PubMed Health⌕ Search

Biomedical subjects

C Chang

Publications and source records attributed to C Chang.

At least 307 records · Page 17Linked to original sources
PubMed1994

[The effects of the cyclopentyl ethinyl estriol on the cardiovascular function of postmenopausal women].

The cardiovascular function of postmenopausal women before and after oral supplement of cyclopentyl ethinyl estriol (CEE3) were evaluated with 3-dimensional ultrasound and Doppler technique. The results are as follows: there were no changes of HR, SBP, DBP, MBP and E2 in postmenopausal women before and after the oral supplement of CEE3. Ves and SVR were obviously reduced (P < 0.001). SV, CO, EF, Vmax V and A were obviously increased (P < 0.001). There were no changes in Ved, E and E/A. The results showed that CEE3 could reinforce the cardiac function and increase cardiac output and also reduce the resistance in peripheral blood vessels in postmenopausal women. It is assumed that the cardioprotective effect of hormone replacement therapy in postmenopausal women may be due not only to changes in lipid profile but also to direct effects of estrogens on central and peripheral hemodynamic parameters.

Estrogen Replacement Therapy↗
PubMed1993

Functional and biochemical characterization of the human potassium channel Kv1.5 with a transplanted carboxyl-terminal epitope in stable mammalian cell lines.

The role of the C-terminal domain of the hPCN1/Kv1.5 delayed rectifier K+ channel was investigated in transfected stable cell lines employing antipeptide and anti-epitope antibodies against hPCN1-cp, an epitope-fusion gene carrying additional sequences encoding a 32 amino acid C-terminal extension. Both wild-type and chimeric genes showed high levels of K+ channel expression. Detailed electrophysiologic characterization showed there to be no significant effect of the C-terminal extension on channel activity. Immunoblots of whole-cell and membrane preparations demonstrated primarily intact protein in which the C-terminal extension was not cleaved from the peptide chain. Two bands were visualized from cells transfected with either the wild-type or chimeric channels; the slower migrating band was a non-N-glycosylated form. The epitope-fusion method will be a useful adjunct to studying the role of functional domains in ion channels, and may provide a means for rapid affinity purification of channel protein.

Amino Acid Sequence↗
PubMed1993

Arabidopsis ethylene-response gene ETR1: similarity of product to two-component regulators.

Ethylene behaves as a hormone in plants, regulating such aspects of growth and development as fruit ripening, flower senescence, and abscission. Ethylene insensitivity is conferred by dominant mutations in the ETR1 gene early in the ethylene signal transduction pathway of Arabidopsis thaliana. The ETR1 gene was cloned by the method of chromosome walking. Each of the four known etr1 mutant alleles contains a missense mutation near the amino terminus of the predicted protein. Although the sequence of the amino-terminal half of the deduced ETR1 protein appears to be novel, the carboxyl-terminal half is similar in sequence to both components of the prokaryotic family of signal transducers known as the two-component systems. Thus, an early step in ethylene signal transduction in plants may involve transfer of phosphate as in prokaryotic two-component systems. The dominant etr1-1 mutant gene conferred ethylene insensitivity to wild-type Arabidopsis plants when introduced by transformation.

Amino Acid Sequence↗
PubMed1993

Immune reactions against hepatitis B viral antigens lead to the rejection of hepatocellular carcinoma in BALB/c mice.

Human hepatitis B virus (HBV) is closely associated with hepatocellular carcinoma. However, the mechanism of carcinogenesis and the immune responses to HBV infection and hepatocellular carcinoma are not clearly understood. Recently, we established BALB/c mouse liver (ML) cell lines and demonstrated that transfection of ML cell lines with HBV dimer DNA resulted in the expression of HBV antigens (1). The HBV-transfected ML cells and the parental ML cells showed similar tumorigenicity in nude mice. However, the HBV-transfected cells had much lower tumorigenicity in BALB/c mice. Similar results were also obtained in two cloned ML cell lines, ML-1.1 and ML-1.2, transfected with plasmid DNA containing HBs, HBc, or HBx gene. Furthermore, adoptive transfer of spleen cells from BALB/c mice immunized with HBsAg- or HBcAg-expressing ML-1.1 cells caused regression of tumor cells expressing the corresponding antigens in nude mice. In addition, transfer of spleen cells from BALB/c mice immunized with purified HBsAg or HBcAg also caused tumor regression. These results demonstrate that HBsAg and HBcAg can induce immunity which leads to the rejection of hepatocellular carcinoma in vivo.

