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Biomedical subjects

X Cheng

Publications and source records attributed to X Cheng.

At least 109 records · Page 6Linked to original sources
PubMed1999

Structure of a binary complex of HhaI methyltransferase with S-adenosyl-L-methionine formed in the presence of a short non-specific DNA oligonucleotide.

We have determined a structure for a complex formed between HhaI methyltransferase (M.HhaI) and S-adenosyl-L-methionine (AdoMet) in the presence of a non-specific short oligonucleotide. M.HhaI binds to the non-specific short oligonucleotides in solution. Although no DNA is incorporated in the crystal, AdoMet binds in a primed orientation, identical with that observed in the ternary complex of the enzyme, cognate DNA, and AdoMet or S-adenosyl-L-homocysteine (AdoHcy). This orientation differs from the previously observed unprimed orientation in the M.HhaI-AdoMet binary complex, where the S+-CH3 unit of AdoMet is protected by a favorable cation-pi interaction with Trp41. The structure suggests that the presence of DNA can guide AdoMet into the primed orientation. These results shed new light on the proposed ordered mechanism of binding and explains the stable association between AdoMet and M.HhaI.

Crystallization↗
PubMed1999

Epiregulin is a potent vascular smooth muscle cell-derived mitogen induced by angiotensin II, endothelin-1, and thrombin.

Vasoactive GTP-binding protein-coupled receptor agonists such as angiotensin II (AII), endothelin-1 (ET-1), and alpha-thrombin (alpha-Thr) have been reported to indirectly stimulate vascular smooth muscle cell (VSMC) proliferation by regulating the expression of one or more autocrine growth factors. Using ion-exchange, gel-filtration, and reverse-phase chromatographic purification methods, we isolated a major mitogenic protein present in AII-stimulated rat aortic smooth muscle (RASM) cell conditioned medium. Twenty N-terminal amino acids of the purified peptide were identified, and they had 75% amino acid sequence identity with mouse epiregulin, an epidermal growth factor (EGF)-related growth factor. We cloned the cDNA for rat epiregulin to determine its pattern of expression in G-protein-coupled receptor agonist-stimulated cells and confirm its activity as a mitogen. After treatment of RASM cells with AII, ET-1, or alpha-Thr for 1 h, induction of two epiregulin transcripts was observed, including a 4.8-kb transcript and a novel transcript of approximately 1.2 kb. Recombinant rat epiregulin was strongly mitogenic for RASM cells, stimulating DNA synthesis to levels similar to those induced by serum or platelet-derived growth factor and approximately 3-fold above that observed with saturating concentrations of EGF. In addition, epiregulin caused rapid EGF receptor activation in RASM cells. However, relative levels of EGF receptor tyrosine phosphorylation stimulated by epiregulin were less than those induced by EGF or betacellulin. Taken together, these results indicate that epiregulin is a potent VSMC-secreted mitogen, induced in common by AII, ET-1, and alpha-Thr, that may contribute to VSMC proliferation and vascular remodeling stimulated by vasoactive agonists.

3T3 Cells↗
PubMed1999

Mechanism of inhibition of DNA (cytosine C5)-methyltransferases by oligodeoxyribonucleotides containing 5,6-dihydro-5-azacytosine.

