Biomedical subjects

F Jiang

Publications and source records attributed to F Jiang.

At least 109 records · Page 6Linked to original sources

PubMed1997

Evidence for redox regulation of the transcription factor NtcA, acting both as an activator and a repressor, in the cyanobacterium Anabaena PCC 7120.

NtcA has been identified as a nitrogen-responsive regulatory protein required for nitrogen assimilation and heterocyst differentiation in cyanobacteria. It is proposed that NtcA functions through the formation of DNA-protein complexes with its specific target sequence within the promoter regions of the regulated genes. In vitro, NtcA of Anabaena PCC 7120 binds to upstream regions of the genes whose products are involved in nitrogen assimilation, but also to the upstream region of rbcLS (carbon-fixation gene), xisA (encoding a site-specific recombinase expressed during heterocyst differentiation) and ntcA (encoding NtcA itself). However, the mechanism by which NtcA serves as a critical regulator for such diverse processes is not understood. With the use of electrophoretic mobility shift assays, NtcA from Anabaena PCC 7120 was here shown to interact with the promoter sequence of the gor gene, encoding glutathione reductase, thereby providing a novel example of NtcA's acting as a repressor, previously found only for the rbcLS gene. Furthermore we demonstrate that the binding of DNA by NtcA is regulated in vitro by a redox-dependent mechanism involving cysteine residues of the NtcA protein. These findings suggest that NtcA is a transcriptional regulator that responds not only to the nitrogen status but also to the cellular redox status, a function that might be particularly significant during heterocyst differentiation.

Anabaena↗

PubMed1997

Structure, recognition and adaptive binding in RNA aptamer complexes.

Novel features of RNA structure, recognition and discrimination have been recently elucidated through the solution structural characterization of RNA aptamers that bind cofactors, aminoglycoside antibiotics, amino acids and peptides with high affinity and specificity. This review presents the solution structures of RNA aptamer complexes with adenosine monophosphate, flavin mononucleotide, arginine/citrulline and tobramycin together with an example of hydrogen exchange measurements of the base-pair kinetics for the AMP-RNA aptamer complex. A comparative analysis of the structures of these RNA aptamer complexes yields the principles, patterns and diversity associated with RNA architecture, molecular recognition and adaptive binding associated with complex formation.

Adenosine Monophosphate↗

PubMed1997

Marked genetic differences between stage pTa and stage pT1 papillary bladder cancer detected by comparative genomic hybridization.

Little is known about the genetic changes underlying invasive tumor growth in bladder cancer. Because alterations that are linked to invasive tumor growth may be detectable in minimally invasive (stage pT1) but not in noninvasive (stage pTa) tumors, we searched for genetic differences between 28 pTa and 28 papillary pT1 bladder tumors by comparative genomic hybridization. Losses of 9q (54%), 9p (39%), and Y (28%) and gains of 1q (14%) were most prevalent in pTa tumors. These changes may play a role in the initiation of noninvasive papillary bladder cancer. The total number of aberrations was higher in pT1 tumors (6.5 +/- 5.4) than in pTa tumors (2.3 +/- 2.1; P = 0.0003), suggesting an increased genetic instability at stage pT1. Specific alterations, which were significantly more frequent in pT1 than in pTa tumors (P < or = 0.05), included deletions at 2q (36% of pT1 tumors), 8p (32%), and 11p (21%) and gains at 1q (54%), 8q (32%), 3p, 3q, 5p, 6p, and 10p (18% each). These loci are candidates for carrying genes involved in invasive tumor growth in bladder cancer. High-level amplifications at 1q22-24, 3p24-25, 6p22, 8p12, 8q21-22, 10p12.1-14, 11q13, 12q15-21, 13q31-33, Xp11-13, and Xq21-22.2 may pinpoint the location of oncogenes with relevance for bladder cancer.

Chromosome Aberrations↗

PubMed1997

Imino proton exchange and base-pair kinetics in the AMP-RNA aptamer complex.

