TRIM6 facilitates SARS-CoV-2 proliferation by catalyzing the K29-typed ubiquitination of NP to enhance the ability to bind viral genomes

The Nucleocapsid Protein (NP) of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is not only the core structural protein required for viral packaging, but also participates in the regulation of viral replication, and its post-translational modifications such as phosphorylation have been shown to be an important strategy for regulating virus proliferation. Our previous work identified NP could be ubiquitinated, as confirmed by two independent studies. But the function of NP ubiquitination is currently unknown. In this study, we first pinpointed TRIM6 as the E3 ubiquitin ligase responsible for NP ubiquitination, binding to NP's CTD via its RING and B-box-CCD domains. TRIM6 promotes the K29-typed polyubiquitination of NP at K102, K347, and K361 residues, increasing its binding to viral genomic RNA. Consistently, functional experiments such as the use of the reverse genetic tool trVLP model and gene knockout of TRIM6 further confirmed that blocking the ubiquitination of NP by TRIM6 significantly inhibited the proliferation of SARS-CoV-2. Notably, the NP of coronavirus is relatively conserved, and the NP of SARS-CoV can also be ubiquitinated by TRIM6, indicating that NP could be a broad-spectrum anti-coronavirus target. These findings shed light on the intricate interaction between SARS-CoV-2 and the host, potentially opening new opportunities for COVID-19 therapeutic development.

TRIM6 silencing for inhibiting growth and angiogenesis of gliomas by regulating VEGFA

Gliomas are the highest prevalent primary central nervous system (CNS) cancers with poor overall survival rate. There is an urgent need to conduct more research into molecular therapies targeting critical elements of gliomas. This study herein targeted to assess the impact of tripartite motif protein 6 (TRIM6) on gliomas. Using public databases, we found the increased TRIM6 expression in tissues of glioma which was linked with worst overall survival. Silencing TRIM6 promoted glioma cell proliferation, migration and angiogenesis, suggesting the promoting effects of TRIM6 on gliomas. Knockdown of TRIM6 expression downregulated the expression levels of Forkhead box M1 (FOXM1) and vascular endothelial growth factor A (VEGFA) in glioma cells. Afterwards, impact of TRIM6 on VEGFA expression was regulated by FOXM1. VEGFA overexpression reversed the decreased abilities of glioma cell proliferation, migration and angiogenesis caused by silencing TRIM6. Furthermore, we also found that TRIM6 promoted the growth of gliomas in the xenograft mouse model. In summary, the expression of TRIM6 was increased which was related to poor prognosis of glioma patients. TRIM6 promoted glioma cell proliferation, migration and angiogenesis through the FOXM1-VEGFA pathway. Therefore, TRIM6 carries capacity to be explored as a novel therapeutic target in clinical.

TRIM6: An Upregulated Biomarker with Prognostic Significance and Immune Correlations in Gliomas

This study investigates the expression and prognostic value of TRIM6 in gliomas, the most prevalent primary brain and spinal cord tumors. Our results show that TRIM6 is predominantly overexpressed in glioma tissues and is associated with reduced overall survival, disease-specific survival, and progression-free interval. Furthermore, TRIM6 expression is correlated with WHO grade and primary treatment outcomes. Functional analysis indicates that interactions between cytokines and their receptors play a critical role in the prognosis of glioma patients. A protein-protein interaction network reveals 10 hub genes closely linked to cytokine-cytokine receptor interaction. In vitro experiments demonstrate that silencing TRIM6 impairs the proliferation, invasion, and migration of glioma cells, while overexpressing TRIM6 enhances these abilities. Additionally, TRIM6 expression is positively associated with the abundance of innate immune cells and negatively associated with the abundance of adaptive immune cells. In summary, TRIM6 is significantly upregulated in gliomas and linked to poor prognosis, making it a potential diagnostic and prognostic biomarker. TRIM6 plays a crucial role in promoting cell viability, clonogenic potential, migration, and invasion in glioma cells. It may regulate glioma progression by modulating cytokine-cytokine receptor interaction, leading to an inflammatory response and an imbalance in immunomodulation, thereby representing a potential therapeutic target.