A key step in the predicted mechanism of enzymatic transfer of methyl groups from S-adenosyl-l-methionine (AdoMet) to cytosine residues in DNA is the transient formation of a dihydrocytosine intermediate covalently linked to cysteine in the active site of a DNA (cytosine C5)-methyltransferase (DNA C5-MTase). Crystallographic analysis of complexes formed by HhaI methyltransferase (M.HhaI), AdoMet and a target oligodeoxyribonucleotide containing 5-fluorocytosine confirmed the existence of this dihydrocytosine intermediate. Based on the premise that 5,6-dihydro-5-azacytosine (DZCyt), a cytosine analog with an sp3-hybridized carbon (CH2) at position 6 and an NH group at position 5, could mimic the non-aromatic character of the cytosine ring in this transition state, we synthesized a series of synthetic substrates for DNA C5-MTase containing DZCyt. Substitution of DZCyt for target cytosines in C-G dinucleotides of single-stranded or double-stranded oligodeoxyribonucleotide substrates led to complete inhibition of methylation by murine DNA C5-MTase. Substitution of DZCyt for the target cytosine in G-C-G-C sites in double-stranded oligodeoxyribonucleotides had a similar effect on methylation by M. HhaI. Oligodeoxyribonucleotides containing DZCyt formed a tight but reversible complex with M.HhaI, and were consistently more potent as inhibitors of DNA methylation than oligodeoxyribonucleotides identical in sequence containing 5-fluorocytosine. Crystallographic analysis of a ternary complex involving M.HhaI, S-adenosyl-l-homocysteine and a double-stranded 13-mer oligodeoxyribonucleotide containing DZCyt at the target position showed that the analog is flipped out of the DNA helix in the same manner as cytosine, 5-methylcytosine, and 5-fluorocytosine. However, no formation of a covalent bond was detected between the sulfur atom of the catalytic site nucleophile, cysteine 81, and the pyrimidine C6 carbon. These results indicate that DZCyt can occupy the active site of M.HhaI as a transition state mimic and, because of the high degree of affinity of its interaction with the enzyme, it can act as a potent inhibitor of methylation.

Animals↗
PubMed1999

Bilateral kidney ligation abolishes pressor response to N(G)-nitro-D-arginine.

We have shown that N(G)-nitro-D-arginine (D-NNA) is 50% as potent as N(G)-nitro-L-arginine (L-NNA) in causing pressor response and 2-3% as potent as L-NNA in inhibiting endothelium-dependent relaxation in vitro. These results suggest in vivo activation of D-NNA. Furthermore, the potency of D-NNA was markedly increased after it had been incubated with homogenate of the kidney, but not plasma or homogenate of the aorta, lungs or liver. This study examined if bilateral ligation of the kidneys attenuated the biological action of D-NNA. I.v. bolus of D-NNA (16 mg/kg), L-NNA (3 mg/kg) and norepinephrine (0.25-16 microg/kg) increased arterial pressure in sham-operated rats. Bilateral ligation of the kidneys abolished pressor response to D-NNA, but not L-NNA and norepinephrine. I.v. bolus D-NNA in sham-operated rats, but not kidney-ligated rats, inhibited relaxation response to acetylcholine in pre-constricted aortic rings ex vivo. These results indicate that the kidney is the primary organ which activates D-NNA.

Acetylcholine↗
PubMed1999

Effects of several drugs on the liver injury induced by delayed-type hypersensitivity to picryl chloride by regulating suppressor or helper T cells.

The effects of histamine, cimetidine, and diphenhydramine on picryl chloride (PCl)-induced ear contact sensitivity, as well as liver injury, were examined in mice. Histamine was found to produce less response in mice to PCl. In contrast, cimetidine, a selective antagonist of histamine type 2 receptor, significantly enhanced the response, while diphenhydramine, a selective antagonist of histamine type 1 receptor showed no effect. The pre-treatment of 2,4, 6-trinitrobenzene sulphonic acid (TNBS) significantly caused a tolerance to the formation of the liver injury induced by delayed-type hypersensitivity (DTH) to PCl. Against the tolerance, the single intravenous administration of 150 mg kg-1 cyclophosphamide (Cy) at 3 days before the TNBS-treatment recovered the response and induced a remarkable elevation of serum transaminases. On the other hand, cyclosporin A protected the liver injury. These observations revealed that the development of acute PCl-DTH liver injury was regulated by the functional state of suppressor and helper T cells.

Animals↗
PubMed1999

Coiling phagocytosis is the predominant mechanism for uptake of the colonic spirochetosis bacterium Serpulina pilosicoli by human monocytes.

