Comparison of cone-beam computed tomography and panoramic radiography for mandibular morphometry

BACKGROUND

The aim of this study was to compare the morphological differences in the mandible between patients with six age groups and to detect the correlation between these parameters on panoramic radiography (PR) and cone-beam computed tomography (CBCT).

MATERIALS AND METHODS

A total of 121 subjects (50 males and 71 females) were included in the study and were divided into six age groups (10-19, 20-29, 30-39, 40-49, 50-59, and 60-69) on the basis of the chronological age. CBCT and PR methods were used to record the mandibular measurements for the same 121 patients. Differences between male and female mandibular morphometric measurements, between right and left side measurements, and differences in age subgroups compared by using independent samples t-test, paired samples t-test, and one-way ANOVA test, respectively. P < 0.05 value was considered statistically significant for all analysis.

RESULTS

Males mostly have higher mandibular measurement values. There were statistically significant differences between CBCT and PR measurements (p < 0.05). PR mostly showed higher values than CBCT measurements.

CONCLUSIONS

Based on the fact that PRs showing significant differences from CBCT in the morphometric measurements made on mandible, it is recommended that forensic doctors and anthropologists consider this information in their age and gender prediction studies.

Oxidative stress-mediated NFκB phosphorylation upregulates p62/SQSTM1 and promotes retinal pigmented epithelial cell survival through increased autophagy

p62 is a scaffolding adaptor implicated in the clearance of protein aggregates by autophagy. Reactive oxygen species (ROS) can either stimulate or inhibit NFκB-mediated gene expression influencing cellular fate. We studied the effect of hydrogen peroxide (H2O2)-mediated oxidative stress and NFκB signaling on p62 expression in the retinal pigment epithelium (RPE) and investigated its role in regulation of autophagy and RPE survival against oxidative damage. Cultured human RPE cell line ARPE-19 and primary human adult and fetal RPE cells were exposed to H2O2-induced oxidative stress. The human apolipoprotein E4 targeted-replacement (APOE4) mouse model of AMD was used to study expression of p62 and other autophagy proteins in the retina. p62, NFκB p65 (total, phosphorylated, nuclear and cytoplasmic) and ATG10 expression was assessed by mRNA and protein analyses. Cellular ROS and mitochondrial superoxide were measured by CM-H2DCFDA and MitoSOX staining respectively. Mitochondrial viability was determined using MTT activity. qPCR-array system was used to investigate autophagic genes affected by p62. Nuclear and cytoplasmic levels of NFκB p65 were evaluated after cellular fractionation by Western blotting. We report that p62 is up-regulated in RPE cells under H2O2-induced oxidative stress and promotes autophagic activity. Depletion of endogenous p62 reduces autophagy by downregulation of ATG10 rendering RPE more susceptible to oxidative damage. NFκB p65 phosphorylation at Ser-536 was found to be critical for p62 upregulation in response to oxidative stress. Proteasome inhibition by H2O2 causes p62-NFκB signaling as antioxidant pre-treatment reversed p62 expression and p65 phosphorylation when RPE was challenged by H2O2 but not when by Lactacystin. p62 protein but not RNA levels are elevated in APOE4-HFC AMD mouse model, suggesting reduction of autophagic flux in disease conditions. Our findings suggest that p62 is necessary for RPE cytoprotection under oxidative stress and functions, in part, by modulating ATG10 expression. NFκB p65 activity may be a critical upstream initiator of p62 expression in RPE cells under oxidative stress.

Dysregulated autophagy in the RPE is associated with increased susceptibility to oxidative stress and AMD

Autophagic dysregulation has been suggested in a broad range of neurodegenerative diseases including age-related macular degeneration (AMD). To test whether the autophagy pathway plays a critical role to protect retinal pigmented epithelial (RPE) cells against oxidative stress, we exposed ARPE-19 and primary cultured human RPE cells to both acute (3 and 24 h) and chronic (14 d) oxidative stress and monitored autophagy by western blot, PCR, and autophagosome counts in the presence or absence of autophagy modulators. Acute oxidative stress led to a marked increase in autophagy in the RPE, whereas autophagy was reduced under chronic oxidative stress. Upregulation of autophagy by rapamycin decreased oxidative stress-induced generation of reactive oxygen species (ROS), whereas inhibition of autophagy by 3-methyladenine (3-MA) or by knockdown of ATG7 or BECN1 increased ROS generation, exacerbated oxidative stress-induced reduction of mitochondrial activity, reduced cell viability, and increased lipofuscin. Examination of control human donor specimens and mice demonstrated an age-related increase in autophagosome numbers and expression of autophagy proteins. However, autophagy proteins, autophagosomes, and autophagy flux were significantly reduced in tissue from human donor AMD eyes and 2 animal models of AMD. In conclusion, our data confirm that autophagy plays an important role in protection of the RPE against oxidative stress and lipofuscin accumulation and that impairment of autophagy is likely to exacerbate oxidative stress and contribute to the pathogenesis of AMD.

