The Regulation Of Transcription Factor Fli-1 To Lipopolysaccharide-induced Interleukin-27 Production And Its Mechanism In Macrophages

Innate immune response is the first defensive line of the body against infectious microbe.How innate immune cells quickly identify a number of different pathogens by limited receptors and make different responses is a very important and attractive field in the research of innate immunity.Toll-like receptors(TLRs)are mainly expressed on the surface of immune cells,and some in endosome and lysosome.They can activate signals by binding to correspongding pathogen-associated molecular patterns(PAMPs),and regulate the production of different types of chemokines,interferon and inflammatory cytokines to clear the pathogens and foreign matters.IL-27 belongs to the IL-6/IL-12 superfamily.IL-27 is unique in having both of pro-inflammation and anti-inflammation properties among the IL-12 superfamily.The mechanism by which IL-27 production is regulated in TLR4-activated innate immune remains largely unclear.Here we show that expression of transcription factor Fli-1 at protein level is increased in macrophages following LPS stimulation.Fli-1 over expression increases LPS-activated IL-27 production in macrophages,while Fli-1 knockdown inhibits LPS-induced IL-27 production in macrophages.Chromatin immunoprecipitation(ChIP)assay reveals that Fli-1 binds the promoter of IL-27p28 subunit after Fli-1 entering cell nucleus.Further experiments manifest that Fli-1 binds the region between-250 and-150 bp upstream of the transcriptional start site of p28 gene and increases p28 gene promoter-controlled transcription.Fli-1 belongs to ETS transcription factor family,which can specifically bind to GGA(A/T)consensus sequence to regulate the transcription of genes.There is a putative Ets binding site at-209/-206 of the promoter of IL-27p28.By mutating the Ets consensus GGAA,Fli-1 and MyD88 overexpression could not increase luciferase activity driven by the p28-250 promoter with mutation in the GGA(A/T)consensus sequence,suggesting that Fli-1 regulated p28 promoter by binding to the GGAA consensus located at-209/-206.These results demonstrate that Fli-1 positively regulates IL-27 production in TLR4-activated immune response by promoting transcription of IL-27 p28 gene.Our finding reveals that Fli-1 can positively regulate IL-27 production in macrophages.Besides that,Fli-1 can cooperate with MyD88 and IRF1 to positively regulate IL-27 p28 gene transcription.All of these results will help us to make further understanding of the regulation mechanism in innate immune response and the pathogenesis of autoimmune diseases,and to provide potential drug targets for treatment of related diseases.