We report on the dynamics of base-pair opening in the ATP-binding asymmetric internal loop and flanking base-pairs of the AMP-RNA aptamer complex by monitoring the exchange characteristics of the extremely well resolved imino protons in the NMR spectrum of the complex. The kinetics of imino proton exchange as a function of basic pH or added ammonia catalyst are used to measure the apparent base-pair dissociation constants and lifetimes of Watson-Crick and mismatched base-pairs, as well as the solvent accessibility of the unpaired imino protons in the complex. The exchange characteristics of the imino protons identify the existence of four additional hydrogen bonds stabilizing the conformation of the asymmetric ATP-binding internal loop that were not detected by NOEs and coupling constants alone, but are readily accommodated in the previously reported solution structure of the AMP-RNA aptamer complex published from our laboratory. The hydrogen exchange kinetics of the non-Watson-Crick pairs in the asymmetric internal loop of the AMP-RNA aptamer complex have been characterized and yield apparent dissociation constants (alphaKd) that range from 10(-2) to 10(-7). Surprisingly, three of these alphaKd values are amongst the lowest measured for all base-pairs in the AMP-RNA aptamer complex. Comparative studies of hydrogen exchange of the imino protons in the free RNA aptamer and the AMP-RNA aptamer complex establish that complexation stabilizes not only the bases within the ATP-binding asymmetric internal loop, but also the flanking stem base-pairs (two pairs on either side) of the binding site. We also outline some preliminary results related to the exchange properties of a sugar 2'-hydroxyl proton of a guanosine residue involved in a novel hydrogen bond that has been shown to contribute to the immobilization of the bound AMP by the RNA aptamer, and whose resonance is narrow and downfield shifted in the spectrum.

Adenosine Monophosphate↗

PubMed1997

A model of orthotopic murine bladder (MBT-2) tumor implants.

We produced a model of orthotopic transplantation in C3H/He mice by transplanting MBT-2 cells. A single-cell suspension of 1.0 x 10(5) MBT-2 cells/0.02 ml was successfully injected into the submucosal layer of the bladder, with an incidence of 100% after four experimental weeks. Inoculated tumor grew expansively into the bladder cavity from the bladder submucosa and invaded the serosa and the surrounding tissue. This model more closely resembled the characteristics of human bladder tumor when compared to other bladder cancer models. The results of the histological observation, electron microscopic examination and DNA content analysis by flow cytometry showed that the transplanted carcinoma maintained the biologic characteristics of the primary tumor.

Animals↗

PubMed1997

p53 protein expression but not mdm-2 protein expression is associated with rapid tumor cell proliferation and prognosis in renal cell carcinoma.

The clinical course of renal cell carcinoma (RCC) is highly variable. Overexpression of the p53 protein has been suggested as a possible prognostic parameter in RCC. Overexpression of the mdm-2 oncogene product has been shown to interact with the p53 function. To investigate the immunohistochemical overexpression of mdm-2 protein in comparison with that of p53 protein in RCC, 50 nonpapillary pT3 RCCs were immunostained for p53 protein (DO-7) and mdm-2 (IF2). Tumor growth fraction (Ki-67 labeling index; MIB-1) was determined by immunohistochemistry. p53 positivity was detected in 16% of tumors. mdm-2 overexpression was seen in 30% of RCCs. There was a significant association between p53 and mdm-2 immunostaining (P = 0.0006), suggesting that mdm-2 protein may contribute to p53 protein stabilization in RCC. p53 overexpression was associated with a high Ki-67 LI (P = 0.0002), suggesting that p53 overexpression is involved in growth control in RCC. Survival analysis showed that Ki-67 LI (P = 0.04) and p53 overexpression were associated with poor prognosis (P = 0.0021), whereas mdm-2 overexpression was not related to patient outcome (P = 0.73). A Cox regression analysis revealed tumor stage (P < 0.001) and p53 overexpression (P < 0.05) to be independent prognostic parameters. It is concluded that p53 but not mdm-2 may be of practical relevance in predicting patient prognosis in RCC.

Carcinoma, Renal Cell↗

PubMed1997

DNA aberrations in urinary bladder cancer detected by flow cytometry and FISH.

