Regulation of Apoptosis by Enteroviruses

Assessment of Kinome-Wide Activity Remodeling upon Picornavirus Infection

Picornaviridae represent a large family of single-stranded positive RNA viruses of which different members can infect both humans and animals. These include the enteroviruses (e.g., poliovirus, coxsackievirus, and rhinoviruses) as well as the cardioviruses (e.g., encephalomyocarditis virus). Picornaviruses have evolved to interact with, use, and/or evade cellular host systems to create the optimal environment for replication and spreading. It is known that viruses modify kinase activity during infection, but a proteome-wide overview of the (de)regulation of cellular kinases during picornavirus infection is lacking. To study the kinase activity landscape during picornavirus infection, we here applied dedicated targeted mass spectrometry-based assays covering ∼40% of the human kinome. Our data show that upon infection, kinases of the MAPK pathways become activated (e.g., ERK1/2, RSK1/2, JNK1/2/3, and p38), while kinases involved in regulating the cell cycle (e.g., CDK1/2, GWL, and DYRK3) become inactivated. Additionally, we observed the activation of CHK2, an important kinase involved in the DNA damage response. Using pharmacological kinase inhibitors, we demonstrate that several of these activated kinases are essential for the replication of encephalomyocarditis virus. Altogether, the data provide a quantitative understanding of the regulation of kinome activity induced by picornavirus infection, providing a resource important for developing novel antiviral therapeutic interventions.

Miltefosine reduces coxsackievirus B3 lethality of mice with enhanced STAT3 activation

Coxsackievirus B3 (CVB3), one serotype of enteroviruses, can induce fatal myocarditis and hepatitis in neonates, but both treatment and vaccine are unavailable. Few reports tested antivirals to reduce CVB3. Several antivirals were developed against other enterovirus serotypes, but these antivirals failed in clinical trials due to side effects and drug resistance. Repurposing of clinical drugs targeting cellular factors, which enhance viral replication, may be another option. Parasite and cancer studies showed that the cellular protein kinase B (Akt) decreases interferon (IFN), apoptosis, and interleukin (IL)-6-induced STAT3 responses, which suppress CVB3 replication. Furthermore, miltefosine, the Akt inhibitor used in the clinic for parasite infections, enhances IL-6, IFN, and apoptosis responses in treated patients, suggesting that miltefosine could be the potential antiviral for CVB3. This study was therefore designated to test the antiviral effects of miltefosine against CVB3 in vitro and especially, in mice, as few studies test miltefosine in vitro, but not in vivo. In vitro results showed that miltefosine inhibited viral replication with enhanced activation of the cellular transcription factor, STAT3, which is reported to reduce CVB3 both in vitro and in mice. Notably, STAT3 knockdown abolished the anti-CVB3 activity of miltefosine in vitro. Mouse studies demonstrated that miltefosine pretreatment reduced CVB3 lethality of mice with decreased virus loads, organ damage, and apoptosis, but enhanced STAT3 activation. Miltefosine could be prophylaxis for CVB3 by targeting Akt to enhance STAT3 activation in the mechanism, which is independent of IFN responses and hardly reported in pathogen infections.

Viroporins Manipulate Cellular Powerhouses and Modulate Innate Immunity

Viruses have a wide repertoire of molecular strategies that focus on their replication or the facilitation of different stages of the viral cycle. One of these strategies is mediated by the activity of viroporins, which are multifunctional viral proteins that, upon oligomerization, exhibit ion channel properties with mild ion selectivity. Viroporins facilitate multiple processes, such as the regulation of immune response and inflammasome activation through the induction of pore formation in various cell organelle membranes to facilitate the escape of ions and the alteration of intracellular homeostasis. Viroporins target diverse membranes (such as the cellular membrane), endoplasmic reticulum, and mitochondria. Cumulative data regarding the importance of mitochondria function in multiple processes, such as cellular metabolism, energy production, calcium homeostasis, apoptosis, and mitophagy, have been reported. The direct or indirect interaction of viroporins with mitochondria and how this interaction affects the functioning of mitochondrial cells in the innate immunity of host cells against viruses remains unclear. A better understanding of the viroporin-mitochondria interactions will provide insights into their role in affecting host immune signaling through the mitochondria. Thus, in this review, we mainly focus on descriptions of viroporins and studies that have provided insights into the role of viroporins in hijacked mitochondria.