The RNA helicase DHX16 recognizes specific viral RNA to trigger RIG-I-dependent innate antiviral immunity

Type I interferons (IFN-I) are essential to establish antiviral innate immunity. Unanchored (or free) polyubiquitin (poly-Ub) has been shown to regulate IFN-I responses. However, few unanchored poly-Ub interactors are known. To identify factors regulated by unanchored poly-Ub in a physiological setting, we developed an approach to isolate unanchored poly-Ub from lung tissue. We identified the RNA helicase DHX16 as a potential pattern recognition receptor (PRR). Silencing of DHX16 in cells and in vivo diminished IFN-I responses against influenza virus. These effects extended to members of other virus families, including Zika and SARS-CoV-2. DHX16-dependent IFN-I production requires RIG-I and unanchored K48-poly-Ub synthesized by the E3-Ub ligase TRIM6. DHX16 recognizes a signal in influenza RNA segments that undergo splicing and requires its RNA helicase motif for direct, high-affinity interactions with specific viral RNAs. Our study establishes DHX16 as a PRR that partners with RIG-I for optimal activation of antiviral immunity requiring unanchored poly-Ub.

Tripartite Motif Protein 6 Promotes Colorectal Cancer Cell Migration and Metastasis via SOCS2-STAT3 Signaling

Colorectal cancer (CRC) is one of the leading causes of cancer death worldwide, with most mortalities being caused by metastases. However, the underlying molecular mechanism of CRC metastases remains largely unknown. Emerging evidence has shown the role of the tripartite motif family, especially tripartite motif protein 6 (TRIM6), in carcinogenesis. In this study, we used CRC cell lines with TRIM6 knockdown and overexpression to investigate the function of TRIM6 in CRC metastasis. We found that TRIM6 promotes CRC cell migration and invasion both in vitro and in vivo. TRIM6 knockdown slows down the migration and invasion processes, whereas TRIM6 overexpression accelerates CRC cell migration and invasion. TRIM6 is potentially the upstream regulatory factor for signal transducer and activator of transcription 3 (STAT3) via the suppressor of cytokine signaling 2 (SOCS2). A total of 70 samples from patients with CRC further confirmed that TRIM6 expression level is positively correlated with STAT3 phosphorylation and negatively correlated with SOCS2 expression. Therefore, TRIM6 could be a potential therapeutic target for CRC metastasis.

The Expression of TRIM6 Activates the mTORC1 Pathway by Regulating the Ubiquitination of TSC1-TSC2 to Promote Renal Fibrosis

Renal fibrosis is considered as the final pathway of all types of kidney diseases, which can lead to the progressive loss of kidney functions and eventually renal failure. The mechanisms behind are diversified, in which the mammalian target of rapamycin (mTOR) pathway is one of the most important regulatory pathways that accounts for the disease. Several processes that are regulated by the mTOR pathway, such as autophagy, epithelial-mesenchymal transition (EMT), and endoplasmic reticulum (ER) stress, are tightly associated with renal fibrosis. In this study, we have reported that the expression of tripartite motif-containing (TRIM) protein 6, a member of TRIM family protein, was highly expressed in renal fibrosis patients and positively correlated with the severity of renal fibrosis. In our established in vitro and in vivo renal fibrosis models, its expression was upregulated by the Angiotensin II-induced nuclear translocation of nuclear factor-κB (NF-κB) p50 and p65. In HK2 cells, the expression of TRIM6 promoted the ubiquitination of tuberous sclerosis proteins (TSC) 1 and 2, two negative regulators of the mTORC1 pathway. Moreover, the knockdown of TRIM6 was found efficient for alleviating renal fibrosis and inhibiting the downstream processes of EMT and ER in both HK2 cells and 5/6-nephrectomized rats. Clinically, the level of TRIM6, TSC1/2, and NF-κB p50 was found closely related to renal fibrosis. As a result, we have presented the first study on the role of TRIM6 in the mTORC1 pathway in renal fibrosis models and our findings suggested that TRIM6 may be a potential target for the treatment of renal fibrosis.

TRIM Proteins in Host Defense and Viral Pathogenesis

Purpose of Review

Tripartite motif (TRIM) proteins are a large group of E3 ubiquitin ligases involved in different cellular functions. Of special interest are their roles in innate immunity, inflammation, and virus replication. We discuss novel roles of TRIM proteins during virus infections that lead to increased pathogenicity.

