The role of granulocyte-macrophage colony-stimulating factor in induction of monocytic differentiation of HL-60 cells: synergistic interaction with 1 alpha, 25-dihydroxyvitamin D3 and interferon-gamma in inducing interleukin-1 beta

1 alpha, 25-Dihydroxyvitamin D3 (D3) (100 nM) and interferon-gamma (IFN-gamma) (100 U/ml) cooperatively inhibited the proliferation of HL-60 cells, and synergistically induced their monocytic differentiation. The growth-promoting effect of granulocyte-macrophage colony-stimulating factor (GM-CSF) (10 ng/ml) was inhibited appreciably by D3 and slightly by IFN-gamma. Despite the clear difference in their effects on growth of HL-60 cells, both IFN-gamma and GM-CSF in combination with D3 induced cell cycle changes, decreasing the number of cells in the S phase and increasing their percentage in the G1/0 phase. GM-CSF alone had no effect on differentiation, but enhanced differentiation induced by D3 distinctly though to a limited extent, and also enhanced monocytic differentiation, including morphological changes of HL-60 cells in the presence of D3 and IFN-gamma. GM-CSF as well as D3 and IFN-gamma induced interleukin-1 beta (IL-1 beta) production by the HL-60 cells, clearly indicating their importance in differentiation of these cells. IFN-gamma and GM-CSF had mutually potentiating effects and induced maximum IL-1 beta production in response to lipopolysaccharide (LPS) in the presence of D3. Thus despite its growth-promoting effect, GM-CSF is a potential inducer of monocytic differentiation of human myeloid leukemia cells, because in cooperation with IFN-gamma it induced monocyte-macrophage differentiation of HL-60 cells in the presence of D3.