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Biomedical subjects

L Guo

Publications and source records attributed to L Guo.

At least 163 records · Page 9Linked to original sources
PubMed2000

[Retinoic acid enhances chemosensitivity of medulloblastoma cells in vitro and its potential mechanism].

OBJECTIVE: To elucidate the chemosensitivity of retinoic acid (RA)-differentiated medulloblastoma Med-3 cells to conventional anti-cancer drug and to determine the potential genetic factor(s) mediating this sensitivity. METHODS: Ten mumol/L RA, 5 micrograms/ml cisplatin (DDP) and their combination with one half concentration of each were used respectively to treat human medulloblastoma cell line Med-3 in vitro. Cell proliferation, morphology and death pattern as well as Fas/FasL expressions were analyzed by multiple approaches. RESULTS: Both soluble and membrane FasL could be detected in the treated and untreated Med-3. Fas was positive in the cytoplasm of Med-3 cells and the cells could produce soluble Fas. DDP had no obvious effect on Fas expression. RA up-regulated Fas expression and translocalization from cytoplasm to cell membrane of the treated cells. Neither RA nor DDP could trigger apoptosis but in combination could effectively induce apoptosis. CONCLUSION: RA could enhance the apoptotic susceptibility of Med-3 cells to DDP presumably through modulating the Fas expression pattern. Combined RA/DDP regimen would have potential clinical value in the management of medulloblastomas.

Antineoplastic Agents↗
PubMed2000

[Contrast study on effect of shenkang injection and benazepril on human glomerular mesangial extracellular matrix].

OBJECTIVE: To explore the intensity of inhibition of Shenkang Injection (SKI) and Benazepril on various ingredients of human glomerular mesangial extracellular matrix (ECM). METHODS: Effect of SKI, a herbal preparation for lowering adverse Qi, despelling turbidness, supplementing Qi and activating circulation, and Benazepril were observed by cultured glomerular mesangial cell technique in vitro. RESULTS: SKI could inhibit the fibronetin, laminin, and type IV collagen of ECM, and the action was dose-dependent. Benazepril could also inhibit the fibronetin and type IV collagen of ECM but was weaker in intensity. CONCLUSION: The effect of SKI was superior to Benazepril in inhibiting ECM.

Angiotensin-Converting Enzyme Inhibitors↗
PubMed2000

[Construction of two eukaryotic expression plasmids pcDNA3/pacA and pcDNA3/pacP expressing surface protein antigen of Streptococcus mutans].

OBJECTIVE: Two gene vaccines which encoded amino terminal and intermediate region in the PAc protein were constructed and the feasibility and safety was investigated, in order to obtain a highly effective and secure anticarious way by immunization. METHODS: The target gene fragments pac-A and pac-P encoded amino terminal and intermediate region of surface protein antigen from Streptococcus mutans were obtained by PCR amplification respectively. Amplification products were isolated by using low melting-temperature agarose and recoveried from the gel. Then the two fragments were digested by Kpn I and Xho I, and ligated to the Kpn I-Xho I-digested eukaryotic shuttle expression vector pcDNA3 to create reconstructed plasmids pcDNA3/pacA and pcDNA3/pacP respectively. The ligated DNAs were transformed into Escherichia coli XL1-Blue. Transformed colonies carrying eukaryotic expression plasmid either pcDNA3/pacA or pcDNA3/pacP were screened by colony hybridization in situ. Then the reconstructed plasmids were isolated and identified by restricted endonuclease digestions, Southern hybridization and DNA sequencing. RESULTS: 1. Two DNA fragments pac-A and pac-P of the predicted size 1.3 kb and 1.2 kb were obtained by PCR amplified. 2. Eukaryotic expression plasmids pcDNA3/pacA and pcDNA3/pacP had been reconstructed correctly. 3. The sequencing data also indicated that the pcDNA3 construct contained the correct sequence and orientation of the two target genes. CONCLUSION: These two plasmids may act as gene vaccines for further study.

Antigens, Surface↗
PubMed2000

[Expression of eukaryotic expression plasmid pcDNA3/pacA and pcDNA3/pacP in mammalian cells].

