SUMO-1 conjugation to human DNA topoisomerase II isozymes

Topoisomerase I-mediated DNA damage induced by camptothecin has been shown to induce rapid small ubiquitin-related modifier (SUMO)-1 conjugation to to poisomerase I. In the current study, we show that topoisomerase II-mediated DNA damage induced by teniposide (VM-26) results in the formation of high molecular weight conjugates of both topoisomerase II alpha and II beta isoz ymes in HeLa cells. Immunological characterization of these conjugates sugg ests that both topoisomerase II alpha and II beta isozymes are conjugated t o SUMO-1, The involvement of SUMO-1/UBC9 in the modification of topoisomera se II isozymes is also supported by the demonstration of physical interacti on between topoisomerase II and SUMO-1/UBC9. Surprisingly, ICRF-193, which does not induce topoisomerase II-mediated DNA damage but traps topoisomeras e II into a circular clamp conformation, is also shown to induce similar SU MO-1 conjugation to topoisomerase II isozymes. In addition, we show that bo th oxidative and heat shock stresses, which can cause protein damage, rapid ly increase nuclear SUMO-1 conjugates. These studies raise the question on whether SUMO-1 conjugation to topoisomerases is an indirect result of a DNA damage response or a direct result because of protein conformational chang es.