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

The expression of seven enzymes involved in the biosynthesis of DNA wa s measured in HL-60 promyelocytic leukemia cells treated with dimethyl sulfoxide (DMSO) or all-trans retinoic acid (RA) to gain information o n their role in the termination of proliferation in cells undergoing g ranulocytic differentiation. The steady-state levels of the mRNAs for topoisomerase I, topoisomerase II, DNA polymerase-alpha, thymidylate s ynthase, thymidine kinase and hypoxanthine-guanine phosphoribosyltrans ferase progressively declined from day 3 to day 7 of exposure to the p olar solvent or the retinoid suggesting that the expression of these e nzymes is coordinately regulated. In contrast, a pronounced difference between the two inducers of differentiation occurred in the expressio n of the mRNA of the M2 subunit of ribonucleotide reductase, with DMSO causing virtually complete inhibition of the expression of the M2 sub unit of the enzyme from day 5 through day 7, with no change in the ste ady-state levels of the mRNA being produced by retinoic acid. Measurem ent of the enzymatic activities of two of these catalysts, thymidylate synthase and thymidine kinase, in cells exposed to the two inducers o f maturation corroborated the findings at the level of the mRNAs, with corresponding decreases in the activity of these enzymes. The finding s collectively demonstrate that the down-regulation of the expression of a relatively wide variety of enzymes involved in DNA replication oc curs as late events in the granulocytic differentiation of HL-60 cells , ensuring that cellular replication cannot occur in terminally differ entiated cells. (C) 1998 Elsevier Science Ltd. All rights reserved.