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C Chang

Publications and source records attributed to C Chang.

At least 271 records · Page 15Linked to original sources
PubMed1995

A critical assessment of brain metabolites: analysis of perchloric acid extracts using proton nuclear magnetic resonance.

A critical assessment of perchloric acid (PCA) brain tissue extracts for precise identification and quantitation of brain metabolites using in vitro proton nuclear magnetic resonance (1H NMR) spectroscopy was studied. One pulse with a presaturation NMR experiment was used. The chemical shifts and coupling networks of the major brain metabolites as a function of pH were characterized by using individual model compounds and a model mixture solution. We found that the conditions of the PCA solution are essential for accurate interpretation of NMR spectra of brain metabolites. The maximum spectral resolution was obtained at pH 4.92. Caution is necessary when using high resolution 1H NMR spectroscopy to identify and quantify brain metabolites.

Animals↗
PubMed1995

The ethylene hormone response in Arabidopsis: a eukaryotic two-component signaling system.

The simple gas ethylene affects numerous physiological processes in the growth and development of higher plants. With the use of molecular genetic approaches, we are beginning to learn how plants perceive ethylene and how this signal is transduced. Components of ethylene signal transduction are defined by ethylene response mutants in Arabidopsis thaliana. The genes corresponding to two of these mutants, etr1 and etr1, have been cloned. The ETR1 gene encodes a homolog of two-component regulators that are known almost exclusively in prokaryotes. The two-component regulators in prokaryotes are involved in the perception and transduction of a wide range of environmental signals leading to adaptive responses. The CTR1 gene encodes a homolog of the Raf family of serine/threonine protein kinases. Raf is part of a mitogen-activated protein kinase cascade known to regulate cell growth and development in mammals, worms, and flies. The ethylene response pathway may, therefore, exemplify a conserved protein kinase cascade regulated by a two-component system. The dominance of all known mutant alleles of ETR1 may be due to either constitutive activation of the ETR1 protein or dominant interference of wild-type activity. The discovery of Arabidopsis genes encoding proteins related to ETR1 suggests that the failure to recover recessive etr1 mutant alleles may be due to the presence of redundant genes.

Journal Article↗
PubMed1995

The expression of prostatic acid phosphatase is transcriptionally regulated in human prostate carcinoma cells.

The expression of prostatic acid phosphatase (PAcP) in three human prostate carcinoma cell lines including LNCaP, DU 145 and PC-3, was studied to explore its potential role as a marker in the progression of prostate cancer. Although Southern blot analysis suggested the presence of PAcP gene in all three prostate carcinoma cell lines, the Northern blot analysis and the reverse transcriptase-polymerase chain reaction (RT-PCR) assay showed that PAcP mRNA can be detected only in LNCaP cells. As one of the major differences between LNCaP cells and PC-3 as well as DU 145 cells is the androgen-sensitivity of LNCaP cells, we then focused on the influence of PAcP expression by the presence of androgen receptor (AR) in human AR cDNA-transfected PC-3 cells and high passages of LNCaP cells. The results demonstrated that the transfection of human AR cDNA into PC-3 cells did not have any detectable effect on the expression of PAcP. Further, in LNCaP cells, while the level of PAcP mRNA diminished upon passage, the AR mRNA level remained approximately the same. Together, these data suggested that the differential expression of PAcP in different prostate carcinoma cells including high passages of LNCaP cells may occur at the transcriptional level and may have little linkage to the expression of AR.

Acid Phosphatase↗
PubMed1995

Sequences in the preC region of duck hepatitis B virus affect pregenomic RNA accumulation.

The pregenomic RNA of hepadnaviruses serves as both the mRNA for the core and polymerase proteins and the RNA template for reverse transcription. We have identified a region in the duck hepatitis B virus pregenomic RNA transcription unit that is critical for the accumulation of this transcript. This 85-nt region, termed alpha, is located within the preC region; deletion of alpha results in drastically reduced steady-state levels of pregenomic RNA. This effect is not due to reduction in transcription initiation or to enhancement of premature polyadenylation at the 5' copy of the viral poly(A) signal. However, this phenotype is suppressed by deletion of a second, larger region (beta) located ca. 1 kb downstream. The activity of the alpha element is tissue- and species-nonspecific; however, it displays absolute orientation-dependence and its activity is influenced by its position within the transcript. Models for its action are discussed.