A novel ATG4B antagonist inhibits autophagy and has a negative impact on osteosarcoma tumors

Autophagy has been implicated in the progression and chemoresistance of various cancers. In this study, we have shown that osteosarcoma Saos-2 cells lacking ATG4B, a cysteine proteinase that activates LC3B, are defective in autophagy and fail to form tumors in mouse models. By combining in silico docking with in vitro and cell-based assays, we identified small compounds that suppressed starvation-induced protein degradation, LC3B lipidation, and formation of autophagic vacuoles. NSC185058 effectively inhibited ATG4B activity in vitro and in cells while having no effect on MTOR and PtdIns3K activities. In addition, this ATG4B antagonist had a negative impact on the development of Saos-2 osteosarcoma tumors in vivo. We concluded that tumor suppression was due to a reduction in ATG4B activity, since we found autophagy suppressed within treated tumors and the compound had no effects on oncogenic protein kinases. Our findings demonstrate that ATG4B is a suitable anti-autophagy target and a promising therapeutic target to treat osteosarcoma.

Deletion of lipoprotein PG0717 in Porphyromonas gingivalis W83 reduces gingipain activity and alters trafficking in and response by host cells

P. gingivalis (Pg), a causative agent of chronic generalized periodontitis, has been implicated in promoting cardiovascular disease. Expression of lipoprotein gene PG0717 of Pg strain W83 was found to be transiently upregulated during invasion of human coronary artery endothelial cells (HCAEC), suggesting this protein may be involved in virulence. We characterized the virulence phenotype of a PG0717 deletion mutant of pg W83. There were no differences in the ability of W83Δ717 to adhere and invade HCAEC. However, the increased proportion of internalized W83 at 24 hours post-inoculation was not observed with W83∆717. Deletion of PG0717 also impaired the ability of W83 to usurp the autophagic pathway in HCAEC and to induce autophagy in Saos-2 sarcoma cells. HCAEC infected with W83Δ717 also secreted significantly greater amounts of MCP-1, IL-8, IL-6, GM-CSF, and soluble ICAM-1, VCAM-1, and E-selectin when compared to W83. Further characterization of W83Δ717 revealed that neither capsule nor lipid A structure was affected by deletion of PG0717. Interestingly, the activity of both arginine (Rgp) and lysine (Kgp) gingipains was reduced in whole-cell extracts and culture supernatant of W83Δ717. RT-PCR revealed a corresponding decrease in transcription of rgpB but not rgpA or kgp. Quantitative proteome studies of the two strains revealed that both RgpA and RgpB, along with putative virulence factors peptidylarginine deiminase and Clp protease were significantly decreased in the W83Δ717. Our results suggest that PG0717 has pleiotropic effects on W83 that affect microbial induced manipulation of host responses important for microbial clearance and infection control.

Porphyromonas gingivalis strain specific interactions with human coronary artery endothelial cells: a comparative study

Both epidemiologic and experimental findings suggest that infection with Porphyromonas gingivalis exacerbates progression of atherosclerosis. As P. gingivalis exhibits significant strain variation, it is reasonable that different strains possess different capabilities and/or mechanisms by which they promote atherosclerosis. Using P. gingivalis strains that have been previously evaluated in the ApoE null atherosclerosis model, we assessed the ability of W83, A7436, 381, and 33277 to adhere, invade, and persist in human coronary artery endothelial (HCAE) cells. W83 and 381 displayed an equivalent ability to adhere to HCAE cells, which was significantly greater than both A7436 and 33277 (P<0.01). W83, 381, and 33277 were more invasive than A7436 (P<0.0001). However, only W83 and A7436 were able to remain viable up to 48 hours in HCAE cell cultures, whereas 381 was cleared by 48 hours and 33277 was cleared by 24 hours. These differences in persistence were in part due to strain specific differences in intracellular trafficking. Both W83 and 381 trafficked through the autophagic pathway, but not A7436 or 33277. Internalized 381 was the only strain that was dependent upon the autophagic pathway for its survival. Finally, we assessed the efficacy of these strains to activate HCAE cells as defined by production of IL-6, IL-8, IL-12p40, MCP-1, RANTES, TNF-α, and soluble adhesion molecules (sICAM-1, sVCAM-1, and sE-selectin). Only moderate inflammation was observed in cells infected with either W83 or A7436, whereas cells infected with 381 exhibited the most profound inflammation, followed by cells infected with 33277. These results demonstrate that virulence mechanisms among different P. gingivalis strains are varied and that pathogenic mechanisms identified for one strain are not necessarily applicable to other strains.