Detection of molecular alterations is of potential significance for diagnosis and prognosis in bladder cancer. Fluorescence in situ hybridization (FISH) allows visualization and quantitation of genes and chromosomes on a cell by cell level and can easily be applied to urinary cells. To evaluate the sensitivity of FISH for detection of DNA aberrations in bladder cancer, formalin-fixed tissues of 293 tumors were examined by FISH and flow cytometry (FCM). Centromere probes for the chromosomes X, Y, 1, 7, 9, and 17 were used for FISH analysis. FISH was more sensitive for detection of quantitative DNA aberrations than FCM. An aberration of at least one chromosome was found in 107 of 108 tumors (99%), which were tetraploid, aneuploid, or multiploid, and in 29 of 49 tumors (59%), which were diploid, by FCM. The frequency of FISH aberrations showed greater differences between pTa (47%) and pT1 tumors (85%; P < 0.0001) than between stages pT1 and pT2-4 (98%). The marked genetic difference between pTa and pT1 tumors argues against the concept of grouping pTa and pT1 tumors together as "superficial bladder cancer." The frequency of tumors with chromosomal aberrations detected by FISH increased with the number of chromosomes examined. Aneusomy was seen in 68% of grade 1 tumors examined for > or = 4 chromosomes, suggesting that the cytological diagnosis of bladder cancer recurrences could be substantially improved by FISH.

Carcinoma, Transitional Cell↗

PubMed1997

Ticks and tick-borne bovine piroplasmosis in the Southmountain pasture of Hunan Province, China.

Ticks and tick-borne bovine piroplasmosis is one of the most serious diseases affecting cattle bred in the Southmountain pasture of Hunan province. An investigation carried out from 1992 to 1995 showed that Theileria sergenti was found in the blood of disease-stricken cows. Ticks were collected from cattle. The species concerned (three genera and four species of ticks: Haemaphysalis vietnamensis, Haemaphysalis longicornis, Ixodes sinensis and Boophilus microplus) were identified by microscopy and their numbers recorded every month. Because H. longicornis is a three-host tick, with the larvae, nymphs and adults all infesting cows and seasonal fluctuations in nymphs and adults correlating with theileriosis outbreaks, this tick species was a potential vector of T. sergenti. Epidemiological studies indicated that this disease usually occurred in summer or autumn. The disease attacked calves from May to August reaching a peak in June or July (as happened from 1992-1994). In cattle, the disease occurred from June to September with a peak in September. The following pathological lesions were observed: haemorrhages were seen in the subcutaneous tissues and serosa, in the intestinal mucosa and the mesenteric lymph nodes. The surface of the abomasum looked like a piece of red cloth. The liver was enlarged, its edge blunt and curled over. The gall bladder was filled with tawny coloured bile. The spleen was enlarged and dark brown. The heart was enlarged with numerous haemorrhagic foci in the auricle. The blood clotted incompletely. Sick cattle were treated with Berenil and imidocarb and the death rate was reduced from 26% to 5.9%.

Animals↗

PubMed1997

Electrical stimulation of the septal region of aged rats improves performance in an open-field maze.

Memory deficits of age and disease may result from dysfunction of septohippocampal structures. Electrical brain stimulation might ameliorate these memory deficits. We show here that septal stimulation of very old rats leads to a marked and progressive improvement in performance in an open-field maze task. Unilateral stimulation of the perforant path is less effective. The frequency of stimulation is important: stimulation at 5 Hz and 50 Hz is effective, whereas stimulation at 0.5 Hz is less effective (though still significantly better than control). Hippocampal (dentate) EEG does not change significantly with septal stimulation frequency. These results may bear on the memory deficit of old age in humans. The results may also bear on the memory deficits seen in human disease states such as Alzheimer's disease.

Aging↗

PubMed1997

Specific labeling approaches to guanine and adenine imino and amino proton assignments in the AMP-RNA aptamer complex.