Serpulina pilosicoli is a newly identified pathogenic spirochete that establishes persistent colonic infections in human beings and animals. Macrophages are one of the key defenses against invasion of mucosal surfaces by bacterial pathogens. Macrophages engulf many bacteria by conventional phagocytosis; however recent studies indicate coiling phagocytosis as a new and important mechanism for internalization of Legionella pneumophila and spirochetes of the genus Borrelia, Leptospira, and Treponema. In this study, THP-1 human monocytic cells were incubated with the human S. pilosicoli strain SP16 and the contribution of coiling and conventional phagocytosis to the total number of phagocytic events were determined by sequential ultrastructural examination between 5 and 45 minutes. The frequency of phagocytosis increased over time from 5.1% after 5 minutes up to 21.9% after 45 minutes with greater than 70% of the events involving coiling phagocytosis. The data indicate that coiling phagocytosis may be a universal mechanism for uptake of pathogenic spirochetes.

Brachyspira↗
PubMed1999

Molecular cloning and sequence analysis of cDNA encoding haemorrhagic toxin acutolysin A from Agkistrodon acutus.

By means of reverse transcription polymerase chain reaction, a full-length cDNA of 1632 bp is amplified from the snake venom gland total RNA of Agkistrodon acutus. Analysis of the nucleotide sequence indicates that the amplified cDNA contains a complete open reading frame encoding 413 amino acid residues including signal peptide sequence, zymogen sequence and proteinase domain. The zymogen sequence contains PKMCGVT motif which is highly conserved in almost all venom metalloproteinases. The metalloproteinase domain contains the conserved signature zinc-binding motif HEXXHXXGXXH in the catalytic region. The predicted amino acid sequence of the metalloproteinase domain is identical to the crystallographic sequence of acutolysin A and also shares high homology with other class I snake venom haemorrhagic toxins.

Agkistrodon↗
PubMed1999

Antithrombotic effects of low-molecular-weight heparin calcium (LMWH-Ca) in experimental models.

The antithrombotic activity of low-molecular-weight heparin calcium (LMWH-Ca) was studied in venous and arterial thrombosis models, arterial thrombosis model in rats, arterio-venous shunt model and venous thrombosis model in rabbits. The data showed that LMWH-Ca reduced thrombus formation in a dose-dependent manner. It suggests that LMWH-Ca is a potent antithrombotic agent for venous thrombosis, and also may be a beneficial therapeutic agent in arterial thrombosis.

Animals↗
PubMed1999

Local tumor recurrence or emergence of a new primary lesion? A molecular analysis.

The distinction between a new primary oral tumor and recurrence may bear significant prognostic implications. Currently, this differentiation relies mainly on tumor location: when both lesions are at or near the same site, the new one is regarded as a recurrence; when the two are at different sites, the second lesion is regarded as a new primary. Recent investigations using molecular analysis have demonstrated that some oral squamous cell carcinomas (SCC) arising from different sites show the same clonogenical changes. In this case report, we studied the clonality of three SCC (one primary, two apparent recurrences) from the right lateral tongue of a young, non-smoking woman by using microsatellite analysis for loss of heterozygosity. The results showed that while the first two tumors were clonogenically similar, the third tumor was clonogenically different and was consistent with the development of a new primary. This result indicates that location of tumors alone is not always reliable in determining whether a new tumor is a recurrence or a new primary lesion.

Adult↗
PubMed1999

Construction of La-tPA vector and expression in the mammary gland of transgenic mice.

Expression vectors of long acting human tissue plasminogen activator (La-tPa) in the mammary gland was constructed using the promoters of sheep beta-lactoglobulin gene (BLG, 5 kb) containing the first and the second introns obtained by PCR. Transgenic mice were established by microinjection. 540 fertilized eggs were injected and 6 transgenic mice were screened out from the offspring by PCR and Southern Blot analysis. The foreign gene integrating rate was 32%. The expression of La-tPA in mammary glands of transgenic mice was confirmed by milk assay and Northern blot analysis. Expression level of La-tPA reached 6 ug/ml in milk of transgenic mice.

Animals↗
PubMed1999

[Allotransplantation of cryopreserved fetal cartilage in plastic surgery].