From BioMEMS to Bionanotechnology: Integrated BioChips for the Detection of Cells and Microorganisms

This paper reviews the interdisciplinary work performed in our group in recent years to develop micro-integrated devices to characterize biological entities. We present the use of electrical and mechanically based phenomena to perform characterization and various functions needed for integrated biochips. One sub-system takes advantage of the dielectrophoretic effect to sort and concentrate cells within a micro-fluidic biochip. Another sub-system measures impedance changes produced by the metabolic activity of cells to determine their viability. A third sub-system is used to detect the mass of bacteria as they bind to micro-mechanical silicon cantilevers. These devices with an electronic signal output can be very useful in producing practical systems for rapid detection and characterization of cells for a wide variety of applications in the food safety and health diagnostics industries.

Ultrasound as a diagnostic tool to differentiate acute from chronic renal failure

AIM

Renal ultrasound (US) is the most appropriate method for imaging renal failure; however, considerable overlap in renal size and renal echogenicity exists between normally and abnormally functioning kidneys. We compared the sonographic features of kidneys in patients with renal failure to investigate the potential role of renal US to distinguish acute from chronic renal failure and assessed the diagnostic role of body surface area-corrected renal length compared to measured renal length.

MATERIALS AND METHODS

We included 127 consecutive patients with serum creatinine levels higher than 3 mg/dl and 33 healthy volunteers. The subjects with acute renal failure (ARF) and chronic renal failure (CRF) were compared for renal length, parenchymal thickness, parenchymal echogenicity, distinctness of the corticomedullary junction, and the presence of stones and cysts.

RESULTS

No significant differences in age, serum albumin, creatinine, weight, height, or gender distribution were found between patients with ARF and those with CRF, except in serum hemoglobin. The right and left kidney parenchymal thickness and renal length were significantly greater in ARF patients than in those with CRF (p < 0.0001). The mean parenchymal thickness and renal length were similar in ARF patients and the control group. Grade I hyperechogenicity was the most common finding during sonography.

CONCLUSIONS

Renal length, parenchymal thickness, and echogenicity differed significantly between patients with acute and chronic renal failure. A renal US examination is still the most appropriate method for imaging renal failure and should be combined with other tests to distinguish acute from chronic renal failure.

Anticardiolipin antibodies in hemodialysis patients with hepatitis C and their role in fistula failure

BACKGROUND/AIMS

Several conflicting results are presently reported regarding raised IgG and IgM-anticardiolipin antibodies (ACA) titers in hemodialysis (HD) patients and their role in vascular access dysfunction. We aimed to determine the prevalence of both IgM and IgG-ACA titers and to analyze retrospectively their role in primary and secondary arteriovenous fistula (AVF) failure in a homogeneous group of HD patients with chronic hepatitis C.

METHODS

This study included 103 adults on maintenance hemodialysis with chronic hepatitis C infection. All participants had blood samples drawn predialysis and after an overnight fast. Analysis included biochemistry, IgG and IgM ACA, Anti-HCV, HBsAg, serum HCV RNA and HCV genotyping.

RESULTS

The prevalence of IgG-ACA was 14.6% (15/103). No patient had a positive value of the IgM-ACA test. HCV replication was detected in 52 of 76 patients. The most common HCV genotype was genotype 1 (90%). The percentage of females was higher in ACA(+) group (p = 0.038). There were no significant differences between subjects with and without ACA-IgG regarding other parameters studied. No difference in regard to AVF survival was detected between ACA(+) and ACA(-) groups (p > 0.05).

CONCLUSION

We found no significant differences in primary or secondary AVF failure between patients with elevated and normal ACA. Therefore, we conclude that AVFF may be caused by factors other than ACA in these patients. More prospective studies are needed to confirm this observation.

Parathyroid Hormone as a Marker for the Differential Diagnosis of Acute and Chronic Renal Failure

It is often difficult to distinguish acute renal failure clinically from chronic renal failure, especially in patients who do not have records of their medical history. We investigated the magnitude of iPTH increase in ARF and the potential role of iPTH as a marker for differential diagnosis of ARF and CRF in new patients referred to our renal unit. We prospectively analyzed 122 (ARF n = 64, CRF n = 58) patients referred to our renal unit with serum creatinine higher than 2 mg/dL. ROC curve analysis was performed to investigate role of iPTH for differentiating ARF from CRF. The sensitivity, specificity, and positive predictive value of iPTH in discrimination of ARF and CRF were calculated. There was no statistically significant difference regarding the means of age, sex distribution, and serum chemistry between patients with ARF or CRF. But serum iPTH (p < 0.0001) levels were lower in patients with ARF than in those with CRF. A cutoff, set at 170 pg/mL for iPTH to discriminate patients with CRF, yielded a sensitivity of 88% and a specificity of 89%. This study confirms that the iPTH measurement is of clinical value in differentiating acute from chronic renal failure.

