In studies with the human promyelocytic
leukemia cell line HL-60, we defined changes in intermediary
purine metabolism that appear to contribute to the regulation of terminal maturation in myeloid cells. When HL-60 cells were exposed to compounds that induce maturation, consistent alterations in
purine metabolism were found to occur within 24 h of culture. Perturbation of
guanosine nucleotide synthesis and decreases of up to 50% in intracellular guanylate pool sizes were associated with the induced maturation of these cells in response to diverse inducing agents. While immature HL-60 cells were observed to synthesize
purine nucleotides by both de novo and salvage pathways, the activity of both pathways decreased in cells induced to mature, although the relative contribution of
purine salvage increased. Moreover, incorporation of the salvage pathway precursor, [14C]
hypoxanthine from the intermediate,
inosine monophosphate (
IMP), into guanylates was reduced by approximately 65% in induced HL-60 cells, reflecting decreased activity of both
hypoxanthine phosphoribosyltransferase and
IMP dehydrogenase. When various inhibitors of
IMP dehydrogenase (mycophenolic acid, 3-deazaguanosine, and 2-beta-D-ribofuranosylthiazole-4-carboxamide) were evaluated for their effects upon HL-60 cells, each agent was found to induce the cells to mature morphologically and functionally. Like other inducers, these agents decreased HL-60 cell proliferation and caused the cells to acquire an ability to phagocytose opsonized yeast and reduce
nitroblue tetrazolium. Each agent reduced intracellular
guanosine nucleotide pool sizes and induced HL-60 cell maturation at micromolar concentrations. These observations suggest that the size of intracellular
guanosine nucleotide pools, the biosynthesis of
guanosine nucleotides, and the activity of
IMP dehydrogenase may be central to the regulation of terminal maturation in myeloid cells.