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

Intercellular 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 pathogen Leishmania donovani from infected macrophages. Exploring the mechanism of how Syntaxin5 acts as an immunostimulant, we have identified the de novo RNA 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 Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=147 SRC="FIGDIR/small/556844v1_ufig1.gif" ALT="Figure 1"> View larger version (28K): org.highwire.dtl.DTLVardef@bfabf8org.highwire.dtl.DTLVardef@1b35346org.highwire.dtl.DTLVardef@203a5corg.highwire.dtl.DTLVardef@1d7a15e_HPS_FORMAT_FIGEXP M_FIG C_FIG O_LIHuR transfers miRNAs to STX5 for export C_LIO_LISTX5 utilizes its N-terminal disordered domain to bind and target miRNAs to endosomes. C_LIO_LIIn its dual role, STX5 uses the SNARE domain to export miRNA by promoting EV biogenesis and release. C_LIO_LISTX5-mediated miRNA export activates macrophage to clear internalized parasites. C_LI