Fas (CD95) induces rapid, TLR4/IRAK4-dependent release of pro-inflammatory HMGB1 from macrophages

Feng Wang,Michael Hawkes,Ziyue Lu,Kevin C Kain,W Conrad Liles,Huan Yang

doi:10.1186/1476-9255-7-30

Abstract

Although Fas (CD95) is recognized as a death receptor that induces apoptosis, recent studies indicate that the Fas/FasL system can induce pro-inflammatory cytokine production by macrophages independent of conventional caspase-mediated apoptotic signaling. The precise mechanism(s) by which Fas activates macrophage inflammation is unknown. We hypothesized that Fas stimulates rapid release of high mobility group box 1 (HMGB1) that acts in an autocrine and/or paracrine manner to stimulate pro-inflammatory cytokine production via a Toll-like receptor-4 (TLR4)/Interleukin-1 receptor associated kinase-4 (IRAK4)-dependent mechanism. Following Fas activation, HMGB1 was released within 1 hr from viable RAW267.4 cells and primary murine peritoneal macrophages. HMGB1 release was more rapid following Fas activation compared to LPS stimulation. Neutralization of HMGB1 with an inhibitory anti-HMGB1 monoclonal antibody strongly inhibited Fas-induced production of tumor necrosis factor (TNF) and macrophage inflammatory protein-2 (MIP-2). Both Fas-induced HMGB1 release and associated pro-inflammatory cytokine production were significantly decreased from Tlr4-/- and Irak4-/- macrophages, but not Tlr2-/- macrophages. These findings reveal a novel mechanism underlying Fas-mediated pro-inflammatory physiological responses in macrophages. We conclude that Fas activation induces rapid, TLR4/IRAK4-dependent release of HMGB1 that contributes to Fas-mediated pro-inflammatory cytokine production by viable macrophages.

Highlights

Fas (CD95) is a 48-kDa, type I transmembrane protein member of the tumor necrosis factor (TNF) receptor family [1]
Recent evidence indicates that high mobility group box 1 (HMGB1) can be released from necrotic cells and from activated macrophages to act as an 'endogenous dangerous signal' or 'alarmin' [24]
Because LPS is recognized to be an important stimulus for activation of HMGB1 release from mφ [32], the release of HMGB1 was compared at different times (1-24 hr) following incubation with mFasL, activating anti-Fas monoclonal antibody (mAb) Jo2 (0.25 μg/ ml), and LPS (0.25 μg/ml), respectively (Figure 1B)

Summary

Introduction

Fas (CD95) is a 48-kDa, type I transmembrane protein member of the TNF receptor family [1]. The endogenous ligand for Fas is FasL (CD178), a 40-kDa, type II homotrimeric transmembrane protein member of the TNF gene family [1,2]. Accumulating evidence indicates that Fas can mediate myeloid differentiation factor 88 (MyD88)/ interleukin-1 receptor-associated kinase-4 (IRAK4)dependent pro-inflammatory responses via mechanisms. In addition to its role in regulation of transcription, HMGB1 has been shown to activate pro-inflammatory responses when released by necrotic cells into the extracellular milieu [19]. Recent evidence indicates that HMGB1 can be released from necrotic cells and from activated macrophages to act as an 'endogenous dangerous signal' or 'alarmin' [24]. HMGB1-induced proinflammatory cytokine production by macrophages has been reported to be TLR4-dependent [28,29,30]

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Conclusion