Acyl-Coenzyme A Synthetase Long-Chain Family Member 4 Is Involved in Viral Replication Organelle Formation and Facilitates Virus Replication via Ferroptosis

Enterovirus infections can cause severe complications, such as poliomyelitis, encephalitis, myocarditis, meningitis, neurological pulmonary edema, and even death. Here, we used genome-wide CRISPR screens to gain new insight into the mechanism by which enteroviruses co-opt host pathways to potentiate replication and propagation. We found that acyl-coenzyme A synthetase long-chain family member 4 (ACSL4) is involved in viral replication organelle formation. ACSL4 is a key component of ferroptosis, an iron-dependent, nonapoptotic programmed cell death. Our results indicated that enteroviruses and coronaviruses can induce ferroptosis via ACSL4. Most importantly, ferroptosis inhibitors, including two FDA-approved drugs, rosiglitazone (ROSI; ACSL4 inhibitor) and pioglitazone (PIO; ACSL4 inhibitor), decreased the viral load of human enteroviruses and coronaviruses, suggesting that ACSL4 is a target for counteracting viral infection. IMPORTANCE We provide the first evidence for the role of ACSL4 in enterovirus replication organelle formation. Moreover, both enteroviruses and coronaviruses induce ferroptosis via ACSL4. These findings establish a novel regulatory mechanism for viral replication. The inhibition of ACSL4 by ferroptosis inhibitors can reduce viral yields of enteroviruses and coronaviruses, including SARS-CoV-2, implying that ACSL4-mediated ferroptosis is a promising therapeutic target for viral diseases.

Apoptosis Enhances the Replication of Human Coronavirus OC43

Human coronavirus OC43 (HCoV-OC43) is one of the coronaviruses causing a mild common cold, but few studies have been made on this strain. Here, we identified the molecular mechanisms involved in HCoV-OC43-induced apoptosis and its implications for viral reproduction in Vero cells and MRC-5 cells. HCoV-OC43 infection induced apoptosis that was accompanied by cleavage of caspase-3 and PARP, degradation of cyclin D1, and cell cycle arrest at S and G2M phases. Dephosphorylation of STAT1 and STAT3, induced by HCoV-OC43 infection, was also associated with HCoV-OC43-mediated apoptosis. The pan-caspase inhibitor effectively prevented HCoV-OC43-induced apoptosis and reduced viral replication, suggesting that apoptosis contributes to viral replication. Collectively our results indicate that HCoV-OC43 induces caspase-dependent apoptosis to promote viral replication in Vero cells and MRC-5 cells.

Myocardial Damage by SARS-CoV-2: Emerging Mechanisms and Therapies

Evidence is emerging that severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) can infect various organs of the body, including cardiomyocytes and cardiac endothelial cells in the heart. This review focuses on the effects of SARS-CoV-2 in the heart after direct infection that can lead to myocarditis and an outline of potential treatment options. The main points are: (1) Viral entry: SARS-CoV-2 uses specific receptors and proteases for docking and priming in cardiac cells. Thus, different receptors or protease inhibitors might be effective in SARS-CoV-2-infected cardiac cells. (2) Viral replication: SARS-CoV-2 uses RNA-dependent RNA polymerase for replication. Drugs acting against ssRNA(+) viral replication for cardiac cells can be effective. (3) Autophagy and double-membrane vesicles: SARS-CoV-2 manipulates autophagy to inhibit viral clearance and promote SARS-CoV-2 replication by creating double-membrane vesicles as replication sites. (4) Immune response: Host immune response is manipulated to evade host cell attacks against SARS-CoV-2 and increased inflammation by dysregulating immune cells. Efficiency of immunosuppressive therapy must be elucidated. (5) Programmed cell death: SARS-CoV-2 inhibits programmed cell death in early stages and induces apoptosis, necroptosis, and pyroptosis in later stages. (6) Energy metabolism: SARS-CoV-2 infection leads to disturbed energy metabolism that in turn leads to a decrease in ATP production and ROS production. (7) Viroporins: SARS-CoV-2 creates viroporins that lead to an imbalance of ion homeostasis. This causes apoptosis, altered action potential, and arrhythmia.

