Steroids dilate nuclear pores imaged with atomic force microscopy

Combined delivery of dexamethasone and plasmid DNA in an animal model of LPS-induced acute lung injury

Dexamethasone was conjugated to low molecular weight polyethylenimine (2kDa, PEI2k). Dexamethasone conjugated PEI2k (PEI2k-Dexa) was evaluated as a combined delivery carrier of dexamethasone and plasmid DNA (pDNA) in an animal model of lipopolysaccharide (LPS) induced acute lung injury (ALI). In vitro transfection of L2 lung epithelial cells, PEI2k-Dexa exhibited higher transfection efficiency than PEI2k or a simple mixture of PEI2k and dexamethasone. In addition, the PEI2k-Dexa/pβ-Luc complexes reduced the levels of pro-inflammatory cytokines in LPS activated Raw 264.7 macrophage cells. The anti-inflammatory effect of PEI2k-Dexa was higher than that of controls. The PEI2k-Dexa/pβ-Luc complexes were administered to mice via intratracheal injection. PEI2k-Dexa had higher pDNA delivery efficiency than PEI2k in the lung and decreased TNF-α and IL-6 in the lung homogenates and bronchoalveolar lavage (BAL) fluid compared with the controls. Furthermore, total protein and immunoglobulin M (IgM) concentrations in BAL fluid were reduced by the PEI2k-Dexa/pβ-Luc complexes. The intratracheal injection of the PEI2k-Dexa/pcDNA-EGFP complexes in the ALI model showed higher EGFP expression compared with PEI2k. Hematoxylin and eosin (H&E) staining showed that PEI2k-Dexa reduced inflammatory reaction in the lung. Therefore, PEI2k-Dexa may be useful for combination gene and drug therapy for ALI.

Polyamidoamine dendrimers as gene delivery carriers in the inner ear: How to improve transfection efficiency

Hair cells in the cochlea can be damaged by various insults, including noise, drugs, infections and presbycusis, which may cause sensorineural hearing loss. Gene therapy is a novel therapeutic technology that, recently, has led to the idea of treating inner ear diseases on a genetic level. Depending on their characteristics, such as a high efficiency in delivery, the capability of specific targeting, multifunctionality, biodegradability, non-toxicity, non-immunogenicity and the capability of limiting DNA degradation, nanovectors, such as polyamidoamine (PAMAM) dendrimers for cellular gene delivery, provide a promising approach to eradicate genetic diseases. They are a new class of highly branched spherical polymers that are highly soluble in aqueous solution. Their unique surface is composed of positively charged primary amine groups which allow them to form stable complexes with plasmid DNA, oligonucleotides, antibodies and drugs. This review provides an overview of the characteristics of PAMAMs which may be used in gene transfer into the cochlea as well as the efforts to improve their transfection efficiency as gene-delivery carriers.

Combinational therapy of ischemic brain stroke by delivery of heme oxygenase-1 gene and dexamethasone

Combinational therapies using genes and drugs are promising therapeutic strategies for various diseases. In this research, a co-delivery carrier of dexamethasone and plasmid DNA (pDNA) was developed by conjugation of dexamethasone to polyethylenimine (2 kDa, PEI2k) for combinational therapy of ischemic brain. Dynamic light scattering, atomic force microscopy and flow cytometry studies showed that the pDNA/dexamethasone-conjugated PEI2k (PEI2k-Dexa) complex was 150 nm in size and was taken up by cells more easily than PEI2k-Dexa only. The tumor necrosis factor-α (TNF-α) level was decreased more efficiently by pDNA/PEI2k-Dexa complex than dexamethasone only in hypoxia activated Raw 264.7 macrophage cells, suggesting that pDNA/PEI2k-Dexa complex increased the delivery efficiency and therapeutic effect of dexamethasone. In in vitro transfection assay, PEI2k-Dexa had higher transfection efficiency than PEI2k and lipofectamine. However, the simple mixture of PEI2k and dexamethasone did not show this effect, suggesting that the conjugation of dexamethasone to polyethylenimine increased DNA delivery efficiency of PEI2k. To evaluate the effects of combinational therapy in vivo, pDNA/PEI2k-Dexa complex was applied to a transient focal ischemia animal model. At 24 h after the injection, mean infarction volume and the TNF-α level were reduced more efficiently in the pDNA/PEI2k-Dexa injection group, compared with the control, pDNA/PEI2k, or dexamethasone injection group. The infarction volume and inflammatory cytokines were further decreased by delivery of pSV-HO-1 using PEI2k-Dexa. Magnetic resonance imaging and microPET studies confirmed the therapeutic effect of pSV-HO-1/PEI2k-Dexa complex at 10 days after the injection. Therefore, pSV-HO-1/PEI2k-Dexa complexes may be useful in combinational therapy for ischemic diseases such as stroke.