Invasion of human coronary artery endothelial cells by Streptococcus mutans OMZ175

INTRODUCTION

Dissemination of oral bacteria into the bloodstream has been associated with eating, oral hygiene, and dental procedures; including tooth extraction, endodontic treatment, and periodontal surgery. Recently, studies identified Streptococcus mutans, the primary etiological agent of dental caries, as the most prevalent bacterial species found in clinical samples from patients who underwent heart valve and atheromatous plaque surgery.

METHODS

By using antibiotic protection assays, we tested the capacity of 14 strains of S. mutans to invade primary human coronary artery endothelial cells (HCAEC).

RESULTS

Serotype e strain B14 and serotype f strain OMZ175 of S. mutans were able to efficiently invade HCAEC. Among the tested strains, serotype f S. mutans OMZ175 was the most invasive, whereas strains of serotype c S. mutans, the most prevalent serotype in dental plaque, were not invasive. Based on its high invasion rate, we further investigated the invasive properties of serotype f OMZ175. Using transmission electron microscopy and antibiotic protection assays we demonstrate that S. mutans OMZ175 is capable of attaching to the HCAEC surface, entering the cells and surviving in HCAEC for at least 29 h.

DISCUSSION

Our findings highlight a potential role for S. mutans in the pathogenesis of certain cardiovascular diseases.

The molecular mechanism of translocation through the nuclear pore complex is highly conserved

In this report we investigated the activity of vertebrate nuclear transport factors in a primitive organism, Amoeba proteus, to better understand evolutionary changes in the transport mechanisms of organisms expected to have different requirements for nucleocytoplasmic exchange. It was initially determined that FxFG-containing nucleoporins and Ran, both of which are essential for nuclear import in vertebrates, as well as yeast, are also present and functional in amoebae. This suggests that there are fundamental similarities in the transport process; however, there are also significant differences. Transport substrates containing either the hnRNP A1 M9 shuttling signal (a GST/GFP/M9 fusion protein) or the classical bipartite NLS (colloidal gold coated with BSA-bipartite NLS conjugates), both of which are effectively transported in vertebrate cells, are excluded from the nucleus when microinjected into amoebae. However, when these substrates are injected along with transportin or importin α/β, respectively, the vertebrate receptors for these signals, they readily accumulate in the nucleoplasm. These results indicate that although the molecular recognition of substrates is not well conserved between vertebrates and amoebae, vertebrate transport receptors are functional in A. proteus, showing that the translocation machinery is highly conserved. Since selected nuclear import pathways can be investigated in the absence of competing endogenous transport, A. proteus might provide a useful in vivo system for investigating specific molecular interactions involved in trafficking.

Analysis of the activity of nuclear export signals using fluorescent BSA conjugates

Here we demonstrate that fluorescein-labeled BSA conjugated with a mixture of nuclear import and export signals can be used to evaluate export activity. The method is based on the assumption that the intracellular distribution of the labeled conjugate [nuclear/cytoplasmic (N/C) fluorescent ratio] is dependent on the relative activity of the import versus the export signals. Using BALB/c cells as a model system, it was shown that this assumption is correct. Thus, the N/C fluorescent ratio increased significantly when an active leucine-rich nuclear export signal was replaced with its inactive mutant form in conjugates that also contained classical nuclear import signals. This approach was then used to demonstrate that the same leucine-rich nuclear export signal, which functions in vertebrates, is also active in amoebae.