OBJECTIVE: To study the applicability of homologous fetal cartilage in plastic surgery. METHODS: Limb and costal cartilage were taken from the dead fetus. The fetal cartilage was then frozen at -80 degrees C and preserved in -196 degrees C liquid nitrogen with a cryoprotective agent. A total of 38 patients received fetal cartilage transplantation. Of them there were 24 saddle nose, 4 auricle defects, 6 secondary deformities of cheiloschisis, 4 mandible deformities. RESULTS: Through follow-up of three and a half years, it was found that none of the transplanted cartilage was absorbed, deformed or rejected due to immunological reaction. The contours were satisfactory except 2 cases with auricle reconstruction. CONCLUSION: The clinical application of homologous fetal cartilages is of value in plastic surgery.

Adolescent↗
PubMed1999

[The relationship between smoking and the incidence of COPD].

OBJECTIVE: To study the relationship between smoking index and the incidence of COPD to persuade smokers quit smoking. METHODS: COPD was diagnosed based on family inquiring, questionnaire and pulmonary function test. The smoking index was calculated by the average cigarettes a day times the years of smoking. RESULTS: 822 cases(account for 24.6% of investigated subjects) of COPD due to smoking were identified, and 624 cases were found (account for 40.4% of investegated subjects) to have a history of both smoking and chronic airway inflammation. The higher the smoking index, the higher the incidence of COPD (above 40%), and the more severe their lung function imparement. The smoking was 71.6% of the cause in COPD patients. CONCLUSIONS: The incidence of COPD associated with smoking is higher in China than that in the Western countries. The incidence of COPD in population with long smoking history is not invariable, while it is gradually rising with increasing smoking index.

Adolescent↗
PubMed1999

[Study on susceptible risk factors for COPD in smokers].

OBJECTIVE: To explore the susceptible risk factors for COPD in smokers. METHODS: 154 patients with COPD (FEV1/FVC < 70%) were recruited as the case group whose smoking index (average cigarettes a day times smoking years) was > or = 300 and there was no complaint of chronic respiratory symptoms. The control group included 154 smokers pair-matched in age(+/- 3 years) gender, residence, absence of COPD (FEV1/FVC > or = 75%) and respiratory symptoms. 23 never-smoking subjects with FEV1/FVC > or = 75% and no respiratory symptoms served as healthy control. The following parameters were evaluated: questionaire, physical examination, ECG, chest X-ray, lung function test, methacholine provocation test of bronchial responsiveness and serum levels of elastase activity, alpha 1-AT activity, MDA, PIIIP, IgE and IgG. RESULTS: The positive rate of bronchial hyperresponsiveness was 78% in the case group, PC20 = (1.4 +/- 1.6) g/L; but 28% in the matched group were positive, PC20 = (2.7 +/- 2.3) g/L, (P < 0.001). No one was found hyperresponsive in the healthy control group. There were no differences in serum PIIIP and IgE between the case and the control groups, but they were markedly higher than those in the healthy control. Serum alpha 1-AT activity, room condition, occupational exposure, smoking habit (deep inhalation), cigarettes with or without filter tip, parents with bronchitis and(or) emphysema history, brothers or sisters with bronchitis history were correlated with COPD, OR being 2.33, 2.00, 1.64, 1.88, 1.76 and 3.67, respectively. Logistic regression revealed that alpha 1-AT activity, bronchial hyperresponsiveness, room condition and occupational exposure, smoking habit and respiratory disease history in family were related to COPD. CONCLUSIONS: alpha 1-AT deficiency may be a risk factor for COPD susceptible smokers. There may be relationship between bronchial hyperresponsiveness and developing COPD, but whether it is the cause or result of COPD needs further study. Smoking may induce elevation of serum PIIIP and IgE, but both of them are not directly related to COPD. Room condition, occupational exposure, smoking habit, and respiratory disease history in family may be associated with COPD in smokers.

China↗
PubMed1999

[Changes of serum elastase, alpha 1-antitrypsin, procollagen III peptide and malonaldehyde in smokers with and without chronic obstructive pulmonary diseases].