Exceptional structural and mechanical flexibility of the nuclear pore complex

Nuclear pore complexes (NPCs) mediate all transport between the cytosol and the nucleus and therefore take centre stage in physiology. While transport through NPCs has been extensively investigated little is known about their structural and barley anything about their mechanical flexibility. Structural and mechanical flexibility of NPCs, however, are presumably of key importance. Like the cell and the cell nucleus, NPCs themselves are regularly exposed to physiological mechanical forces. Besides, NPCs reveal striking transport properties which are likely to require fairly high structural flexibility. The NPC transports up to 1,000 molecules per second through a physically 9 nm wide channel which repeatedly opens to accommodate macromolecules significantly larger than its physical diameter. We hypothesised that NPCs possess remarkable structural and mechanical stability. Here, we tested this hypothesis at the single NPC level using the nano-imaging and probing approach atomic force microscopy (AFM). AFM presents the NPC as a highly flexible structure. The NPC channel dilates by striking 35% on exposure to trans-cyclohexane-1,2-diol (TCHD), which is known to transiently collapse the hydrophobic phase in the NPC channel like receptor-cargo complexes do in transit. It constricts again to its initial size after TCHD removal. AFM-based nano-indentation measurements show that the 50 nm long NPC basket can astonishingly be squeezed completely into the NPC channel on exposure to incremental mechanical loads but recovers its original vertical position within the nuclear envelope plane when relieved. We conclude that the NPC possesses exceptional structural and mechanical flexibility which is important to fulfilling its functions.

Intracellular organelle-targeted non-viral gene delivery systems

Gene therapy is a rapidly growing approach for the treatment of various diseases. To achieve successful gene therapy, a gene delivery system is necessary to overcome several barriers in the extracellular and intracellular spaces. Polymers, peptides, liposomes and nanoparticles developed as gene carriers have achieved efficient cellular uptake of genes. Among these carriers, cationic polymers and peptides have been further developed as intracellular organelle-targeted delivery systems. The cytoplasm, nucleus and mitochondria have been considered primary targets for gene delivery using targeting moieties or environment-responsive materials. In this review, we explore recently developed non-viral gene carriers based on reducible systems specialized to target the cytoplasm, nucleus and mitochondria.

Investigation of polyethylenimine-grafted-triamcinolone acetonide as nucleus-targeting gene delivery systems

BACKGROUND

Nuclear membrane is one of the main barriers in polymer mediated intracellular gene delivery. To improve the transgenic activity and safety of nonviral vector, triamcinolone acetonide (TA) as a nuclear localization signal was conjugated with different molecular weight polyethylenimine (PEI).

METHODS

Different molecular weight PEI [600, 1800, 25,000 (25k)] was conjugated with TA to synthesize PEI-TA by two-step reaction. Their physicochemical characteristics, in vitro cytotoxicity and transfection efficiency were evaluated. To investigate the difference of transfection efficiency of various molecular weight PEI-TA, their transfection mechanism was further investigated by confocal microscopy and competition assay. Transgenic expression in vivo was evaluated by injection into hepatic portal vein of mice.

RESULTS

All PEI-TA could form nanosize polyplexes with DNA and their physicochemical properties resemble each other. Their cytotoxicities were negligible compared to PEI 25k. The order of transfection efficiency was PEI 1800-TA > PEI 600-TA > PEI 25k-TA. A transfection mechanism study displayed that TA could inhibit considerably the transgenic activity of PEI 1800-TA and PEI 600-TA, but that of PEI 25k-TA was not inhibited. It was suggested that PEI 1800-TA and PEI 600-TA might translocate into the nucleus. Confocal microscopy investigation verified this suggestion. The data strongly suggested that the transfection efficiency of PEI 1800-TA in vivo was much higher than that of PEI 25k, which was consistent with the results obtained in vitro.

