Efficacy and safety of Sinovac vaccine administered in patients undergoing hemodialysis

INTRODUCTION

COVID-19 disease is more serious and fatal in patients on dialysis treatment due to their immunosuppressive status. In this study, we aimed to evaluate the protection and safety of Sinovac vaccine, which is an inactivated vaccine, in patients undergoing hemodialysis.

METHODOLOGY

A control group consisting of 220 hemodialysis patients (HD group) and 648 healthcare professionals who were healthy in our institution were included in the study. Quant II IgG anti-Spike antibody was measured 3 weeks after two doses of Sinovac vaccine were administered to both groups.

RESULTS

The antibody response after two doses of Sinovac vaccine was 85.2% in the HD group and 99.8% in the control group. The mean antibody level before vaccination in the HD group was 3.5 ± 7.2 AU/mL and increased significantly 3 weeks after two doses of vaccine (mean 751 ± 1196 AU/mL). The control group's mean antibody level after vaccination was 1723 ± 1878 AU/mL. The mean antibody level after vaccination in the control group was significantly higher than the HD group (p < 0.0001). Despite higher levels of anti-Spike antibodies in the control group, post-vaccination antibody response was acceptable in both HD and control groups. The HD group was significantly older (mean 64 ± 12 years) than the control group (36 ± 10 years) (p < 0.0001).

CONCLUSIONS

Although dialysis patients are immunocompromised, and some may not develop antibodies to the virus as strongly as healthy people, this study revealed that dialysis patients developed significant amounts of antibodies. Being old or on dialysis is an independent predictor of low antibody response to the Sinovac vaccine.

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.

An unresolved issue: The relationship between spot urine protein-to-creatinine ratio and 24-hour proteinuria

Objective

To investigate the relationship between spot urine protein-to-creatinine (sP/Cr) ratio and 24-h protein excretion in patients with different diagnoses.

Methods

This retrospective study analysed data from the medical records of patients admitted for24-h proteinuria determination who also had sP/Cr ratio data for the same day.

Results

A total of 1222 urine samples obtained from 694 adult outpatients were analysed. The mean ± SD age of the patients was 53.6 ± 15.9 years. The mean ± SD 24-h proteinuria and sP/Cr were 1.7 ± 2.4 g/day and 1.8 ± 2.4, respectively. The correlation between the sP/Cr and 24-h protein excretion was high (R² = 0.89). The sP/Cr ratio accounted for 72% of the variability in 24-h proteinuria in the entire study population. Areas under the curve for 24-h proteinuria at 0.3 g/day, 1.0 g/day and 3.0 g/day were 0.940, 0.966, and 0.949, respectively. The mean + 2SD limits of agreement were between +2.99 and –2.73 g/day according to the Bland Altman analysis.

Conclusion

This current study found a clinically unacceptable deviation between 24-h proteinuria and sP/Cr ratio. Therefore, the sP/Cr ratio cannot replace 24-h proteinuria. A new method using spot urine protein and creatinine values that is able to minimize under or over estimation is still warranted.

Hyaluronic Acid as a New Biomarker to Differentiate Acute Kidney Injury From Chronic Kidney Disease

INTRODUCTION

It may be difficult to differentiate acute kidney injury from chronic kidney disease in patients with no past medical reports of kidney function. This study aimed to investigate the role of serum hyaluronic acid (HA), which is known as a marker of fibrosis, in differential diagnosis of kidney failure.

MATERIALS AND METHODS

A total of 90 patients (52 women and 38 mne) admitted to our renal unit with uremia for the first time were included. Serum HA level was measured. The diagnostic role of the test was investigated using the receiver operator curve curves.

RESULTS

The mean age of the patients was 54.6 ±17.9 years. The diagnosis was chronic kidney disease (CKD) in 41.1%, acute kidney injury (AKI) in 48.9%, AKI on CKD in 6.7% (3 died without a diagnosis). The mean serum HA was significantly higher in the CKD group (146.1 ± 119.3 ng/mL) than the AKI group (68.9 ± 69.1 ng/mL; P < .001). Serum HA significantly correlated with proteinuria (r = 0.717, P < .001) and serum albumin level (r = - 0.599, P < .001) in the CKD group only. Serum HA cutoff level of 61 ng/dL had a sensitivity of 82% and specificity of 67% for differential diagnosis of AKI and CKD.