Animals↗
PubMed1995

Identification of a new enhancer in the promoter region of human TR3 orphan receptor gene. A member of steroid receptor superfamily.

Human TR3 orphan receptor is a member of the steroid/thyroid hormone receptor superfamily and is the human homologue of the proteins encoded by the rat NGFI-B and mouse nur77 genes. These genes are induced rapidly by androgens/growth factors and may have functions related to cell proliferation, differentiation, and apoptosis. To investigate the TR3 orphan receptor gene transcriptional regulation, a 2.3-kilobase genomic DNA fragment containing the TR3 orphan receptor gene promoter region was isolated, sequenced, and characterized. Sequence homology search within this promoter region revealed some potential cis-acting elements such as cAMP response element, interleukin-6 response element, estrogen response element, and GC box. Deletion analysis and chloramphenicol acetyltransferase assay also showed a novel cis-acting element of TR3 orphan receptor gene (NCAE-TR3), 200-181 base pairs upstream of the transcriptional start site. Gel retardation assay further demonstrated that some nuclear factors can bind to this NCAE-TR3. Together, our data suggest that NCAE-TR3 could be a new enhancer element associated with the transcription of an early response gene for mitogenesis and apoptosis.

Animals↗
PubMed1995

Identification of human TR2 orphan receptor response element in the transcriptional initiation site of the simian virus 40 major late promoter.

A DNA response element (TR2RE-SV40) for the TR2 orphan receptor, a member of the steroid-thyroid hormone receptor superfamily, has been identified in the simian virus 40 (SV40) +55 region (nucleotide numbers 368-389, 5'-GTTAAGGTTCGTAGGTCATGGA-3'). Electrophoretic mobility shift assay, using in vitro translated TR2 orphan receptor with a molecular mass of 67 kilodaltons, showed a specific binding with high affinity (dissociation constant = 9 nM) for this DNA sequence. DNA-swap experiments using chloramphenicol acetyl-transferase assay demonstrated that androgen can suppress the transcriptional activities of SV40 early promoter via the interaction between this TR2RE-SV40 and the chimeric receptor AR/TR2/AR with the DNA-binding domain of the TR2 orphan receptor flanked by the N-terminal and androgen-binding domains of the androgen receptor. In addition, this TR2RE-SV40 can function as a repressor to suppress the transcriptional activities of both SV40 early and late promoters. Together, these data suggest the TR2RE-SV40 may represent the first identified natural DNA response element for the TR2 orphan receptor that may function as a repressor for the SV40 gene expression.

Animals↗
PubMed1995

Magnetic resonance microscopy of hamster olfactory bulb: a histological correlation.

BACKGROUND: Magnetic Resonance Imaging (MRI) has been widely used as a noninvasive diagnostic tool for obtaining morphological, metabolic, and functional information from tissue. However, its potential application in observing detailed structure comparable to that of the light microscope has not yet been fully explored. In order to evaluate the usefulness of MR microscopy, a high resolution three-dimensional (3-D) technique was applied to observe the laminar structure of the mammalian olfactory bulb (OB). METHODS: Adult male hamsters (Mesocrecitus auratus) were used as an animal model. Hamster OB and the attached anterior olfactory nucleus were removed from the skull for the MRI examinations. The images were performed with a Bruker AMX-400 system equipped with microimaging accessories. T2 weighted 3-D spin echo sequence was used with a field of view of 9 mm and data matrix of 128*128*128. The in-plane resolution was 70*70*70 microns. Histological preparation, including vibratome sectioning at 40 microns and Nissl staining, were used for light microscopic evaluations and comparisons. RESULTS: Five distinct layers from the superficial to the center of the OB were distinguished in the MR images of coronal, sagittal and horizontal slices. As compared to the histological sections at the corresponding cutting planes, the laminar structure of the OB displayed in the MR microscopic images correlated well with its counterparts. CONCLUSIONS: MR microscopy is capable of detecting cellular variation of unsectioned and unstained tissue. It can also be easily applied to obtain spatial information with good resolution. It appears to provide a great potential for diagnostic pathology.

Animals↗
PubMed1995

Molecular characterization of human CD94: a type II membrane glycoprotein related to the C-type lectin superfamily.

