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Biomedical subjects

J Tsai

Publications and source records attributed to J Tsai.

At least 91 records · Page 5Linked to original sources
PubMed1992

Farnesylation of YDJ1p is required for function at elevated growth temperatures in Saccharomyces cerevisiae.

The Saccharomyces cerevisiae YDJ1 protein (YDJ1p) contains a C-terminal "CaaX box" motif common to proteins that are modified by prenylation. In the present study we show that YDJ1p is a specific substrate for both yeast and mammalian protein farnesyltransferase enzymes in vitro. A mutant form of YDJ1p, in which the conserved cysteine of the CaaX box is mutated to a serine (ydj1-S406p), cannot be farnesylated in vitro. After expression in S. cerevisiae, ydj1-S406p displays a reduced electrophoretic mobility and an increased cytosolic localization in subcellular fractionation experiments when compared to wild type YDJ1p. Expression of ydj1-S406 in cells lacking YDJ1 results in a temperature-sensitive growth phenotype in S. cerevisiae. These data indicate that farnesylation of YDJ1p is required for its function at elevated temperatures.

Alkyl and Aryl Transferases↗
PubMed1992

Gonococcal transferrin-binding protein 1 is required for transferrin utilization and is homologous to TonB-dependent outer membrane receptors.

The pathogenic Neisseria species are capable of utilizing transferrin as their sole source of iron. A neisserial transferrin receptor has been identified and its characteristics defined; however, the biochemical identities of proteins which are required for transferrin receptor function have not yet been determined. We identified two iron-repressible transferrin-binding proteins in Neisseria gonorrhoeae, TBP1 and TBP2. Two approaches were taken to clone genes required for gonococcal transferrin receptor function. First, polyclonal antiserum raised against TBP1 was used to identify clones expressing TBP1 epitopes. Second, a wild-type gene copy was cloned that repaired the defect in a transferrin receptor function (trf) mutant. The clones obtained by these two approaches were shown to overlap by DNA sequencing. Transposon mutagenesis of both clones and recombination of mutagenized fragments into the gonococcal chromosome generated mutants that showed reduced binding of transferrin to whole cells and that were incapable of growth on transferrin. No TBP1 was produced in these mutants, but TBP2 expression was normal. The DNA sequence of the gene encoding gonococcal TBP1 (tbpA) predicted a protein sequence homologous to the Escherichia coli and Pseudomonas putida TonB-dependent outer membrane receptors. Thus, both the function and the predicted protein sequence of TBP1 were consistent with this protein serving as a transferrin receptor.

Amino Acid Sequence↗
PubMed1991

Alleles at four HLA class II loci determined by oligonucleotide hybridization and their associations in five ethnic groups.

The use of polymerase chain reaction (PCR) and oligonucleotide hybridization offers a new approach for the definition of HLA class II alleles. It has been possible to determine 43 alleles of DRB1, four of DRB3, two of DRB4, four of DRB5, eight of DQA1, and 14 of DQB1. These alleles are inherited together in members of families and form closely associated groups which are found repeatedly and in characteristic patterns in different populations. We have determined the HLA class II alleles and analyzed their association in 431 healthy unrelated subjects including 161 North American Caucasians, 53 Latin Americans, 61 Blacks, 88 Chinese, and 68 Israeli Jews. For-locus haplotypes (DRB1; DRB3/4/5; DQA1; DQB1) were derived from 79 B cell lines and the analysis of segregation in 34 nuclear families. The B-cell lines yielded 37 and the families showed the same, and 20 other, haplotypic combinations. In addition to these 57 haplotypes, associated alleles were assigned in the unrelated panels following certain rules. The resulting haplotypes were assigned to groups known to share associated alleles. The groups were: 1) DR1, DR2, and DRw10 (13 haplotypes); 2) DR3 and DRw6 (26 haplotypes); 3) DR5 and DRw8 (24 haplotypes); 4) DR4, DR7, and DR9 (24 haplotypes). Their distribution in populations with different ethnic backgrounds was analyzed. The expressed DRB4 allele and its null mutant were determined by PCR and oligonucleotide hybridization. The different DR7 haplotypes resulting from these determinations were analyzed in a panel of 130 North American Caucasoids. This comprehensive analysis of class II HLA haplotypes in human populations should be useful in understanding the role of these genes and in various applications including anthropology, disease susceptibility, and transplantation of allogeneic organs and tissues.

