Functional Characterization of NLRC5 and DDX46 in the Regulation of Innate Immune Responses
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The NOD-like receptor protein NLRC5 inhibits TLR-induced NF-ҡB and viral infection-mediated type I interferon signaling in vitro. In the first project, we generated NLRC5 knockout mice to characterize the regulatory function of NLRC5. NLRC5 deficiency enhances Toll-like receptor-induced NF-ҡB signaling and type I IFN-mediated antiviral immunity in mouse embryonic fibroblasts (MEFs). NLRC5 deficiency also increases proinflammatory cytokine response and antiviral immunity in mouse immune cells. In addition, we confirmed that NLRC5 regulates the transcription of MHC class I gene. Our findings indicate that NLRC5 is a regulator with multiple functions by negatively regulating proinflammatory responses and positively regulating MHC class I gene expression. The inflammasome is a large protein complex that leads to apoptosis and proinflammatory responses. One of the well-studied inflammasome transduces the activation signal through NLRP3. NLRP3 inflammasome is known to be activated through ASC oligomerization induced by varieties of stimulations; however, the mechanism remains unknown. Some of the DDX family proteins have been reported to sense DNA or RNA to activate type I IFN signaling pathway. By screening DDX family proteins in 293T cells reconstituted with the inflammasome system, we found that DDX46 enhanced NLRP3 inflammasome activity. Knockdown of DDX46 in THP-1 cells reduces inflammasome activity and IL-1β release after crystalline stimulations. DDX46 is cleaved by activated caspase-3 after silica stimulation in mouse macrophages. Furthermore, cleaved DDX46 interacts with the NLRP-ASC complex following silica stimulation. The positive regulatory role of cleaved DDX46 in silica-mediated NLRP3 inflammasome activation was confirmed in the 293T cell system by its strong ability to interact with ASC. Together, our findings indicate that cleaved DDX46 acts as a bridge to promote the interaction between NLRP3 and ASC after crystalline stimulation.
Tong, Yanzheng (2014). Functional Characterization of NLRC5 and DDX46 in the Regulation of Innate Immune Responses. Doctoral dissertation, Texas A&M University. Available electronically from