Potent inhibition of cell density-dependent apoptosis and enhancement of survival by dimethyl sulfoxide in human myeloblastic HL-60 cells.

Human myeloblastic cell line HL-60 cells undergo apoptosis during in vitro culture in a cell density-dependent manner, and this cell density-dependent apoptosis was observed when the concentration of cultured cells exceeded 8-10 x 10(5) cells/ml. Dimethyl sulfoxide (DMSO), a differentiation inducer of HL-60 cells, did not amplify, but rather potently inhibited, this apoptosis. In a low density culture condition, DMSO attenuated proliferation of HL-60 cells in spite of its inhibition of apoptosis. In contrast, DMSO did support cell survival under high cell density conditions, and DMSO-treated HL-60 cells reached an extremely high concentration of 2-3 x 10(6) cells/ml, a condition which could never be possible in a usual culture environment. Thus, DMSO exerted dual effects on cell proliferation, i.e., growth inhibition and apoptosis inhibition, and the sum of these effects resulted in an apparently distinct phenomenon according to the culture conditions including cell density.