Regulation of functional nuclear pore size in fibroblasts

Protein-NLS-coated gold particles up to approximately 250 Å in diameter are transported through the nuclear pores in normal, proliferating BALB/c 3T3 cells. This size can increase or decrease, depending on cellular activity. It has been suggested that increases in functional pore size are related to a reduction in the amount of available p53. To further test this hypothesis, we investigated the effects of cycloheximide and pifithrin-α, which inhibits p53-dependent transcriptional activation, on nuclear transport. After 3 hours in cycloheximide, there was a significant increase in the size of the gold particles that entered the nucleoplasm. When the incubation period was extended to 6 hours or longer, transport capacity returned to the control level. By using proteasome inhibitors, it was shown that the cycloheximide-dependent increase in functional pore size was due to the inhibition of protein synthesis, consistent with the fact that p53 is a short-lived protein, and requires the activity of at least two different factors. Although cycloheximide increases the functional diameter of the channel available for signal-mediated transport by approximately 60 Å, it had no significant effect on either the import rate of small NLS-containing substrates (FITC-BSA-NLS), or passive diffusion of fluorescent-labeled proteins across the envelope. This suggests that changes in transport capacity were not caused by an increase in overall pore diameter but instead are due to a transient increase in pore size that accompanies signal-mediated transport. Pifithrin-α also caused an increase in functional pore diameter without altering the import rate of FITC-BSA-NLS, providing further support for the view that p53 can initiate changes in nuclear transport capacity.

NTF2 monomer-dimer equilibrium

Nuclear transport factor 2 (NTF2) mediates nuclear import of RanGDP, a central component of many nuclear trafficking pathways. NTF2 is a homodimer and each chain has independent binding sites for RanGDP and nuclear pore proteins (nucleoporins) that contain FxFG sequence repeats. We show here that the monomer-dimer dissociation constant for NTF2 obtained by sedimentation equilibrium ultracentrifugation is in the micromolar range, indicating that a substantial proportion of cellular NTF2 may be monomeric. To investigate the functional significance of NTF2 dimerization, we engineered a series of point mutations at the dimerization interface and one of these (M118E) remained monomeric below concentrations of 150 microM. CD spectra and X-ray crystallography showed that M118E-NTF2 preserved the wild-type NTF2 fold, although its thermal stability was 20 deg. C lower than that of the wild-type. M118E-NTF2 bound both RanGDP and FxFG nucleoporins less strongly, suggesting that dissociation of the NTF2 dimer could facilitate RanGDP release and thus nucleotide exchange after it had been transported into the nucleus. Moreover, colloidal gold coated with M118E-NTF2 showed reduced binding to Xenopus oocyte nuclear pores. Overall, our results indicate that dimer formation is important for NTF2 function and give insight into the formation of heterodimers by mRNA export factors such as TAP1 and NXT1 that contain NTF2-homology domains.

Interaction between NTF2 and xFxFG-containing nucleoporins is required to mediate nuclear import of RanGDP

Nuclear transport factor 2 (NTF2) is a small, homodimeric protein that binds to both RanGDP and xFxFG repeat-containing nucleoporins, such as yeast Nsp1p and vertebrate p62. NTF2 is required for efficient nuclear protein import and has been shown to mediate the nuclear import of RanGDP. We have used the crystal structures of rat NTF2 and its complex with RanGDP to design a mutant, W7A-NTF2, in which the affinity for xFxFG-repeat nucleoporins is reduced while wild-type binding to RanGDP is retained. The 2.5 A resolution crystal structure of W7A-NTF2 is virtually superimposable upon the wild-type protein structure, indicating that the mutation had not introduced a more general conformational change. Therefore, our data suggest that the exposed side-chain of residue 7 is crucial to the interaction between NTF2 and xFxFG repeat-containing nucleoporins. Consistent with its reduced affinity for xFxFG nucleoporins, fluorescently labelled W7A-NTF2 binds less strongly to the nuclear envelope of permeabilized cultured cells than wild-type NTF2 and, when microinjected into Xenopus oocytes, colloidal gold coated with W7A-NTF2 binds less strongly to the central channel of nuclear pore complexes than wild-type NTF2-coated gold. Significantly, W7A-NTF2 only weakly stimulated the nuclear import of fluorescein-labelled RanGDP, providing direct evidence that an interaction between NTF2 and xFxFG repeat-containing nucleoporins is required to mediate the nuclear import of RanGDP.

Signal-mediated nuclear transport in the amoeba

The evolutionary changes that occur in signal-mediated nuclear transport would be expected to reflect an increasing need to regulate nucleocytoplasmic exchanges as the complexity of organisms increases. This could involve changes in both the composition and structure of the pore complex, as well as the cytosolic factors that mediate transport. In this regard, we investigated the transport process in amoebae (Amoeba proteus and Chaos carolinensis), primitive cells that would be expected to have less stringent regulatory requirements than more complex organisms. Colloidal gold particles, coated with bovine serum albumin (BSA) conjugated with simple (large T) nuclear localization signals (NLSs), bipartite (nucleoplasmin) NLSs or mutant NLSs, were used to assay nuclear import. It was found that in amoebae (1) the diameter of the particles that are able to enter the nucleoplasm is significantly less than in vertebrate cells, (2) the simple NLS is more effective in mediating nuclear import than the bipartite NLS, and (3) the nucleoporins do not appear to be glycosylated. Evidence was also obtained suggesting that, in amoebae, the simple NLS can mediate nuclear export.

