Host serine proteases TMPRSS2 and TMPRSS11D mediate proteolytic activation and trypsin-independent infection in group A rotaviruses

Structural basis of TMPRSS11D specificity and autocleavage activation

Transmembrane Protease, Serine-2 (TMPRSS2) and TMPRSS11D are human proteases that enable SARS-CoV-2 and Influenza A/B virus infections, but their biochemical mechanisms for facilitating viral cell entry remain unclear. We show these proteases spontaneously and efficiently cleave their own zymogen activation motifs, activating their broader protease activity on cellular substrates. We determine TMPRSS11D co-crystal structures with a native and an engineered activation motif, revealing insights into its autocleavage activation and distinct substrate binding cleft features. Leveraging this structural data, we develop nanomolar potency peptidomimetic inhibitors of TMPRSS11D and TMPRSS2. We show that a broad serine protease inhibitor that underwent clinical trials for TMPRSS2-targeted COVID-19 therapy, nafamostat mesylate, was rapidly cleaved by TMPRSS11D and converted to low activity derivatives. In this work, we develop mechanistic insights into human protease viral tropism and highlight both the strengths and limitations of existing human serine protease inhibitors, informing future drug discovery efforts targeting these proteases.

DON/DRP-104 as potent serine protease inhibitors implicated in SARS-CoV-2 infection: Comparative binding modes with human TMPRSS2 and novel therapeutic approach

Human transmembrane serine protease 2 (TMPRSS2) is an important member of the type 2 transmembrane serine protease (TTSP) family with significant therapeutic markings. The search for potent TMPRSS2 inhibitors against severe acute respiratory syndrome coronavirus 2 infection with favorable tissue specificity and off-site toxicity profiles remains limited. Therefore, probing the anti-TMPRSS2 potential of enhanced drug delivery systems, such as nanotechnology and prodrug systems, has become compelling. We report the first in silico study of TMPRSS2 against a prodrug, [isopropyl(S)-2-((S)-2-acetamido-3-(1H-indol-3-yl)-propanamido)-6-diazo-5-oxo-hexanoate] also known as DRP-104 synthesized from 6-Diazo-5-oxo-l-norleucine (DON). We performed comparative studies on DON and DRP-104 against a clinically potent TMPRSS2 inhibitor, nafamostat, and a standard serine protease inhibitor, 4-(2-Aminoethyl) benzenesulfonyl fluoride (AEBSF) against TMPRSS2 and found improved TMPRSS2 inhibition through synergistic binding of the S1/S1' subdomains. Both DON and DRP-104 had better thermodynamic profiles than AEBSF and nafamostat. DON was found to confer structural stability with strong positive correlated inter-residue motions, whereas DRP-104 was found to confer kinetic stability with restricted residue displacements and reduced loop flexibility. Interestingly, the Scavenger Receptor Cysteine-Rich (SRCR) domain of TMPRSS2 may be involved in its inhibition mechanics. Two previously unidentified loops, designated X (270-275) and Y (293-296) underwent minimal and major structural transitions, respectively. In addition, residues 273-277 consistently transitioned to a turn conformation in all ligated systems, whereas unique transitions were identified for other transitioning residue groups in each TMPRSS2-inhibitor complex. Intriguingly, while both DON and DRP-104 showed similar loop transition patterns, DRP-104 preserved loop structural integrity. As evident from our systematic comparative study using experimentally/clinically validated inhibitors, DRP-104 may serve as a potent and novel TMPRSS2 inhibitor and warrants further clinical investigation.

