SAMHD1 Inhibits Multiple Enteroviruses by Interfering with the Interaction between VP1 and VP2 Proteins

ZYG11B suppresses multiple enteroviruses by triggering viral VP1 degradation

Enterovirus 71 (EV71) is a major cause of hand, foot, and mouth disease, particularly affecting pediatric populations worldwide. The role of ZYG11B, a CUL2-complex-associated E3 ubiquitin ligase from the Zyg-11 family, in antiviral defense against EV71 remains unclear. To our knowledge, this study is the first to reveal that ZYG11B targets EV71 VP1 for proteasomal degradation via the ubiquitin-proteasome pathway, with CRL2ZYG11B complex activity specifically driving K33-linked ubiquitination. Mass spectrometry and immunoprecipitation analyses confirmed the interaction between ZYG11B and VP1 and identified key domains required for binding both VP1 and CUL2. Comparative analyses showed that VP1 ubiquitination sites are highly conserved across related enteroviruses, including CA6, CA16, and EVD68. Functional assays further demonstrated that ZYG11B restricts these viruses, highlighting its potential as a broad-spectrum antiviral target. These findings establish ZYG11B as a critical effector in host antiviral responses and support its therapeutic potential for managing enterovirus infections.

IMPORTANCE

E3 ubiquitin ligases and deubiquitinases have become important topics of competition between viruses and hosts. Here, we identified CRL2ZYG11B as an E3 ubiquitin ligase complex capable of degrading structural protein VP1 of enteroviruses, making ZYG11B a broad-spectrum antiviral factor. We first proposed the inhibitory effect of ZYG11B on viruses and identified the structural domains of ZYG11B connecting substrates and CUL2, providing new targets for the design of antiviral drugs.

Platelet factor 4-derived C15 peptide broadly inhibits enteroviruses by disrupting viral attachment

Platelet factor 4 (PF4) has been shown to regulate several viral infections. Our previous study demonstrated that PF4 inhibits the entry of enterovirus A 71 (EV71) and coxsackievirus A16 (CA16), which cause hand, foot, and mouth disease (HFMD). In this study, we report that PF4 also inhibits the circulating HFMD pathogen coxsackievirus A6 (CA6) and the re-emerging enterovirus D68 (EVD68). A 15-amino acid peptide, C15, at the C-terminus of PF4 confers anti-viral activity against multiple enteroviruses (EVs) besides CA6 and EVD68, including EV71 and CA16. Mechanistic studies revealed that wild-type C15 with a net-positive charge (+3), but not its mutants C15M and C15A (both -1), specifically binds to the VP3 capsid protein of CA6 and EVD68, thereby disrupting their attachment to the host cell surface. In addition, VP3 of EVs contains a conserved domain (residues 155-170) crucial for binding to C15. An aspartic acid residue at position 156 imparts a net-negative charge to this domain, which, when substituted with a neutrally charged amino acid, reduces the binding affinity of VP3 for C15. Additionally, C15 protects neonatal mice from lethal challenge upon a CA6 infection. These results suggest that C15 is a promising broad-spectrum anti-viral candidate against multiple EVs.

IMPORTANCE

EVs, which pose a significant public health threat, can be classified into 15 species, with EV-A, -B, -C, and -D infecting humans and causing a wide range of diseases, from mild illnesses, such as HFMD, to more severe conditions, such as acute flaccid paralysis. The emergence of new and alternative strains highlights the urgent need for broad-spectrum anti-viral agents. In this study, we identified that the C15 of PF4 exhibits potent anti-viral activity against multiple EVs by binding to their surface and blocking their entry into host cells. Furthermore, C15 provides significant protection in vivo. These findings highlight the potential of C15 as a broad-spectrum anti-viral candidate. Our study opens a new avenue for developing treatments to combat the diverse and evolving threats posed by EVs.

Regulation of viral replication by host restriction factors

Viral infectious diseases, caused by numerous viruses including severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), influenza A virus (IAV), enterovirus (EV), human immunodeficiency virus (HIV), hepatitis B virus (HBV), and human papillomavirus (HPV), pose a continuous threat to global health. As obligate parasites, viruses rely on host cells to replicate, and host cells have developed numerous defense mechanisms to counteract viral infection. Host restriction factors (HRFs) are critical components of the early antiviral response. These cellular proteins inhibit viral replication and spread by impeding essential steps in the viral life cycle, such as viral entry, genome transcription and replication, protein translation, viral particle assembly, and release. This review summarizes the current understanding of how host restriction factors inhibit viral replication, with a primary focus on their diverse antiviral mechanisms against a range of viruses, including SARS-CoV-2, influenza A virus, enteroviruses, human immunodeficiency virus, hepatitis B virus, and human papillomavirus. In addition, we highlight the crucial role of these factors in shaping the host-virus interactions and discuss their potential as targets for antiviral drug development.

