PubMed Health⌕ Search

Biomedical subjects

A Shih

Publications and source records attributed to A Shih.

At least 19 recordsLinked to original sources
PubMed1995

Cloning of AL-1, a ligand for an Eph-related tyrosine kinase receptor involved in axon bundle formation.

REK7 is an Eph-related tyrosine kinase receptor expressed exclusively in the nervous system, predominantly in hippocampus and cortex. A soluble REK7-IgG fusion protein, produced to analyze the biological role of REK7, prevents axon bundling in cocultures of cortical neurons with astrocytes, a model of late stage nervous system development and differentiation. Using REK7-IgG as an affinity reagent, we purified and cloned a novel REK7 ligand called AL-1, a GPI-linked protein homologous to other members of an emerging ligand family. Membrane attachment of AL-1 appears necessary for receptor activation, since REK7 on cortical neurons is efficiently activated by transfected cells expressing GPI-linked AL-1, but not by soluble AL-1. Consistent with this, soluble AL-1 blocks axon bundling. Our findings, together with the observation that both molecules are expressed in the brain, suggest a role in the formation of neuronal pathways, a crucial feature of nervous system development and regeneration.

Amino Acid Sequence↗
PubMed1995

Separate domains of the Ran GTPase interact with different factors to regulate nuclear protein import and RNA processing.

The small Ras-related GTP binding and hydrolyzing protein Ran has been implicated in a variety of processes, including cell cycle progression, DNA synthesis, RNA processing, and nuclear-cytosolic trafficking of both RNA and proteins. Like other small GTPases, Ran appears to function as a switch: Ran-GTP and Ran-GDP levels are regulated both by guanine nucleotide exchange factors and GTPase activating proteins, and Ran-GTP and Ran-GDP interact differentially with one or more effectors. One such putative effector, Ran-binding protein 1 (RanBP1), interacts selectively with Ran-GTP. Ran proteins contain a diagnostic short, acidic, carboxyl-terminal domain, DEDDDL, which, at least in the case of human Ran, is required for its role in cell cycle regulation. We show here that this domain is required for the interaction between Ran and RanBP1 but not for the interaction between Ran and a Ran guanine nucleotide exchange factor or between Ran and a Ran GTPase activating protein. In addition, Ran lacking this carboxyl-terminal domain functions normally in an in vitro nuclear protein import assay. We also show that RanBP1 interacts with the mammalian homolog of yeast protein RNA1, a protein involved in RNA transport and processing. These results are consistent with the hypothesis that Ran functions directly in at least two pathways, one, dependent on RanBP1, that affects cell cycle progression and RNA export, and another, independent of RanBP1, that affects nuclear protein import.

Amino Acid Sequence↗
PubMed1994

Mutagenesis identifies amino-terminal residues of nerve growth factor necessary for Trk receptor binding and biological activity.

Limited proteolysis and site-directed mutagenesis of human nerve growth factor (hNGF) was utilized to determine the role of the NH2 terminus in p140TrkA (TrkA) receptor function. Purified (6-118)hNGF, representing deletion of the first 5 NH2-terminal residues, is 9-fold less potent than (1-118)hNGF in displacing 125I-hNGF from TrkA. The deletion of a further 4 residues to form (10-118)hNGF is nearly 300-fold less potent. (6-118)hNGF is only 2-4-fold less potent than (1-118)hNGF in eliciting TrkA autophosphorylation and PC12 cell neurite outgrowth, suggesting that the first 5 residues of the NH2 terminus are necessary for full TrkA binding activity but may be less critical for potent receptor activation and intracellular signaling. In contrast, purified mutant H4D results in a nearly 1000-fold loss in TrkA binding at 4 degrees C relative to (1-118)hNGF, at least 10-fold less potency of TrkA autophosphorylation, and 30-fold loss of potency in PC12 cell differentiation. NH2-terminal hBDNF/hNGF and hNT3/hNGF chimeric mutants further affected these activities suggesting that the NH2-terminal sequence specificity of hNGF contributes to structural interactions necessary for TrkA receptor binding and ligand-induced signaling. The potency of binding of all hNGF variants to the low affinity NGF receptor p75 was largely unaffected indicating distinct structural contributions of the NH2-terminal region of hNGF to the binding to TrkA versus p75.

