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Biomedical subjects

C C Kao

Publications and source records attributed to C C Kao.

At least 91 records · Page 5Linked to original sources
PubMed1990

Dissection of functional domains in the adenovirus 2 early 1B 55K polypeptide by suppressor-linker insertional mutagenesis.

To determine whether the viral replication functions of the adenovirus E1B 55K protein play a role in its ability to transform cloned rat embryo fibroblast cells in culture, we constructed an extensive series of insertion mutations throughout the 55K gene. The mutations were recombined into infectious virus and characterized for their abilities to produce stable 55K protein in HeLa cells, replicate virus in HeLa cells, express late viral proteins efficiently, and transform CREF cells following infection. Mutant 55K transforming activity in primary baby rat kidney cells was also assayed following DNA transfection. The functions required for viral replication are encoded in several patches of the 55K linear sequence, while the CREF transforming functions are sensitive to all of the insertions. An insertion at amino acid 380 created a mutant virus which was reduced in transforming activity, but was not reduced for viral replication. Therefore, a function required for efficient transformation of CREF cells can be separated from functions required for late gene expression and viral replication. Transformation of BRK cells following DNA transfection was reduced by complete disruption of the 55K protein gene, but was not significantly affected by any of the insertions.

Adenovirus Early Proteins↗
PubMed1990

Domains required for in vitro association between the cellular p53 and the adenovirus 2 E1B 55K proteins.

The 55K protein encoded by the adenovirus 2 E1B gene is required for complete cellular transformation and binds the cellular protein p53. Using an in vitro immunoprecipitation assay, we mapped the domains in both 55K and p53 required for the interaction of the two proteins. The domain in p53 mapped to the amino terminal 123 residues. There are several domains in the 495 residue 55K polypeptide which contribute to stable association with p53, with the most essential region mapping between residues 224 and 354. Mutations which prevented 55K-p53 binding were not more defective for transformation than other mutations which did not affect binding.

Adenovirus Early Proteins↗
PubMed1989

Yeast TATA-box transcription factor gene.

The first step in the transcription of most protein-encoding genes in eukaryotes is the binding of a transcription factor to the TATA-box promoter element. This TATA-box transcription factor was purified from extracts of the yeast Saccharomyces cerevisiae by using reconstitution of in vitro transcription reactions as an assay. The activity copurified with a protein whose sodium dodecyl sulfate/polyacrylamide gel mobility is 25 kDa. The sequence of the amino-terminal 21 residues of this protein was determined by sequential Edman degradation. A yeast genomic library was screened with mixed oligonucleotides encoding six residues of the protein sequence. The yeast TATA-box factor gene was cloned, and DNA sequencing revealed a 720-base-pair open reading frame encoding a 27,016-Da protein. The identity of the clone was confirmed by expressing the gene in Escherichia coli and detecting TATA-box factor DNA binding and transcriptional activities in extracts of the recombinant E. coli. The TATA-box factor gene was mapped to chromosome five of S. cerevisiae. RNA blot hybridization and nuclease S1 analysis indicated that the major TATA-box factor mRNA is 1.3 kilobases, including an unusually long 5' untranslated region of 188 +/- 5 nucleotides. Homology searches showed a region of distant similarity to the calcium-binding structures of calpains, a structure that has a conformation similar to the helix-turn-helix motif of DNA binding proteins.

Amino Acid Sequence↗
PubMed1989

Topical growth factors and wound contraction in the rat: Part II. Platelet-derived growth factor and wound contraction in normal and steroid-impaired rats.

