MicroRNA miR-24-3p Promotes Porcine Reproductive and Respiratory Syndrome Virus Replication through Suppression of Heme Oxygenase-1 Expression

Porcine reproductive and respiratory syndrome virus (PRRSV) is one of the most economically important viruses affecting the swine industry worldwide. Our previous research showed that PRRSV downregulates the expression of heme oxygenase-1 (HO-1), a pivotal cytoprotective enzyme, postinfection and that overexpression of HO-1 inhibits PRRSV replication. MicroRNAs regulate gene expression at the posttranscriptional level and have recently been demonstrated to play vital roles in pathogenhost interactions. The present study sought to determine whether microRNAs modulate HO-1 expression and, by doing so, regulate PRRSV replication. Using bioinformatic prediction and experimental verification, we demonstrate that HO-1 expression is regulated by miR-24-3p. A direct interaction between miR-24-3p and HO-1 mRNA was confirmed using a number of approaches. Overexpression of miR-24-3p significantly decreased HO-1 mRNA and protein levels. PRRSV infection induced miR24-3p expression to facilitate viral replication. The suppressive effect of HO-1 induction by protoporphyrin IX cobalt chloride (CoPP; a classical inducer of HO-1 expression) on PRRSV replication in MARC-145 cells and primary porcine alveolar macrophages could also be reversed by overexpression of miR-24-3p. Collectively, these results suggested that miR-24-3p promotes PRRSV replication through suppression of HO-1 expression, which not only provides new insights into virus-host interactions during PRRSV infection but also suggests potential new antiviral strategies against PRRSV infection. IMPORTANCE MicroRNAs (miRNAs) play vital roles in viral infections by regulating the expression of viral or host genes at the posttranscriptional level. Heme oxygenase-1 (HO-1), a pivotal cytoprotective enzyme, has antiviral activity for a number of viruses, such as Ebola virus, hepatitis C virus, human immunodeficiency virus, and our focus, PRRSV, which causes great economic losses each year in the swine industry worldwide. Here, we show that PRRSV infection induces host miRNA miR-24-3p expression and that miR-24-3p regulates HO-1 expression through both mRNA degradation and translation repression. Suppression of HO-1 expression by miR-24-3p facilitates PRRSV replication. This work lends credibility to the hypothesis that an arterivirus can manipulate cellular miRNAs to enhance virus replication by regulating antiviral responses following viral infection. Therefore, our findings provide new insights into the pathogenesis of PRRSV.