Suppression of KSHV lytic replication and primary effusion lymphoma by selective RNF5 inhibition

Discovery of host genetic factors through multi-locus GWAS against toxoplasmosis in sheep: addressing one health perspectives

Toxoplasma gondii stands as one of the most successful pathogens, capable of infecting nearly all warm-blooded species. It is estimated that up to 50% of human population might harbor Toxoplasmosis infections. One of the primary transmission routes is the consumption of tissue cysts from infected farm animals used for food production. Thus, controlling Toxoplasmosis in farm animals is of vital importance for human health and food safety. Selective breeding in farm animals, where available, could complement classical control measures like biosecurity measures, vaccination, and test-and-cull methods. This multidisciplinary approach will make the eradication of Toxoplasmosis more effective. For this purpose, we conducted four multi-locus genome-wide association (GWA) approaches to identify the polygenic factors underlying innate resistance to Toxoplasma gondii in naturally infected sheep. Our findings indicate that 16 single nucleotide polymorphisms (SNPs), exhibiting varying degrees of statistical power, play a significant role in host immunity against T. gondii infection. We propose the genes containing these SNPs or located within 100 ± Kb of them (PLSCR5, EPHA3, DGKB, IL12B, CGA, WDR64, TMEM158, CLMP, and SIAE) as potential candidate genes. This study represents the first exploration of host genetic factors against Toxoplasmosis in livestock, utilizing the ovine paradigm as its foundation.

Primary effusion lymphoma: therapeutic strategies targeting viral and cellular mechanisms

INTRODUCTION

Primary effusion lymphoma (PEL) is a rare subtype of B-cell lymphoma primarily affecting immunocompromised and elderly individuals. Given the dismal survival rates associated with traditional treatments, studying novel therapeutic approaches to improve patient outcomes is critical.

AREAS COVERED

This review focuses on developing therapeutic options for PEL that target particular viral and cellular mechanisms involved in PEL pathogenesis. Since the CHOP regimen was associated with a lower median survival rate, alternative treatments, including stem cell transplantation, have also been explored, but have generally produced unsatisfactory results. Therefore, novel therapeutic agents are under investigation, including antiretroviral drugs targeting viral pathways and treatments targeting particular cellular processes, such as DNA damage, epigenetics, apoptotic, and immune-modulatory pathways showing promising outcomes in preclinical and clinical research, increasing PEL treatment efficacy while minimizing toxicity. In this review, we conducted a comprehensive literature search using PubMed, and Google Scholar for studies published between 1989 and 2024.

EXPERT OPINION

Further research is needed to refine the appropriate combination methods and strategies behind drug interactions. Targeted therapies could be investigated further to improve therapeutic efficacy and reduce toxicity in this type of lymphoma.

RNF5 inhibits HBV replication by mediating caspase-3-dependent degradation of core protein

The RING finger protein 5 (RNF5), an E3 ubiquitin ligase, has demonstrated significant antiviral activity against various viruses, including severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and Kaposi's sarcoma-associated herpesvirus (KSHV). However, its role in hepatitis B virus (HBV) replication has not been previously studied. In this study, we demonstrate that RNF5 effectively inhibits HBV replication by promoting the degradation of the HBV Core protein through a Caspase-3-dependent pathway. We first show that RNF5 expression is upregulated in HBV-infected cells and patient samples, suggesting a role in the host's antiviral response. Subsequently, we investigate the mechanism by which RNF5 mediates its antiviral effect, finding that RNF5 targets the Core protein for degradation independently of its E3 ubiquitin ligase activity. The degradation of Core protein is mediated through a Caspase-3-dependent mechanism rather than the proteasomal pathway. Interestingly, RNF5's antiviral function does not rely on ubiquitination, indicating an alternative pathway involving apoptosis-related processes. These findings highlight the multifunctional role of RNF5 and suggest that targeting RNF5 could serve as a novel therapeutic approach to control HBV replication, providing new insights into the development of antiviral therapies against HBV.

Repurposing alcohol-abuse drug disulfiram for the treatment of KSHV-infected primary effusion lymphoma by activating antiviral innate immunity

Cancer remains a leading cause of global mortality, characterized by high treatment costs, and generally poor prognoses. Developing new anti-cancer drugs requires substantial investment, extended development timelines, and a high failure rate. Therefore, repurposing existing US Food and Drug Administration (FDA)-approved drugs for other diseases as potential anti-cancer therapies offers a faster and more cost-effective approach. Primary effusion lymphoma (PEL) is an aggressive B-cell malignancy linked to Kaposi's sarcoma-associated herpesvirus (KSHV) infection. In this study, we identified that disulfiram (DSF), an FDA-approved medication for alcohol dependence, acts as a potent inhibitor of KSHV-positive PEL. DSF suppresses PEL cell proliferation by inducing apoptosis through the activation of innate antiviral immunity. Remarkably, DSF effectively impedes KSHV reactivation and virion production in both PEL and endothelial cells. Inhibition of TANK binding kinase 1 (TBK1) or interferon regulatory factor 3 (IRF3), essential activators of antiviral innate immunity, reverses DSF's effects on PEL cell survival and KSHV reactivation. Furthermore, DSF treatment significantly hinders the initiation and progression of PEL tumors in a xenograft mouse model, with this effect was notably abolished by TBK1 depletion. Our findings highlighted DSF as a promising therapeutic agent for targeting persistent KSHV infection and treating PEL tumors.

