Intracellular oligonucleotide hybridization detected by fluorescence resonance energy transfer (FRET).

Fluorescence resonance energy transfer (FRET) was used to study hybrid formation and dissociation after microinjection of oligonucleotides (ODNs) into living cells. A 28-mer phosphodiester ODN (+PD) was synthesized and labeled with a 3' rhodamine (+PD-R). The complementary, antisense 5'-fluorescein labeled phosphorothioate ODN (-PT-F) was specifically quenched by addition of the +PD-R. In solution, the -PT-F/+PD-R hybrid had a denaturation temperature of 65 +/- 3 degrees C detected by both absorbance and FRET. Hybridization between the ODNs occurred within 1 minute at 17 microM and was not appreciably affected by the presence of non-specific DNA. The pre-formed hybrid slowly dissociated (T1/2 approximately 3 h) in the presence of a 300-fold excess of the unlabeled complementary ODN and could be degraded by DNAse I. Upon microinjection into the cytoplasm of cells, pre-formed fluorescent hybrids dissociated with a half-time of 15 minutes, which is attributed to the degradation of the phosphodiester. Formation of the hybrid from sequentially injected ODNs was detected by FRET transiently in the cytoplasm and later in the cell nucleus, where nearly all injected ODNs accumulate. This suggests that antisense ODNs can hybridize to an intracellular target, of exogenous origin in these studies, in both the cytoplasm and the nucleus.     

Intracellular traffic of oligodeoxynucleotides in and out of the nucleus: effect of exportins and DNA structure

The delivery of oligodeoxynucleotides (ODNs) into cells is widely utilized for antisense, antigene, aptamer, and similar approaches to regulate gene and protein activities based upon the ODNs' sequence-specific recognition. Short pieces of DNA can also be generated in biological processes, for example, after degradation of viral or bacterial DNA. However, the mechanisms that regulate intracellular trafficking and localization of ODNs are not fully understood. Here we study the effects of major transporters of microRNA, exportin-1 (Exp1) and exportin-5 (Exp5), on the transport of single-stranded ODNs in and out of the nucleus. For this, we employed a fluorescent microscopy-based assay to quantitatively measure the redistribution of ODNs between the nucleus and cytoplasm of live cells. By measuring the fluorescent signal of the nuclei we observed that after delivery into cells via cationic liposomes ODNs rapidly accumulated inside nuclei. However, after removal of the ODN/liposome containing media, we found re-localization of ODNs from the nuclei to cytoplasm of the cells over the time course of several hours. Downregulation of the Exp5 gene by siRNA resulted in a slight increase of ODN uptake into the nucleus, but the kinetics of ODN efflux to the cytoplasm was not affected. Inhibition of Exp1 with leptomycin B somewhat slowed down the clearance of ODNs from the nucleus; however, within 6 hours most of the ODN were still being cleared form the nucleus. ODNs that could form intramolecular G-quadruplex structures behaved differently. They also accumulated in nuclei, although at a lesser extent than unstructured ODN, but they remained there for up to 20 hours after transfection, causing significant cell death. We conclude that Exp1 and Exp5 are not the major transporters of our ODNs out of the nucleus, and that the transport of ODNs is strongly affected by their secondary structure.     

Microinjection of fluorescent tubulin into dividing sea urchin cells

To follow the dynamics of microtubule (MT) assembly and disassembly during mitosis in living cells, tubulin has been covalently modified with the fluorochrome 5-(4,6-dichlorotriazin-2-yl)aminofluorescein and microinjected into fertilized eggs of the sea urchin Lytechinus variegatus. The changing distribution of the fluorescent protein probe is visualized in a fluorescence microscope coupled to an image intensification video system. Cells that have been injected with fluorescent tubulin show fluorescent linear polymers that assemble very rapidly and radiate from the spindle poles, coincident with the position of the astral fibers. No fluorescent polymer is apparent in other areas of the cytoplasm. When fluorescent tubulin is injected near the completion of anaphase, little incorporation of fluorescent tubulin into polymer is apparent, suggesting that new polymerization does not occur past a critical point in anaphase. These results demonstrate that MT polymerization is very rapid in vivo and that the assembly is both temporally and spatially regulated within the injected cells. Furthermore, the microinjected tubulin is stable within the sea urchin cytoplasm for at least 1 h since it can be reutilized in successive daughter cell spindles. Control experiments indicate that the observed fluorescence is dependent on MT assembly. The fluorescence is greatly diminished upon treatment of the cells with cold or colchicine agents known to cause the depolymerization of assembled MT. In addition, cells injected with fluorescent bovine serum albumin or assembly-incompetent fluorescent tubulin do not exhibit fluorescence localized in the spindle but rather appear diffusely fluorescent throughout the cytoplasm.     

