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Biomedical subjects

M Li

Publications and source records attributed to M Li.

At least 451 records · Page 25Linked to original sources
PubMed1999

Loss of anti-mitotic effects of Bcl-2 with retention of anti-apoptotic activity during tumor progression in a mouse model.

Bcl-2 is an anti-apoptotic and anti-proliferative protein over-expressed in several different human cancers including breast. Gain of Bcl-2 function in mammary epithelial cells was superimposed on the WAP-TAg transgenic mouse model of breast cancer progression to determine its effect on epithelial cell survival and proliferation at three key stages in oncogenesis: the initial proliferative process, hyperplasia, and cancer. During the initial proliferative process, Bcl-2 strongly inhibited both apoptosis and mitotic activity. However as tumorigenesis progressed to hyperplasia and adenocarcinoma, the inhibitory effects on mitotic activity were lost. In contrast, anti-apoptotic activity persisted in both hyperplasias and adenocarcinomas. These results demonstrate that the inhibitory effect of Bcl-2 on epithelial cell proliferation and apoptosis can separate during cancer progression. In this model, retention of anti-apoptotic activity with loss of anti-proliferative action resulted in earlier tumor presentation.

Adenocarcinoma↗
PubMed1999

Immunocytochemical localization of the beta(3) subunit of the gamma-aminobutyric acid(A) receptor in the rat brain.

A novel anti-beta(3) subunit-specific GABA(A) receptor (GABA(A)R) antibody has been prepared by immunizing a rabbit with a bacterial fusion protein of the large intracellular loop of the beta(3) subunit. The antiserum immunoprecipitated the solubilized GABA(A) receptor. The anti-beta(3) antibody was affinity purified on immobilized beta(3) large intracellular loop peptide. In immunoblots, the purified antibody reacted with a 57 KDa peptide. Immunocytochemistry with the affinity-purified antibody has revealed the localization of the beta(3) subunit in the rat brain. A comparative study with the immunocytochemical distribution of the beta(2) subunit has also been performed. There are areas of the brain and cell types where the distribution of beta(2) and beta(3) overlap (i.e., cerebral cortex, cerebellum,and most layers of the olfactory bulb). There are also clear differences in the expression of beta(3) and beta(2) in other brain areas and cell types. Thus, high beta(3) but low or no beta(2) expression was observed in the corpus striatum and in granule cells of the olfactory bulb. In the hippocampus the expression of beta(3) was considerably higher than that of beta(2), but some hippocampal interneurons showed high expression of beta(2). High beta(2) but little or no expression of beta(3) was observed in thalamic nuclei, substantia nigra, globus pallidus, inferior colliculus and the short axon cells of the olfactory bulb.

Animals↗
PubMed1999

A clinical analysis of 836 cases with electric injury.

Eight hundred thirty-six patients with electric injury were admitted to Shanghai Power Hospital from 1972 to 1998. The majority of electric injury patients were young or middle-aged industrial workers from both cities and rural areas. These patients were classified into three categories depending on the type of electric injury: (1) electric shock; (2) electric contact burn injury; (3) electric arc burn. In our study of wound management, we focused on three areas: first, the choice of operation time in electric burn injury; second, the methods of wound management on the injured extremities, especially the hands and upper limbs; third, functional site wounds that included some exposed blood vessels. Nerves and tendons were covered and repaired by various flaps. Through the analysis of 836 electric injury cases, we summarized our experience of treating electric injury with the purpose of increasing our knowledge in the area of electric injury prevention and treatment.

Accidents, Occupational↗
PubMed1999

CD8 T cell ignorance or tolerance to islet antigens depends on antigen dose.

