REGULATION OF THE EXPRESSION OF ENZYMES INVOLVED IN THE REPLICATION OF DNA IN CHEMICALLY-INDUCED MONOCYTIC MACROPHAGIC DIFFERENTIATION OF HL-60 LEUKEMIA-CELLS/

The expression of a number of housekeeping enzymes of DNA biosynthesis was measured in HL-60 promyelocytic leukemia cells undergoing monocyt ic/macrophagic differentiation following treatment with 12-O-tetradeca noylphorbol 13-acetate (TPA) or 1 alpha,25-dihydroxyvitamin D-3 (vitam in D-3). Progressive decreases in the steady-state levels of the mRNAs for thymidylate synthase, topoisomerase II, and hypoxanthine-guanine phosphoribosyltransferase occurred following exposure to TPA or vitami n D-3. In contrast, the steady-state levels of the mRNAs for thymidine kinase, topoisomerase I, and DNA polymerase-alpha did not decrease un til days 3-5 of treatment with vitamin D-3 and then progressively decl ined thereafter. The mRNAs for thymidine kinase and topoisomerase I de creased slightly and the mRNA for DNA polymerase-alpha by 30-40%, and then remained constant between days 1 to 3 of treatment with the phorb ol ester. The M2 subunit of ribonucleotide reductase exhibited an even greater difference, with no change in the steady-state concentration of mRNA over 3 days of exposure to TPA or vitamin D-3. On days 5-7 of treatment with vitamin D-3, essentially complete loss of the expressio n of the mRNA for the M2 subunit of ribonucleotide reductase occurred. Measurement of the enzymatic activities of thymidylate synthase and t hymidine kinase in cells exposed to either of the inducers of maturati on corroborated the findings at the level of the mRNAs, with correspon ding decreases in the activity of these enzymes. The results indicate that the down-regulation of the expression of housekeeping enzymes of DNA replication occurs as late events in HL-60 cells undergoing monocy tic/macrophagic differentiation, implying that the decreases in their gene expression are the result of the termination of proliferation rat her than an initiating event in the cessation of DNA biosynthesis. (C) 1998 Elsevier Science Ltd. All rights reserved.