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Biomedical subjects

L Xu

Publications and source records attributed to L Xu.

At least 757 records · Page 42Linked to original sources
PubMed1992

POU-specific domain of Oct-2 factor confers 'octamer' motif DNA binding specificity on heterologous Antennapedia homeodomain.

The bipartite DNA binding domain of the POU family of transcription factors contains a 'POU-specific' domain unique to this class of factors and a 'POU homeodomain' homologous to other homeodomains. We compared DNA binding of the Oct-2 factor POU domain and the Antennapedia (Antp) homeodomain with a chimeric Oct-2/Antp protein in which the distantly related Antp homeodomain was substituted for the Oct-2 POU homeodomain. The Oct-2/Antp chimeric protein bound both the octamer and the Antp sites efficiently, indicating that DNA binding specificity is contributed by both components of the POU domain.

Antennapedia Homeodomain Protein↗
PubMed1992

Expression of a cardiac Ca(2+)-release channel isoform in mammalian brain.

Mammalian brain possesses ryanodine-sensitive Ca2+ channels, which in muscle cells mediate rapid Ca2+ release from intracellular stores during excitation-contraction coupling. Analysis of bovine brain ryanodine receptor (RyR) channels suggests specific expression of the cardiac-muscle RyR isoform in mammalian brain. Localization using cardiac-muscle RyR-specific antibodies and antisense RNA revealed that brain RyRs were present in dendrites, cell bodies and terminals of rat forebrain, and highly enriched in the hippocampus. Activity of skeletal-muscle RyR channels is coupled to sarcolemmal voltage sensors, in contrast with cardiac-muscle RyR channels, which are known to be Ca(2+)-induced Ca(2+)-release channels. Thus Ca(2+)-induced Ca2+ release from intracellular stores mediated by brain RyR channels may be a major Ca(2+)-signalling pathway in specific regions of mammalian brain, and hence may play a fundamental role in neuronal Ca2+ homoeostasis.

Animals↗
PubMed1992

Vascular smooth muscle cells exhibit increased growth in response to elevated glucose.

Diabetes mellitus is associated with an increased risk of cardiovascular disease. In order to elucidate the association between hyperglycemia and vascular complications, the growth patterns of vascular smooth muscle cells were studied under high glucose conditions. We examined the effect of culturing porcine aortic smooth muscle cells (PVSMC) in high glucose (25 mM, HG) on total cell protein, cell volume, DNA synthesis and cell number. We observed that cells cultured in HG had higher total cell protein content which was associated with increased cell volume as compared to the cells cultured under normoglycemic conditions (5.5 mM glucose, NG). PVSMC cultured in HG also had 1.4 fold increased growth rate and a greater fetal calf serum-induced DNA synthesis rate compared to cells cultured in NG. These observations suggest for the first time that elevated glucose could lead to both hypertrophic and hyperplastic effects in PVSMC. We also examined protein kinase C (PKC) activities as well as the cellular levels of the 12-lipoxygenase product, 12-hydroxyeicosatetraenoic acid (12-HETE) in NG and HG as possible mechanisms for the enhanced growth effects in HG. The results show that PVSMC cultured in HG have increased PKC activity as well as increased levels of 12-HETE. Therefore hyperglycemia may be linked to accelerated vascular disease by increasing smooth muscle cell growth and proliferation.

12-Hydroxy-5,8,10,14-eicosatetraenoic Acid↗
PubMed1992

The 30 S lobster skeletal muscle Ca2+ release channel (ryanodine receptor) has functional properties distinct from the mammalian channel proteins.

