Importin α: functions as a nuclear transport factor and beyond

Structured Tandem Repeats in Protein Interactions

Tandem repeats (TRs) in protein sequences are consecutive, highly similar sequence motifs. Some types of TRs fold into structural units that pack together in ensembles, forming either an (open) elongated domain or a (closed) propeller, where the last unit of the ensemble packs against the first one. Here, we examine TR proteins (TRPs) to see how their sequence, structure, and evolutionary properties favor them for a function as mediators of protein interactions. Our observations suggest that TRPs bind other proteins using large, structured surfaces like globular domains; in particular, open-structured TR ensembles are favored by flexible termini and the possibility to tightly coil against their targets. While, intuitively, open ensembles of TRs seem prone to evolve due to their potential to accommodate insertions and deletions of units, these evolutionary events are unexpectedly rare, suggesting that they are advantageous for the emergence of the ancestral sequence but are early fixed. We hypothesize that their flexibility makes it easier for further proteins to adapt to interact with them, which would explain their large number of protein interactions. We provide insight into the properties of open TR ensembles, which make them scaffolds for alternative protein complexes to organize genes, RNA and proteins.

The Influenza A Virus Replication Cycle: A Comprehensive Review

Influenza A virus (IAV) is the primary causative agent of influenza, colloquially called the flu. Each year, it infects up to a billion people, resulting in hundreds of thousands of human deaths, and causes devastating avian outbreaks with worldwide losses worth billions of dollars. Always present is the possibility that a highly pathogenic novel subtype capable of direct human-to-human transmission will spill over into humans, causing a pandemic as devastating if not more so than the 1918 influenza pandemic. While antiviral drugs for influenza do exist, they target very few aspects of IAV replication and risk becoming obsolete due to antiviral resistance. Antivirals targeting other areas of IAV replication are needed to overcome this resistance and combat the yearly epidemics, which exact a serious toll worldwide. This review aims to summarise the key steps in the IAV replication cycle, along with highlighting areas of research that need more focus.

A Kpna1-deficient psychotropic drug-induced schizophrenia model mouse for studying gene-environment interactions

KPNA1 is a mediator of nucleocytoplasmic transport that is abundantly expressed in the mammalian brain and regulates neuronal differentiation and synaptic function. De novo mutations in Kpna1 have been identified using genome-wide association studies in humans with schizophrenia; however, it remains unclear how KPNA1 contributes to schizophrenia pathogenesis. Recent studies have suggested a complex combination of genetic and environmental factors that are closely related to psychiatric disorders. Here, we found that subchronic administration of phencyclidine, a psychotropic drug, induced vulnerability and behavioral abnormalities consistent with the symptoms of schizophrenia in Kpna1-deficient mice. Microarray assessment revealed that the expression levels of dopamine d1/d2 receptors, an RNA editing enzyme, and a cytoplasmic dynein component were significantly altered in the nucleus accumbens brain region in a gene-environment (G × E) interaction-dependent manner. Our findings demonstrate that Kpna1-deficient mice may be useful as a G × E interaction mouse model for psychiatric disorders and for further investigation into the pathogenesis of such diseases and disorders.

The African Swine Fever Virus Virulence Determinant DP96R Suppresses Type I IFN Production Targeting IRF3

DP96R of African swine fever virus (ASFV), also known as uridine kinase (UK), encodes a virulence-associated protein. Previous studies have examined DP96R along with other genes in an effort to create live attenuated vaccines. While experiments in pigs have explored the impact of DP96R on the pathogenicity of ASFV, the precise molecular mechanism underlying this phenomenon remains unknown. Here, we describe a novel molecular mechanism by which DP96R suppresses interferon regulator factor-3 (IRF3)-mediated antiviral immune responses. DP96R interacts with a crucial karyopherin (KPNA) binding site within IRF3, disrupting the KPNA-IRF3 interaction and consequently impeding the translocation of IRF3 to the nucleus. Under this mechanistic basis, the ectopic expression of DP96R enhances the replication of DNA and RNA viruses by inhibiting the production of IFNs, whereas DP96R knock-down resulted in higher IFNs and IFN-stimulated gene (ISG) transcription during ASFV infection. Collectively, these findings underscore the pivotal role of DP96R in inhibiting IFN responses and increase our understanding of the relationship between DP96R and the virulence of ASFV.

Analysis of the effects of importin α1 on the nuclear translocation of IL-1α in HeLa cells

Interleukin-1α (IL-1α), a cytokine released by necrotic cells, causes sterile inflammation. On the other hand, IL-1α is present in the nucleus and also regulates the expression of many proteins. A protein substrate containing a classical nuclear localization signal (cNLS) typically forms a substrate/importin α/β complex, which is subsequently transported to the nucleus. To the best of our knowledge, no study has directly investigated whether IL-1α-which includes cNLS-is imported into the nucleus in an importin α/β-dependent manner. In this study, we noted that all detected importin α subtypes interacted with IL-1α. In HeLa cells, importin α1-mediated nuclear translocation of IL-1α occurred at steady state and was independent of importin β1. Importin α1 not only was engaged in IL-1α nuclear transport but also concurrently functioned as a molecule that regulated IL-1α protein level in the cell. Furthermore, we discussed the underlying mechanism of IL-1α nuclear translocation by importin α1 based on our findings.

Structural and functional characterization of siadenovirus core protein VII nuclear localization demonstrates the existence of multiple nuclear transport pathways

Adenovirus protein VII (pVII) plays a crucial role in the nuclear localization of genomic DNA following viral infection and contains nuclear localization signal (NLS) sequences for the importin (IMP)-mediated nuclear import pathway. However, functional analysis of pVII in adenoviruses to date has failed to fully determine the underlying mechanisms responsible for nuclear import of pVII. Therefore, in the present study, we extended our analysis by examining the nuclear trafficking of adenovirus pVII from a non-human species, psittacine siadenovirus F (PsSiAdV). We identified a putative classical (c)NLS at pVII residues 120-128 (120PGGFKRRRL128). Fluorescence polarization and electrophoretic mobility shift assays demonstrated direct, high-affinity interaction with both IMPα2 and IMPα3 but not IMPβ. Structural analysis of the pVII-NLS/IMPα2 complex confirmed a classical interaction, with the major binding site of IMPα occupied by K124 of pVII-NLS. Quantitative confocal laser scanning microscopy showed that PsSiAdV pVII-NLS can confer IMPα/β-dependent nuclear localization to GFP. PsSiAdV pVII also localized in the nucleus when expressed in the absence of other viral proteins. Importantly, in contrast to what has been reported for HAdV pVII, PsSiAdV pVII does not localize to the nucleolus. In addition, our study demonstrated that inhibition of the IMPα/β nuclear import pathway did not prevent PsSiAdV pVII nuclear targeting, indicating the existence of alternative pathways for nuclear localization, similar to what has been previously shown for human adenovirus pVII. Further examination of other potential NLS signals, characterization of alternative nuclear import pathways, and investigation of pVII nuclear targeting across different adenovirus species is recommended to fully elucidate the role of varying nuclear import pathways in the nuclear localization of pVII.