Existing Evidence for Influenza B Virus Adaptations to Drive Replication in Humans as the Primary Host

Influenza B virus (IBV) is one of the two major types of influenza viruses that circulate each year. Unlike influenza A viruses, IBV does not harbor pandemic potential due to its lack of historical circulation in non-human hosts. Many studies and reviews have highlighted important factors for host determination of influenza A viruses. However, much less is known about the factors driving IBV replication in humans. We hypothesize that similar factors influence the host restriction of IBV. Here, we compile and review the current understanding of host factors crucial for the various stages of the IBV viral replication cycle. While we discovered the research in this area of IBV is limited, we review known host factors that may indicate possible host restriction of IBV to humans. These factors include the IBV hemagglutinin (HA) protein, host nuclear factors, and viral immune evasion proteins. Our review frames the current understanding of IBV adaptations to replication in humans. However, this review is limited by the amount of research previously completed on IBV host determinants and would benefit from additional future research in this area.

Upamostat: a serine protease inhibitor for antiviral, gastrointestinal, and anticancer indications

INTRODUCTION

Serine proteases are involved in many normal metabolic processes but also contribute to diseases of several organ systems, including viral and gastrointestinal diseases and oncology. Upamostat is an orally bioavailable prodrug of WX-UK1, which is most active against trypsins and closely related enzymes.

AREAS COVERED

Research over the past two decades suggests several diseases in the three areas noted above which upamostat may be active. Upamostat has been studied clinically against several cancers and for outpatient treatment of COVID-19. Preclinical and clinical pharmacokinetic and metabolism studies demonstrate good bioavailability, sustained tissue levels, and high concentrations of the active moiety, WX-UK1, in stool, potentially important for treatment of gastrointestinal diseases. Clinical studies suggest activity against SARS-CoV-2; results against pancreatic cancer are also encouraging, though studies in both indications are not definitive. The drug was very well tolerated for periods of 2 weeks to several months.

EXPERT OPINION

Upamostat is an orally bioavailable serine protease inhibitor with an excellent safety profile and favorable pharmacokinetic properties. It has demonstrated preliminary evidence of efficacy against COVID-19, and nonclinical data suggest potential applicability against other viral illnesses, gastrointestinal diseases, and cancer.

Advances in the development of antivirals for rotavirus infection

Rotavirus (RV) causes 200,000 deaths per year and imposes a serious burden to public health and livestock farming worldwide. Currently, rehydration (oral and intravenous) remains the main strategy for the treatment of rotavirus gastroenteritis (RVGE), and no specific drugs are available. This review discusses the viral replication cycle in detail and outlines possible therapeutic approaches including immunotherapy, probiotic-assisted therapy, anti-enteric secretory drugs, Chinese medicine, and natural compounds. We present the latest advances in the field of rotavirus antivirals and highlights the potential use of Chinese medicine and natural compounds as therapeutic agents. This review provides an important reference for rotavirus prevention and treatment.

Isolation and Characterization of Distinct Rotavirus A in Bat and Rodent Hosts

Rotavirus A (RVA) causes diarrheal disease in humans and various animals. Recent studies have identified bat and rodent RVAs with evidence of zoonotic transmission and genome reassortment. However, the virological properties of bat and rodent RVAs with currently identified genotypes still need to be better clarified. Here, we performed virus isolation-based screening for RVA in animal specimens and isolated RVAs (representative strains: 16-06 and MpR12) from Egyptian fruit bat and Natal multimammate mouse collected in Zambia. Whole-genome sequencing and phylogenetic analysis revealed that the genotypes of bat RVA 16-06 were identical to that of RVA BATp39 strain from the Kenyan fruit bat, which has not yet been characterized. Moreover, all segments of rodent RVA MpR12 were highly divergent and assigned to novel genotypes, but RVA MpR12 was phylogenetically closer to bat RVAs than to other rodent RVAs, indicating a unique evolutionary history. We further investigated the virological properties of the isolated RVAs. In brief, we found that 16-06 entered cells by binding to sialic acids on the cell surface, while MpR12 entered in a sialic acid-independent manner. Experimental inoculation of suckling mice with 16-06 and MpR12 revealed that these RVAs are causative agents of diarrhea. Moreover, 16-06 and MpR12 demonstrated an ability to infect and replicate in a 3D-reconstructed primary human intestinal epithelium with comparable efficiency to the human RVA. Taken together, our results detail the unique genetic and virological features of bat and rodent RVAs and demonstrate the need for further investigation of their zoonotic potential. IMPORTANCE Recent advances in nucleotide sequence detection methods have enabled the detection of RVA genomes from various animals. These studies have discovered multiple divergent RVAs and have resulted in proposals for the genetic classification of novel genotypes. However, most of these RVAs have been identified via dsRNA viral genomes and not from infectious viruses, and their virological properties, such as cell/host tropisms, transmissibility, and pathogenicity, are unclear and remain to be clarified. Here, we successfully isolated RVAs with novel genome constellations from three bats and one rodent in Zambia. In addition to whole-genome sequencing, the isolated RVAs were characterized by glycan-binding affinity, pathogenicity in mice, and infectivity to the human gut using a 3D culture of primary intestinal epithelium. Our study reveals the first virological properties of bat and rodent RVAs with high genetic diversity and unique evolutional history and provides basic knowledge to begin estimating the potential of zoonotic transmission.

