High Mobility Group Box 1 Protein Binding to Lipopolysaccharide Facilitates Transfer of Lipopolysaccharide to CD14 and Enhances Lipopolysaccharide-Mediated TNF-α Production in Human Monocytes

Abstract

LPS-binding protein (LBP) is a central mediator that transfers LPS to CD14 to initiate TLR4-mediated proinflammatory response. However, a possibility of another LPS transfer molecule has been suggested because LBP-deficient mice showed almost normal inflammatory response after LPS injection. In this study, we describe the novel finding that high mobility group box 1 protein (HMGB1) recently identified as a mediator of sepsis has a function of LPS transfer for a proinflammatory response. We used ELISA and surface plasmon resonance to show that HMGB1 binds LPS in a concentration-dependent manner and that the binding is stronger to lipid A moiety than to the polysaccharide moiety of LPS. This binding was inhibited by LBP and polymyxin B. Using native PAGE and fluorescence-based LPS transfer analyses, we show that HMGB1 can catalytically disaggregate and transfer LPS to both soluble CD14 protein and to human PBMCs in a dose-dependent manner. However, this effect was dramatically reduced to the baseline level when HMGB1 was heat inactivated. Furthermore, a mixture of HMGB1 and LPS treatment results in a higher increase in TNF-α production in human PBMCs and peripheral blood monocytes than LPS or HMGB1 treatment alone or their summation. Thus, we propose that HMGB1 plays an important role in Gram-negative sepsis by catalyzing movement of LPS monomers from LPS aggregates to CD14 to initiate a TLR4-mediated proinflammatory response.

High-mobility group box 1 accelerates lipopolysaccharide-induced lung fibroblast proliferation in vitro: involvement of the NF-κB signaling pathway

“…29 In addition HMGB1 binding to LPS has been reported to facilitate LPS cellular transformation to a CD14+ profile that enhances LPSmediated TNF-α production in human monocytes. 30 The present study fits with these prior data, and also provides new clues about the mechanisms involved, as described below.…”

“…3,5,28 Our finding that HMGB1 can enhance LPSinduced lung fibroblast proliferation is novel, yet consistent with findings of cooperative effects in other types of cells, including synovial fibroblasts, macrophages, and human monocytes. [29][30][31] For example, Wahamaa et al 32 showed that HMGB1 increased LPS-induced secretion of cytokines, such as tumor necrosis factor-α (TNF-α), interleukin (IL)-6, and IL-8, in synovial fibroblasts. HMGB1 was also shown to enhance the proinflammatory activity of LPS in activated macrophages by promoting the phosphorylation of p38 mitogen-activated protein kinase.…”

Lipopolysaccharide Activates Toll-like Receptor 4 (TLR4)-mediated NF-κB Signaling Pathway and Proinflammatory Response in Human Pericytes

“…Here, we have also demonstrated up-regulation of different chemokines and cytokines at both transcript and protein levels in HBVPs after exposure to HMGB1 albeit at lower levels than those observed with LPS as HMGB1 constitutes a comparatively weak TLR4 activator (40). In fact, it has been proposed that HMGB1 only exhibits full proinflammatory activity when complexed to LPS (42) because a combination of HMGB1 and LPS results in a higher increase in TNF-␣ production in human peripheral blood monocytes than LPS or HMGB1 treatment alone (43). Alternatively, HMGB1 signaling in HBVPs may be more dependent on CD14 expres- sion than LPS signaling as optimal HMGB1-dependent TLR4 activation seems to require this coreceptor at least in murine macrophages (44).…”

High Mobility Group Nucleosomal Binding Domain 2 (HMGN2) SUMOylation by the SUMO E3 Ligase PIAS1 Decreases the Binding Affinity to Nucleosome Core Particles

“…Post-translational modifications of HMG proteins can alter their interactions with DNA and proteins, and consequently, affect their biological activities (1). HMGB1, for example, could be phosphorylated and/or acetylated by pro-inflammatory signals and translocated to the cytoplasm for secretion (12,13) to induce proinflammatory response (14,15). The binding of HMGN pro-teins to nucleosomes can be altered by HMGN modification.…”