Human colony-stimulating factor-producing lung cancer tissue releases a differentiation-inducing factor for human leukemic cells

: Human lung cancer that induced marked granulocytosis in both the patient and tumor-transplanted nude mice (G2 mice) and from which conditioned medium (G2-T-CM) exhibited human and mouse active colony-stimulating activity (CSA) has been reported (K. Ikeda et al. Cancer Res 1985; 45:4144-4249). Recently, we found differentiation-inducing activity (DIA) in G2-T-CM, which differentiated human promyelocytic leukemic cells (HL-60) to macrophage-like cells. Differentiated HL-60 cells were considered to be mature macrophages as judged by the positivity of butyrate esterase activity, the acquisition of Fc receptor, and the increment in capacity of phagocytosis and nitroblue tetrazolium reduction. The DIA in G2-T-CM was not attributed to interferons known to have DIA, because interferon activity was not found in G2-T-CM by bioassay (less than 4 U/ml) and by radioimmunoassay for gamma-IFN (less than 0.1 U/ml). Molecular weight of DIA was 36,000 Da and separated from CSA of which molecular weight was 22,000 Da by gel filtration on Sephadex G-150. DIA and CSA were also separated on chromatofocusing chromatography, because isoelectric point of DIA was mainly less than 4.0 and that of CSA was 4.3-5.7. This DIA was stable after heat treatment (56 degrees C for 30 min or 100 degrees C for 10 min) and in acidic condition (pH 2.0 for 24 hr). G2-T-CM is a good source of differentiation-inducing factor for further purification and molecular cloning.