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HMGB1 is phosphorylated by classical protein kinase C and is secreted by a calcium-dependent mechanism

 Young Joo Oh  ;  Ju Ho Youn  ;  Yeounjung Ji  ;  Sang Eun Lee  ;  Kook Jin Lim  ;  Ji Eun Choi  ;  Jeon-Soo Shin 
 JOURNAL OF IMMUNOLOGY, Vol.182(9) : 5800-5809, 2009 
Journal Title
Issue Date
v3-Phosphoinositide-Dependent Protein Kinases ; Animals ; Calcium/physiology* ; Cell Line ; Cells, Cultured ; Down-Regulation/immunology ; HMGB1 Protein/antagonists & inhibitors ; HMGB1 Protein/metabolism* ; HMGB1 Protein/secretion* ; Humans ; Lipopolysaccharides/physiology ; Mice ; Monocytes/enzymology ; Monocytes/metabolism ; Monocytes/secretion ; Phosphorylation ; Protein Kinase C/antagonists & inhibitors ; Protein Kinase C/metabolism ; Protein Kinase C/physiology* ; Protein-Serine-Threonine Kinases/physiology ; Signal Transduction/immunology
High-mobility group box 1 protein (HMGB1) has been studied as a key mediator of inflammatory diseases, including sepsis. Regulating secretion is important in the control of HMGB1-mediated inflammation. Previously, it was shown that HMGB1 needs to be phosphorylated for secretion. In this study, we show that HMGB1 is phosphorylated by the classical protein kinase C (cPKC) and is secreted by a calcium-dependent mechanism. For this study, RAW264.7 cells and human peripheral blood monocytes were treated with PI3K inhibitors wortmannin, LY294002, and ZSTK474, resulting in inhibition of LPS-stimulated HMGB1 secretion, whereas inhibitors of NF-kappaB and MAPKs p38 and ERK showed no inhibition. Akt inhibitor IV and mammalian target of rapamycin inhibitor rapamycin did not inhibit HMGB1 secretion. However, the PKC inhibitors Gö6983 (broad-spectrum PKC), Gö6976 (cPKC), and Ro-31-7549 (cPKC) and phosphoinositide-dependent kinase 1 inhibitor, which results in protein kinase C (PKC) inhibition, inhibited LPS-stimulated HMGB1 secretion. PKC activators, PMA and bryostatin-1, enhanced HMGB1 secretion. In an in vitro kinase assay, HMGB1 was phosphorylated by recombinant cPKC and by purified nuclear cPKC from LPS-stimulated RAW264.7 cells, but not by casein kinase II or cdc2. HMGB1 secretion was also induced by the calcium ionophore A23187 and inhibited by the Ca(2+) chelators BAPTA-AM and EGTA. These findings support a role for Ca(2+)-dependent PKC in HMGB1 secretion. Thus, we propose that cPKC is an effector kinase of HMGB1 phosphorylation in LPS-stimulated monocytes and PI3K-phosphoinositide-dependent kinase 1 may act in concert to control HMGB1 secretion independent of the NF-kappaB, p38, and ERK pathways.
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1. College of Medicine (의과대학) > Dept. of Microbiology (미생물학교실) > 1. Journal Papers
Yonsei Authors
Shin, Jeon Soo(신전수) ORCID logo https://orcid.org/0000-0002-8294-3234
Youn, Ju Ho(윤주호)
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