The secondary structure of a recently identified ATP-binding RNA aptamer consists of a purine-rich 11-residue internal loop positioned opposite a single guanine bulge flanked on either side by helical stem segments. The ATP ligand targets the internal loop and bulge domains, inducing a structural transition in this RNA segment on complex formation. Specifically, 10 new slowly exchanging proton resonances in the imino, amino and sugar hydroxyl chemical shift range are observed on AMP-RNA aptamer complex formation. This paper outlines site-specific labeling approaches to identify slowly exchanging imino (guanine) and amino (guanine and adenine) protons in internal loop and bulge segments of compact RNA folds such as found in the AMP-RNA aptamer complex. One approach incorporates 15N-labeled guanine (N1 imino and N2 amino positions) and 15N-labeled adenine (N6 amino position), one residue at a time, in the AMP-binding RNA aptamer, with labeling incorporation through chemical synthesis facilitated by generating the aptamer from two separate strands. The unambiguous assignments deduced from the 15N labeling studies have been verified from an independent labeling strategy where individual guanines in the internal loop have been replaced, one at a time, by inosines and assignments were made on the basis of the large 2 ppm downfield shift of the guanine imino protons on inosine substitution. The strengths and limitations of the inosine-for-guanine substitution approach emerge from our studies on the AMP-RNA aptamer complex. The assignment of the internal loop and bulge imino and amino protons was critical in our efforts to define the solution structure of the AMP-RNA aptamer complex since these slowly exchanging protons exhibit a large number of long-range intramolecular NOEs within the RNA, as well as intermolecular NOEs to the AMP in the complex. The current application of specific 15N and inosine labeling approaches for exchangeable imino and imino proton assignments in the nonhelical segments of an RNA aptamer complex in our laboratory complements selective 2H and 13C approaches to assign nonexchangeable base and sugar protons in RNA and ligand-RNA complexes reported in the literature.

Adenosine Monophosphate↗

PubMed1997

Mechanisms of electrical field stimulation-induced vasodilatation in the guinea-pig basilar artery: the role of endothelium.

1. The role of endothelium in neuronal vasodilatation elicited by electrical field stimulation (EFS) was investigated in preparations of the isolated guinea-pig basilar artery in which the tone was raised with prostaglandin F2 alpha. 2. In preparations with intact endothelium, EFS produced frequency-dependent dilatations which were not affected by guanethidine but were slightly yet significantly reduced by atropine (1 microM), and were blocked by tetrodotoxin (1 microM) and the nitric oxide synthase inhibitor L-NAME (10 microM). 3. Dilatations were elicited by acetylcholine (3 microM); these were blocked by L-NAME and atropine (1 microM). 4. Dilatations were elicited by nicotine (100 microM); these were blocked by L-NAME and hexamethonium (100 microM). 5. Dilation elicited by sodium nitroprusside (SNP, 3 microM) was not affected by L-NAME. 6. The inhibitory effects of L-NAME were partially prevented by L-arginine (1 microM). 7. Removal of the endothelium resulted in a significant reduction of dilatations elicited by EFS, elimination of the dilator action of acetylcholine, but enhancement of that to SNP. 8. The results suggest that EFS-induced vasodilatation is mediated in part by the nitrergic transmitter and in part endothelium derived relaxing factor (EDRF) activated by acetylcholine released from cholinergic nerves.

Animals↗

PubMed1997

Cardiolipin is not essential for the growth of Saccharomyces cerevisiae on fermentable or non-fermentable carbon sources.

Cardiolipin is a unique dimeric phospholipid, which is present throughout the eukaryotic kingdom and is specifically localized in mitochondrial membranes. It is widely believed that mitochondria possess an essential requirement for this phospholipid. To determine whether cardiolipin is essential for yeast growth, we generated a cardiolipin synthase null mutant by disrupting the CLS1 gene (open reading frame YDL142c on chromosome IV) of Saccharomyces cerevisiae. Biochemical analysis of the mutant indicated that it had no cardiolipin synthase activity and no cardiolipin in its membranes. The enzyme phosphatidylglycerolphosphate synthase, which catalyses the committed step of the cardiolipin pathway, remained unaffected in the null mutant. Haploid cells containing the null allele are viable in media containing glucose, galactose or glycerol/ethanol as the sole carbon source, although growth in galactose or glycerol/ethanol is somewhat reduced in the mutant compared with the wild type. These results indicate that cardiolipin is not essential for the growth of S. cerevisiae in fermentable or non-fermentable carbon sources.

