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L Chen

Publications and source records attributed to L Chen.

At least 1,207 records · Page 67Linked to original sources
PubMed1994

Solid-phase peptide synthesis and biological activity of bovine thymopoietin II (bTP-II).

Bovine thymopoietin (bTP), a 49 amino acid polypeptide, was synthesized using Merrifield's solid-phase peptide synthesis methodology. The polypeptide was purified using anion-exchange chromatography and reversed-phase HPLC and characterized by mass spectrometry and amino acid analysis of the full-length peptide and of products derived from digestion with Staphylococcus aureus V8 protease. The biological activity of the synthesized product was tested in several assay systems. Synthetic bTP was found to induce the expression of Thy 1.2 antigen on T-lymphocytes from athymic mice, in agreement with previous studies on the biological activity of endogenous bTP. Biological activity at skeletal muscle and neuronal nicotinic acetylcholine receptor sites, as reported by others for bTP, could not be confirmed in our studies. The absence of biological activity at nicotinic receptor sites may be related to the results of a recent report demonstrating the presence of a cobratoxin-like molecule in preparations of natural bTP. These data indicate that synthetic peptides have an important role for the evaluation of the specificity of the biological activity of polypeptides.

Amino Acid Sequence↗
PubMed1994

The Bacillus subtilis sigma D-dependent operon encoding the flagellar proteins FliD, FliS, and FliT.

During a genetic screen to identify metalloregulated loci in Bacillus subtilis, we isolated a Tn917-lacZ insertion in the second gene of an operon downstream of the flagellin (hag) gene. Sequence analysis indicates that this gene encodes a homolog of the enteric flagellar filament cap protein FliD. The fliD gene is followed by homologs of the fliS and fliT genes. Transcription of the fliD-lacZ fusion is sigma D dependent, with peak expression at the end of logarithmic-phase growth. Like other sigma D-dependent genes, expression of fliD-lacZ is greatly reduced by mutations in genes essential for assembly and function of the basal body and hook complex (class II functions). These results suggest that B. subtilis flagellar genes are organized in a hierarchy of gene expression similar to that found in enteric bacteria with hag and fliD as class III genes. Expression from the fliD operon promoter, but not the hag promoter, is repressed by iron, which suggests that the target of metalloregulation is the promoter rather than the sigma D protein.

Amino Acid Sequence↗
PubMed1994

A homeodomain protein related to caudal regulates intestine-specific gene transcription.

The continually renewing epithelium of the intestinal tract arises from the visceral endoderm by a series of complex developmental transitions. The mechanisms that establish and maintain the processes of cellular renewal, cell lineage allocation, and tissue restriction and spatial assignment of gene expression in this epithelium are unknown. An understanding of the regulation of intestine-specific gene regulation may provide information on the molecular mechanisms that direct these processes. In this regard, we show that intestine-specific transcription of sucrase-isomaltase, a gene that is expressed exclusively in differentiated enterocytes, is dependent on binding of a tissue-specific homeodomain protein (mouse Cdx-2) to an evolutionarily conserved promoter element in the sucrase-isomaltase gene. This protein is a member of the caudal family of homeodomain genes which appear to function in early developmental events in Drosophila melanogaster, during gastrulation in many species, and in intestinal endoderm. Unique for this homeodomain gene family, we show that mouse Cdx-2 binds as a dimer to its regulatory element and that dimerization in vitro is dependent on redox potential. These characteristics of the interaction of Cdx-2 with its regulatory element provide for a number of potential mechanisms for transcriptional regulation. Taken together, these findings suggest that members of the Cdx gene family play a fundamental role both in the establishment of the intestinal phenotype during development and in maintenance of this phenotype via transcriptional activation of differentiated intestinal genes.

Amino Acid Sequence↗
PubMed1994

Biological activity of the growth factor-induced cytokine N51: structure-function analysis using N51/Interleukin-8 chimeric molecules.

