TLR4-dependent Lipopolysaccharide-induced Shedding of Tumor Necrosis Factor Receptors in Mouse Bone Marrow Granulocytes

Abstract

We reported previously that bone marrow granulocytes respond to small amounts of enterobacterial lipopolysaccharide (LPS) via a CD14-independent and TLR4-mediated mechanism by de novo expression of an inducible receptor (CD14) and by down-modulation of a constitutive receptor (L-selectin). In this report we address another effect of LPS: the down-regulation of receptors for tumor necrosis factor-␣. In mouse bone marrow cells (BMC), this down-regulation is detectable soon (20 min) after exposure of the cells to low levels (0.5 ng/ml) of LPS. This temperature-dependent effect is rather selective for LPS and requires the presence of a conventional lipid A structure in the LPS molecule and a functional TLR4 molecule in the cells. The down-modulation, due to a shedding of the receptors, is blocked by p38 MAPK inhibitors, by a furin inhibitor, and by three metalloproteinase inhibitors (BB-3103, TIMP-2, and TIMP-3). In contrast, inhibitors of MEK, protein kinase C, cAMP-dependent protein kinase, and kinases of the Src family do not block the shedding. Analysis of BMC from mice lacking tumor necrosis factor receptor-1 (CD120a ؊/؊ ) or tumor necrosis factor receptor-2 (CD120b ؊/؊ ) indicates that the LPS-induced shedding is specific for CD120b. Thus, exposure of BMC to LPS triggers a rapid shedding of CD120b via a protein kinase Cand Src-independent pathway mediated by p38 MAPK, furin, and metalloproteinase. The additive effects of furin and metalloproteinase inhibitors suggest that these enzymes are involved in parallel shedding pathways.Two major cell types, the neutrophilic granulocyte and the monocyte/macrophage, are associated with susceptibility to infections (1). Both derive from granulocyte-type progenitor cells present in the bone marrow. Therefore, a better knowledge of the events following the interaction of bacterial lipopolysaccharide (LPS) 1 with bone marrow granulocytes can help us to understand some of its in vivo effects. We have shown in a previous study (2) that granulocytes from the bone marrow of LPS-responsive mice express an inducible LPS-binding site on their cell surface after exposure in vivo or in vitro to nanomolar concentrations of LPS. This cell surface molecule was identified later as CD14 (3, 4). In contrast to this expression of a receptor, many surface markers are actually down-modulated after exposure of cells to LPS. This has been observed in macrophages with mannose receptors (5), scavenger receptors (6), interleukin 6 receptors (7), CSF-M receptors (8), and TNF-␣ receptors (TNF-R) (9). Concerning BMC, we found in a previous study (10) that LPS induced in these cells a marked down-regulation of TNF-R, in the absence of any direct binding of LPS to TNF-R. Because TNF-␣ and its receptors play a prominent role in inflammation and in LPS-induced septic shock (11, 12), we considered that the mechanism by which LPS induces the down-regulation of TNF-R in BMC would deserve closer scrutiny. The two known TNF-␣ receptors CD120a (p55) and CD120b (p75) have gained wide interest because of their ...

Effect of ultraviolet radiation on the expression of pp38MAPK and furin in human keratinocyte‐derived cell lines

“…7 and Table 1). The differences in the expression of these molecules in these two keratinocyte-derived cell lines are unknown, and may be a result of tumorigenesis, although further study is needed to confirm this correlation between these proteins as suggested in other cell types (25,26).…”

“…Recent studies using proprotein convertase inhibitors have demonstrated that increased furin expression is associated with enhancement of metastatic spread and tumour cell proliferation (21,22), probably as a result of the activation of MMP involved in extracellular matrix degradation (23,24). While furin mRNA expression has been shown to be induced by UVR (19), its protein expression has not been investigated but the association between furin and pp38 has been implied in granulocytes (25) and HEK293 kidney cells (26).…”

Ectodomain shedding of angiotensin converting enzyme 2 in human airway epithelia

“…Endotoxin activates the shedding of receptors in several cell types (22,48,49,62), a property attributed to modulation of ADAM17 activity (22). The increases in sACE2 after cytokine stimulation were not due to increased ACE2 mRNA transcription because quantitative PCR showed no ACE2 mRNA induction after IL-1␤ and TNF␣ stimulation (data not shown).…”

Tumor Necrosis Factor-α (TNF-α) Regulates Shedding of TNF-α Receptor 1 by the Metalloprotease-Disintegrin ADAM8: Evidence for a Protease-Regulated Feedback Loop in Neuroprotection

“…After TNF-␣ stimulation, as observed under disease conditions, TNF receptor release is increased. In cell culture systems, soluble TNF receptors are produced in response to numerous stimuli, such as TNF-␣, bacterial lipopolysaccharides (LPS), phorbol esters (tetradecanoylphorbol acetate), and IL-10, or after T-cell and neutrophil activation (Leeuwenberg et al, 1994;Pedron et al, 2003). An aminopeptidase, ARTS-1 (Cui et al, 2002(Cui et al, , 2003 and ADAM17/TACE (Black et al, 1997;Moss et al, 1997), a member of the family of ADAM proteins, have so far been identified as proteases responsible for ectodomain shedding of TNF receptors.…”