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Biomedical subjects

R G Zhang

Publications and source records attributed to R G Zhang.

At least 19 recordsLinked to original sources
PubMed2001

Structure of Thermotoga maritima stationary phase survival protein SurE: a novel acid phosphatase.

BACKGROUND: The rpoS, nlpD, pcm, and surE genes are among many whose expression is induced during the stationary phase of bacterial growth. rpoS codes for the stationary-phase RNA polymerase sigma subunit, and nlpD codes for a lipoprotein. The pcm gene product repairs damaged proteins by converting the atypical isoaspartyl residues back to L-aspartyls. The physiological and biochemical functions of surE are unknown, but its importance in stress is supported by the duplication of the surE gene in E. coli subjected to high-temperature growth. The pcm and surE genes are highly conserved in bacteria, archaea, and plants. RESULTS: The structure of SurE from Thermotoga maritima was determined at 2.0 A. The SurE monomer is composed of two domains; a conserved N-terminal domain, a Rossman fold, and a C-terminal oligomerization domain, a new fold. Monomers form a dimer that assembles into a tetramer. Biochemical analysis suggests that SurE is an acid phosphatase, with an optimum pH of 5.5-6.2. The active site was identified in the N-terminal domain through analysis of conserved residues. Structure-based site-directed point mutations abolished phosphatase activity. T. maritima SurE intra- and intersubunit salt bridges were identified that may explain the SurE thermostability. CONCLUSIONS: The structure of SurE provided information about the protein's fold, oligomeric state, and active site. The protein possessed magnesium-dependent acid phosphatase activity, but the physiologically relevant substrate(s) remains to be identified. The importance of three of the assigned active site residues in catalysis was confirmed by site-directed mutagenesis.

Amino Acid Sequence↗
PubMed2001

Crystal structure of the global regulator FlhD from Escherichia coli at 1.8 A resolution.

FlhD is a 13.3 kDa transcriptional activator protein of flagellar genes and a global regulator. FlhD activates the transcription of class II operons in the flagellar regulon when complexed with a second protein FlhC (21.5 kDa). FlhD also regulates other expression systems in Escherichia coli. We are seeking to understand this plasticity of FlhD's DNA-binding specificity and, to this end, we have determined the crystal structure of the isolated FlhD protein. The structure was solved by substituting seleno-methionine for natural sulphur-methionine in FlhD, crystallizing the protein and determining the structure factor phases by the method of multiple-energy anomalous dispersion (MAD). The FlhD protein is dimeric. The dimer is tightly coupled, with an intimate contact surface, implying that the dimer does not easily dissociate. The FlhD monomer is predominantly alpha-helical. The C-termini of both FlhD monomers (residues 83-116) are completely disrupted by crystal packing, implying that this region of FlhD is highly flexible. However, part of the C-terminus structure in chain A (residues 83-98) was modelled using a native FlhD crystal. What is seen in chain A suggests a classic DNA-binding, helix-turn-helix (HTH) motif. FlhD does not bind DNA by itself, so it may be that the DNA-binding HTH motif becomes rigidly defined only when FlhD forms a complex with some other protein, such as FlhC. If this were true, it might explain how FlhD exhibits plasticity in its DNA-binding specificity, as each partner protein with which it forms a complex could allosterically affect the binding specificity of its HTH motif. A disulphide bridge is seen between the unique cysteine residues (Cys-65) of FlhD native homodimers. Alanine substitution at Cys-65 does not affect FlhD transcription activator activity, suggesting that the disulphide bond is not necessary for either dimer stability or this function of FlhD. Electrostatic potential analysis indicates that dimeric FlhD has a negatively charged surface.

Crystallization↗
PubMed2001

Antihepatoma effect of alpha-fetoprotein antisense phosphorothioate oligodeoxyribonucleotides in vitro and in mice.

AIM: To evaluate antihepatoma effect of antisense phosphorothioate oligodeoxyribonucleotides (S-ODNs) targeted to alpha-fetoprotein (AFP) genes in vitro and in nude mice. METHODS: AFP gene expression was examined by immunocytochemical method or enzyme-linked immunosorbent assay. Effect of S-ODNs on SMMC-7721 human hepatoma cell growth in vitro was determined using microculture tetrazolium assay. In vitro antitumor activities of S-ODNs were monitored by measuring tumor weight differences in treated and control mice bearing SMMC-7721 xenografts. Induction of cell apoptosis was evaluated by fluorescence-activated cell sorter (FACS) analysis. RESULTS: Antisense S-ODN treatment led to reduced AFP gene expression. Specific antisense S-ODNs, but not control S-ODNs, inhibited the growth of hepatoma cells in vitro. In vitro, only antisense S-ODNs exhibited obvious antitumor activities. FACS analysis revealed that the growth inhibition by antisense S-ODNs was associated with their cell apoptosis induction. CONCLUSION: Antisense S-ODNs targeted to AFP genes inhibit the growth of human hepatoma cells and solid hepatoma, which is related to their cell apoptosis induction.

