Reduction in Topoisomerase II Activity Differentiation of Human Leukemia Cells Associated with a Novobiocin- and Phorbol-12-myristate-13-acetate-induced

Studies were conducted to determine the possible involvement of DNA topoisomerase II (Topo II) in the induction of differentiation in two human promyeloc)tic 111 (ill leukemia cell variants that are either sus ceptible or resistant to differentiation induced by phorbol-12-myristate13-acetate (I'M \). a protein kinase C activator. The acquisition of maturation markers and changes in the activity, level, and phosphorylation of Topo II were determined after treatment with either novobiocin, a Topo II inhibitor, or I'MA. Novobiocin at 50-150 MMinduced differ entiation in the 111-20? cells but not in the HL-525 cells, although both cell types were equally susceptible to novobiocin-evoked cytotoxicity. In both cell types, novobiocin induced similar reductions in topoisomerase I activity but different reductions in Topo II activity. Treatment with novobiocin at 150 n\\ for 6 h or at 2 HIMfor 30 min resulted in a 4-fold or higher reduction in Topo II activity in the differentiation-susceptible III -2(1? cells but not in the differentiation-resistant HL-525 cells. A differential response in Topo II activity was also observed after treatment with I'M \. The novobiocin-evoked decrease in Topo II activity seems to be due to an enhanced enzyme proteolysis, whereas the PMA-elicited decrease in Topo II activity is associated with an increase in Topo II phosphor) lai ion. l-(5-Isoquinolinesulfonyl)-2-methylpiperazine, which is an inhibitor of protein kinases, including protein kinase C, diminished the novobiocin-elicited proteolysis of Topo II and the PMA-induced Topo II phosphorylation, as well as the decrease in Topo II activity and the acquisition of differentiation markers induced by either novobiocin or PMA. These results suggest that induction of differentiation in HL-60 cells by novobiocin or PMA is associated with a reduction in Topo II activity, mediated directly or indirectly by a protein kinase(s), perhaps protein kinase C.