SAMHD1 enhances HIV-1-induced apoptosis in monocytic cells via the mitochondrial pathway

Sterile alpha motif (SAM) and histidine-aspartate (HD) domain-containing protein 1 (SAMHD1) inhibits HIV-1 replication in non-dividing cells by reducing the intracellular dNTP pool. SAMHD1 enhances spontaneous apoptosis in cells, but its effects on HIV-1-induced apoptosis and the underlying mechanisms remain unknown. Here we uncover a new mechanism by which SAMHD1 enhances HIV-1-induced apoptosis in monocytic cells through the mitochondrial pathway. We found that endogenous SAMHD1 enhances apoptosis levels induced by HIV-1 infection in dividing THP-1 cells. Mechanistically, SAMHD1 expression decreases the mitochondrial membrane potential and promotes cytochrome c release induced by HIV-1 infection in THP-1 cells, thereby enhancing mitochondrial apoptotic pathway. SAMHD1-enhanced apoptosis is associated with increased expression of the pro-apoptotic protein BCL-2-interacting killer (BIK) in cells. We further demonstrated that BIK contributes to SAMHD1-enhanced apoptosis during HIV-1 infection. Overall, our results reveal an unappreciated regulatory mechanism of SAMHD1 in enhancing HIV-1-induced apoptosis via the mitochondrial pathway in monocytic cells.

Emerging Therapeutics in the Fight Against EV-D68: A Review of Current Strategies

Enterovirus-D68 (EV-D68) was first identified in 1962 in pediatric patients with acute respiratory conditions in California, USA (US). From the 1970s to 2005, EV-D68 was underestimated due to limited data and serotyping methods. In 2014, the United States experienced outbreaks of acute flaccid myelitis (AFM) in children EV-D68 positive. WIN-like compounds (pleconaril, pocapavir, and vapendavir) bind to the virus capsid and have been tested against various enteroviruses (EVs) in clinical trials. However, these compounds encountered issues with resistance and adverse effects, which impeded their approval by the Food and Drug Administration (FDA). Presently, the medical field lacks FDA-approved antiviral treatments or vaccines for EV-D68. Ongoing research efforts are dedicated to identifying viable therapeutics to address EV-D68 infections. This review explores the current advancements in antiviral therapies and potential therapeutics to mitigate the significant impact of EV-D68 infection control.

Unveiling the Connection: Viral Infections and Genes in dNTP Metabolism

Deoxynucleoside triphosphates (dNTPs) are crucial for the replication and maintenance of genomic information within cells. The balance of the dNTP pool involves several cellular enzymes, including dihydrofolate reductase (DHFR), ribonucleotide reductase (RNR), and SAM and HD domain-containing protein 1 (SAMHD1), among others. DHFR is vital for the de novo synthesis of purines and deoxythymidine monophosphate, which are necessary for DNA synthesis. SAMHD1, a ubiquitously expressed deoxynucleotide triphosphohydrolase, converts dNTPs into deoxynucleosides and inorganic triphosphates. This process counteracts the de novo dNTP synthesis primarily carried out by RNR and cellular deoxynucleoside kinases, which are most active during the S phase of the cell cycle. The intracellular levels of dNTPs can influence various viral infections. This review provides a concise summary of the interactions between different viruses and the genes involved in dNTP metabolism.

Impaired influenza A virus replication by the host restriction factor SAMHD1 which inhibited by PA-mediated dephosphorylation of the host transcription factor IRF3

BACKGROUND

Influenza A virus (IAV) can cause severe and life-threatening illness in humans and animals. Therefore, it is important to search for host antiviral proteins and elucidate their antiviral mechanisms for the development of potential treatments. As a part of human innate immunity, host restriction factors can inhibit the replication of viruses, among which SAM and HD domain containing deoxynucleoside triphosphate triphosphohydrolase 1 (SAMHD1) can restrict the replication of viruses, such as HIV and enterovirus EV71. Viruses also developed countermeasures in the arms race with their hosts. There are few reports about whether SAMHD1 has a restriction effect on IAV.

METHODS

To investigate the impact of IAV infection on SAMHD1 expression in A549 cells, we infected A549 cells with a varying multiplicity of infection (MOI) of IAV and collected cell samples at different time points for WB and RT-qPCR analysis to detect viral protein and SAMHD1 levels. The virus replication level in the cell culture supernatant was determined using TCID50 assay. Luciferase assay was used to reveal that H5N1 virus polymerase acidic protein (PA) affected the activity of the SAMHD1 promoter. To assess the antiviral capacity of SAMHD1, we generated a knockdown and overexpressed cell line for detecting H5N1 replication.