Effects of a hexameric deoxyriboguanosine run conjugation into CpG oligodeoxynucleotides on their immunostimulatory potentials

CpG oligodeoxynucleotides (ODNs) are promising immunomodulatory agents for treating human diseases and vaccine development. Phosphodiester CpG ODNs were demonstrated to have poor immunostimulatory potentials for cytokine production. However, the conjugation of consecutive deoxyriboguanosine residues, called a dG run, at the 3' terminus of phosphodiester CpG ODNs significantly enhanced TNF-alpha and IL-12 production from mouse splenic dendritic cells (DCs). The optimal induction of cytokine production was achieved by the addition of a hexameric dG (dG6) run. In contrast, the existence of a dG6 run either at the 5' terminus of phosphodiester CpG ODNs or at the 3' terminus of phosphorothioate CpG ODNs diminished CpG-mediated cytokine induction, suggesting that the effects of a dG run depend on its location and the chemical property of the ODN backbone, respectively. In addition, we provided the evidence that the conjugation of a dG6 run caused the structural transformation of CpG ODNs, which facilitates their targeting into mouse APCs such as splenic DCs, B cells, and peritoneal macrophages with a scavenger receptor type A ligand specificity. Among primary APCs, DCs were the most potent for CpG ODN-mediated IL-12 production. Furthermore, we demonstrated that the conjugation of a dG6 run into the 3' terminus of phosphodiester CpG ODNs was crucial for their ability to generate Th1 immunity in vivo. Thus, the conjugation of a dG6 run into phosphodiester CpG ODNs would be an alternative way to optimize their immunostimulatory potentials in vitro and in vivo.     

Tracking of microinjected DNA in live cells reveals the intracellular behavior and elimination of extrachromosomal genetic material

We here addressed the basic question, how does extrachromosomal DNA behave when it is placed in the nuclear or the cytoplasmic environment and how is it eliminated? To do this, we tracked microinjected DNA molecules in live cells. In the cytoplasm, the diffusion of microinjected DNA was inhibited in a size- and linearity-dependent manner, probably by the intermediate filament. This was followed by the rapid disappearance of the DNA fluorescent signal. In the nucleus, the diffusion was also dependent on the size of the molecule and was accompanied by the aggregation of the DNA. The aggregation may be due to a putative DNA-binding molecule, whose level is high during the G1 phase. Surprisingly, the injected DNA could move across the nuclear membrane and appeared in the cytoplasm, which suggests the presence of a transport system. The intracytoplasmic behavior and the elimination of such DNA was obviously different from the DNA that was directly injected at the cytoplasm. The DNA remaining in the nucleus appeared to be stable and persisted in the nucleus or, after cell division, in the cytoplasm, for more than one cell cycle. These findings provide a novel and basic understanding of the behavior and elimination of a wide variety of extrachromosomal genetic material.     

Erythrocyte-mediated microinjection of horseradish peroxidase into BHK cells

In order to establish the distribution with time of proteins microinjected into mammalian cells, horseradish peroxidase (HRP) was microinjected into baby hamster kidney (BHK) cells using chicken erythrocyte ghosts. At time intervals following initiation of fusion between ghosts and target cells, samples were fixed with aldehydes and the peroxidase visualized by reaction with diaminobenzidine and viewing by light and electron microscopy. At 10 min, the reaction product was observed within the cytoplasm of 60% of the microinjected cells, but was excluded from the nucleus and membranous organelles. In the other 40% of microinjected cells, the reaction product was also observed within the nucleus. At 30 min, the reaction product was observed to be evenly distributed throughout the cell, including the nucleus but excluded from organelles. By 6 h, the reaction product was present almost exclusively within the nucleus of 63% of microinjected cells. At all time points, 20–30% of the erythrocytes ghosts appear to have been taken up by cells by phagocytosis rather than fusion, as evidenced by the presence of peroxidase reaction product within intact and fragmented erythrocyte ghosts in the cytoplasm of target cells. Cells incubated with a lanthanum solution following fusion excluded this electron dense tracer, indicating that the cytoplasmic compartment is not opened during exposure to polyethylene glycol.     

