

Geroscience puts mechanisms of aging as a driver of the most common age-related diseases and dysfunctions. Under this perspective, addressing the basic mechanisms of aging will produce a better understanding than addressing each disease pathophysiology individually. Worldwide, despite greater functional impairment, life expectancy is higher in women than in men. Gender differences in the prevalence of multimorbidity lead mandatory to the understanding of the mechanisms underlying gender-related differences in multimorbidity patterns and disability-free life expectancy. Extensive literature suggested that inflammaging is at the crossroad of aging and age-related diseases. In this review, we highlight the main evidence on sex/gender differences in the mechanisms that foster inflammaging, i.e. the age-dependent triggering of innate immunity, modifications of adaptive immunity, and accrual of senescent cells, underpinning some biomarkers of inflammaging that show sex-related differences. In the framework of the "gender medicine perspective", we will also discuss how sex/gender differences in inflammaging can affect sex differences in COVID-19 severe outcomes.

Coexistence of Anti-Ro52 Antibodies in Anti-MDA5 Antibody-Positive Dermatomyositis Is Highly Associated With Rapidly Progressive Interstitial Lung Disease and Mortality Risk

OBJECTIVE

Interstitial lung disease (ILD) is a common extramuscular complication contributing to significant morbidity and mortality in patients with dermatomyositis (DM) who are positive for antimelanoma differentiation-associated gene 5 antibody (anti-MDA5+). We conducted this study to investigate the association of anti-Ro52 antibodies with clinical characteristics and prognosis in patients with anti-MDA5+ DM.

METHODS

We assessed a cohort of 246 patients with anti-MDA5+ DM. To calculate hazard ratios and 95% CIs for rapidly progressive ILD (RP-ILD) and death while controlling for potential confounders, variables selected by univariate Cox regression analysis were included in a multivariate Cox regression model with the stepwise forward-selection method. A 2-tailed analysis with P < 0.05 was considered to be statistically significant.

RESULTS

A total of 246 patients with anti-MDA5+ DM were enrolled; 70 patients were male, and the patient group had an average age of 53.1 (12.4) years. Anti-Ro52 was present in 64.2% (158/246) patients. Patients with anti-MDA5+ DM who were positive for anti-Ro52 had a higher rate of RP-ILD (log-rank P < 0.001) and a higher mortality rate (log-rank P = 0.01). For patients with anti-MDA5+ DM who were positive for anti-Ro52, those with a short disease course and high inflammation were at increased risk of RP-ILD and death. The appearance of active rash was an independent protective factor of death.

CONCLUSION

Anti-Ro52 antibodies were highly prevalent in patients with anti-MDA5+ DM, and their coexistence correlated with a higher rate of RP-ILD and mortality. Patients with a short disease course, with increased inflammation, and without rash were more likely to have a poor prognosis.

Cytosolic TGM2 promotes malignant progression in gastric cancer by suppressing the TRIM21-mediated ubiquitination/degradation of STAT1 in a GTP binding-dependent modality

BACKGROUND

Previous studies have revealed the critical role of transglutaminase 2 (TGM2) as a potential therapeutic target in cancers, but the oncogenic roles and underlying mechanisms of TGM2 in gastric cancer (GC) are not fully understood. In this study, we examined the role and potential mechanism of TGM2 in GC.

METHODS

Western blotting, immunohistochemistry, CCK8, colony formation and transwell assays were used to measure TGM2 expression in the GC cells and tissues and to examine the in vitro role of TGM2 in GC. Xenograft and in vivo metastasis experiments were performed to examine the in vivo role of TGM2 in GC. Gene set enrichment analysis, quantitative PCR and western blotting were conducted to screen for potential TGM2 targets involved in GC. Gain/loss-of-function and rescue experiments were conducted to detect the biological roles of STAT1 in GC cells in the context of TGM2. Co-immunoprecipitation, mass spectrometry, quantitative PCR and western blotting were conducted to identify STAT1-interacting proteins and elucidate their regulatory mechanisms. Mutations in TGM2 and two molecules (ZM39923 and A23187) were used to identify the enzymatic activity of TGM2 involved in the malignant progression of GC and elucidate the underlying mechanism.