Viral Targeting of Importin Alpha-Mediated Nuclear Import to Block Innate Immunity

Cellular nucleocytoplasmic trafficking is mediated by the importin family of nuclear transport proteins. The well-characterized importin alpha (IMPA) and importin beta (IMPB) nuclear import pathway plays a crucial role in the innate immune response to viral infection by mediating the nuclear import of transcription factors such as IRF3, NFκB, and STAT1. The nuclear transport of these transcription factors ultimately leads to the upregulation of a wide range of antiviral genes, including IFN and IFN-stimulated genes (ISGs). To replicate efficiently in cells, viruses have developed mechanisms to block these signaling pathways. One strategy to evade host innate immune responses involves blocking the nuclear import of host antiviral transcription factors. By binding IMPA proteins, these viral proteins prevent the nuclear transport of key transcription factors and suppress the induction of antiviral gene expression. In this review, we describe examples of proteins encoded by viruses from several different families that utilize such a competitive inhibition strategy to suppress the induction of antiviral gene expression.

Nuclear transport proteins: structure, function, and disease relevance

Proper subcellular localization is crucial for the functioning of biomacromolecules, including proteins and RNAs. Nuclear transport is a fundamental cellular process that regulates the localization of many macromolecules within the nuclear or cytoplasmic compartments. In humans, approximately 60 proteins are involved in nuclear transport, including nucleoporins that form membrane-embedded nuclear pore complexes, karyopherins that transport cargoes through these complexes, and Ran system proteins that ensure directed and rapid transport. Many of these nuclear transport proteins play additional and essential roles in mitosis, biomolecular condensation, and gene transcription. Dysregulation of nuclear transport is linked to major human diseases such as cancer, neurodegenerative diseases, and viral infections. Selinexor (KPT-330), an inhibitor targeting the nuclear export factor XPO1 (also known as CRM1), was approved in 2019 to treat two types of blood cancers, and dozens of clinical trials of are ongoing. This review summarizes approximately three decades of research data in this field but focuses on the structure and function of individual nuclear transport proteins from recent studies, providing a cutting-edge and holistic view on the role of nuclear transport proteins in health and disease. In-depth knowledge of this rapidly evolving field has the potential to bring new insights into fundamental biology, pathogenic mechanisms, and therapeutic approaches.

Nuclear ERK1/2 signaling potentiation enhances neuroprotection and cognition via Importinα1/KPNA2

Cell signaling is central to neuronal activity and its dysregulation may lead to neurodegeneration and cognitive decline. Here, we show that selective genetic potentiation of neuronal ERK signaling prevents cell death in vitro and in vivo in the mouse brain, while attenuation of ERK signaling does the opposite. This neuroprotective effect mediated by an enhanced nuclear ERK activity can also be induced by the novel cell penetrating peptide RB5. In vitro administration of RB5 disrupts the preferential interaction of ERK1 MAP kinase with importinα1/KPNA2 over ERK2, facilitates ERK1/2 nuclear translocation, and enhances global ERK activity. Importantly, RB5 treatment in vivo promotes neuroprotection in mouse models of Huntington's (HD), Alzheimer's (AD), and Parkinson's (PD) disease, and enhances ERK signaling in a human cellular model of HD. Additionally, RB5-mediated potentiation of ERK nuclear signaling facilitates synaptic plasticity, enhances cognition in healthy rodents, and rescues cognitive impairments in AD and HD models. The reported molecular mechanism shared across multiple neurodegenerative disorders reveals a potential new therapeutic target approach based on the modulation of KPNA2-ERK1/2 interactions.

Distribution of importin-α isoforms in poultry species and their tissue- and age-related differences

While importin-α is well studied in mammals, the knowledge in avian species is still limited. In this study, we compared the mRNA expression patterns of five importin-α isoforms in the respiratory tract, liver, and spleen of chickens, turkeys, and pekin ducks in two different age-groups. In addition, we determined the distribution of importin-α in selected tissue of conchae, trachea, and lung of post-hatch chickens at all cellular levels by immunohistochemical staining. Our results indicate that importin-α3 is the most abundant isoform in the respiratory tract of chickens, turkeys, and pekin ducks. Moreover, importin-α is expressed as a gradient with lowest mRNA levels in the conchae and highest levels in the lung. The mRNA expression levels of most isoforms were higher in tissues from post-hatch chickens and turkeys in comparison to the corresponding embryos. In contrast to that, duck embryos mostly show higher mRNA expression levels of importin-α than post-hatch ducks.

Nuclear Import and Export of YAP and TAZ

Yes-associated Protein (YAP) and its paralog Transcriptional Coactivator with PDZ-binding Motif (TAZ) are major regulators of gene transcription/expression, primarily controlled by the Hippo pathway and the cytoskeleton. Integrating an array of chemical and mechanical signals, they impact growth, differentiation, and regeneration. Accordingly, they also play key roles in tumorigenesis and metastasis formation. Their activity is primarily regulated by their localization, that is, Hippo pathway- and/or cytoskeleton-controlled cytosolic or nuclear sequestration. While many details of such prevailing retention models have been elucidated, much less is known about their actual nuclear traffic: import and export. Although their size is not far from the cutoff for passive diffusion through the nuclear pore complex (NPC), and they do not contain any classic nuclear localization (NLS) or nuclear export signal (NES), evidence has been accumulating that their shuttling involves mediated and thus regulatable/targetable processes. The aim of this review is to summarize emerging information/concepts about their nucleocytoplasmic shuttling, encompassing the relevant structural requirements (NLS, NES), nuclear transport receptors (NTRs, karyophererins), and NPC components, along with the potential transport mechanisms and their regulation. While dissecting retention vs. transport is often challenging, the emerging picture suggests that YAP/TAZ shuttles across the NPC via multiple, non-exclusive, mediated mechanisms, constituting a novel and intriguing facet of YAP/TAZ biology.

Physical model of the nuclear membrane permeability mechanism

Nuclear cytoplasmic transport is mediated by many receptors that recognize specific nuclear localization signals on proteins and RNA and transport these substrates through nuclear pore complexes. Facilitated diffusion through nuclear pore complexes requires the attachment of transport receptors. Despite the relatively large tunnel diameter, some even small proteins (less than 20-30 kDa), such as histones, pass through the nuclear pore complex only with transport receptors. Over several decades, considerable material has been accumulated on the structure, architecture, and amino acid composition of the proteins included in this complex and the sequence of many receptors. We consider the data available in the literature on the structure of the nuclear pore complex and possible mechanisms of nuclear-cytoplasmic transport, applying the theory of electrostatic interactions in the context of our data on changes in the electrokinetic potential of nuclei and our previously proposed physical model of the mechanism of facilitated diffusion through the nuclear pore complex (NPC). According to our data, the main contribution to the charge of the nuclear membrane is made by anionic phospholipids, which are part of both the nuclear membrane and the nuclear matrix, which creates a potential difference between them. The nuclear membrane is a four-layer phospholipid dielectric, so the potential vector can only pass through the NPC, creating an electrostatic funnel that "pulls in" the positively charged load-NLS-NTR trigger complexes. Considering the newly obtained data, an improved model of the previously proposed physical model of the mechanism of nuclear-cytoplasmic transport is proposed. This model considers the contribution of electrostatic fields to the transportation speed when changing the membrane's thickness in the NPC basket at a higher load.

The role of nuclear pores and importins for herpes simplex virus infection

Microtubule transport and nuclear import are functionally connected, and the nuclear pore complex (NPC) can interact with microtubule motors. For several alphaherpesvirus proteins, nuclear localization signals (NLSs) and their interactions with specific importin-α proteins have been characterized. Here, we review recent insights on the roles of microtubule motors, capsid-associated NLSs, and importin-α proteins for capsid transport, capsid docking to NPCs, and genome release into the nucleoplasm, as well as the role of importins for nuclear viral transcription, replication, capsid assembly, genome packaging, and nuclear capsid egress. Moreover, importin-α proteins exert antiviral effects by promoting the nuclear import of transcription factors inducing the expression of interferons (IFN), cytokines, and IFN-stimulated genes, and the IFN-inducible MxB restricts capsid docking to NPCs.