CONCLUSIONS

Low molecular weight PEI-TA could translocate into the nucleus efficiently. PEI 1800-TA presented higher transgenic activity and it has a great potential for gene therapy as a nonviral carrier.

Nonviral vectors for the delivery of small interfering RNAs to the CNS

While efficient methods for cell line transfection are well described, for primary neurons a high-yield method different from those relying on viral vectors is lacking. Viral vector-based primary neuronal infection has several drawbacks, including complexity of vector preparation, safety concerns and the generation of immune and inflammatory responses, when used in vivo. This article will cover the different approaches that are being used to efficiently deliver genetic material (both DNA and small interfering RNA) to neuronal tissue using nonviral vectors, including the use of cationic lipids, polyethylenimine derivatives, dendrimers, carbon nanotubes and the combination of carbon-made nanoparticles with dendrimers. The effectiveness, both in vivo and in vitro, of the different methods to deliver genetic material to neural tissue is discussed.

Global motions of the nuclear pore complex: insights from elastic network models

The nuclear pore complex (NPC) is the gate to the nucleus. Recent determination of the configuration of proteins in the yeast NPC at approximately 5 nm resolution permits us to study the NPC global dynamics using coarse-grained structural models. We investigate these large-scale motions by using an extended elastic network model (ENM) formalism applied to several coarse-grained representations of the NPC. Two types of collective motions (global modes) are predicted by the ENMs to be intrinsically favored by the NPC architecture: global bending and extension/contraction from circular to elliptical shapes. These motions are shown to be robust against tested variations in the representation of the NPC, and are largely captured by a simple model of a toroid with axially varying mass density. We demonstrate that spoke multiplicity significantly affects the accessible number of symmetric low-energy modes of motion; the NPC-like toroidal structures composed of 8 spokes have access to highly cooperative symmetric motions that are inaccessible to toroids composed of 7 or 9 spokes. The analysis reveals modes of motion that may facilitate macromolecular transport through the NPC, consistent with previous experimental observations.

Dexamethasone-conjugated polyethylenimine as an efficient gene carrier with an anti-apoptotic effect to cardiomyocytes

BACKGROUND

Dexamethasone is a potent glucocorticoid with anti-inflammatory effects. Dexamethasone can protect ischemic cardiomyocytes from apoptosis. To apply the anti-apoptotic effect of dexamethasone to ischemic disease gene therapy, dexamethasone-conjugated polyethylenimine (PEI-Dexa) was synthesized and evaluated as an anti-apoptotic gene carrier.

METHODS

PEI-Dexa was synthesized with low molecular weight polyethylenimine (PEI2K, 2 kDa). The transfection efficiency and cytotoxicity of PEI-Dexa were evaluated by luciferase assay and the MTT assay. To evaluate the anti-apoptotic effect, PEI-Dexa/DNA complex was transfected into cells and the cells were treated with H(2)O(2). Cell viability and apoptosis level were measured by the MTT assay and caspase-3 assay, respectively.

RESULTS

A transfection assay into H9C2 rat cardiomyocytes showed that PEI-Dexa had the highest transfection efficiency at an 8 : 1 weight ratio (PEI-Dexa/DNA). At this ratio, PEI-Dexa had higher transfection efficiency than high molecular polyethylenimine (PEI25K, 25 kDa) and PEI2K. In addition, the cytotoxicity of PEI-Dexa was lower than that of PEI25K. To evaluate the anti-apoptotic effect, PEI-Dexa/pSV-Luc or PEI2K/pSV-Luc was transfected into H9C2 cells and the cells were treated with H(2)O(2). PEI-Dexa was found to reduce caspase-3 activity and increase cell viability compared to PEI2K. Heme oxygenase-1 (HO-1) can protect ischemic cardiomyocytes from apoptosis. Therefore, pSV-HO-1 was cloned and transfected into H9C2 cells using PEI-Dexa. The cells transfected with PEI-Dexa/pSV-HO-1 complex had lower caspase-3 activity and higher viability than the cells transfected with PEI-Dexa/pSV-Luc complex after the H(2)O(2) treatment.

