Topoisomerase II binds importin {alpha} isoforms and exportin/CRM1 but does not shuttle between the nucleus and cytoplasm in proliferating cells
- Division of Cancer Biology and Genetics, Cancer Research Institute, Queen's University, Kingston, ON, K7L 3N6 (Canada)
- Max Delbrueck Center for Molecular Medicine, Robert Roessle Str 10, 13125 Berlin (Germany)
- Department of Medical Microbiology, Immunology and Cell Biology, Southern Illinois University School of Medicine, Springfield, IL 62794 (United States)
- Department of Biopharmaceutical Sciences, University of Illinois at Chicago, Chicago, IL 60612 (United States)
Resistance to anticancer drugs that target DNA topoisomerase II (topo II) isoforms {alpha} and/or {beta} is associated with decreased nuclear and increased cytoplasmic topo II{alpha}. Earlier studies have confirmed that functional nuclear localization and export signal sequences (NLS and NES) are present in both isoforms. In this study, we show that topo II {alpha} and {beta} bind and are imported into the nucleus by importin {alpha}1, {alpha}3, and {alpha}5 in conjunction with importin {beta}. Topo II{alpha} also binds exportin/CRM1 in vitro. However, wild-type topo II{alpha} has only been observed in the cytoplasm of cells that are entering plateau phase growth. This suggests that topo II{alpha} may shuttle between the nucleus and the cytoplasm with the equilibrium towards the nucleus in proliferating cells but towards the cytoplasm in plateau phase cells. The CRM1 inhibitor Leptomycin B increases the nuclear localization of GFP-tagged topo II{alpha} with a mutant NLS, suggesting that its export is being inhibited. However, homokaryon shuttling experiments indicate that fluorescence-tagged wild-type topo II {alpha} and {beta} proteins do not shuttle in proliferating Cos-1 or HeLa cells. We conclude that topo II {alpha} and {beta} nuclear export is inhibited in proliferating cells so that these proteins do not shuttle.
- OSTI ID:
- 20972115
- Journal Information:
- Experimental Cell Research, Journal Name: Experimental Cell Research Journal Issue: 3 Vol. 313; ISSN 0014-4827; ISSN ECREAL
- Country of Publication:
- United States
- Language:
- English
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