• Molecules and Cells
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• 제45권11호
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• pp.855-867
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• 2022

For proper function of proteins, their subcellular localization needs to be monitored and regulated in response to the changes in cellular demands. In this regard, dysregulation in the nucleocytoplasmic transport (NCT) of proteins is closely associated with the pathogenesis of various neurodegenerative diseases. However, it remains unclear whether there exists an intrinsic regulatory pathway(s) that controls NCT of proteins either in a commonly shared manner or in a target-selectively different manner. To dissect between these possibilities, in the current study, we investigated the molecular mechanism regulating NCT of truncated ataxin-3 (ATXN3) proteins of which genetic mutation leads to a type of polyglutamine (polyQ) diseases, in comparison with that of TDP-43. In Drosophila dendritic arborization (da) neurons, we observed dynamic changes in the subcellular localization of truncated ATXN3 proteins between the nucleus and the cytosol during development. Moreover, ectopic neuronal toxicity was induced by truncated ATXN3 proteins upon their nuclear accumulation. Consistent with a previous study showing intracellular calcium-dependent NCT of TDP-43, NCT of ATXN3 was also regulated by intracellular calcium level and involves Importin α3 (Imp α3). Interestingly, NCT of ATXN3, but not TDP-43, was primarily mediated by CBP. We further showed that acetyltransferase activity of CBP is important for NCT of ATXN3, which may acetylate Imp α3 to regulate NCT of ATXN3. These findings demonstrate that CBP-dependent acetylation of Imp α3 is crucial for intracellular calcium-dependent NCT of ATXN3 proteins, different from that of TDP-43, in Drosophila neurons.

• Molecules and Cells
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• 제26권3호
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• pp.291-298
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• 2008

Human karyopherin ${\beta}3$, highly homologous to a yeast protein secretion enhancer (PSE1), has often been reported to be associated with a mediator of a nucleocytoplasmic transport pathway. Previously, we showed that karyopherin ${\beta}3$ complemented the PSE1 and KAP123 double mutant. Our research suggested that karyopherin beta has an evolutionary function similar to that of yeast PSE1 and/or KAP 123. In this study, we performed yeast two-hybrid screening to find a protein which would interact with karyopherin ${\beta}3$ and identified apolipoprotein A-I (apo A-I), a secretion protein with a primary function in cholesterol transport. By using in vitro binding assay, co-immunoprecipitation, and colocalization studies, we defined an interaction between karyopherin ${\beta}3$ and apo A-I. In addition, overexpression of karyopherin ${\beta}3$ significantly increased apo A-I secretion. These results suggest that karyopherin ${\beta}3$ plays a crucial role in apo A-I secretion. These findings may be relevant to the study of a novel function of karyopherin ${\beta}3$ and coronary artery diseases associated with apo A-I.

• Molecules and Cells
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• 제43권11호
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• pp.899-908
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• 2020

Intrinsically disordered proteins or regions (IDPs or IDRs) are widespread in the eukaryotic proteome. Although lacking stable three-dimensional structures in the free forms, IDRs perform critical functions in various cellular processes. Accordingly, mutations and altered expression of IDRs are associated with many pathological conditions. Hence, it is of great importance to understand at the molecular level how IDRs interact with their binding partners. In particular, discovering the unique interaction features of IDRs originating from their dynamic nature may reveal uncharted regulatory mechanisms of specific biological processes. Here we discuss the mechanisms of the macromolecular interactions mediated by IDRs and present the relevant cellular processes including transcription, cell cycle progression, signaling, and nucleocytoplasmic transport. Of special interest is the multivalent binding nature of IDRs driving assembly of multicomponent macromolecular complexes. Integrating the previous theoretical and experimental investigations, we suggest that such IDR-driven multiprotein complexes can function as versatile allosteric switches to process diverse cellular signals. Finally, we discuss the future challenges and potential medical applications of the IDR research.

• Toxicological Research
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• 제25권1호
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• pp.35-40
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• 2009

TCDD (2,3,7,8-tetrachlorodibenzo-p-dioxin) and related halogenated aromatic hydrocarbons elicit a diverse spectrum of biochemical and toxic responses in laboratory animals and mammalian cells in culture. Toxicity and carcinogenicity of TCDD is well established but the molecular mechanism is still poorly understood. Here, we found the noble responsive genes to TCDD using the differential display analysis. Treatment of HepG2 cells with TCDD showed a significantly different mRNA expression pattern from the untreated cells in differential display analysis. The differentially displayed bands were isolated and used as probes in dot blot and Northern blot analyses. Of thirty-five isolated differentially displayed bands, only two bands were confirmed as positive in dot blot and Northern blot analyses. The nucleotides sequences of these clones were analyzed and the search of Genebank database revealed that one clone is highly homologous with RanBP2 (Ras-related nuclear protein binding protein2; 92%) and the other is an unknown gene. RanBP2 is a nucleoporin with SUMO E3 ligase activity that functions in both nucleocytoplasmic transport and mitosis and its role as a novel tumor suppressor has been recently proposed. Thus, these results may suggest the clue elucidating the toxic mechanism of TCDD through RanBP2.

• Molecules and Cells
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• 제46권6호
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• pp.374-386
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• 2023

Thermal stress induces dynamic changes in nuclear proteins and relevant physiology as a part of the heat shock response (HSR). However, how the nuclear HSR is fine-tuned for cellular homeostasis remains elusive. Here, we show that mitochondrial activity plays an important role in nuclear proteostasis and genome stability through two distinct HSR pathways. Mitochondrial ribosomal protein (MRP) depletion enhanced the nucleolar granule formation of HSP70 and ubiquitin during HSR while facilitating the recovery of damaged nuclear proteins and impaired nucleocytoplasmic transport. Treatment of the mitochondrial proton gradient uncoupler masked MRP-depletion effects, implicating oxidative phosphorylation in these nuclear HSRs. On the other hand, MRP depletion and a reactive oxygen species (ROS) scavenger non-additively decreased mitochondrial ROS generation during HSR, thereby protecting the nuclear genome from DNA damage. These results suggest that suboptimal mitochondrial activity sustains nuclear homeostasis under cellular stress, providing plausible evidence for optimal endosymbiotic evolution via mitochondria-to-nuclear communication.