CONCLUSIONS

PEI-Dexa is an efficient gene carrier with an anti-apoptotic effect and may be useful for anti-apoptotic gene therapy in combination with pSV-HO-1.

PAMAM-triamcinolone acetonide conjugate as a nucleus-targeting gene carrier for enhanced transfer activity

The excellent transfection efficiency and viability are essential for successful gene therapy. It suggested that when bound to its glucocorticoid receptor, glucocorticoid steroid can dilate the nuclear pore complexes and facilitated the transport of pDNA into the nucleus. In this research, the two different degrees of substitution of PAMAM-triamcinolone acetonide (PAMAM-TA) conjugates were synthesised for efficient translocation of pDNA into the nucleus. The physicochemical properties of the polyplexes were investigated by agarose gel electrophoresis, Zeta-sizer and TEM. They both could form nano-size polyplexes with pDNA. The polyplexes were very stable and showed excellent buffering capacities, facilitating endosomal escape, and no obvious difference was found between them. The TA-conjugated PAMAM-mediated transfection of luciferase and EGFP genes showed better transfer activity than native PAMAM and was comparable to the PEI 25K (polyethylenimine), and lower cytotoxicity in HEK 293 and HepG 2 cells. Even with 10% serum, their transfer activity was still high relatively. In addition, confocal microscopy examination confirmed that the enhancing mechanism for enhanced gene transfer activity of PAMAM-TA conjugate may involve the nuclear translocation of the polyplex. The low substituted degree of TA to 0.22 did not interrupt its nuclear localization potency. These findings demonstrated that the TA-grafted PAMAM dendrimer is a potential candidate as a safe and efficient gene delivery carrier for gene therapy.

Structure-transfection activity relationships with glucocorticoid-polyethyl-enimine conjugate nuclear gene delivery systems

Efficient nuclear gene delivery is essential for successful gene therapy. It was previously reported that the transport of DNA into nucleus may be facilitated by glucocorticoid (GC). In this study, five glucocorticoids with different structures and potencies were conjugated with low molecular weight PEI 1800, and the degree of substitution of glucocorticoids was controlled to be close to each other. The glucocorticoid-polyethylenimine (GC-PEI)/pDNA complexes were prepared and their physico-chemical properties and transfection efficiency were investigated. The results showed that the complexes had similar physico-chemical properties, but their transfection activities were different statistically. In order to explore the reason of this difference, the affinity of GC-PEI polymer with GC receptor was analyzed by the application of molecular docking, and the correlation between transfection activity and the potency of five GC was investigated. The result showed that receptor binding of five GC was different and transgene expression enhanced linearly with the increasing GC potency, but logP. In addition, confocal microscopy examination confirmed that GC-PEI/DNA complexes were more effectively translocated in the nucleus than PEI 25K or PEI 1800 complexes and the cytotoxicities of the GC-PEI polymers were lower than that of PEI 25K. These results demonstrated that transfection activity of GC-PEI polymer correlated with its GC potency, and this regularity might be useful for the development of more efficient GC substituted polymer as promising nuclear-targeting carrier.

Nanomedicine--challenge and perspectives

The application of nanotechnology concepts to medicine joins two large cross-disciplinary fields with an unprecedented societal and economical potential arising from the natural combination of specific achievements in the respective fields. The common basis evolves from the molecular-scale properties relevant to the two fields. Local probes and molecular imaging techniques allow surface and interface properties to be characterized on a nanometer scale at predefined locations, while chemical approaches offer the opportunity to elaborate and address surfaces, for example, for targeted drug delivery, enhanced biocompatibility, and neuroprosthetic purposes. However, concerns arise in this cross-disciplinary area about toxicological aspects and ethical implications. This Review gives an overview of selected recent developments and applications of nanomedicine.

