Roles of DNA Topoisomerases in Transcription in HuT 78 Cells Treated with Interleukin‐2

Abstract

DNA topoisomerase I (Topo I) breaks and rejoins one strand of DNA, and DNA topoisomerase (Topo II) breaks and rejoins both strands of DNA. Nuclei of human cells contain two type I enzymes, Topo I and Topo IIIα, and two type II enzymes, Topo IIα and Topo IIβ. We are investigating the involvement of these enzymes in transcription in HuT 78 cells, a human T cell leukemia line that expresses CD 25, a high affinity receptor for interleukin‐2 (IL‐2). The specific activities of both Topo I and Topo II increased several fold in nuclear extracts prepared from HuT 78 cells within the first 12 hrs. after treatment with IL‐2 suggesting that both Topo I and Topo II function in transcription in activated human T cells. We are using specific monoclonal antibodies and antitumor drugs to determine which of the four human DNA topoisomerases are activated upon mitogenesis of HuT 78 by IL‐2. Evidence to date suggests that Topo I is the principal swivelase for transcription and Topo IIβ, a component of the chromosomal scaffold, is the main enzyme that breaks and rejoins DNA in order to make a loop of chromatin accessible for transcription. This work was supported by 5G11 HD052388‐02 and CA 74388.