The 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate (Chaps)-solubilized ryanodine receptor (RyR) of lobster skeletal muscle has been isolated by rate density centrifugation as a 30 S protein complex. Sodium dodecyl sulfate-polyacrylamide gel electrophoretic analysis of the purified 30 S receptor revealed a single high molecular weight protein band with a mobility intermediate between those of the mammalian skeletal and cardiac M(r) 565,000 RyR polypeptides. Immunoblot analysis showed no or only minimal cross-reactivity with the rabbit skeletal and canine cardiac RyR polypeptides. By immunofluorescence the lobster RyR was localized to the junctions of the A-I bands. Following planar lipid bilayer reconstitution of the purified 30 S lobster RyR, single channel K+ and Ca2+ currents were observed which were modified by ryanodine and optimally activated by millimolar concentrations of cis (cytoplasmic) Ca2+. Vesicle-45Ca2+ flux measurements also indicated an optimal activation of the lobster Ca2+ channel by millimolar Ca2+, whereas 45Ca2+ efflux from mammalian skeletal and cardiac muscle sarcoplasmic reticulum (SR) vesicles is optimally activated by micromolar Ca2+. Further, mammalian muscle SR Ca2+ release activity is modulated by Mg2+ and ATP, whereas neither ligand appreciably affected 45Ca2+ efflux from lobster SR vesicles. These results suggested that lobster and mammalian muscle express immunologically and functionally distinct SR Ca2+ release channel protein complexes.

Animals↗
PubMed1992

DMC1: a meiosis-specific yeast homolog of E. coli recA required for recombination, synaptonemal complex formation, and cell cycle progression.

DMC1 is a new meiosis-specific yeast gene. Dmc1 protein is structurally similar to bacterial RecA proteins. dmc1 mutants are defective in reciprocal recombination, accumulate double-strand break (DSB) recombination intermediates, fail to form normal synaptonemal complex (SC), and arrest late in meiotic prophase. dmc1 phenotypes are consistent with a functional relationship between Dmc1 and RecA, and thus eukaryotic and prokaryotic mechanisms for homology recognition and strand exchange may be related. dmc1 phenotypes provide further evidence that recombination and SC formation are interrelated processes and are consistent with a requirement for DNA-DNA interactions during SC formation. dmc1 mutations confer prophase arrest. Additional evidence suggests that arrest occurs at a meiosis-specific cell cycle "checkpoint" in response to a primary defect in prophase chromosome metabolism. DMC1 is homologous to yeast's RAD51 gene, supporting the view that mitotic DSB repair has been recruited for use in meiotic chromosome metabolism.

Amino Acid Sequence↗
PubMed1992

Divergent effects of taxol on tumor necrosis factor-alpha-mediated cytolysis of ovarian carcinoma cells.

OBJECTIVE: Our objective was to study the combined effect of taxol and tumor necrosis factor-alpha on the cytolysis of human ovarian carcinoma cell lines, because taxol has been shown to be active against ovarian carcinoma and has also been shown to increase tumor necrosis factor-alpha release from macrophages. STUDY DESIGN: The combined effect of taxol and tumor necrosis factor-alpha on the cell lines Caov-3, SK-OV-3, NIH:OVCAR-3, and A2780, which are sensitive to the cytolytic effect of tumor necrosis factor-alpha in the presence of inhibitors of protein synthesis, was investigated with a 24-hour chromium 51 release assay. RESULTS: At therapeutic concentrations taxol caused a significant increase in tumor necrosis factor-alpha-mediated cytolysis of Caov-3 and A2780 (p < or = 0.05). By contrast, taxol caused a decrease in the tumor necrosis factor-alpha-mediated cytolysis of SK-OV-3 and NIH:OVCAR-3 (p < or = 0.01). CONCLUSION: These results suggest that ovarian carcinomas have a heterogeneous response to the chemotherapeutic effect of taxol.

Carcinoma↗
PubMed1992

The use of capillary electrophoresis to identify cationic proteins in human parotid saliva.

Eight proteins, HRPs 1, 2, 3, 4, 5 and 6, lysozyme and histatin 6, are the major cationic components of the parotid salivas of normal healthy individuals. Histatins 2 and 4 appear to be further degradation products of the HRPs. Capillary electrophoresis separates all of these eight components, thus allowing future studies to correlate protein concentration with antimicrobial activity in health and disease.