CONCLUSIONS

Serum HA level may be used as tool to differentiate AKI from CKD. Further larger studies are warranted to clarify the definite the role of this marker.

A novel factor for primary arteriovenous fistula failure: hyperinsulinism

INTRODUCTION

Dysfunction of vascular access is an important reason of morbidity for dialysis patients and it is a major factor affecting the economical burden of hemodialysis. The preferred type of vascular access is creation of an arteriovenous fistula (AVF). However, the problem of fistula maturation rate is still a challenge. Herein, we tried to search the role of hyperinsulinism and insulin resistance as a new predictor of primary AVF failure (pAVFF) that may be a cause of intimal damage.

METHODS

We included 119 patients (73 male and 46 female) with a diagnosis of end-stage renal disease (ESRD) who had undergone an AVF operation by a vascular surgeon. The AVF was examined for presence of thrill on the first postoperative day. A successful cannulation with two fistula needles with a blood flow of 250 mL/min for at least one complete dialysis session, after 4 weeks of AVF surgery was defined as functioning access. Insulin resistance in our patients was determined by the standard homeostasis model assessment (homa-IR). A logistic-regression analysis was performed to investigate the independent factors related with pAVFF.

FINDINGS

Detection of pAVFF occurred in 27 (22.7%) patients. The presence of thrill, amount of daily proteinuria, insulin levels, homa-IR, and serum albumin levels were found to be significantly different between patients with fistula failure and those without pAVFF. The logistic-regression analysis of preoperative factors revealed the following OR (odds ratio) and 95% CI values: homa-IR 1.205 (1.063-1.366) (p = 0.004), serum albumin 0.398 (0.178-0.892) (p = 0.025), and the amount of daily proteinuria 1.307 (1.012-1.688) (p = 0.041). Even after addition of the presence of postoperative thrill on AVF, which was a postoperative strong clinical factor to the analysis, mean homa-IR and mean serum albumin continued to be independent predictors of pAVFF.

DISCUSSION

Insulin resistance or hyperinsulinism may be a significant cause of pAVFF, which emphasizes the role of endothelium in fistula dysfunction.

Type 4 renal tubular acidosis in a patient with lupus nephritis

Although renal tubular acidosis (RTA) is a rare complication of systemic lupus erythematosus (SLE), type 4 RTA associated with lupus nephritis is extremely rare. A 20-year-old woman presented with malaise and edema in the lower extremities and face. She had multiple lymphadenopathies. There were 20% eosinophil in blood smear and 32% in bone marrow aspiration. Serology revealed positive antinuclear antibody at 1:1000 titer, positive double-stranded DNA antibodies, and low complements C3 and C4 levels. Urinary sediment was active and urinary protein excretion was 4.8 g/d. The SLE Disease Activity Index score was 23. A high SLE Disease Activity Index scores was proposed as a potential risk factor for type 4 RTA. Type 4 RTA may complicate SLE, and specifically, patients with high SLEDAI scores and lymphadenopathy may pose a high risk. Our patient responded successfully to immunomodulatory therapy.

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.

[Investigation of anticardiolipin antibodies in chronic hepatitis B infection together with total anti-delta positivity]

Anticardiolipin antibodies (ACAs) are formed against phospholipids in various clinical conditions such as autoimmune diseases, malignancy, infectious diseases, alcohol-related and hepatic cirrhosis. The aims of this study were to investigate the presence of ACAs in patients with chronic hepatitis B together with positive total anti-delta antibodies, and to investigate the relationship between age, gender, and some laboratory parameters (ALT, AST, albumin, globulin, platelet number) of patients with chronic hepatitis delta virus (HDV) infection, who were positive or negative for ACAs. A total of 60 patients (43 male, 17 female) with chronic hepatitis D infection [HBsAg positive, HBeAg negative, anti-HBe positive, anti-HBc IgG positive, anti-HBc IgM negative, total anti-delta positive, anti-HCV negative] and 30 patients (21 male, 9 female) without hepatitis D infection [HBsAg positive, HBeAg negative, anti-HBe positive, anti-HBc IgG positive, anti-HBc IgM negative, total anti-delta negative, anti-HCV negative] as control group were included to the study. ACA IgG and IgM were searched by a commercial microELISA kit (Euroimmun, Germany). The statistical evaluation was performed with Pearson's chi-square test, Student's t-test, and Fisher's exact test. Total ACAs positivity rate of 60 patients with chronic HDV infection, was found as 13.3%, in which four of the patients were positive for only ACA IgM, while four was positive for only IgG. Positivity for both ACA IgG and ACA IgM could not be detected in these patients. No patients in the control group had positivity for ACAs (IgG and/or IgM). A statistically significant difference was observed in terms of ACA positivity between patients with and without HDV infection (p< 0.05). After all, there was no statistically significant correlation between ACAs positivity and the age, sex, and laboratory parameters of the patients with chronic HDV infection, except lower serum albumin levels (p= 0.004). Although the data of this study revealed a statistically significant positive correlation between chronic HDV infection and anticardiolipin antibodies, it is clear that there is a need for further studies on this subject.