OBJECTIVE: Prior to the use of pcDNA3/pacA and pcDNA3/pacP in vivo, the transcription and expression products of these two eukaryotic expression plasmids in mammalian cells were detected. METHODS: The eukaryotic expression plasmids pcDNA3/pacA and pcDNA3/pacP were transfected into COS-7 cells respectively with liposome according to the manufacturer's protocol. In order to generate stable transfectants, after a 48 h incubation period in regular Dulbecco's modified Eagle's medium (DMEM) supplemented with 10% heat inactivated fetal bovine serum, cells were treated with neomycin (1 mg.ml-1 of G418) and maintained under continuous selective pressure. G418-resistant colonies, which became visible after 2 weeks, were isolated and screened for expression of the vector-encoded protein. The control transfections were performed with the pcDNA3 vector and without recombinant as well as vector plasmid DNA. The mRNA transcriptions of the two insertional genes were detected by RT-PCR assay and their expression products were analysed by labelled-avidin-biotin enzymed-linked immunosorbent assay, flow cytometry and Western blotting. The cells transfected by pcDNA3 were used as the negative control. RESULTS: 1. The two eukaryotic expression plasmids could be correctly transcripted and translated under the control of the CMV immediate early promoter in mammalian cells. 2. The protein products could be detected in cell plasma, cell membrane and the culture supernatant. CONCLUSION: The two eukaryotic expression plasmids pcDNA3/pacA and pcDNA3/pacP can express protein products which were encoded by insertional gene pac-A and pac-P in mammalian cells.

Animals↗
PubMed2000

[Modern spectral estimation of ICP-AES].

The inductively coupled plasma atomic emission spectrometry (ICP-AES) and its signal characteristics were discussed using modern spectral estimation technique. The power spectra density (PSD) was calculated using the auto-regression (AR) model of modern spectra estimation. The Levinson-Durbin recursion method was used to estimate the model parameters which were used for the PSD computation. The results obtained with actual ICP-AES spectra and measurements showed that the spectral estimation technique was helpful for the better understanding about spectral composition and signal characteristics.

Regression Analysis↗
PubMed2000

[Study on color reaction of copper(II)-neocuprine-glutathione-alcohol system].

The colour reaction of glutathione with copper(II)-neocuproine-alcohol was investigated in the present paper. The absorbance increased distinctly by about 13.8% when alcohol was added to the system. The maximum absorption wavelength lambda max of [Cu (neocuproine)2]+ was at 456 nm and the apparent molar absorptivity was 1.2 x 10(4) L.mol-1.cm-1 in the selected system. Linear dynamic relationship was obtained in the concentration range of 2-24 micrograms.mL-1 for glutathione. The regression equation was as following: A = 0.0104 + 0.0385c. The correlation coefficients was 0.9998. The recoveries obtained were between 98.5% and 99.9%. The relative standard deviations were less than 0.9% for all analyses. This method was used to determine glutathione in soybean extracts by the electromagnetic field technique and satisfactory results were obtained.

Antineoplastic Agents↗
PubMed1999

Analysis of the kinase-related protein gene found at human chromosome 3q21 in a multi-gene cluster: organization, expression, alternative splicing, and polymorphic marker.

We report the amino acid sequence, genomic organization, tissue expression, and alternative splice patterns for the human kinase related protein (KRP) gene, as well as the discovery of a new CA repeat sequence polymorphic marker in an upstream intron of the myosin light chain kinase (MLCK) gene. The KRP/MLCK genetic locus is a prototype for a recently discovered paradigm in which an independently regulated gene for a non-enzymic protein is embedded within a larger gene for a signal transduction enzyme, and both classes of proteins are involved in the regulation of the same cellular structure. The MLCK/KRP gene cluster has been found only in higher vertebrates and is localized to human chromosome 3q21. The determination of the human KRP amino acid sequence through cDNA sequence analysis and its comparison to the exon/intron organization of the human KRP gene revealed an alternative splice pattern at the start of KRP exon 2, resulting in the insertion of a single glutamic acid in the middle of the protein. Examination of tissue distribution using Northern blot analysis revealed that the human expression pattern is more similar to the well-characterized chicken KRP gene expression pattern than to rodent or rabbit. Unexpected differences of the human gene from other species is the apparent expression of the human gene products in adult cardiac muscle, an observation that was pursued further by the production of a site-directed antiserum and immunohistochemistry analysis. The results reported here provide insight into the conserved and variable features of this late evolving genetic paradigm, raise new questions about the molecular aspects of cardiac muscle regulation, and provide tools needed for future clinical studies. The comparative analysis of the MLCK/KRP locus, combined with the recent discovery of a similar genomic relationship among other signal transduction proteins, suggest a diverse distribution of this theme among signal transduction systems in higher vertebrate genomes and indicate the utility of comparative genomics in revealing late evolving genetic paradigms.

Adult↗
PubMed1999

Specific lipopolysaccharide found in cystic fibrosis airway Pseudomonas aeruginosa.