Biology and biophysics of the nuclear pore complex and its components

Nucleocytoplasmic exchange of proteins and ribonucleoprotein particles occurs via nuclear pore complexes (NPCs) that reside in the double membrane of the nuclear envelope (NE). Significant progress has been made during the past few years in obtaining better structural resolution of the three-dimensional architecture of NPC with the help of cryo-electron tomography and atomic structures of domains from nuclear pore proteins (nucleoporins). Biophysical and imaging approaches have helped elucidate how nucleoporins act as a selective barrier in nucleocytoplasmic transport. Nucleoporins act not only in trafficking of macromolecules but also in proper microtubule attachment to kinetochores, in the regulation of gene expression and signaling events associated with, for example, innate and adaptive immunity, development and neurodegenerative disorders. Recent research has also been focused on the dynamic processes of NPC assembly and disassembly that occur with each cell cycle. Here we review emerging results aimed at understanding the molecular arrangement of the NPC and how it is achieved, defining the roles of individual nucleoporins both at the NPC and at other sites within the cell, and finally deciphering how the NPC serves as both a barrier and a conduit of active transport.

Dexamethasone-conjugated low molecular weight polyethylenimine as a nucleus-targeting lipopolymer gene carrier

Dexamethasone, a glucocorticoid steroid, can dilate the nuclear pore complexes and translocate into the nucleus when it is bound to its glucocorticoid receptor, suggesting that the transport of DNA into the nucleus may be facilitated by the reagent. In this research, dexamethasone was conjugated to low molecular weight polyethylenimine (2 kDa) for efficient translocation of the polymer/DNA complex into the nucleus. Polyethylenimine (PEI)-dexamethasone (PEI-Dexa) was synthesized by one-step reaction using the Traut's reagent. In gel retardation assay, the PEI-Dexa/DNA complex was completely retarded at or above 0.3/1 weight ratio (polymer/DNA). The average size distributions and zeta-potential values of the complexes were measured at various weight ratios. In vitro transfection assay showed that the PEI-Dexa/DNA complex had higher gene delivery efficiency compared to PEI 2kDa/DNA complex. The localization of PEI-Dexa/plasmid DNA complexes in the nucleus was confirmed by using total internal reflection fluorescence and Nomarski differential interference contrast microscope as well as confocal microscope. Therefore, with efficient nuclear translocation and low cytotoxicity, PEI-Dexa may be useful for nonviral gene therapy.

Single-molecule fluorescence analysis of cellular nanomachinery components

Recent progress in proteomics suggests that the cell can be conceived as a large network of highly refined, nanomachine-like protein complexes. This working hypothesis calls for new methods capable of analyzing individual protein complexes in living cells and tissues at high speed. Here, we examine whether single-molecule fluorescence (SMF) analysis can satisfy that demand. First, recent technical progress in the visualization, localization, tracking, conformational analysis, and true resolution of individual protein complexes is highlighted. Second, results obtained by the SMF analysis of protein complexes are reviewed, focusing on the nuclear pore complex as an instructive example. We conclude that SMF methods provide powerful, indispensable tools for the structural and functional characterization of protein complexes. However, the transition from in vitro systems to living cells is in the initial stages. We discuss how current limitations in the nanoscopic analysis of living cells and tissues can be overcome to create a new paradigm, nanoscopic biomedicine.

Atomic force microscopy imaging of actin cortical cytoskeleton of Xenopus laevis oocyte

In this study we report an atomic force microscopy (AFM) investigation of the actin cortical cytoskeleton of Xenopus laevis oocytes. Samples consisted of inside-out orientated plasma membrane patches of X. laevis oocytes with overhanging cytoplasmic material. They were spread on a freshly cleaved mica surface, subsequently treated with Triton X-100 detergent and chemically fixed. The presence of actin fibres in oocyte patches was proved by fluorescence microscopy imaging. Contact mode AFM imaging was performed in air in constant force conditions. Reproducible high-resolution AFM images of a filamentous structure were obtained. The filamentous structure was identified as an actin cortical cytoskeleton, investigating its disaggregation induced by cytochalasin D treatment. The thinnest fibres showed a height of 7 nm in accordance with the diameter of a single actin microfilament. The results suggest that AFM imaging can be used for the high-resolution study of the actin cortical cytoskeleton of the X. laevis oocyte and its modifications mediated by the action of drugs and toxins.

