Biology subjects

Sah, V.

Publications and source records attributed to Sah, V..

8 recordsLinked to original sources

bioRxiv2026

Snail restricts SARS-CoV-2 entry by limiting ACE2 expression as part of broader remodelling of epithelial determinants of viral tropism

Pre-existing state of the host cell is a major determinant of the host susceptibility to viral infection. Here, we identify the epithelial-mesenchymal transition transcription factor Snail as a host restriction factor for SARS-CoV-2. Snail loss markedly increased SARS-CoV-2 replication, whereas Snail overexpression and complementation restricted viral replication. Transcriptomic analysis of Snail knockout cells revealed remodelling of epithelial surface-associated programs, including apical membrane, brush border, and junctional pathways. ACE2, the cellular receptor for SARS-CoV-2, was among the genes upregulated in Snail knockout cells. Snail negatively regulated ACE2 transcription, leading to reduced ACE2 transcript and protein abundance and, consequently, lower SARS-CoV-2 entry. Consistent with this, ACE2 promoter activity was higher in Snail knockout cells, which was reduced following Snail complementation. As a means to counter Snail's antiviral functions, SARS-CoV-2 infection progressively depleted Snail protein in different cell culture models, while SNAI1 transcript abundance was surprisingly maintained or increased under the same conditions. Proteasome inhibition and protein-turnover analyses failed to account for this depletion. We find that SARS-CoV-2 infection resulted in reduced association of SNAI1 with polysomes at later stages of infection coinciding with virus-induced host translational suppression, resulting in lower protein synthesis. Together, these findings identify Snail as a regulator of the epithelial entry landscape that limits ACE2-associated SARS-CoV-2 entry and shapes cellular permissiveness, with broader implications for cellular determinants of viral tropism. SARS-CoV-2, in turn, progressively depletes this short-lived antiviral regulator, revealing how virus-induced translational shutoff can remodel pre-existing host cell states and thereby alter cellular susceptibility during infection.

microbiology↗

bioRxiv2025

STING is a key driver of Japanese encephalitis virus induced inflammatory response

Interferon (IFN) and inflammation are the key early defence mechanisms that combat pathogen infection. The cytosolic DNA sensor cGAS activates immune signaling via the stimulator of interferon genes (STING) protein. Emerging evidence suggests crosstalk between innate immune DNA and RNA sensing, implicating a role of STING protein in RNA virus infection. This study characterizes STING in the context of Japanese encephalitis virus (JEV), an RNA virus of the flaviviridae family. We observe that activation of type I IFN through MAVS is essential for cGAS and STING activation. Knockdown, null mutant and inhibitor studies confirmed that STING restricts JEV replication independently of IFN{beta} signaling and autophagy. Transcriptomic analysis of STINGgt/gt bone-marrow derived macrophages (BMDMs) showed enhanced IFN response, but reduced activation of inflammatory cytokines and chemokines. Phosphorylated STING was recruited on the virus replication complex (RC), marked by the non-structural protein NS1, subsequently triggering the assembly of the NLRP3 inflammasome on the RC. STING proton channel activity was essential for NLRP3 inflammasome activation, IL-1{beta} production, and activation of pyroptotic cell death markers. Stinggt/gt mice, showed higher viremia, earlier disease onset, reduced survival, and decreased brain inflammation. These findings establish STING as a key regulator of JEV-induced inflammation and antiviral defence.

microbiology↗

bioRxiv2025

MAVS Orchestrates a Potent IFN-independent Antiviral Immunity by Preserving Mitochondrial Integrity

Intrinsic antiviral defenses can restrict infection independent of paracrine interferon (IFN) signaling. While mitochondrial homeostasis is essential for immunity, its direct role in viral restriction remains incompletely understood. Here, we identify mitochondrial antiviral signaling protein (MAVS) as a central effector of a potent IFN-independent antiviral immunity orchestrated though mitochondrial safeguarding. We demonstrate that MAVS is critical for mitochondrial integrity as its loss leads to mitochondrial fragmentation, depolarization, and elevated mitophagy, alongside impaired bioenergetics and protein import. Mechanistically, MAVS maintains mitochondrial integrity by stabilizing the translocase of the outer membrane (TOM) complex and sustaining the abundance of its core components. Remarkably, this mitochondria-driven immunity restricts SARS-CoV-2 replication even under IFN-deficient conditions, and operates alongside the IFN pathways during JEV infection. Our findings redefine MAVS as a mitochondrial guardian that preserves organellar stability to enact host defense. These results highlight mitochondrial integrity as a fundamental determinant of broad antiviral immunity, integrating intrinsic and IFN-dependent mechanisms to counteract viral pathogenesis.

immunology↗

bioRxiv2022

SARS-CoV-2 Variant Delta Potently Suppresses Innate Immune Response and Evades Interferon-Activated Antiviral Responses

Delta variant of SARS-CoV-2 has caused more severe infections than its previous variants. We studied the host innate immune response to Delta, Alpha and two earlier variants to map the evolution of the recent ones. Our biochemical and transcriptomic studies reveal that Alpha and Delta have progressively evolved over the ancestral variants by silencing innate immune response, thereby limiting cytokine and chemokine production. Though Alpha silenced RLR pathway just as Delta, it failed to persistently silence the innate immune response unlike Delta. Both Alpha and Delta have evolved to resist IFN treatment while they are still susceptible to RLR activation, further highlighting the importance of RLR-mediated, IFN-independent mechanisms in restricting SARS-CoV-2. Our studies reveal that SARS-CoV-2 Delta has integrated multiple mechanisms to silence host innate immune response and evade IFN response. Deltas silent replication and sustained suppression of host innate immune response, possibly resulting in delayed or reduced intervention by the adaptive immune response, could potentially contribute to the severe symptoms and poor recovery index associated with it.

