TNF-α-Converting Enzyme Cleaves the Macrophage Colony-Stimulating Factor Receptor in Macrophages Undergoing Activation

Abstract

We previously reported that macrophage activators such as LPS, IL-2, and IL-4 down-modulate the M-CSFR via a mechanism involving protein kinase C and phospholipase C. In this study, we showed that M-CSFR is shed from macrophage surface and identified the protease responsible for M-CSFR cleavage and down-modulation. The shedding of M-CSFR elicited by phorbol esters (tetradecanoylphorbol myristate acetate (TPA)) or LPS in murine BAC.1-2F5 macrophages was prevented by cation chelators, as well as hydroxamate-based competitive inhibitors of metalloproteases. We found that the protease cleaving M-CSFR is a transmembrane enzyme and that its expression is controlled by furin-like serine endoproteases, which selectively process transmembrane metalloproteases. M-CSFR down-modulation was inhibited by treating cells in vivo, before TPA stimulation, with an Ab raised against the extracellular, catalytic domain of proTNF-converting enzyme (TACE). TACE expression was confirmed in BAC.1-2F5 cells and found inhibited after blocking furin-dependent processing. Using TACE-negative murine Dexter-ras-myc cell monocytes, we found that in these cells TPA is unable to down-modulate M-CSFR expression. These data indicated that TACE is required for the TPA-induced M-CSFR cleavage. The possibility that the cleavage is indirectly driven by TACE via the release of TNF was excluded by treating cells in vivo with anti-TNF Ab. Thus, we concluded that TACE is the protease responsible for M-CSFR shedding and down-modulation in mononuclear phagocytes undergoing activation. The possible physiological relevance of this mechanism is discussed.

Phorbol 12-Myristate 13-Acetate-Induced Release of the Colony-Stimulating Factor 1 Receptor Cytoplasmic Domain into the Cytosol Involves Two Separate Cleavage Events

“…This is consistent with an observation showing that there is no increase in CSF-1 receptor phosphorylation upon activation of PKC (22). It has been found recently that release of the extracellular domain of the CSF-1 receptor is mediated by TACE (59). TACE is a cell surface-associated metalloprotease that is composed of an extracellular catalytic domain, a transmembrane domain, and a small cytoplasmic domain (34).…”

The ADAMs family of metalloproteases: multidomain proteins with multiple functions

“…Shedding of the receptor by PKC activators generates a soluble form that is still competent for ligand binding, and down-modulates CSF-1 signaling and inactivates macrophages. CSF-1 receptor shedding is blocked by metalloprotease inhibitors as well as by an antibody to the catalytic site of ADAM17 (Rovida et al 2001). The reduction of cell surface CSF-1 receptor by TPA treatment is also effectively abolished in ADAM17 deficient monocytes.…”

Differential Effects of CpG DNA on IFN-β Induction and STAT1 Activation in Murine Macrophages versus Dendritic Cells: Alternatively Activated STAT1 Negatively Regulates TLR Signaling in Macrophages

“…Total STAT1 levels served as an internal control within the experiment. We and others showed that LPS and CpG DNA caused a loss of cell surface CSF-1R due to cleavage of the extracellular domain, whereas IFN-␥ only modestly down-regulated cell surface CSF-1R expression (34,36,42,43). Consistent with these previous findings, CSF-1R levels in extranuclear extracts were markedly reduced in response to LPS and CpG DNA, but were only modestly affected by IFN-␥ (Fig.…”