Stress-mediated inhibition of the classical nuclear protein import pathway and nuclear accumulation of the small GTPase Gsp1p

Yeast profilin mutants inhibit classical nuclear import and alter the balance between actin and tubulin levels

Profilin is a small protein that controls actin polymerization in yeast and higher eukaryotes. In addition, profilin has emerged as a multifunctional protein that contributes to other processes in multicellular organisms. This study focuses on profilin (Pfy1) in the budding yeast Saccharomyces cerevisiae. The primary sequences of yeast Pfy1 and its metazoan orthologs diverge vastly. However, structural elements of profilin are conserved among different species. To date, the full spectrum of Pfy1 functions has yet to be defined. The current work explores the possible involvement of yeast profilin in nuclear protein import. To this end, a panel of well-characterized yeast profilin mutants was evaluated. The experiments demonstrate that yeast profilin (i) regulates nuclear protein import, (ii) determines the subcellular localization of essential nuclear transport factors, and (iii) controls the relative abundance of actin and tubulin. Together, these results define yeast profilin as a moonlighting protein that engages in multiple essential cellular activities.

Oxidative stress and signaling through EGFR and PKA pathways converge on the nuclear transport factor RanBP1

Nuclear protein trafficking requires the soluble transport factor RanBP1. The subcellular distribution of RanBP1 is dynamic, as the protein shuttles between the nucleus and cytoplasm. To date, the signaling pathways regulating RanBP1 subcellular localization are poorly understood. During interphase, RanBP1 resides mostly in the cytoplasm. We show here that oxidative stress concentrates RanBP1 in the nucleus, and our study defines the underlying mechanisms. Specifically, RanBP1's cysteine residues are not essential for its oxidant-induced relocation. Furthermore, our pharmacological approaches uncover that signaling mediated by epidermal growth factor receptor (EGFR) and protein kinase A (PKA) control RanBP1 localization during stress. In particular, pharmacological inhibitors of EGFR or PKA diminish the oxidant-dependent relocation of RanBP1. Mutant analysis identified serine 60 and tyrosine 103 as regulators of RanBP1 nuclear accumulation during oxidant exposure. Taken together, our results define RanBP1 as a target of oxidative stress and a downstream effector of EGFR and PKA signaling routes. This positions RanBP1 at the intersection of important cellular signaling circuits.

Circular RNA circRILPL1 promotes nasopharyngeal carcinoma malignant progression by activating the Hippo-YAP signaling pathway

Circular RNAs (circRNAs) play an important regulatory role in the pathogenesis and progression of nasopharyngeal carcinoma (NPC), which have not been thoroughly elucidated. In this study, we revealed for the first time that circRILPL1 was upregulated in NPC, weakened adhesion and decreased stiffness of NPC cells, and promoted NPC proliferation and metastasis in vitro and in vivo. Mechanistically, circRILPL1 inhibited the LATS1-YAP kinase cascade by binding to and activating ROCK1, resulting in decrease of YAP phosphorylation. Binding and cooperating with transport receptor IPO7, circRILPL1 promoted the translocation of YAP from the cytoplasm to the nucleus, where YAP enhanced the transcription of cytoskeleton remodeling genes CAPN2 and PXN. By which, circRILPL1 contributed to the pathogenesis of NPC. Our results demonstrated that circRILPL1 promoted the proliferation and metastasis of NPC through activating the Hippo-YAP signaling pathway by binding to both ROCK1 and IPO7. Highly expressed circRILPL1 in NPC may serve as an important biomarker for tumor diagnosis and may also be a potential therapeutic target.

Importin alpha family NAAT/IBB domain: Functions of a pleiotropic long chameleon sequence

Nuclear transport is essential for eukaryotic cell survival and regulates the movement of functional molecules in and out of the nucleus via the nuclear pore. Transport is facilitated by protein-protein interactions between cargo and transport receptors, which contribute to the expression and regulation of downstream genetic information. This chapter focuses on the molecular basis of the multifunctional nature of the importin α family, the representative transport receptors that bring proteins into the nucleus. Importin α performs multiple functions during the nuclear transport cycle through interactions with multiple molecules by a single domain called the IBB domain. This domain is a long chameleon sequence, which can change its conformation and binding mode depending on the interaction partners. By considering the evolutionarily conserved biochemical/physicochemical propensities of the amino acids constituting the functional complex interfaces, together with their structural properties, the mechanisms of switching between multiple complexes formed via IBB and the regulation of downstream functions are examined in detail. The mechanism of regulation by IBB indicates that the time has come for a paradigm shift in the way we view the molecular mechanisms by which proteins regulate downstream functions through their interactions with other molecules.

The Nuclear Transporter Importin 13 Can Regulate Stress-Induced Cell Death through the Clusterin/KU70 Axis

The cellular response to environmental stresses, such as heat and oxidative stress, is dependent on extensive trafficking of stress-signalling molecules between the cytoplasm and nucleus, which potentiates stress-activated signalling pathways, eventually resulting in cell repair or death. Although Ran-dependent nucleocytoplasmic transport mediated by members of the importin (IPO) super family of nuclear transporters is believed to be responsible for nearly all macromolecular transit between nucleus and cytoplasm, it is paradoxically known to be significantly impaired under conditions of stress. Importin 13 (IPO13) is a unique bidirectional transporter that binds to and releases cargo in a Ran-dependent manner, but in some cases, cargo release from IPO13 is affected by loading of another cargo. To investigate IPO13's role in stress-activated pathways, we performed cell-based screens to identify a multitude of binding partners of IPO13 from human brain, lung, and testes. Analysis of the IPO13 interactome intriguingly indicated more than half of the candidate binding partners to be annotated for roles in stress responses; these included the pro-apoptotic protein nuclear clusterin (nCLU), as well as the nCLU-interacting DNA repair protein KU70. Here, we show, for the first time, that unlike other IPOs which are mislocalised and non-functional, IPO13 continues to translocate between the nucleus and cytoplasm under stress, retaining the capacity to import certain cargoes, such as nCLU, but not export others, such as KU70, as shown by analysis using fluorescence recovery after photobleaching. Importantly, depletion of IPO13 reduces stress-induced import of nCLU and protects against stress-induced cell death, with concomitant protection from DNA damage during stress. Overexpression/FACS experiments demonstrate that nCLU is dependent on IPO13 to trigger stress-induced cell death via apoptosis. Taken together, these results implicate IPO13 as a novel functional nuclear transporter in cellular stress, with a key role thereby in cell fate decision.

