RNA Binding of Syntaxin 5 Synergises Membrane Fusion to Accelerate miRNA Export, Activate Macrophage and Clear Pathogens

Abstract

AbstractIntercellular miRNA exchange acts as a key mechanism to control gene expression post-transcriptionally in mammalian cells. Regulated export of repressive miRNAs allows the expression of inflammatory cytokines in activated macrophages. Intracellular trafficking of miRNAs from endoplasmic reticulum to endosomes is a rate determining step in miRNA export process and plays an important role in controlling cellular miRNA level and inflammatory processes in macrophages. We have identified the SNARE protein Syntaxin5 to show a synchronized expression pattern with miRNA activity loss in activated mammalian macrophage cells. Syntaxin 5 is both necessary and sufficient for macrophage activation and clearance of the intracellular pathogenLeishmania donovanifrom infected macrophages. Exploring the mechanism of how Syntaxin5 acts as an immunostimulant, we have identified thede novoRNA binding property of this SNARE protein that binds specific miRNAs and facilitates their accumulation in endosomes in a cooperative manner with human ELAV protein HuR to ensure export of miRNAs and allows the expression of miRNA-repressed cytokines. Conversely, in its dual role in miRNA export, this SNARE protein prevents lysosomal targeting of endosomes by enhancing the fusion of miRNA-loaded endosomes with plasma membrane to ensure accelerated release of extracellular vesicles and associated miRNAs.Graphical AbstractHuR transfers miRNAs to STX5 for exportSTX5 utilizes its N-terminal disordered domain to bind and target miRNAs to endosomes.In its dual role, STX5 uses the SNARE domain to export miRNA by promoting EV biogenesis and release.STX5-mediated miRNA export activates macrophage to clear internalized parasites.