The wound contraction model described in Part I was used to study topically applied, recombinant platelet-derived growth factor (rPDGF-BB) and wound contraction in normal and steroid-impaired rats. Circular wounds 4 cm in size were made on the dorsum of the rats with halothane anesthesia. Five groups of 20 normal rats each were treated with the vehicle alone and four concentrations of rPDGF-BB (0.5, 1.0, 3.0, and 10.0 micrograms/ml). Four groups of 20 steroid-impaired rats each were treated with the vehicle alone and three concentrations of rPDGF-BB (0.5, 1.0, and 3.0 micrograms/ml). The wounds were dressed with 2 x 2 gauze, Adaptic, 4 x 4 gauze, and Tubigrip. The investigators were blinded to the treatments until the completion of the experiment, and the treatments were applied in random order. Dressings were changed every 2 to 3 days for 14 days and the wound areas were determined, expressed as a fraction of the original, and plotted versus time. The areas under the curves and the means of the fraction open each day were compared between groups using Student's t-test. The treatment with 3.0-micrograms/ml rPDGF-BB accelerated the rate of wound contraction in the steroid-impaired animals (p less than 0.05).

Administration, Topical↗
PubMed1986

Evaluation of aztreonam, cefoperazone, latamoxef and ceftazidime in the hamster colitis model.

Aztreonam, ceftazidime, cefoperazone and latamoxef (moxalactam) were evaluated in a hamster model for antibiotic-associated colitis. Aztreonam, a novel monocyclic beta-lactam antibiotic specifically directed against aerobic Gram-negative bacteria with limited activity against Gram-positive and anaerobic bacteria did not cause haemorrhagic caecitis and death in hamsters when administered intraperitioneally or orally. Quantitative caecal cultures showed no changes in the anaerobic caecal microflora of hamsters treated intraperitoneally with aztreonam and only a temporary decrease in anaerobic Gram-negative bacilli in hamsters treated orally. Clostridium difficile and its cytotoxin were not present in these animals. Parenteral administration of ceftazidime also did not affect the anaerobic caecal microflora or cause caecitis. However, when given orally, ceftazidime suppressed the anaerobic caecal microflora and a lethal C. difficile-induced caecitis developed. Latamoxef or cefoperazone given parenterally resulted in caecitis and death in five days with marked changes in the anaerobic caecal microflora and C. difficile present in the caecal contents of these animals. The lethal haemorrhagic caecitis observed in this study was indistinguishable from that seen in the clindamycin-induced colitis model in the hamster. The possible correlation of these findings to gastrointestinal disturbances as a complication of antibiotic therapy in humans is discussed.

Administration, Oral↗
PubMed1984

Observation of cultured peripheral non-neuronal cells implanted into the transected spinal cord.

We have previously reported that cultured peripheral non-neuronal cells could be used as an adjunct to spinal cord reconstruction with the delayed nerve graft technique. The cultured cells appeared to enhance axonal regeneration and with their use the time it took for axons from the spinal cord stumps to reach the nerve graft was reduced. To gain insight into the possible mechanisms through which peripheral non-neuronal cells can foster CNS regeneration, we have now investigated the behaviour of the peripheral non-neuronal cells after implantation into the spinal cord. Autologous mixed non-neuronal cell cultures were prepared from cat sciatic nerve biopsies and labeled in culture with tritiated thymidine. The labeled cells were implanted so as to completely fill the gap in the spinal cord produced by a narrow "slit transection". Light-and electron-microscopic autoradiography was used to identify the cells 3 and 7 days after implantation and to determine their proximity to, and possible interaction with, axons in the spinal cord stumps. The implanted peripheral cells were frequently found near spinal cord axons and axon terminals. Some of the labeled cells ensheathed axons in which case they displayed morphological characteristics of Schwann cells. Other labeled cells had characteristics of fibroblasts and were surrounded by an extracellular matrix rich in collagen fibrils. Many of the labeled cells contained phagocytosed myelin debris. These observations are consistent with the implanted cells acting to enhance regeneration in the spinal cord either by direct interaction with axons (ensheathment) or indirectly via the production of soluble neuronotrophic factors or a favorable extracellular matrix. The ability of the implanted cells to rapidly move into the spinal cord stumps and attain positions close to spinal cord axons would be an important factor for any of these mechanisms.

Animals↗
PubMed1983

Sulfur metabolism in the biosynthesis of monobactams.