Karyopherins in the Remodeling of Extracellular Matrix: Implications in Tendon Injury

Rotator Cuff Tendinopathies (RCT) are debilitating conditions characterized by alterations in the extracellular matrix (ECM) of the shoulder tendon, resulting in pain, discomfort, and functional limitations. Specific mediators, including HIF-1α, TGF-β, MMP-9 and others have been implicated in the morphological changes observed in the tendon ECM. These mediators rely on karyopherins, a family of nuclear proteins involved in nucleo-cytoplasmic transport; however, the role of karyopherins in RCT remains understudied despite their potential role in nuclear transport mechanisms. Also, the understanding regarding the precise contributions of karyopherins in RCT holds great promise for deciphering the underlying pathophysiological mechanisms of the disease and potentially fostering the development of targeted therapeutic strategies. This article critically discusses the implications, possibilities, and perspectives of karyopherins in the pathophysiology of RCT.

ZBTB34 is a hepatocellular carcinoma-associated protein with a monopartite nuclear localization signal

ZBTB34 is a novel zinc finger protein with an unknown function. In this study, the gene expression and survival prognosis of ZBTB34 were analyzed across tumors based on the TCGA datasets. According to the bioinformatics analysis and qPCR results, liver hepatocellular carcinomas exhibit a high level of ZBTB34 expression. Additionally, the experiment supported the bioinformatics analysis findings that ZBTB34 expression was regulated by miR-125b-5p and that ZBTB34 affected ZBTB10, POLR1B, and AUH expression in HepG2 cells. Biological software analysis further revealed that ZBTB34 contains a monopartite nuclear localization signal (NLS). Arginine and lysine inside the putative NLS were substituted using the alanine-scanning mutagenesis method. The findings showed that the ability of ZBTB34 to enter the nucleus was abolished by the alanine substitution of the sequence 320RGGRARQKRA329 and the mutation of Lys327 and Arg328 residues. ZBTB34 was co-immunoprecipitated with importin α1, importin α3, importin α4, and importin β1, according to the results of the co-immunoprecipitation assay. In conclusion, ZBTB34 is a hepatocellular carcinoma-associated protein with a monopartite NLS. The nuclear import of ZBTB34 is mediated by importin α1, importin α3, importin α4, and importin β1. ZBTB34 performs its biological functions via a putative miR-125b-5p/ZBTB34/(ZBTB10, POLR1B, and AUH) signaling axis in HepG2 cells.

Mechanisms of NURR1 Regulation: Consequences for Its Biological Activity and Involvement in Pathology

NURR1 (Nuclear receptor-related 1 protein or NR4A2) is a nuclear protein receptor transcription factor with an essential role in the development, regulation, and maintenance of dopaminergic neurons and mediates the response to stressful stimuli during the perinatal period in mammalian brain development. The dysregulation of NURR1 activity may play a role in various diseases, including the onset and progression of neurodegenerative diseases, and several other pathologies. NURR1 is regulated by multiple mechanisms, among which phosphorylation by kinases or SUMOylation are the best characterized. Both post-translational modifications can regulate the activity of NURR1, affecting its stability and transcriptional activity. Other non-post-translational regulatory mechanisms include changes in its subcellular distribution or interaction with other protein partners by heterodimerization, also affecting its transcription activity. Here, we summarize the currently known regulatory mechanisms of NURR1 and provide a brief overview of its participation in pathological alterations.

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.

Using the Culex pipiens sperm proteome to identify elements essential for mosquito reproduction

Mature sperm from Culex pipiens were isolated and analyzed by mass spectrometry to generate a mature sperm proteome dataset. In this study, we highlight subsets of proteins related to flagellar structure and sperm motility and compare the identified protein components to previous studies examining essential functions of sperm. The proteome includes 1700 unique protein IDs, including a number of uncharacterized proteins. Here we discuss those proteins that may contribute to the unusual structure of the Culex sperm flagellum, as well as potential regulators of calcium mobilization and phosphorylation pathways that regulate motility. This database will prove useful for understanding the mechanisms that activate and maintain sperm motility as well as identify potential molecular targets for mosquito population control.

RKIP localizes to the nucleus through a bipartite nuclear localization signal and interaction with importin α to regulate mitotic progression

Raf kinase inhibitor protein (RKIP) is a multifunctional modulator of intracellular signal transduction. Although most of its functions have been considered cytosolic, we show here that the localization of RKIP is primarily nuclear in both growing and quiescent Madin-Darby canine kidney epithelial cells and in Cal-51 and BT-20 human breast cancer cells. We have identified a putative bipartite nuclear localization signal (NLS) in RKIP that maps to the surface of the protein surrounding a known regulatory region. Like classical NLS sequences, the putative NLS of RKIP is rich in arginine and lysine residues. Deletion of and point mutations in the putative NLS lead to decreased nuclear localization. Point mutation of all the basic residues in the putative NLS of RKIP particularly strongly reduces nuclear localization. We found consistent results in reexpression experiments with wildtype or mutant RKIP in RKIP-silenced cells. A fusion construct of the putative NLS of RKIP alone to a heterologous reporter protein leads to nuclear localization of the fusion protein, demonstrating that this sequence alone is sufficient for import into the nucleus. We found that RKIP interacts with the nuclear transport factor importin α in BT-20 and MDA-MB-231 human breast cancer cells, suggesting importin-mediated active nuclear translocation. Taken together, these findings suggest that a bipartite NLS in RKIP interacts with importin α for active transport of RKIP into the nucleus and that this process may be involved in the regulation of mitotic progression. Evaluating the biological function of nuclear localization of RKIP, we found that the presence of the putative NLS is important for the role of RKIP in mitotic checkpoint regulation in MCF-7 human breast cancer cells.

Ran GTPase and Its Importance in Cellular Signaling and Malignant Phenotype

Ran is a member of the Ras superfamily of proteins, which primarily regulates nucleocytoplasmic trafficking and mediates mitosis by regulating spindle formation and nuclear envelope (NE) reassembly. Therefore, Ran is an integral cell fate determinant. It has been demonstrated that aberrant Ran expression in cancer is a result of upstream dysregulation of the expression of various factors, such as osteopontin (OPN), and aberrant activation of various signaling pathways, including the extracellular-regulated kinase/mitogen-activated protein kinase (ERK/MEK) and phosphatidylinositol 3-kinase/Protein kinase B (PI3K/Akt) pathways. In vitro, Ran overexpression has severe effects on the cell phenotype, altering proliferation, adhesion, colony density, and invasion. Therefore, Ran overexpression has been identified in numerous types of cancer and has been shown to correlate with tumor grade and the degree of metastasis present in various cancers. The increased malignancy and invasiveness have been attributed to multiple mechanisms. Increased dependence on Ran for spindle formation and mitosis is a consequence of the upregulation of these pathways and the ensuing overexpression of Ran, which increases cellular dependence on Ran for survival. This increases the sensitivity of cells to changes in Ran concentration, with ablation being associated with aneuploidy, cell cycle arrest, and ultimately, cell death. It has also been demonstrated that Ran dysregulation influences nucleocytoplasmic transport, leading to transcription factor misallocation. Consequently, patients with tumors that overexpress Ran have been shown to have a higher malignancy rate and a shorter survival time compared to their counterparts.

