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Biomedical subjects

E Cheung

Publications and source records attributed to E Cheung.

At least 37 records · Page 2Linked to original sources
PubMed1995

Nucleotide sequence and characterization of the Saccharomyces cerevisiae RPL19A gene encoding a homolog of the mammalian ribosomal protein L19.

A gene designated RPL19A has been identified in the region downstream from the 3'-end of the Saccharomyces cerevisiae MIS1 gene encoding the mitochondrial C1-tetrahydrofolate synthase. The gene codes for the yeast ribosomal protein YL19 which exhibits 57.5% identify with the mammalian ribosomal protein L19. RPL19A is one of two functional copies of the YL19 gene located on chromosome II. The disruption of RPL19A has no effect on the growth of the yeast. The RPL19A gene contains an intron located near the 5'-end. The 5'-flanking region contains one similar and one complete UASrpg upstream activating sequence. RPL19A was also found to be adjacent to the chromosome II AAC3 gene, encoding the mitochondrial ADP/ATP carrier protein.

Amino Acid Sequence↗
PubMed1994

Altered responses to hypoglycemia of healthy elderly people.

Many elderly people are treated with medications or are subjected to diseases which can cause hypoglycemia. We conducted the following studies to assess whether alterations in counterregulatory hormone release, decreased awareness of warning symptoms or alterations in psychomotor performance might increase the susceptibility of the elderly to hypoglycemia. Healthy, nonobese young (n = 10, age < 30) and old (n = 9, age > 65) subjects underwent paired hyperinsulinaemic clamp studies (insulin infusion rate 60 mU/m2.min). In the control study, glucose was kept at 5.0 mmol/L for 5 h. In the hypoglycemic study, glucose was kept at 5 mmol/L for 1 h and was lowered in stepwise fashion to 4.4, 3.8, 3.3, and 2.8 mmol/L in each subsequent hour. Subjects were blinded as to which study they were undergoing. Counterregulatory hormones were measured and a hypoglycemic symptom checklist was administered every 15 min in each study. Neuropsychological tests were performed at regular intervals. The glucose threshold for release of counterregulatory hormones was defined as the glucose level at which the values during the hypoglycemic study first exceeded values during the control study by 2 SD. The glucose threshold for glucagon and epinephrine release was higher in the young (approximately 3.3 mmol/L) than the old (approximately 2.8 mmol/L) and the epinephrine responses to hypoglycemia were also greater in the young. The threshold for release of GH (approximately 3.3 mmol/L) and norepinephrine and cortisol (approximately 2.8 mmol/L) was similar in each age group, as was the magnitude of release of these hormones. Although the variance in symptoms scores was large, the elderly appeared to have reduced awareness of the autonomic but not neuroglycopenic symptoms of hypoglycemia. There was no difference between young and old in the effect of hypoglycemia on neuropsychologic tests. We conclude that healthy elderly people may have impaired release of glucagon and epinephrine in response to hypoglycemia and reduced awareness of the autonomic symptoms of hypoglycemia.

Adult↗
PubMed1994

Counterregulatory hormone responses to hypoglycemia in the elderly patient with diabetes.

In patients with non-insulin-dependent diabetes mellitus (NIDDM), the risk of severe or fatal hypoglycemia associated with the use of oral agents or insulin increases exponentially with age. We conducted this study with the hypothesis that this increased susceptibility to hypoglycemia is caused by alterations in release of counterregulatory hormones and psychomotor performance during hypoglycemia. Ten healthy nonobese elderly subjects (74 +/- 1 years of age; body mass index, 24.5 +/- 0.6 kg/m2) and 10 nonobese elderly NIDDM subjects (72 +/- 1 years of age; body mass index, 25.6 +/- 0.9 kg/m2) underwent two hyperinsulinemic glucose clamp studies (insulin infusion, 60 mU.m-2 x min-1). In the control study, glucose was maintained at 5 mM for 5 h; in the hypoglycemic study, glucose was kept at 5 mM for 1 h and then lowered in a stepwise fashion to 4.4, 3.8, 3.3, and 2.8 mM in each subsequent hour. At regular intervals in each study, neuropsychological tests were performed, counterregulatory hormones were measured, and a hypoglycemic symptom questionnaire was administered. At a glucose level of 2.8 mM, NIDDM patients had reduced incremental glucagon (normal subjects, 114 +/- 18 ng/l; NIDDM subjects, 63 +/- 9 ng/l; P < 0.05) and growth hormone responses (normal subjects, 13.8 +/- 1.0 micrograms/l; NIDDM subjects, 7.0 +/- 2.0 micrograms/l; P < 0.01) and increased epinephrine (normal subjects, 925 +/- 198 pM; NIDDM subjects, 4175 +/- 824 pM; P < 0.001) and cortisol responses (normal subjects, 291 +/- 49 nM; NIDDM subjects, 524 +/- 92 mM; P < 0.05). Symptom scores were similar in both groups at all levels of glycemia.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed1993

