Induction and function of 2',5'-oligoadenylate synthetase in differentiation of mouse myeloid leukemia cells

The activity of 2′,5′-oligoadenylate synthetase (2-5A synthetase), known to be induced by interferon, was detected in mouse myeloid leukemic M1 cells only when they differentiated to phagocytic cells after incubation with conditioned medium (CM) from rat embryo cells. However, no interferon activity occurred in culture fluids of CM-treated M1 cells, although some activity was detected in the cell extracts. When anti-interferon serum was added to M1 cell cultures, the induction of 2-5A synthetase by CM was suppressed. These results suggest that CM stimulated the M1 cells to produce a minute amount of interferon, which was reponsible for induction of the 2-5A synthetase activity. On the other hand, development of the phagocytic activity of M1 cells could not be influenced by addition of antiserum. Interferon added exogenously per se neither induced phagocytic activity of M1 cells, nor did it enhance the CM-induced differentiation of the cells. Moreover, dexamethasone, which induced differentiation of M1 cells, was not capable of inducing 2-5A synthetase. These results indicate that interferon and/or 2-5A synthetase plays no essential part in the differentiation of M1 cells.