Development, characterization, and subcellular location of DNAse activity in HL-60 cells and monocytes

The digestion of DNA from intact bacteria by human phagocytic cells was measured by the release of solubilized radiolabeled DNA. Two subclones from the human promyelocytic HL-60 cell line were unable to digest bacterial DNA unless they were previously induced to mature by incubation for several days with 1.25% dimethylsulfoxide (DMSO). The maximal capacity of DMSO-induced HL-60 cells to digest DNA was similar to that of monocytes purified from peripheral blood (PB) and much greater than that of neutrophils. The increasing capacity to digest DNA during maturation was associated with the development of acid DNAse activity, measured in a cell-free system, and slightly preceded development of 12-O-tetradecanoyl phorbol 13-acetate-stimulated respiratory burst activity. The acid DNAse had a pH optimum of 5.0 and did not require the presence of calcium or 2-mercaptoethanol (2-ME). A third subclone of HL-60 cells was able to digest DNA from intact bacteria without previous maturation, however, and this was associated with the presence of an alkaline DNAse which had a pH optimum between 7.0 and 8.0 and showed a dependence on calcium and 2-ME for maximal activity. The subcellular location of acid DNAse in DMSO-induced HL-60 cells was similar to that of monocytes in having a bimodal distribution on fractionated sucrose density gradients. The dense peak (mean density 1.195 g/mL) was located in the same region of the gradient as primary granule enzymes but the light peak (mean density 1.137 g/mL) did not codistribute with either plasma membrane, endoplasmic reticulum, or mitochondria, suggesting accumulation in a different organelle.