Animals↗
PubMed1993

RAP30/74 (transcription factor IIF) is required for promoter escape by RNA polymerase II.

RNA polymerase II-associating proteins (RAP30 and RAP74) are subunits of the transcription factor called variously RAP30/74, TFIIF, beta gamma, and FC. This factor is required for accurate transcription by RNA polymerase II, in addition to other basal transcription factors. Using recombinant human RAP30 and RAP74, the functions of these subunits have been tested separately during the initiation and elongation phases of transcription. RAP30 is required to form a Sarkosyl-resistant complex at 0.25% Sarkosyl, so RAP30 is required for initiation. RAP74, however, stimulates transcription when added after Sarkosyl, indicating that RAP74 is dispensable for initiation. The same result is obtained using a pulse-chase protocol in which accurately initiated RNA is labeled during a short pulse, followed by a chase with excess unlabeled nucleoside triphosphates. RAP30 is required in order to label the transcript during the pulse, but RAP74 is not. RAP74 must be added during the chase, however, in order to obtain a short runoff transcript. The following conclusions can be drawn from these experiments: 1) RAP30 is an initiation factor; 2) RAP74 is not required for ATP hydrolysis in initiation, which precedes phosphodiester bond formation; 3) RAP74 is not required for template strand separation; 4) RAP74 is not required to initiate phosphodiester bond formation; and 5) RAP74 is required for very early elongation.

Adenoviruses, Human↗
PubMed1993

Identification of an androgen-induced C3-P4 DNA binding protein in the cytosol of rat ventral prostate.

A DNA binding protein C3-P4 was detected in the rat ventral prostate cytosol by gel retardation assay using a 32P-labeled 31 base pair synthetic oligomers (sequence deduced from the rat prostatic steroid binding protein C3-1 gene promoter -149 to -119) as a probe. The DNA binding activity of C3-P4 DNA binding protein is sequence specific, with preference for single strand and coding strand exclusive. This protein can be detected in many androgen target tissues and controlled well by androgen in the rat ventral prostate, we speculate that this DNA binding protein may function as an accessory factor to androgen receptor (AR) for the regulation of the C3-1 gene expression.

Animals↗
PubMed1993

Failure of senescent human fibroblasts to express the insulin-like growth factor-1 gene.

Senescent human diploid fibroblasts express several growth-regulated genes but fail to express others. In this paper we show, by a very sensitive technique (reverse transcriptase-polymerase chain reaction), that senescent cells fail to express insulin-like growth factor-1 (IGF-1) mRNA, which is expressed in moderate amounts by young cells. Human fibroblasts immortalized by transfection with a temperature-sensitive SV40 T antigen gene regain the ability to express IGF-1 mRNA, but only at the permissive temperature of 34 degrees C. Under these conditions, the immortalized human fibroblasts grow even in 1% serum. At the restrictive temperature of 39 degrees C, the temperature-sensitive T antigen is nonfunctional, IGF-1 RNA is not detectable, and the cells fail to grow even in 10% serum. The failure to express IGF-1 mRNA in postsenescent cells can be ascribed, at least in part, to a transcriptional mechanism. Despite the correlation among immortalization by SV40 T antigen, expression of IGF-1, and growth, it seems unlikely that the failure to express IGF-1 is the sole cause of cellular senescence; other requirements must be postulated.

Antigens, Polyomavirus Transforming↗
PubMed1993

The use of a DNA-binding domain replacement method for the detection of a potential TR3 orphan receptor response element in the mouse mammary tumor virus long terminal repeat.

