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Changes in Topoisomerase I Levels and Localization during Myeloid Maturation in Vitro and in Vivo¹

Oncology Center, Johns Hopkins Hospital [S. H. K., M. C., P. J. B., J. E. K.], and Department of Pharmacology and Molecular Sciences, Johns Hopkins University School of Medicine [S. H. K.], Baltimore, Maryland 21287

Changes in topoisomerase I (topo I) levels and localization were examined during the course of granulocytic maturation in vitro and in vivo. Western blotting revealed that granulocytic maturation in DMSO-treated HL-60 human leukemia cells was accompanied by a 5-fold decrease in topo I polypeptide content. Consistent with this result, 3- to 5-fold higher concentrations of the topo I poison camptothecin were required to stabilize topo I-DNA adducts in DMSO-treated HL-60 cells compared to untreated cells. Northern blotting revealed that these changes occurred without any decrease in topo I message. Immunolocalization studies revealed that these quantitative changes were accompanied by redistribution of topo I away from the nucleoli, where it was prominently accumulated in untreated HL-60 cells, to a more uniform nuclear distribution in DMSO-treated cells.

Similar changes occurred during granulocytic maturation in human marrow in vivo. Western blotting revealed that topo I levels in normal progranulocytes were 50% as high as those in HL-60 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 cells. Two other polypeptides that are concentrated in nucleoli, poly(ADP-ribose) polymerase and B23/nucleophosmin, also decreased during the course of granulocytic maturation. These changes were accompanied by an alteration in topo I localization similar to that observed in HL-60 cells during the course of granulocytic maturation. Conversely, treatment of human lymphocytes with the mitogenic lectin concanavalin A resulted in a 3-fold increase in topo I polypeptide content concomitant with a prominent increase in the amount of nucleolar antigen. These observations not only provide a context for understanding the recent observation that topo I levels are higher in human leukemia specimens than in normal marrow but also raise the possibility that elevated topo I levels in other cells might reflect alterations in nucleolar structure and function.

¹ Supported in part by American Cancer Society Grant DHP-46. S. H. K. is a Scholar of the Leukemia Society of America. M. C. was supported in part by a fellowship from the Medical Research Council of Canada and funds from the Johns Hopkins Oncology Center Core Grant CA06973.

² To whom correspondence should be addressed, at Division of Oncology Research, Guggenheim 1328, Mayo Clinic, 200 First St., S. W., Rochester, MN 55905. Reprints of this article will not be available.

³ Present address: National Cancer Institute, Bethesda, MD 20892.

Received 11/ 2/94. Accepted 1/19/95.

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