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Updated: Aug 19, 2026

Analysis of mRNA Nuclear Export Kinetics in Mammalian Cells by Microinjection
Published on: December 4, 2010
Identification of functional nuclear export sequences in human topoisomerase IIalpha and beta
Shelagh E L Mirski1, Juliane C Bielawski, Susan P C Cole
1Cancer Research Laboratories, Queen's University, Ont, Kingston, Canada K7L 3N6. selm@post.queensu.ca
Abstract:
Nuclear localization of topoisomerase IIalpha and beta is important for normal cell function as well as being a determinant of tumour cell sensitivity to topoisomerase II-targeting chemotherapeutic agents. However, topoisomerase II is cytoplasmic under certain circumstances, indicating that it may undergo active nuclear export. We have examined the ability of Leu-rich potential nuclear export signal (NES) sequences present in human topoisomerase IIalpha and beta to direct the export of a green fluorescent protein-glutathione-S-transferase fusion protein following microinjection into HeLa cell nuclei. Of 12 sequences tested, only one potential NES sequence from the comparable location in each isoform (alphaNES(1018-1028) and betaNES(1034-1044)) was active. Mutation of hydrophobic residues in alphaNES(1018-1028) and betaNES(1034-1044) substantially reduced their nuclear export activity as did leptomycin B treatment of microinjected cells. Our results provide the first evidence of active nuclear export of topoisomerase II and suggest it is mediated by a CRM1-dependent pathway.
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