Nuclear localisation sequences of chloride intracellular channels 1 and 4 facilitate nuclear import via interactions with import mediator importin-α: An empirical and theoretical perspective

Chloride intracellular channel proteins (CLICs) display ubiquitous expression, with each member exhibiting specific subcellular localisation. While all CLICs, except CLIC3, exhibit a highly conserved putative nuclear localisation sequence (NLS), only CLIC1, CLIC3 and CLIC4 exist within the nucleus. The CLIC4 NLS, 199-KVVAKKYR-206, appears crucial for nuclear entry and interacts with mouse nuclear import mediator Impα isoform 1, omitting the IBB domain (mImpα1ΔIBB). The essential nature of the basic residues in the CLIC4 NLS has been established by the fact that mutating out these residues inhibits nuclear import, which in turn is linked to cutaneous squamous cell cancer. Given the conservation of the CLIC NLS, CLIC1 likely follows a similar import pathway to CLIC4. Peptides of the CLIC1 (Pep1; Pep1_S C/S mutant) and CLIC4 (Pep4) NLSs were designed to examine binding to human Impα isoform 1, omitting the IBB domain (hImpα1ΔIBB). Molecular docking indicated that the core CLIC NLS region (KKYR) forms a similar binding pattern to both mImpα1ΔIBB and hImpα1ΔIBB. Fluorescence quenching demonstrated that Pep1_S (K_d  ≈ 237 μM) and Pep4 (K_d  ≈ 317 μM) bind hImpα1ΔIBB weakly. Isothermal titration calorimetry confirmed the weak binding interaction between Pep4 and hImpα1ΔIBB (K_d  ≈ 130 μM) and the presence of a proton-linked effect. This weak interaction may be due to regions distal from the CLIC NLS needed to stabilise and strengthen hImpα1ΔIBB binding. Additionally, this NLS may preferentially bind another hImpα isoform with different flexibility properties.

Diagnostic and Prognostic Profiling of Nucleocytoplasmic Shuttling Genes in Hepatocellular Carcinoma

One of the key features of eukaryotic cells is the separation of nuclear and cytoplasmic compartments by a double-layer nuclear envelope. This separation is crucial for timely regulation of gene expression, mRNA biogenesis, cell cycle, and differentiation. Since transcription takes place in the nucleus and the major part of translation in the cytoplasm, proper distribution of biomolecules between these two compartments is ensured by nucleocytoplasmic shuttling proteins - karyopherins. Karyopherins transport biomolecules through nuclear pores bidirectionally in collaboration with Ran GTPases and utilize GTP as the source of energy. Different karyopherins transport different cargo molecules that play important roles in the regulation of cell physiology. In cancer cells, this nucleocytoplasmic transport is significantly dysregulated to support increased demands for the import of cell cycle-promoting biomolecules and export of cell cycle inhibitors and mRNAs. Here, we analysed genomic, transcriptomic and proteomic data from published datasets to comprehensively profile karyopherin genes in hepatocellular carcinoma. We have found out that expression of multiple karyopherin genes is increased in hepatocellular carcinoma in comparison to the normal liver, with importin subunit α-1, exportin 2, importin subunit β-1 and importin 9 being the most over-expressed. More-over, we have found that increased expression of these genes is associated with higher neoplasm grade as well as significantly worse overall survival of liver cancer patients. Taken together, our bioinformatic data-mining analysis provides a comprehensive geno-mic and transcriptomic landscape of karyopherins in hepatocellular carcinoma and identifies potential members that could be targeted in order to develop new treatment regimens.

KPNA2 promotes angiogenesis by regulating STAT3 phosphorylation

PURPOSE

Angiogenesis is involved in many pathological and physiological processes and is mainly driven by hypoxia. Karyopherin subunit alpha 2 (KPNA2), a member of the nuclear transport protein family, was recently shown to be induced by hypoxia in various types of tumours, so we aimed to investigate the role and mechanism of KPNA2 in angiogenesis under hypoxia.

MATERIALS AND METHODS

After overexpression or knockdown of KPNA2 in human umbilical vein endothelial cells (HUVEC) by adenovirus vector infection, the tube formation, proliferation and migration of HUVEC under hypoxia were detected by tubule formation assay, 5-ethynyl-2'-deoxyuridine (EdU) staining and Transwell assay, respectively. After overexpression or knockdown of KPNA2 in a murine hindlimb ischemia model by local injection of purified adenovirus vector into the gastrocnemius muscle, blood flow changes were examined with a laser Doppler system. Changes in KPNA2-binding proteins under hypoxia were detected by immunoprecipitation-mass spectrometry (IP-MS) and co-immunoprecipitation (Co-IP). The effect of KPNA2 on signal transducer and activator of transcription 3 (STAT3) was detected by Western blotting and quantitative RT‒PCR.

RESULTS

KPNA2 was upregulated in the HUVEC hypoxia model and murine hindlimb ischemia model. Overexpression of KPNA2 increased the proliferation, migration and tube formation of HUVEC under hypoxia, while knockdown of KPNA2 reduced the proliferation, migration and tube formation of HUVEC. Overexpression of KPNA2 promoted the restoration of blood flow in the murine hindlimb ischemia model, while knockout of KPNA2 inhibited the restoration of blood flow in the murine hindlimb ischemia model. Mechanistically, hypoxia promoted the binding of STAT3 to KPNA2. Overexpression of KPNA2 promoted STAT3 phosphorylation and then upregulated vascular endothelial growth factor (VEGF) and angiopoietin 2(ANGPT2), whereas knockdown of KPNA2 inhibited STAT3 phosphorylation and then downregulated VEGF and ANGPT2.

CONCLUSION

Our study demonstrates that hypoxia promotes the binding of STAT3 to KPNA2 and KPNA2 promotes angiogenesis under hypoxia by promoting the binding of STAT3 and JAK1 and regulating STAT3 phosphorylation.

Mandatory vaccinations, the segregation of citizens, and the promotion of inequality in the modern democracy of Greece and other democratic countries in the era of COVID-19

During the COVID-19 pandemic, the Greek authorities enforced a vaccination mandate for healthcare workers (HCWs). At the same time, multiple concerns were raised about the epidemiological profile of Greece in addition to the ethical status of the harsh measures and their impact on employees, organizations, society, and public health. According to the World Health Organization (WHO), considerations regarding the evidence of vaccine safety and effectiveness, necessity, and proportionality should be clearly evaluated by before imposing mandatory vaccination policies. We discuss the issues regarding the mechanics of the transmission and contraction of SARS-CoV-2, the toxicity of COVID-19 vaccines, and the impact of the suspension of HCWs who did not vaccinate versus the potential expected benefits in addition to whether the vaccine mandates were justified considering the overall epidemiological context.