Amino Acid Sequence↗
PubMed1994

Clinical and angiographic variables affecting the progression of coronary artery disease as determined by quantitative angiography.

To assess by serial quantitative angiography, the significance of clinical and angiographic variables that affect the progression of coronary artery disease (CAD). Progression of disease by sequential angiography is unpredictable and the role of clinical risk factors controversial. Various intervention trials have demonstrated less progression and even regression in hyperlipidemic patients. Correlates of progression have included a younger age, unstable angina, and greater involvement of the coronary arteries, with few studies looking at angiographic features of individual lesions. Serial angiograms on 74 patients were analyzed by computer assisted quantitative angiography using absolute measurements. A total of 99 diseased segments were analyzed for progression defined as an absolute reduction of 20% in luminal cross-sectional area. A preliminary correlation coefficient was calculated for each of the clinical and angiographic variables to detect any association with progression, and the odds ratio determined. The presence of any of the clinical risk factors-diabetes, hypertension, serum cholesterol, smoking, and a family history of coronary disease could not predict progression. The use of beta blockers was three times less likely to be associated with progression (odds ratio 0.33). While the presence of distal disease was associated with progression of a more proximal lesion (odds ratio 2.4), eccentricity, branch point location, lesion length, calcification, thrombus, or the presence of collaterals did not influence progression of disease in an individual segment. In conclusion, the presence of any of the clinical risk factors could not predict progression of disease in an individual coronary segment as determined by serial quantitative angiography, and the use of beta blockers and the absence of coexistent distal disease was associated with less progression of disease in an individual coronary segment. This may be related to changes in wall stress, reduced platelet interactions, and the integrity and permeability of the vascular endothelium to lipids.

Adrenergic beta-Antagonists↗
PubMed1992

Human seminal relaxin is a product of the same gene as human luteal relaxin.

Unlike that of other species, which have only one gene encoding relaxin, the human genome contains two nonallelic genes for relaxin, designated H1 and H2, which encode markedly different relaxin peptides. Whereas human relaxin gene H2 is selectively expressed in the ovary, no ovarian expression of gene H1 has been detected. Since relaxin is actively produced in the human male, it is possible to postulate divergent gene expression of relaxin in the male and female. We examined this question directly through the structural determination of human seminal relaxin and its comparison with the structure of human luteal relaxin. Partially purified relaxin, prepared from pooled human seminal plasma which had been delipidated by extraction with acid acetone and hexane, subjected to two cycles of HPLC and an additional purification step by ion-exchange chromatography, was further purified by immunoaffinity chromatography, using a monoclonal antibody to the H2 relaxin A chain which cross-reacts with synthetic H1 relaxin, followed by an additional HPLC step performed on a C4 reverse-phase column. The recovered, purified relaxin was then analyzed by N-terminal gas-phase sequencing and fast atom bombardment mass spectroscopy for determination of the amino acid sequence and molecular ions of the A and B chains, respectively. The results demonstrate that the structure of the predominant relaxin in human semen plasma is derived from the product of the H2 gene, consisting of a N-terminal pyroglutamic acid A-24 A chain and a mixture of B-26 and B-27 B chains. With the exception of degradation of the seminal relaxin B chain C-terminus, this structure is identical to the structure of human luteal relaxin. Therefore, both human seminal and luteal relaxin are products of the H2 gene.

Amino Acid Sequence↗
PubMed1991

Evolutionary implications of primate endogenous retroviruses.

Endogenous DNA sequences related to retroviruses are probably present in all primates. By using approaches based on the polymerase chain reaction, two separate studies have revealed the evolutionary history of some of these sequences. In the first study, a retrovirus-like reverse transcriptase (RT) sequence homologous to that of Baboon endogenous virus (BaEV) has been identified in both Old World monkeys and African apes, but not in humans or Asian apes. This RT sequence is highly conserved at the amino acid level, but not the nucleotide level, in the baboon, African green monkey, Java macaque, chimpanzee, and gorilla. The patterns of nucleotide substitution indicate functional conservation and suggest that this RT sequence was present in the primate germline before apes and Old World monkeys diverged about 30 million years ago. In the second study, a comparison of endogenous proviral DNAs and their adjacent sequences has been used to analyze the evolutionary history of three previously reported human endogenous retroviruses, HERV-E(4.14), HERV-R(3), and HERV-Ia. It is shown that these retroviruses have also been resident in the primate line since before the ape-Old World monkey divergence. The implications of the presence of functionally conserved RT genes in the germlines of primates, and the potential for using integration sites as tools for analyzing phylogenetic relationships among primates and their retroviruses, are discussed.

