PURINE METABOLISM IN PROMYELOCYTIC HL-60 AND DIMETHYLSULFOXIDE-DIFFERENTIATED HL-60 CELLS

Purine metabolism was studied in the human promyelocytic leukaemic cell line HL60 both before and after differentiation by dimethylsulphoxide (DMSO) treatment in vitro. DMSO-induced differentiation had no effect on the steady-state concentration of 5-phosphoribosylpyrophosphate pyrophosphate (PRPP), even though the activity of the oxidative seg ment of the pentose phosphate pathway (OPP) increased two-fold and the activities of glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase were enhanced 3-6 times. [C-14]-formate incorporation, on the other hand, showed that undifferentiated HL60 cells produced purines by the de novo pathway at six-fold the rate of the differentiated cells and at three times the rate measured in polymorphonuclear leukocytes (PMNs) separated from human blood. This is consistent with significantly higher activities (two to five-fold) of the key regulatory enzymes of the de novo purine synthesis pathway (PRPP synthetase, amido-phosphoribosyl transferase and adenylosuccinate synthase) in the undifferentiated cells. Labelling the cells with [C-14]-hypoxanthine showed that there was an active salvage pathway in the HL60 cells which remained unaltered by differentiation. The activities of the salvage enzymes were also the same, although hypoxanthine was taken up at twice the rate by the undifferentiated cells. Human PMNs had an active salvage pathway, but their rate was five times lower than that of the HL60 cells, consistent with much lower activities (three to eight-fold) of the salvage pathway enzymes. These observations suggest that regulation of the synthesis and activities of the purine nucleotide synthesis enzymes may play an important role in the regulation of differentiation of myeloid cells.