人工诱骗子的入核分布对核因子-κB活性的调控作用

探讨了由核定位信号(NLS)多肽介导的核因子-κB(NF-κB)寡核苷酸诱骗子(ODNs decoy)进入HeLa细胞核的效率,以及对细胞核内NF-κB活性的调控作用。利用双功能交联剂(Sulfo-SMCC)共价交联末端氨基修饰的ODNs decoy和末端巯基修饰的NLS多肽,形成NLS多肽共价连接的ODNs decoy。依靠TransME转染试剂的辅助转染NLS-ODNs decoy进入HeLa细胞,用荧光显微镜观察荧光标记的NLS-ODNs在细胞内的分布。用MTT法检测HeLa细胞的活力,以凝胶迁移实验(EMSA)检测TNF-α诱导的HeLa细胞核抽提物中NF-κB的活性。结果表明,NLS多肽成功地连接到ODNs decoy上,NLS-ODNs可高效入核,入核率达到17.9%。转染NLS-ODNs进入HeLa细胞,对细胞活力无明显影响,而显著抑制核内NF-κB的活性。结果表明NLS多肽可提高ODNs decoy的入核效率,显著增强诱骗子对NF-κB活性的抑制效果。     

Relationship between the structure of chromosomal protein HMG1 and its accumulation in the cell nucleus

When microinjected into the cytoplasm of cultured mammalian cells, non-histone chromosomal protein HMG1 migrates into the nucleus and binds to the chromatin. To define the features of the HMG1 molecule which are essential for this activity, fragments of HMG1 and chemically modified HMG1 molecules were injected into HeLa cells and the capacity of each of these probes to accumulate in the nucleus was measured by an autoradiographic technique. Fragments representing the C-terminal and central portions of HMG1 did not concentrate in the nucleus; a fragment which consisted of the N-terminal two-thirds of the molecule and which lacked the 41 consecutive aspartate and glutamate residues located near the C-terminal end of the molecule accumulated to about the same extent as intact HMG1. When the amino groups of HMG1 were chemically modified, there was a progressive loss in the ability of the protein to accumulate in the nucleus; derivatization of one-fourth of the total amino groups reduced the concentration of microinjected protein in the nucleus relative to that in the cytoplasm to one-half of the original value. In contrast, modification of one-fourth of the total carboxyl groups did not significantly affect the capacity of HMG1 to accumulate in the nucleus, although further modification resulted in decreased nuclear accumulation. Iodination of tyrosine residues was without effect and modification of the cysteine residues had only a modest effect on the ability of HMG1 to concentrate in the nucleus.     

Informational molecules in amoebae: an attempt to follow injected fractions using autoradiography

Cytoplasmic fractions from Amoeba discoides contain informational molecules which, when injected into A. proteus, may influence the characters of resulting clones. An attempt was made to follow and locate these molecules by autoradiography. Using either 3H-uridine or 3H-leucine, radioactive fractions of A. discoides were microinjected into A. proteus and cells examined at varying times after injection. A. discoides were injected with the same preparations to serve as controls. Grain counts were compared for equivalent areas of nucleus and cytoplasm, and results expressed in terms of the ratio between nucleus and cytoplasm. When the light microsomal or the supernatant fractions were injected, the level of labelled molecules was higher in the nucleus than the cytoplasm in over 50% of the cells examined after 6 h, except for those cells injected with 3H-leucine-labelled supernatant material when only 15% cells showed a nuclear/cytoplasmic grain count greater than 1.1. After some purification by sucrose density gradient centrifugation, 'information-containing' peaks '13' from the light microsomal fraction, and '16' from the supernatant fraction were injected. A different pattern of results was obtained. The problems of interpreting these results in the light of known migratory molecules and strain incompatibility are discussed.     