Amino Acid Sequence↗
PubMed1991

Copper loading of hearts increases postischemic reperfusion injury.

We studied the role of copper as a potential mediator of postischemic reperfusion injury in the isolated, perfused rat heart. Hearts were equilibrated with Krebs-Henseleit buffer for 10 minutes and then loaded with copper by way of perfusion with buffer containing 20 microM copper(II)-bis-histidial for 30 minutes. Control hearts were perfused with Krebs-Henseleit buffer alone during the loading period. Hearts than were washed with buffer for 10 minutes and subjected to 20 minutes of normothermic global ischemia followed by 30 minutes of reperfusion. Atomic absorption spectroscopy revealed a 67% increase in total copper content in loaded hearts by the end of the wash. By the end of the 30-minute period of reperfusion, control hearts demonstrated a 50-60% recovery of myocardial function as determined by peak systolic pressure, contractility, and heart rate. In contrast, copper-loaded hearts exhibited virtually no functional recovery within the 30-minute time period. Using salicylate as a probe, we determined that peak and duration of .OH formation appears to be increased in copper-loaded hearts during reperfusion. Furthermore, efflux of lactic dehydrogenase was significantly increased in copper-loaded hearts. Our results clearly demonstrate that increasing cardiac content of copper results in enhanced postischemic reperfusion injury associated with increased formation of .OH, thus suggesting an important catalytic role for this transition metal.

Analysis of Variance↗
PubMed1991

Primary structure and biological activity of human brain-derived neurotrophic factor.

Brain-derived neurotrophic factor (BDNF) is a 27-kDa basic protein of noncovalently linked 13.5-kD subunits related to nerve growth factor and is produced by the central nervous system (CNS). BDNF has been shown to promote the survival of neurons located in or directly connected with the CNS and is likely to function in adjusting the cell number within neuronal populations to the need of this projection field. Here we describe the primary structure of a human BDNF cDNA, the biological activities of pure recombinant human BDNF, and the tissue distribution of rat BDNF. BDNF mRNA can be found in some peripheral tissues as well as in the CNS, and recombinant human BDNF is a potent neurotrophic factor for primary peripheral sensory neurons.

Amino Acid Sequence↗
PubMed1991

Identification and characterization of a human homolog of the Schizosaccharomyces pombe ras-like gene YPT-3.

The Polymerase Chain Reaction was used to amplify ras and ras-like sequences from two human cDNA libraries. Members corresponding to each of the three major ras-subfamilies (ras, rho, and rab/YPT) were identified. The one homologous to rab/YPT, referred to here as YL8, appears to be the human homolog of the recently reported Schizosaccharomyces pombe YPT3 gene. The YL8 gene could encode a guanine nucleotide binding protein of 216 amino acids with about 70% amino acid sequence identity to S. pombe YPT3, and is transcriptionally active in a variety of human cell lines.

Amino Acid Sequence↗
PubMed1990

Primary structure and biological activity of a novel human neurotrophic factor.

During development, each tissue receives and maintains a number of specific neuronal projections that are adequate to sustain its function. The mechanism by which this intricate process occurs is not well understood, but it has been proposed that diffusible neurotrophic factors derived from the target tissue may be involved. Here we describe the identification of a novel human protein that is important for the growth, differentiation, and survival of primary sympathetic and placode-derived sensory neurons. This polypeptide, designated neuronotrophin-3, has a broad tissue distribution and is structurally related to both nerve growth factor and brain-derived neurotrophic factor. Its unique range of trophic and differentiation-inducing activities suggests that it is likely to play a wide role in defining the fate and function of nerve cells during development.

Amino Acid Sequence↗
PubMed1990

Characterization of four novel ras-like genes expressed in a human teratocarcinoma cell line.

A mixed-oligonucleotide probe was used to identify four ras-like coding sequences in a human teratocarcinoma cDNA library. Two of these sequences resembled the rho genes, one was closely related to H-, K-, and N-ras, and one shared only the four sequence domains that define the ras gene superfamily. Homologs of the four genes were found in genomic DNA from a variety of mammals and from chicken. The genes were transcriptionally active in a range of human cell types.

