ERYTHROID-DIFFERENTIATION AND POLY(ADP-RIBOSE) SYNTHESIS IN FRIEND-LEUKEMIA CELLS

Nicotinamide, a specific inhibitor of poly(ADP-ribose) synthetase, was a moderate inducer of Hb synthesis in Friend erythroid leukemia cells (FLC). The effect of other inducers, such as dimethyl sulfoxide (DMSO), hexamethylene-bisacetamide (HMBA) and butyrate, on poly(ADP-ribose) synthesis was examined. The extent of poly(ADP-ribose) synthesis in nuclei of FLC treated with DMSO or HMBA began to decrease before many phenotypic changes including Hb production and reached 30-50% of the level of nontreated control when the cells enter the stationary phase. FLC variants unresponsive to HMBA or DMSO did not exhibit as low an activity of poly(ADP-ribose) synthesis as their parent cells did by treatment with these inducers. Butyrate stimulated poly(ADP-ribose) synthesis transiently but distinctly (about 50%) at an early stage of culture (6-24 h), but suppressed it at a later stage. Neither the cell growth nor degradation of poly(ADP-ribose) is correlated with the effect of inducers. The level of poly(ADP-ribose) synthesis is correlated with the differentiation of FLC.