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Biomedical subjects

P Liang

Publications and source records attributed to P Liang.

At least 109 records · Page 6Linked to original sources
PubMed1993

Inhibitory effect of xylamine on the uptake of [3H]dopamine into isolated striatal synaptosomes of the rats.

The synaptosomal preparations from Wistar rat striata show a Na(+)-dependent, nomifensine-sensitive uptake of [3H]dopamine([3H]DA). Xylamine, a nitrogen mustard, attenuated this uptake of [3H]DA into the synaptosomes (IC50 = 0.2 microM). The dose-dependent reduction of [3H]DA uptake by xylamine indicated competitive kinetics. Action of xylamine was modified if the active transport inhibitor, ouabain or iodoacetate, was also incubated during the pretreatment period or if the content of Na+ in medium was changed. Also, xylamine displaced the binding of [3H]mazindol in a correlative way with the inhibition of [3H]DA uptake. However, the activity of Na+, K(+)-ATPase in synaptosomes was not modified by xylamine at concentrations sufficient to block the uptake of [3H]DA. These findings suggest that xylamine has the ability to compete with the transport of [3H]DA into striatal synaptosomes through an effect on the carrier instead of an action on enzymatic activity.

Animals↗
PubMed1993

Identification by differential display of alpha 6 integrin as a candidate tumor suppressor gene.

A new method of differential expression cloning called differential display (DD) has been used to screen for novel tumor suppressor genes involved in breast cancer. The screen is based on positive selection at the mRNA level for genes expressed in normal mammary epithelial cells but decreased or lost in corresponding tumor cells. A candidate tumor suppressor gene recovered by DD is integrin alpha-6 (alpha 6), a component of the heterodimeric integrin receptors alpha 6 beta 1 and alpha 6 beta 4. Loss of alpha 6 expression was confirmed in total RNAs by Northern blot analysis and by immunostaining with alpha 6 antibodies. Consistent with these cell culture findings, previous immunostaining of mammary tissue sections has identified decreased alpha 6 protein expression during breast tumor progression. Southern blot analysis demonstrated that alpha 6 gene is present in tumor cell lines, suggesting that reexpression may be inducible by pharmacological intervention. The likelihood that alpha 6 may have tumor suppressing activity is supported by growing evidence of a central role for integrins in transducing growth control and differentiation signals from growth factors and the extracellular matrix (ECM).

Base Sequence↗
PubMed1992

Differential display and cloning of messenger RNAs from human breast cancer versus mammary epithelial cells.

Identification of the genes that are specifically expressed in tumor cells but not in normal cells (oncogenes), or vice versa (tumor suppressor genes), is important for understanding the molecular basis of cancer. The differential display technique was applied to compare mRNAs from normal and tumor-derived human mammary epithelial cells, cultured under the same conditions. Complementary DNA fragments corresponding to several apparently differentially expressed mRNAs were recovered and sequenced. They exhibit characteristics of the 3' end of eukaryotic mRNA, as predicted by the method. A complementary DNA fragment seen only in the normal cell was used as a probe to isolate its corresponding complementary DNA clone from a library. Northern analysis confirmed its differential expression. Thus, this method can be used for detecting, cloning, and sequencing of genes that are unique to a host of biological and disease processes.

Base Sequence↗
PubMed1992

Differential display of eukaryotic messenger RNA by means of the polymerase chain reaction.

Effective methods are needed to identify and isolate those genes that are differentially expressed in various cells or under altered conditions. This report describes a method to separate and clone individual messenger RNAs (mRNAs) by means of the polymerase chain reaction. The key element is to use a set of oligonucleotide primers, one being anchored to the polyadenylate tail of a subset of mRNAs, the other being short and arbitrary in sequence so that it anneals at different positions relative to the first primer. The mRNA subpopulations defined by these primer pairs were amplified after reverse transcription and resolved on a DNA sequencing gel. When multiple primer sets were used, reproducible patterns of amplified complementary DNA fragments were obtained that showed strong dependence on sequence specificity of either primer.

Base Sequence↗
PubMed1992

Ultracytochemical studies on Trichomonas hominis.

The results of ultracytochemical studies on Trichomonas hominis showed that ACPase and CMPase were mainly located in the mature face sacs of the primary lysosomes, digestive vacuoles, as well as in the parabasal body. TPPase and NADPase were found in the saccules at the mature face and the intermediate saccules of parabasal body respectively. This study revealed that T. hominis had well-developed parabasal bodies. Negative COase and catalase reactions indicated that T. hominis lacked both mitochondria and microbody. Hydrogenosome was stained well with the Ur-Pb-Cu impregnation technique.

Acid Phosphatase↗
PubMed1992

Selection and identification of antigenic determinant of Mycobacterium tuberculosis H37Ra strain.