Swine RNF5 positively regulates the antiviral activity of IFITM1 by mediating the degradation of ABHD16A

Interferon-inducible transmembrane (IFITM) proteins are broad-spectrum antiviral factors that confer cellular resistance to virus invasion. α/β-Hydrolase domain-containing 16A (ABHD16A) has recently been identified as a novel depalmitoylase that can inhibit the antiviral activity of IFITM proteins by catalyzing the depalmitoyl reaction; this pattern may be crucial for the host to avoid damage caused by excessive immune response. However, it remains largely elusive about how host cells regulate the activity of ABHD16A. In the present study, we performed the AlphaFold2-based protein-protein interaction prediction and identified swine E3 ubiquitin ligase ring finger protein 5 (sRNF5) as a sABHD16A-interacting protein and negatively regulated the stability of sABHD16A. Using immunofluorescence and co-immunoprecipitation techniques, we uncovered that sRNF5 targeted sABHD16A for ubiquitination and degradation via the proteasomal pathway at residues K3 and K452. Furthermore, sABHD16A catalyzed the depalmitoylation of sIFITM1, which obstructed the antiviral function of sIFITM1, while sRNF5 caused ubiquitination of sABHD16A, which attenuated the depalmitoylation effect on sIFITM1, and consequently restored the antiviral activity of sIFITM1. Collectively, our findings demonstrate for the first time that sRNF5 positively regulates the antiviral function of sIFITM1 by mediating the degradation of sABHD16A, which expands the biological functions of RNF5 and ABHD16A in immune regulation. Moreover, our work highlights the well-designed interplay between RNF5, ABHD16A, and IFITM, which balances antiviral immune responses to avoid the disorders induced by excessive immune response.

IMPORTANCE

Interferon and interferon-stimulated genes play significant and protective roles in the host's defense against viral infection. IFITM family proteins, which can be strongly induced by interferon, have been identified as the first line of defense to prevent invasion of various viruses. Further analysis reveals the antiviral activity of IFITMs depends on palmitoylation/depalmitoylation. Recently, we reported that ABHD16A, as the first depalmitoylase of IFITMs, negatively regulated the antiviral activity of IFITMs. However, these raise crucial questions: how ABHD16A is regulated and remained in a balanced manner? Here, we show that swine RNF5 attenuates the negative regulation of sIFITM1 against virus invasion by modifying sABHD16A through ubiquitination and guiding sABHD16A for degradation. Thus, sRNF5-sABHD16A interplay plays an indispensable role in regulating immune response and avoiding the disorders induced by elevated interferon levels. Overall, our findings extend the upstream subtle regulatory molecular mechanism of IFITMs and provide potential targets for viral disease therapy.

Molecular Mechanisms of Kaposi Sarcoma-Associated Herpesvirus (HHV8)-Related Lymphomagenesis

Approximately 15-20% of cancers are caused by viruses. Kaposi sarcoma-associated herpesvirus (KSHV), also known as human herpesvirus 8 (HHV8), is an oncogenic virus that is the etiologic agent of not only Kaposi sarcoma but also the lymphoproliferative disorders, primary effusion lymphoma (PEL) and multicentric Castleman disease (MCD). KSHV can infect a broad tropism of cells, including B lymphocytes, wherein KSHV encodes specific viral proteins that can transform the cell. KSHV infection precedes the progression of PEL and MCD. KSHV establishes lifelong infection and has two phases of its lifecycle: latent and lytic. During the latent phase, viral genomes are maintained episomally with limited gene expression. Upon sporadic reactivation, the virus enters its replicative lytic phase to produce infectious virions. KSHV relies on its viral products to modulate host factors to evade immune detection or to co-opt their function for KSHV persistence. These manipulations dysregulate normal cell pathways to ensure cell survival and inhibit antiviral immune responses, which in turn, contribute to KSHV-associated malignancies. Here, we highlight the known molecular mechanisms of KSHV that promote lymphomagenesis and how these findings identify potential therapeutic targets for KSHV-associated lymphomas.

RING finger protein 5 protects against acute myocardial infarction by inhibiting ASK1

BACKGROUND

Myocardial infarction (MI) is a major disease with high morbidity and mortality worldwide. However, existing treatments are far from satisfactory, making the exploration of potent molecular targets more imperative. The E3 ubiquitin ligase RING finger protein 5 (RNF5) has been previously reported to be involved in several diseases by regulating ubiquitination-mediated protein degradation. Nevertheless, few reports have focused on its function in cardiovascular diseases, including MI.