There are two major mechanisms reported to prevent the autoreactivity of islet-specific CD8(+) T cells: ignorance and tolerance. When ignorance is operative, naïve autoreactive CD8(+) T cells ignore islet antigens and recirculate without causing damage, unless activated by an external stimulus. In the case of tolerance, CD8(+) T cells are deleted. Which factor(s) contributes to each particular outcome was previously unknown. Here, we demonstrate that the concentration of self antigen determines which mechanism operates. When ovalbumin (OVA) was expressed at a relatively low concentration in the pancreatic islets of transgenic mice, there was no detectable cross-presentation, and the CD8(+) T cell compartment remained ignorant of OVA. In mice expressing higher doses of OVA, cross-presentation was detectable and led to peripheral deletion of OVA-specific CD8(+) T cells. When cross-presentation was prevented by reconstituting the bone marrow compartment with cells incapable of presenting OVA, deletional tolerance was converted to ignorance. Thus, the immune system uses two strategies to avoid CD8(+) T cell-mediated autoimmunity: for high dose antigens, it deletes autoreactive T cells, whereas for lower dose antigens, it relies on ignorance.

Adoptive Transfer↗
PubMed1999

Determination of benzo[a]pyrene-DNA adducts by solid-matrix phosphorescence.

It has been demonstrated for the first time that linear relationships can be obtained between the solid-matrix phosphorescence (SMP) and the percent modification of benzo[a]pyrene-7,8-dihydrodiol-9,10-epoxide (BPDE)-DNA adducts. The samples of DNA were modified with BPDE at levels of 5.0 x 10(-3), 1.0 x 10(-3), 5.0 x 10(-4), 1.0 x 10(-4), 5.0 x 10(-5), and 1.0 x 10(-5%). In addition, the changes in the SMP intensities of a given percentage of DNA adduct were investigated as a function of sample size, and linear relationships were also acquired. With the different percentages of modified DNA, very good reproducibility of the SMP signals was obtained. Data were acquired with both Whatman 1PS paper and 30% TlNO3/sodium acetate as solid matrixes. The limit of detection for the BPDE-DNA adducts was 2 adducts in 10(7) bases for both Whatman 1PS paper and 30% TlNO3/sodium acetate. In addition, it was shown that it would be important to develop a standard procedure for the preparation of the BPDE-DNA samples if different batches of DNA were used in the preparation procedure.

Benzo(a)pyrene↗
PubMed1999

Synthesis and antitumour activity of novel diterpenequinone salvicine and the analogs.

A novel diterpenequinone named salvicine (4), structurally modified derivative of a natural product, and a series of the novel analogs have been prepared. Most of the analogs were found to be potently active against tumor cell lines in vitro. Further study on 4 in vivo demonstrated that it possessed a significant antineoplastic activity against murine S-180 Sarcoma and Lewis lung cancer, and human lung adenocarcinoma xenografts A-549 and LAX-83. The preclinical studies of 4 are now under way.

Animals↗
PubMed1999

Localization and dynamic relocalization of mammalian Rad52 during the cell cycle and in response to DNA damage.

The importance of RAD52 in establishment and maintenance of genomic structure has been established by genetic experiments in the yeast Saccharomyces cerevisiae, where mutation of RAD52 has been shown to diminish DNA repair and recombination of a variety of markers, including the rDNA [1] [2] [3]. Biochemical analysis has shown that yeast and mammalian Rad52 proteins have some identical functions in vitro [4] [5] [6], but targeted deletion of Rad52 in vertebrates has little effect on repair and recombination [7] [8]. These results raise the question of whether mammalian Rad52 does indeed function in recombination and/or repair. Here we show that Rad52 is distributed throughout the nucleoplasm in actively cycling mammalian cells and is localized specifically to the nucleoli in S phase. In response to ionizing radiation, Rad52 relocalizes to form distinctive foci which are distributed throughout the nucleus and which colocalize with Rad50 foci in the DNA damage response. These data suggest that rDNA recombination and DNA repair are functions shared by mammalian Rad52 and its S. cerevisiae homolog, and provide evidence for the coordinated action of Rad50 and Rad52 in DNA repair.

Acid Anhydride Hydrolases↗
PubMed1999

Differential stimulation of PKC phosphorylation of potassium channels by ZIP1 and ZIP2.