A new procedure for the selection of the antigenic determinant of Mycobacterium tuberculosis H37Ra strain is described. The bacterium components destroyed by ultrasonic were isolated by 15% SDS-PAGE, transferred onto nitrocellulose membrane, immunostained with McAbs against H37Ra. One McAb-positive fragment was obtained using the Western blot analysis. The molecular weight of the antigenic determinant is 35,000 dalton. The antigenic determinant is of immunological reactivity with McAb and TB patients' sera in dot-immunoassay and demonstrated in delayed skin tests in guinea pigs. The amino acid composition of the antigenic determinant was analysed. These suggest that the Western blot analysis may be a useful tool for the analysis of the antigenic determinant.

Amino Acids↗
PubMed1992

HDL and apolipoprotein A1 (apo A1). Their effects on retardation of lipid deposition in aortic intima.

The aim of this study is to clarify whether apo A1 displays a similar role as that of HDL in preventing the development of experimental atherosclerosis. Results were obtained from 4 groups of experiments. (1) Result from 4 successive experiments of tree shrews indicated that high serum HDL level is the main factor in preventing the development of experimental atherosclerosis; (2) Results from 4 successive experiments in rabbits showed that both HDL and apo A1 were able to decrease the extent of lipid deposition and atheromatous lesion developed in the aortic intima; (3) Apo A1 also inhibited the number of monocytes/macrophages infiltrated in aortic intima at the initial stage of fatty streak formation; (4) Similar as HDL, apo A1 phospholipid liposomes promoted markedly the clearance ability of smooth muscle cells on intracellular cholesterol. Conclusively, apo A1 is effective in preventing the development of experimental atherosclerosis. Further study, however, is required to detect an ideal combination of apo A1 with other component, e.g., phospholipid.

Animals↗
PubMed1991

Assignment of the nucleotide binding sites and the mechanism of substrate inhibition of Escherichia coli adenylate kinase.

Site-directed mutagenesis of key amino acids of adenylate kinase has been used to suggest a new model for the location of the AMP and ATP binding sites. Phe-86 and Tyr-133, which are in close contact with the inhibitor Ap5A according to previous crystallographic results, have been independently changed to tryptophan and other amino acids. The Phe-86----Trp mutant had a 3- to 6-fold change in the Km for ATP and a 44-fold increase in the Km for AMP with a simultaneous loss of AMP substrate inhibition. Thus Phe-86 is probably in close contact with bound AMP. The Tyr-133----Trp mutant showed no large effects on enzyme kinetics and suggests that the previous assignment of Ap5A occupying natural adenosine binding sites is probably incorrect. A temperature-sensitive Leu-107----Gln mutant showed a 6-fold decrease in the Km for ATP and no effect on AMP binding, suggesting that this amino acid is near the ATP binding site. Changes in the fluorescence of single tryptophan-containing mutant enzymes provided specific information about AMP and ATP binding. The fluorescence results are consistent with the kinetic studies, and also suggest that AMP substrate inhibition is caused by the formation of an abortive complex that prevents the release of product.

Adenosine Monophosphate↗
PubMed1991

[Electron microscopic cytochemistry studies on membrane-bound organelles of Trichomonas hominis].

This paper presents the results of an electron microscopy cytochemistry study on the membrane-bound organelles of Trichomonas hominis. Acid phosphatase (ACP) and cytidine monophosphatase (CMPase) were located in the primary lysosomes, digestive vacuoles, as well as in the parabasal body stacks, being usually in its mature surface sacs. Thiamine pyrophosphatase (TPPase) and nicotinamide adenine dinucleotide phosphatase (NADPase) were found in the saccules, being on the mature surface and in the intermediate saccules of parabasal body stacks, respectively. The reactive products of peroxidase (POase) were seen only in the digestive vacuoles. Cytochrome oxidase (COase) and catalase (Cat) reactions were both negative. It is suggested that T. hominis lacks mitochondrion and microbody but possesses hydrogenosome. The parabasal body, endoplasmic reticulum and hydrogenosome were stained well with the U-Pb-Cu impregnation technique.

Animals↗
PubMed1991

[Pathologic study on megakaryocytes in chronic myeloproliferative disorders].

Megakaryocytes in 42 cases of Chronic Myeloproliferative Disorders were studied pathologically, and a classification of these disorders was suggested. Abnormal megakaryocytes were classified as immature, mature, naked-nuclear, micro-, giant, multinucleated and dysplastic types based on the degree of maturity, the number of ploidy, and the presence or absence of atypia. Immunohistochemical studies indicated that antibodies against platelet glycoprotein Ib, IIb/IIIa as well as VIII R:Ag are highly specific for the detection of megakaryocytes, especially the morphologically unrecognizable ones. With regard to the identification of micromegakaryocytes, nuclear size, shape and degree of cytoplasmic maturity were emphasized. In addition to the classification, the clinic-pathological significance of abnormal megakaryocytes is discussed.

