• Ko-ichi Kawahara, Kamal Krishna Biswas, Masako Unoshima, Takashi Ito, Kiyoshi Kikuchi, Yoko Morimoto, Masahiro Iwata, Salunya Tancharoen, Yoko Oyama, Kazunori Takenouchi, Yuko Nawa, Noboru Arimura, Meng Xiao Jie, Binita Shrestha, Naoki Miura, Toshiaki Shimizu, Kentaro Mera, Shin-ichiro Arimura, Noboru Taniguchi, Hideo Iwasaka, Sonshin Takao, Teruto Hashiguchi, and Ikuro Maruyama.
• Department of Laboratory and Vascular Medicine Cardiovascular and Respiratory Disorders Advanced Therapeutics, Kagoshima University Graduate School of Medical and Dental Science, Kagoshima 890-8520, Japan.
• Cardiovasc. Pathol. 2008 May 1; 17 (3): 129-38.

BackgroundC-reactive protein (CRP) is widely used as a sensitive biomarker for inflammation. Increasing evidence suggests that CRP plays a role in inflammation. High-mobility group box-1 (HMGB1), a primarily nuclear protein, is passively released into the extracellular milieu by necrotic or damaged cells and is actively secreted by monocytes/macrophages. Extracellular HMGB1 as a potent inflammatory mediator has stimulated immense curiosity in the field of inflammation research. However, the molecular dialogue implicated between CRP and HMGB1 in delayed inflammatory processes remains to be explored.Methods And ResultsThe levels of HMGB1 in culture supernatants were determined by Western blot analysis and enzyme-linked immunosorbent assay in macrophage RAW264.7 cells. Purified CRP induced the release of HMGB1 in a dose- and time-dependent fashion. Immunofluorescence analysis revealed nuclear translocation of HMGB1 in response to CRP. The binding of CRP to the Fc gamma receptor in RAW264.7 cells was confirmed by fluorescence-activated cell sorter analysis. Pretreatment of cells with IgG-Fc fragment, but not IgG-Fab fragment, efficiently blocked this binding. CRP triggered the activation of p38MAPK and ERK1/2, but not Jun N-terminal kinase. Moreover, both p38MAPK inhibitor SB203580 and small interfering RNA significantly suppressed the release of HMGB1, but not the MEK1/2 inhibitor U-0126.ConclusionWe demonstrated for the first time that CRP, a prominent risk marker for inflammation including atherosclerosis, could induce the active release of HMGB1 by RAW264.7 cells through Fc gamma receptor/p38MAPK signaling pathways, thus implying that CRP plays a crucial role in the induction, amplification, and prolongation of inflammatory processes, including atherosclerotic lesions.

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