TACE is responsible for ectodomain shedding of M-CSFR. (A) Monocytes were cultured for 48 hours in the absence or presence of GM-CSF and IL-4 in combination. TACE inhibitor, TAPI-0, was added at the indicated concentrations. Soluble M-CSFR levels in culture supernatants were measured by ELISA. Data are expressed as means ± SD; *P < .05. (B) Surface expression of M-CSFR was analyzed by flow cytometry. The levels of M-CSFR in the absence of GM-CSF and IL-4 in combination are shown in gray. (C) Effects of TACE inhibition on phosphorylation of M-CSFR in monocytes in the absence or presence of GM-CSF and IL-4 in combination. Monocytes were cultured for 1 day in the absence or presence of GM-CSF and IL-4 in combination. TAPI-0 was added at 10μM as indicated. After stimulation with M-CSF for 5 minutes, the cells were fixed and stained with antiphosphorylated M-CSFR antibody. Phosphorylated M-CSFR levels were analyzed by flow cytometry, and provided as a red line. Background staining with normal IgG is shown in gray.