Amino Acid Sequence↗
PubMed1989

Detection of multiple, novel reverse transcriptase coding sequences in human nucleic acids: relation to primate retroviruses.

A variety of chemically synthesized oligonucleotides designed on the basis of amino acid and/or nucleotide sequence data were used to detect a large number of novel reverse transcriptase coding sequences in human and mouse DNAs. Procedures involving Southern blotting, library screening, and the polymerase chain reaction were all used to detect such sequences; the polymerase chain reaction was the most rapid and productive approach. In the polymerase chain reaction, oligonucleotide mixtures based on consensus sequence homologies to reverse transcriptase coding sequences and unique oligonucleotides containing perfect homology to the coding sequences of human T-cell leukemia virus types I and II were both effective in amplifying reverse transcriptase-related DNA. It is shown that human DNA contains a wide spectrum of retrovirus-related reverse transcriptase coding sequences, including some that are clearly related to human T-cell leukemia virus types I and II, some that are related to the L-1 family of long interspersed nucleotide sequences, and others that are related to previously described human endogenous proviral DNAs. In addition, human T-cell leukemia virus type I-related sequences appear to be transcribed in both normal human T cells and in a cell line derived from a human teratocarcinoma.

Amino Acid Sequence↗
PubMed1987

Cloned extrachromosomal circular DNA copies of the human transposable element THE-1 are related predominantly to a single type of family member.

The 2300 base-pair transposon-like human element, THE-1, has been identified in the extrachromosomal circular DNA of the established human cell line HeLa as a relatively homogeneous population of covalently closed 1900 base-pair molecules. THE-1, which has been classified tentatively as a retroviral-like transposable element (a retrotransposon), is present in the extrachromosomal circular DNA of African green monkey (BSC-1) and human lymphoblastoid (Jurkat) cell lines. The 1900 base-pair extrachromosomal elements isolated and cloned from HeLa cells (1) appear to contain only THE-1-specific nucleotide sequences, (2) are circularized versions of the linear chromosomal sequence, and (3) are related predominantly to a single, or single type of, family member.

Autoradiography↗
PubMed1978

Multiple autotransplantation of rat mammary induced by 7,12-dimethylbenz[a]anthracene: brief communication.

Mammary tumors induced in outbred Sprague-Dawley rats by 7,12-dimethylbenz]a]anthracene were excised, cut into 1- to 2-mm3 pieces, and then autotransplanted sc along the mammary line at six sites. Following an average period of 20--30 days, these autografts grew to approximately 2 cm in diameter in 32 of 48 rats (67%). Autografts in the other 33% of the rats remained dormant. Mammary tumors transplanted into allogeneic hosts failed to grow. Tumors derived from autotransplantation were indistinguishable from their primary tumors with respect to their histologic features, the nature of hormone dependency, the content of estrogen receptors, and their ability to incorporate [3H]leucine. Furthermore, autotransplanted tumors derived from a single primary tumor varied little with regard to the preceding parameters; thus they provided an opportunity for serial sampling of individual tumors for repeated morphologic and biochemical evaluations.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed1977

Effect of intrauterine estriol on reproductive function in the rabbit.

The effect of intrauterine estriol on spontaneous ovulation, ovum fertilization, blastocyst development, and blastocyst implantation in rabbits has been investigated. Estriolreleasing intrauterine capsules constructed of biocompatible polymer were implanted in one uterine horn of adult New Zealand White female rabbits, while placebo-containing capsules were implanted into the contralateral horn. The animals were artificially inseminated and ovulated or mated to fertile bucks. The does were killed and their reproductive tracts were examined 54 hours, 6 days, and 10 days after ovulation-inducing injection or after coitus. The results indicate that intrauterine estriol released at a steady state rate of 1.25 mug/day effectively inhibits blastocyst development and implantation. This contraceptive effect was clearly local, since implantations in the contralateral,placebo-bearing horn were not inhibited. Furthermore, the same dose of estriol, when released systemically from a subcutaneously placed capsule, had no effect on implantation. Intrauterine estriol appeared also to have no effect on spontaneous ovulation or ovum fertilization.

Animals↗