Targeting of protein modification enzymes is a key biochemical step to achieve specific and effective posttranslational modifications. Two alternatively spliced ZIP1 and ZIP2 proteins are described, which bind to both Kvbeta2 subunits of potassium channel and protein kinase C (PKC) zeta, thereby acting as a physical link in the assembly of PKCzeta-ZIP-potassium channel complexes. ZIP1 and ZIP2 differentially stimulate phosphorylation of Kvbeta2 by PKCzeta. They also interact to form heteromultimers, which allows for a hybrid stimulatory activity to PKCzeta. Finally, ZIP1 and ZIP2 coexist in the same cell type and are elevated differentially by neurotrophic factors. These results provide a mechanism for specificity and regulation of PKCzeta-targeted phosphorylation.

Alternative Splicing↗
PubMed1999

Leukemia inhibitory factor and its receptor promote adipocyte differentiation via the mitogen-activated protein kinase cascade.

Extracellular factors and intracellular signaling pathways involved in early events of adipocyte differentiation are poorly defined. It is shown herein that expression of leukemia inhibitory factor (LIF) and LIF receptor is developmentally regulated during adipocyte differentiation. Preadipocytes secrete bioactive LIF, and an antagonist of LIF receptor inhibits adipogenesis. Genetically modified embryonic stem (ES) cells combined with culture conditions to commit stem cells into the adipocyte lineage were used to examine the requirement of LIF receptor during in vitro development of adipose cells. The capacity of embryoid bodies derived from lifr(-/-) ES cells to undergo adipocyte differentiation is dramatically reduced. LIF addition stimulates adipocyte differentiation of Ob1771 and 3T3-F442A preadipocytes and that of peroxisome proliferator-activated receptor gamma2 ligand-treated mouse embryonic fibroblasts. Expression of the early adipogenic transcription factors C/EBPbeta and C/EBPdelta is rapidly stimulated following exposure of preadipose cells to LIF. The selective inhibitors of mitogen-activated protein kinase kinase, i.e. PD98059 and U0126, inhibit LIF-induced C/EBP gene expression and prevent adipocyte differentiation induced by LIF. These results are in favor of a model that implicates stimulation of LIF receptor in the commitment of preadipocytes to undergo terminal differentiation by controlling the early expression of C/EBPbeta and C/EBPdelta genes via the mitogen-activated protein kinase cascade.

Adipocytes↗
PubMed1999

Images of oligomeric Kv beta 2, a modulatory subunit of potassium channels.

The Shaker type voltage-gated potassium (K+) channel consists of four pore-forming Kv alpha subunits. The channel expression and kinetic properties can be modulated by auxiliary hydrophilic Kv beta subunits via formation of heteromultimeric Kv alpha-Kv beta complexes. Because each (Kv alpha)4 could recruit more than one Kv beta subunit and different Kv beta subunits could potentially interact, the stoichiometry of alpha-beta and beta-beta complexes is therefore critical for understanding the functional regulation of Shaker type potassium channels. We expressed and purified Kv beta 2 subunit in Sf9 insect cells. The purified Kv beta 2, examined by atomic force and electron microscopy techniques, is found predominately as a square-shaped tetrameric complex with side dimensions of 100 x 100 A2 and height of 51 A. Thus, Kv beta 2 is capable of forming a tetramer in the absence of pore-forming alpha subunits. The center of the Kv beta 2 complex was observed to be the most heavily stained region, suggesting that this region could be part of an extended tubular structure connecting the inner mouth of the ion permeation pathway to the cytoplasmic environment.

Amino Acid Sequence↗
PubMed1999

Magnetite Nanoparticles Prepared by Precipitation from Partially Reduced Ferric Chloride Aqueous Solutions.