A comprehensive analysis of mRNA expression profiles of Esophageal Squamous Cell Carcinoma reveals downregulation of Desmoglein 1 and crucial genomic targets

AIM

Esophageal Squamous Cell Carcinoma (ESCC) is a histological subtype of esophageal cancer that begins in the squamous cells in the esophagus. In only 19% of the ESCC-diagnosed patients, a five-year survival rate has been seen. This necessitates the identification of high-confidence biomarkers for early diagnosis, prognosis, and potential therapeutic targets for the mitigation of ESCC.

METHOD

We performed a meta-analysis of 10 mRNA datasets and identified consistently perturbed genes across the studies. Then, integrated with ESCC ATLAS to segregate 'core' genes to identify consequences of primary gene perturbation events leading to gene-gene interactions and dysregulated molecular signaling pathways. Further, by integrating with toxicogenomics data, inferences were drawn for gene interaction with environmental exposures, trace elements, chemical carcinogens, and drug chemicals. We also deduce the clinical outcomes of candidate genes based on survival analysis using the ESCC related dataset in The Cancer Genome Atlas.

RESULT

We identified 237 known and 18 novel perturbed candidate genes. Desmoglein 1 (DSG1) is one such gene that we found significantly downregulated (Fold Change =-1.89, p-value = 8.2e-06) in ESCC across six different datasets. Further, we identified 31 'core' genes (that either harbor genetic variants or are regulated by epigenetic modifications) and found regulating key biological pathways via adjoining genes in gene-gene interaction networks. Functional enrichment analysis showed dysregulated biological processes and pathways including "Extracellular matrix", "Collagen trimmer" and "HPV infection" are significantly overrepresented in our candidate genes. Based on the toxicogenomic inferences from Comparative Toxicogenomics Database we report the key genes that interacted with risk factors such as tobacco smoking, zinc, nitroso benzylmethylamine, and drug chemicals such as cisplatin, Fluorouracil, and Mitomycin in relation to ESCC. We also point to the STC2 gene that shows a high risk for mortality in ESCC patients.

CONCLUSION

We identified novel perturbed genes in relation to ESCC and explored their interaction network. DSG1 is one such gene, its association with microbiota and a clinical presentation seen commonly with ESCC hints that it is a good candidate for early diagnostic marker. Besides, in this study we highlight candidate genes and their molecular connections to risk factors, biological pathways, drug chemicals, and the survival probability of ESCC patients.

Serotype I and II Feline Coronavirus Replication and Gene Expression Patterns of Feline Cells-Building a Better Understanding of Serotype I FIPV Biology

