TNF-alpha-converting enzyme cleaves the macrophage colony-stimulating factor receptor in macrophages undergoing activation

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 macropha ge surface and identified the protease responsible for M-CSFR cleavage and down-modulation. The shedding of M-CSFR elicited by phorbol esters (tetrade canoylphorbol myristate acetate (TPA)) or LPS in murine BAC.1-2F5 macrophag es was prevented by cation chelators, as well as hydroxamate-based competit ive inhibitors of metalloproteases. We found that the protease cleaving M-C SFR is a transmembrane enzyme and that its expression is controlled by furi n-like serine endoproteases, which selectively process transmembrane metall oproteases, M-CSFR down-modulation was inhibited by treating cells in vivo, before TPA stimulation, with an Ab raised against the extracellular, catal ytic domain of proTNF-converting enzyme (TACE). TACE expression was confirm ed in BAC.1-2F5 cells and found inhibited after blocking furin-dependent pr ocessing. Using TACE-negative murine Dexter-ras-myc cell monocytes, we foun d that in these cells TPA is unable to down-modulate M-CSFR expression. The se 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 re lease 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 possi ble physiological relevance of this mechanism is discussed.