Alleles↗
PubMed1991

Changes of duodenal pH and pancreatic exocrine function after upper G-I intraluminal ethanol administration.

Using 3 outbred dogs with pancreatic, gastric and jejunal fistulas, we examined changes in pancreatic exocrine secretion, duodenal pH and plasma CCK concentration after intragastric or intrajejunal administration of ethanol. Intragastric administration of 20% or 40% ethanol significantly lowered the pH in the duodenal cavity, and pancreatic fluid secretion and bicarbonate excretion were stimulated. Intrajejunal administration of ethanol elicited stronger responses. Plasma CCK concentration was not changed or was only slightly lowered by ethanol administration in the digestive tract. It is assumed that stimulation of pancreatic exocrine secretion was mediated by the secretion of gastric acid.

Animals↗
PubMed1990

Genetic evidence that Neisseria gonorrhoeae produces specific receptors for transferrin and lactoferrin.

Transferrin (TF) and lactoferrin (LF) are probably the major sources of iron (Fe) for Neisseria gonorrhoeae in vivo. We isolated mutants of N. gonorrhoeae FA19 that were unable to grow with Fe bound to either TF (TF-) or LF (LF-) or to both TF and LF ([TF LF]-). The amount of Fe internalized by each of the mutants was reduced to background levels from the relevant iron source(s). The wild-type parent strain exhibited saturable specific binding of TF and LF; receptor activity was induced by Fe starvation. The TF(-)-specific or LF(-)-specific mutants were almost completely lacking in receptor activity for TF or LF, respectively, whereas the [TF LF]- mutants bound both TF and LF as well as the wild-type strain. All mutants utilized citrate and heme normally as Fe sources. These results demonstrate that ability to bind TF or LF is essential for gonococci to scavenge appreciable amounts of Fe from these sources in vitro. In addition, the TF and LF Fe acquisition pathways are linked by the mutual use of a nonreceptor gene product that is essential to Fe scavenging from both of these sources; this gene product is not required for Fe acquisition from other sources.

Binding, Competitive↗
PubMed1990

Gonococci are survivors.

Gonococci are capable of prolonged survival in untreated infection, and frequently reinfect persons with repeated and recent infection, despite considerable mucosal and systemic immune response to infection. Multiple mechanisms help to explain how this is achieved, including variations in surface antigen expression; production of an extracellular IgA protease; employment of antigens that preferentially stimulate host production of antibodies that block the killing activity of other antibodies; masking of critical epitopes by chemical modification of surface structures; molecular mimicry of host antigens; shedding of antigens in the form of outer membrane blebs; and, subverting certain nonimmunological antimicrobial defenses to the use of the bacterium. Moreover, gonococci are capable of considerable phenotypic adaptation to changing environmental conditions in vivo. This paper briefly reviews these concepts.

Adaptation, Physiological↗
PubMed1990

[Effects of intragastric and intrajejunal ethanol administration on canine pancreatic exocrine secretion and duodenal pH].

The effect of ethanol on pancreatic exocrine secretion and intraduodenal pH was investigated in 3 dogs, after making pancreatic, gastric, and jejunal fistula. After intragastric and intrajejunal administration of ethanol the intraduodenal pH went down and pancreatic juice, pancreatic bicarbonate output was increased. The integrated value of pancreatic juice, pancreatic bicarbonate and pancreatic protein output was greater in case of intrajejunal administration rather than intragastric administration of the ethanol. After intragastric and intrajejunal administration of the ethanol the plasma concentration of CCK was unchanged. The decrease of intraduodenal pH and increase of pancreatic exocrine secretion was though be mainly due to the secondary action of gastric acid secretion stimulated by ethanol.

Animals↗
PubMed1989

Altered glucose metabolism in microvessels from patients with Alzheimer's disease.