IPO7 Promotes Odontoblastic Differentiation and Inhibits Osteoblastic Differentiation Through Regulation of RUNX2 Expression and Translocation

RUNX2, an important transcriptional factor for both odontoblastic and osteoblastic differentiation, is upregulated during osteoblastic differentiation, but downregulated during late odontoblastic differentiation. However, the specific mechanism of the different RUNX2 expression in bone and dentin remains largely unknown. Importin 7 (IPO7), a member of the karyopherin β-superfamily, mediates nucleocytoplasmic transport of proteins. In this study, we found that IPO7 was increasingly expressed from pre-odontoblasts to mature odontoblasts. IPO7 expression was increased with odontoblastic differentiation of mouse dental papilla cells (mDPCs) and knockdown of IPO7-inhibited cell differentiation. While in MC3T3-E1 cells, IPO7 was decreased during osteoblastic differentiation and knockdown of IPO7-promoted cell differentiation. In mPDCs, IPO7 was able to bind with some odontoblastic transcription factors, and imported them into the nucleus, but not with RUNX2. Furthermore, IPO7 inhibited the total RUNX2 expression by promoting HDAC6 nuclear localization during odontoblastic differentiation. However, in MC3T3-E1 cells, IPO7 inhibited the nuclear distribution of RUNX2 but did not affect the total protein level of RUNX2. In conclusion, we found that IPO7 promotes odontoblastic differentiation and inhibits osteoblastic differentiation through regulating RUNX2 expression and translocation differently.

Identification of the Karyopherin Superfamily in Maize and Its Functional Cues in Plant Development

Appropriate nucleo-cytoplasmic partitioning of proteins is a vital regulatory mechanism in phytohormone signaling and plant development. However, how this is achieved remains incompletely understood. The Karyopherin (KAP) superfamily is critical for separating the biological processes in the nucleus from those in the cytoplasm. The KAP superfamily is divided into Importin α (IMPα) and Importin β (IMPβ) families and includes the core components in mediating nucleocytoplasmic transport. Recent reports suggest the KAPs play crucial regulatory roles in Arabidopsis development and stress response by regulating the nucleo-cytoplasmic transport of members in hormone signaling. However, the KAP members and their associated molecular mechanisms are still poorly understood in maize. Therefore, we first identified seven IMPα and twenty-seven IMPβ genes in the maize genome and described their evolution traits and the recognition rules for substrates with nuclear localization signals (NLSs) or nuclear export signals (NESs) in plants. Next, we searched for the protein interaction partners of the ZmKAPs and selected the ones with Arabidopsis orthologs functioning in auxin biosynthesis, transport, and signaling to predict their potential function. Finally, we found that several ZmKAPs share similar expression patterns with their interacting proteins, implying their function in root development. Overall, this article focuses on the Karyopherin superfamily in maize and starts with this entry point by systematically comprehending the KAP-mediated nucleo-cytoplasmic transport process in plants, and then predicts the function of the ZmKAPs during maize development, with a perspective on a closely associated regulatory mechanism between the nucleo-cytoplasmic transport and the phytohormone network.

Ivermectin Inhibits HBV Entry into the Nucleus by Suppressing KPNA2

Hepatitis B virus (HBV) specifically infects human hepatocytes and increases the risks of cirrhosis and liver cancer. Currently, nucleic acid analogs are the main therapeutics for chronic hepatitis caused by HBV infection. Although nucleic acid analogs can eliminate HBV DNA by inhibiting HBV reverse transcriptase, they cannot lead to negative conversion of covalently closed circular DNA (cccDNA) and hepatitis B surface antigen (HBsAg). In this study, we revealed that the antifilarial drug ivermectin suppresses HBV production by a different mechanism from the nucleic acid analog entecavir or Na⁺ taurocholate co-transporting polypeptide-mediated entry inhibitor cyclosporin A. Ivermectin reduced the levels of several HBV markers, including HBsAg, in HBV-infected human hepatocellular carcinoma cells (HepG2-hNTCP-C4 cells) and humanized mouse hepatocytes (PXB hepatocytes). In addition, ivermectin significantly decreased the expression of HBV core protein and the nuclear transporter karyopherin α2 (KPNA2) in the nuclei of HepG2-hNTCP-C4 cells. Furthermore, depletion of KPNA1-6 suppressed the production of cccDNA. These results suggest that KPNA1-6 is involved in the nuclear import of HBV and that ivermectin suppresses the nuclear import of HBV by inhibiting KPNA2. This study demonstrates the potential of ivermectin as a novel treatment for hepatitis B.

A novel likely pathogenic variant in the FBXO32 gene associated with dilated cardiomyopathy according to whole‑exome sequencing

Background

Familial dilated cardiomyopathy (DCM) is a genetic heart disorder characterized by progressive heart failure and sudden cardiac death. Over 250 genes have been reported in association with DCM; nonetheless, the genetic cause of most DCM patients has been unknown. The goal of the present study was to determine the genetic etiology of familial DCM in an Iranian family.

Methods

Whole-exome sequencing was performed to identify the underlying variants in an Iranian consanguineous family with DCM. The presence of the candidate variant was confirmed and screened in available relatives by PCR and Sanger sequencing. The pathogenic effect of the candidate variant was assessed by bioinformatics analysis, homology modeling, and docking.

Results

One novel likely pathogenic deletion, c.884_886del: p.Lys295del, in F-box only protein 32 (muscle-specific ubiquitin-E3 ligase protein; FBXO32) was identified. Based on bioinformatics and modeling analysis, c.884_886del was the most probable cause of DCM in the studied family.

Conclusions

Our findings indicate that variants in FBXO32 play a role in recessive DCM. Variants in FBXO32 may disturb the degradation of target proteins in the ubiquitin–proteasome system and lead to severe DCM. We suggest considering this gene variants in patients with recessively inherited DCM.

Bioinformatics and Functional Analysis of a New Nuclear Localization Sequence of the Influenza A Virus Nucleoprotein

Influenza viruses deliver their genome into the nucleus of infected cells for replication. This process is mediated by the viral nucleoprotein (NP), which contains two nuclear localization sequences (NLSs): NLS1 at the N-terminus and a recently identified NLS2 (²¹²GRKTR²¹⁶). Through mutagenesis and functional studies, we demonstrated that NP must have both NLSs for an efficient nuclear import. As with other NLSs, there may be variations in the basic residues of NLS2 in different strains of the virus, which may affect the nuclear import of the viral genome. Although all NLS2 variants fused to the GFP mediated nuclear import of GFP, bioinformatics showed that 98.8% of reported NP sequences contained either the wild-type sequence ²¹²GRKTR²¹⁶ or ²¹²GRRTR²¹⁶. Bioinformatics analyses used to study the presence of NLS2 variants in other viral and nuclear proteins resulted in very low hits, with only 0.4% of human nuclear proteins containing putative NLS2. From these, we studied the nucleolar protein 14 (NOP14) and found that NLS2 does not play a role in the nuclear import of this protein but in its nucleolar localization. We also discovered a functional NLS at the C-terminus of NOP14. Our findings indicate that NLS2 is a highly conserved influenza A NP sequence.

The use of Ivermectin for the treatment of COVID-19: Panacea or enigma?

The outbreak of SARS-CoV-2 pandemic has triggered unprecedented social, economic and health challenges. To control and reduce the infection rate, countries employed non-pharmaceutical measures such as social distancing, isolation, quarantine, and the use of masks, hand and surface sanitisation. Since 2021 a global race for COVID-19 vaccination ensued, mainly due to a lack of equitable vaccine production and distribution. To date, no treatments have been demonstrated to cure COVID-19. The scientific World is now considering the potential use of Ivermectin as a prophylactic and treatment for COVID-19. Against this background, the objective of this study is to review the literature to demystify the enigma or panacea in the use of Ivermectin. This paper intends to investigate literature which supports the existence or shows the nonexistence of a causal link between Ivermectin, COVID-19 mortality and recovery. There are inconsistent results on the effectiveness of Ivermectin in the treatment of COVID-19 patients. Some studies have asserted that in a bid to slow down the transmission of COVID-19, ivermectin can be used to inhibit the in vitro replication of SARS-CoV-2. The pre-existing health system burdens can be alleviated as patients treated prophylactically would reduce hospital admissions and stem the spread of COVID-19. On a global scale, Ivermectin is currently used by about 28% of the world's population, and its adoption is presently about 44% of countries. However, the full administration of this drug would require further tests to establish its clinical effectiveness and efficacy.