Animals↗
PubMed2001

[Telomerase activity inhibition and apoptosis induction of BEL-7404 human hepatoma cells by antisense oligonucleotides to telomerase RNA component].

Telomerase activity was detected in all of four human hepatoma cells but absent in normal liver tissue. Telomerase activity of BEL-7404 human hepatoma cells was inhibited effectively by antisense oligonucleotide to telomerase RNA component at final concentration of 1 mumol/L, whereas sense and missense oligonucleotides have no effects on its activity. The inhibition of telomerase activity was weakened, as the concentration of antisense oligonucleotide decreased. Treating BEL-7404 human hepatoma cells 96 hours continuously by the antisense oligomers at final concentration of 5 mumol/L, the morphology of treated cells changed and apoptosis percent of the cells increased markedly.

Apoptosis↗
PubMed2000

Using a non-radioisotopic, quantitative TRAP-based method detecting telomerase activities in human hepatoma cells.

A non-radioisotopic, quantitative TRAP-based telomerase activity assay was established mainly by using SYBR Green-I staining instead of radioisotope. Comparing with conventional radioisotope based method, it was better in reproducibility and accuracy. Using this method, we found telomerase activities were absent in normal human liver cells, while detected in all of four human hepatoma cell lines (BEL-7404, SMMC-7721, QGY-7903 and HCCM) without significant differences.

Animals↗
PubMed2000

Human hepatoma cell telomerase activity inhibition and cell cycle modulation by its RNA component antisense oligodeoxyribonucleotides.

AIM: To investigate the effects of human telomerase RNA component antisense oligodeoxyribonucleotides on telomerase activity of human hepatoma cells and their effects on cell cycle distribution. METHODS: Modified telomeric repeat amplification protocol was used to detect telomerase activity. Cell cycle was analyzed by flow cytometer. RESULTS: Telomerase activity was detected in all of four human hepatoma cell lines but absent in normal liver cells. Antisense oligomers to human telomerase RNA component (hTR) inhibited telomerase activity of BEL-7404 human hepatoma cells markedly in vitro. After in vitro treatment with antisense oligomers for 96 h, cell cycle of BEL-7404 human hepatoma cells was mainly arrested at G2/M phase. CONCLUSION: Antisense oligomers to hTR inhibited telomerase activity of BEL-7404 human hepatoma cells in vitro and resulted in cell cycle arrest at G2/M phase.

Carcinoma, Hepatocellular↗
PubMed1999

Chromosome 3 imbalances are the most frequent aberration found in non-small cell lung carcinoma.

The chromosomal imbalances in nine cases of primary non-small cell lung cancer (NSCLC) and two cell lines derived from normal human bronchial epithelial (HBE) tissue were identified by comparative genomic hybridization (CGH). Gain of material from 3q and loss of 3p material were the most frequent changes in the primary tumors. Other commonly found imbalances included gain of material from 1q, 7p, 8q, 9q, 17q and 20q, and losses involving 4, 5q, 8p, 10 and 13q. High level gain was found in two cases, both encompassing the 3q23-q27 region. Loss of 3p was also found in both of the HBE cell lines suggesting that loss of one or more tumor supressor genes on 3p may be important for epithelial transformation and could be involved in the earlier stages of lung cancer development.

Adult↗
PubMed1999

Biomedical study on combined effects of simulated weightlessness and emergent depressurization of spacecraft.

Cabin emergent depressurization (CED) may occur in spacecraft during manned space flight. The purpose of this paper was to study the combined effects of simulated weightlessness (SW) and CED factors on humans and animals. It was found that the amplitude of T wave of human electrocardiograms (ECG) significantly decreased in bed rest and hypoxia compared with the control condition (P<0.05), and that suspension with pure O2 induced severer edema in the lungs of rats than that in only a pure O2 environment. SW and pure O2 caused middle ear congestion and decreased the barofunction during pressure changes. These results indicate that human response to CED factors become more serious under SW because of the blood redistribution.