Amino Acid Sequence↗

PubMed1997

Photodynamic therapy of 9L gliosarcoma with liposome-delivered photofrin.

The effect of Photofrin encapsulated in a liposome delivery vehicle for photodynamic therapy (PDT) of the 9L gliosarcoma and normal rat brain was tested. We hypothesized that the liposome vehicle enhances therapeutic efficacy, possibly by increasing tumor tissue concentration of Photofrin. Male Fisher rats bearing a 9L gliosarcoma were treated 16 days after intracerebral tumor implantation with either Photofrin in dextrose (n = 5) or Photofrin in liposome (n = 6). Nontumor-bearing animals were treated with Photofrin delivered either in dextrose (n = 4) or liposome (n = 4) vehicle. Tissue concentrations of Photofrin delivered either in dextrose (n = 4) or liposome (n = 4) vehicle were measured in tumor, brain adjacent to tumor and in normal brain tissue. Photofrin was administered (intraperitoneally) at a dose of 12.5 mg/kg and PDT (17 J/cm2 of 632 nm light at 100 mW/cm2) was performed 24 h after Photofrin administration. Brains were removed 24 h after PDT and stained with hematoxylin and eosin for analysis of cellular damage. The PDT using Photofrin in the liposome vehicle caused significantly more damage to the tumor (P < 0.001) than did PDT with Photofrin in dextrose. The PDT of tumor with Photofrin delivered in liposomes caused a 22% volume of cellular necrosis, while PDT of tumor with Photofrin delivered in dextrose caused only scattered cellular damage. Photofrin concentration in tumors was significantly higher (P = 0.021) using liposome (33.8 +/- 18.9 micrograms/g) compared to dextrose delivery (5.5 +/- 1.5 micrograms/g). Normal brain was affected similarly in both groups, with only scattered cellular necrosis. Our data suggest that the liposome vehicle enhances the therapeutic efficacy of PDT treatment of 9L tumors.

Animals↗

PubMed1997

[The effects of pressure on cultured bovine trabecular meshwork cells].

OBJECTIVE: To observe the effects of pressure on trabecular meshwork cells. METHODS: Bovine trabecular meshwork cells were cultured and submitted to different amounts of hydrostatic pressure. Cellular morphology and phagocytic function were observed under inverted phase-contrast microscope, light microscope and electron microscope. RESULTS: Compared with the control group, the cells under 2.0 kPa or 2.67 kPa for 48 hours had no remarkable difference in criteria observed. Those under 4.0 kPa for 24 hours showed slight changes in structure and a mild decrease in phagocytic function. The damage appeared more severe if the pressure was higher or lasted longer. CONCLUSION: Trabecular meshwork cells can only bear pressure below a certain level. They may be destroyed structurally or impaired functionally by pressure over this level.

Animals↗

PubMed1997

[Investigation on hepatitis G virus (HGV) infection among different populations in Shenzhen].

A reverse transcription polymerase chain reaction assay with nested primers (RT-nested PCR) deduced from the 5' untranslated region of HGV genome was established to detect HGV RNA. By using this assay, we tested the serum samples of 106 paid blood donors, 80 intravenous drug users and 168 cases with viral hepatitis in Shenzhen, China. The positive rates of HGV RNA were 8.5%, 46.3% and 7.7%, respectively. The positive rates of HGV RNA in 61 cases with chronic hepatitis B and 33 cases with chronic hepatitis C were 8.2% and 21.2%. Among the 33 cases with chronic hepatitis C, the positive rate of HGV RNA in 15 cases infected with HCV by blood or blood products was 40.0%, compared with 1.7% in 18 cases without exposure to blood or blood products (P<0.05). The results of this study suggest that HGV infection is common in paid blood donors; the intravenous drug user is the population at high risk for HGV infection; the patients with post-transfusion chronic hepatitis C are often supperinfected with HGV.

Adult↗

PubMed1997

Base dynamics in a UUCG tetraloop RNA hairpin characterized by 15N spin relaxation: correlations with structure and stability.