RESULTS

In this study, we demonstrated elevated TGM2 expression in the GC tissues, which closely related to pathological grade, and predicted poor survival in patients with GC. TGM2 overexpression or knockdown promoted (and inhibited) cell proliferation, migration, and invasion, which were reversed by STAT1 knockdown or overexpression. Further studies showed that TGM2 promoted GC progression by inhibiting STAT1 ubiquitination/degradation. Then, tripartite motif-containing protein 21 (TRIM21) was identified as a ubiquitin E3 ligase of STAT1 in GC. TGM2 maintained STAT1 stability by facilitating the dissociation of TRIM21 and STAT1 with GTP-binding enzymatic activity. A23187 abolished the role of TGM2 in STAT1 and reversed the pro-tumor role of TGM2 in vitro and in vivo.

CONCLUSIONS

This study revealed a critical role and regulatory mechanism of TGM2 on STAT1 in GC and highlighted the potential of TGM2 as a therapeutic target, which elucidates the development of medicine or strategies by regulating the GTP-binding activity of TGM2 in GC.

Genome-wide screening of sex-biased genetic variants potentially associated with COVID-19 hospitalization

Sex-biased difference in coronavirus disease 2019 (COVID-19) hospitalization has been observed as that male patients tend to be more likely to be hospitalized than female patients. However, due to the insufficient sample size and existed studies that more prioritized to sex-stratified COVID-19 genome-wide association study (GWAS), the searching for sex-biased genetic variants showing differential association signals between sexes with COVID-19 hospitalization was severely hindered. We hypothesized genetic variants would show potentially sex-biased genetic effects on COVID-19 hospitalization if they display significant differential association effect sizes between male and female COVID-19 patients. By integrating two COVID-19 GWASs, including hospitalized COVID-19 patients vs. general population separated into males (case = 1,917 and control = 221,174) and females (case = 1,343 and control = 262,886), we differentiated the association effect sizes of each common single nucleotide polymorphism (SNP) within the two GWASs. Twelve SNPs were suggested to show differential COVID-19 associations between sexes. Further investigation of genes (n = 58) close to these 12 SNPs resulted in the identification of 34 genes demonstrating sex-biased differential expression in at least one GTEx tissue. Finally, 5 SNPs are mapped to 8 genes, including rs1134004 (GADD45G), rs140657166 (TRIM29 and PVRL1), rs148143613 (KNDC1 and STK32C), rs2443615 (PGAP2 and TRIM21), and rs2924725 (CSMD1). The 8 genes display significantly differential gene expression in blood samples derived from COVID-19 patients compared to healthy controls. These genes are potential genetic factors contributing to sex differences in COVID-19 hospitalization and warranted for further functional studies.

E3 ubiquitin ligase RNF6 promotes antiviral immune responses through enhancing the expression of interferon stimulated genes in myeloid cells

Interferon signaling is closely associated with clearance of viral infections as well as the development of systemic lupus erythematosus (SLE). Therefore, from a clinical perspective, it is important to identify the key regulators involved in interferon signaling pathways. In this study, we identified that RNF6, as an interferon inducible E3 ubiquitin ligase, promoted the interferon-dependent antiviral response. Knock-down of RNF6 greatly attenuated expression of ISGs and the transcriptional activity of ISRE. Specifically, increased RNF6 expression in myeloid cells of patients with SLE correlated with high expression of ISGs. Our results uncover RNF6 as a positive mediator in the antiviral immune responses and suggest that RNF6 may contribute to predict interferon signaling in SLE.

DExH/D-box helicases at the frontline of intrinsic and innate immunity against viral infections