The nuclear import factor p10 regulates the functional size of the nuclear pore complex during oogenesis

Previtellogenic, stage-1 Xenopus oocytes produce mainly 5S and tRNA, whereas vitellogenic oocytes, stages 2–6, synthesize predominantly 18S and 28S rRNA. Using nucleoplasmin-coated gold as a transport substrate, it was determined that the shift in synthesis from small to large RNAs during oogenesis is accompanied by an increase in both the rates of signal-mediated nuclear import and the functional size of nuclear pores. It was observed that, despite the reduction in transport capacity, gold still accumulated at the cytoplasmic surface of the pores in stage-1 oocytes. This suggested that transport in these cells is limited by translocation factors, rather than by cytoplasmic binding factors. Analysis of extracts prepared from stage-1 and vitellogenic oocytes revealed that the transport factor p10 is more abundant in stage-1 cells. Microinjection of purified p10 into stage-2 oocytes reduced the nuclear import of large gold particles to the level observed in stage-1 cells. It is concluded that p10 can modulate transport through the pores by regulating the functional size of the central transporter element.

The location of the transport gate in the nuclear pore complex

Signal-mediated nuclear transport is a gated process that occurs through a central transporter element located within the pore complex. The purpose of this investigation was to identify the region of the transporter that functions as the gate; i.e. the region that restricts passive diffusion of macromolecules through the pores. To accomplish this, small gold particles coated with polyethylene glycol (PEG; total particle diameter 40–70 A) or large PEG-particles (total diameter 110–270 A) were microinjected into the cytoplasm or nucleoplasm of Xenopus oocytes. Since PEG does not contain either nuclear import or export signals, it is assumed that the particles distribute by simple diffusion. The cells were fixed after 5 or 30 minutes and subsequently examined using TEM. The distribution of the particles located adjacent to and within the pore complexes was then mapped. The results obtained at both 5 and 30 minutes after cytoplasmic injections of small gold were basically the same. The particles readily entered the transporter but, on the average, were approximately 11 times more concentrated in the cytoplasmic half of this structure. The opposite distribution was observed following nuclear injections, i.e. the particles that were located in the transporter were approximately 7 times more numerous in the nuclear half. Our data indicate that there is a single transport gate located in the central domain of the transporter that restricts passive diffusion. The large particles that were injected into the cytoplasm migrated to the surface of the pore complex, but entered the transporter less frequently than small gold. Interestingly, the diffusion of large PEG-particles to the surface of the pores following nuclear injection was greatly restricted; however, this was not the case for similar size particles that were coated with protein containing nuclear export signals (NES). The latter results suggest that the NES is not only required for translocation, but also for migration within the nucleoplasm.

Stimulation of nuclear import by simian virus 40-transformed cell extracts is dependent on protein kinase activity

We previously reported that both the nuclear import rate of large karyophilic gold particles and the functional size of the pores are significantly greater in simian virus 40-transformed fibroblasts (the SV-T2 cell line) than in nontransformed BALB/c 3T3 cells. In this study, we found that cytosolic fractions obtained from SV-T2 cultures can increase nuclear transport capacity (both import rate and pore size) when microinjected into BALB/c 3T3 cells. The transport-enhancing function of the extracts can be abolished by the protein kinase inhibitors staurosporine and K252a as well as 5'-p-fluorosulfonylbenzoyladenosine and protein phosphatase 2A, which, although less specific, also interfere with kinase activity. Increases in transport capacity of the same magnitude as that produced by the SV-T2 extracts were obtained by microinjecting protein kinase A or C or recombinant mitogen-activated protein kinase. These data provide further support for the interpretation that the enhancer is a protein kinase. From experiments performed with specific kinase inhibitor peptides, it appears likely that protein kinase C is the active factor in the SV-T2 cytosolic fractions; however, this will require further verification. It was also determined, by using gold particles coated with bovine serum albumin conjugated to synthetic nuclear localization signal peptides that lacked phosphorylation sites, that the enhancer affects the transport machinery rather than the activity of the nuclear localization signals.

Variations in signal-mediated nuclear transport during the cell cycle in BALB/c 3T3 cells

Signal-mediated nuclear import was investigated in proliferating BALB/c 3T3 cells 1, 2, 4, 6, 8, 12, 18, and 21 h after the onset of anaphase. Using nucleoplasmin-coated colloidal gold particles to assay transport capacity, it was found that import was greatest at 1 h postanaphase (after complete reformation of the nuclear envelope). At this time, both the relative rate of gold uptake and the functional size of the transport channels were significantly greater than in control cells, which were randomly selected from nonsynchronized cultures. At 21 h, there was a decrease in the size of the transport channel, but not the rate of nuclear import. This suggests that these two factors are regulated independently. No changes in transport capacity, compared to controls, were detected at other times in the cell cycle.

