Human antigen R controls lung fibroblast function in response to cigarette smoke

Cigarette smoke remains the leading cause of preventable death worldwide. Human antigen R (HuR) is an RNA-binding protein that exerts post-transcriptional control over the expression of mRNA in response to various stimuli including cigarette smoke. Although HuR is extensively expressed in the respiratory system including lung structural cells, the molecular function of HuR in lung cells is largely unexplored. Therefore, we evaluated HuR function in primary human lung fibroblasts. HuR was silenced using siRNA, cells were exposed to cigarette smoke and RNA-sequencing was performed using the Illumina NextSeq550. We also performed RIP-seq to comprehensively profile HuR binding to target RNA. qRT-PCR and western blot were performed to evaluate <i>PTGS2</i> and <i>IL-8</i> mRNA and protein expression, respectively. A two-way ANOVA followed by a post-hoc test was used to determine statistical significance. Our data shows that HuR controls hundreds of genes at the basal level and in response to cigarette smoke, genes that are involved in numerous physiological responses including inflammation, eicosanoid production and oxidative stress. HuR also bound to more mRNA in lung fibroblasts in response to cigarette smoke. Knock-down studies further confirmed that HuR suppresses two key proteins associated with inflammation- PTGS2/COX-2 and IL-8- by regulating mRNA stability. Our results show that HuR plays fundamental roles in maintaining pulmonary cellular homeostasis in response to noxious stimuli, which suggests that therapeutic targeting of HuR may alleviate prevalent and deadly lung diseases caused by environmental exposures.