Recent Findings

TRIM proteins regulate different antiviral and inflammatory signaling pathways, mostly by promoting ubiquitination of important factors including pattern recognition receptors, adaptor proteins, kinases, and transcription factors that are involved in type I interferon and NF-κB pathways. Therefore, viruses have developed mechanisms to target TRIMs for immune evasion. New evidence is emerging indicating that viruses have the ability to directly use TRIMs and the ubiquitination process to enhance the viral replication cycle and cause increased pathogenesis. A new report on TRIM7 also highlights the potential pro-viral role of TRIMs via ubiquitination of viral proteins and suggests a novel mechanism by which ubiquitination of virus envelope protein may provide determinants of tissue and species tropism.

Summary

TRIM proteins have important functions in promoting host defense against virus infection; however, viruses have adapted to evade TRIM-mediated immune responses and can hijack TRIMs to ultimately increase virus pathogenesis. Only by understanding specific TRIM-virus interactions and by using more in vivo approaches can we learn how to harness TRIM function to develop therapeutic approaches to reduce virus pathogenesis.

TRIM6 promotes colorectal cancer cells proliferation and response to thiostrepton by TIS21/FoxM1

BACKGROUND

Tripartite motif-containing proteins (TRIM) play a crucial role in carcinogenesis. Little attention has been focused on the possible functions of TRIM6 on carcinogenesis.

METHODS

The expression levels of TRIM6 were assessed in colorectal cancer (CRC) samples. TRIM6 expression was knocked down in CRC cell lines, and subjected to Cell counting kit-8 (CCK-8), bromodeoxyuridine (BrdU) incorporation and cell cycle assays. Immunoprecipitation and proteomics analysis was performed to identify potential associated proteins of TRIM6.

RESULTS

TRIM6 expression was up-regulated in CRC samples and TRIM6 expression may be an independent prognostic marker for CRC. Knocking down TRIM6 expression suppressed CRC cell proliferation, induced cell cycle arrested at G2/M phase and increased sensitivity to 5-fluorouracil and oxaliplatin. TIS21, an anti-proliferative protein involved in the regulation of G2/M arrest, was identified as an interaction partner of TRIM6. Moreover, CRC cells with TRIM6 overexpression showed decreased TIS21 protein stability. TIS21 ubiquitination was increased in CRC cells overexpressing TRIM6, but not in those overexpressing TRIM6 E3 catalytic mutant (C15A). Further, Lys5 was essential for TRIM6 mediated TIS21 ubiquitination. TIS21 overexpression reversed the induced effects of TRIM6 overexpression on CRC cell proliferation, and the levels of forkhead box M1 (FoxM1), phosphorylated FoxM1, Cyclin B1 and c-Myc. Thiostrepton, a specific inhibitor for FoxM1, was less effective in anti-proliferative activity against CRC cells with lower level of TRIM6 in vitro and in vivo.

CONCLUSIONS

Our study suggests that TRIM6 promotes the progression of CRC via TIS21/FoxM1.

VAMP8 Contributes to the TRIM6-Mediated Type I Interferon Antiviral Response during West Nile Virus Infection

Several members of the tripartite motif (TRIM) family of E3 ubiquitin ligases regulate immune pathways, including the antiviral type I interferon (IFN-I) system. Previously, we demonstrated that TRIM6 is involved in IFN-I induction and signaling. In the absence of TRIM6, optimal IFN-I signaling is reduced, allowing increased replication of interferon-sensitive viruses. Despite having evolved numerous mechanisms to restrict the vertebrate host's IFN-I response, West Nile virus (WNV) replication is sensitive to pretreatment with IFN-I. However, the regulators and products of the IFN-I pathway that are important in regulating WNV replication are incompletely defined. Consistent with WNV's sensitivity to IFN-I, we found that in TRIM6 knockout (TRIM6-KO) A549 cells, WNV replication is significantly increased and IFN-I induction and signaling are impaired compared to wild-type (wt) cells. IFN-β pretreatment was more effective in protecting against subsequent WNV infection in wt cells than TRIM6-KO, indicating that TRIM6 contributes to the establishment of an IFN-induced antiviral response against WNV. Using next-generation sequencing, we identified VAMP8 as a potential factor involved in this TRIM6-mediated antiviral response. VAMP8 knockdown resulted in reduced JAK1 and STAT1 phosphorylation and impaired induction of several interferon-stimulated genes (ISGs) following WNV infection or IFN-β treatment. Furthermore, VAMP8-mediated STAT1 phosphorylation required the presence of TRIM6. Therefore, the VAMP8 protein is a novel regulator of IFN-I signaling, and its expression and function are dependent on TRIM6 activity. Overall, these results provide evidence that TRIM6 contributes to the antiviral response against WNV and identify VAMP8 as a novel regulator of the IFN-I system.IMPORTANCE WNV is a mosquito-borne flavivirus that poses a threat to human health across large discontinuous areas throughout the world. Infection with WNV results in febrile illness, which can progress to severe neurological disease. Currently, there are no approved treatment options to control WNV infection. Understanding the cellular immune responses that regulate viral replication is important in diversifying the resources available to control WNV. Here, we show that the elimination of TRIM6 in human cells results in an increase in WNV replication and alters the expression and function of other components of the IFN-I pathway through VAMP8. Dissecting the interactions between WNV and host defenses both informs basic molecular virology and promotes the development of host- and virus-targeted antiviral strategies.