The effects of SV40 large T antigen and p53 on nuclear transport capacity in BALB/c 3T3 cells

In a previous study, it was found that the microinjection of purified SV40 large T antigen into the cytoplasm of BALB/c 3T3 cells significantly increased both the relative rate of signal-mediated nuclear transport and the functional size of the transport channels that are located within the pores. In this investigation, a series of mutants were employed to identify the region of large T responsible for the permeability increase. Plasmids encoding wild-type or mutant forms of large T were injected into the nucleoplasm of proliferating BALB/c 3T3 cells, and the nuclear import of nucleoplasmin-coated gold particles was analyzed approximately 18 h later. The large T mutants that were not effective in inducing the increase in nuclear transport capacity were also unable to bind p53. Further evidence that transport activity and p53 binding localize to the same region of large T was obtained by simultaneously injecting plasmids that overexpress wild-type or mutant p53 and plasmids that encode active forms of large T. It was found that wild-type p53 prevented the large T-induced transport increase; however, mutant p53, which is unable to bind to large T, had no effect. Decreasing the concentration of endogenous p53 in cells that do not contain large T, by injecting anti-p53 antibodies or plasmids that express mutant p53, resulted in a significant increase in the nuclear import of nucleoplasmin-coated gold. The latter results suggest that p53 might normally act as a transport suppressor.

Regulation of nuclear transport in proliferating and quiescent cells

Previously, we compared signal-mediated nuclear transport in proliferating and quiescent BALB/c 3T3 cells and found that both the relative rate of nuclear uptake and the functional size of the transport channels were significantly greater in proliferating cells. In this study, the possible causes of these permeability differences were investigated. To determine if the decrease in transport capacity in quiescent cells was due to a reduction in the availability of soluble cytoplasmic factors (i.e., ATP or receptors for nuclear location sequences), or changes in the properties of the pores themselves, proliferating and quiescent cells were fused, and nuclear import of nucleoplasmin-coated gold (NP-gold) particles was assayed in the heterokaryons 50-60 min later. Significant differences in nuclear uptake were maintained following fusion, even though the two nuclei shared a common cytoplasm, consistent with the view that permeability is regulated at the level of the pores. Cell shape also influenced signal-mediated nuclear import. This was demonstrated by studying transport in rounded and flattened cells attached to different-size palladium domains that were deposited on a nonadhesive substrate. Based on analysis of the nuclear uptake rates of large (110-270 A in diameter) and small (50-80 A in diameter) coated gold particles, it was determined that the functional size of the pores was significantly greater in flattened cells. The effect of growth factors on recovery of nuclear transport capacity following serum depletion was also analyzed. Partial recovery was achieved by treating cells with physiological concentrations of EGF, IGF-1, or PDGF; however, complete recovery required both EGF and IGF-1.

Signal-mediated nuclear transport in simian virus 40-transformed cells is regulated by large tumor antigen

Transformation of cultured cells with simian virus 40 (SV40), or transfection with the early region of the SV40 genome, causes a significant increase in both the rate of signal-mediated nuclear transport and the functional size of the transport channels (located in the pore complexes). By microinjecting purified large tumor (T) antigen into the cytoplasm of murine BALB/c 3T3 cells, we have demonstrated that this protein alone can account for the increase in transport capacity. The T antigen-dependent changes can be partially inhibited by cycloheximide and require a functional nuclear localization sequence. Although necessary, the nuclear localization sequence by itself cannot produce the observed variations in nuclear permeability and presumably function in a "helper" capacity, in association with another, as yet unidentified domain.

Signal-mediated nuclear transport in proliferating and growth-arrested BALB/c 3T3 cells

Mediated transport across the nuclear envelope was investigated in proliferating and growth-arrested (confluent or serum starved) BALB/c 3T3 cells by analyzing the nuclear uptake of nucleoplasmin-coated colloidal gold after injection into the cytoplasm. Compared with proliferating cells the nuclear uptake of large gold particles (110-270 A in diameter, including the protein coat) decreased 5.5-, 33-, and 78-fold, respectively, in 10-, 14-17-, and 21-d-old confluent cultures; however, the relative uptake of small particles (total diameter 50-80 A) did not decrease with increasing age of the cells. This finding suggests that essentially all pores remain functional in confluent populations, but that most pores lose their capacity to transport large particles. By injecting intermediate-sized gold particles, the functional diameters of the transport channels in the downgraded pores were estimated to be approximately to 130 and 110 A, in 14-17- and 21-d-old cultures, respectively. In proliferating cells, the transport channels have a functional diameter of approximately 230 A. The mean diameters of the pores (membrane-to-membrane distance) in proliferating and confluent cells (728 and 712 A, respectively) were significantly different at the 10%, but not the 5%, level. No differences in pore density (pore per unit length of membrane) were detected. Serum-deprived cells (7-8 d in 1% serum or 4 d in 0.5% serum) also showed a significant decrease in the nuclear uptake of large, but not small, gold particles. Thus, the permeability effects are not simply a function of high cell density but appear to be growth related. The possible functional significance of these findings is discussed.