Aerospace Medicine↗
PubMed1998

Randomized clinical trial on the combination of preoperative irradiation and surgery in the treatment of adenocarcinoma of gastric cardia (AGC)--report on 370 patients.

PURPOSE: An attempt was made to define the role of radiotherapy before operation for AGC. METHODS AND MATERIALS: From January 1978 to May 1989, a prospective randomized trial on preoperative radiotherapy (R+S) vs. surgery alone (S) for AGC was carried out in 370 patients. Patients were randomized into a combined group (R+S, 171 patients) or a surgery alone group (S, 199 patients) by the envelope method. 8-MV photon or telecobalt was used for the preoperative radiation therapy, using anterior-posterior opposing parallel fields to deliver 40 Gy to the cardia, lower segment of the esophagus, fundus, lesser curvature, and hepatogastric ligament. Surgery was performed after 2 to 4 weeks rest. RESULTS: The 5- and 10-year survival rates of the R+S Group and the S Alone Group were 30.10% and 19.75%, 20.26% and 13.30%, respectively. The survival curves of these two groups diverged right from the beginning after the operation over the ninth year. Statistics by Kaplan-Meier log rank test proves that the difference is significant (chi2 = 6.74, p = 0.0094). The immediate results were: resection rate 89.5% and 79.4% (p < 0.01); pathologic stage after resection T2 12.9% and 4.5% (p < 0.01), T4 40.3% and 51.3% (p < 0.05), lymph node metastasis rates 64.3% and 84.9% (p < 0.001); operative mortality rates 0.6% and 2.5%; intrathoracic leak rates 1.8% and 4.0%, respectively. The causes of failure were: local uncontrol and recurrence 38.6% vs. 51.7% (p < 0.025), regional lymph node metastasis 38.6% vs. 54.6% (p < 0.005), distant metastasis 24.3% vs. 24.7%. CONCLUSION: Preoperative radiation therapy is able to improve the results of surgery for adenocarcinoma of the gastric cardia.

Adenocarcinoma↗
PubMed1996

2q-, a non-random chromosomal abnormality in human non-small-cell lung cancer.

Many cytogenetic studies have been carried out on human lung cancer. However the chromosomal alterations in human lung cancers are often complex, making it difficult to identify some abnormal chromosomes by routine cytogenetic studies. Using FISH (fluorescence in situ hybridization), we studied the alterations of chromosome 2, 3, and 17 in four human bronchial epithelial cell lines, two human non-small-cell lung cancer (NSCLC) cell lines, and 12 primary NSCLC specimens. 2q- was found in three out of four human bronchial epithelial cell lines, two NSCLC cell lines, and three out of seven primary NSCLC specimens tested. 3p- was noted in five cases of twelve primary NSCLC patients examined. 3p- was the first cytogenetic discovery and the most prominent abnormality in lung cancer. 2q- has rarely been reported in human lung cancer but loss of heterozygosity by RFLP analysis for 2q had been reported in human NSCLC. Our results indicate that 2q- was also a non-random chromosomal abnormality in the early stage of the development of human NSCLC. There would be one or more putative tumor suppressor gene(s) on the long arm of chromosome 2. Loss of the gene(s) presumably contributes to the carcinogenesis of human non-small-cell lung cancer.

Adult↗
PubMed1995

The 2.4 A crystal structure of cholera toxin B subunit pentamer: choleragenoid.

Cholera toxin, a heterohexameric AB5 enterotoxin released by Vibrio cholera, induces a profuse secretory diarrhea in susceptible hosts. Choleragenoid, the B subunit pentamer of cholera toxin, directs the enzymatic A subunit to its target by binding the GM1 gangliosides exposed on the luminal surface of intestinal epithelial cells. The crystal structure of choleragenoid has been independently solved and refined at 2.4 A resolution by combining single isomorphous replacement with non-crystallographic symmetry averaging. The structure of the B subunits, and their pentameric arrangement, closely resembles that reported for the intact holotoxin, choleragen, the heat-labile enterotoxin from Escherichia coli, and for a choleragenoid-GM1 pentasaccharide complex. In the absence of the A subunit the central cavity of the B pentamer is a highly solvated channel. The binding of choleragenoid to the A subunit or to its receptor pentasaccharide modestly affects the local stereochemistry without perceptibly altering the subunit interface.

Amino Acid Sequence↗
PubMed1995

The three-dimensional crystal structure of cholera toxin.

