Human antigen R transfers miRNA to Syntaxin 5 to synergize miRNA export from activated macrophages.

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 the endoplasmic reticulum to endosomes is a rate-determining step in the miRNA export process and plays an important role in controlling cellular miRNA levels and inflammatory processes in macrophages. We have identified the SNARE protein Syntaxin 5 (STX5) to show a synchronized expression pattern with miRNA activity loss in activated mammalian macrophage cells. STX5 is both necessary and sufficient for macrophage activation and clearance of the intracellular pathogen Leishmania donovani from infected macrophages. Exploring the mechanism of how STX5 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 ELAVL1 protein, Human antigen R. This activity ensures the 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 the plasma membrane to ensure accelerated release of extracellular vesicles and associated miRNAs.

Biofilm-a Syntrophic Consortia of Microbial Cells: Boon or Bane?

Biofilm is the conglomeration of microbial cells which is associated with a surface. In the recent times, the study of biofilm has gained popularity and vivid research is being done to know about the effects of biofilm and that it consists of many organisms which are symbiotic in nature, some of which are human pathogens. Here, in this study, we have discussed about biofilms, its formation, relevance of its presence in the biosphere, and the possible remediations to cope up with its negative effects. Since removal of biofilm is difficult, emphasis has been made to suggest ways to prevent biofilm formation and also to devise ways to utilize biofilm in an economically and environment-friendly method.

Target-Dependent Coordinated Biogenesis of Secondary MicroRNAs by miR-146a Balances Macrophage Activation Processes.

MicroRNAs (miRNAs) repress protein expression by binding to the target mRNAs. Exploring whether the expression of one miRNA can regulate the abundance and activity of other miRNAs, we noted the coordinated biogenesis of miRNAs in activated macrophages. miRNAs with higher numbers of binding sites (the "primary" miRNAs) induce expression of other miRNAs ("secondary" miRNAs) having binding sites on the 3' untranslated region (UTR) of common target mRNAs. miR-146a-5p, in activated macrophages, acts as a "primary" miRNA that coordinates biogenesis of "secondary" miR-125b, miR-21, or miR-142-3p to target new sets of mRNAs to balance the immune responses. During coordinated biogenesis, primary miRNA drives the biogenesis of secondary miRNA in a target mRNA- and Dicer1 activity-dependent manner. The coordinated biogenesis of miRNAs was observed across different cell types. The target-dependent coordinated miRNA biogenesis also ensures a cumulative mode of action of primary and secondary miRNAs on the secondary target mRNAs. Interestingly, using the "primary" miR-146a-5p-specific inhibitor, we could inhibit the target-dependent biogenesis of secondary miRNAs that can stop the miRNA-mediated buffering of cytokine expression and inflammatory response occurring in activated macrophages. Computational analysis suggests the prevalence of coordinated biogenesis of miRNAs also in other contexts in human and in mouse.

Leishmania survives by exporting miR-146a from infected to resident cells to subjugate inflammation.

Leishmania donovani, the causative agent of visceral leishmaniasis, infects and resides within tissue macrophage cells. It is not clear how the parasite infected cells crosstalk with the noninfected cells to regulate the infection process. During infection, Leishmania adopts a dual strategy for its survival by regulating the intercellular transport of host miRNAs to restrict inflammation. The parasite, by preventing mitochondrial function of host cells, restricts the entry of liver cell derived miR-122-containing extracellular vesicles in infected macrophages to curtail the inflammatory response associated with miR-122 entry. On contrary, the parasite up-regulates the export of miR-146a from the infected macrophages. The miR-146a, associated with the extracellular vesicles released by infected cells, restricts miR-122 production in hepatocytes while polarizing neighbouring naïve macrophages to the M2 state by affecting the cytokine expression. On entering the recipient macrophages, miR-146a dominates the miRNA antagonist RNA-binding protein HuR to inhibit the expression of proinflammatory cytokine mRNAs having HuR-interacting AU-rich elements whereas up-regulates anti-inflammatory IL-10 by exporting the miR-21 to polarize the recipient cells to M2 stage.