Amino Acid Sequence↗
PubMed1992

Production of recombinant human interferon-alpha 1 by Escherichia coli using a computer-controlled cultivation process.

Genetically engineered E. coli K12 BMH-71-18 with plasmid PBV-867 was used for constitutive expression of human interferon-alpha 1 (IFN) with a defined medium. A manual, time-based, fed-batch cultivation process produced a cell density of 26.3 g l-1 (OD550 89), an IFN activity of 1.55 x 10(8) IU l-1 and a specific IFN productivity of 0.65 x 10(6) IU g-1. An analysis was conducted to characterize the problems involved in the high density microbial processes of recombinant protein production. The strategy suggested by the analysis is to establish a nutrient feeding profile that improves both the plasmid stability and the overall productivity of IFN. The nutrient feeding procedure developed here was based on the growth dynamics and a glucose consumption model. By using this procedure to continuously supply nutrients during cultivations, cell density reached 58 to 80 g l-1 and the specific IFN productivities of these runs were increased over that of the manual process. Nutrient feeding rates were found to affect the specific IFN productivity substantially. The optimized process achieved an IFN activity of 1.26 x 10(9) IU l-1, a cell density of 58 g l-1 and a specific IFN productivity of 2.2 x 10(7) IU g-1. More significantly, the overall productivity IU l-1 h-1 of the optimized, computer-controlled cultivation process was increased 12.9-fold over that of the manual cultivation process.

Cloning, Molecular↗
PubMed1992

Suppression of the 2f1-f2 otoacoustic emission in humans.

Suppression of the 2f1-f2 distortion-product otoacoustic emission (DPOAE), stimulated with primaries, f1 and f2, in the frequency regions of 1, 2, and 4 kHz was measured in one ear of 14 human subjects with normal hearing. Suppression rate functions were generated with a suppressor at either 1, 2, or 4 kHz increasing in level from 30 to 76 dB SPL for the corresponding f1 and f2 combinations. Stimulus levels for DPOAEs were L1 = 70 dB SPL and L2 adjusted to produce the highest amplitude DPOAE for each ear (range, 0 to 6 dB below L1). Results indicated that DPOAEs were reduced 3 dB in amplitude for a mean suppressor level of 61 dB SPL. Maximum amplitude reduction occurred at a mean suppressor level of 69 dB SPL. These levels varied little for the three stimulus frequency regions. Mean slopes of the rate functions decreased as stimulus frequency region increased. Suppression tuning curves (STCs) were generated in the same three frequency regions and with L1 at either 70 or 55 dB SPL and L2 adjusted individually for each ear. The tips of the STCs were at frequencies associated with f1 and f2. The tip regions of the STCs for the 4-kHz stimulus condition were more complex in that they contained more multiple minima than did those for the 1- and 2-kHz regions. Results confirm that optimal suppression of the 2f1-f2 DPOAE occurs for frequencies in the vicinity of f1 and f2 rather than at 2f1-f2.

Acoustic Stimulation↗
PubMed1992

Cochlear microphonics and recruitment.

In this study, bilateral cochlear microphonics (CM) were evoked by tone burst simultaneously. A speaker was put in head-food axis 2 m from the mid-point of a given line connecting the bilateral external meatus. Five normal persons and 68 cases (34 cases of Meniere's disease, 27 cases of sudden hearing loss, and 7 cases of low-tone sensory hearing loss without vertigo) with unilateral sensory hearing loss and recruitment, in addition to 2 cases of bilateral Meniere's disease with recruitment were examined. CM shifted in normal and hearing loss ears and was absent in profound and totally deaf ears. When recruitment was present, CM at corresponding frequencies were enlarged and prolongated in 60 cases. Some of the enlarged and prolongated CM decayed slowly, others quickly. Meanwhile the CM of the opposite normal ear decreased obviously. The presence of enlarged and prolongated CM may indicate an increase of abnormal excitability of the hair cells caused by some pathological stimulations. This would cause excitability of the hair cells in the opposite cochlea to be inhibited by the effect of the efferent system. In such a condition, the patients complained that the stimulating sound was heard louder in the disordered ear than that in the opposite normal ear. CM was slightly enlarged during sleep.