Current state of knowledge of human DNA polymerase eta protein structure and disease-causing mutations

POLη, encoded by the POLH gene, is a crucial protein for replicating damaged DNA and the most studied specialized translesion synthesis polymerases. Mutations in POLη are associated with cancer and the human syndrome xeroderma pigmentosum variant, which is characterized by extreme photosensitivity and an increased likelihood of developing skin cancers. The myriad of structural information about POLη is vast, covering dozens of different mutants, numerous crucial residues, domains, and posttranslational modifications that are essential for protein function within cells. Since POLη is key vital enzyme for cell survival, and mutations in this protein are related to aggressive diseases, understanding its structure is crucial for biomedical sciences, primarily due to its similarities with other Y-family polymerases and its potential as a targeted therapy-drug for tumors. This work provides an up-to-date review on structural aspects of the human POLη: from basic knowledge about critical residues and protein domains to its mutant variants, posttranslational modifications, and our current understanding of therapeutic molecules that target POLη. Thus, this review provides lessons about POLη's structure and gathers critical discussions and hypotheses that may contribute to understanding this protein's vital roles within the cells.

Antiparasitic Drugs against SARS-CoV-2: A Comprehensive Literature Survey

More than two years have passed since the viral outbreak that led to the novel infectious respiratory disease COVID-19, caused by the SARS-CoV-2 coronavirus. Since then, the urgency for effective treatments resulted in unprecedented efforts to develop new vaccines and to accelerate the drug discovery pipeline, mainly through the repurposing of well-known compounds with broad antiviral effects. In particular, antiparasitic drugs historically used against human infections due to protozoa or helminth parasites have entered the main stage as a miracle cure in the fight against SARS-CoV-2. Despite having demonstrated promising anti-SARS-CoV-2 activities in vitro, conflicting results have made their translation into clinical practice more difficult than expected. Since many studies involving antiparasitic drugs are currently under investigation, the window of opportunity might be not closed yet. Here, we will review the (controversial) journey of these old antiparasitic drugs to combat the human infection caused by the novel coronavirus SARS-CoV-2.

Invasion and Propagation of White Spot Syndrome Virus: Hijacking of the Cytoskeleton, Intracellular Transport Machinery, and Nuclear Import Transporters

The pathogenesis of white spot syndrome virus (WSSV) is largely unclear. In this study, we found that actin nucleation and clathrin-mediated endocytosis were recruited for internalization of WSSV into crayfish hematopoietic tissue (Hpt) cells. This internalization was followed by intracellular transport of the invading virions via endocytic vesicles and endosomes. After envelope fusion within endosomes, the penetrated nucleocapsids were transported along microtubules toward the periphery of the nuclear pores. Furthermore, the nuclear transporter CqImportin α1/β1, via binding of ARM repeat domain within CqImportin α1 to the nuclear localization sequences (NLSs) of viral cargoes and binding of CqImportin β1 to the nucleoporins CqNup35/62 with the action of CqRan for docking to nuclear pores, was hijacked for both targeting of the incoming nucleocapsids toward the nuclear pores and import of the expressed viral structural proteins containing NLS into the cell nucleus. Intriguingly, dysfunction of CqImportin α1/β1 resulted in significant accumulation of incoming nucleocapsids on the periphery of the Hpt cell nucleus, leading to substantially decreased introduction of the viral genome into the nucleus and remarkably reduced nuclear import of expressed viral structural proteins with NLS; both of these effects were accompanied by significantly inhibited viral propagation. Accordingly, the survival rate of crayfish post-WSSV challenge was significantly increased after dysfunction of CqImportin α1/β1, also showing significantly reduced viral propagation, and was induced either by gene silencing or by pharmacological blockade via dietary administration of ivermectin per os. Collectively, our findings improve our understanding of WSSV pathogenesis and support future antiviral designing against WSSV. IMPORTANCE As one of the largest animal DNA viruses, white spot syndrome virus (WSSV) has been causing severe economical loss in aquaculture due to the limited knowledge on WSSV pathogenesis for an antiviral strategy. We demonstrate that the actin cytoskeleton, endocytic vesicles, endosomes, and microtubules are hijacked for WSSV invasion; importantly, the nuclear transporter CqImportin α1/β1 together with CqRan were recruited, via binding of CqImportin β1 to the nucleoporins CqNup35/62, for both the nuclear pore targeting of the incoming nucleocapsids and the nuclear import of expressed viral structural proteins containing the nuclear localization sequences (NLSs). This is the first report that NLSs from both viral structure proteins and host factor are elaborately recruited together to facilitate WSSV infection. Our findings provide a novel explanation for WSSV pathogenesis involving systemic hijacking of host factors, which can be used for antiviral targeting against WSSV disease, such as the blockade of CqImportin α1/β1 with ivermectin.

Transcription factor dynamics in plants: Insights and technologies for in vivo imaging

Biochemical and genetic approaches have been extensively used to study transcription factor (TF) functions, but their dynamic behaviors and the complex ways in which they regulate transcription in plant cells remain unexplored, particularly behaviors such as translocation and binding to DNA. Recent developments in labeling and imaging techniques provide the necessary sensitivity and resolution to study these behaviors in living cells. In this review, we present an up-to-date portrait of the dynamics and regulation of TFs under physiologically relevant conditions and then summarize recent advances in fluorescent labeling strategies and imaging techniques. We then discuss future prospects and challenges associated with the application of these techniques to examine TFs' intricate dance in living plants.

Prospective mode of action of Ivermectin: SARS-CoV-2

The well-known anti-helminthic drug ivermectin (IVM) has been established as an example of drug repurposing for the management of SARS-CoV-2 infection. Various study has been done to understand the inhibitory mechanism of IVM against SARS-CoV-2 targets. Broadly, IVM has been categorized as a host-directed agent and the proposed mechanism involves inhibition of the IMPα/ß1-mediated nuclear import of viral proteins. In addition, in vitro/in vivo and molecular docking/dynamic simulation studies suggested multitargets mechanism of IVM against SARS-CoV-2. Present manuscript attempts to provide an overview of the detailed mechanism of action based on experimental and computational studies. The knowledge of binding interaction of IVM and SARS-CoV-2 targets will give the direction to developed new and potential anti-COVID agents.

Therapeutic nucleus-access BNCT drug combined CD47-targeting gene editing in glioblastoma

Glioblastoma is the most common brain primary malignant tumor with the highest mortality. Boron neutron capture therapy (BNCT) can efficiently kill cancer cells on the cellular scale, with high accuracy, short course and low side-effects, which is regarded as the most promising therapy for malignant brain tumors like glioma. As the keypoint of BNCT, all boron delivery agents currently in clinical use are beset by insufficient tumor uptake, especially in the tumor nucleus, which limits the clinical application of BNCT. In this study, nuclear targeting of boron is achieved by DOX-CB, consisting of doxorubicin (DOX) and carborane (CB) utilizing the nuclear translocation property of DOX. The nucleus of GL261 cells takes up almost three times the concentration of boron required for BNCT. To further kill glioma and inhibit recurrence, a new multifunctional nanoliposome delivery system DOX-CB@lipo-pDNA-iRGD is constructed. It combines DOX-CB with immunotherapy strategy of blocking macrophage immune checkpoint pathway CD47-SIRPα by CRISPR-Cas9 system, coupling BNCT with immunotherapy simultaneously. Compared with clinical drug Borocaptate Sodium (BSH), DOX-CB@lipo-pDNA-iRGD significantly enhances the survival rate of tumor-bearing mice, reduces tumor stemness, and improves the prognosis. The excellent curative effect of this nanoliposome delivery system provides an insight into the combined treatment of BNCT.