Cystic fibrosis (CF) patients develop chronic airway infections with Pseudomonas aeruginosa (PA). Pseudomonas aeruginosa synthesized lipopolysaccharide (LPS) with a variety of penta- and hexa-acylated lipid A structures under different environmental conditions. CF patient PA synthesized LPS with specific lipid A structures indicating unique recognition of the CF airway environment. CF-specific lipid A forms containing palmitate and aminoarabinose were associated with resistance to cationic antimicrobial peptides and increased inflammatory responses, indicating that they are likely to be involved in airway disease.

Acylation↗
PubMed1999

Risk factors for meningioma in adults: a case-control study in northeast China.

A hospital case-control study of meningioma was conducted in Heilongjiang Province in northeast China between September 1989 and December 1996. It included 183 cases of newly diagnosed primary meningioma and 366 individually matched hospital controls with non-neoplastic and non-neurological disease selected from six major hospitals. Cases and controls were matched by sex, age and area of residence and interviewed in the hospital wards to obtain information on medical history, occupation and lifestyle. No association with liquor or beer consumption was apparent. Cigarette smoking was positively associated with meningioma risk in women but not in men. In women, compared with non-smokers, the adjusted OR for pack-years of smoking above the median (124) was 6.2 (CI 2.04-18.87). Both of these observations contrast with the results of a study of glioma in the same population, using similar methods. The risk of meningioma was positively associated with reported occupational exposure to lead, tin, cadmium and ionising radiation in both genders.

Adult↗
PubMed1999

A mutant form of human protein farnesyltransferase exhibits increased resistance to farnesyltransferase inhibitors.

Protein farnesyltransferase (FTase) is a key enzyme responsible for the lipid modification of a large and important number of proteins including Ras. Recent demonstrations that inhibitors of this enzyme block the growth of a variety of human tumors point to the importance of this enzyme in human tumor formation. In this paper, we report that a mutant form of human FTase, Y361L, exhibits increased resistance to farnesyltransferase inhibitors, particularly a tricyclic compound, SCH56582, which is a competitive inhibitor of FTase with respect to the CAAX (where C is cysteine, A is an aliphatic amino acid, and X is the C-terminal residue that is preferentially serine, cysteine, methionine, glutamine or alanine) substrates. The Y361L mutant maintains FTase activity toward substrates ending with CIIS. However, the mutant also exhibits an increased affinity for peptides terminating with CIIL, a motif that is recognized by geranylgeranyltransferase I (GGTase I). The Y361L mutant also demonstrates activity with Ha-Ras and Cdc42Hs proteins, substrates of FTase and GGTase I, respectively. In addition, the Y361L mutant shows a marked sensitivity to a zinc chelator HPH-5 suggesting that the mutant has altered zinc coordination. These results demonstrate that a single amino acid change at a residue at the active site can lead to the generation of a mutant resistant to FTase inhibitors. Such a mutant may be valuable for the study of the effects of FTase inhibitors on tumor cells.

Alkyl and Aryl Transferases↗
PubMed1999

Isolation and characterization of novel cold-sensitive dnaA mutants of Escherichia coli.

We developed an efficient method for isolation of novel dnaA mutations based on PCR mutagenesis in the presence of manganese ion and shuffling of dnaA-carrying plasmids in a dnaA deletion host bacterium. Using this system, we obtained 30 cold-sensitive mutants from 4000 clones carrying plasmids with a mutagenized dnaA gene. All 27 cold-sensitive mutants analyzed were defective in DNA replication; none had a DnaAcos (over-initiation) phenotype. Nucleotide sequencing revealed that novel 15 alleles (mutations in 14 amino acid residues) are responsible for the cold-sensitive phenotype and are all located in the carboxy-terminal half of the DnaA protein.

Adaptation, Physiological↗
PubMed1999

Photorhabdus luminescens W-14 insecticidal activity consists of at least two similar but distinct proteins. Purification and characterization of toxin A and toxin B.

Both the bacterium Photorhabdus luminescens alone and its symbiotic Photorhabdus-nematode complex are known to be highly pathogenic to insects. The nature of the insecticidal activity of Photorhabdus bacteria was investigated for its potential application as an insect control agent. It was found that in the fermentation broth of P. luminescens strain W-14, at least two proteins, toxin A and toxin B, independently contributed to the oral insecticidal activity against Southern corn rootworm. Purified toxin A and toxin B exhibited single bands on native polyacrylamide gel electrophoresis and two peptides of 208 and 63 kDa on SDS-polyacrylamide gel electrophoresis. The native molecular weight of both the toxin A and toxin B was determined to be approximately 860 kDa, suggesting that they are tetrameric. NH2-terminal amino acid sequencing and Western analysis using monospecific antibodies to each toxin demonstrated that the two toxins were distinct but homologous. The oral potency (LD50) of toxin A and toxin B against Southern corn rootworm larvae was determined to be similar to that observed with highly potent Bt toxins against lepidopteran pests. In addition, it was found that the two peptides present in toxin B could be processed in vitro from a 281-kDa protoxin by endogenous P. luminescens proteases. Proteolytic processing was shown to enhance insecticidal activity.

