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

Young Joo Oh1, Ju Ho Youn, Yeounjung Ji

  • 1Department of Microbiology, Brain Korea 21 Project for Medical Science, Yonsei University College of Medicine, Seoul, Korea.

Journal of Immunology (Baltimore, Md. : 1950)
|April 22, 2009
PubMed

Insights

High-mobility group box 1 protein (HMGB1) secretion, a key factor in inflammation, is regulated by phosphorylation via classical protein kinase C (cPKC) in a calcium-dependent manner. This pathway is crucial for controlling HMGB1 release in inflammatory responses.

Area of Science:

  • Immunology
  • Cell Biology
  • Molecular Biology

Background:

  • High-mobility group box 1 protein (HMGB1) is a critical mediator in inflammatory diseases like sepsis.
  • Regulation of HMGB1 secretion is essential for controlling its inflammatory role.
  • Previous research indicated that HMGB1 phosphorylation is a prerequisite for its secretion.

Purpose of the Study:

  • To investigate the specific protein kinase involved in HMGB1 phosphorylation and secretion.
  • To elucidate the role of calcium signaling in HMGB1 secretion.
  • To determine the signaling pathways regulating LPS-stimulated HMGB1 secretion.

Main Methods:

  • Utilized RAW264.7 cells and human peripheral blood monocytes.
  • Employed specific inhibitors and activators for various signaling pathways, including PI3K, NF-kappaB, MAPKs, Akt, mTOR, and PKC.
  • Performed in vitro kinase assays using recombinant and purified cPKC.
  • Investigated the effect of calcium ionophore and chelators on HMGB1 secretion.

Main Results:

  • Classical protein kinase C (cPKC) was identified as the kinase responsible for HMGB1 phosphorylation.
  • HMGB1 secretion was dependent on calcium ions.
  • Inhibitors of cPKC and phosphoinositide-dependent kinase 1 (PDK1) significantly inhibited LPS-stimulated HMGB1 secretion.
  • PKC activators enhanced HMGB1 secretion.
  • PI3K inhibitors also reduced HMGB1 secretion, suggesting a role for PI3K-PDK1 in conjunction with cPKC.
  • NF-kappaB, p38, and ERK pathways were not found to be involved in regulating HMGB1 secretion.

Conclusions:

  • Classical protein kinase C (cPKC) acts as the effector kinase for HMGB1 phosphorylation in LPS-stimulated monocytes.
  • Calcium-dependent mechanisms and cPKC signaling are central to HMGB1 secretion.
  • The PI3K-PDK1 pathway may cooperate with cPKC to control HMGB1 secretion, independently of NF-kappaB, p38, and ERK pathways.

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