RNA Targets and Function ofTopoisomerase 3βin Reducing Cellular Stress

Abstract

AbstractTopoisomerase 3β (Top3β) relaxes DNA and RNA, and it is the only Topoisomerase found to work on RNAs. We isolated and identified the naturally cross-linked RNA targets of Top3β in Drosophila. Top3β is particularly active on long RNAs, RNAs with many splice sites, and RNAs that are localized in large cells. Demonstrating the importance of its enzymatic activity, Top3β without the hydroxyl group that is needed for its covalent binding to the RNA, prevents normal expression and subcellular localization of the gene products of the identified targets. At the cellular level, Top3β activity is needed to maintain the morphology of the neuromuscular junction in adult flies and to prevent premature loss of coordinated movement and aging. Alterations in humanTop3βhave been associated with several neurological diseases and cancers. The homologs of genes and (pre)mRNAs mis-expressed in these conditions show the same characteristics identified in the DrosophilaTop3βtargets, suggesting that the Drosophila can model the function of humanTop3β. Testing the role of the enzymatic activity of Top3β in the ALS/FTD-associated RNA (G4C2)49assay for neurodegeneration, revealed thatTop3β+clearly reduced the neurodegenerative activity of this RNA. Therefore, this study not only identified RNA targets of Top3β but also showed the physiological relevance of the enzymatic activity of Top3β toward its RNA targets in different situations.