Cellular Stress Induces Nucleocytoplasmic Transport Deficits Independent of Stress Granules

Stress granules are non-membrane bound granules temporarily forming in the cytoplasm in response to stress. Proteins of the nucleocytoplasmic transport machinery were found in these stress granules and it was suggested that stress granules contribute to the nucleocytoplasmic transport defects in several neurodegenerative disorders, including amyotrophic lateral sclerosis (ALS). The aim of this study was to investigate whether there is a causal link between stress granule formation and nucleocytoplasmic transport deficits. Therefore, we uncoupled stress granule formation from cellular stress while studying nuclear import. This was carried out by preventing cells from assembling stress granules despite being subjected to cellular stress either by knocking down both G3BP1 and G3BP2 or by pharmacologically inhibiting stress granule formation. Conversely, we induced stress granules by overexpressing G3BP1 in the absence of cellular stress. In both conditions, nuclear import was not affected demonstrating that stress granule formation is not a direct cause of stress-induced nucleocytoplasmic transport deficits.

Nuclear transporter Importin-13 plays a key role in the oxidative stress transcriptional response

The importin superfamily member Importin-13 is a bidirectional nuclear transporter. To delineate its functional roles, we performed transcriptomic analysis on wild-type and Importin-13-knockout mouse embryonic stem cells, revealing enrichment of differentially expressed genes involved in stress responses and apoptosis regulation. De novo promoter motif analysis on 277 Importin-13-dependent genes responsive to oxidative stress revealed an enrichment of motifs aligned to consensus sites for the transcription factors specificity protein 1, SP1, or Kruppel like factor 4, KLF4. Analysis of embryonic stem cells subjected to oxidative stress revealed that Importin-13-knockout cells were more resistant, with knockdown of SP1 or KLF4 helping protect wild-type embryonic stem cells against stress-induced death. Importin-13 was revealed to bind to SP1 and KLF4 in a cellular context, with a key role in oxidative stress-dependent nuclear export of both transcription factors. The results are integral to understanding stress biology, highlighting the importance of Importin-13 in the stress response.

Conformation of the nuclear pore in living cells is modulated by transport state

While the static structure of the nuclear pore complex (NPC) continues to be refined with cryo-EM and x-ray crystallography, in vivo conformational changes of the NPC remain under-explored. We developed sensors that report on the orientation of NPC components by rigidly conjugating mEGFP to different NPC proteins. Our studies show conformational changes to select domains of nucleoporins (Nups) within the inner ring (Nup54, Nup58, Nup62) when transport through the NPC is perturbed and no conformational changes to Nups elsewhere in the NPC. Our results suggest that select components of the NPC are flexible and undergo conformational changes upon engaging with cargo.

Ran participates in deltamethrin stress through regulating the nuclear import of Nrf2

The small GTPase Ran has a variety of biological functions, one of the most prominent of which is to regulate nucleocytoplasmic transport. In our previous study, it was suggested that Ran is involved in the deltamethrin (DM) stress. In addition, Keap1-Nrf2-ARE pathway was also confirmed to be associated with DM stress. We report here that under DM stress, interfering Ran or nuclear transport factor Ntf2 by RNAi could suppress the nuclear import of nuclear transcription factor Nrf2 which then down-regulates the expressions of detoxification enzyme genes (Cyp4d20, Cyp4ae1, GstD5, Sod3, etc.), ultimately resulting in a significant apoptosis of Drosophila Kc cells. In contrast, after overexpressing Ran in Kc cells, Nrf2 has a higher concentration in the nucleus, and the expressions of detoxification enzyme genes are up-regulated, while the DM-induced apoptosis is significantly lower than that of the control group. Additionally, we preliminary found silencing Ntf2 or Ran could prevent the nuclear import of transcription factor Dif under DM stress, subsequently decreased expressions of antimicrobial peptide genes (Drsl1). In summary, our data mainly indicates that Ran may participate in DM stress through regulating the nuclear import of Nrf2, which could help to study the mechanism of deltamethrin resistance.

Traffic jam at the nuclear pore: All roads lead to nucleocytoplasmic transport defects in ALS/FTD

Amyotrophic lateral sclerosis (ALS) is a fatal late-onset neurodegenerative disease that specifically affects the function and survival of spinal and cortical motor neurons. ALS shares many genetic, clinical, and pathological characteristics with frontotemporal dementia (FTD), and these diseases are now recognized as presentations of a disease spectrum known as ALS/FTD. The molecular determinants of neuronal loss in ALS/FTD are still debated, but the recent discovery of nucleocytoplasmic transport defects as a common denominator of most if not all forms of ALS/FTD has dramatically changed our understanding of the pathogenic mechanisms of this disease. Loss of nuclear pores and nucleoporin aggregation, altered nuclear morphology, and impaired nuclear transport are some of the most prominent features that have been identified using a variety of animal, cellular, and human models of disease. Here, we review the experimental evidence linking nucleocytoplasmic transport defects to the pathogenesis of ALS/FTD and propose a unifying view on how these defects may lead to a vicious cycle that eventually causes neuronal death.

Thioredoxin-related transmembrane protein 2 (TMX2) regulates the Ran protein gradient and importin-β-dependent nuclear cargo transport

TMX2 is a thioredoxin family protein, but its functions have not been clarified. To elucidate the function of TMX2, we explored TMX2-interacting proteins by LC-MS. As a result, importin-β, Ran GTPase (Ran), RanGAP, and RanBP2 were identified. Importin-β is an adaptor protein which imports cargoes from cytosol to the nucleus, and is exported into the cytosol by interaction with RanGTP. At the cytoplasmic nuclear pore, RanGAP and RanBP2 facilitate hydrolysis of RanGTP to RanGDP and the disassembly of the Ran-importin-β complex, which allows the recycling of importin-β and reentry of Ran into the nucleus. Despite its interaction of TMX2 with importin-β, we showed that TMX2 is not a transport cargo. We found that TMX2 localizes in the outer nuclear membrane with its N-terminus and C-terminus facing the cytoplasm, where it co-localizes with importin-β and Ran. Ran is predominantly distributed in the nucleus, but TMX2 knockdown disrupted the nucleocytoplasmic Ran gradient, and the cysteine 112 residue of Ran was important in its regulation by TMX2. In addition, knockdown of TMX2 suppressed importin-β-mediated transport of protein. These results suggest that TMX2 works as a regulator of protein nuclear transport, and that TMX2 facilitates the nucleocytoplasmic Ran cycle by interaction with nuclear pore proteins.

