Production of differentiation-inhibiting factor in cultured mouse myeloid leukemia cells treated with retinoic acid.

Mouse myeloid leukemia cells (M1) could be induced to differentiate into mature macrophages and granulocytes with dexamethasone or proteinaceous inducer. Retinoic acid inhibited functional and morphological differentiation of M1 cells, but the pyridyl analog of retinoic acid had no effect. M1 cells could be induced to produce a factor(s) inhibiting their own differentiation to macrophage- and granulocyte-like cells by retinoic acid but not by its pyridyl analog. This factor(s) inhibited induction by inducers of phagocytic activity, locomotive activity, lysozyme activity, and morphological changes in M1 cells. The production of the inhibitory factor(s) by M1 cells incubated with retinoic acid was inhibited by a low concentrations (5--10 ng/ml) of actinomycin D. The inhibitory factor seemed to be a protein(s), since it was susceptible to heat treatment and proteases. The effect of retinoic acid in inducing production of the inhibitory factor(s) by M1 cells seemed to be reversible, since it was low on washing the cells with fresh medium. Therefore, induction of this inhibitory factor may be involved in the mechanism of inhibition of functional and morphological differentiation of M1 cells by retinoic acid.