Comprehensive siRNA-based screening of human and mouse TLR pathways identifies species-specific preferences in signaling protein use

摘要

Toll-like receptors (TLRs) are a major class of pattern recognition receptors, which mediate the response of innate immune cells to microbial stimuli. To systematically determine the roles of gene products in canonical TLR signaling pathways, we conducted an RNA interference (RNAi)-based screen in human and mouse macrophages. We observed a pattern of conserved signaling module dependencies across species, but found notable species-specific requirements at the level of individual gene products. Among these, we identified unexpected differences in interleukin 1 receptor-associated kinase (IRAK) protein use between the human and mouse TLR pathways. Whereas TLR signaling in mouse macrophages depended primarily on IRAK4 and IRAK2, with little or no role for IRAK1, TLR signaling and proinflammatory cytokine production in human macrophages were highly dependent on IRAK1 and were less affected by perturbations of IRAK4 or IRAK2. The differential sensitivity of human and mouse cells to the loss of IRAK4 was reflected in the inability of the IRAK4 orthologs to rescue signaling in IRAK4-deficient macrophages from the other species, and in a mouse-specific requirement for the kinase activity of IRAK4 in TLR responses in macrophages. Our study also identified a critical role for IRAK1 in TLR signaling in humans, which could potentially explain the association of IRAK1 with several autoimmune diseases. Furthermore, we demonstrated how systematic screening can be used to identify important characteristics of innate immune responses across species and more optimal therapeutic targets for regulating human TLR-dependent outputs.