Amino Acid Sequence↗
PubMed1999

Association of diabetes mellitus and chronic hepatitis C virus infection.

While patients with liver disease are known to have a higher prevalence of glucose intolerance, preliminary studies suggest that hepatitis C virus (HCV) infection may be an additional risk factor for the development of diabetes mellitus. To further study the correlation of HCV infection and diabetes, we performed a retrospective analysis of 1,117 patients with chronic viral hepatitis and analyzed whether age, sex, race, hepatitis B virus (HBV) infection, HCV infection, and cirrhosis were independently associated with diabetes. In addition, a case-control study was conducted to determine the seroprevalence of HCV infection in a cohort of 594 diabetics and 377 clinic patients assessed for thyroid disease. In the former study after the exclusion of patients with conditions predisposing to hyperglycemia, diabetes was observed in 21% of HCV-infected patients compared with 12% of HBV-infected subjects (P =.0004). Multivariate analysis revealed that HCV infection (P =.02) and age (P =.01) were independent predictors of diabetes. In the diabetes cohort, 4.2% of patients were found to be infected with HCV compared with 1.6% of control patients (P =.02). HCV genotype 2a was observed in 29% of HCV-RNA-positive diabetic patients versus 3% of local HCV-infected controls (P <.005). In conclusion, the data suggest a relatively strong association between HCV infection and diabetes, because diabetics have an increased frequency of HCV infection, particularly with genotype 2a. Furthermore, it is possible that HCV infection may serve as an additional risk factor for the development of diabetes, beyond that attributable to chronic liver disease alone.

Adult↗
PubMed1999

A potential mechanism for selective control of cap-independent translation by a viral RNA sequence in cis and in trans.

Highly efficient cap-independent translation initiation at the 5'-proximal AUG is facilitated by the 3' translation enhancer sequence (3'TE) located near the 3' end of barley yellow dwarf virus (BYDV) genomic RNA. The role of the 3'TE in regulating viral translation was examined. The 3'TE is required for translation and thus replication of the genomic RNA that lacks a 5' cap (Allen et al., 1999, Virology253:139-144). Here we show that the 3'TE also mediates translation of uncapped viral subgenomic mRNAs (sgRNA1 and sgRNA2). A 109-nt viral sequence is sufficient for 3'TE activity in vitro, but additional viral sequence is necessary for cap-independent translation in vivo. The 5' extremity of the sequence required in the 3' untranslated region (UTR) for cap-independent translation in vivo coincides with the 5' end of sgRNA2. Thus, sgRNA2 has the 3'TE in its 5' UTR. Competition studies using physiological ratios of viral RNAs showed that, in trans, the 109-nt 3'TE alone, or in the context of 869-nt sgRNA2, inhibited translation of genomic RNA much more than it inhibited translation of sgRNA1. The divergent 5' UTRs of genomic RNA and sgRNA1 contribute to this differential susceptibility to inhibition. We propose that sgRNA2 serves as a novel regulatory RNA to carry out the switch from early to late gene expression. Thus, this new mechanism for temporal control of translation control involves a sequence that stimulates translation in cis and acts in trans to selectively inhibit translation of viral mRNA.

3' Untranslated Regions↗
PubMed1999

Receptors for polytropic and xenotropic mouse leukaemia viruses encoded by a single gene at Rmc1.

The onset of leukaemia caused by type C retroviruses (MLV) in mice is accelerated by the emergence of recombinant polytropic or mink cell focus-forming (MCF) viruses. Susceptibility to infection by polytropic/MCF and also by closely related xenotropic MLV has been mapped to Rmc1 on mouse chromosome 1 (refs 5-7). To identify this gene, we introduced an expression cDNA library prepared from mouse NIH3T3 fibroblasts into nonpermissive hamster cells and screened these cells for acquired susceptibility to MCF viruses encoding beta-galactosidase and G418 resistance. From hamster cell clones identified in the screen, we recovered a mouse cDNA that maps to Rmc1 and confers MCF MLV infection when expressed in nonpermissive cell lines. It encodes a membrane protein related to Syg1p (suppressor of yeast G alpha deletion; ref. 8). The receptor-binding domain of the MCF MLV envelope protein binds specifically to Xenopus laevis oocytes that express mouse Syg1, suggesting it functions as a receptor that mediates virus entry. We also obtained the cDNA encoding human SYG1. When expressed in hamster cells, it establishes infectivity by MCF MLV as well as xenotropic MLV, which do not infect laboratory mice.

3T3 Cells↗