Subcellular localization of X-linked inhibitor of apoptosis protein (XIAP) in cancer: does that matter?

X-linked inhibitor of apoptosis protein (XIAP) finely tunes the balance between survival and death to control homeostasis. XIAP is found aberrantly expressed in cancer, which has been shown to promote resistance to therapy-induced apoptosis and confer poor outcome. Despite its predominant cytoplasmic localization in human tissues, growing evidence implicates the expression of XIAP in other subcellular compartments in sustaining cancer hallmarks. Herein, we review our current knowledge on the prognostic role of XIAP localization and discuss molecular mechanisms underlying differential biological functions played in each compartment. The comprehension of XIAP subcellular shuttling and functional dynamics might provide the rationale for future anticancer therapeutics.

BMP10 expression in the adult rat central nervous system

Bone morphogenetic protein 10 (BMP10), is a member of the transforming growth factor β (TGFβ) superfamily. Although BMP10 plays pivotal roles during development, including vascular development and cardiogenesis, little information is available for BMP10 expression in the central nervous system (CNS). We, thus, investigated BMP10 expression in the adult rat CNS using immunohistochemistry. BMP10 was intensely expressed in most neurons and their axons. Furthermore, we found that astrocytes and ependymal cells also express BMP10 protein. These data indicate that BMP10 is widely expressed throughout the adult CNS, and this abundant expression strongly supports the idea that BMP10 also plays important roles in the adult CNS.

Biochemical propensity mapping for structural and functional anatomy of importin α IBB domain

Importin α has been described as a nuclear protein transport receptor that enables proteins synthesized in the cytoplasm to translocate into the nucleus. Besides its function in nuclear transport, an increasing number of studies have examined its non-nuclear transport functions. In both nuclear transport and non-nuclear transport, a functional domain called the IBB domain (importin β binding domain) plays a key role in regulating importin α behavior, and is a common interacting domain for multiple binding partners. However, it is not yet fully understood how the IBB domain interacts with multiple binding partners, which leads to the switching of importin α function. In this study, we have distinguished the location and propensities of amino acids important for each function of the importin α IBB domain by mapping the biochemical/physicochemical propensities of evolutionarily conserved amino acids of the IBB domain onto the structure associated with each function. We found important residues that are universally conserved for IBB functions across species and family members, in addition to those previously known, as well as residues that are presumed to be responsible for the differences in complex-forming ability among family members and for functional switching.

Nuclear-capture of endosomes depletes nuclear G-actin to promote SRF/MRTF activation and cancer cell invasion

Signals are relayed from receptor tyrosine kinases (RTKs) at the cell surface to effector systems in the cytoplasm and nucleus, and coordination of this process is important for the execution of migratory phenotypes, such as cell scattering and invasion. The endosomal system influences how RTK signalling is coded, but the ways in which it transmits these signals to the nucleus to influence gene expression are not yet clear. Here we show that hepatocyte growth factor, an activator of MET (an RTK), promotes Rab17- and clathrin-dependent endocytosis of EphA2, another RTK, followed by centripetal transport of EphA2-positive endosomes. EphA2 then mediates physical capture of endosomes on the outer surface of the nucleus; a process involving interaction between the nuclear import machinery and a nuclear localisation sequence in EphA2's cytodomain. Nuclear capture of EphA2 promotes RhoG-dependent phosphorylation of the actin-binding protein, cofilin to oppose nuclear import of G-actin. The resulting depletion of nuclear G-actin drives transcription of Myocardin-related transcription factor (MRTF)/serum-response factor (SRF)-target genes to implement cell scattering and the invasive behaviour of cancer cells.

Potentilla discolor ameliorates LPS-induced inflammatory responses through suppressing NF-κB and AP-1 pathways

Potentilla discolor Bunge (PD) is a traditional Chinese medicine which has been widely used for the treatment of various inflammatory diseases (e.g., diarrhea, fever and furuncle). However, few studies focused on its effect on classical inflammation. This study aimed to investigate the anti-inflammatory effect and potential mechanism of the ethanol extract of the whole herbs of PD (EPD) in lipopolysaccharide (LPS)-induced inflammatory models. The obtained results showed that EPD decreased supernatant NO, tumor necrosis factor-α (TNF-α) and monocyte chemoattractant protein-1 (MCP-1) in LPS-activated RAW264.7 cells and mouse peritoneal macrophages. Moreover, its effect on NO was attributed to the suppression of iNOS expression rather than its activity. At the transcriptional level, EPD suppressed iNOS, TNF-α and MCP-1 mRNA expressions in LPS-stimulated RAW264.7 cells. Further study showed that EPD didn't affect the phosphorylation and degradation of IκBα, but yet impeded the nuclear translocation of p65 to inhibit NF-κB activation. Meanwhile, it also prevented JNK, ERK1/2 and p38 phosphorylation to dampen the activation of AP-1. In endotoxemia mouse model, EPD not only decreased interleukin-6, TNF-α and MCP-1 levels in serum, but also potently ameliorated diarrhea. These findings provide the theoretical basis for PD to treat inflammatory diseases, especially intestinal inflammation.

Polycation-Mediated Transfection: Mechanisms of Internalization and Intracellular Trafficking

Polyplex-mediated gene transfection is now in its' fourth decade of serious research, but the promise of polyplex-mediated gene therapy has yet to fully materialize. Only approximately one in a million applied plasmids actually expresses. A large part of this is due to an incomplete understanding of the mechanism of polyplex transfection. There is an assumption that internalization must follow a canonical mechanism of receptor mediated endocytosis. Herein, we present arguments that untargeted (and most targeted) polyplexes do not utilize these routes. By incorporating knowledge of syndecan-polyplex interactions, we can show that syndecans are the "target" for polyplexes. Further, it is known that free polycations (which disrupt cell-membranes by acid-catalyzed hydrolysis of phospholipid esters) are necessary for (untargeted) endocytosis. This can be incorporated into the model to produce a novel mechanism of endocytosis, which fits the observed phenomenology. After membrane translocation, polyplex containing vesicles reach the endosome after diffusing through the actin mesh below the cell membrane. From there, they are acidified and trafficked toward the lysosome. Some polyplexes are capable of escaping the endosome and unpacking, while others are not. Herein, it is argued that for some polycations, as acidification proceeds the polyplexes excluding free polycations, which disrupt the endosomal membrane by acid-catalyzed hydrolysis, allowing the polyplex to escape. The polyplex's internal charge ratio is now insufficient for stability and it releases plasmids which diffuse to the nucleus. A small proportion of these plasmids diffuse through the nuclear pore complex (NPC), with aggregation being the major cause of loss. Those plasmids that have diffused through the NPC will also aggregate, and this appears to be the reason such a small proportion of nuclear plasmids express mRNA. Thus, the structural features which promote unpacking in the endosome and allow for endosomal escape can be determined, and better polycations can be designed.