TR3 orphan receptor is a human homologue of the mouse nur77, N10 and rat NGFI-B, TIS1 genes which may represent an early response gene involved in the control of cell proliferation. We have studied potential target genes for TR3 orphan receptor using the DNA-binding domain replacement method. We found that mouse mammary tumor virus long terminal repeat-linked chloramphenicol acetyltransferase expression can be activated in transfected cells by a chimeric androgen receptor/TR3 orphan receptor/androgen receptor construct (AR/TR3/AR) in the presence of androgen. By deletion analysis, a region with 20 nucleotides in length between positions -1178 and -1159 of the mouse mammary tumor virus long terminal repeat was confirmed as a potential TR3 orphan receptor response element. These results suggest that feasibility of using the DNA-binding domain replacement method to detect target sequences of orphan receptors.

Androgens↗
PubMed1993

Characterization of the DNA double strand break repair defect in scid mice.

The scid mutation in CB-17 mice confers a profound immunodeficiency, resulting from an inability to rearrange immunoglobulin and T-cell receptor genes during lymphocyte development. Moreover, we and others have recently demonstrated in these scid mice a hypersensitivity to the lethal effects of ionizing radiation and a defect in DNA double strand break rejoining. In this report, we further characterize the radiosensitivity and repair defect in cells from scid mice. In order to determine whether scid cells were specifically sensitive to agents that produce double strand breaks, restriction enzymes RsaI and Sau3AI were introduced into scid and parental C.B-17 cells by electroporation. scid cells were 2-fold more sensitive than C.B-17 cells to both the blunt and the staggered end cuts produced by these restriction enzymes. However, the scid cells proficiently ligated both staggered and blunt ends of transfected plasmids. To determine whether the extent of DNA rejoining in scid cells was dependent on the initial dose of gamma-rays, final levels of DNA double strand break rejoining in scid and C.B-17 cells were quantitated by asymmetric field inversion gel electrophoresis. The results indicate an apparent difference in repair levels dependent on the dose of gamma-rays, ranging from 75% rejoining at 10 Gy to 40% rejoining at 50 Gy. In contrast, > 90% rejoining was observed in control C.B-17 cells at all doses. Delineating the links between these aberrant recombinational events, abnormal V(D)J recombination, and double strand break repair defects, will aid in the understanding of the basic mechanisms involved in these processes.

Animals↗
PubMed1993

Crystallization and preliminary X-ray crystallographic analysis of alpha-amylase from Bacillus subtilis.

Large crystals of alpha-amylase from Bacillus subtilis have been obtained at room temperature using polyethylene glycol 6000 as precipitant. They grow to typical dimensions of 0.25 mm x 0.3 mm x 2.0 mm in five days. The crystals belong to the orthorhombic space group P2(1)2(1)2(1), with unit cell dimensions of a = 85.46 A, b = 166.5 A and c = 332.7 A. The asymmetric unit seems to contain eight molecules of alpha-amylase, with crystal volume per protein mass (Vm) of 2.69 A3/Da and solvent content of 54.3% by volume. Despite a very long c-axis, the crystals diffracted to about 2.2 A Bragg spacing using the rotating anode X-rays and were resistant to damage by X-rays. Thus they are suitable for structure determination by X-ray methods at high resolution. X-ray diffraction data have been collected to 3.4 A Bragg spacing from a native crystal.

Bacillus subtilis↗
PubMed1993

Immunolocalization of androgen receptor in the small, preovulatory, and postovulatory follicles of laying hens.