Identification of a nuclear localization signal and importin beta members mediating NUAK1 nuclear import inhibited by oxidative stress

NUAK1 is a serine/threonine kinase member of the AMPK-α family. NUAK1 regulates several processes in tumorigenesis; however, its regulation and molecular targets are still poorly understood. Bioinformatics analysis predicted that the majority of NUAK1 localizes in the nucleus. However, there are no studies about the regulation of NUAK1 subcellular distribution. Here, we analyzed NUAK1 localization in several human cell lines, mouse embryo fibroblasts, and normal mouse tissues. We found that NUAK1 is located in the nucleus and also in the cytoplasm. Through bioinformatics analysis and studies comparing subcellular localization of wild type and NUAK1 mutants, we identified a conserved bipartite nuclear localization signal at the N-terminal domain of NUAK1. Based on mass spectrometry analysis, we found that NUAK1 interacts with importin-β members including importin-β1 (KPNB1), importin-7 (IPO7), and importin-9 (IPO9). We confirmed that importin-β members are responsible for NUAK1 nuclear import through the inhibition of importin-β by Importazole and the knockdown of either IPO7 or IPO9. In addition, we found that oxidative stress induces NUAK1 cytoplasmic accumulation, indicating that oxidative stress affects NUAK1 nuclear transport. Thus, our study is the first evidence of an active nuclear transport mechanism regulating NUAK1 subcellular localization. These data will lead to investigations of the molecular targets of NUAK1 according to its subcellular distribution, which could be new biomarkers or targets for cancer therapies.

Inhibition of Karyopherin-α2 Augments Radiation-Induced Cell Death by Perturbing BRCA1-Mediated DNA Repair

Ionizing radiation (IR) has been widely used in the treatment of cancer. Radiation-induced DNA damage triggers the DNA damage response (DDR), which can confer radioresistance and early local recurrence by activating DNA repair pathways. Since karyopherin-α2 (KPNA2), playing an important role in nucleocytoplasmic transport, was significantly increased by IR in our previous study, we aimed to determine the function of KPNA2 with regard to DDR. Exposure to radiation upregulated KPNA2 expression in human colorectal cancer HT29 and HCT116 cells and breast carcinoma MDA-MB-231 cells together with the increased expression of DNA repair protein BRCA1. The knockdown of KPNA2 effectively increased apoptotic cell death via inhibition of BRCA1 nuclear import following IR. Therefore, we propose that KPNA2 is a potential target for overcoming radioresistance via interruption to DDR.

Lamin A mutation impairs interaction with nucleoporin NUP155 and disrupts nucleocytoplasmic transport in atrial fibrillation

Atrial fibrillation (AF) is the most common cardiac arrhythmia. Here, we show the identification and functional characterization of one AF-associated mutation p.Arg399Cys in lamin A/C. Co-immunoprecipitation and GST pull-down assays demonstrate that lamin A/C interacts with NUP155, which is a nucleoporin and causes AF when mutated. Lamin A/C mutation p.Arg399Cys impairs the interaction between lamin A/C and NUP155, and increases extractability of NUP155 from the nuclear envelope (NE). Mutation p.Arg399Cys leads to aggregation of lamin A/C in the nucleus, although it does not impair the integrity of NE upon cellular stress. Mutation p.Arg399Cys inhibits the export of HSP70 mRNA and the nuclear import of HSP70 protein. Electrophysiological studies show that mutation p.Arg399Cys decreases the peak cardiac sodium current by decreasing the cell surface expression level of cardiac sodium channel Na_v 1.5, but does not affect I_Kr potassium current. In conclusion, our results indicate that lamin A/C mutation p.Arg399Cys weakens the interaction between nuclear lamina (lamin A/C) and the nuclear pore complex (NUP155), leading to the development of AF. The findings provide a novel molecular mechanism for the pathogenesis of AF.

Transcriptional response of honey bee (Apis mellifera) to differential nutritional status and Nosema infection

Background

Bees are confronting several environmental challenges, including the intermingled effects of malnutrition and disease. Intuitively, pollen is the healthiest nutritional choice, however, commercial substitutes, such as Bee-Pro and MegaBee, are widely used. Herein we examined how feeding natural and artificial diets shapes transcription in the abdomen of the honey bee, and how transcription shifts in combination with Nosema parasitism.

Results

Gene ontology enrichment revealed that, compared with poor diet (carbohydrates [C]), bees fed pollen (P > C), Bee-Pro (B > C), and MegaBee (M > C) showed a broad upregulation of metabolic processes, especially lipids; however, pollen feeding promoted more functions, and superior proteolysis. The superiority of the pollen diet was also evident through the remarkable overexpression of vitellogenin in bees fed pollen instead of MegaBee or Bee-Pro. Upregulation of bioprocesses under carbohydrates feeding compared to pollen (C > P) provided a clear poor nutritional status, uncovering stark expression changes that were slight or absent relatively to Bee-Pro (C > B) or MegaBee (C > M). Poor diet feeding (C > P) induced starvation response genes and hippo signaling pathway, while it repressed growth through different mechanisms. Carbohydrate feeding (C > P) also elicited ‘adult behavior’, and developmental processes suggesting transition to foraging. Finally, it altered the ‘circadian rhythm’, reflecting the role of this mechanism in the adaptation to nutritional stress in mammals.

Nosema-infected bees fed pollen compared to carbohydrates (PN > CN) upheld certain bioprocesses of uninfected bees (P > C). Poor nutritional status was more apparent against pollen (CN > PN) than Bee-Pro (CN > BN) or MegaBee (CN > MN). Nosema accentuated the effects of malnutrition since more starvation-response genes and stress response mechanisms were upregulated in CN > PN compared to C > P. The bioprocess ‘Macromolecular complex assembly’ was also enriched in CN > PN, and involved genes associated with human HIV and/or influenza, thus providing potential candidates for bee-Nosema interactions. Finally, the enzyme Duox emerged as essential for guts defense in bees, similarly to Drosophila.

Conclusions

These results provide evidence of the superior nutritional status of bees fed pollen instead of artificial substitutes in terms of overall health, even in the presence of a pathogen.

Electronic supplementary material

The online version of this article (10.1186/s12864-018-5007-0) contains supplementary material, which is available to authorized users.