Natural killer (NK) cells preferentially express several genes of the C-type lectin superfamily which have been implicated in the regulation of NK cell function. We demonstrate that CD94 is a type II membrane protein encoded by a unique gene of the C-type lectin superfamily. While homology of CD94 with the NK cell-associated NKR-P1 and NKG2 C-type lectin genes is limited to the structural motifs conserved in the carbohydrate recognition domain, all of these genes are on human chromosome 12, the syntenic of mouse chromosome 6, where genes of the NK complex (NKR-P1 and Ly-49) are located. An unexpected feature of CD94 is the essential absence of a cytoplasmic domain, implying that association with other receptors may be necessary for the function of this molecule.

Amino Acid Sequence↗
PubMed1995

Crystallization, molecular replacement solution, and refinement of tetrameric beta-amylase from sweet potato.

Sweet potato beta-amylase is a tetramer of identical subunits, which are arranged to exhibit 222 molecular symmetry. Its subunit consists of 498 amino acid residues (Mr 55,880). It has been crystallized at room temperature using polyethylene glycol 1500 as precipitant. The crystals, growing to dimensions of 0.4 mm x 0.4 mm x 1.0 mm within 2 weeks, belong to the tetragonal space group P4(2)2(1)2 with unit cell dimensions of a = b = 129.63 A and c = 68.42 A. The asymmetric unit contains 1 subunit of beta-amylase, with a crystal volume per protein mass (VM) of 2.57 A3/Da and a solvent content of 52% by volume. The three-dimensional structure of the tetrameric beta-amylase from sweet potato has been determined by molecular replacement methods using the monomeric structure of soybean enzyme as the starting model. The refined subunit model contains 3,863 nonhydrogen protein atoms (488 amino acid residues) and 319 water oxygen atoms. The current R-value is 20.3% for data in the resolution range of 8-2.3 A (with 2 sigma cut-off) with good stereochemistry. The subunit structure of sweet potato beta-amylase (crystallized in the absence of alpha-cyclodextrin) is very similar to that of soybean beta-amylase (complexed with alpha-cyclodextrin). The root-mean-square (RMS) difference for 487 equivalent C alpha atoms of the two beta-amylases is 0.96 A. Each subunit of sweet potato beta-amylase is composed of a large (alpha/beta)8 core domain, a small one made up of three long loops [L3 (residues 91-150), L4 (residues 183-258), and L5 (residues 300-327)], and a long C-terminal loop formed by residues 445-493. Conserved Glu 187, believed to play an important role in catalysis, is located at the cleft between the (alpha/beta)8 barrel core and a small domain made up of three long loops (L3, L4, and L5). Conserved Cys 96, important in the inactivation of enzyme activity by sulfhydryl reagents, is located at the entrance of the (alpha/beta)8 barrel.

Amino Acid Sequence↗
PubMed1995

Selective adhesion of functional microtubules to patterned silane surfaces.

We show that microtubule polymers can be immobilized selectively on lithographically patterned silane surfaces while retaining their native properties. Silane films were chemisorbed on polished silicon wafers or glass coverslips and patterned using a deep UV lithographic process developed at the Naval Research Laboratory. Hydrocarbon and fluorocarbon alkyl silanes, as well as amino and thiol terminal alkyl silanes, were investigated as substrates for microtubule adhesion with retention of biological activity. Microtubules were found to adhere strongly to amine terminal silanes while retaining the ability to act as substrates for the molecular motor protein kinesin. Aminosilane patterns with linewidths varying from 1 to 50 microns were produced lithographically and used to produce patterns of selectively adhered microtubules. Microtubules were partially aligned on the patterned lines by performing the immobilization in a fluid flow field. Patterns were imaged with atomic force microscopy and differential interference contrast microscopy. Motility assays were carried out using kinesin-coated beads and observed with differential interference contrast microscopy. Kinesin bead movement on the patterned microtubules was comparable to movement on microtubule control surfaces.

Animals↗
PubMed1995

Plasticity of craniomandibular muscle function: 31P magnetic resonance spectroscopy of the rabbit masseter muscle.