Rapid nuclear accumulation of injected oligodeoxyribonucleotides.

The intracellular transport and fate of nucleic acids is poorly understood. To study this process, we injected fluorescent oligodeoxyribonucleotides (oligos) into the cytoplasm of CV-1 epithelial cells and primary human fibroblasts. Rapid nuclear accumulation was found with the phosphodiester (PD), phosphorothioate (PT), and methylphosphonate (MP) forms of a 28-mer oligo complimentary to the rev mRNA of the human immunodeficiency virus type 1. Migration of the oligos in the cytoplasm was slower than diffusion of a coinjected dextran, but the oligos freely diffused into the nucleus. Nuclear incorporation was temperature but not energy dependent. The intranuclear distribution of the oligos was influenced by the chemistry of internucleoside linkages. The PD oligos and, to a lesser extent, the PT oligos colocalized with small nuclear ribonucleoproteins (snRNPs), whereas the MP oligos colocalized with concentrated regions of genomic DNA. These data have important implications for our understanding of the transport and accumulation of exogenous nucleic acids in mammalian nuclei, and the assay described could potentially be used for testing the efficacy of oligos designed as therapeutic agents.     

A Cell-Permeable Fluorescent Polymeric Thermometer for Intracellular Temperature Mapping in Mammalian Cell Lines

Changes in intracellular temperatures reflect the activity of the cell. Thus, the tool to measure intracellular temperatures could provide valuable information about cellular status. We previously reported a method to analyze the intracellular temperature distribution using a fluorescent polymeric thermometer (FPT) in combination with fluorescence lifetime imaging microscopy (FLIM). Intracellular delivery of the FPT used in the previous study required microinjection. We now report a novel FPT that is cell permeable and highly photostable, and we describe the application of this FPT to the imaging of intracellular temperature distributions in various types of mammalian cell lines. This cell-permeable FPT displayed a temperature resolution of 0.05°C to 0.54°C within the range from 28°C to 38°C in HeLa cell extracts. Using our optimized protocol, this cell-permeable FPT spontaneously diffused into HeLa cells within 10 min of incubation and exhibited minimal toxicity over several hours of observation. FLIM analysis confirmed a temperature difference between the nucleus and the cytoplasm and heat production near the mitochondria, which were also detected previously using the microinjected FPT. We also showed that this cell-permeable FPT protocol can be applied to other mammalian cell lines, COS7 and NIH/3T3 cells. Thus, this cell-permeable FPT represents a promising tool to study cellular states and functions with respect to temperature.     

Distribution of actin in spreading macrophages: a comparative study on living and fixed cells

The distribution of actin in proteose peptone-elicited murine peritoneal macrophages is examined with fluorescent analog cytochemistry (FAC), immunofluorescence, and electron microscopy (EM). Living adherent macrophages, microinjected with 5- iodoacetamidofluorescence-labeled actin, show a rather uniform distribution of actin with punctuate and linear fluorescence in the thin peripheral areas of the cell. Apparent incorporation of a portion of linear fluorescence in the thin peripheral areas of the cell. Apparent incorporation of a portion of the microinjected actin into the cell’s actin cytoskeleton is also demonstrated when microinjected cells are subsequently examined for fluorescein fluorescence after fixation and extraction. However, a substantial perinuclear pool of actin, observed with FAC, is lost when microinjected cells are prepared for immunofluorescence using standard fixation methods. These results suggest that part of the cellular actin, possibly nonfilamentous or oligomeric, can be extracted during the normal preparative steps for immunofluorescence. When the dynamic distributin of actin structures is examined in living cells, extension of the cell’s periphery is associated with the formation of punctuate structures. The distribution of the most stable, nonextractable actin structures in fixed cells at different stages of spreading is quantified using rhodamine-labeled phalloidin and antiactin indirect immunofluorescence. At early stages, the rounded cells show cortical bands of fluorescence surrounding the nuclear region with punctuate structures directly above the plane of the attached plasma membrane. At later time periods, fully spread cells contain both punctuate and linear fluorescent structures. Adherent macrophage membranes, a preparation in which the attached membrane and membrane-cortex are isolated by shearing away the unattached plasma membrane and underlying cytoplasm, show punctuate and linear fluorescence when stained with rhodamine-labeled phalloidin. When the same cell remnant is negatively stained and examined with EM, the fluorescent punctuate structures coincide with electron-dense foci and associated radiating thin filaments. We suggest that the optimal approach for elucidating the distribution of cytoskeletal and contractile proteins involved in motile processes is a combined approach using all three techniques. Although each technique is subject to potential artifacts and limitations, the use of FAC can permit the visualization of both the soluble and stabilized components of the cytoskeleton in living, functional cells. A qualitative method for determining differences in local concentrations of proteins is also presented.     