Previous studies have indicated that androgens may act directly on the ovarian follicles to regulate their functions. The aim of this study was to localize androgen receptor (AR) in the small, preovulatory and postovulatory follicles of laying hens by an immunocytochemical method and Western blot analysis. Small follicles embedded in the stroma (SF), small white follicles protruding from the surface of ovary (SWF), the third largest (F3) and largest follicles (F1), and the most recent postovulatory follicle (POF) were obtained from hens approximately 4 or 10 hr before the expected time of ovulation. Frozen sections of these follicles were immunostained by using anti-human AR antibody. Furthermore, the granulosa cells and theca tissue of preovulatory follicles (F1 and F2) approximately 4 hr before the expected time of ovulation were processed for western blot analysis for AR. The majority of granulosa cell of SF showed negligible AR immunoreaction, whereas all of the granulosa cells of SWF, F3, F1, and POF exhibited a strong AR immunoreaction. Thecal interstitial cells in SWF, F3, and F1 stained positive for AR, and those in POF showed only a weak immunoreaction. The thecal fibroblasts of SWF, F3, and F1 also showed a positive AR immunoreaction, whereas those of POF stained weakly. No significant difference in the AR localization in the ovary was observed between 4 and 10 hr before the expected time of ovulation. Western blot analysis indicated that the granulosa cells and thecal tissue contained AR protein of molecular weight of approximately 120,000.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Ten nucleotide differences, five of which cause amino acid changes, are associated with the Ah receptor locus polymorphism of C57BL/6 and DBA/2 mice.

We have analysed by heteroduplex formation (HF), single stranded conformational polymorphism (SSCP), denaturing gradient gel electrophoresis (DGGE), and nucleotide sequencing the cDNAs of the Ahrb-1 and Ahrd allelic forms of the aromatic hydrocarbon receptor (AhR) present in inbred strains of mice. The Ahrb-1 allele, found in the C57BL and C57BR strains, encodes a 95 kDa receptor with an affinity for ligand 15-20 times higher than the affinity of the 104 kDa receptor encoded by the Ahrd allele, found in the DBA/2 strain. Five overlapping fragments of the AhR coding sequence were obtained from liver RNA by reverse transcriptase synthesis of a cDNA first strand, followed by polymerase chain reaction amplification of these cDNA sequences (RT-PCR). Analysis by HF and SSCP revealed the presence of sequence differences in three of the five fragments. When the complete nucleotide sequence of the coding regions was determined by PCR sequencing, we found a total of ten nucleotide differences between the two alleles, nine of which localized to the three fragments where differences were detected by HF and SSCP. Five of the differences are silent. Of the other five, one changes the opal termination codon in Ahrb-1 to the codon for Arg in Ahrd, extending translation of the mRNA by 43 amino acids and accounting for the larger size of the AhR peptide in DBA/2 mice. One of the four remaining differences causes the replacement of a leucine residue in Ahrb-1 by a proline residue in Ahrd, and breaks a potential alpha-helix near the AhR Q-rich region; it is likely that structural changes associated with this amino acid change are responsible for the differences in agonist affinity observed between the Ah receptors of these two strains of mice.

Amino Acid Sequence↗
PubMed1993

Typing of serum-soluble HLA-B27 antigen by ELISA.

An ELISA using serum as soluble HLA antigen source was developed for HLA-B27 typing. Two sandwich assays were run in parallel. The first assay utilized a monoclonal antibody (mAb) reacting with a determinant expressed by both HLA-B7 and B27 antigens; the other assay utilized a mAb reactive with HLA-B7 antigens but not with HLA-B27 antigens. After incubation with serum samples, bound HLA antigen was detected using an anti-beta 2m antibody conjugated to peroxidase and a chromogenic substrate. Absorbance of each well was measured at 490 nm. Based on analysis of absorbances obtained with panels of specimens of known HLA phenotypes, a mathematical algorithm was developed to derive the specimen HLA-B27 phenotype from its ELISA absorbance values. Despite the lack of monospecific mAb, an accurate HLA-B27 typing was possible. 362 specimens (including 151 HLA-B27-positive) were tested. Agreement between microlymphocytotoxicity and ELISA was 99.2%. No correlation between the level of HLA-B27 antigen reactivity and the amount of total HLA class I antigen in serum was observed. This report demonstrates the possibility of using serum-soluble HLA antigen and ELISA technology for histocompatibility testing. The assay offers several significant advantages over microlymphocytotoxicity: no need for cell preparation, batch testing capabilities and objective, reproducible interpretation of results.