METHODS

In this study, we established RNF5 knockout mice through precise CRISPR-mediated genome editing and utilized left anterior descending coronary artery ligation in 9-11-week-old male C57BL/6 mice. Subsequently, serum biochemical analysis and histopathological examination of heart tissues were performed. Furthermore, we engineered adenoviruses for modulating RNF5 expression and subjected neonatal rat cardiomyocytes to oxygen-glucose deprivation (OGD) to mimic ischemic conditions, demonstrating the impact of RNF5 manipulation on cellular viability. Gene and protein expression analysis provided insights into the molecular mechanisms. Statistical methods were rigorously employed to assess the significance of experimental findings.

RESULTS

We found RNF5 was downregulated in infarcted heart tissue of mice and NRCMs subjected to OGD treatment. RNF5 knockout in mice resulted in exacerbated heart dysfunction, more severe inflammatory responses, and increased apoptosis after MI surgery. In vitro, RNF5 knockdown exacerbated the OGD-induced decline in cell activity, increased apoptosis, while RNF5 overexpression had the opposite effect. Mechanistically, it was proven that the kinase cascade initiated by apoptosis signal-regulating kinase 1 (ASK1) activation was closely regulated by RNF5 and mediated RNF5's protective function during MI.

CONCLUSIONS

We demonstrated the protective effect of RNF5 on myocardial infarction and its function was dependent on inhibiting the activation of ASK1, which adds a new regulatory component to the myocardial infarction associated network and promises to enable new therapeutic strategy.

Membralin is required for maize development and defines a branch of the endoplasmic reticulum-associated degradation pathway in plants

Endoplasmic reticulum (ER)-associated degradation (ERAD) plays key roles in controlling protein levels and quality in eukaryotes. The Ring Finger Protein 185 (RNF185)/membralin ubiquitin ligase complex was recently identified as a branch in mammals and is essential for neuronal function, but its function in plant development is unknown. Here, we report the map-based cloning and characterization of Narrow Leaf and Dwarfism 1 (NLD1), which encodes the ER membrane-localized protein membralin and specifically interacts with maize homologs of RNF185 and related components. The nld1 mutant shows defective leaf and root development due to reduced cell number. The defects of nld1 were largely restored by expressing membralin genes from Arabidopsis thaliana and mice, highlighting the conserved roles of membralin proteins in animals and plants. The excessive accumulation of β-hydroxy β-methylglutaryl-CoA reductase in nld1 indicates that the enzyme is a membralin-mediated ERAD target. The activation of bZIP60 mRNA splicing-related unfolded protein response signaling and marker gene expression in nld1, as well as DNA fragment and cell viability assays, indicate that membralin deficiency induces ER stress and cell death in maize, thereby affecting organogenesis. Our findings uncover the conserved, indispensable role of the membralin-mediated branch of the ERAD pathway in plants. In addition, ZmNLD1 contributes to plant architecture in a dose-dependent manner, which can serve as a potential target for genetic engineering to shape ideal plant architecture, thereby enhancing high-density maize yields.

RNF5: inhibiting antiviral immunity and shaping virus life cycle

RNF5 is an E3 ubiquitin ligase involved in various physiological processes such as protein localization and cancer progression. Recent studies have shown that RNF5 significantly inhibits antiviral innate immunity by promoting the ubiquitination and degradation of STING and MAVS, which are essential adaptor proteins, as well as their downstream signal IRF3. The abundance of RNF5 is delicately regulated by both host factors and viruses. Host factors have been found to restrict RNF5-mediated ubiquitination, maintaining the stability of STING or MAVS through distinct mechanisms. Meanwhile, viruses have developed ingenious strategies to hijack RNF5 to ubiquitinate and degrade immune proteins. Moreover, recent studies have revealed the multifaceted roles of RNF5 in the life cycle of various viruses, including SARS-CoV-2 and KSHV. Based on these emerging discoveries, RNF5 represents a novel means of modulating antiviral immunity. In this review, we summarize the latest research on the roles of RNF5 in antiviral immunity and virus life cycle. This comprehensive understanding could offer valuable insights into exploring potential therapeutic applications focused on targeting RNF5 during viral infections.

Downregulation of EphA2 stability by RNF5 limits its tumor-suppressive function in HER2-negative breast cancers

Ephrin receptor A2 (EphA2) plays dual functions in tumorigenesis through ligand-independent tumor promotion or ligand-dependent tumor suppression. However, the regulation of EphA2 tumor-suppressive function remains unclear. Here, we showed that RNF5 interacts with EphA2 and induces its ubiquitination and degradation, decreases the stability and cell surface distribution of EphA2 and alters the balance of its phosphorylation at S897 and Y772. In turn, RNF5 inhibition decreases ERK phosphorylation and increases p53 expression through an increase in the EphA2 level in HER2-negative breast cancer cells. Consequently, RNF5 inhibition increases the adhesion and decreases the migration of HER2-negative breast cancer cells, and RNF5 silencing suppresses the growth of xenograft tumors derived from ER-positive, HER2-negative breast cancer cells with increased EphA2 expression and altered phosphorylation. RNF5 expression is inversely correlated with EphA2 expression in breast cancers, and a high EphA2 level accompanied by a low RNF5 level is related to better survival in patients with ER-positive, HER2-negative breast cancers. These studies revealed that RNF5 negatively regulates EphA2 properties and suppresses its tumor-suppressive function in HER2-negative breast cancers.