Alterations in the nucleocytoplasmic transport in apoptosis: Caspases lead the way

Apoptosis is a mode of regulated cell death that is indispensable for the morphogenesis, development and homeostasis of multicellular organisms. Caspases are cysteine-dependent aspartate-specific proteases, which function as initiators and executors of apoptosis. Caspases are cytosolic proteins that can cleave substrates located in different intracellular compartments during apoptosis. Many years ago, the involvement of caspases in the regulation of nuclear changes, a hallmark of apoptosis, was documented. Accumulated data suggest that apoptosis-associated alterations in nucleocytoplasmic transport are also linked to caspase activity. Here, we aim to discuss the current state of knowledge regarding this process. Particular attention will be focused on caspase nuclear entry and their functions in the demolition of the nucleus upon apoptotic stimuli.

Roles of the Skn7 response regulator in stress resistance, cell wall integrity and GA biosynthesis in Ganoderma lucidum

The transcription factor Skn7 is a highly conserved fungal protein that participates in a variety of processes, including oxidative stress adaptation, fungicide sensitivity, cell wall biosynthesis, cell cycle, and sporulation. In this study, a homologous gene of Saccharomyces cerevisiae Skn7 was cloned from Ganoderma lucidum. RNA interference (RNAi) was used to study the functions of Skn7, and the two knockdown strains Skn7i-5 and Skn7i-7 were obtained in G. lucidum. The knockdown of GlSkn7 resulted in hypersensitivity to oxidative and cell wall stresses. The concentrations of chitin and β-1,3-glucan distinctly decreased in the GlSkn7 knockdown strains compared with those of the wild type (WT). In addition, the expression of cell wall biosynthesis related genes was also significantly down-regulated and the thickness of the cell wall also significantly reduced in the GlSkn7 knockdown strains. The intracellular reactive oxygen species (ROS) content and ganoderic acids biosynthesis increased significantly in the GlSkn7 knockdown strains. Interestingly, the level of intracellular ROS and the content of ganoderic acids decreased after N-acetyl-L-cysteine (NAC), an ROS scavenger, was added, indicating that GlSkn7 might regulate ganoderic acids biosynthesis via the intracellular ROS level. The transcript level of GlSkn7 were up-regulated in osmotic stress, heat stress and fungicide condition. At the same time, the content of ganoderic acids in the GlSkn7 knockdown strains also changed distinctly in these conditions. Overall, GlSkn7 is involved in stress resistance, cell wall integrity and ganoderic acid biosynthesis in G. lucidum.

TaNTF2, a contributor for wheat resistance to the stripe rust pathogen

Nuclear Transport Factor 2 (NTF2) functions as a critical regulator in balancing the GTP-and GDP-bound forms of Ran, a class of evolutionarily conserved small GTP-binding protein. During the incompatible interaction between wheat-Puccinia striiformis f. sp. tritici (Pst), a cDNA fragment encoding a putative wheat NTF2 gene was found to be significantly induced, suggesting a potential role in wheat resistance to Pst. In this work, the full length of TaNTF2 was obtained, with three copies located on 7A, 7B and 7D chromosomes, respectively. QRT-PCR further verified the up-regulated expression of TaNTF2 in response to avirulent Pst. In addition, TaNTF2 was also induced by exogenous hormone applications, especially JA treatment. Transient expression of TaNTF2 in tobacco cells confirmed its subcellular localization in the cytoplasm, perinuclear area and nucleus. And virus induced gene silencing (VIGS) was used to identify the function of TaNTF2 during an incompatible wheat-Pst interaction. When TaNTF2 was knocked down, resistance of wheat to avirulentPst was decreased, with a bigger necrotic spots, and higher numbers of hyphal branches and haustorial mother cells. Our results demonstrated that TaNTF2 was a contributor for wheat resistance to the stripe rust pathogen, which will help to comprehensively understand the NTF2/Ran modulating mechanism in wheat-Pst interaction.

Enhanced karyopherin-α2 expression is associated with carcinogenesis in patients with intraductal papillary mucinous neoplasms

BACKGROUND/OBJECTIVES

Intraductal papillary mucinous neoplasms (IPMN) can become malignant. Karyopherin-α2 (KPNA2) plays a central role in nucleocytoplasmic transport and is associated with various types of cancer. The current study examined pancreatic KPNA2 expression in cancer patients and evaluated its association with clinicopathological factors, cancer cell proliferation.

METHODS

KPNA2 expression was investigated by immunohistochemistry in 40 surgically resected IPMN samples and its association with clinicopathological factors and Ki-67 expression were examined.

RESULTS

Eighteen IPMN samples (45% of patients) showed positive KPNA2 expression. KPNA2 expression levels in IPMN tissue with invasive carcinoma were significantly higher than those in adjacent normal tissues and in IPMN tissue with low-to high-grade dysplasia. KPNA2 expression correlated with pathological malignancy and Ki-67 labeling index and KPNA2 and Ki-67 expression was co-localized in nuclei. E2F were co-localized with KPNA2 in the IPMN tissues with high expression of KPNA2. KPNA2 expression was enhanced in the invasion front and in proliferating Ki-67-positive cells. In addition, KPNA2 expression in IPMN tissues was associated with older age, dilation of main pancreatic duct diameter, the presence of nodules, and histological type.

CONCLUSION

KPNA2 expression is associated with carcinogenesis of IPMN through the adenoma-carcinoma sequence.

Karyopherin alpha 2 expression is a novel diagnostic and prognostic factor for colorectal cancer

Colorectal cancer (CRC) is the fourth most common cancer and the second leading cause of cancer-associated mortality in Western countries. CRC treatment is dependent on the preoperative and postoperative condition of patients. At present, the prognostic value of conventional parameters for the estimation of patient prognosis is limited. The aim of the present study was to investigate the expression of karyopherin α2 (KPNA2) in cancerous and healthy colon tissues and to evaluate the prognostic factors for patients with primary CRC. KPNA2 expression in CRC and paired normal tissues was analyzed by immunohistochemistry and reverse transcription-quantitative polymerase chain reaction (RT-qPCR). In addition, serum KPNA2 expression was evaluated by enzyme-linked immunosorbent assay. Subsequently, the association between KPNA2 expression in CRC tissues and patient clinicopathological features was analyzed. Kaplan-Meier analysis was utilized to investigate the prognostic value of KPNA2 expression on overall survival rates following radical surgery for the treatment of CRC. Immunohistochemistry and RT-qPCR revealed that KPNA2 expression was significantly increased in CRC tissues compared with paired normal tissues. Serum KPNA2 expression was significantly increased in CRC patients compared with healthy individuals. Furthermore, KPNA2 expression was observed to positively correlate with Tumor-Node-Metastasis stage, lymph node involvement, tumor differentiation, infiltration depth, lymphovascular invasion and perineural invasion, which are factors known to affect the prognosis of CRC patients following surgery. In addition, increased KPNA2 expression was associated with decreased overall survival and disease-free survival rates. Patients not suited for surveillance regimens may be identified at initial biopsy test with a positive KPNA2 immunohistochemistry. Increased serum expression of KPNA2 may be utilized as a diagnostic factor for patients with CRC. High nuclear KPNA2 expression may serve as a novel predictor of survival following radical colorectal surgery in CRC patients. The results of the present study may improve individualized risk stratification, leading to the optimization of therapies for CRC patients.