RESULTS

In this study, we observed that SAMHD1 can restrict the intracellular replication of H5N1 and that the H5N1 viral protein PA can downregulate the expression of SAMHD1 by affecting SAMHD1 transcriptional promoter activity. We also found that SAMHD1's ability to restrict H5N1 is related to phosphorylation at 592-tyrosine.

CONCLUSIONS

In conclusion, we found that SAMHD1 may affect the replication of IAVs as a host restriction factor and be countered by PA. Furthermore, SAMHD1 may be a potential target for developing antiviral drugs.

The host antiviral protein SAMHD1 suppresses NF-κB activation by interacting with the IKK complex during inflammatory responses and viral infection

Sterile alpha motif and histidine-aspartate (HD) domain-containing protein 1 (SAMHD1) inhibits HIV-1 replication in nondividing cells by reducing the intracellular dNTP pool. SAMHD1 also suppresses NF-κB activation induced by inflammatory stimuli and viral infections. Specifically, SAMHD1-mediated reduction of NF-κB inhibitory protein (IκBα) phosphorylation is important for the suppression of NF-κB activation. However, while the inhibitors of NF-κB kinase subunit alpha and beta (IKKα and IKKβ) regulate IκBα phosphorylation, the mechanism by which SAMHD1 regulates phosphorylation of IκBα remains unclear. Here, we report that SAMHD1 suppresses phosphorylation of IKKα/β/γ via interaction with IKKα and IKKβ, thus inhibiting subsequent phosphorylation of IκBα in monocytic THP-1 cells and differentiated nondividing THP-1 cells. We show that knockout of SAMHD1 enhanced phosphorylation of IKKα, IKKβ, and IKKγ in THP-1 cells treated with the NF-κB activator lipopolysaccharide or infected with Sendai virus and SAMHD1 reconstitution inhibited phosphorylation of IKKα/β/γ in Sendai virus-infected THP-1 cells. We demonstrate that endogenous SAMHD1 interacted with IKKα and IKKβ in THP-1 cells and recombinant SAMHD1 bound to purified IKKα or IKKβ directly in vitro. Mapping of these protein interactions showed that the HD domain of SAMHD1 interacts with both IKKα and IKKβ and that the kinase domain of IKKα and the ubiquitin-like domain of IKKβ are required for their interactions with SAMHD1, respectively. Moreover, we found that SAMHD1 disrupts the interaction between upstream kinase TAK1 and IKKα or IKKβ. Our findings identify a new regulatory mechanism by which SAMHD1 inhibits phosphorylation of IκBα and NF-κB activation.

Vemurafenib Inhibits Enterovirus A71 Genome Replication and Virus Assembly

Enterovirus A71 (EV-A71) infection is a major cause of hand, foot, and mouth disease (HFMD), which may be occasionally associated with severe neurological complications. There is currently a lack of treatment options for EV-A71 infection. The Raf-MEK-ERK signaling pathway, in addition to its critical importance in the regulation of cell growth, differentiation, and survival, has been shown to be essential for virus replication. In this study, we investigated the anti-EV-A71 activity of vemurafenib, a clinically approved B-Raf inhibitor used in the treatment of late-stage melanoma. Vemurafenib exhibits potent anti-EV-A71 effect in cytopathic effect inhibition and viral load reduction assays, with half maximal effective concentration (EC50) at nanomolar concentrations. Mechanistically, vemurafenib interrupts both EV-A71 genome replication and assembly. These findings expand the list of potential antiviral candidates of anti-EV-A71 therapeutics.

Host Restrictive Factors Are the Emerging Storm Troopers Against Enterovirus: A Mini-Review

Enterovirus infection continues to be a global health problem. The lack of specific drugs and broad-spectrum vaccines means an urgent need to develop effective strategies against enteroviruses. Host restrictive factors are a class of intrinsic host antiviral factors that have been broadly defined and investigated during HIV infections and have great significance for drug development and treatment design. In recent years, the essential role of host restrictive factors in regulating enteroviral infections has been gradually recognized and investigated. An increasing number of studies have shown that host-restrictive factors regulate multiple steps in the life cycle of enteroviruses. This mini-review discusses the restrictive factors against enteroviruses, their antiviral mechanism, and the arms race between them and enteroviruses. We also summarise the pathways that enteroviruses use to impair host antiviral signals. This mini-review characterizes the essential role of host restriction factors in enterovirus infections, which provides ideas and potential targets for antiviral drug design by regulating host restrictive factors. It also reveals potential future research on the interplay between host restrictive factors and enteroviruses.