Plugs in nuclear pores: transcripts in early oocyte development identified with nanotechniques

Throughout oogenesis, huge amounts of RNA are produced that are needed for early development. Early stages of oocyte development are characterized by high transcriptional activity whereas translation of maternal RNA dominates late stages. Nuclear pore complexes (NPCs), located in the nuclear envelope (NE), mediate bidirectional macromolecule exchange between the nuclear and cytosolic compartments including RNA export. Here, we report on structural correlates of this transport pathway at single NPC level. Using atomic force microscopy (AFM), we imaged the nucleoplasmic ("inner") surface of the NE of Xenopus laevis oocytes in different stages of development. We found that NPC frequency per nucleus increases with maturation. However, individual NPCs are more active in immature stages. In early stages, known for high transcriptional activity, we found nearly 10% of NPC central channels plugged with a 400-800 kDa mass. In contrast, the incidence of plugged NPCs was below 1% in late oocyte stages. On-site RNA digestion led to a change in plug shape from prominent to flat while plug mass decreased by almost 20%. Quantitative AFM analysis revealed that RNase exposure reduced total nucleoplasmic NPC mass by about 58 and 25% in early and late stage oocytes, respectively. We conclude: (i) NPCs of immature oocytes are more active in RNA transport, (ii) Plugs identified at the nucleoplasmic entrance of NPC central channels represent ribonucleoproteins exiting the nucleus, (iii) RNA is a structural component of the NPC nanomachine.

Route of glucocorticoid-induced macromolecules across the nuclear envelope as viewed by atomic force microscopy

Glucocorticoids are vital steroid hormones. The physiologic activities of these hydrophobic molecules predominantly require translocation of glucocorticoid-initiated macromolecules (GIMs), proteins and mRNA transcripts, in and out of the nucleus, respectively. The bidirectional transport of GIMs is mediated by nuclear pore complexes (NPCs) that span the nuclear envelope at regular distances. The transport proceeds through the NPC central channel, whose interior is lined up by hydrophobic proteins. The NPC channel is assumed to dilate while hydrophobic cargos are being translocated through. Upon glucocorticoid injection into a glucocorticoid-sensitive cell, Xenopus laevis oocyte, and using atomic force microscopy, we have recently unraveled the long unexplored paths that GIMs take through the nuclear envelope and described interactions of GIMs with NPCs. In so doing, surprising and intriguing observations were made and the following conclusions were drawn: glucocorticoid-initiated proteins evoke NPC channel dilation before physical interaction with the NPC. NPC channel dilation is apparently transmitted through binding of glucocorticoid-induced proteins to NPC-associated filaments or yet unknown structures in the cytoplasmic nuclear envelope surface. The transport of both proteins and ribonucleoproteins seems to be non-randomly confined to local areas on either nuclear envelope site, the so-called hot spots.

The nuclear pore complex up close

Transport between the nucleus and cytoplasm is mediated by nuclear pore complexes (NPCs), perforations in the double-membrane of the nuclear envelope. NPCs are huge protein assemblies made up of distinct subcomplexes. The complex modular nature of the NPC and limitations in the current experimental approaches render the analysis of NPCs and nucleocytoplasmic transport at the molecular level difficult. Recent efforts in the NPC/nucleocytoplasmic transport field have focused on elucidating the core components that make up NPC structure (or the lack thereof) and function. These include results obtained by more conventional methods, such as electron microscopy or biochemical strategies, as well as more advanced applications, such as X-ray crystallography and atomic force microscopy.

Measurement of dimensions of pentagonal doughnut-shaped C-reactive protein using an atomic force microscope and a dual polarisation interferometric biosensor

In order to develop the C-reactive protein (CRP) sensor chips for clinical detection of atherosclerosis and coronary heart disease, we used an atomic force microscope (AFM) and a dual polarization interferometric (DPI) biosensor to probe the surface ultrastructure and to measure the dimensions of CRP. A single pentagonal structure was directly visualized by AFM, and quantitative measurements of the dimensions of the protein were provided. The average height calculated for each pentagonal CRP particle was approximately 3.03+/-0.37 nm, which basically corresponds to that (36 A in protomer diameter) previously obtained from the structure of CRP determined by X-ray crystallography. Moreover, a experiment using dual polarization interferometric (DPI) as a biosensor was then performed, and the average monolayer thickness value (3.18+/-0.43 nm) that was calculated basically corresponds to that obtained from the experimental value (3.03+/-0.37 nm) of the height measured by an AFM method for CRP. Further investigations will be performed to study the surface ultrastructure of a single pentagonal CRP molecule, and for this purpose a CRP sample (at low concentration) was scanned in vacuum by AFM. The higher-resolution images clearly revealed the presence of doughnut-shaped CRP molecules. In addition, phase images of CRP molecules were captured simultaneously with their height images, and the lateral dimensions of the doughnut-shaped CRP molecules were then measured. It was found that the average values calculated for the outer diameter (11.13+/-1.47 nm) and pore diameter (3.52+/-0.42 nm) are respectively close to those (102 A in outer diameter and 30 A in pore diameter) previously obtained from the structure of CRP determined by X-ray crystallography. This study represents the first direct characterization of the surface ultrastructure and dimensional measurement of the CRP molecule on the sensor chip.