Microvessels isolated from temporal cortex of patients with Alzheimer's disease showed decreased uptake of glucose when compared with vessels from age-matched or young control subjects. This was due to decreased hexokinase activity in the Alzheimer samples, as determined by ion exchange chromatography. This finding was confirmed independently by determination of the phosphorylation constant for hexokinase, K3, using positron emission tomography. The results suggest that Alzheimer's disease may result from a global defect in brain energy metabolism.

Adult↗
PubMed1989

Airway obstruction due to goiter in older patients.

It has been shown that goiters can progressively enlarge to compress the surrounding trachea or esophagus and result in incapacitating obstructive symptoms or potentially fatal airway obstruction. The potential of a goiter to become hyperactive also exists. Recently, we have seen three older patients with longstanding untreated "benign" goiters who presented difficult management decisions. Given the likelihood of progressive growth of a goiter and the increased life expectancy of these patients with goiters, it is essential to perform flow-volume loop studies while following these patients.

Aged↗
PubMed1989

Cultured human retinal pigment epithelial cells express basic fibroblast growth factor and its receptor.

Basic fibroblast growth factor (bFGF) has been implicated in the maintenance of neuronal differentiation, the induction of neovascularization and intravitreal proliferative diseases. We have found that human retinal pigment epithelial (RPE) cells grown in vitro transcribe the bFGF gene and synthesize a peptide that crossreacts with anti-bFGF antibodies. In culture, these cells appear to release activity with biological and biochemical properties similar to bFGF. RPE cells have specific bFGF receptors and proliferate in response to bFGF. Thus, it is possible that the RPE cell is an important source of retinal bFGF and may respond to bFGF in an autocrine manner.

Amino Acid Sequence↗
PubMed1989

ATFresno: a phenotype linking ataxia-telangiectasia with the Nijmegen breakage syndrome.

This report describes twin girls with typical features of ataxia-telangiectasia, including increased alpha-fetoprotein, radio-resistant DNA synthesis, characteristic chromosome abnormality, and immunodeficiency. They have, in addition, microcephaly and mental retardation. Complementation studies were performed utilizing Sendai virus--mediated fusion of fibroblast cell lines. Complementation was observed with patients in ataxia-telangiectasia complementation groups A, C, and E but not with the cell line from a patient with the Nijmegen breakage syndrome, in which patients have microcephaly, radio-resistant DNA synthesis, chromosome aberrations, and immunodeficiency but lack ataxia and telangiectasia. These data suggest that the Nijmegen breakage syndrome and the patients described here are not genetically distinct entities but form a spectrum of one disorder.

Ataxia Telangiectasia↗
PubMed1989

Staphylococcal pericarditis. An atypical presentation.

Purulent pericarditis is typically an acute and often catastrophic illness. The case presented herein has unusual manifestations of pericarditis caused by Staphylococcus aureus. The clinical course was indolent and prolonged, and unlike the usual case, no primary source could be found.

Aged↗
PubMed1988

Loss of transferrin receptor activity in Neisseria meningitidis correlates with inability to use transferrin as an iron source.

Although Neisseria meningitidis does not produce siderophores, it is able to obtain iron from human transferrin. We observed saturable specific binding of 125I-labeled human transferrin to meningococci. Human lactoferrin and mouse transferrin did not compete with human transferrin for binding, whereas human apotransferrin and 100% iron-saturated transferrin competed equally well. Meningococci thus have a specific receptor for human transferrin. Scatchard analysis yielded a relatively low Kd of 0.7 microM and an apparent copy number of 2,900 receptors per CFU. Receptor activity was iron-regulated. A meningococcal transformant specifically unable to utilize transferrin as an iron source had decreased transferrin receptor activity. These data are consistent with the hypothesis that receptor-mediated binding of transferrin is a rate-limiting step in meningococcal iron uptake from transferrin.

Blotting, Western↗
PubMed1987

Growth hormone-releasing factor releases ACTH from an AtT-20 mouse pituitary tumor cell line but not from normal pituitary cells.

