CHANGES IN TOPOISOMERASE-I LEVELS AND LOCALIZATION DURING MYELOID MATURATION IN-VITRO AND IN-VIVO

Changes in topoisomerase I (topo I) levels and localization were exami ned during the course of granulocytic maturation in vitro and in vivo. Western blotting revealed that granulocytic maturation in DMSO-treate d HL-60 human leukemia cells was accompanied by a 5-fold decrease in t opo I polypeptide content. Consistent with this result, 3- to 5-fold h igher concentrations of the topo I poison camptothecin were required t o stabilize topo I-DNA adducts in DMSO-treated HL-60 cells compared to untreated cells. Northern blotting revealed that these changes occurr ed without any decrease in topo I message. Immunolocalization studies revealed that these quantitative changes were accompanied by redistrib ution of topo I away from the nucleoli, where it was prominently accum ulated in untreated HL-60 cells, to a more uniform nuclear distributio n in DMSO-treated cells. Similar changes occurred during granulocytic maturation in human marrow in vivo. Western blotting revealed that top o I levels in normal progranulocytes were 50% as high as those in HL-6 0 cells, levels in metamyelocytes were 35% as high as HL-60 cells, and levels in peripheral blood granulocytes were 5% as high as HL-60 cell s. Two other polypeptides that are concentrated in nucleoli, poly(ADP- ribose) polymerase and B23/nucleophosmin, also decreased during the co urse of granulocytic maturation. These changes were accompanied by an alteration in topo I localization similar to that observed in HL-60 ce lls during the course of granulocytic maturation. Conversely, treatmen t of human lymphocytes with the mitogenic lectin concanavalin A result ed in a 3-fold increase in topo I polypeptide content concomitant with a prominent increase in the amount of nucleolar antigen. These observ ations not only provide a contest for understanding the recent observa tion that topo I levels are higher in human leukemia specimens than in normal marrow but also raise the possibility that elevated topo I lev els in other cells might reflect alterations in nucleolar structure an d function.