The masseter muscle was studied during postnatal development of the rabbit from the juvenile to adult stage in which the oral function was altered during maturation by modifying the diet to soft food. The muscle was assessed using phosphate magnetic resonance (31P NMR) spectroscopy with a single-turn copper surface coil to study potential changes in phosphate metabolism. The 31P NMR spectra consisted of five peaks related to unbound forms of inorganic phosphate (Pi), creatine phosphate (PCr), and three peaks related to the adenosine triphosphate (ATP). The masseter was assessed in one group of five rabbits at 8 weeks postnatally (juvenile) and after 4 months of this experimental group masticating on soft food. They were compared with a control group of five rabbits raised on a normal hard diet. The Pi/PCr ratio increased in the adult masseter much higher during twitching, tetany, and periodic contraction than in the juvenile regardless as to whether the adult animal had been raised from the juvenile period on soft or hard diet. There were relatively few differences between the experimental adult animals raised on a soft diet and the normal adult animals despite the soft diet animals demonstrating a significantly lower weight and smaller muscle mass. These findings suggest that chronic underuse of the masseter muscle by decreasing the masticatory loads has a minimal effect on the phosphate metabolism of the maturing masseter.

Adaptation, Physiological↗
PubMed1995

Age-dependent neurotoxicity of striatal lesions produced by aminooxyacetic acid: quantitative in vitro 1H NMR spectroscopic studies.

Aminooxyacetic acid, a potent inhibitor of the mitochondrial malate-aspartate shunt, was used to assess the role of mitochondrial energy metabolism in damaged brain of rats of different age groups. Three age groups--juvenile (< 1 month), young adult (3-4 months), and adult (7 months)--were subjected to examine the age-related aminooxyacetic acid effect. We measured the absolute concentrations of metabolites in perchloric acid extracts of rat striatum after intraperitoneal administration of aminooxyacetic acid using 1H NMR spectroscopy. Among aminooxyacetic acid-treated groups, a twofold increase of GABA concentration was observed in juveniles and young adults, and a threefold elevation of GABA level was observed in adults, whereas there were no significant differences of alanine and glutamate levels in all three aminooxyacetic acid-treated groups as compared with the age-matched controls. Statistically significant decreases of N-acetylaspartate, glutamine, and creatine levels were detected in treated adults. A statistically significant elevation of lactate concentration was found in the adult treated group. These data have demonstrated that the impairment of energy metabolism in rat striatum induced by aminooxyacetic acid can be revealed by quantitative in vitro 1H NMR spectroscopy and that aminooxyacetic acid produces age-dependent striatal abnormalities.

Aging↗
PubMed1995

Effect of maturation on 31P magnetic resonance spectroscopy of the rabbit masseter muscle.

This work studies the dynamic metabolic changes of the rabbit masseter muscle during post-natal development. The composition and proportion of oxidative and glycolytic muscle fibers alter during maturation. The masseter muscle, as most muscles of the craniofacial region, exhibits unusual development in composition of isoforms of myosin. The effect of this unusual composition on the dynamic metabolic properties of the masseter muscle have not been assessed. The metabolism of the rabbit masseter muscle was studied by means of 31P-nuclear magnetic resonance (NMR) spectroscopy. Contraction was elicited by electrical stimulation of the muscle in the anesthetized animal. Five animals were studied at 8 weeks and 24 weeks so that both the juvenile and adult stages could be evaluated. The dynamic biochemical changes in the masseter muscle were studied by the analysis of NMR spectra. A single-turn surface coil (copper) was used, and the original signal was treated with Fourier transforms to obtain 31P spectra. The low signal-to-noise ratio required averaging 16 acquisitions (acquisition time = 400 msec, repetition rate = 1.8 sec) in 30 sec and then obtaining continuous spectra for 27 min. Each averaged spectrum demonstrated five peaks: inorganic phosphate (Pi), creatine phosphate (PCr), and three peaks related to adenosine triphosphate (ATP). The protocol involved recording an initial three-minute rest period, stimulating the muscle at 5 Hz for 3 min twice, separated by three-minute rest periods, and stimulating the muscle at 50 Hz twice for 3 min separated by rest periods. The Pi/PCr ratio increased significantly in the adult masseter during both 5-Hz stimulations, evoking twitching, and the first 50-Hz stimulation, evoking tetany (repeated ANOVA, P < 0.05). The resting pH (6.96 +/- 0.13) was significantly lowered during both twitching (6.85 +/- 0.10; P < 0.0038) and tetany (6.55 +/- 0.13; P < 0.0001), but only in the adult masseter muscle. These finding suggest that the adult masseter muscle possesses more glycolytic fibers as it modifies its metabolism during postnatal development.