Antibodies, Monoclonal↗
PubMed1990

Combined histochemical and biochemical analysis of sex hormone dependence of ferric nitrilotriacetate-induced renal lipid peroxidation in ddY mice.

Ferric nitrilotriacetate (Fe-NTA) induces renal proximal tubular necrosis, a consequence of lipid peroxidation, that finally leads to a high incidence of renal adenocarcinoma in rats and mice. Male animals are much more susceptible than female animals to both effects. Moreover, the distribution of the susceptible proximal tubules is different between male and female animals. The present study investigated the effects of castration and sex hormones on Fe-NTA-induced renal lipid peroxidation. Male and female ddY mice were either left untreated, castrated, and/or treated with testosterone or estriol. Histochemical (reactivity to cold Schiff's reagent) and biochemical (thiobarbituric acid-reactive substance) evaluations were performed 1 h after the i.p. injection of Fe-NTA (5 mg iron/kg). Testosterone treatment and/or oophorectomy increased the Schiff positivity of the renal cortical proximal tubules and the amount of thiobarbituric acid-reactive substance (testosterone-treated female greater than intact female, P less than 0.005; castrated female greater than intact female, P less than 0.1; castrated and testosterone-treated female greater than intact female, P less than 0.005). In contrast, estriol treatment and/or orchiectomy decreased the Schiff positivity of the renal cortical proximal tubules and the amount of thiobarbituric acid-reactive substance (estriol-treated male less than intact male, P less than 0.01; castrated male less than intact male, P less than 0.01; castrated and estriol-treated male less than intact male, P less than 0.005). Estradiol treatment produced similar results to estriol treatment (estradiol-treated male less than intact male, P less than 0.005). Castration and/or administration of the opposite sex hormone reversed the sex difference in the distribution of proximal tubules susceptible to lipid peroxidation. However, the i.v. injection to male mice, 5 min prior to the Fe-NTA treatment, of conjugated estrogen that is promptly excreted via the urine produced no significant effect. Thus, altered metabolic pathways rather than the direct scavenging activity of estrogens seem to be involved in the sex hormone-dependent difference of lipid peroxidation. Genetically determined sex hormone status appears to have influenced the incidence of Fe-NTA-induced renal adenocarcinoma in intact animals.

Acetates↗
PubMed1990

Inhibition of zygote formation and embryo development in mice immunized with monoclonal antisperm antibodies.

Passive immunization of female mice by the intraperitoneal administration of ascitic fluids containing monoclonal antisperm antibodies blocked the development of mouse zygotes to morulae and blastocysts when cultured in vitro. Radioiodinated YWK-I monoclonal antibodies were prepared and administered intraperitoneally to female mice. Significant radioactivity was found in washes of the oviductal lumens. The results suggest that antisperm antibodies block fertilization and may have a deleterious effect on early developing embryos.

Animals↗
PubMed1989

Efficient cloning of a mutant adenylate-kinase-encoding gene from Escherichia coli.

An optimized system has been developed for the transfer of a mutant gene from the Escherichia coli chromosome to a plasmid carrying the wild type (wt) allele. The wt allele was first cloned into a low-copy-number, self-transmissible plasmid with a single EcoRI, HindIII, and BamHI site. The plasmid was then transferred to a mutant strain that had been previously transformed with a high-copy-number plasmid carrying the recA+ gene to allow efficient homologous recombination. A 15% frequency of homogenotization was obtained during cloning of an adk gene that encodes a temperature-sensitive adenylate kinase (AK). The mutant AK had decreased mobility on sodium dodecyl sulfate-polyacrylamide gels compared with the wt enzyme. This was due to a point mutation that changed leucine-107 in the wt enzyme to glutamine-107 in the mutant enzyme as determined by nucleotide sequencing.

Adenylate Kinase↗
PubMed1989

[Electron microscopic study of mucus secretion in gastric carcinoma and its pathologic significance].

The genesis, ultrastructure and fate of mucin granule in cancer cells are described, and lysosomal degradation (crinophagy) was confirmed by demonstration of cytidine monophosphatase activity. Mucin granules usually appeared as those in the goblet cell, but were heterogenous. The chemical nature of mucin or the histogenesis of tumor should not be determined simply by depending on certain features of mucin granule, because these mucin granules might be influenced by the direction of cell differentiation, the maturity of mucin granule, and the abnormalities in its development. In this paper, different patterns of mucus secretion in various histologic types are described, and their pathologic significance is discussed.

Adenocarcinoma↗