High Mobility Group Box-1 protein (HMGB1) interacts with multiple Toll like receptors

High mobility group box 1(HMGB1), originally described as a DNA-binding protein, can also be released extracellularly and functions as a late mediator of inflammatory responses. Although recent reports indicated that the receptor for advanced glycation endproducts (RAGE), as well as Toll-like receptors (TLR2 and TLR4), were involved in cellular activation by HMGB1, there has been little evidence of direct association between HMGB1 and these receptors. To examine this issue, we used fluorescence resonance energy transfer (FRET) and immunoprecipitation to directly investigate cell surface interactions of HMGB1 with TLR2, TLR4, and RAGE. FRET images in RAW 264.7 macrophages demonstrated association of HMGB1 with TLR2 and TLR4, but not RAGE. Transient transfections into HEK293 cells showed that HMGB1 induced cellular activation and NF-κB dependent transcription through TLR2 or TLR4, but not RAGE. Co-immunoprecipitation also found interaction between HMGB1 and TLR2 as well as TLR4, but not with RAGE. These studies provide the first direct evidence that HMGB1 can interact with both TLR2 and TLR4, and also supply an explanation for the ability of HMGB1 to induce cellular activation and generate inflammatory responses that are similar to those initiated by LPS.