Ninjurin1 promotes macrophage-induced inflammation through direct binding to lipopolysaccharide

Abstract

Ninjurin1 is a transmembrane protein involved in macrophage migration and adhesion during inflammation. It was recently reported that the repression of Ninjurin1 attenuated the lipopolysaccharide (LPS)-induced inflammatory response in macrophages

however, the precise mechanism by which Ninjurin1 modulates LPS-induced inflammation remains poorly understood. In the present study, it was found that the interaction between Ninjurin1 and LPS contributed to the LPS-induced inflammatory response. Notably, pull-down assays using lysates from HEK293T cells transfected with human or mouse Ninjurin1 and biotinylated LPS (LPS-biotin) showed that LPS directly bound Ninjurin1. Subsequently, LPS binding assays with various truncated forms of Ninjurin1 protein revealed that amino acids (aa) 81–100 of Ninjurin1 were required for LPS binding. In addition, knockdown experiments using Ninj1 siRNA resulted in decreased nitric oxide (NO) and tumor necrosis factor-alpha (TNFα) secretion upon LPS treatment in Raw264.7 cells. Collectively, our results suggest that Ninjurin1 regulates the LPS-induced inflammatory response through its direct binding to LPS, thus, identifying Ninjurin1 as a putative target for the treatment of inflammatory diseases, such as sepsis and inflammation-associated carcinogenesis.