Differential expression of human topoisomerase III alpha during the cell cycle progression in HL-60 leukemia cells and human peripheral blood lymphocytes

Human topoisomerase III alpha (huTop IIIa) has been demonstrated to belong to type IA subfamily. In this study, we found that huTop IIIa expressed con stitutively and remained at high levels throughout the cell cycle in HL-60 cells when compared to the cell-cycle-dependent expression of huTop III alp ha in phytohemagglutinin-activated peripheral blood lymphocytes. During the cell cycle progression, this protein remained accentuated in the nucleolus without significant translocation from the nucleolus to the nucleoplasm. I n addition, during the course of granulocytic maturation in DMSO-treated HL -60 cells, huTop III alpha levels decreased when cells stopped proliferatio n and nucleoli diminished in size, However, its level remained unchanged du ring the course of monocytic maturation of vitamin D-3-treated HL-60 cells which still retained its proliferative capacity and did not change the size of the nucleolus. The data suggested that huTop III alpha is involved in r DNA metabolism, such as rDNA transcription. Its cellular level appeared to be under control during the cell cycle progression of normal lymphocytes, b ut was found to be deregulated in HL-60 cells which may be associated with the tumor transformed cell. phenotypes. (C) 2000 Academic Press.