HuR enhances SARS-CoV-2 non-structural protein translation through the genomic 5'-UTR, by promoting polypyrimidine tract-binding protein binding

Abstract

Severe acute respiratory syndrome-coronavirus-2 (SARS-CoV-2) viral RNA associates with different RNA-binding host proteins at each stage of its life cycle. We found sequence dependent binding of one such important protein, human antigen R (HuR) to SARS-CoV-2 5'UTR and studied its potential role in virus life cycle. The knockdown and knockout studies revealed importance of such binding in viral translation. We identified 5'-UTR mutations in SARS-CoV-2 variants of concern that altered the HuR-binding affinity. Interestingly, HuR enhanced non-structural protein translation through the genomic 5'-UTR, by promoting polypyrimidine tract-binding protein binding to the 5'-UTR. However, HuR suppressed the structural protein translation from sub genomic 5UTR. HuR knockout increased the sensitivity to remdesivir treatment by decreasing its half-maximal inhibitory concentration. An antisense oligonucleotide (whose binding site overlapped the HuR-binding site) reduced viral RNA levels in wild-type cells but not HuR-knockout cells. Our results indicate that HuR regulates the balance between SARS-CoV-2 structural and non-structural proteins and guides the infection of viral variants, implying that HuR can potentially be targeted for therapeutic interventions. Author SummaryViruses interacts with various host proteins throughout their life cycle. One significant protein is HuR, an RNA-binding protein that regulates RNA stability and translation. HuR binds to viral RNAs at the 5UTR or 3UTR, impacting their translation and replication. We identified conserved HuR binding sites in the SARS-CoV-2 5UTR across different beta coronaviruses. This binding enhanced the initiation of translation from the genomic 5 UTR, increasing the production of non-structural proteins essential for viral replication. Additionally, we discovered that another host protein, PTB, promotes HuR binding to the viral 5 UTR, facilitating its loading onto ribosomes. Conversely, HuR plays an antagonistic role concerning subgenomic RNAs (sgRNAs), which code for structural proteins, by regulating and limiting their levels. This dual regulation indicates that the virus exploits HuR for its benefit while the host employs it to control viral spread. Targeting HuR may help manipulate the SARS-CoV-2 life cycle. We found that HuR knockout increased sensitivity to the antiviral drug Remdesivir. Using an antisense oligonucleotide to block HuR binding effectively reduced viral RNA levels. Our findings highlight the critical role of HuR in regulating viral protein production and its potential as a therapeutic target.