The permeability of the nuclear envelope in dividing and nondividing cell cultures

The objective of this study was to determine whether the permeability characteristics of the nuclear envelope vary during different phases of cellular activity. Both passive diffusion and signal-mediated transport across the envelope were analyzed during the HeLa cell cycle, and also in dividing, confluent (growth-arrested), and differentiated 3T3-L1 cultures. Colloidal gold stabilized with BSA was used to study diffusion, whereas transport was investigated using gold particles coated with nucleoplasmin, a karyophilic Xenopus oocyte protein. The gold tracers were microinjected into the cytoplasm, and subsequently localized within the cells by electron microscopy. The rates of diffusion in HeLa cells were greatest during the first and fifth hours after the onset of anaphase. These results correlate directly with the known rates of pore formation, suggesting that pores are more permeable during or just after reformation. Signal-mediated transport in HeLa cells occurs through channels that are located within the pore complexes and have functional diameters up to 230-250 A. Unlike diffusion, no significant differences in transport were observed during different phases of the cell cycle. A comparison of dividing and confluent 3T3-L1 cultures revealed highly significant differences in the transport of nucleoplasmin-gold across the envelope. The nuclei of dividing cells not only incorporated larger particles (230 A versus 190 A in diameter, including the protein coat), but the relative uptake of the tracer was about seven times greater than that in growth-arrested cells. Differentiation of confluent cells to adipocytes was accompanied by an increase in the maximum diameter of the transport channel to approximately 230 A.

Virus-like particles from the poison glands of the parasitic wasp Biosteres longicaudatus (Hymenoptera: Braconidae)

Two virus-like particles occur in the venom apparatus (poison glands) associated with the ovaries of the parasitic wasp Biosteres longicaudatus (Hymenoptera: Braconidae). The venom apparatus consists of accessory gland filaments (tubules) (AGFs) and a short, carrot-shaped, muscular sac, Dufour's gland. Rod-shaped particles measuring 250–300 nm long and 60–70 nm wide with convex ends occur in 100% of the cells examined along the middle third of the AGFs. These particles are associated with an electron-dense crystalline matrix within a stroma surrounded by vesicles. Similar particles are present in vacuoles in 76–90% of the epidermal cells in the pharate pupal host, Anastrepha suspensa (Diptera: Tephritidae), after parasitization by B. longicaudatus. The second type of particle is spherical and has an outer membrane with a beaded surface. It is about 250 nm in diameter and has an electron-dense biconcave central core with two lateral bodies, and resembles entomopoxviruses. Such particles occur within a stroma in 80–90% of the cells along the proximal third of the AGF, and within its lumen, to which the cells are connected by a short, cuticle-lined duct. These AGF cells are morphologically distinct from those containing the rod-shaped particles. The "mature" spherical particles accumulate in the Dufour's gland, which empties into the median oviduct, and are injected into the host by the wasp during oviposition. Similar particles are present in 63–80% of the hemocytes of parasitized hosts.

EM visualization of nucleocytoplasmic transport processes

The nuclear envelope is strategically located between the nucleoplasm and cytoplasm, and, as such, can play a major role in controlling cellular activity by regulating the exchange of macromolecules between these two compartments. The nuclear pore complexes, which are located within circular areas formed by fusion of the inner and outer membranes of the envelope, represent the primary, if not the exclusive, exchange sites. Individual pores are able to function in both protein import and RNA efflux from the nucleus. Translocation of macromolecules occurs by either passive diffusion or facilitated transport through central channels within the pores. The functional size of the diffusion channel is approximately 9 to over 12 nm in diameter depending on the cell type. The width of the transport channel varies as a function of the number and effectiveness of the specific nuclear targeting signals contained within the permeant molecule. The maximum diameter of the channel can be over 26 nm. Nucleocytoplasmic exchanges can be regulated either by (1) differences in the properties of the transported molecule (molecular size and signal content) or (2) changes in the properties of the pore complexes, which can effect both diffusion and transport.