Intranasal Delivery of Peptide-Morpholinos to Knockdown Influenza Host Factors in Mice

Influenza viruses replicate primarily in the lung tissue of different host species. For efficient replication the virus utilizes host factors that are expressed in target cells. Cell-penetrating peptide-conjugated Morpholino oligomers (PPMOs) designed to target viral proteins have shown promising results as potential antiviral drugs in tissue culture and animal models. However, since viruses tend to have high rates of mutations, targeting viral proteins may result in viral escape mutants. An alternative approach to inhibit virus replication with PPMOs is to target host factors that are required for virus replication. Delivery of PPMO through the intranasal route has been shown to be effective in knockdown of host factors or microbial genes leading to protection against respiratory pathogens and reduced microbial burden. In addition, protective host innate antiviral immune responses in the lung can be studied by knockdown of immune signaling factors using PPMOs. Here we describe a successful approach using PPMOs to knockdown either proviral or antiviral host factors leading to changes in influenza virus replication in the lungs of mice, providing a tool to investigate immune responses and host-virus interactions in vivo.

The Host E3-Ubiquitin Ligase TRIM6 Ubiquitinates the Ebola Virus VP35 Protein and Promotes Virus Replication

Ebola virus (EBOV), a member of the Filoviridae family, is a highly pathogenic virus that causes severe hemorrhagic fever in humans and is responsible for epidemics throughout sub-Saharan, central, and West Africa. The EBOV genome encodes VP35, an important viral protein involved in virus replication by acting as an essential cofactor of the viral polymerase as well as a potent antagonist of the host antiviral type I interferon (IFN-I) system. By using mass spectrometry analysis and coimmunoprecipitation assays, we show here that VP35 is ubiquitinated on lysine 309 (K309), a residue located on its IFN antagonist domain. We also found that VP35 interacts with TRIM6, a member of the E3-ubiquitin ligase tripartite motif (TRIM) family. We recently reported that TRIM6 promotes the synthesis of unanchored K48-linked polyubiquitin chains, which are not covalently attached to any protein, to induce efficient antiviral IFN-I-mediated responses. Consistent with this notion, VP35 also associated noncovalently with polyubiquitin chains and inhibited TRIM6-mediated IFN-I induction. Intriguingly, we also found that TRIM6 enhances EBOV polymerase activity in a minigenome assay and TRIM6 knockout cells have reduced replication of infectious EBOV, suggesting that VP35 hijacks TRIM6 to promote EBOV replication through ubiquitination. Our work provides evidence that TRIM6 is an important host cellular factor that promotes EBOV replication, and future studies will focus on whether TRIM6 could be targeted for therapeutic intervention against EBOV infection.IMPORTANCE EBOV belongs to a family of highly pathogenic viruses that cause severe hemorrhagic fever in humans and other mammals with high mortality rates (40 to 90%). Because of its high pathogenicity and lack of licensed antivirals and vaccines, EBOV is listed as a tier 1 select-agent risk group 4 pathogen. An important mechanism for the severity of EBOV infection is its suppression of innate immune responses. The EBOV VP35 protein contributes to pathogenesis, because it serves as an essential cofactor of the viral polymerase as well as a potent antagonist of innate immunity. However, how VP35 function is regulated by host cellular factors is poorly understood. Here, we report that the host E3-ubiquitin ligase TRIM6 promotes VP35 ubiquitination and is important for efficient virus replication. Therefore, our study identifies a new host factor, TRIM6, as a potential target in the development of antiviral drugs against EBOV.