Adult↗
PubMed1992

Gene transfer in vivo with DNA-liposome complexes: safety and acute toxicity in mice.

DNA can be introduced into a variety of cell types after formation of liposomal complexes with cationic lipids. In this report, conditions have been established to optimize the production of DNA-liposome complexes that efficiently transfect cells. The safety and toxicity of this method of gene delivery have been assessed after in vivo administration, either by intravenous or direct intratumor injection. Nine to eleven days after intravenous injection, DNA was found primarily in heart and lung tissue by PCR analysis. No abnormalities were evident from histologic examination of tissue, examination of tissue-specific serum enzymes, routine biochemical parameters, or electrocardiographic monitoring. DNA-liposome complexes can therefore be used for the delivery of recombinant genes in vivo with minimal toxicity.

Animals↗
PubMed1992

Gene transfer in vivo with DNA-liposome complexes: lack of autoimmunity and gonadal localization.

Direct gene transfer into localized arterial segments can be performed in vivo by transfection with DNA-liposome complexes. This technique holds promise for the treatment of human diseases, including malignancy and cardiovascular disorders. We have previously characterized the potential toxicity of this form of treatment in mice in vivo (Stewart et al., 1992). In this report, we examined two issues relevant to long-term expression of foreign recombinant genes: (i) the potential for autoimmune damage to major organs and (ii) DNA localization in gonadal tissue. Autoimmunity and toxicity of allogeneic major histocompatibility (MHC) gene transfer was assessed in mice after induction of an immune response to a recombinant murine class I MHC gene by direct gene transfer in vivo. Histological examination of brain, heart, lung, liver, kidney, spleen, and skeletal muscle revealed no clinically significant immunopathology or organ damage. The toxicity of gene delivery by DNA liposomes was also analyzed in pigs and rabbits in vivo. No histopathology was observed following the introduction of plasmids encoding several different gene products, and analysis of serum following DNA liposome delivery revealed no abnormalities of serum biochemical parameters. The potential for transfer of recombinant DNA into testes and ovary in animals was evaluated by the polymerase chain reaction. Although evidence of recombinant plasmid was consistently observed in transfected, but not untransfected, arterial sites and occasionally in lung, kidney, spleen, and liver, no plasmid DNA was detected in testes or ovary. These studies suggest that uptake of recombinant DNA following direct gene transfer by liposomal transfection in major organs is not associated with autoimmunity, toxicity, or gonadal localization.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Properties of B cell stage specific and ubiquitous nuclear factors binding to immunoglobulin heavy chain gene switch regions.

The Ig heavy chain (IgH) constant region (CH) class switch is manifested by DNA deletions which exchange the C mu gene of a functional VDJ-CH rearrangement for a C gamma, C epsilon or C alpha gene. Repetitive sequences (S regions) 5' of each CH gene mediate CH gene switch recombination by an illegitimate mechanism. S mu can be subdivided into S mu 5' (non-repetitive) and S mu 3' (repetitive) components with recombination occurring in either part. Here, we describe the properties of ubiquitous and B cell stage specific S mu binding factors NFS mu-U1 and NFS mu-B1 respectively. U1 only bound to S mu 5' sequences, and B1 to S mu 5', S mu 3' sequences and to other S regions with varying affinities. DMS and OP-Cu footprinting revealed the sequence AAAAAGCATGGCTGA in the U1 site while the B1 S mu 5' site overlapped the 3' end of the U1 binding site and also contained additional 3' flanking S mu repeat motifs (GAGCTGAGATGGGTGGGCT). Binding site competition assays reveal that NFS mu-B1 is either very related or identical to S alpha BP (described by Waters et al., Mol. Cell Biol. 9:5594, 1989) and BSAP (identified by Barberis et al., Genes Devl. 4:849, 1990) which were shown to bind to two sequences upstream of the S alpha repeats and within the promoters of sea urchin histone genes respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Nucleotide sequence, function, activation, and evolution of the cryptic asc operon of Escherichia coli K12.