Small GTPases and Stress Responses of vvran1 in the Straw Mushroom Volvariella volvacea

Small GTPases play important roles in the growth, development and environmental responses of eukaryotes. Based on the genomic sequence of the straw mushroom Volvariella volvacea, 44 small GTPases were identified. A clustering analysis using human small GTPases as the references revealed that V. volvacea small GTPases can be grouped into five families: nine are in the Ras family, 10 are in the Rho family, 15 are in the Rab family, one is in the Ran family and nine are in the Arf family. The transcription of vvran1 was up-regulated upon hydrogen peroxide (H₂O₂) stress, and could be repressed by diphenyleneiodonium chloride (DPI), a NADPH oxidase-specific inhibitor. The number of vvran1 transcripts also increased upon cold stress. Diphenyleneiodonium chloride, but not the superoxide dismutase (SOD) inhibitor diethy dithiocarbamate (DDC), could suppress the up-regulation of vvran1 gene expression to cold stress. These results combined with the high correlations between gene expression and superoxide anion (O₂⁻) generation indicated that vvran1 could be one of the candidate genes in the downstream of O₂⁻ mediated pathways that are generated by NADPH oxidase under low temperature and oxidative stresses.

Karyopherin Alpha 1 Regulates Satellite Cell Proliferation and Survival by Modulating Nuclear Import

Satellite cells are stem cells with an essential role in skeletal muscle repair. Precise regulation of gene expression is critical for proper satellite cell quiescence, proliferation, differentiation and self-renewal. Nuclear proteins required for gene expression are dependent on the nucleocytoplasmic transport machinery to access to nucleus, however little is known about regulation of nuclear transport in satellite cells. The best characterized nuclear import pathway is classical nuclear import which depends on a classical nuclear localization signal (cNLS) in a cargo protein and the heterodimeric import receptors, karyopherin alpha (KPNA) and beta (KPNB). Multiple KPNA1 paralogs exist and can differ in importing specific cNLS proteins required for cell differentiation and function. We show that transcripts for six Kpna paralogs underwent distinct changes in mouse satellite cells during muscle regeneration accompanied by changes in cNLS proteins in nuclei. Depletion of KPNA1, the most dramatically altered KPNA, caused satellite cells in uninjured muscle to prematurely activate, proliferate and undergo apoptosis leading to satellite cell exhaustion with age. Increased proliferation of satellite cells led to enhanced muscle regeneration at early stages of regeneration. In addition, we observed impaired nuclear localization of two key KPNA1 cargo proteins: p27, a cyclin-dependent kinase inhibitor associated with cell cycle control and lymphoid enhancer factor 1, a critical cotranscription factor for β-catenin. These results indicate that regulated nuclear import of proteins by KPNA1 is critical for satellite cell proliferation and survival and establish classical nuclear import as a novel regulatory mechanism for controlling satellite cell fate. Stem Cells 2016;34:2784-2797.

KPNA2 is a nuclear export protein that contributes to aberrant localisation of key proteins and poor prognosis of breast cancer

Background:

It is recognised that modulations of the nuclear import of macromolecules have a role in changing cellular phenotypes and carcinogenesis. We and others have noticed that aberrant subcellular localisation of DNA damage response (DDR) proteins in breast cancer (BC) is associated with loss-of-function phenotype. This study aims to investigate the biological and clinical significance of the nucleocytoplasmic transport protein karyopherin α-2 (KPNA2), and its role in controlling DDR proteins subcellular localisation in BC.

Methods:

A large (n=1494) and well-characterised series of early-stage invasive BC with a long-term follow-up was assessed for KPNA2 protein by using immunohistochemistry.

Results:

KPNA2 expression was associated with the subcellular localisation of key DDR proteins that showed cytoplasmic expression including BRCA1, RAD51, SMC6L1, γH2AX, BARD1, UBC9, PIAS1 and CHK1. High level of KPNA2 was associated not only with cytoplasmic localisation of these proteins but also with their low/negative nuclear expression. Positive KPNA2 expression was associated with negative oestrogen receptor and triple-negative phenotype. Survival analysis showed that KPNA2 was associated with poor outcome (P<0.0001), but this effect was not independent of other prognostic variables.

Conclusions:

This study provides further evidence for the complexity of DDR mechanism in BC, and that KNPA2 has a role in the aberrant subcellular localisation of DDR proteins with subsequent impaired function.

A novel bicistronic sensor vector for detecting caspase-3 activation

INTRODUCTION

Apoptosis is involved in pathological cell death of a wide range of human diseases. One of the most important biochemical markers of apoptosis is activation of caspase-3. Ability to detect caspase-3 activation early in the pathological process is important for determining the timing for interfering with apoptosis initiation and prevention of cell damage. Techniques allowing detection of caspase-3 activity at a single cell level show increased sensitivity, compared to biochemical assays; therefore, we developed a novel bicistronic caspase-3 sensor vector enabling detection of caspase-3 activity in individual cells.

METHODS

We employed green fluorescent protein (GFP) as a reporter for caspase-3 activation in our constructs and assessed the functionality of the generated constructs in transiently transfected Neuro2A and HEK293 cells under basal conditions and following application of okadaic acid (OA) or staurosporine (STS) to induce apoptosis. To ensure responsiveness of the new sensor vector to active caspase-3, we co-transfected the sensor with plasmid(s) overexpressing active caspase-3 and quantified GFP fluorescence using a plate reader.

RESULTS

We observed an increase in GFP expression in cells transfected with the new bicistronic caspase-3 sensor in response to both OA and STS. We also showed a significant increase in GFP fluorescence intensity in cells co-expressing the sensor with the plasmid(s) encoding active caspase-3.

DISCUSSION

We generated a novel bicistronic caspase-3 sensor vector which relies on a transcription factor/response element system. The obtained sensor combines high sensitivity of the single cell level detection with the possibility of automated quantification.