OBJECTIVE: Serum elastase, alpha(1)-antitrypsin (alpha(1)-AT), procollagen III peptide (PIIIP) and malonaldehyde (MDA) were studied in smokers with and without chronic obstructive pulmonary disease (COPD) to explore the roles of these factors in COPD induced by smoking. METHODS: A design of 154-pair case-control study was used. alpha(1)-AT, MDA and PIIIP were determined with colorimetric method, fluo-spectrophotometric method and radio-immunological assay, respectively, in non-smoker control and smokers with and without COPD. RESULTS: Serum PIIIP content was increased in smokers and alpha(1)-AT decreased significantly in patients with COPD. CONCLUSION: Decreased alpha(1)-AT may be a susceptible factor in the development of COPD caused by smoking.

Adult↗
PubMed1999

[Strain screening and fermentation conditions of a novel heparinase-producing strain].

The novel heparinase-producing bacterial strain Corynebacterium sp. was screened and isolated from soil. The optimum medium composition is (g/L): Trypticase 20, NaCl 1, K2HPO4 2.5, MgSO4 0.5, Heparin 2, maltose 20, pH 6.5. The optimum growth temperature was 27 degrees C while, maximum enzyme production was achieved at temperature 31 degrees C. When cultured at a rotating shaker at 30 degrees C for 24 hours, 200 r/min, 40 mL medium in 500 mL flask, the Production of heparinase reached 1700 u/L.

Corynebacterium↗
PubMed1999

[Nucleotide sequence at position -155 to +25 of the 5' flanking region of the angiotensinogen gene of Han people].

OBJECTIVE: To study the polymorphism of 5'-flanking region of angiotensinogen gene and relations to essential hyperfension. METHODS: The nucleotide sequence at position -155 to +25 of the 5'-flanking region in angiotensinogen gene of Han people in Chinese population was identified by applying PCR-single stranded conformational polymorphism(SSCP) and PCR-directed sequencing. RESULTS: (1) The Han people carry an adenylate(A), instead of a cytidylate(C) at position -20 of the 5'-flanking region of AGT gene; (2) A new mutation T-->A at position -46 was detected and A-allele frequencies was similar in both hypertensives and normotensive controls. CONCLUSIONS: The variant T-->A at position -46 of AGT gene was not associated with hypertension, but an adenylate (A) at position -20 of the 5'-flanking region of AGT gene. might be an genetic marker for Hans people.

5' Flanking Region↗
PubMed1999

[Characterization of HA1 genes of influenza A (H1N1) viruses isolated in Shenzhen City].

OBJECTIVE: To understand the molecular bases of intention of influenza virus activity and emergence of "O" phase of influenza A(H1N1) strains in human population in Shenzhen in recently years, and also the evolutionary characterization of influenza A(H1N1) HA1 gene. METHODS: Virion RNA was transcribed into cDNA by reverse transcriptase, cDNA was amplified by PCR, the products of PCR were purified. Afterward, RNA sequence analysis was performed by the dideoxynucleotide chain termination method using synthetic oligodeoxynucleotide primers. Finally, phylogenetic analysis of the sequencing data was performed with MegAlign (version 1.03) and Editseq (version 3.69) softwares. RESULTS: Since 1995, there were three different genetic lineages of influenza A(H1N1) virus HA1 gene cocirculating in men in Shenzhen city. Adding one and deleting one of potential glycosylation sites at 54 and 155 positions of amino acid sequences on HA1 protein domain of H1N1 viruses isolated recently was found as compared with those of A/Singapore/6/86(H1N1) virus. Meanwhile, there were some differences of amino acid sequences on HA1 protein molecules among H1N1 viruses tested and A/Singapore/6/86 (H1N1) virus. CONCLUSION: The intention of influenza A(H1N1) virus activity occurred since 1995 was due to emergence of substitution in amino acid sequences, especially the appearance of one addition and one deletion of potential glycosylation sites on their HA1 protein domains, and also was due to occurrence of influenza A(H1N1) virus with feature of "O" phase.

Amino Acid Sequence↗