The immediate-early gene N51/KC encodes a protein which following expression in the baculovirus system and purification to apparent homogeneity is able to induce chemotaxis and intracellular Ca2+ flux, to compete for 125I-labeled interleukin-8 (IL-8) binding, and upon iodination, to bind specifically to human neutrophils. The activity of N51/KC can be distinguished from that of IL-8 by a number of criteria. First, at equivalent concentrations, the specific binding of [125I]N51/KC to human neutrophils is about 10 times less than that of [125I]IL-8. Second, the competition studies of [125I]IL-8 with IL-8 define a single class of high-affinity receptors, while the presence of both a high- and a low-affinity class of receptors is defined by N51/KC. Third, although the changes in intracellular Ca2+ of fura-2/AM-preloaded human neutrophils elicited by N51/KC and IL-8 are similar, pretreatment of the cells with N51/KC did not result in a loss of response to a subsequent treatment with IL-8; in contrast, treatment with IL-8 did result in the subsequent desensitization to N51/KC. To further characterize N51/KC, mutants and hybrids of N51/KC and IL-8 were produced and analyzed for the ability to compete for [125I]IL-8 binding and elicit intracellular Ca2+ changes in human neutrophils. Two important observations came from these studies. First, the N51/IL-8I hybrid in which the N51/KC sequence between cysteines 2 and 3 (or first disulfide bond) is replaced by the corresponding sequence in IL-8 shows IL-8-like properties, indicating that this region is important for specific receptor recognition. Second, the N51 delta III and IL-8 delta III C-terminus deletion mutants were biologically inactive, but the hybrid molecules N51/IL-8III and IL-8/N51III, in which the C termini were exchanged, had biological activities similar to that of the wild-type molecules, demonstrating that the presence of the C terminus is essential for the biological activity of these chemokines but does not confer receptor specificity.

Amino Acid Sequence↗
PubMed1994

An rRNA variable region has an evolutionarily conserved essential role despite sequence divergence.

Regions extremely variable in size and sequence occur at conserved locations in eukaryotic rRNAs. The functional importance of one such region was determined by gene reconstruction and replacement in Tetrahymena thermophila. Deletion of the D8 region of the large-subunit rRNA inactivates T. thermophila rRNA genes (rDNA): transformants containing only this type of rDNA are unable to grow. Replacement with an unrelated sequence of similar size or a variable region from a different position in the rRNA also inactivated the rDNA. Mutant rRNAs resulting from such constructs were present only in precursor forms, suggesting that these rRNAs are deficient in either processing or stabilization of the mature form. Replacement with D8 regions from three other organisms restored function, even though the sequences are very different. Thus, these D8 regions share an essential functional feature that is not reflected in their primary sequences. Similar tertiary structures may be the quality these sequences share that allows them to function interchangeably.

Animals↗
PubMed1994

An unusual late relapse in pathologic stage I non-seminomatous germ cell tumor: case report and review of the literature.

Late relapses are exceedingly uncommon in patients with pathologic stage (PS) I non-seminomatous germ cell tumors (NSGCT) of the testis treated with inguinal orchiectomy and retroperitoneal lymph node dissection (RPLND). We describe an unusual patient with PSI NSGCT who relapsed 40 months after surgery. The only evidence of recurrent disease was an elevated serum alpha-fetoprotein level, and complete remission was achieved following the prompt institution of combination chemotherapy. To our knowledge, this is the first report of a late relapse in PSI NSGCT of the testis manifested only as an elevated tumor marker.

Adult↗
PubMed1994

The Caenorhabditis elegans MYOD homologue HLH-1 is essential for proper muscle function and complete morphogenesis.

A family of muscle-specific helix-loop-helix transcription factors (myoD, myogenin, myf-5 and MRF4) has been implicated in the control of vertebrate skeletal myogenesis. Searches for homologues of this family in Caenorhabditis elegans identified a single family member, hlh-1, which is expressed in striated muscles and their clonal precursors. We have isolated a null allele of hlh-1 following chemical mutagenesis. Animals homozygous for the null mutation produce contractile body-wall muscles, although muscle contractions are weak and coordination is defective. In addition to the evident muscle defects, mutant animals fail to complete embryonic elongation and die as larvae or young adults. Ultrastructural analysis of the mutant muscle reveals an apparently normal local lattice of thick and thin filaments, with more global defects in sarcomere organization and muscle cell placement. Mosaic studies using the point mutation and an extrachromosomal transgene indicate that the requirement for hlh-1 is fully zygotic, with no maternal hlh-1 requirement for either muscle development or viability.

Alleles↗
PubMed1994

Sebaceous carcinoma arising in a benign dermoid cyst of the ovary.

Sebaceous carcinoma in a ovarian dermoid cyst is a rare entity. The present patient has survived 54 months and has no evidence of recurrence after total abdominal hysterectomy, bilateral salpingo-oophorectomy and adjuvant chemotherapy with cisplatin, vinblastine, and bleomycin.