We studied the biosynthesis of monobactams with respect to sulfur metabolism in Chromobacterium violaceum, Acetobacter sp., and Agrobacterium radiobacter. All three organisms used inorganic sulfur for monobactam production. When sulfur-containing amino acids were assayed as a source of sulfur for monobactam production, C. violaceum used cystine but not cysteine or methionine, Acetobacter sp. used all three compounds, and A. radiobacter used none. 35S from cysteine, methionine, and sodium sulfate was incorporated into monobactam by Acetobacter sp. Cell-free extracts of all three organisms were shown to possess cysteine desulfhydrase activity. In Acetobacter sp., this activity was constitutive, required pyridoxal phosphate, and had a pH optimum of 9.5. Extensive loss of 3H from L-[3-3H]cysteine was seen upon desulfhydration; no evidence of serine formation was found. Active sulfate was formed in cell-free extracts of A. radiobacter, and, since inorganic sulfur was used by all three organisms, it is likely that the sulfamate group of monobactams is produced via active sulfate.

Acetobacter↗
PubMed1982

Reconstruction of the contused cat spinal cord by the delayed nerve graft technique and cultured peripheral non-neuronal cells.

Previously, surgical reconstruction of the transected dog spinal cord by the delayed nerve graft technique has been shown to result in reinnervation of the nerve graft by axons. In the present study, we compared the results of surgical reconstruction of the severely contused cat spinal cord by the delayed nerve graft technique alone to those after reconstruction with a similar nerve graft plus cultured peripheral non-neuronal cells implanted between the grafted nerve and the spinal cord stumps. The spinal cord-nerve graft junction was examined by light and electron microscopy. The cultured cells were prelabelled with tritiated thymidine and their location after implantation determined by autoradiography. By 3 days after spinal cord reconstruction, the prelabelled cells were present at the junction and had migrated into the nerve graft and also into the spinal cord stumps where they were observed near axons. By 7 days, physical connections were observed bridging the junction between the spinal cord and nerve graft and axons ensheathed by Schwann cells had already penetrated at least 1 mm into the nerve graft. Wound healing took at least a week longer in animals repaired with a nerve graft alone. At one year or later after reconstructive surgery, in both groups of animals, the grafted nerve was reinnervated with myelinated and unmyelinated axons. Thus, the severely contused cat spinal cord could be reconstructed with the delayed nerve graft technique alone but the use of the cultured cells appeared to enhance wound healing and decrease the time required for axon elongation into the nerve graft.

Animals↗
PubMed1981

Non-neuronal cell cultures from dorsal root ganglia of the adult cat: production of Schwann-like cell lines.

There are several methods available for the production of Schwann cell cultures from fetal and neonatal peripheral nervous tissue. We have investigated methods for producing Schwann cell-rich cultures from adult tissue. Dorsal root ganglia from normal adult cats were used to initiate explant cultures or subjected to primary dissociation. The resulting cultures were compared in terms of growth, the proportions of fibroblastic and Schwann-like cells in primary cultures and the effects of subculture on the relative frequency of these cell types. We found that excision and transfer of explanted ganglion pieces after 14 days in culture produced a secondary outgrowth rich in small, bipolar, spindle-shaped Schwann-like cells. Subculture of this outgrowth produced secondary cultures of predominantly Schwann-like cells with typical spindle-shaped morphology. The use of antimitotic agents in the media to inhibit fibroblast growth was not observed to be necessary or beneficial with this adult tissue. Primary dissociation of ganglia with enzymes (trypsin or collagenase) and mechanical agitation was even more effective in producing secondary cultures and cell lines that were, by morphological criteria, predominantly or exclusively Schwann-like cells. One of these Schwann-like cell lines, designated GSA, has been carried over 24 subcultures while retaining characteristic Schwann cell morphology. Cells of this line have been examined by scanning and transmission electron microscopy. Karyotype analysis indicates a chromosome complement consistent with the species of origin, a normal cat.

Animals↗
PubMed1981

Cultures enriched in Schwann-like cells from dissociated nerve segments of the adult cat.

Methods for producing Schwann cell-rich cultures from nerve segments of the adult cat were investigated. Efficient dissociation was achieved with a combination of collagenase and trypsin. Differential attachment of elements within the resulting suspension allowed production of Schwann cell-rich cultures derived by outgrowth from slowly attaching segments of degenerating myelin sheath tube containing Schwann-like cells. Rapid trypsinization during subculture further increased the proportion of Schwann-like cells in these cultures to 90% or more.