Increased stability and antiviral activity of 2'-O-phosphoglyceryl derivatives of (2'-5')oligo(adenylate)

Metabolically stable analogues of (2'-5')oligo(adenylate), (2'-5')(A)n, might constitute a new class of antiviral agents as they mimic some of the effects of interferons. 2'-O-phosphoglyceryl derivatives of (2'-5')(A)n oligomers, (2'-5')(A)n-PGro have been synthesized by chemical modification of their terminal ribose residue. Such analogues are resistant to degradation by phosphodiesterases but remain sensitive to phosphatase activity, at least in cell-free extracts. In line with its increased stability, (2'-5')(A)n-PGro has a powerful antiviral activity against an RNA virus when microinjected with micropipettes into the cytoplasm of intact cells. This antiviral activity remains transient however, possibly as a consequence of degradation in intact cells. Since (2'-5')(A)n and its derivatives do not easily cross cell membranes, their possible use in antiviral chemotherapy is tightly linked with the development of vectors suitable for their administration in vivo.     

Nuclear translocation of the calcium-binding protein ALG-2 induced by the RNA-binding protein RBM22

By yeast two-hybrid screening using the calcium-binding protein ALG-2 as bait a new target of ALG-2 was identified, the RNA-binding protein RBM22. In order to confirm these interactions in vivo we prepared fluorescent constructs by using the monomeric red fluorescent protein to label ALG-2 and the enhanced green fluorescent protein to label RBM22. Confocal microscopy of NIH 3T3 cells transfected with either ALG-2 or RBM22 expression constructs encoding fluorescent fusion proteins alone revealed that the majority of ALG-2 was localized in the cytoplasm whereas RBM22 was located in the nucleus. When cells were co-transfected with expression vectors encoding both fusion proteins ALG-2 was found in the nucleus indicating that RBM22 which can shuttle between the cytoplasm and the nucleus may play a role in nuclear translocation of ALG-2. Using zebrafish as a model mRNA homologues of ALG-2 and RBM22 were microinjected into the blastodisc-yolk margin of zebrafish embryos at the 1-cell stage followed by monitoring the fusion proteins during development of the zebrafish. Hereby, we observed that ALG-2 alone evenly distributed within the cell, whereas in the presence of RBM22 the two proteins co-localized within the nucleus. More than 95% of the two proteins co-localized within the same area in the nucleus suggesting a functional interaction between the Ca(2+)-signaling protein ALG-2 and the RNA-binding protein RBM22.     

Use of antisense oligodeoxynucleotides to study the physiological functions of neuropeptide Y

Stimulation of appetite and regulation of reproductive hormone secretion are two well-known physiological effects of neuropeptide Y (NPY) that have been affirmed using the antisense oligodeoxynucleotide (ODN) approach. Because NPY-producing neurons are concentrated in a narrow band in the arcuate nucleus of the hypothalamus, ODNs injected intracerebroventricularly have easy access to them. In an early study intracerebroventricular administration of an unmodified phosphodiester ODN sequence blocked de novo NPY synthesis and prevented the preovulatory surge release of gonadotropins. Microinjection directly into the arcuate nucleus attenuated NPY-related feeding, however, to unequivocally block the effects of NPY on feeding behavior, long-term inhibition of NPY gene expression was required. This was achieved using phosphorothioated ODNs that, unlike the phosphodiester sequences, are not subject to rapid degradation in vivo. Central administration of these modified ODNs elicited toxic effects that were circumvented by end-capping the sequences. Similar end-capped phosphorothioated ODN sequences have been used to identify the NPY receptor subtypes involved in stimulation of feeding.     