Algorithms↗
PubMed1993

High-level cryIVD and cytA gene expression in Bacillus thuringiensis does not require the 20-kilodalton protein, and the coexpressed gene products are synergistic in their toxicity to mosquitoes.

Interactions among the 20-kDa protein gene and the cytA and cryIVD genes located in a 9.4-kb HindIII fragment were studied. A series of plasmids containing a combination of these different genes was constructed by using the Escherichia coli/Bacillus thuringiensis shuttle vector pHT3101. The plasmids were then used to transform an acrystalliferous strain, cryB, derived from B. thuringiensis subsp. kurstaki. The results from sodium dodecyl sulfate-polyacrylamide gel electrophoresis and immunoblot analyses suggest that although the 20-kDa protein is required for the efficient CytA protein production in E. coli, it is not required in B. thuringiensis. With or without the truncated 20-kDa protein gene, the CtyA and/or CryIVD proteins are produced and form parasporal inclusions in B. thuringiensis cells. However, more-efficient expression is obtained when a second protein, probably acting as a chaperonin, is present. In addition, the time course studies show that the CytA and CryIVD proteins are coordinately produced. Both the crude B. thuringiensis culture and purified inclusions from each recombinant B. thuringiensis strain are toxic to Culex quinquefasciatus larvae. The parasporal inclusions formed in B. thuringiensis cells are mosquitocidal, with CytA synergizing CryIVD toxicity.

Animals↗
PubMed1993

Properties of initiator-associated transcription mediated by GAL4-VP16.

Transcription associated with a terminal deoxynucleotide transferase gene initiator element is shown to respond to the transcription factor GAL4-VP16 both in vivo and in vitro. High-level transcription requires both an intact initiator element and bound activator. Transcription from this initiator-directed promoter is synergistic in vivo in that five GAL4 DNA binding sites yield 36 times the expression of a single site. Promoters dominated by initiator and TATA elements respond similarly to several GAL4-based activators, including GAL4-Sp1, GAL4-CTF, GAL4(1-147), GAL4-p53, GAL4-C/EBP, and GAL4-ER(EF), as well as GAL4-VP16 and Sp1. These and other similarities suggest that primary activation of TATA- and initiator-dominated promoters occurs at common steps. Since the initial assembly steps do not appear to be common for the two promoter types, the results place interesting constraints on models for how activation occurs.

Animals↗
PubMed1993

Electrophysiological effects of high cocaine concentrations on intact canine heart. Evidence for modulation by both heart rate and autonomic nervous system.

BACKGROUND: Previous clinical reports have suggested that cocaine intoxication may produce severe ventricular arrhythmias due to a direct effect on the heart. However, the effects of high plasma levels of cocaine on the electrophysiology of the heart have not been well characterized and remain poorly understood. METHODS AND RESULTS: The purpose of this study was to characterize the electrophysiological effects of high doses of cocaine on the in situ dog heart. In dogs anesthetized with morphine and alpha-chloralose, cocaine (2-11 micrograms/mL) increased both atrial and ventricular refractory periods and produced rate-dependent increases in atrial, atrioventricular, His-Purkinje, and ventricular conduction intervals. The time constant for the onset of cocaine's conduction slowing effect following a reduction in pacing cycle length from 400 to 260 msec was approximately two beats, and the time constant for diastolic recovery from conduction slowing was approximately 200 msec, which are similar to values reported for several class Ib antiarrhythmic drugs. Cocaine produced a rate-dependent increase in QT interval that was greatest at high heart rates yet produced no change in the ST (QT-QRS) interval. This suggests that high plasma levels of cocaine delay repolarization primarily via slowing of conduction. Cocaine's effects on both atrioventricular and intraventricular conduction were significantly larger in autonomically blocked than in autonomically intact animals. CONCLUSIONS: We conclude that high plasma levels of cocaine, similar to those reported in autopsy reports following fatal cocaine overdose in humans, produce significant rate-dependent conduction slowing effects on atrial, atrioventricular, and ventricular conduction in the in situ heart. These rate-dependent effects are intensified following autonomic blockade.

Animals↗