Adenocarcinoma, Sebaceous↗
PubMed1994

Regional brain activity of free radical defense enzymes in autopsy samples from patients with Alzheimer's disease and from nondemented controls.

Several lines of evidence support the hypothesis that oxygen free radicals are involved in the destruction of neurons in various degenerative disorders of the central nervous system. The activities of superoxide dismutase, catalase and glutathione peroxidase, three enzymes that contribute to the cellular defenses against free radical damage, were measured in different areas of autopsy brains from patients with Alzheimer's disease and from age matched controls. All brains were removed within 24 hours of the time of death and were cut in half sagitally. One half was stored frozen at -86 degrees C and the other half was examined histologically to confirm the presence or absence of Alzheimer's disease. Samples were taken from the frozen half for the enzyme assays. In control brains, the activity of superoxide dismutase is significantly higher in the cerebellum, frontal cortex and hippocampus than it is in the temporal cortex, parietal cortex and entorhinal cortex. The activity of catalase is significantly higher in cerebellum and frontal cortex than in hippocampus, parietal cortex and entorhinal cortex. Glutathione peroxidase activity is uniform across all brain areas studied. In Alzheimer's brains, superoxide dismutase activity is not statistically different among the various brain regions studied, but it is significantly lower than control in the cerebellum (-27%), frontal cortex (-27%) and hippocampus (-35%). Catalase is significantly higher in Alzheimer's cerebellum, frontal cortex and temporal cortex than in Alzheimer's hippocampus, parietal cortex and entorhinal cortex. However, there are no significant differences in catalase activity between Alzheimer's and control samples.(ABSTRACT TRUNCATED AT 250 WORDS)

Alzheimer Disease↗
PubMed1994

[Fast detection of Alu DNA in human tissues by Alu-PCR].

This paper reports a direct PCR method for the detection of Alu DNA in 18 different kinds of human tissue using primers of Alu 9.1 and Alu 9.2 without DNA extraction. The results showed that besides fresh tissues, some formalin fixed paraffin embedded tissues can be correctly analyzed with PCR. Different amounts of PCR products were obtained from different types of tissues. The duration of fixation in formalin is an important factor exerting an influence on the quantity of the high molecular weight DNA and the results of PCR. No obvious influence of the duration of storage of paraffin embedded tissues on the PCR results was observed. This method is quite simple, sensitive and rapid to perform. It can be performed under a condition of avoiding contamination of DNA and DNase as well as the detrimental phenol and chloroform.

Base Sequence↗
PubMed1994

[Gas chromatographic analysis of C1-C6 fatty acids in rat fecal samples].

A gas chromatography procedure was performed to determine C1-C6 fatty acids in rat feces. Acidated fecal homogenate was extracted with ethyl ether-petroleum ether (1 + 1). After adding tetramethylammonium hydroxide to the extract, the quaternary ammonium salts of the fatty acids could react with ethyl bromide in the presence of N,N-dimethyl acetamide producing corresponding esters. The derived products were separated by the column packed with ethylene glycol succinate polyester and were determined with Flame ionization detector (FID). The extractive efficiencies of C1-C6 fatty acids from the fecal samples were 88.5%-100%, and the recoveries ranged from 82.4% to 110.8% with the coefficients of variation of 3.2%-10.9%. The detection limits were at 1ppm. The optimum conditions of esterification are discussed. The method is safe and rapid, and has been applied to the analysis of C1-C6 fatty acids in rat feces.

Animals↗
PubMed1994

[Penetrating keratoplasty for bullous keratopathy].

A retrospective review for bullous keratopathy in our hospital from 1985 to 1992 was studies. Among the cases with bullous keratopathy, 14 were performed with antiglaucoma operation and cataract extraction, 12 that experienced a contusion or penetrating trauma history underwent cataract operation. IOL implantation seen in 3 patients, 4 cases were associated with vitreous contact to cornea after cataract extraction, the other 4 cases had advanced glaucoma. Besides, there were 1 case of Fuch's endothelium dystrophy, ICE syndrome and severe herpes simplex keratitis, respectively. The preoperation visual acuity of them was all less than finger count. The follow-up was 3 months to 5 years. The results showed the grafts of 28 cases (70%) were clear, 7 cases (17.5%) semi-clear, 5 cases (12.5%) opaque. Postoperatively, all of the patients escaped from the pain and 22 cases achieved a visual acuity of 0.02-0.7. Some good advice in treatment of bullous keratopathy were proposed.

