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Topoisomerase II binds importin alpha isoforms and exportin/CRM1 but does not shuttle between the nucleus and

Shelagh E L Mirski1, Kathryn E Sparks, Beate Friedrich

  • 1Division of Cancer Biology and Genetics, Cancer Research Institute, Queen's University, Kingston, ON, Canada K7L 3N6.

Experimental Cell Research
|December 22, 2006
PubMed

Insights

DNA topoisomerase II (topo II) nuclear export is inhibited in proliferating cells, preventing shuttling. This explains how topo IIalpha accumulates in the nucleus during cell growth, impacting anticancer drug resistance.

Area of Science:

  • Molecular Biology
  • Cell Biology
  • Biochemistry

Background:

  • Anticancer drug resistance targeting DNA topoisomerase II (topo II) is linked to altered topo IIalpha localization.
  • Both topo II alpha and beta isoforms possess nuclear localization and export signals.

Purpose of the Study:

  • To investigate the nuclear import and export mechanisms of topo II alpha and beta.
  • To understand the role of topo II localization in cellular proliferation and drug resistance.

Main Methods:

  • In vitro binding assays with importins and exportin/CRM1.
  • Analysis of GFP-tagged topo IIalpha localization in cells treated with Leptomycin B.
  • Homokaryon shuttling experiments in Cos-1 and HeLa cells.

Main Results:

  • Topo II alpha and beta bind importins for nuclear import.
  • Topo IIalpha binds exportin/CRM1 in vitro.
  • Nuclear export of topo II alpha and beta appears inhibited in proliferating cells, preventing shuttling.

Conclusions:

  • Topo II nuclear export is actively inhibited in proliferating cells.
  • This inhibition maintains nuclear localization of topo II, potentially influencing drug response.
  • Altered nucleocytoplasmic shuttling of topo II isoforms is a key factor in cellular response to anticancer therapies.

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