Opposite effects of miR-155 in the initial and later stages of lipopolysaccharide(LPS)-induced inflammatory response

Although microRNA-155(miR-155)is considered a pro-inflammatory mediator,cumulative evidence indicates that it also has anti-inflammatory effects in macrophages and dendritic cells.In this study,we identified the dramatic expression changes of more than half of potential miR-155-targeted genes upon lipopolysaccharide(LPS)stimulation;223 genes were down-regulated and 85 genes were up-regulated,including suppressor of cytokine signaling 1(SOCS1)and transforming growth factor-β-activated kinase 1-binding protein 2(TAB2),two well-known genes involved in miR-155-mediated regulation of the Toll-like receptor 4(TLR4)signaling pathway.We also found that miR-155 acted as an anti-inflammatory mediator in the initial stage of LPS-induced inflammatory response mainly through repressing TAB2 protein translation,and as a proinflammatory mediator by down-regulating SOCS1 in the later stage.Meanwhile,overexpression of TAB23'untranslated region(UTR)in macrophages promoted the development of endotoxin tolerance by competing for binding with miR-155,which resulted in an elevated expression level of SOCS1 protein.These findings provide new insights for understanding the regulatory mechanisms in fine-tuning of LPS-induced innate immune response.