DExH/D-box helicases are essential nucleic acid and ribonucleoprotein remodelers involved in all aspects of nucleic acid metabolism including replication, gene expression and post-transcriptional modifications. In parallel to their importance in basic cellular functions, DExH/D-box helicases play multiple roles in viral life cycles, with some of them highjacked by viruses or negatively regulating innate immune activation. However, other DExH/D-box helicases have recurrently been highlighted as direct antiviral effectors or as positive regulators of innate immune activation. Innate immunity relies on the ability of Pathogen Recognition Receptors to recognize viral signatures and trigger the production of interferons (IFNs) and pro-inflammatory cytokines. Secreted IFNs interact with their receptors to establish antiviral cellular reprogramming via expression regulation of the interferon-stimulated genes (ISGs). Several DExH/D-box helicases have been reported to act as viral sensors (DDX3, DDX41, DHX9, DDX1/DDX21/DHX36 complex), and others to play roles in innate immune activation (DDX60, DDX60L, DDX23). In contrast, the DDX39A, DDX46, DDX5 and DDX24 helicases act as negative regulators and impede IFN production upon viral infection. Beyond their role in viral sensing, the ISGs DDX60 and DDX60L act as viral inhibitors. Interestingly, the constitutively expressed DEAD-box helicases DDX56, DDX17, DDX42 intrinsically restrict viral replication. Hence, DExH/D-box helicases appear to form a multilayer network of primary and secondary factors involved in both intrinsic and innate antiviral immunity. In this review, we highlight recent findings on the extent of antiviral defences played by helicases and emphasize the need to better understand their immune functions as well as their complex interplay.

Anti-Ro52/TRIM21 serological subsets identify differential clinical and laboratory parameters

Introduction

Anti-Ro52/tripartite motif-containing protein 21 (TRIM21) IgG is one of the most common autoantibodies found in systemic autoimmune diseases and is typically found in conjunction with anti-Ro60 and/or anti-La. A retrospective, cross-sectional study was undertaken to examine the clinical and laboratory features of two serological subsets: patients with anti-Ro52/TRIM21 autoantibodies in the absence of anti-Ro60 and anti-La (isolated anti-Ro52/TRIM21) and patients with anti-Ro52/TRIM21 in the presence of anti-Ro60 and/or anti-La.

Methods

Over a 12-month period, patients tested positive for anti-Ro52/TRIM21 via line immunoassay (LIA) at the Westmead Hospital (Australia) immunopathology laboratory were included. The presence of anti-Ro60 and/or anti-La via same LIA was noted. Associated laboratory and medical records were perused to extract demographic, laboratory, and clinical information.

Results

There were 346 patients within the study period, and 39.9% of the patients positive for anti-Ro52/TRIM21 lacked anti-Ro60/anti-La autoantibodies. Isolated anti-Ro52/TRIM21 patients tend to be older, have lower anti-Ro52/TRIM21 titres, have lower rheumatoid factors, and have lower proportions of neutropaenia compared to patients who were positive for anti-Ro52/TRIM21 and anti-Ro60/La. This occurred independent to diagnoses of Sjögren’s syndrome or systemic lupus erythematosus. Coexisting neurological syndromes, pulmonary pathologies, and malignancies were more prevalent in the isolated anti-Ro52/TRIM21 subset.

Conclusions

Patients with isolated anti-Ro52/TRIM21 tend to have distinct and important clinical and laboratory associations. It is unclear if these patients evolve or remain a stable subset and how they originate immunologically. Longitudinal and prospective studies are required to ascertain the overall predictive and prognostic value of this stratification.

Key Points • Anti-Ro52/TRIM21 is an autoantibody found in autoimmunity and non-immunological conditions. • Sixty percent of anti-Ro52/TRIM21 patients are positive for anti-Ro60. • Isolated anti-Ro52/TRIM21 has reduced anti-Ro52/TRIM21 and rheumatoid factor titres. • Isolated anti-Ro52/TRIM21 is associated with anaemia and malignancies.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10067-022-06299-5.

The roles of E3 ligases in Hepatocellular carcinoma

Hepatocarcinogenesis is a complex multistep biological process involving genetic and epigenetic alterations that are accompanied by activation of oncoproteins and inactivation of tumor suppressors, which in turn results in Hepatocellular carcinoma (HCC), one of the common tumors with high morbidity and mortality worldwide. The ubiquitin-proteasome system (UPS) is the key to protein degradation and regulation of physiological and pathological processes, and E3 ligases are key enzymes in the UPS that contain a variety of subfamily proteins involved in the regulation of some common signal pathways in HCC. There is growing evidence that many structural or functional dysfunctions of E3 are engaged in the development and progression of HCC. Herein, we review recent research advances in HCC-associated E3 ligases, describe their structure, classification, functional roles, and discuss some mechanisms of the abnormal activation or inactivation of the HCC-associated signal pathway due to the binding of E3 to known substrates. In addition, given the success of proteasome inhibitors in the treatment of malignant cancers, we characterize the current knowledge and future prospects for targeted therapies against aberrant E3 in HCC.