Enhancement of Growth of a Mouse Macrophage Cell Line by a Tumor Promoter and Granulocyte-Macrophage Colony-stimulating Factor¹

The macrophage-like cell line Mm-1 consists of spontaneously differentiated cells of a clonal line of mouse myeloid leukemia cells (MI). Mm-1 cells were seeded in soft agar on a harder agar base in the presence or absence of ascitic fluid from rats bearing hepatoma AH-130. Although a few colonies developed in the absence of ascitic fluid, the number of colonies was significantly increased by addition of the ascitic fluid. Further addition of 12-O-tetradecanoylphorbol-13-acetate (TPA) synergistically enhanced formation of colonies of Mm-1 cells in the presence of the ascitic fluid, although TPA alone had no effect. In the presence of 2.5 or 5% ascitic fluid, TPA (3.2 × 10⁻⁷ m) caused a 1.5- to 3-fold increase in the number of colonies over the number without TPA.

A positive correlation was found between the tumor-promoting activities of several plant diterpenes and their enhancing effects on growth of Mm-1 cells in semisolid agar in the presence of ascitic fluid from rats bearing hepatoma AH-130. Ascitic fluid contains granulocyte-macrophage colony-stimulating factor (GM-CSF). Conditioned media containing GM-CSF from embryo cells, peritoneal macrophages, and Yoshida sarcoma cells, or highly purified GM-CSF's from human urine and mouse L-cells also acted synergistically with TPA in increasing the number of colonies of Mm-1 cells. On the other hand, neither epidermal growth factor nor fibroblast growth factor with or without TPA stimulated colony formation of Mm-1 cells. These results indicate that colony formation of Mm-1 cells is stimulated as a result of the specific interaction of the tumor promoter with growth factor(s), possibly GM-CSF.