Biology subjects

St Clair, L. A.

Publications and source records attributed to St Clair, L. A..

4 recordsLinked to original sources

bioRxiv2022

Human sialidase activity is vital for dengue virus serotype 2 infection

The human sialidase enzymes (or neuraminidases, NEU1-4) are glycoside hydrolases that catalyze the removal of sialic acid residues from glycoconjugates, including many bioactive glycoproteins and glycolipids. Through their physiochemical effect on glycoconjugates, sialic acid residues are thought to play vital roles in the control of cellular signaling. In previous studies, it was demonstrated that NEU1-4 activity was increased in cells infected with dengue virus serotype 2 (DENV2). Additionally, it was demonstrated that the DENV2 NS1 protein was sufficient for inducing increased NEU1-4 activity in both in vivo and in vitro models, and that this increased activity was linked to endothelial hyperpermeability and vascular leakage, a hallmark of severe dengue disease. However, the role of increased NEU1-4 activity in the viral lifecycle was not understood. Here, we used siRNA-mediated loss of function studies to evaluate the effect of inhibition of sialidase activity on the DENV2 lifecycle. Our analyses uncovered that apart from their importance for viral pathogenesis, NEU1-4 activity was vital for DENV2 viral replication and egress. Moreover, we characterized the inter-relationship between NEU 1-4, and determined that there was a transcriptional dependency of NEU1-3 on NEU4.

microbiology↗

bioRxiv2022

RNase L-mediated RNA decay alters 3' end formation and splicing of host mRNAs

The antiviral endoribonuclease, RNase L, is a vital component of the mammalian innate immune response that destroys host and viral RNA to reduce viral gene expression. Herein, we show that a consequence of RNase L-mediated decay of cytoplasmic host RNAs is the widespread re-localization of RNA-binding proteins (RBPs) from the cytoplasm to the nucleus, due to the presence of nuclear RNA. Concurrently, we observe global alterations to host RNA processing in the nucleus, including alterations of splicing and 3 end formation, with the latter leading to downstream of gene (DoG) transcripts. While affecting many host mRNAs, these alterations are pronounced in mRNAs encoding type I and type III interferons and coincide with the retention of their mRNAs in the nucleus. Similar RNA processing defects also occur during infection with either dengue virus or SARS-CoV-2 when RNase L is activated. These findings reveal that the distribution of RBPs between the nucleus and cytosol is fundamentally dictated by the availability of RNA in each compartment and thus viral infections that trigger cytoplasmic RNA degradation alter RNA processing due to the nuclear influx of RNA binding proteins.

immunology↗

bioRxiv2021

Acyl-CoA Thioesterases; a rheostat that controls activated fatty acids modulates dengue virus serotype 2 replication

During infection with dengue viruses (DENVs), the lipid landscape within host cells is significantly altered to assemble membrane platforms that support viral replication and particle assembly. Fatty acyl-CoAs are key intermediates in the biosynthesis of complex lipids that form these membranes. They also function as key signaling lipids in the cell. Here, we carried out loss of function studies on acyl-CoA thioesterases (ACOTs), a family of enzymes that hydrolyze fatty acyl-CoAs to free fatty acids and coenzyme A, to understand their influence on the lifecycle of DENVs. Loss of function of the type I ACOTs 1 (cytoplasmic) and 2 (mitochondrial) together significantly increased DENV serotype 2 (DENV2) viral replication and infectious particle release. However, isolated knockdown of mitochondrial ACOT2 significantly decreased DENV2 protein translation, genome replication, and infectious virus release. Furthermore, loss of ACOT7 function, a mitochondrial type II ACOT, similarly suppressed DENV2. As ACOT1 and ACOT2 are splice variants, these data suggest that location (cytosol and mitochondria, respectively) rather than function of these proteins may account for the differences in DENV2 infection phenotype. Additionally, loss of mitochondrial ACOT2 and ACOT7 expression also altered the expression of several ACOTs located in multiple organelle compartments within the cell highlighting a complex relationship between ACOTs in the DENV2 virus lifecycle.

microbiology↗

bioRxiv2021

Rapid decay of host basal mRNAs during SARS-CoV-2 infection perturbs host antiviral mRNA biogenesis and export

A key feature of the mammalian innate immune response to viral infection is the transcriptional induction of interferon (IFN) genes, which encode for secreted proteins that prime the antiviral response and limit viral replication and dissemination. A hallmark of severe COVID-19 disease caused by SARS-CoV-2 is the low presence of IFN proteins in patient serum despite elevated levels of IFN-encoding mRNAs, indicative of post-transcriptional inhibition of IFN protein production. Herein, we show SARS-CoV-2 infection limits type I and type III IFN biogenesis by preventing the release of mRNA from their sites of transcription and/or triggering their nuclear degradation. In addition, SARS-CoV-2 infection inhibits nuclear-cytoplasmic transport of IFN mRNAs as a consequence of widespread cytosolic mRNA degradation mediated by both activation of the host antiviral endoribonuclease, RNase L, and by the SARS-CoV-2 protein, Nsp1. These findings argue that inhibition of host and/or viral Nsp1-mediated mRNA decay, as well as IFN treatments, may reduce viral-associated pathogenesis by promoting the innate immune response.

immunology↗