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Biomedical subjects

Y S Cheng

Publications and source records attributed to Y S Cheng.

At least 127 records · Page 7Linked to original sources
PubMed1983

Different mRNAs induced by interferon in cells from inbred mouse strains A/J and A2G.

Treatment of cells from inbred mouse strains A/J and A2G with interferon resulted in the development of different antiviral states for influenza viruses. A2G mice-derived cells that carry the resistance gene Mx were efficiently protected by interferon against influenza viruses, whereas the interferon protection against the same viruses in wild-type A/J mice-derived cells was only marginal. The two cell types, however, were equally protected by interferon against vesicular stomatitis virus and other non-orthomyxoviruses. The interferon-induced mRNAs of mouse embryonic fibroblast cells that carried either homozygous wild-type alleles or homozygous Mx alleles were compared. The isolated polysome-bound mRNAs from A/J (+/+) and A2G (Mx/Mx) cells were translated in a cell-free translation system, and the translation products were analyzed after two-dimensional gel electrophoresis. New mRNAs coding for at least eight proteins with molecular weights (MW) ranging from 30,000 to 80,000 were found in interferon-treated cells but not in control cells. Differences in the interferon-induced mRNAs from A/J and A2G cells were also found. An mRNA coding for a 72,000-MW protein was found in interferon-treated A2G cells but not in interferon-treated A/J cells. Interferon-treated A/J cells, on the other hand, contained an mRNA coding for a 65,000-MW protein that was not found in interferon-treated A2G cells. The in vitro-synthesized 65,000-MW protein efficiently bound to GMP. Cytoplasmic extracts prepared from interferon-treated A/J cells also contained a GMP-binding 65,000-MW protein that was undetectable in similarly treated A2G cells.

Animals↗
PubMed1982

Elemental analysis of freeze-dried thin sections of Samanea motor organs: barriers to ion diffusion through the apoplast.

Leaflet movements in the legume Samanea saman are dependent upon massive redistribution of potassium (K), chloride (Cl), and other solutes between opposing (extensor and flexor) halves of the motor organ (pulvinus). Solutes are known to diffuse through the apoplast during redistribution. To test the possibility that solute diffusion might be restricted by apoplastic barriers, we analyzed elements in the apoplast in freeze-dried cryosections of pulvini using scanning electron microscopy/x-ray microanalysis. Large discontinuities in apoplastic K and Cl at the extensor-flexor interface provide evidence for a barrier to solute diffusion. The barrier extends from the epidermis on upper and lower sides of the pulvinus to cambial cells in the central vascular core. It is completed by hydrophobic regions between phloem and cambium, and between xylem rays and surrounding vascular tissue, as deduced by discontinuities in apoplastic solutes and by staining of fresh sections with lipid-soluble Sudan dyes. Thus, symplastic pathways are necessary for ion redistribution in the Samanea pulvinus during leaflet movement. In pulvini from leaflets in the closed state, all cells on the flexor side of the barrier have high internal as well as external K and Cl, whereas cells on the extensor side have barely detectable internal or external K or Cl. Approximately 60% of these ions are known to migrate to the extensor during opening; all return to the flexor during subsequent closure. We propose that solutes lost from shrinking cells in the outer cortex diffuse through the apoplast to plasmodesmata-rich cells of the inner cortex, collenchyma, and phloem; and that solutes cross the barrier by moving through plasmodesmata.

Cell Wall↗
PubMed1981

Detection of phosphotyrosine-containing 34,000-dalton protein in the framework of cells transformed with Rous sarcoma virus.

Phosphotyrosine-containing 34,000-dalton protein is detected by treatment of a two-dimensional gel of cellular framework with 1 M NaOH at 40 degrees C for 1 hr. The alkali-resistant 32PO4-labeled 34,000-dalton protein is detected in various cell lines transformed by Rous sarcoma virus but not in lines transformed by simian virus 40, polyoma virus, herpes simplex II virus, adenovirus type 2, or chemical carcinogens. In addition, interferons or fibronectin matrices have no detectable effect on the phosphorylation of the 34,000-dalton protein in Rous sarcoma virus-transformed cells.

Animals↗
PubMed1981

A model for aerosol deposition in the human tracheobronchial region.