Cytoplasmic trafficking of the canine parvovirus capsid and its role in infection and nuclear transport

To begin a successful infection, viruses must first cross the host cell plasma membrane, either by direct fusion with the membrane or by receptor-mediated endocytosis. After release into the cytoplasm those viruses that replicate in the nucleus must target their genome to that location. We examined the role of cytoplasmic transport of the canine parvovirus (CPV) capsid in productive infection by microinjecting two antibodies that recognize the intact CPV capsid into the cytoplasm of cells and also by using intracellular expression of variable domains of a neutralizing antibody fused to green fluorescence protein. The two antibodies tested and the expressed scFv all efficiently blocked virus infection, probably by binding to virus particles while they were in the cytoplasm and before entering the nucleus. The injected antibodies were able to block most infections even when injected 8 h after virus inoculation. In control studies, microinjected capsid antibodies did not interfere with CPV replication when they were coinjected with an infectious plasmid clone of CPV. Cytoplasmically injected full and empty capsids were able to move through the cytosol towards the nuclear membrane in a process that could be blocked by nocodazole treatment of the cells. Nuclear transport of the capsids was slow, with significant amounts being found in the nucleus only 3 to 6 h after injection.     

Localization of AMP kinase is regulated by stress, cell density, and signaling through the MEK-->ERK1/2 pathway

5'-AMP-activated protein kinase (AMPK) serves as an energy sensor and is at the center of control for a large number of metabolic reactions, thereby playing a crucial role in Type 2 diabetes and other human diseases. AMPK is present in the nucleus and cytoplasm; however, the mechanisms that regulate the intracellular localization of AMPK are poorly understood. We have now identified several factors that control the distribution of AMPK. Environmental stress regulates the intracellular localization of AMPK, and upon recovery from heat shock or oxidant exposure AMPK accumulates in the nuclei. We show that under normal growth conditions AMPK shuttles between the nucleus and the cytoplasm, a process that depends on the nuclear exporter Crm1. However, nucleocytoplasmic shuttling does not take place in high-density cell cultures, for which AMPK is confined to the cytoplasm. Furthermore, we demonstrate that signaling through the mitogen-activated protein kinase kinase (MEK)-->extracellular signal-regulated kinase 1/2 (ERK1/2) cascade plays a crucial role in controlling the proper localization of AMPK. As such, pharmacological inhibitors that interfere with this pathway alter AMPK distribution under nonstress conditions. Taken together, our studies identify novel links between the physiological state of the cell, the activation of MEK-->ERK1/2 signaling, and the nucleocytoplasmic distribution of AMPK. This sets the stage to develop new strategies to regulate the intracellular localization of AMPK and thereby the modification of targets that are relevant to human disease.     

Uptake, cellular distribution and novel cellular binding proteins of immunostimulatory CpG oligodeoxynucleotides in glioblastoma cells

Glioblastomas are the most malignant and most frequent brain tumors and exciting targets of gene and immunotherapy. Despite rapid development of experimental therapy little is known about the cellular behaviour of therapeutic oligodeoxynucleotides (ODNs). Here we designed uptake, cellular distribution and cellular binding proteins of immunostimulatory CpG-ODNs in glioblastoma cells by flow cytometry, fluorescence microscopy and mass spectrometry. Our data show that the phosphorothioate (PS) CpG-ODNs uptake in T98G and C6 cells is dose-, time-, temperature-dependent and independent of the CpG dinucleotides. Uptake can be inhibited by sodium azide, polyanions but not by chloroquine. After internalisation FITC labelled CpG-ODNs showed a spotted distribution in cytoplasm. Dozens of cellular binding proteins were identified using mass spectrometry. The binding of ODNs to proteins is dependent on modification and sequence but independent on CpG motif. ODNs bind to cellular proteins that are important for RNA processing and transport. Furthermore, three novel membrane proteins were identified, which might contribute to uptake of ODNs. ODNs binding to these proteins might interfere with the physiological function and thus might cause unwanted effects. Such binding also might influence the uptake efficiency or cellular distribution of therapeutic ODNs.