Hot Spot Formation in the Nuclear Envelope of Oocytes in Response to Steroids

A Glucocorticoid-sensitive cell rapidly responds to hormone stimulation with bidirectional exchange of specific macromolecules between cytosol and nucleus. Glucocorticoid-initiated macromolecules (GIMs) must overcome the nuclear envelope (NE) to enter or leave the nucleus. GIM translocation occurs through nuclear pore complexes (NPCs) that span the NE. We investigated the question whether transport of GIMs through NPCs occurs random or involves selected groups of NPCs (hot spots). Glucocorticoid receptors were expressed in Xenopus laevis oocytes and GIM transport was activated by triamcinolone acetonide, a potent synthetic glucocorticoid analogon. Glucocorticoid receptors associated with the NE and the chromatin were identified using western blot analysis and, at single molecule level, atomic force microscopy. Fluorescence-labeled dextran was used to describe passive NE permeability. We observed that after hormone injection (i) small GIMs, most likely GRs, localize within seconds on both sides of the NE. (ii) large GIMs, most likely ribonucleoproteins, localize within minutes on NPCs at the nucleoplasmic side (iii) both small and large GIMs accumulate on selected NPC clusters (iv) NE permeability transiently decreases when GIMs attach to NPCs. We conclude that GIM transport across the nuclear barrier does not randomly take place but is carried out by a selected population of NPCs.

The nuclear barrier is structurally and functionally highly responsive to glucocorticoids

Nuclear pore complexes mediate and control transport between the cytosol and the nucleus. They form a highly selective and, thus, tight nuclear barrier between these compartments. The nuclear barrier provides the cell with the opportunity to control access to its DNA, a defining feature of eukaryotes. The tightness of the nuclear barrier is therefore physiologically pivotal and any remarkable change in its structure and permeability can prove pathophysiological, e.g. as a result of viral attack. However, there is accumulating evidence that nuclear barrier structure and permeability are highly responsive to hydrophobic cargos of crucial physiological and therapeutic relevance, glucocorticoids (steroid hormones). The present review highlights the glucocorticoid-induced effects on the nuclear barrier structure and permeability concluding that they are physiologically essential to mediate glucocorticoid action.

Nuclear envelope barrier leak induced by dexamethasone

Nuclear pore complexes (NPCs) are multiprotein channels that span the nuclear envelope. They strongly limit the efficiency of gene transfection by restriction of nuclear delivery of exogenously applied therapeutic macromolecules. NPC dilation could significantly increase this efficiency. Recently, it was shown in oocytes of Xenopus laevis that NPCs dilate from about 82 to 110 nm within min after injection of the glucocorticoid analog dexamethasone (dex). In the present paper we analyzed by means of atomic force microscopy the structural details of NPC dilation and correlated them with functional changes in nuclear envelope permeability. 5-11 min after Dex injection NPC dilation was found at its maximum (approximately 140 nm). In addition, a yet unknown configuration, so-called giant pore, up to 300 nm in diameter, was visualized. Giant pore formation was paralleled by an increase in nuclear envelope permeability tested by electrophysiology and confocal fluorescence microscopy. Even large macromolecules lacking any nuclear localization signal (77 kDa FITC-dextran, molecule diameter up to 36 nm) could gain access to the nucleus. We conclude that dex transiently opens unspecific pathways for large macromolecules. Dex treatment could be potentially useful for improving the efficiency of nuclear gene transfection.