Proteomics approaches for the identification of protease substrates during virus infection

Proteases precisely and irreversibly catalyze the hydrolysis of peptide bonds, regulating the fate, localization, and activity of many proteins. Consequently, proteolytic activity plays an important role in fundamental cellular processes such as differentiation and migration, immunological and inflammatory reactions, apoptosis and survival. During virus infection, host proteases are involved in several processes, from cell entry to initiation, progression and resolution of inflammation. On the other hand, many viruses encode their own highly specific proteases, responsible for the proteolytic processing of viral proteins, but, at the same time, to cleave host proteins to corrupt antiviral host responses and adjust protein activity to favor viral replication. Traditionally, protease substrate identification has been addressed by means of hypothesis-driven approaches, but recent advances in proteomics have made a toolkit available to uncover the extensive repertoire of host proteins cleaved during infection, either by viral or host proteases. Here, we review the currently available proteomics-based methods that can and have contributed to the systematic and unbiased identification of new protease substrates in the context of virus-host interactions. The role of specific proteases during the course of virus infections will also be highlighted.

Rhinovirus and Cell Death

Rhinoviruses (RVs) are the etiological agents of upper respiratory tract infections, particularly the common cold. Infections in the lower respiratory tract is shown to cause severe disease and exacerbations in asthma and COPD patients. Viruses being obligate parasites, hijack host cell pathways such as programmed cell death to suppress host antiviral responses and prolong viral replication and propagation. RVs are non-enveloped positive sense RNA viruses with a lifecycle fully contained within the cytoplasm. Despite decades of study, the details of how RVs exit the infected cell are still unclear. There are some diverse studies that suggest a possible role for programmed cell death. In this review, we aimed to consolidate current literature on the impact of RVs on cell death to inform future research on the topic. We searched peer reviewed English language literature in the past 21 years for studies on the interaction with and modulation of cell death pathways by RVs, placing it in the context of the broader knowledge of these interconnected pathways from other systems. Our review strongly suggests a role for necroptosis and/or autophagy in RV release, with the caveat that all the literature is based on RV-A and RV-B strains, with no studies to date examining the interaction of RV-C strains with cell death pathways.

Effects of Deformed Wing Virus Infection on Expressions of Immune- and Apoptosis-Related Genes in Western Honeybees (Apis mellifera)

Honeybees are globally threatened by several pathogens, especially deformed wing virus (DWV), as the presence of DWV in western honeybees is indicative of colony loss. The high mortality rate is further exacerbated by the lack of effective treatment, and therefore understanding the immune and apoptosis responses could pave an avenue for the treatment method. In this study, DWV was directly injected into the white-eyed pupae stage of western honeybees (Apis mellifera). The DWV loads and selected gene responses were monitored using the real-time PCR technique. The results showed that honeybee pupae that were injected with the highest concentration of viral loads showed a significantly higher mortality rate than the control groups. Deformed wings could be observed in newly emerged adult bees when the infected bees harbored high levels of viral loads. However, the numbers of viral loads in both normal and crippled wing groups were not significantly different. DWV-injected honeybee pupae with 104 and 107 copy numbers per bee groups showed similar viral loads after 48 h until newly emerged adult bees. Levels of gene expression including immune genes (defensin, abaecin, and hymenoptaecin) and apoptosis genes (buffy, p53, Apaf1, caspase3-like, caspase8-like, and caspase9-like) were analyzed after DWV infection. The expressions of immune and apoptosis genes were significantly different in infected bees compared to those of the control groups. In the pupae stage, the immune genes were activated by injecting DWV (defensin and hymenoptaecin) or Escherichia coli (defensin, abaecin, and hymenoptaecin), a positive control. On the contrary, the expression of apoptosis-related genes (buffy, caspase3-like, caspase8-like, and caspase9-like genes) was suppressed at 96 h post-infection. In DWV-infected newly emerged adult bees, abaecin, hymenoptaecin, Apaf1, and caspase8-like genes were upregulated. However, these genes were not significantly different between the normal and crippled wing bees. Our results suggested that DWV could activate the humoral immunity in honeybees and that honeybee hosts may be able to protect themselves from the virus infection through immune responses. Apoptosis gene expressions were upregulated in newly emerged adult bees by the virus, however, they were downregulated during the initial phase of viral infection.