Intramolecular dynamics of guanine and uracil bases in a 14-nt RNA hairpin including the extraordinarily stable UUCG tetraloop were studied by 15N spin relaxation experiments that are sensitive to structural fluctuations occurring on a time scale of picoseconds to nanoseconds. The relaxation data were interpreted in the framework of the anisotropic model-free formalism, using assumed values for the chemical shift anisotropies of the 15N spins. The rotational diffusion tensor was determined to be symmetric with an axial ratio of 1.34 +/- 0.12, in agreement with estimates based on the ratio of the principal moments of the inertia tensor. The model-free results indicate that the bases of the G x U pair in the tetraloop are at least as rigid as the interior base pairs in the stem, whereas the 5'-terminal guanine is more flexible. The observed range of order parameters corresponds to base fluctuations of 19-22 degrees about the chi torsion angle. The results reveal dynamical consequences of the unusual structural features in the UUCG tetraloop and offer insights into the configurational entropy of hairpin formation.

Base Composition↗

PubMed1996

RNA folding topology and intermolecular contacts in the AMP-RNA aptamer complex.

We report below on the NMR structural characterization of the complex between AMP and a 40-mer RNA aptamer in aqueous solution. Resonance assignments are based on multinuclear multidimensional NMR studies on complexes uniformly 13C, 15N-labeled with either AMP or the RNA aptamer. AMP binds to an internal loop (labeled G7-G8-A9-A10-G11-A12-A13-A14-C15-U16-G17) and bulge (G34 positioned opposite the internal loop) segment in the RNA aptamer, and our NMR study provides insights into features of the RNA folding topology and the molecular recognition events in the AMP binding pocket on the RNA. Specifically, the helical stems are extended by G-G mismatch formation from either direction into the internal loop/bulge segment of the RNA aptamer on complex formation. The internal loop adopts a unique fold with the purine ring of AMP intercalated between A10 and G11 in the complex. The G8-A9-A10-AMP segment adopts certain stacking features in common with a GNRA turn and is closed by the G7.G11 mismatch pair. The purine rings of A12 and G34 (syn) are stacked on each other and participate in stablizing the AMP intercalation site. A large number of intermolecular NOEs have been identified between the AMP ligand and the G8, A10, G11, G17, U18, and G34 residues on the RNA aptamer in the complex. The Watson-Crick edge of the AMP is oriented toward the exocyclic amino group of G8, suggestive of a hydrogen-bonding alignment between G8 and AMP in the complex. The AMP sugar ring is positioned in the minor groove of the rightward helical stem centered about the G17.G34 mismatch and U18.A33 Watson-Crick pairs. The AMP binds to one face of the folded internal loop/bulge segment of the RNA aptamer while the opposite face is capped by a stacked alignment of the A13-A14-C15-U16 segment located toward the 3'-end of the internal loop segment. Globally, the two helical stems of the RNA aptamer are aligned approximately orthogonal to each other with tertiary interactions centered about the internal loop/bulge segment generating the AMP binding site on the RNA.

Adenosine Monophosphate↗

PubMed1996

Structural basis of RNA folding and recognition in an AMP-RNA aptamer complex.

The catalytic properties of RNA and its well known role in gene expression and regulation are the consequence of its unique solution structures. Identification of the structural determinants of ligand recognition by RNA molecules is of fundamental importance for understanding the biological functions of RNA, as well as for the rational design of RNA Sequences with specific catalytic activities. Towards this latter end, Szostak et al. used in vitro selection techniques to isolate RNA sequences ('aptamers') containing a high-affinity binding site for ATP, the universal currency of cellular energy, and then used this motif to engineer ribozymes with polynucleotide kinase activity. Here we present the solution structure, as determined by multidimensional NMR spectroscopy and molecular dynamics calculations, of both uniformly and specifically 13C-, 15N-labelled 40-mer RNA containing the ATP-binding motif complexed with AMP. The aptamer adopts an L-shaped structure with two nearly orthogonal stems, each capped proximally by a G x G mismatch pair, binding the AMP ligand at their junction in a GNRA-like motif.

Adenosine Monophosphate↗