Snakebite-induced acute kidney injury: data from Southeast Anatolia

Renal failure is an important complication of snakebite and a major cause of mortality. We aimed to study the clinical profile of snake envenomation in Southeast Anatolia, Turkey, in an adult population. We retrospectively analyzed the records of 200 snakebite victims from 1998 to 2006 at the Dicle University School of Medicine, Diyarbakir, Turkey. Sixteen patients (8%) developed AKI (acute kidney injury). Of those, 25% required dialysis and 18% died. There was no difference between groups in age, arrival time to hospital, and hospital stay time. Both groups received similar hydration and therapy at admission. Disseminated intravascular coagulation (DIC) was observed in 25% of the AKI group and was significantly higher than the non-AKI group (7.1%; p = 0.014). There was no significant difference regarding hemoglobin, platelet levels, and prothrombin time at admission. The prevalence of thrombocytopenia (<150,000 K/UL ) was 60% in the AKI group and 40% in the non-AKI group (p > 0.05). WBC count was significantly higher in the AKI group than in those without AKI (p = 0.001); serum albumin was significantly lower in the AKI group than in those without AKI (p = 0.013). AKI is an important complication of snakebite that may lead to mortality. Despite some troublesome aspects due to its retrospective design, this is a large series from Southeast Anatolia of Turkey in an adult population. Subjects with high WBC, low albumin, and DIC should be closely followed up for the development of AKI.

Thrombosis of temporal artery and renal vein in Kimura-disease-related nephrotic syndrome

Kimura disease (KD) is an angiolymphoid proliferative disorder of unknown etiology, occurs mainly in Asian patients, presenting with subcutaneous slowly growing masses, with a predilection for preauricular and submandibular regions. The clinical course of the disease is thought to be benign. Concomitant peripheral blood eosinophilia and elevated serum immunoglobulin E levels are often observed. Main systemic manifestation of the KD is renal involvement. Renal abnormalities, notably proteinuria and nephrotic syndrome have been found to be associated with KD. We report a 42-year-old man with KD and a steroid-sensitive membraneous nephrotic syndrome with bilaterally temporal artery and renal vein thrombosis. This is the first reported case of KD associated nephrotic syndrome complicated with wide arterial and venous thrombosis from Anatolia.

Rapid Tumor Lysis Syndrome in a Patient with Metastatic Colon Cancer as a Complication of Treatment with 5-Fluorouracil/Leucoverin and Irinotecan

Tumor lysis syndrome is a potentially fatal complication of anticancer therapy that is usually seen in patients with bulky, rapidly proliferating, treatment-sensitive tumors such as hematological malignancies, but it rarely occurs in a variety of solid tumors such as colorectal carcinoma. Combination chemotherapy with infusional 5-fluorouracil/leucoverin and irinotecan has been recently accepted as the first treatment option for metastatic colorectal cancer. We present a case of tumor lysis syndrome in a patient with metastatic colon carcinoma that occurred 72 hrs after the initial course of a combination chemotherapy with irinotecan and 5-fluorouracil/leucoverin. Despite the immediate treatment with aggressive hydration by a sodium bicarbonate infusion, followed by forced diuresis and uricolytic therapy, he died of a sudden cardiac arrest complicated by acute renal failure. Our case indicates that administration of 5-fluorouracil/leucoverin and irinotecan for bulky tumors of colorectal origin with a rapid doubling time may induce an acute tumor lysis syndrome, which necessitates frequent laboratory monitoring and a close follow-up of the patient as well as prompt initiation of appropriate therapeutic measures.

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.

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.