Disruption of the ran system by cysteine oxidation of the nucleotide exchange factor RCC1

Transport regulation by the Ran GTPase requires its nuclear localization and GTP loading by the chromatin-associated exchange factor RCC1. These reactions generate Ran protein and Ran nucleotide gradients between the nucleus and the cytoplasm. Cellular stress disrupts the Ran gradients, but the specific mechanisms underlying this disruption have not been elucidated. We used biochemical approaches to determine how oxidative stress disrupts the Ran system. RCC1 exchange activity was reduced by diamide-induced oxidative stress and restored with dithiothreitol. Using mass spectrometry, we found that multiple solvent-exposed cysteines in RCC1 are oxidized in cells treated with diamide. The cysteines oxidized in RCC1 included Cys93, which is solvent exposed and unique because it becomes buried upon contact with Ran. A Cys93Ser substitution dramatically reduced exchange activity through an effect on RCC1 binding to RanGDP. Diamide treatment reduced the size of the mobile fraction of RCC1-green fluorescent protein in cells and inhibited nuclear import in digitonin-permeabilized cell assays. The Ran protein gradient was also disrupted by UV-induced stress but without affecting RCC1 exchange activity. Our data suggest that stress can disrupt the Ran gradients through RCC1-dependent and RCC1-independent mechanisms, possibly dependent on the particular stress condition.

Separate responses of karyopherins to glucose and amino acid availability regulate nucleocytoplasmic transport

The subcellular distribution of yeast β-importins inverts upon acute glucose deprivation, likely due to collapse of the RanGTP nuclear–cytoplasmic gradient. This redistribution of β-importins likely results in rapid widespread alterations of the traffic of macromolecules between the nucleus and cytoplasm in response to glucose limitation.

The importin-β family members (karyopherins) mediate the majority of nucleocytoplasmic transport. Msn5 and Los1, members of the importin-β family, function in tRNA nuclear export. tRNAs move bidirectionally between the nucleus and the cytoplasm. Nuclear tRNA accumulation occurs upon amino acid (aa) or glucose deprivation. To understand the mechanisms regulating tRNA subcellular trafficking, we investigated whether Msn5 and Los1 are regulated in response to nutrient availability. We provide evidence that tRNA subcellular trafficking is regulated by distinct aa-sensitive and glucose-sensitive mechanisms. Subcellular distributions of Msn5 and Los1 are altered upon glucose deprivation but not aa deprivation. Redistribution of tRNA exportins from the nucleus to the cytoplasm likely provides one mechanism for tRNA nuclear distribution upon glucose deprivation. We extended our studies to other members of the importin-β family and found that all tested karyopherins invert their subcellular distributions upon glucose deprivation but not aa deprivation. Glucose availability regulates the subcellular distributions of karyopherins likely due to alteration of the RanGTP gradient since glucose deprivation causes redistribution of Ran. Thus nuclear–cytoplasmic distribution of macromolecules is likely generally altered upon glucose deprivation due to collapse of the RanGTP gradient and redistribution of karyopherins between the nucleus and the cytoplasm.

A pathway linking oxidative stress and the Ran GTPase system in progeria

Maintaining the Ran GTPase at a proper concentration in the nucleus is important for nucleocytoplasmic transport. Previously we found that nuclear levels of Ran are reduced in cells from patients with Hutchinson-Gilford progeria syndrome (HGPS), a disease caused by constitutive attachment of a mutant form of lamin A (termed progerin) to the nuclear membrane. Here we explore the relationship between progerin, the Ran GTPase, and oxidative stress. Stable attachment of progerin to the nuclear membrane disrupts the Ran gradient and results in cytoplasmic localization of Ubc9, a Ran-dependent import cargo. Ran and Ubc9 disruption can be induced reversibly with H2O2. CHO cells preadapted to oxidative stress resist the effects of progerin on Ran and Ubc9. Given that HGPS-patient fibroblasts display elevated ROS, these data suggest that progerin inhibits nuclear transport via oxidative stress. A drug that inhibits pre-lamin A cleavage mimics the effects of progerin by disrupting the Ran gradient, but the effects on Ran are observed before a substantial ROS increase. Moreover, reducing the nuclear concentration of Ran is sufficient to induce ROS irrespective of progerin. We speculate that oxidative stress caused by progerin may occur upstream or downstream of Ran, depending on the cell type and physiological setting.

Hyperosmotic stress sustains cytokine-stimulated phosphorylation of STAT3, but slows its nuclear trafficking and impairs STAT3-dependent transcription

Persistent STAT3 phosphorylation and nuclear retention are hallmarks of a range of pathologies suggesting the importance of STAT3 transcriptional responses in disease progression. Since hyperosmotic stress (HOS) is a hallmark of diseases such as diabetes and asthma, we analysed the impact of HOS on cytokine-stimulated STAT3 signalling. In contrast to transient STAT3 Y705 and S727 phosphorylation in murine embryonic fibroblasts (MEFs) stimulated by the interleukin-6 family cytokine, leukemia inhibitory factor (LIF), under non-stress conditions, HOS induced by sorbitol treatment increased STAT3 S727 but not Y705 phosphorylation. Strikingly, combined LIF+HOS treatment stimulated persistent STAT3 Y705 and S727 phosphorylation and nuclear localisation, but STAT3 nuclear accumulation was slowed during HOS, likely reflecting the mislocalisation of Ran and importin-α3 during HOS that also reduced the nuclear localisation of classical importin-α/β-recognised nuclear import cargoes. Strikingly, combined LIF+HOS exposure, even though stimulating STAT3 phosphorylation and nuclear accumulation did not elicit a transcriptional output, as demonstrated by qPCR analyses of its target genes SOCS3 and c-Fos. Our analysis thus shows for the first time that HOS can disconnect nuclear, phosphorylated STAT3 from transcriptional outcomes, and emphasizes the importance of assessing STAT3 target gene changes in addition to STAT3 phosphorylation status and localisation.