Spherical magnetite particles with mean diameter of about 10 nm or less were prepared by means of a reduction-precipitation method with ferric chloride as starting material, which was partially reduced to ferrous salts by Na2SO3 before alkalinizing with ammonia. It was found that the nature of the product depends strongly on the initial ratio R0 = [Fe3+]0/[SO2-3]0. The most appropriate ratio was 3 as proved by X-ray diffraction analysis on the samples although the initial concentration of ferric chloride can be different. Particle diameter increased from ca. 3 to ca. 11 nm with an increase of the concentration of aqueous ferric chloride from 0.075 to 0.45 mol dm-3. The advantage of this method lies in the formation of a red intermediate during the reduction process, which enables us to prevent the reoxidation of the ferrous ions by adding precipitation agents at the end of the reduction reaction without the protection of nitrogen or argon. Copyright 1999 Academic Press.

Journal Article↗
PubMed1999

Apoptosis-linked gene product ALG-2 is a new member of the calpain small subunit subfamily of Ca2+-binding proteins.

ALG-2 is a newly discovered Ca2+-binding protein which has been demonstrated to be directly linked to apoptosis. Structurally, ALG-2 is expressed as a single polypeptide chain corresponding to a 22 kDa protein containing five putative EF-hand Ca2+-binding sites. In this work, we have developed an efficient expression and purification scheme for recombinant ALG-2. Utilizing this protocol, we can routinely obtain purified recombinant protein with a yield of approximately 100 mg per liter of bacterial cell cultures. Gel filtration and chemical cross-linking experiments have shown that Ca2+-free ALG-2 forms a weak homodimer in solution. Biochemical and spectroscopic studies of truncated and point mutants of ALG-2 demonstrated that the fifth EF-hand Ca2+-binding motif is likely to participate in the formation of the dimer complex. Experimentally, both the amino- and carboxyl-terminal truncated mutants of ALG-2 have shown their ability to retain the structural, as well as, Ca2+-binding integrity when individually expressed in bacteria. In this respect, the N-terminal domain encompasses the first two EF-hands, and the C-terminal domain contains the remaining three EF-hands. Combining mutagenesis and spectroscopic studies, we showed that ALG-2 possesses two strong Ca2+-binding sites. Employing fluorescence spectroscopy and circular dichroism, we showed that the binding of Ca2+ to ALG-2 induced significant conformational changes in both the N-terminal and C-terminal domains of the protein. Furthermore, our studies demonstrated that Ca2+ binding to both strong Ca2+-binding sites of ALG-2 is required for ion-induced aggregation of the protein. We also report here the expression, purification, and partial characterization of a Ca2+-binding-deficient ALG-2 mutant (Glu47Ala/Glu114Ala). In light of its much decreased affinity for Ca2+, this mutant could prove to be instrumental in elucidating the Ca2+-mediated function of ALG-2 within the context of its cellular environment.

Animals↗
PubMed1999

Characterization of MALS/Velis-1, -2, and -3: a family of mammalian LIN-7 homologs enriched at brain synapses in association with the postsynaptic density-95/NMDA receptor postsynaptic complex.

Protein assembly at the postsynaptic density (PSD) of neuronal synapses is mediated in part by protein interactions with PSD-95/discs large/zona occludens-1 (PDZ) motifs. Here, we identify MALS-1, -2, -3, a family of small synaptic proteins containing little more than a single PDZ domain. MALS-1, -2, and -3 are mammalian homologs LIN-7, a Caenorhabditis elegans protein essential for vulval development. In contrast to functions for LIN-7 in epithelial cells, MALS-1 and -2 are selectively expressed in specific neuronal populations in brain and are enriched in PSD fractions. In cultured hippocampal neurons, MALS proteins are clustered together with PSD-95 and NMDA type glutamate receptors, consistent with a postsynaptic localization for MALS proteins. Immunoprecipitation and affinity chromatography studies readily identify association of MALS with PSD-95 and an NMDA receptor subunit. The PDZ domain of MALS selectively binds to peptides terminating in E-T/S-R/X-V/I/L, which corresponds to the C terminus of NMDA type 2 receptors and numerous other ion channels at the PSD. This work suggests a role for MALS proteins in regulating recruitment of neurotransmitter receptors to the PSD.

