Dissecting how inflammation-induced tenascin-C regulates the master mediator of inflammation miR-155

During infection conserved microbial components are detected by innate immune cells such as macrophages which possess pattern recognition receptors, including Toll-like receptors (TLRs). Once activated, TLRs initiate inflammatory responses that culminate with the production of inflammatory mediators such as cytokines that subsequently prime specific adaptive immune responses. Dysregulation of this process can lead to inflammatory and autoimmune diseases such as sepsis, rheumatoid arthritis and systemic lupus erythematosus. Therefore TLR signalling must be tightly regulated. MicroRNAs, small noncoding RNAs, are important regulators of gene expression that control TLR signalling and cytokine synthesis. Several microRNAs are induced upon infection by TLR activation in macrophages and these microRNAs function by targeting the 3' untranslated region (UTR) of mRNAs encoding components of the TLR signalling system and the downstream cytokines. We found that the extracellular matrix glycoprotein tenascin-C (TN-C) regulates the production of the pro-inflammatory cytokine TNF-a in macrophages activated by the bacterial component lipopolysaccharide (LPS). TN-C does this by regulating the expression of the microRNA miR-155. However, how TN-C exactly regulates miR-155 biogenesis is unknown. The overall hypothesis of the project builds on our preliminary data which suggests that TN-C regulates miR-155 biogenesis at the post-transcriptional level. Specifically, in the presence of TN-C enzymatic cleavage of the miR-155 primary transcript by Drosha in the nucleus is significantly more efficient. The aims are: 1. Determine the molecular mechanism by which TN-C regulates miR-155 processing in the nucleus. 2. Establish whether the identified regulatory mechanism is specific to miR-155 or applies to other miRNAs. The project will benefit from the expertise of the Piccinini group (molecular immunology, microRNAs and cell biology) and Jopling group (microRNA regulation).