Nucleolin Mediates LPS-induced Expression of Inflammatory Mediators and Activation of Signaling Pathways

In this study, we investigated the effects of nucleolin on lipopolysaccharide (LPS)-induced activation of MAPK and NF-KappaB (NF-kappa B) signaling pathways and secretion of TNF-alpha, IL-1 beta and HMGB1 in THP-1 monocytes. Immunofluorescence assay and Western blotting were used to identify the nucleolin expression in cell membrane, cytoplasm and nucleus of THP-1 monocytes. Inactivation of nucleolin was induced by neutralizing antibody against nucleolin. THP-1 monocytes were pretreated with anti-nucleolin antibody for 1 h prior to LPS challenge. The irrelevant IgG group was used as control. Secretion of inflammatory mediators (TNF-alpha, IL-1 beta and HMGB1) and activation of MAPK and NF-kappa B/I-kappa B signaling pathways were examined to assess the effects of nucleolin on LPS-mediated inflammatory response. Nucleolin existed in cell membrane, cytoplasm and nucleus of THP-1 monocytes. Pretreatment of anti-nucleolin antibody significantly inhibited the LPS-induced secretion of TNF-alpha, IL-1 beta and HMGB1. P38, JNK, ERK and NF-kappa B subunit p65 inhibitors could significantly inhibit the secretion of IL-1 beta, TNF-alpha and HMGB1 induced by LPS. Moreover, the phosphorylation of p38, JNK, ERK and p65 (or nuclear translocation of p65) was significantly increased after LPS challenge. In contrast, pretreatment of anti-nucleolin antibody could significantly inhibit the LPS-induced phosphorylation of p38, JNK, ERK and p65 (or nuclear translocation of p65). However, the irrelevant IgG, as a negative control, had no effect on LPS-induced secretion of TNF-alpha and IL-1 beta and phosphorylation of p38, JNK, ERK and p65 (or nuclear translocation of p65). We demonstrated that nucleolin mediated the LPS-induced activation of MAPK and NF-kappa B signaling pathways, and regulated the secretion of inflammatory mediators (TNF-alpha, IL-1 beta and HMGB1).