immunology↗

bioRxiv2021

Suppression of Global Protein Translation in SARS-CoV-2 Infection

Viruses employ distinct strategies to ensure efficient translation of their mRNAs over the host transcripts. SARS-CoV-2 targets host mRNAs and ribosomes to favor its own protein synthesis. However, the modulation of the key signal pathways that control the host protein translation machinery during SARS-CoV-2 infection has not been sufficiently addressed. Here, by employing an early variant and a Delta variant isolate that evolved later in the pandemic demonstrates that SARS-CoV-2 infection results in massive polysome collapse starting from 24 hpi, a hallmark of global translation inhibition. Unexpectedly, eIF2 phosphorylation, commonly targeted by viruses to induce translation arrest, was not involved in the translation arrest, suggesting that SARS-CoV-2 countermeasures by the virus to suppress ISR. eIF4E phosphorylation remained unaltered during the infection, ruling out its involvement in the preferential translation of SARS-CoV-2 transcripts. We find that SARS-CoV-2 infection consistently causes mTORC1 inhibition in a comparable manner across both variants indicating that the virus likely targets mTORC1 pathway to suppress host translation. Interestingly, mTORC1 inhibition by SARS-CoV-2 did not impact the polysomal loading of ribosomal protein transcripts rpS3 and rpL26, suggesting that 5TOP mRNAs are spared from the translation suppression and that ribosomal protein synthesis remains active during the infection. Pharmacological activation of mTORC1 did not significantly impact viral replication, suggesting that mTORC1 inhibition might be selectively restricting the host mRNAs from accessing the translation machinery, facilitating a more robust translation of viral transcripts. This study provides new insights into the molecular interactions by which SARS-CoV-2 variants, despite their different clinical outcomes, converge on a conserved mechanism to manipulate host translation regulatory pathways.

microbiology↗

bioRxiv2021

N440K variant of SARS-CoV-2 has Higher Infectious Fitness

Several variants of SARS-CoV-2 have been emerging across the globe, continuing to threaten the efforts to end COVID-19 pandemic. Recent data indicate the prevalence of variants with N440K Spike substitution in several parts of India, which is under the second wave of the pandemic. Here, we first analyze the prevalence of N440K variants within the sequences submitted from India and identify a rising trend of its spread across various clusters. We then compare the replicative fitness and infectivity of a prototype of this variant with two other previously prevalent strains. The N440K variant produced ten times higher infectious viral titers than a prevalent A2a strain, and over 1000 folds higher titers than a much less prevalent A3i strain prototype in Caco2 cells. Similar results were detected in Calu-3 cells as well, confirming the increased potency of the N440K variant. Interestingly, A3i strain showed the highest viral RNA levels, but the lowest infectious titers in the culture supernatants, indicating the absence of correlation between the RNA content and the infectivity of the sample. N440K mutation has been reported in several viral sequences across India and based on our results, we predict that the higher infectious titers achieved by N440K variant could possibly lead to its higher rate of transmission. Availability of more sequencing data in the immediate future would help understand the potential spread of this variant in more detail.

microbiology↗

bioRxiv2021

Inactivation of SARS-CoV-2 by β-propiolactone Causes Aggregation of Viral Particles and Loss of Antigenic Potential

Inactivated viral preparations are important resources in vaccine and antisera industry. Of the many vaccines that are being developed against COVID-19, inactivated whole-virus vaccines are also considered effective. {beta}-propiolactone (BPL) is a widely used chemical inactivator of several viruses. Here, we analyze various concentrations of BPL to effectively inactivate SARS-CoV-2 and their effects on the biochemical properties of the virion particles. BPL at 1:2000 (v/v) concentrations effectively inactivated SARS-CoV-2. However, higher BPL concentrations resulted in the loss of both protein content as well as the antigenic integrity of the structural proteins. Higher concentrations also caused substantial aggregation of the virion particles possibly causing undesirable outcomes including a potential immune escape by infectious virions, and a loss in antigenic potential. We also identify that the viral RNA content in the culture supernatants can be a direct indicator of their antigenic content. Our findings may have important implications in the vaccine and antisera industry during COVID-19 pandemic.

microbiology↗

bioRxiv2021

Development of Equine Immunoglobulin Fragment F(ab')2 with High Neutralizing Capability against SARS-CoV-2

The ongoing pandemic, COVID-19, caused by SARS-CoV-2 has taken the world, and especially the scientific community by storm. While vaccines are being introduced into the market, there is also a pressing need to find potential drugs and therapeutic modules. Remdesivir is one of the antivirals currently being used with a limited window of action. As more drugs are being vetted, passive immunotherapy in the form of neutralizing antibodies can provide immediate action to combat the increasing numbers of COVID-positive cases. Herein, we demonstrate that equines hyper-immunized with chemically inactivated SARS-CoV-2 generate high titers of antibody with a strong virus neutralizing potential. ELISA performed with pooled antisera displayed highest immunoglobulin titer on 42 days post-immunization, at 1:51,200 dilutions. F(ab)2 immunoglobulin fragments generated from the pools also showed very high, antigen-specific affinity at 1:102,400 dilutions. Finally, in vitro virus neutralization assays confirmed that different pools of F(ab)2 fragments could successfully neutralize SARS-CoV-2 with titers well above 25,000, indicating the potential of this strategy in treating severe COVID-19 cases with high titers. The F(ab)2 was able to cross neutralize another SARS-CoV-2 strain, demonstrating its efficacy against the emerging viral variants and the importance of this approach in our efforts of eradication of COVID-19. In conclusion, this study demonstrates that virus-neutralizing antibodies raised in equines can potentially be used as a treatment regimen in the form of effective passive immunotherapy to combat COVID-19.

immunology↗