Activation of DNA topoisomerase I and DNA topoisomerase II in nuclei of interleukin‐2‐treated HuT 78 cells

Abstract

The activities of DNA topoisomerase I and DNA topoisomerase II were measured in HuT 78 cells, a human T cell lymphoma cell line, after treatment of the cells with interleukin‐2 (IL‐2). HuT 78 cells were treated with 1,000 units IL‐2/ml, and extracts of the nuclei were prepared from 0 to 12 hours after treatment. The activity of DNA topoisomerase I was assayed by relaxation of supercoiled pBR322 DNA. The activity of DNA topoisomerase II was assayed by unknotting of P4 DNA, decatenation of kinetoplast DNA, and cleavable complex formation. The decatenation activity was sensitive to etoposide, an inhibitor of DNA topoisomerase II. The specific activities of both enzymes were determined in units/mg protein. The specific activities of both DNA topoisomerase I and DNA topoisomerase II increased 3‐ to 11‐fold in nuclear extracts prepared from HuT 78 cells in three transient, concomitant peaks observed at 0.5, 4, and 10 hrs after treatment with IL‐2. The specific activities of both enzymes returned to baseline values after each peak. These results indicate that the activities of DNA topoisomerase I and DNA topoisomerase II are extensively regulated in activated human T cells, and they suggest that both DNA topoisomerase I and DNA topoiosmerase II function in both transcription and DNA replication in IL‐2‐activated T cells. This work was supported by grants from the Morrison Trust and the NIH (HD 52388).