Biology subjects

Harshan, K. H.

Publications and source records attributed to Harshan, K. H..

8 recordsLinked to original sources

bioRxiv2021

Regulation of eIF2α Phosphorylation by MAPKs Influences Polysome Stability and Protein Translation

Regulation of protein translation occurs primarily at the level of initiation and is mediated by multiple signaling pathways, majorly mechanistic target of rapamycin complex 1 (mTORC1), mitogen-activated protein kinases (MAPKs), and the eukaryotic translation initiation factor eIF2. While mTORC1 and eIF2 influence the polysome stability, MAPKs influence the phosphorylation of the cap-binding protein eIF4E and are known to influence translation of only a small set of mRNAs. Here, we demonstrate that p38 MAPK and ERK1/2 regulate translation through integrated stress response (ISR) pathways. Dual inhibition (dual-Mi) of p38 MAPK and ERK1/2 caused substantial phosphorylation of eIF2 in a synergistic manner, resulting in near-absolute collapse of polysomes. This regulation was independent of Mnk1/2, a well-studied mediator of translation regulation by the MAPKs. Dual-Mi-induced polysome dissociation was far more striking than that caused by sodium arsenite, a strong inducer of ISR. Interestingly, induction of ISR caused increased p38 phosphorylation, and its inhibition resulted in stronger polysome dissociation, indicating the importance of p38 in the translation activities. Thus, our studies demonstrate a major, unidentified role for ERK1/2 and more particularly p38 MAPK in the maintenance of homeostasis of polysome association and translation activities.

biochemistry↗

bioRxiv2021

Glycolytic inhibitor 2-Deoxy-D-glucose attenuates SARS-CoV-2 multiplication in host cells and weakens the infective potential of progeny virions

The COVID-19 pandemic is an ongoing public health emergency of international concern. While a lot of efforts are being invested in vaccinating the population, there is also an emergent requirement to find potential therapeutics to effectively counter this fast mutating SARS-CoV-2 virus-induced pathogenicity. Virus-infected host cells switch their metabolism to a more glycolytic phenotype. This switch induced by the virus is needed for faster production of ATP and higher levels of anabolic intermediates, required for new virion synthesis and packaging. In this study, we used 2-Deoxy-D-glucose (2-DG) to target and inhibit the metabolic reprogramming induced by SARS-CoV-2 infection. Our results showed that virus infection induces glucose influx and glycolysis resulting in selective high accumulation of the fluorescent glucose/2-DG analogue, 2-NBDG in these cells. Subsequently, 2-DG inhibits glycolysis in infected cells thereby reducing the virus multiplication and alleviates the cells from virus induced cytopathic effect (CPE) and cell death. Herein, we demonstrate that the crucial Nglycosites (N331 and N343) of RBD in spike protein of progeny virions produced from 2-DG treated cells were found unglycosylated and defective with compromised infectivity potential. In line with earlier reported observations, our study also showed that 2-DG mediated metabolic inhibiton can attenuate SARS-COV-2 multiplication. In addition, mechanistic study revealed that the inhibition of SARS-COV-2 multiplication is attributed to 2-DG induced un-glycosylation of spike protein. Our findings strengthen the notion that 2-DG effectively inhibits SARS-CoV-2 multiplication. Therefore, based on its previous human trials in different types of Cancer and Herpes patients, it could be a potential molecule to study in COVID-19 patients.

cell biology↗

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↗

bioRxiv2020

Retinoic acid Inducible Gene-I like Receptors Activate Snail and Slug to Limit RNA Viral Infections

RLRs sense cytosolic non-self RNAs including viral RNAs before mounting a response leading to the activation of Type-I IFNs. Here, we identify a previously unknown regulation of Snail, a transcription regulator known in EMT, during RNA viral infections and describe its possible implication. RNA viral infections, poly (I:C) transfection and ectopic expression of RLR components activated Snail and Slug in epithelial cells. Detailed examination revealed that MAVS and phosphorylated IRF3 are essential in this regulation. We identified two ISREs in SNAI1 promoter region and their alterations rendered the promoter non-responsive to phospho-IRF3 in luciferase assay. Ectopic expression of Snail and Slug activated RLR pathway and dramatically limited RNA viral infections in epithelial cells pointing to their antiviral functions. Thus, Snail and Slug are transcriptionally regulated by RLRs in a similar manner as IFN-{beta} and they in turn promote RLR pathway possibly strengthening the antiviral state in the cell.

immunology↗

bioRxiv2020

An Inexpensive RT-PCR Endpoint Diagnostic Assay for SARS-CoV-2 Using Nested PCR: Direct Assessment of Detection Efficiency of RT-qPCR Tests and Suitability for Surveillance

With a view to extending testing capabilities for the ongoing SARS-CoV-2 pandemic we have developed a test that lowers cost and does not require real time quantitative reverse transcription polymerase chain reaction (RT-qPCR). We developed a reverse transcription nested PCR endpoint assay (RT-nPCR) and showed that RT-nPCR has comparable performance to the standard RT-qPCR test. In the course of comparing the results of both tests, we found that the standard RT-qPCR test can have low detection efficiency (less than 50%) in a real testing scenario which may be only partly explained by low viral representation in many samples. This finding points to the importance of directly monitoring detection efficiency in test environments. We also suggest measures that would improve detection efficiency.

molecular biology↗