An aerosol deposition model in the human tracheobronchial tree based on impaction and sedimentation is proposed. Using this model, a mean deposition radius of conducting airways can be obtained from in vivo T-B deposition data or from physical dimensions of human lung casts. Agreement was found between the model and deposition data for three normal healthy subjects in the literature. Contributions of sedimentation to T-B deposition is estimated to be 42 - 78% at 250 cm3/sec average inspiration flow rate, and decreased to 8-29% at 750 cm3/sec average inspiration flow rate. Mean deposition radii are estimated to be 0.33 to 0.43 cm and correlate with pulmonary functional residual capacities.

Aerosols↗
PubMed1981

Expression of keratin and vimentin intermediate filaments in rabbit bladder epithelial cells at different stages of benzo[a]pyrene-induced neoplastic progression.

Rabbit bladder epithelium, grown on collagen gels and exposed to the chemical carcinogen benzo[a]pyrene, produced nontumorigenic altered foci as well as tumorigenic epithelial cell lines during 120-180 d in culture. Immunofluorescence studies revealed extensive keratin filaments in both primary epithelial cells and benzo[a]pyrene-induced altered epithelial foci but showed no detectable vimentin filaments. The absence of vimentin expression in these cells was confirmed by two-dimensional gel electrophoresis. In contrast, immunofluorescence staining of the cloned benzo[a]pyrene-transformed rabbit bladder epithelial cell line, RBC-1, revealed a reduction in filamentous keratin concomitant with the expression of vimentin filaments. The epithelial nature of this cell line was established by the observation that cells injected into nude mice formed well-differentiated adenocarcinomas. Frozen sections of such tumors showed strong staining with antikeratins antibodies, but no detectable staining with antivimentin antibodies. These results demonstrated a differential expression of intermediate filament type in cells at different stages of neoplastic progression and in cells maintained in different growth environments. It is apparent that the expression of intermediate filaments throughout neoplastic progression is best studied by use of an in vivo model system in parallel with culture studies.

Animals↗
PubMed1981

Association of phenotypic reversion of transformed cells induced by interferon with morphological and biochemical changes in the cytoskeleton.

The distribution of microfilament bundles, intermediate filaments, microtubules, vinculin plaques, and extracellular fibronectin matrices was examined by indirect immunofluorescence in X-ray-transformed C3H/10T1/2 cells. The transformed phenotype correlated with a lack of actin cables and vinculin-containing plaques. Prolonged treatment of these transformed cells with interferon resulted in a reversion of the transformed phenotype which was associated with the reappearance of extensive microfilament bundles together with vinculin-containing plaques. Both interferon-treated and untreated transformed cells displayed a similar distribution of mitochondria, intermediate filaments, microtubules, and fibronectin. Significant qualitative and quantitative differences between the two types of cells were found in the proteins associated with the cytoskeletal framework by two-dimensional gel analysis.

Animals↗
PubMed1979

Purification and characterization of protease III from Escherichia coli.

An endoproteolytic enzyme of Escherichia coli, designated protease III, has been purified about 9,600-fold to homogeneity with a 6% yield. The purified enzyme consists of a single polypeptide chain of Mr 110,000 and is most active at pH 7.4. Protease III is very sensitive to metal-chelating agents and reducing agents. The EDTA-inactivated enzyme can be reactivated by Zn2+, Co2+ or Mn2+. Protease III is devoid of activity toward aminopeptidase, carboxypeptidase, or esterase substrates but rapidly degrades small proteins. When fragments of beta-galactosidase are used as substrates for protease III, the enzyme preferentially degrades proteins with molecular weights of less than 7,000. Protease III cleaves the oxidized insulin B chain at two sites with an initial rapid cleavage at Tyr-Leu (16-17) and a second slower cut at Phe-Tyr (25-26).

Cations, Divalent↗
PubMed1979

Isolation and characterization of mutations in the structural gene for protease III (ptr).

Escherichia coli mutants defective in protease III were isolated by enzyme assays of heavily mutagenized colones. One mutant produced thermolabile enzyme, and it is presumed to have a mutation in the structural gene of protease III. Two other mutants mapping at the same site had less than 5% of the wild-type protease III level. The genetic locus of these mutations, designated ptr, was located at approximately 60 min on the E. coli linkage map based on its high frequency (70%) of contransduction by P1 with argA. Strains with less than 5% of the wild-type protease III activity grew normally and degraded nonsense fragments of beta-galactosidase at wild-type rates.

