ABSTRACT
Objective: COVID-19 has emerged as a significant global health crisis causing devastating effects on world population accounting for over 6 million deaths worldwide. Although acute RTI is the prevalent cause of morbidity, kidney outcomes centered on a spectrum of AKI have evolved over the course of the pandemic. Especially the emerging variants have posed a daunting challenge to the scientific communities, prompting an urging requirement for global contributions in understanding the viral dynamics. In addition to canonical genes, several subgroup- specific accessory genes are located between the S and E genes of coronaviruses regarding which little is known. Previous studies have shown that accessory proteins (aps) in viruses function as viroporins that regulate viral infection, propagation and egress [1]. In this study we attempted to characterize the function of aps of coronavirus variants as ion channels. Furthermore, we also probed the interaction of ap4 with the host system. Method(s): Serial passaging (selection pressure), growth kinetics, confocal imaging, genome sequence analysis and proteomics were performed in Huh-7, MRC5 cells and/or human monocyte derived macrophages. Potassium uptake assay was performed in a Saccharo myces cerevisiae strain, which lacks the potassium transporters trk1 and trk2. Ion conductivity experiments were performed in Xenopus laevis oocytes using Two Electrode Voltage Clamp (TEVC) method. Result(s): Serial passaging demonstrated the acquisition of several frameshift mutations in ORF4 resulting in C-terminally truncated protein versions (ap4 and ap4a) and indicate a strong selection pressure against retaining a complete ORF4 in vitro. Growth kinetics in primary cells illustrated a reduction of viral titers when the full-length ap4 was expressed compared to the C-terminally truncated protein ap4a. Confocal imaging showed that ap4 and ap4a are not exclusively located in a single cellular compartment. Potassium uptake assay in yeast and TEVC analyses in Xenopus oocytes showed that ap4 and ap4a act as a weak K+ selective ion channel. In addition, accessory proteins of other virus variants also elicited microampere range of currents. Conclusion(s): Our study provides the first evidence that ap4 and other accessory proteins of coronavirus variants act as viroporins. Future studies are aimed at demonstrating the role of ap4 during the viral life cycle by modulating ion homeostasis of host cell in vivo (interacting proteins obtained from proteomic studies) and thereby serve as a tool for potential drug target.
ABSTRACT
Background: The CoV-2 envelope (E) protein plays an important role in virus assembly, budding, immunopathogenesis and disease severity. E protein has ion channel activity, is located in Golgi and ER membranes of infected cells and is associated with inflammasome activation and immune dysregulation. Here we report that BIT225, an investigational HIV clinical compound, inhibits E ion channel activity and prevents body weight loss and mortality and reduces inflammation in lethally infected K18-hACE2 transgenic mice. BIT225 efficacy was observed when dosing was initiated before or 24 h or 48 h after infection. Method(s): SARS-CoV-2 E protein ion channel activity and Xenopus TMEM16A were measured in Xenopus oocytes. K18-hACE2 transgenic mice were infected intranasally with 104 pfu SARS CoV 2 (US-WA1/2020) and dosed orally twice daily with BIT225 for up to 12 Days. Dosing was initiated 12 h pre-infection or 24 h or 48 h post-infection. Disease parameters measured were survival, body weight, viral RNA by qPCR and infectious virus titre (plaque assay) in lung tissue homogenates and serum. In addition, levels of pro-inflammatory cytokines (IL-6, IL-1alpha, IL-1beta, TNFalpha & TGFbeta, MCP-1) were measured in lung and serum samples. Result(s): BIT225 inhibited ion channel activity of E-protein, but not that of TMEM16A in Xenopus oocytes. BIT225 dosed at 300mg/kg BID for 12 days starting 12 h pre-infection completely prevented body weight loss and mortality in SARS-CoV-2 infected K18 mice (n=12), while all vehicle-dosed animals reached a mortality endpoint by day 9 across two studies (n=12). Figure 1 shows results from a time of addition study: When treatment with BIT225 started at 24 h post-infection, body weight loss and mortality was also prevented (100% survival, n=5). In the group of mice where treatment started at 48 h after infection, body weight loss and mortality were prevented in 4 of 5 mice. Treatment efficacy was associated with significant reduction in lung viral load (3.5 log10), virus titer (4000 pfu/ml) and lung and serum cytokine levels. Conclusion(s): BIT225 is an inhibitor of SARS-CoV-2 E-protein viroporin activity. In the K18 model BIT225 protected mice from weight loss and death, inhibited virus replication and reduced inflammation. These effects were noted when treatment with BIT225 was initiated before or 24-48 hours after infection and validate viroporin E as a viable antiviral target and support the clinical study of BIT225 in treatment of SARS-CoV-2.
ABSTRACT
Functional investigations of enzymes involving cellular expression systems are important for pharmacological studies. The precise control of expression is challenging in transiently transfected mammalian cell lines. Here, we explored the ability of Xenopus laevis oocytes to express a membrane-bound enzyme for functional characterization using standard 96-well plates and a fluorescence-based plate reader assay. We microinjected oocytes with cRNA encoding the angiotensin converting enzyme 2 (ACE2) and measured the enzymatic activity in single oocytes using a commercial fluorescence-based assay. The injected oocytes showed up to a 50-fold increase in fluorescence compared to uninjected oocytes. This fluorescence intensity was dose-dependent on the amount of ACE2 cRNA. These results suggest that Xenopus oocytes can be used for the functional evaluation of membrane-bound enzymes, decreasing the experimental workload.