Kinase activity of TBK1 is required for its binding to STING, but not for its recruitment to the Golgi

Abstract Stimulator of interferon genes (STING) is an innate immune protein for DNA pathogens. In response to the emergence of DNA in the cytosol, STING relocates from the endoplasmic reticulum (ER) to the Golgi and induces the type I interferon response through cytosolic TANK-binding kinase 1 (TBK1). The molecular mechanism underlying TBK1 activation by STING remains poorly understood. Here we report a cell system by which STING and TBK1 are simultaneously monitored. The system utilizes STING/TBK1-double knockout (KO) cells, fluorescent protein-tagged TBK1 and STING, and super-resolution microscopy. After STING stimulation, TBK1 is directly recruited to the trans-Golgi network (TGN), not to the other parts of the Golgi. The recruitment of TBK1 does not require its kinase activity. C-terminal STING variants (ΔC9 and L373A), in which the TBK1-STING binding interface is mutated or deleted, induce the recruitment of TBK1. These results indicate that the kinase activity of TBK1 or the C-terminal motif of STING is not required for its recruitment to TGN, but rather for the formation of the stable STING signalling complex at TGN.