Characterization of sublines of HL-60 human leukemia cells resistant to induction of differentiation by butyric acid.

HL-60 human leukemia cells undergo terminal differentiation when cultured with butyric acid. To produce cells resistant to the maturation-inducing effects of butyric acid, two strategies were followed. First, HL-60 cells were mutagenized and cultured in soft agar with inducing concentrations of butyric acid. Four clones were isolated resistant to a wide variety of differentiation inducers, including butyric acid. Second, HL-60 cells were cultured in gradually increasing concentrations of butyric acid until a normal growth rate was achieved in medium containing greater than 1 mM butyric acid. These cells retained their ability to be induced to mature to neutrophils with dimethylsulfoxide, retinoic acid, and actinomycin D; and to monocyte/macrophage like cells with tetradecanoylphorbol acetate and 1,25-(OH)2 vitamin D3. However, they no longer underwent terminal differentiation when butyric acid was added in increasing concentration, even when cytotoxic concentrations were used. The mutagenized clones cells appeared permanently butyrate resistant, but the selected clones reverted to the wild-type state when grown in the absence of butyric acid. The selected cells continued to express myeloperoxidase; the mutagenized lines did not. Thus, by using two different protocols, HL-60 cells resistant to the cytotoxic and maturation-inducing effects of butyric acid can be produced that have varied phenotypic characteristics.