The effect of improved glycemic control on cognitive functions in the elderly patient with diabetes.

BACKGROUND: A number of studies have found that cognitive function is impaired in elderly patients with non-insulin dependent diabetes mellitus (NIDDM) when compared with age-matched non-diabetic controls. In addition, it has been reported that elderly NIDDM patients who have poor glycemic control have a greater impairment in cognition that elderly NIDDM patients with good control. We conducted the following prospective study to determine if improved glycemic control would result in an improvement in cognitive function in elderly patients with NIDDM: METHODS: Sixteen untreated elderly patients with NIDDM underwent a battery of neuropsychologic tests on two occasions, separated by at least two weeks. They were then started on an oral hypoglycemic agent. After they had been on a stable dose of medication for 6 months the neuropsychologic tests were repeated. RESULTS: Fasting glucose decreased significantly after treatment (before: 13.8 +/- 1.2 mmol/l; after 8.4 +/- 0.4 mmol/l, p < .01). After 6 months of treatment patients had improvement in their scores on the Grooved Pegboard, Trail Making-Part A, Stroop-Word Naming, Cued Recall and Picture Arrangement tests (all p < .05). CONCLUSIONS: Improved glycemic control in the elderly patient with NIDDM may have beneficial effects on selective areas of cognition.

Affect↗
PubMed1990

Ethanol treatment induces a delayed segmentation anomaly in the chick embryo.

A repeatable somite anomaly is described that results from the incubation of cultured chick embryos in the presence of ethanol. The anomaly comprises a misalignment of approximately five consecutive pairs of somites such that one of each pair is displaced cranially by up to one-half a somite length. The appearance of the malformation is delayed by approximately six somite pairs after the beginning of treatment. These characteristics were shared by embryos treated at the stage of gastrulation (no somites yet present) up to embryos possessing ten pairs of somites at treatment time. The deleterious effect did not appear to result from a disruption in the mechanics of the segmentation process itself, since isolated segmental plates were able to form normal intersomitic clefts in the presence of ethanol. Similarly, there were apparently no alterations in the compaction process that occurs at the cranial end of the segmental plate, since both the contractile and adhesive components were unaffected, as judged by the distributions of actin and fibronectin. The potential mechanisms of the anomaly are discussed with reference to similar segmental defects produced by heat shock. In view of earlier results indicating that cells in the primitive streak at gastrulation are sensitive to the presence of ethanol, it is proposed that this somite anomaly is due to a disruption in the contribution of these mesoderm cells to the segmental plate.

Abnormalities, Drug-Induced↗
PubMed1988

Transferrin and iron requirements of embryonic mesoderm cells cultured in hydrated collagen matrices.

Very early embryonic mesoderm cells were taken from the primitive streak-stage chick embryo and cultured in a matrix of type I collagen in the presence of serum. Previous work has shown that under these conditions cells do not leave the explant and move in the collagen in the absence of supplemented avian transferrin. Cells explanted onto tissue culture plastic in the presence of serum do not require this transferrin supplement. These observations were investigated further by culturing cells in collagen in the presence of the lipophilic iron chelator, ferric pyridoxal isonicotinoyl hydrazone (FePIH), which can replace transferrin as an iron-delivery agent. Under conditions in which FePIH could effectively stimulate chick embryo myoblast growth, no such long-term stimulation was obtained with the early mesoderm cells in collagen. This suggested that for mesoderm cells, FePIH could not replace transferrin. Antibody to the transferrin receptor and to transferrin itself inhibited growth of myoblasts in collagen and on plastic, and of mesoderm cells in collagen. Mesoderm cells on plastic, however, were refractory to the presence of the antibody directed to the receptor and seemed to show a low dependency on transferrin-delivered iron under these conditions, inasmuch as antiserum to transferrin itself only caused a partial inhibition of outgrowth. The results suggest that mesoderm cells in collagen require transferrin for both iron uptake and for another unspecified function. It is consistent with the results to propose that transferrin binding might modulate the cells' attachment to collagen, thus influencing outgrowth. The distribution of the actin cytoskeleton in mesoderm cells actively migrating in collagen, such as in the presence of transferrin, suggests a stronger attachment to the collagen than nonmigrating cells.