Adolescent↗
PubMed1994

[Comparative study of organ storage solutions for rat liver preservation: effects of HX and Collins I solution on sinusoidal lining cells and hepatic functions].

The liver sinusoidal lining cell injury and biochemical function changes were studied with isolated perfusion after rat livers had been preserved in HX solution or in Collins II solution. Seventy inbred Wistar rats were randomly divided into control group (n = 10), group H (preserved with HX solution, n = 30), and group C (preserved with Collins II solution, n = 30). The effects of the storage solutions were assessed by measuring the sinusoidal lining cell mortality (SLCM), Krebs-Henseleit perfusate ketone body ratio (PKBR), the hepatic sugar release (SL), and the number of livers secreting bile during isolated perfusion. The results suggest that the HX solution be much superior to Collins II solution in preventing sinusoidal lining cell injury and maintaining normal hepatic functions.

Animals↗
PubMed1994

[Clinical observation and management of the filtration bleb after trabeculectomy].

The author reports 42 patients (56 eyes) of glaucoma performed trabeculectomy under operating microscope from August 1991 to April 1993. After operation the conjunctival filtration blebs were observed in details. The formation rate of ideal blebs was 80.3%. The success rate of operation was 87.5%. The author discusses the mechanisms of lowered intraocular pressure in trabeculectomy and the relation between the type of filtration bleb and intraocular pressure. The author believes that the formation of functional subconjunctival filtration blebs is the key to successful operation. The management of non-functional filtration blebs is presented in this paper.

Adolescent↗
PubMed1994

Regulation of CD9 expression during 12-O-tetradecanoyl-phorbol-13-acetate- induced differentiation of human myeloid leukemia (HL-60) cells.

CD9 antigen is a member of the tetra spans superfamily of proteins which are expressed on the surface of a variety of hematopoietic and epithelial cell types. CD9 appears to play a role in platelet activation and to enhance sensitivity of cells to diphtheria toxin through its association with the diphtheria toxin receptor. Although several studies indicate that treatment of specific hematopoietic cells with the tumor promoter, 12-O-tetradecanoylphorbol-13-acetate (TPA), induces CD9 expression, the mechanisms by which CD9 expression is regulated have not been elucidated. Here, we provide evidence that, in HL-60 cells, increases in the level of CD9 protein occur in parallel with TPA-induced differentiation. More than 80% of HL-60 cells exposed to 17 nM TPA become CD9 positive within 24 h. CD9 mRNA levels increase within 8-10 h after starting TPA treatment. Activation of CD9 transcription occurs during the same time period. Both transcriptional activation and accumulation of CD9 mRNA require protein synthesis. However, once CD9 mRNA has accumulated, inhibition of protein synthesis has no effect on its level or rate of turnover. These results suggest that CD9 expression in TPA-treated HL-60 cells is regulated at the transcriptional level and that activation of transcription occurs subsequent to the production of proteins induced as an immediate-early response to TPA. Since CD9 expression is not induced in HL-60TR cells, which respond to TPA but are resistant to its differentiating effects, the results also indicate that CD9 expression may serve as a marker for monocyte/macrophage differentiation of HL-60 cells.

Antigens, CD↗
PubMed1994

[Mapping of full-length murine renin-2 gene].

A 24kb fragment containing full-length renin-2 gene and its flanking sequence was obtained by digesting the pKG-R2D with XhoI. This fragment was cleaved with single enzyme (EcoRI, KpnI and BamHI), and combined enzymes (EcoRI/KpnI, KpnI/BamHI and BamHI/EcoRI), respectively. The digests were electrophoresed on 0.8% agarose plates and transferred onto NC membranes. Radioactive probes of 735bp and 1400bp, templates of which were from half and full-length of renin-1 cDNA, respectively were used for Southern hybridization. On the basis of electrophoresis and hybridization patterns, a restriction map was constructed in this paper.

Animals↗
PubMed1994

[The effects of Panax quinquefolium saponin (PQS) and its monomer ginsenoside on heart].

Experiments have shown that PQS (0.03-3 mg/ml) can inhibit the contractility of papillary muscle of guinea pigs, and on depolarized sample of papillary muscle with high potassium, PQS (0.03-0.3 mg/ml) can increase this contractility. Monomer saponin-Re (10 mg/kg),-Rb3 (30 mg/kg) can inhibit the hemodynamic indication of rats, but pseudogisenoside-F11 (10 mg/kg) acts the other way round. These results prove that PQS contains two components of opposite actions.

Animals↗