The cryptic asc (previous called "SAC") operon of Escherichia coli K12 has been completely sequenced. It encodes a repressor (ascG); a PTS enzyme IIasc for the transport of arbutin, salicin, and cellobiose (ascF); and a phospho-beta-glucosidase that hydrolyzes the sugars which are phosphorylated during transport (ascB). ascG and ascFB are transcribed from divergent promoters. The cryptic operon is activated by the insertion of IS186 into the ascG (repressor) gene. The ascFB genes are paralogous to the cryptic bglFB genes, and ascG is paralogous to galR. The duplications that gave rise to these paralogous genes are estimated to have occurred approximately 320 Mya, a time that predates the divergence of E. coli and Salmonella typhimurium.

Amino Acid Sequence↗
PubMed1992

Salivary anti-candidal assays.

Inhibition of Candida albicans blastospore viability by parotid, submandibular-sublingual and whole salivas could not be determined by direct assay of yeast cells in each respective saliva. Determination of antifungal activity could, however, be carried out if saliva was first preincubated with Candida cells and this was immediately followed by removal of saliva and resuspension of yeast cells in nonenriched buffers of pH 5-7 for appropriate incubation periods. To attain accurate reproducible quantitative data, parotid, submandibular-sublingual and whole salivas each required different preincubation times with C. albicans as well as prior acidification and boiling. Acidification was also necessary for optimizing the germ tube assay although, in contrast to blastospore viability, inhibition of blastospore-germ tube conversion could be determined directly in saliva. Salivary antifungal effects on blastospore division were negligible at yeast cell concentrations greater than 10(6) colony-forming units per ml and were found to be independent of pH, whereas salivary inhibition of germ tube formation was significant only at pH 5 in the assay systems employed. The requirement for acidification and an observed enhancement of antifungal activity on aqueous dilution of the saliva suggested that only a fraction of the salivary antifungal components present in saliva were available in the free form to exert their biological activity. These results open up the possibility of investigating salivary antifungal activity in human health and disease.

Antifungal Agents↗
PubMed1992

One-step purification of histidine-rich polypeptides form human parotid saliva and determination of anti-candidal activity.

Immunoadsorption affinity chromatography was used to selectively purify the family of the histidine-rich polypeptides (HRPs) from human parotid saliva. The immunoadsorbent was prepared by coupling an enriched preparation of horse anti-(HRPs 2, 3, 4, 5 and 6) IgG to protein G. Both freshly collected stimulated untreated and acidified boiled salivas (5 ml) were applied to the affinity column. When native saliva was used it appeared that all of the components of saliva, with the exception of the HRPs, were present in the fraction nonadsorbed to the affinity column; however, recovery of the HRPs with 0.2 M sodium acetate-HCl, pH 1.8, was poor. Yields of HRPs desorbed from the column with the pH 1.8 treatment were significantly improved if salivary HRP proteolysis was delayed immediately after collection by acidifying the saliva to pH 4.5 followed by a short boiling time period, which neither affected HRP quantification nor biological activity. Affinity chromatography results were checked both by cationic polyacrylamide gel and by capillary electrophoresis. Antifungal activity was found to reside only in the low pH HRP fraction of the immunoadsorbent column, suggesting that it is the histidine-rich family of polypeptides that is responsible for salivary antifungal action.

Antifungal Agents↗