SWO1 modulates cell wall integrity under salt stress by interacting with importin ɑ in Arabidopsis

Maintenance of cell wall integrity is of great importance not only for plant growth and development, but also for the adaptation of plants to adverse environments. However, how the cell wall integrity is modulated under salt stress is still poorly understood. Here, we report that a nuclear-localized Agenet domain-containing protein SWO1 (SWOLLEN 1) is required for the maintenance of cell wall integrity in Arabidopsis under salt stress. Mutation in SWO1 gene results in swollen root tips, disordered root cell morphology, and root elongation inhibition under salt stress. The swo1 mutant accumulates less cellulose and pectin but more lignin under high salinity. RNA-seq and ChIP-seq assays reveal that SWO1 binds to the promoter of several cell wall-related genes and regulates their expression under saline conditions. Further study indicates that SWO1 interacts with importin ɑ IMPA1 and IMPA2, which are required for the import of nuclear-localized proteins. The impa1 impa2 double mutant also exhibits root growth inhibition under salt stress and mutations of these two genes aggravate the salt-hypersensitive phenotype of the swo1 mutant. Taken together, our data suggest that SWO1 functions together with importin ɑ to regulate the expression of cell wall-related genes, which enables plants to maintain cell wall integrity under high salinity.

Dominant KPNA3 Mutations Cause Infantile-Onset Hereditary Spastic Paraplegia

OBJECTIVE

Hereditary spastic paraplegia (HSP) is a highly heterogeneous neurologic disorder characterized by lower-extremity spasticity. Here, we set out to determine the genetic basis of an autosomal dominant, pure, and infantile-onset form of HSP in a cohort of 8 patients with a uniform clinical presentation.

METHODS

Trio whole-exome sequencing was used in 5 index patients with infantile-onset pure HSP to determine the genetic cause of disease. The functional impact of identified genetic variants was verified using bioinformatics and complementary cellular and biochemical assays.

RESULTS

Distinct heterozygous KPNA3 missense variants were found to segregate with the clinical phenotype in 8 patients; in 4 of them KPNA3 variants had occurred de novo. Mutant karyopherin-α3 proteins exhibited a variable pattern of altered expression level, subcellular distribution, and protein interaction.

INTERPRETATION

Our genetic findings implicate heterozygous variants in KPNA3 as a novel cause for autosomal dominant, early-onset, and pure HSP. Mutant karyopherin-α3 proteins display varying deficits in molecular and cellular functions, thus, for the first time, implicating dysfunctional nucleocytoplasmic shuttling as a novel pathomechanism causing HSP. ANN NEUROL 2021;90:738-750.

Importin α2 association with chromatin: Direct DNA binding via a novel DNA-binding domain

The nuclear transport of proteins is important for facilitating appropriate nuclear functions. The importin α family proteins play key roles in nuclear transport as transport receptors for copious nuclear proteins. Additionally, these proteins possess other functions, including chromatin association and gene regulation. However, these nontransport functions of importin α are not yet fully understood, especially their molecular-level mechanisms and consequences for functioning with chromatin. Here, we report the novel molecular characteristics of importin α binding to diverse DNA sequences in chromatin. We newly identified and characterized a DNA-binding domain-the Nucleic Acid Associating Trolley pole domain (NAAT domain)-in the N-terminal region of importin α within the conventional importin β binding (IBB) domain that is necessary for nuclear transport of cargo proteins. Furthermore, we found that the DNA binding of importin α synergistically coupled the recruitment of its cargo protein to DNA. This is the first study to delineate the interaction between importin α and chromatin DNA via the NAAT domain, indicating the bifunctionality of the importin α N-terminal region for nuclear transport and chromatin association.

Importins: Diverse roles in male fertility

Regulated nucleocytoplasmic transport is central to the changes in gene expression that underpin cellular development and homeostasis, including in the testis, and proteins in the importin family are the predominant facilitators of cargo transport through the nuclear envelope. Reports documenting cell-specific profiles of importin transcripts and proteins during spermatogenesis led us to hypothesize that importins facilitate developmental switches in the testis. More recently, importins have been shown to serve additional functions, both inside and outside the nucleus; these include acting as subcellular scaffolding, mediating cellular stress responses, and controlling transcription. This paper seeks to provide an overview and update on the functions of importin proteins, with a focus on testis development and spermatogenesis. We present an extended survey of importins by combining published single cell RNAseq data with immunohistochemistry on developing and adult mouse testes. This approach reinforces and broadens knowledge of importins in biological processes, including in spermatogenesis and during testis development, revealing additional avenues for impactful investigations.

Contribution of Energy Dysfunction to Impaired Protein Translation in Neurodegenerative Diseases

Impaired energy homeostasis and aberrant translational control have independently been implicated in the pathogenesis of neurodegenerative diseases. AMP kinase (AMPK), regulated by the ratio of cellular AMP and ATP, is a major gatekeeper for cellular energy homeostasis. Abnormal regulation of AMPK has been reported in several neurodegenerative diseases, including Alzheimer’s disease (AD) and amyotrophic lateral sclerosis (ALS). Most importantly, AMPK activation is known to suppress the translational machinery by inhibiting the mechanistic target of rapamycin complex 1 (mTORC1), activating translational regulators, and phosphorylating nuclear transporter factors. In this review, we describe recent findings on the emerging role of protein translation impairment caused by energy dysregulation in neurodegenerative diseases.

Types of nuclear localization signals and mechanisms of protein import into the nucleus

Nuclear localization signals (NLS) are generally short peptides that act as a signal fragment that mediates the transport of proteins from the cytoplasm into the nucleus. This NLS-dependent protein recognition, a process necessary for cargo proteins to pass the nuclear envelope through the nuclear pore complex, is facilitated by members of the importin superfamily. Here, we summarized the types of NLS, focused on the recently reported related proteins containing nuclear localization signals, and briefly summarized some mechanisms that do not depend on nuclear localization signals into the nucleus. Video Abstract.

CSE1L promotes nuclear accumulation of transcriptional coactivator TAZ and enhances invasiveness of human cancer cells

The transcriptional coactivator with PDZ-binding motif (TAZ) (WWTR1) induces epithelial-mesenchymal transition and enhances drug resistance in multiple cancers. TAZ has been shown to interact with transcription factors in the nucleus, but when phosphorylated, translocates to the cytoplasm and is degraded through proteasomes. Here, we identified a compound TAZ inhibitor 4 (TI-4) that shifted TAZ localization to the cytoplasm independently of its phosphorylation. We used affinity beads to ascertain a putative target of TI-4, chromosomal segregation 1 like (CSE1L), which is known to be involved in the recycling of importin α and as a biomarker of cancer malignancy. We found that TI-4 suppressed TAZ-mediated transcription in a CSE1L-dependent manner. CSE1L overexpression increased nuclear levels of TAZ, whereas CSE1L silencing delayed its nuclear import. We also found via the in vitro coimmunoprecipitation experiments that TI-4 strengthened the interaction between CSE1L and importin α5 and blocked the binding of importin α5 to TAZ. WWTR1 silencing attenuated CSE1L-promoted colony formation, motility, and invasiveness of human lung cancer and glioblastoma cells. Conversely, CSE1L silencing blocked TAZ-promoted colony formation, motility, and invasiveness in human lung cancer and glioblastoma cells. In human cancer tissues, the expression level of CSE1L was found to correlate with nuclear levels of TAZ. These findings support that CSE1L promotes the nuclear accumulation of TAZ and enhances malignancy in cancer cells.