Actins↗
PubMed1988

Extracellular matrix synthesis is required for the movement of sclerotome and neural crest cells on collagen.

During early embryogenesis cells of several different populations disperse by active cell movement from one location to another. Preexisting extracellular materials are major determinants of these dispersal patterns, but the cells are also able to modify their substrata by synthesizing and secreting extracellular matrix molecules as they move. In order to determine the contribution made by these deposited materials, several tissues from the early chick embryo have been cultured in the presence of inhibitors of extracellular matrix synthesis and secretion. The tissues examined were sclerotome cells from differentiated somites and neural crest cells. For comparison, undifferentiated somites were also cultured. The movement of these cells was compared in type I collagen gel culture and in conventional culture on artificial substrata. Inhibitors of collagen synthesis were used (cis-hydroxy proline and L-azetidine-2-carboxylic acid) in addition to a proteoglycan inhibitor (p-nitrophenyl-xylopyranoside) and a secretion inhibitor (monensin). Results indicate that sclerotome cells require collagen synthesis for movement in a collagen matrix. Reversal of the effects of collagen inhibitors, by proline and type II collagen, suggest that sclerotome cells normally condition the type I matrix in order to move in it. Inhibition of proteoglycan synthesis produced the greatest effect on the movement of neural crest cells regardless of the substratum, confirming an important role for these molecules in the crest migratory routes. The attachment of all cells to collagen was highly sensitive to the presence of monensin, which is known to reduce the deposition of glycosaminoglycans and fibronectin. These results suggest that conditioning of the extracellular matrix by newly synthesized material is required for cell attachment and movement during early development.

Animals↗
PubMed1988

Effects of HNK-1 monoclonal antibody on the substratum attachment and survival of neural crest and sclerotome cells in culture.

The sclerotome portion of the differentiating embryonic chick somite becomes infiltrated by neural crest cells prior to its dispersal towards the embryonic axis. This means that sclerotome cells explanted into culture for the purpose of examining their interactions in vitro are contaminated with a proportion of neural crest cells. The purpose of this study was to explore the neural crest cell adhesion epitope recognized by the HNK-1 monoclonal antibody and ways in which this antibody can be used to eliminate neural crest cells from mixed culture by selective cytotoxicity. Immunofluorescence technique, under the conditions used here, indicated that the antibody appeared to stain all the mesenchymal (i.e. neural crest) cells emigrating from pieces of embryonic neural tube in culture. Examination of the effects of HNK-1 suggests that the antibody interacts with substratum-binding sites on the neural crest cell surface. On fibronectin-coated substrata the antibody tended to inhibit neurite outgrowth but left the cells relatively well spread, while on laminin substrata the effect was to discourage both neurite extension and cell spreading, causing cell retraction. These results suggest that the cell surface epitope recognized by HNK-1 influences neurite outgrowth, neurite adhesiveness or both. Failure of cell spreading on laminin suggests interaction with the laminin binding sites on the cell body. Elimination of the crest cells from mixed culture with sclerotome was achieved by culturing the cells in the presence of HNK-1 antibody and complement during the period required for complete cell outgrowth from the sclerotome explant.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1987

Altered type I protein kinase in adhesion defective CHO cell variants.

