Long noncoding RNA PARAL1 regulates myeloid dendritic cell differentiation and TLR signaling.

Dendritic cells (DCs) are professional antigen presentation cells (APCs) that bridge innate and adaptive immune functions to contain pathogenic threats. Long noncoding RNAs (lncRNAs) are implicated in regulating biological processes, including inflammation and immunity. However, the knowledge of myeloid DC-expressed lncRNA repertoire and their regulatory functions is limited. Here we profiled lncRNA expression kinetics during monocyte-to-DC (moDC) differentiation and characterized their functional roles. Our RNA-seq data identified a repertoire of differentially expressed lncRNAs associated with moDC differentiation and a large subset of these lncRNAs are distinct from M1 or M2 macrophages. We selected two DC-enriched lncRNAs and observed that PARAL1 silencing, or overexpression modulates DC surface markers expression. Importantly, PARAL1 RNAi significantly reduced, while its overexpression upregulated the levels of multiple TLRs. Upon treatment with TLR agonists PARAL1 knockdown cells exhibit reduced NF-κB, IRF3 and IRF7 phosphorylation substantiating its role in potentiating TLR signaling. Mechanistically, PARAL1 silencing showed significant downregulation of multiple NF-κB-induced genes and time-dependent inhibition of proinflammatory cytokine secretion upon challenge with TLR agonists. Finally, PARAL1 RNAi in DCs significantly impaired antigen processing and presentation to T cells. Overall, this study characterized novel functions of PARAL1 in regulating DC differentiation, TLR-dependent innate immunity and activation of adaptive immune response.