Adenosine Triphosphate↗
PubMed1995

Expression of nuclear hormone receptors in the rat supraoptic nucleus.

To investigate the role of nuclear hormone receptors on neuropeptide gene expression in the hypothalamo-neurohypophyseal system (HNS) of the rat, a survey was made of members of the nuclear hormone receptor superfamily that are expressed in the supraoptic nucleus (SON). A polymerase chain reaction cloning strategy based on homologies in the DNA-binding domain of AGGTCA-binding factors was devised for the identification of receptors in microdissected SON tissue. Cloning of the amplified products led to the identification of five true receptors, thyroid hormone receptor-alpha (THR alpha), retinoic acid receptor-alpha, retinoic acid receptor-gamma, retinoid X receptor-alpha, and retinoid X receptor-gamma, as well as four orphan receptors, apolipoprotein AI regulatory protein (ARP-1), chicken ovalbumin upstream promoter transcription factor I (COUP-TF I), estrogen-related receptor 2, and testis receptor 4 (TR4). Dot-blot screening of amplified gene fragment analysis showed that THR alpha, ARP-1, TR4, and COUP-TF I were the most abundant factors expressed in the SON region, in the order THR alpha > ARP-1 > TR4 approximately COUP-TF I. THR alpha has previously been localized to HNS neurons. In situ hybridization analysis showed that ARP-1, COUP-TF I, and TR4 were not expressed in magnocellular neurons at appreciable levels, but rather in surrounding structures. Furthermore, in lactating female rats there were no significant differences in the composition of the nine identified nuclear hormone receptors in the SON region compared with control animals. From these experiments, it is concluded that there is a multitude of hypothalamically expressed nuclear hormone receptors, but that only THR alpha is expressed at relatively high abundance in HNS neurons. This indicates that the peptide-producing magnocellular neurons of the SON express a specific set of transcription factors of the nuclear hormone receptor family.

Amino Acid Sequence↗
PubMed1995

Androgen receptor: an overview.

The action of androgens in regulating development and growth is mediated by androgen receptor (AR). AR is a member of the steroid hormone receptor superfamily, a class of receptors that function through their ability to regulate the transcription of specific genes. The AR is located in various target tissues, with its levels and activity altered with the onset of various cellular events (e.g., sexual development, malignant transformation). The modulation of AR levels occurs through a number of mechanisms, including transcription, and is regulated by various factors (e.g., androgens). The ability of AR to modulate gene transcription is through its interaction with specific DNA sequences located near or within the target gene promoter. The importance of the AR in reproductive physiology has been emphasized by the finding of AR mutations, leading to a variety of disorders, including testicular feminization syndrome. In this article, we review the structure and function of AR and the role AR plays in the function of the mammalian system.

Animals↗
PubMed1995

Deletion of integrated hepatitis B virus genome and cellular flanking sequences in hepatocellular carcinoma cells in BALB/c mice.

We have previously reported the establishment of well-differentiated BALB/c mouse liver (ML) cell lines. Transfection of these cell lines with hepatitis B virus (HBV) DNA led to the expression of HBV-specific antigens and integration of HBV sequences in the cellular genome. Two cloned HBV-transfected ML cell lines, ML-2(HBV) and ML-3(HBV), expressed viral antigens and were highly tumorigenic in nude mice. However, the tumorigenicity of the two cell lines was significantly reduced in BALB/c mice. Southern blot analyses showed that the integrated HBV sequences were retained in tumors growing in nude mice but deleted in tumors growing in BALB/c mice. Furthermore, the deletion of HBV DNA was accompanied by deletion of chromosomal sequences flanking the HBV integration sites. In ML-2(HBV) cells, a significant reduction in chromosomal number was also observed. These results suggest that the immune response of BALB/c mice selected against hepatocellular carcinoma (HCC) cells expressing viral antigens and led to the proliferation of cells with deleted HBV sequences and concomitant chromosome aberrations. By using this mechanism, HCC cells escape the immune surveillance and gain the advantage of cell growth.

Animals↗