ADv cells are Chinese hamster ovary (CHO) cell variants which cannot adhere to fibronectin coated substrata (Harper & Juliano: J. Cell Biol., 1980; Nature 1981a,b). We have shown that the defect in some clones of ADv cells is distal to the initial interaction between fibronectin and its cell surface receptors (Cheung and Juliano: Exp. Cell Res., 1984), and that it extends to fibronectin mediated aggregation and endocytosis. The adhesion defect in some ADv clones can be corrected by raising intracellular cAMP levels (Cheung & Juliano: J. Cell Physiol., 1985). Here we examine the protein kinase activities and phosphorylation patterns in an adhesion defective variant clone ADv F11CA11. Analysis of the cAMP dependent protein kinase activity (cAdPK) in crude extracts of F11CA11 cells shows an apparent increase in K (activation) as compared to wild type (WT) CHO cell extracts. Further, the DE-52 cellulose chromatography profile of cAdPK in the F11CA11 variant is markedly different from WT in that the type I cAdPK peak elicited by 1 microM cAMP is essentially missing in F11CA11, while the type II cAdPK peak is similar to that in WT. Raising the cAMP level to 100 microM elicits a type I peak in F11CA11 with about 45% of the activity of the WT peak. Binding studies with 3H-cAMP reveal that the type I peak in F11CA11 has a Kd of 1.7 X 10(-8) M as compared to 2.0 X 10(-9) M for WT, whereas the type II peak Kd is approximately 1 X 10(-9) M for both WT and F11CA11. Two-dimensional polyacrylamide gel analysis of 32Pi labeled WT cells and F11CA11 cells with or without cAMP treatment reveals the presence of a protein(s) of 50 kilodaltons which is phosphorylated in WT cells and in cAMP treated F11CA11 cells but not in untreated F11CA11 cells. These findings, coupled with our previous observations, strongly indicate that the adhesion defect in ADvF11CA11 cells is associated with an altered type I cAdPK having lower affinity for cAMP. At normal cellular cAMP levels this enzyme fails to phosphorylate one or more critical protein substrates; however, by raising internal cAMP levels, the defect can be overcome. Thus type I cAdPK seems to play an important role in the regulation of fibronectin mediated cell adhesion, cell aggregation, and endocytosis.

Animals↗
PubMed1987

Ethanol treatment inhibits mesoderm cell spreading in the gastrulating chick embryo.

Gastrulating chick embryos in culture were treated with ethanol solutions, following which the mesoderm cells migrating from the primitive streak were examined by scanning electron microscopy. Morphometric analysis of cell shape showed that mesoderm cells from treated embryos were significantly more rounded and therefore less well spread than controls, and showed fewer filopodial contacts with the overlying basement membrane. This result was only obtainable for cells leading the migration from the primitive streak, since the following cells in the mesodermal mass apparently did not show this difference. The ethanol concentration required to obtain a reliable effect was 5%, while lower concentrations produced highly variable results. The mesoderm cells were also examined for their in vitro responsiveness to ethanol by investigating their adhesiveness and cytoskeleton. No effect was observed on cell-glass adhesion as judged by interference reflection microscopy using up to 1% ethanol. This concentration did, however, disrupt the actin cytoskeleton of cultured cells when stained with NBD-phallacidin, but lower concentrations were ineffective. It is concluded that ethanol treatment of cultured embryos has a significant effect on the substratum relationships of some migrating mesoderm cells.

Animals↗
PubMed1986

Direct measurements of intramolecular electron transfer rates between cytochrome c and cytochrome c peroxidase: effects of exothermicity and primary sequence on rate.

Rapid mixing of ferrocytochrome c peroxidase [cyt c peroxidase(II)] and ferricytochrome c [cyt c(III)] results in the reduction of cyt c(III) by cyt c peroxidase(II). In 10 mM phosphate, pH 7.0, the rate of decay of cyt c peroxidase(II) and the rate of accumulation of cyt c(II) give equal first-order rate constants: k = 0.23 +/- 0.02 s-1. Equivalent results are obtained by pulse radiolysis using isopropanol radical as the reducing agent. This rate is independent of the initial cyt c(III):cyt c peroxidase(II) ratios. These results are consistent with unimolecular electron transfer occurring within a cyt c(III)-cyt c peroxidase(II) complex. When cyt c is replaced by porphyrin cyt c (iron-free cyt c), a complex still forms with cyt c peroxidase. On radiolysis, using e-aq as the reducing agent, intracomplex electron transfer occurs from the porphyrin cyt c anion radical to cyt c peroxidase(III) with k = 150 s-1. This large rate increase with increasing delta G degrees suggests that the barrier for intracomplex electron transfer is large. Finally, we have briefly investigated how the cyt c peroxidase(II)----cyt c(III) rate depends on the primary structure of cyt c(III). We find the reactivity order to be as follows: yeast (k = 3.4 s-1) greater than horse (k = 0.3 s-1) greater than tuna (k = 0.2 s-1). These results mirror a report [Ho, P. S., Sutoris, C., Liang, N., Margoliash, E. & Hoffman, B. M. (1985) J. Am. Chem. Soc. 107, 1070-1071] on excited state reactions of the cyt c/cyt c peroxidase couple.