Amino Acid Sequence↗
PubMed1999

Gain of Bcl-2 is more potent than bax loss in regulating mammary epithelial cell survival in vivo.

The impact of gain of Bcl-2 function on mammary epithelial cell survival was compared with loss of Bax function during the two stages of mammary gland involution. Bcl-2 gain of function reduced apoptosis 50% during the first stage and increased cell survival 70% during the second stage. Complete loss of Bax reduced apoptosis by 20% during the first stage without second stage effect. Partial loss of Bax was ineffective but increased cell survival 2.4-fold when combined with Bcl-2 gain. Gain of Bcl-2 function is more potent than loss of Bax function in regulating mammary epithelial cell survival in vivo.

Animals↗
PubMed1999

Inhibition of caspase-1 slows disease progression in a mouse model of Huntington's disease.

Huntington's disease is an autosomal-dominant progressive neurodegenerative disorder resulting in specific neuronal loss and dysfunction in the striatum and cortex. The disease is universally fatal, with a mean survival following onset of 15-20 years and, at present, there is no effective treatment. The mutation in patients with Huntington's disease is an expanded CAG/polyglutamine repeat in huntingtin, a protein of unknown function with a relative molecular mass of 350,000 (M(r) 350K). The length of the CAG/polyglutamine repeat is inversely correlated with the age of disease onset. The molecular pathways mediating the neuropathology of Huntington's disease are poorly understood. Transgenic mice expressing exon 1 of the human huntingtin gene with an expanded CAG/polyglutamine repeat develop a progressive syndrome with many of the characteristics of human Huntington's disease. Here we demonstrate evidence of caspase-1 activation in the brains of mice and humans with the disease. In this transgenic mouse model of Huntington's disease, expression of a dominant-negative caspase-1 mutant extends survival and delays the appearance of neuronal inclusions, neurotransmitter receptor alterations and onset of symptoms, indicating that caspase-1 is important in the pathogenesis of the disease. In addition, we demonstrate that intracerebroventricular administration of a caspase inhibitor delays disease progression and mortality in the mouse model of Huntington's disease.

Animals↗
PubMed1999

Design of a fluid energy single vessel powder processor for pharmaceutical use.

This study introduces a motionless novel single vessel powder processor designed to carry out all of the unit operations in the preparation of powders for tableting. The processor used controllable fluid dynamics to provide the energy for each unit operation. The vessel design was evaluated using a computational fluid dynamics model which indicated the flow necessary for the intended processing operations to take place. The processor performance was evaluated experimentally for two unit processes: particle size reduction and dry powder mixing. The processor was found capable of reducing the size of lactose granules from a median particle diameter of 459 microm to a median particle diameter of 182 microm within 5 min under optimal process conditions. It was found that a formulation containing lactose granules (373 microm median particle diameter) and a model drug, sodium chloride (30 microm), could be mixed to an improved degree of homogeneity in comparison with equivalent powders blended using a conventional turbulent tumbling technique. It was concluded that a processor having controllable fluid dynamics offered the potential to perform multi-task processing of powders.

Chemistry, Pharmaceutical↗
PubMed1999

A 1-Mb bacterial clone contig spanning the endometrial cancer deletion region at 1p32-p33.

Our laboratory previously reported a high frequency of loss of heterozygosity (LOH) at 1p32-p33 in endometrial cancers. LOH at 1p32-p33 is a specific feature of one of the most aggressive forms of endometrial carcinoma, uterine papillary serous cancer (UPSC). The minimum region of allelic loss in UPSC is defined by D1S190 and D1S447, an interval corresponding to less than 1 cM. Here we describe the construction and characterization of a sequence-ready clone contig that spans the deletion region. The contig consists of 24 bacterial artificial chromosome clones and 18 P1 artificial chromosome clones and spans approximately 1050 kb. The consensus region of allelic loss between D1S190 and D1S447 represents approximately 792 kb. Eight previously described ESTs have been positioned within the contig.

Blotting, Southern↗