GSE159459
Molecular characterization of endosomal self RNA Rmrp-engaged TLR3 dimerization to prime innate activation
In this study, we demonstrate that endosome-localized self RNA Rmrp directly binds to TLR3 and induces TLR3 dimerization in the early endosome but does not interact with endosome-localized TLR7, TLR8, TLR9 or cytoplasmic RNA sensor RIG-I under homeostatic conditions. Cryo-EM structure of Rmrp-TLR3 complex reveals a novel lapped conformation of TLR3 dimer engaged by Rmrp, which is distinct from the activation mechanism by dsRNA and the specific structural feature at the 3'-end of Rmrp is critical for its functional interaction with TLR3. Furthermore, K42 residue of TLR3 is essential for binding to Rmrp and subsequent dimerization. Rmrp dissociates from TLR3 following endosomal acidification, generating a matured TLR3 dimer which is primed for innate recognition and activation. Myeloid-cell deficiency of Rmrp reduces TLR3 dimerization and attenuates TLR3-mediated antiviral responses against influenza A both in vitro and in vivo. Overall design: Two RNA-seq experiments were performed by extracting early endosome and lysosome RNAs from RAW264.7 cells, then analyzed using Illumina Xten. iCLIP experiment was performed using anti-HA antibody in RAW264.7 cells overexressing HA-TLR3, and then analyzed by Illumina HiSeq2500 SE50 sequencing