Intermolecular disulfide bonds between nucleoporins regulate karyopherin-dependent nuclear transport

Disulfide (S-S) bonds play important roles in the regulation of protein function and cellular stress responses. In this study, we demonstrate that distinct sets of nucleoporins (Nups), components of the nuclear pore complex (NPC), form S-S bonds and regulate nuclear transport through the NPC. Kinetic analysis of importin β demonstrated that the permeability of the NPC was increased by dithiothreitol treatment and reduced by oxidative stress. The permeability of small proteins such as GFP was not affected by either oxidative stress or a reducing reagent. Immunoblot analysis revealed that the oxidative stress significantly induced S-S bond formation in Nups 358, 155, 153 and 62 but not 88 and 160. The direct involvement of cysteine residues in the formation of S-S bonds was confirmed by mutating conserved cysteine residues in Nup62, which abolished the formation of S-S bonds and enhanced the permeability of the NPC. Knocking down Nup62 reduced the stress-inducible S-S bonds of Nup155, suggesting that Nup62 and Nup155 are covalently coupled via S-S bonds. From these results, we propose that the inner channel of the NPC is somehow insulated from the cytoplasm and is more sensitive than the cytoplasm to the intracellular redox state.

The functional role of the novel biomarker karyopherin α 2 (KPNA2) in cancer

In recent years, Karyopherin α 2 (KPNA2) has emerged as a potential biomarker in multiple cancer forms. The aberrant high levels observed in cancer tissue have been associated with adverse patient characteristics, prompting the idea that KPNA2 plays a role in carcinogenesis. This notion is supported by studies in cancer cells, where KPNA2 deregulation has been demonstrated to affect malignant transformation. By virtue of its role in nucleocytoplasmic transport, KPNA2 is implicated in the translocation of several cancer-associated proteins. We provide an overview of the clinical studies that have established the biomarker potential of KPNA2 and describe its functional role with an emphasis on established associations with cancer.

Altered transcription factor trafficking in oxidatively-stressed neuronal cells

Age-related neurodegenerative diseases are associated with alterations in gene expression in affected neurons. One of the mechanisms that could account for this is altered subcellular localization of transcription factors, which has been observed in human post-mortem brains of each of the major neurodegenerative diseases, including Parkinson's disease (PD). The specific mechanisms are yet to be elucidated; however a potential mechanism involves alterations in nuclear transport. In this study, we examined the nucleocytoplasmic trafficking of select transcription factors in response to a PD-relevant oxidative injury, 6-hydroxydopamine (6OHDA). Utilizing a well-established model of ligand-regulated nucleocytoplasmic shuttling, the glucocorticoid receptor, we found that 6OHDA selectively impaired nuclear import through an oxidative mechanism without affecting nuclear export or nuclear retention. Interestingly, impaired nuclear import was selective as Nrf2 (nuclear factor E2-related factor 2) nuclear localization remained intact in 6OHDA-treated cells. Thus, oxidative stress specifically impacts the subcellular localization of some but not all transcription factors, which is consistent with observations in post-mortem PD brains. Our data further implicate a role for altered microtubule dependent trafficking in the differential effects of 6OHDA on transcription factor import. Oxidative disruption of microtubule-dependent nuclear transport may contribute to selective declines in transcriptional responses of aging or diseased dopaminergic cells.

Intrinsic and extrinsic negative regulators of nuclear protein transport processes

The nuclear-cytoplasmic protein transport is a critical process in cellular events. The identification of transport signals (nuclear localization signal and nuclear export signal) and their receptors has facilitated our understanding of this expanding field. Nuclear transport must be appropriately regulated to deliver proteins through the nuclear pore when their functions are required in the nucleus, and to export them into the cytoplasm when they are not needed in the nucleus. Altered nuclear transport processes have been observed in stressed cells, which would change gene expressions. Some viruses interfere with nuclear transport in host cells to evade immune defense. Moreover, certain transport factors negatively regulate nuclear protein transport in cells. Understanding the regulatory mechanisms of nuclear-cytoplasmic trafficking not only provides important information about cellular processes, but also is of use for developing specific inhibitors for transport pathways.

Nuclear transport: a switch for the oxidative stress-signaling circuit?

Imbalances in the formation and clearance of reactive oxygen species (ROS) can lead to oxidative stress and subsequent changes that affect all aspects of physiology. To limit and repair the damage generated by ROS, cells have developed a multitude of responses. A hallmark of these responses is the activation of signaling pathways that modulate the function of downstream targets in different cellular locations. To this end, critical steps of the stress response that occur in the nucleus and cytoplasm have to be coordinated, which makes the proper communication between both compartments mandatory. Here, we discuss the interdependence of ROS-mediated signaling and the transport of macromolecules across the nuclear envelope. We highlight examples of oxidant-dependent nuclear trafficking and describe the impact of oxidative stress on the transport apparatus. Our paper concludes by proposing a cellular circuit of ROS-induced signaling, nuclear transport and repair.

Nuclear retention of importin α coordinates cell fate through changes in gene expression

Various cellular stresses including oxidative stress induce a collapse of the Ran gradient, which causes accumulation of importin α in the nucleus and a subsequent block of nuclear protein import. However, it is unknown whether accumulated importin α performs roles in the nucleus after its migration in response to stress. In this study, we found that nuclear-retained importin α2 binds with DNase I-sensitive nuclear component(s) and exhibits selective upregulation of mRNA encoding Serine/threonine kinase 35 (STK35) by microarray analysis. Chromatin immunoprecipitation and promoter analysis demonstrated that importin α2 can access to the promoter region of STK35 and accelerate its transcription in response to hydrogen peroxide exposure. Furthermore, constitutive overexpression of STK35 proteins enhances caspase-independent cell death under oxidative stress conditions. These results collectively reveal that nuclear-localized importin α2 influences gene expression and contributes directly to cell fate outcomes including non-apoptotic cell death.

Identification of two functional nuclear localization signals mediating nuclear import of liver receptor homologue-1

Liver receptor homologue-1 (LRH-1) is a member of the nuclear receptor superfamily. We characterized two functional nuclear localization signals (NLSs) in LRH-1. NLS1 (residues 117-168) overlaps the second zinc finger in the DNA binding domain. Mutagenesis showed that the zinc finger structure and two basic clusters on either side of the zinc finger loop are critical for nuclear import of NLS1. NLS2 (residues 169-204) is located in the Ftz-F1 box that contains a bipartite signal. In full-length LRH-1, mutation of either NLS1 or NLS2 had no effect on nuclear localization, but disruption of both NLS1 and NLS2 resulted in the cytoplasmic accumulation of LRH-1. Either NLS1 or NLS2 alone was sufficient to target LRH-1 to the nucleus. Both NLS1 and NLS2 mediate nuclear transport by a mechanism involving importin α/β. Finally, we showed that three crucial basic clusters in the NLSs are involved in the DNA binding and transcriptional activities of LRH-1.