Animals↗
PubMed1980

An ultrastructural study on the reactive oligodendrocytes, myeloclasts, and myelophages in transected dog spinal cord.

As early as 1 to 3 hr after cord transection, proliferation of many reactive oligodendrocytes was observed. Bundles of microfilaments and microtubules were observed in those cells that sent out long, complex pseudopodlike processes near the area of injury. These reactive oligodendrocytes may be comparable to Vaughn's multipotential glia cells. Between 1 day and 1 wk, hypertrophy of the oligodendrocytes was observed. These hypertrophied oligodendrocytes also became hyperactive and infiltrated into the axons within the myelin sheath. These infiltrating hyperactive oligodendrocytes had a scanty fibrillary cytoplasm and are believed to correspond to Jakob's "myeloclasts". The infiltration of macrophages into the nerve fibers and myelin sheaths was also observed. These macrophages were found to be very active in phagocytosis and removal of degenerated debris within the nerve fiber and are believed to represent the "myelophages" described by Jakob in 1913.

Animals↗
PubMed1977

Concentration and dilution of the urine in partially hepatectomized, conscious rats.

1. The influence of partial hepatectomy on urinary concentrating ability and renal tissue sodium was determined in conscious rats deprived of water for 24 h. In comparison with a sham operation, partial hepatectomy resulted in: a) a 50% reduction in free-water reabsorption, urinary osmolality, and osmolal urine-to-plasma ratio; b) depression of free-water reabsorption at similar levels of osmolal clearance above 200 microliter/min per ml of GFR during the infusion of hypertonic NaCl and vasopressin; and c) a 30% reduction in sodium content of the renal papilla and outer medulla. 2. The renal response to an intravenous water load (2.5% glucose infused to 2.5% of body wt at 0.4 ml/min) was determined in sham-operated and partially hepatectomized, conscious rats. By 60 min after the water load, both groups had excreted practically all of the load. However, during and for 30 min after the infusion in the partially hepatectomized group, the percent of the water load excreted, urine flow, and free-water clearance were significantly reduced while urinary osmolality and osmolal urine-to-plasma ratio were significantly elevated. 3. These experiments demonstrate that shortly after partial removal of the liver the renal concentrating ability is defective and the excretion of a water load is not grossly impaired.

Animals↗
PubMed1977

Right-hemisphere language dominance in a case of left-hemisphere arteriovenous malformation.

This paper reports a case of surgical removal of a left-hemisphere arteriovenous malformation (AVM) in a left-handed adult without subsequent speech or language deficit. Preoperative intracarotid amobarbital testing indicated right-hemisphere language dominance. Our patient demonstrated no language involvement prior to or following surgery. We speculate the congenital nature of a left-hemisphere AVM may dictate right-hemisphere language dominance, thereby explaining the lack of residuals following removal of AVMs in left-hemisphere speech and motor areas.

Adult↗
PubMed1977

Electron microscopic observations of the mechanisms of terminal club formation in transected spinal cord axons.

Following transection of spinal cords, axoplasmic flow occurred in the axons both proximal and distal to the transection. In the proximal axonal stump, the direction of flow was proximo-distal whereas in the distal axonal stump the direction of flow was disto-proximal. Thus the flows in transected axons were all directed toward the point of transection. Electron microscopic observation of the spinal cord tissue bordering at the cut ends of spinal cord stumps showed various structural changes in the axons and myelin sheaths of the transected fibers near the cut ends which interfered with the axoplasmic flow leading to the formation of the terminal clubs. Five prototypes of changes in axons and myelin sheaths near the cut ends of fibers are described and the mechanism of terminal club formation is discussed. It seemed that the terminal clubs within the transected spinal cord stumps rere of the axoplasmic flow toward the cut ends of the fibers, and (2) interference by structural changes which developed within individual fibers consequent to spinal cord injury.

Animals↗