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* Department of Surgery, University of Pittsburgh, Pittsburgh, PA 15213;
Department of Pharmacology and Cancer Biology, Duke University, Durham, NC 27710; and
Department of Critical Care Medicine, University of Pittsburgh, Pittsburgh, PA 15213
The chromatin-binding factor high-mobility group box 1 (HMGB1) functions as a proinflammatory cytokine and late mediator of mortality in murine endotoxemia. Although serine phosphorylation of HMGB1 is necessary for nucleocytoplasmic shuttling before its cellular release, the protein kinases involved have not been identified. To investigate if calcium/calmodulin-dependent protein kinase (CaMK) IV serine phosphorylates and mediates the release of HMGB1 from macrophages (M
) stimulated with LPS, RAW 264.7 cells or murine primary peritoneal M were incubated with either STO609 (a CaMKIV kinase inhibitor), KN93 (a CaMKIV inhibitor), or we utilized cells from which CaMKIV was depleted by RNA interference (RNAi) before stimulation with LPS. We also compared the LPS response of primary M isolated from CaMKIV+/+ and CaMKIV–/– mice. In both cell types LPS induced activation and nuclear translocation of CaMKIV, which preceded HMGB1 nucleocytoplasmic shuttling. However, M treated with KN93, STO609, or CaMKIV RNAi before LPS showed reduced nucleocytoplasmic shuttling of HMGB1 and release of HMGB1 into the supernatant. Additionally, LPS induced serine phosphorylation of HMGB1, which correlated with an interaction between CaMKIV and HMGB1 and with CaMKIV phosphorylation of HMGB1 in vitro. In cells, both HMGB1 phosphorylation and interaction with CaMKIV were inhibited by STO609 or CaMKIV RNAi. Similarly, whereas CaMKIV+/+ M showed serine phosphorylation of HMGB1 in response to LPS, this phosphorylation was attenuated in CaMKIV–/– M. Collectively, our results demonstrate that CaMKIV promotes the nucleocytoplasmic shuttling of HMGB1 and suggest that the process may be mediated through CaMKIV-dependent serine phosphorylation of HMGB1.
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1 This work was supported by Grant 1KL2 RR024154-01 (to M.R.R.) from the National Center for Research Resources (NCRR), a component of the National Institutes of Health (NIH), and the NIH Roadmap for Medical Research. This work was also supported by NIH grant DK074701 (to A.R.M.).
2 X.Z. and D.W. contributed equally to this work.
3 Address correspondence and reprint requests to Dr. Matthew R. Rosengart, Department of Surgery, University of Pittsburgh, 200 Lothrop Street, Pittsburgh, PA 15213. E-mail address: rosengartmr{at}upmc.edu
4 Abbreviations used in this paper: HMGB1, high-mobility group box 1; CaMK, calcium/calmodulin-dependent protein kinase; M, macrophage; NLS, nuclear localization signal; RNAi, RNA interference; siRNA, small interfering RNA.
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