The clinical manifestations of cholera are largely attributable to the actions of a secreted hexameric AB5 enterotoxin (choleragen). We have independently solved and refined the three-dimensional structure of choleragen at 2.5 A resolution. The structure of the crystalline toxin closely resembles that described for the heat-labile enterotoxin from Escherichia coli (LT) with which it shares 80% sequence homology. In both cases, the wedge-shaped A subunit is loosely held high above the plane of the pentameric B subunits by the tethering A2 chain. The most striking difference between the two toxins occurs at the carboxyl terminus of the A2 chain. Whereas the last 14 residues of the A2 chain of LT threading through the central pore of the B5 assembly form an extended chain with a terminal loop, the A2 chain of choleragen remains a nearly continuous alpha-helix throughout its length. The four carboxyl-terminal residues of the A2 chain (KDEL sequence), disordered in the crystal structure of LT, are clearly visible in choleragen's electron-density map. In the accompanying article we describe the three-dimensional structure of the isolated B pentamer of cholera toxin (choleragenoid). Comparison of the crystalline coordinates of choleragen, choleragenoid, and LT provides a solid three-dimensional foundation for further experimental investigation. These structures, along with those of related toxins from Shigella dysenteria and Bordetella pertussis, offer a first step towards the rational design of new vaccines and anti-microbial agents.

Amino Acid Sequence↗
PubMed1995

Prospective multimodality treatment of SCLC--experience during the past 18 years.

Lung cancer has been one of the leading malignancies in China. Since 1989 it has ranked first among common malignancies in the male population, and second in females. In 1975, a multimodality treatment study group for lung cancer was organized in our institute. The group has since expanded to 15 institutions in the Beijing and Tianjin area during the past four years. The present communication is based on our experiences and data, and tries to explain the treatment strategy of our study group.

Antineoplastic Combined Chemotherapy Protocols↗
PubMed1995

[Clinical significance of c-myc gene in esophageal squamous cell carcinoma].

Using polymerase chain reaction, we analysed 41 samples of esophageal squamous cell cancer at molecular level. Amplification of c-myc gene was found in 16 (39%). C-myc gene amplification was found to be related to lymph node metastasis, TNM staging (P < 0.01) and also prognosis (P < 0.05). We thought that c-myc gene was the prognosis factor for the patients with esophageal squamous cell carcinoma.

Adult↗
PubMed1994

[NDPK/nm23 expression and its correlation with lymph node metastasis in human lung cancer].

Using labelled streptavidin-biotin (LSAB) method, we examined the expression of nucleoside diphosphate kinase(NDPK), the product of metastasis suppressor gene nm23, in human lung cancer. Of 88 patients tested, 48 (54.5%) showed positive staining. The positive staining rate was higher in adenocarcinoma (28/42, 66.7%) than in squamous cell carcinoma (20/46, 43.5%; P < 0.05). Higher incidence of positive staining was also found in squamous cell carcinoma without hilar or mediastinal lymph node metastasis (16/27, 59.3%) than in that with hilar or mediastinal lymph node involvement (4/19, 21.1%; P < 0.05). NDPK/nm23 was equally expressed in adenocarcinoma irrespective of lymph node status. In both cell types of carcinoma, expression of NDPK/nm23 was not correlated with tumor cell differentiation, nor was it correlated with the P-TNM staging. Our results suggest that NDPK/nm23 may play different roles in the pathogenesis and metastasis of human pulmonary squamous cell carcinoma and adenocarcinoma. Its expression levels are inversely correlated with lymph node metastasis in squamous cell carcinoma.

Adenocarcinoma↗
PubMed1994

[Surgical results of neck reconstruction in esophageal cancer located at and above the high mid-thoracic segment--a report of 414 cases].

From July 1960 through 1990, a total of 414 patients with esophageal carcinoma, including cervical 29 cases, upper thoracic 239 cases and high mid-thoracic 146 cases, were operated on with reconstruction in neck. The overall resectability rate was 90.8%. The incidences of anastomotic leakage and recurrent laryngeal nerve injury were 20.5% and 12%, respectively. The resection mortality was 7.4% (within 30 days postoperatively). The 1-, 3-, 5-, 10- and 15-years survival rates were 72.3%, 39.5%, 33.1%, 26.6% and 20.5%, respectively. The authors consider that cervical esophagogastrostomy for reconstruction of esophagus after subtotal esophagectomy is an important method and a routine operative type for the surgical management of esophageal cancer at or above high mid-thoracic segment. The main factors influencing the postoperative long-term results were p-TNM stage, lymph node metastasis and the type of resection, either palliative or curative. The preoperative irradiation might remarkably increase resectability, but hardly improved long-term survival.

Adult↗