Chromosome Mapping↗
PubMed1978

Characterization of a Bacillus cereus protease mutant defective in an early stage of spore germination.

Temperature-sensitive sporulation mutants of Bacillus cereus were screened for intracellular protease activity that was more heat labile than that of the parental strain. One mutant grew as well as the wild type at 30 and 37 degrees C but sporulated poorly at 37 degrees C in an enriched or minimal medium. These spores germinated very slowly in response to alanine plus adenosine or calcium dipicolinate. During germination, spores produced by the mutant rapidly became heat sensitive, but released dipicolonic acid and mucopeptide fragments more slowly than the wild type and decreased only partially in density while remaining phase white (semirefractile). In freeze-etch electron micrographs, the mature spores were deficient in the outer cross-patched coat layer. During germination, the spore coat changes associated with wild-type germination occurred very slowly in this mutant. Although the original mutant was also a pyrimidine auxotroph, reversion to prototrophy did not alter any of the phenotypic properties discussed. Selection of revertants that germinated rapidly or sporulated well at 37 degrees C, however, resulted in restoratin of all wild-type properties (exclusive of the pyrimidine requirement) including heat-stable protease activity. The reversion frequency was consistent with an initial point mutation, indicating that a protease alteration resulted in production of spores defective in a very early stage of germination.

Bacillus cereus↗
PubMed1977

Characterization and function of intracellular proteases in sporulating Bacillus cereus.

Intracellular proteases from sporulating Bacillus cereus have been purified by ammonium sulfate fractionation, heat treatment and DEAE cellulose column chromatography. After the last purification step, two protease activities, with an activity ratio of about thirty to one are resolved. Both proteases are resistant to o-phenanthroline but sensitive to phenyl methyl sulfonyl fluoride. Their separation by polyacrylamide gel electrophoresis and DEAE cellulose column chromatography, their difference in heat sensitivity and a mutation affecting only the major intracellular protease (IP1) suggest that the two are products of distinct genes. An IP1 mutant previously shown to produce coat defective spores (4) also turnsover protein with a reduced rate during late sporulation stages. Correlated with the slower turnover rate in this mutant is the more rapid disappearance of IP1. A partial revertant of this mutant has a protein turnover rate intermediate between that of the original mutant and wild type. These correlations imply that IP1 has an important role in protein turnover during sporulation.

Bacillus cereus↗
PubMed1977

Pregnancy in liver cirrhosis and/or portal hypertension.

Clinical features of pregnancy in women with liver cirrhosis and/or portal hypertension have been reviewed. Termination of pregnancy is seldom indicated in a woman with compensated cirrhosis or a young woman with extrahepatic venous obstruction. However, the risk of spontaneous abortion is increased in cirrhotic women without shunt even if there is no deterioration of liver function. The risk of bleeding from esophageal varices or deterioration of liver function is usually unpredictable. Shunt surgery can be done with relatively little effect on both the mother and the fetus if conservative measurements fail to control the hematemesis. Vaginal delivery can be anticipated in most women, and cesarean section should be preserved for obstetric indications. The risk of postpartum hemorrhage is greatly increased, particularly in patients with previous shunt surgery. Perinatal loss is high because of the increased rate of premature delivery and stillbirth. Maternal prognosis is grave in women with cirrhosis.

Abortion, Spontaneous↗
PubMed1977

Alterations of spore coat processing and protein turnover in a Bacillus cereus mutant with a defective postexponential intracellular protease.

A mutant with an alteration in the major intracellular serine protease produced by postexponential Bacillus cereus was isolated by screening mutants defective in spore germination. The purified enzyme from the mutant is more labile to heat and alkaline pH than the protease from the wild type. Protease activity appears at the same time as in the wild type but only reaches 50% of the specific activity and decays more rapidly during sporulation. Coincident with the decay is a decrease in the rate of protein turnover. Generation of amino acids by turnover seems to be important for sporulation because the number of spores produced by the mutant is increased 4- to 10-fold by addition of casamino acids. As anticipated, the mutant produces spores that germinate poorly but, surprisingly, these spores are very deficient in coat protein. Coat antigen is present in cell extracts of mutant and wild type, however, both as large molecules not found on mature spores and as spore coat protein monomers. The large molecules rapidly disappear in a pulse chase experiment in the wild type with some increase in the coat monomers. In mutant extracts, however, this large coat antigen is slowly and improperly processed.

Antigens, Bacterial↗