Corticotropin-releasing factor (CRF) and both human pancreatic growth hormone-releasing factor (hp-GRF) and rat hypothalamic GRF (rh-GRF) stimulated ACTH release from neoplastic AtT-20 mouse pituitary tumor cells in a dose-dependent fashion, with CRF inducing a 10-fold increase and GRF a maximal increment of approximately one-half that of CRF. Neither rh-GRF nor hp-GRF induced ACTH release in normal anterior pituitary cells. Pretreatment with either dexamethasone or somatostatin prior to the addition of rh-GRF inhibited the increase in ACTH release. Both ovine CRF and rh-GRF stimulated adenosine 3,5-monophosphate production in AtT-20 cells. The weak but clearly discernible effect of GRF on ACTH release from AtT-20 cells may be due to an abnormality in the AtT-20 cell receptor.

Adrenocorticotropic Hormone↗
PubMed1987

Tissue kallikrein in rat brain and pituitary: regional distribution and estrogen induction in the anterior pituitary.

We have detected tissue kallikrein and kallikrein mRNA in various brain regions with a kallikrein direct RIA and with nucleic acid hybridization using a kallikrein cDNA probe. In the direct RIA, rat urinary kallikrein-like activity was found in the pituitary and pineal glands, hypothalamus, cerebral cortex, cerebellum, and brain stem. Pituitary and pineal gland kallikrein concentrations were significantly higher than those in other regions. Only in pituitary was there a significant difference in tissue kallikrein concentration according to sex, with glands from female rats showing levels 4-fold higher than those from male rats. Kallikrein mRNAs were detected in all of the regions and were about 4-fold higher in female than in male pituitary gland. Northern blot analyses show sex dimorphism of pituitary kallikrein mRNA, similar in size to submandibular gland and kidney mRNA. In castrated male rats, whole pituitary kallikrein content was reduced to 50% of the control value and increased 1.7-fold with testosterone replacement and 18-fold with 17 beta-estradiol treatment. Neither T4 nor cortisol affected whole pituitary kallikrein levels in the castrated male rat, but testosterone decreased pituitary kallikrein in normal female rats by 35%. When anterior pituitary or neurointermediate lobe extracts were separately examined, immunoreactive kallikrein was 10.2- and 1.3-fold higher respectively, in female than in male rat lobes. Estradiol benzoate (30 micrograms/kg) administration increased kallikrein levels 90- and 22-fold, respectively, in the anterior pituitary of gonadectomized male and female rats, while it increased by only 40-50% kallikrein levels in the male and female neurointermediate lobe. In dot blot analysis, kallikrein mRNA levels were increased 5-fold by 17 beta-estradiol in the whole pituitary of castrated male rats. In the cytoplasmic dot hybridization analysis, estradiol benzoate treatment increased kallikrein mRNA levels 54-fold in the anterior pituitary of ovariectomized rats. The data show that a tissue kallikrein indistinguishable thus far from a urinary kallikrein is widely distributed in brain and pituitary and that levels of enzyme and mRNA are comparable in certain central sites. Kallikrein levels in the anterior and neurointermediate pituitaries are differentially regulated by estrogen.

Animals↗
PubMed1987

Autoimmune thrombocytopenia and primary biliary cirrhosis with hypoglycemia and insulin receptor autoantibodies. A case report.

A 43-year-old woman with spontaneous episodes of neuroglycopenic hypoglycemia was found to have immune-mediated thrombocytopenic purpura and primary biliary cirrhosis. Hypoglycemia along with hyperinsulinemia suggested insulinoma. Serum c-peptide levels were disproportionately low, raising the possibility of factitious hypoglycemia. The patient's plasma contained circulating insulin receptor autoantibodies, thought to cause hypoglycemia by their insulin-like actions. With prednisone therapy, her other autoimmune features improved, and the hypoglycemia eventually resolved. Hypoglycemia mediated by insulin receptor autoantibodies should be considered in patients with fasting hypoglycemia and features suggesting an underlying autoimmune disorder before pursuing more invasive procedures. High-dose steroids may be life-saving in this disorder.

Adult↗