Traffic control at the nuclear pore

The proper communication between organelles is essential for many aspects of eukaryotic life. The coordination of nuclear and cytoplasmic activities in particular is of pivotal importance and depends on transport in and out of the nucleus. The material which translocates through nuclear pores is diverse; it includes numerous proteins, RNAs and large ribonucleoprotein complexes like ribosomal subunits. To ensure the correct nucleocytoplasmic distribution of these components, appropriate mechanisms have to be in place which control traffic across the nuclear envelope. A growing number of studies support the notion that transport through nuclear pore complexes is intimately linked to cell physiology. As such, it has become evident that changes in the cellular environment, either by externally applied stress, aging or disease, alter nuclear traffic. Due to the progress made in the past few years, we are now beginning to understand these processes at the molecular level. Thus, the concept emerges that stress or disease conditions correlate with signaling events which aim at the nuclear transport apparatus. Here, we summarize results from recent publications that provide evidence for the hypothesis that changes in cell physiology modulate nuclear traffic by targeting multiple transport factors. We propose that this traffic control is at least in part mediated by specific signaling events.

Dissecting the signaling events that impact classical nuclear import and target nuclear transport factors

BACKGROUND

Signaling through MEK-->ERK1/2 and PI3 kinases is implicated in many aspects of cell physiology, including the survival of oxidant exposure. Oxidants play a role in numerous physiological and pathophysiological processes, many of which rely on transport in and out of the nucleus. However, how oxidative stress impacts nuclear trafficking is not well defined.

METHODOLOGY/PRINCIPAL FINDINGS

To better understand the effect of stress on nucleocytoplasmic trafficking, we exposed cells to the oxidant diethyl maleate. This treatment activated MEK-->ERK1/2 as well as PI3 kinase-->Akt cascades and triggered the inhibition of classical nuclear import. To define the molecular mechanisms that regulate nuclear transport, we examined whether MEK and PI3 kinase signaling affected the localization of key transport factors. Using recently developed tools for image acquisition and analysis, the subcellular distributions of importin-alpha, CAS, and nucleoporins Nup153 and Nup88 were quantified in different cellular compartments. These studies identified specific profiles for the localization of transport factors in the nucleus and cytoplasm, and at the nuclear envelope. Our results demonstrate that MEK and PI3 kinase signaling as well as oxidative stress control nuclear trafficking and the localization of transport components. Furthermore, stress not only induced changes in transport factor distribution, but also upregulated post-translational modification of transport factors. Our results are consistent with the idea that the phosphorylation of importin-alpha, CAS, Nup153, and Nup88, and the O-GlcNAc modification of Nup153 increase when cells are exposed to oxidant.

CONCLUSIONS/SIGNIFICANCE

Our studies defined the complex regulation of classical nuclear import and identified key transport factors that are targeted by stress, MEK, and PI3 kinase signaling.

Oxidative stress inhibits nuclear protein export by multiple mechanisms that target FG nucleoporins and Crm1

Nuclear transport of macromolecules is regulated by the physiological state of the cell and thus sensitive to stress. To define the molecular mechanisms that control nuclear export upon stress, cells were exposed to nonlethal concentrations of the oxidant diethyl maleate (DEM). These stress conditions inhibited chromosome region maintenance-1 (Crm1)-dependent nuclear export and increased the association between Crm1 and Ran. In addition, we identified several repeat-containing nucleoporins implicated in nuclear export as targets of oxidative stress. As such, DEM treatment reduced Nup358 levels at the nuclear envelope and redistributed Nup98. Furthermore, oxidative stress led to an increase in the apparent molecular masses of Nup98, Nup214, and Nup62. Incubation with phosphatase or beta-N-acetyl-hexosaminidase showed that oxidative stress caused the phosphorylation of Nup98, Nup62, and Nup214 as well as O-linked N-acetylglucosamine modification of Nup62 and Nup214. These oxidant-induced changes in nucleoporin modification correlated first with the increased binding of Nup62 to the exporter Crm1 and second with the reduced interaction of Nup62 with other FxFG-containing nucleoporins. Together, oxidative stress up-regulated the binding of Crm1 to Ran and affected multiple repeat-containing nucleoporins by changing their localization, phosphorylation, O-glycosylation, or interaction with other transport components. We propose that the combination of these events contributes to the stress-dependent regulation of Crm1-mediated protein export.

Conformational targeting of fibrillar polyglutamine proteins in live cells escalates aggregation and cytotoxicity

BACKGROUND

Misfolding- and aggregation-prone proteins underlying Parkinson's, Huntington's and Machado-Joseph diseases, namely alpha-synuclein, huntingtin, and ataxin-3 respectively, adopt numerous intracellular conformations during pathogenesis, including globular intermediates and insoluble amyloid-like fibrils. Such conformational diversity has complicated research into amyloid-associated intracellular dysfunction and neurodegeneration. To this end, recombinant single-chain Fv antibodies (scFvs) are compelling molecular tools that can be selected against specific protein conformations, and expressed inside cells as intrabodies, for investigative and therapeutic purposes.

METHODOLOGY/PRINCIPAL FINDINGS

Using atomic force microscopy (AFM) and live-cell fluorescence microscopy, we report that a human scFv selected against the fibrillar form of alpha-synuclein targets isomorphic conformations of misfolded polyglutamine proteins. When expressed in the cytoplasm of striatal cells, this conformation-specific intrabody co-localizes with intracellular aggregates of misfolded ataxin-3 and a pathological fragment of huntingtin, and enhances the aggregation propensity of both disease-linked polyglutamine proteins. Using this intrabody as a tool for modulating the kinetics of amyloidogenesis, we show that escalating aggregate formation of a pathologic huntingtin fragment is not cytoprotective in striatal cells, but rather heightens oxidative stress and cell death as detected by flow cytometry. Instead, cellular protection is achieved by suppressing aggregation using a previously described intrabody that binds to the amyloidogenic N-terminus of huntingtin. Analogous cytotoxic results are observed following conformational targeting of normal or polyglutamine-expanded human ataxin-3, which partially aggregate through non-polyglutamine domains.

CONCLUSIONS/SIGNIFICANCE

These findings validate that the rate of aggregation modulates polyglutamine-mediated intracellular dysfunction, and caution that molecules designed to specifically hasten aggregation may be detrimental as therapies for polyglutamine disorders. Moreover, our findings introduce a novel antibody-based tool that, as a consequence of its general specificity for fibrillar conformations and its ability to function intracellularly, offers broad research potential for a variety of human amyloid diseases.