Feline infectious peritonitis (FIP) is a disease of domestic cats caused by the genetic variant of the feline coronavirus (FCoV) and feline infectious peritonitis virus (FIPV), currently grouped into two serotypes, I and II. Although serotype I FIPV is more prevalent in cats with FIP, serotype II has been more extensively studied in vitro due to the relative ease in propagating this viral serotype in culture systems. As a result, more is known about serotype II FIPV than the more biologically prevalent serotype I. The primary cell receptor for serotype II has been determined, while it remains unknown for serotype I. The recent development of a culture-adapted feline cell line that more effectively propagates serotype I FIPV, FCWF-4 CU, derived from FCWF-4 cells available through the ATCC, offers the potential for an improved understanding of serotype I FIPV biology. To learn more about FIPV receptor biology, we determined targeted gene expression patterns in feline cells variably permissive to replication of serotype I or II FIPV. We utilized normal feline tissues to determine the immunohistochemical expression patterns of two known coronavirus receptors, ACE2 and DC-SIGN. Lastly, we compared the global transcriptomes of the two closely related FCWF-4 cell lines and identified viral transcripts with potential importance for the differential replication kinetics of serotype I FIPV.

Evolutionary history of type II transmembrane serine proteases involved in viral priming

Type II transmembrane serine proteases (TTSPs) are a family of trypsin-like membrane-anchored serine proteases that play key roles in the regulation of some crucial processes in physiological conditions, including cardiac function, digestion, cellular iron homeostasis, epidermal differentiation, and immune responses. However, some of them, in particular TTSPs expressed in the human airways, were identified as host factors that promote the proteolytic activation and spread of respiratory viruses such as influenza virus, human metapneumovirus, and coronaviruses, including SARS-CoV-2. Given their involvement in viral priming, we hypothesized that members of the TTSP family may represent targets of positive selection, possibly as the result of virus-driven pressure. Thus, we investigated the evolutionary history of sixteen TTSP genes in mammals. Evolutionary analyses indicate that most of the TTSP genes that have a verified role in viral proteolytic activation present signals of pervasive positive selection, suggesting that viral infections represent a selective pressure driving the evolution of these proteases. We also evaluated genetic diversity in human populations and we identified targets of balancing selection in TMPRSS2 and TMPRSS4. This scenario may be the result of an ancestral and still ongoing host–pathogen arms race. Overall, our results provide evolutionary information about candidate functional sites and polymorphic positions in TTSP genes.

[Investigation of viruses harbored by wild animals: toward pre-emptive measures against future zoonotic diseases]

Zoonoses are caused by pathogens transmitted from animals. To prepare mitigating measures against emerging zoonoses, it is imperative to identify animal reservoirs that carry potential pathogens and also elucidate the transmission routes of these pathogens. Under the continuous collaboration with counterparts from Zambia and Indonesia, we have so far identified various viruses in wild animals. Some of the identified viruses were phylogenetically distinct from known virus species and this finding led to approved new virus species by the International Committee on Taxonomy of Viruses (ICTV). Our studies provided new insights into the divergence, natural hosts and lifecycle of viruses. Through the exploration and characterization of viruses in animals, we will endeavor to contribute to the existing knowledge on viral pathogens in wild animals. This is cardinal for evidence-based preemptive measures against future zoonoses.

Perspectives for the optimization and utility of the rotavirus reverse genetics system

Following Kobayashi and colleagues' seminal paper in 20171, in the past four years the rotavirus (RV) field has witnessed a burst in research and publications based on the use of a fully plasmid-based RV reverse genetics systems and subsequent modifications2,3. However, in most cases, the rotaviral strain under interrogation has been the prototypic simian RV SA11-L2 strain (G3P[2]). Of note, a variety of other weakly-to-modestly replication-competent animal and human RV strains, bioluminescent and fluorescent reporter viruses, and clinical isolates of human RVs have proved hard or impossible to rescue using the original reverse genetics system2,4, highlighting a critical need to further enhance the recovery efficiency and expand the rescue tool kit. A number of further modifications of the initial reverse genetics system have enabled the rescue of other RV strains such as the human RV KU and CDC-9 strains, and a murine RV D6/2-like strain4,5. Here, we discuss future possible modifications of existing RV reverse genetics systems to further increase efficiency based on past experience with the improvement of influenza A virus recovery. The development of RV to accommodate the insertion and expression of heterologous sequences has substantial potential in the design of next-generation RV vaccine candidates and enteric viral vectors.