Role Of KLF4 In Regulating The Expression Of IL-6 Induced By LPS

Sepsis is the systemic inflammatory response syndrome(SIRS) induced by infectibn.It has been emphasized that lipopolysacchride(LPS) plays an important role in the pathogenesis of sepsis by initiating the immune system.Many studies have demonstrated that LPS mediates activation of multiple signal-transduction pathways and some inflammation-related transcriptional factors,and then promotes the expression of multiple target inflammatory genes.However,the particular mechanisms of sepsis are still obscure.IL-6 is an important inflammatory mediator,which can be stimulated by LPS.LPS can activate NF-κB signaling pathway through a complex combination of components which includes Toll-like receptor,CD14 and MD-2.The activated NF-κB could translate into the nucleus,then it activates the expression of IL-6.Kruppel-like factor 4(KLF4),a member of Sp1/KLF zinc-finger transcriptional factor family,binds to the binding sites including GC box, CACCC box and basic transcription elements on the promoters of target genes,to regulate the expression of target genes directly.By regulating the expression of the target genes,KLF4 plays important roles in cellular proliferation and differentiation,embryogenesis and the development of carcinoma.However on the expression pattem of KLF4 under LPS treatment,and the roles and mechanisms of KLF4 in regulating the expression of inflammatory genes is not delineated.Our previously research from cDNA microarray assays revealed that the expression level of KLF4 was up-regulated in lung tissues at 2 h,and further increased up to more than 10 times of the normal level at 20 h after LPS injection. KLF4 can be induced by IFN-γ,LPS or TNF-αin macrophages.KLF4 can induce iNOS(inducible nitric-oxide synthase,iNOS)through the promoter region of KLF4.And it can inhibit PAI-Ⅰ(plasminogen activator inhibitor type-Ⅰ,PAI-Ⅰ)expression.Thus it plays a key role in pro-inflammatory activation.Recent study has demonstrated that KLF4 plays an important role in regulating the endothelial cell's inflammatory response.Our studies have demonstrated that KLF4 can regulate IL-1β, IL-10 and post-inflammatory mediators HMGB-1 directly.These results indicate that KLF4 may be an important transcriptional factor participating in the expression regulation of inflammatory mediator genes.Our study uses RAW264.7 cells over-expresses KLF4,and inhibited the expression of KLF4 gene in RAW264.7 macrophages by transfection of KLF4 antisense oligonucleotides.Then,according to the screening results from bioinformatics and our study,we selected IL-6 to investigate the effect of KLF4 on its expression and release under normal condition and LPS treatment.The results showed that,overexpression of KLF4 could inhibit the expression and release of IL-6 induced by LPS, on the other hand,the inhibition of KLF4 by antisense oligonucleotides could promote the expression and release of IL-6.The results from EMSA demonstrated that KLF4 could not bind to the KLF4 binding sites on the promoter of IL-6 gene.The results from luciferase reporter gene assay demonstrated that KLF4 could inhibit the transcriptional activity of IL-6 gene.In summary these results show that,KLF4 may play an important role in SIRS by LPS.