Amino Acid Sequence↗
PubMed1985

cAMP-induced phenotypic reversion of adhesion, aggregation, and endocytosis in adhesion-defective CHO cell variants.

ADvF11 cells are a CHO adhesion variant which, unlike wild type (WT) cells, are not able to adhere to fibronectin (Fn) coated substrata or to be aggregated by Fn-beads. However, ADvF11 cells bind Fn-beads to the same extent as WT cells, thus suggesting that the defect(s) associated with ADvF11 cells are distal to the initial receptor-ligand binding event (Cheung and Juliano, Exp. Cell Res. 152:127, 1984). In this communication we report that cAMP analogs such as dibutyryl-cAMP (dbcAMP) and 8-bromo-cAMP are able to correct defect(s) associated with ADvF11 cells enabling them to adhere to Fn-coated dishes and to aggregate in the presence of Fn-beads. However, only approximately 40% of ADvF11 cells were found to be responsive to dbcAMP suggesting heterogeneity in the cell population with respect to dbcAMP sensitivity. Further analysis of this partial response led us to isolate a subclone of ADvF11 cells, F11CA11, which is highly responsive to dbcAMP treatment. Induction of Fn-mediated cell adhesion and aggregation in F11CA11 by dbcAMP is both time and dose dependent. Optimal responses were obtained after overnight incubation in alpha-MEM containing, 1% fetal calf serum, 4% bovine serum albumin, 0.5 mM dbcAMP and 0.2 mM methyl-isobutyl-xanthine (MIX), a phosphodiesterase inhibitor. Under these conditions, 70-80% of F11CA11 cells were found to be adherent, compared to 5-7% of untreated F11CA11 cells and 95-100% of WT cells. Aggregation of dbcAMP-MIX treated F11CA11 cells induced by Fn-beads also approached that of WT cells. In addition, treatment with dbcAMP-MIX markedly increased the ability of F11CA11 cells to internalize Fn-beads. The maintenance of the adherent phenotype required the constant presence of dbcAMP-MIX. Removal of dbcAMP-MIX from the incubation medium resulted in return to the original nonadhesive phenotype. Thus, elevation of cAMP levels can dramatically modify the behavior of F11CA11 cells with respect to fibronectin mediated adhesion, aggregation and endocytosis, in effect causing a phenotypic reversion of all three parameters to wild type status. This suggests that the mechanisms for adhesion, aggregation and endocytosis may each involve regulation by cyclic AMP-protein kinase systems.

1-Methyl-3-isobutylxanthine↗
PubMed1984

CHO cell aggregation induced by fibronectin-coated beads. Differences between wild-type and adhesion-variant cells.

ADvF11 (F11), a Chinese Hamster Ovary (CHO) cell variant, is defective in its ability to adhere to fibronectin (Fn)-coated substrata but will adhere to substrata coated with poly-L-lysine, conA or extracellular matrix (ECM) [1]. We have observed that both F11 and CHO wild-type (WT) cells were able to bind 3H-Fn beads in a similar manner; however, only WT cells and not F11 cells aggregate in the presence of Fn beads. Both cell types aggregated similarly in the presence of lectins. Fn-bead-mediated aggregation was blocked by low temperature and aggregation did not occur when formaldehyde-fixed WT cells were used. Colchicine, tetracaine and cytochalasin B were not effective in blocking aggregation induced by Fn beads. These results suggest that: 1. Both WT and F11 cells have surface membrane-binding sites for Fn. 2. The aggregation defect in F11 cells is distal to the initial interaction between the cell surface and Fn, but proximal to the cytoskeletal rearrangements required for cell adhesion.

Animals↗