Biomedical subjects

B Lin

Publications and source records attributed to B Lin.

At least 91 records · Page 5Linked to original sources

PubMed2000

Melting transition in a quasi-two-dimensional colloid suspension: influence of the colloid-colloid interaction

We report the results of a study, using digital video microscopy, of the melting transition in a quasi-two-dimensional suspension of uncharged silica spheres. This system was chosen to further test the dependence of the two-dimensional melting transition on the functional form of the colloid-colloid interaction. Our experimental data show that the solid phase undergoes a first order transition directly to the liquid phase. The system studied yields no evidence of the existence of a hexatic phase interpolating between the solid and liquid phases in the melting process.

Journal Article↗

PubMed2000

Direct measurements of constrained brownian motion of an isolated sphere between two walls

We report the results of direct measurements, using video microscopy in combination with optical tweezers, of constrained diffusion of an isolated uncharged PMMA sphere in a density-matched fluid confined between two parallel flat walls. Our experimental methodology allows us to study the hindered diffusion of the sphere as an explicit function of its distance from the walls, without interference from sedimentation or from electrostatic interaction between the particle and the walls. The measured diffusion coefficients are used to test the predictions of the wall drag effect predicted by several approximate theoretical analyses. We find a quantitative agreement with the behavior predicted using a hydrodynamic analysis that independently superimposes the wall drag effects arising from each wall. Our results imply, indirectly, that neglect of multiple interactions with the colloid sphere of the perturbations of the pressure and velocity fields induced by each wall leads to an underestimate of the influence of the wall on the drag force experienced by the particle.

Journal Article↗

PubMed2000

Core protein phosphorylation modulates pregenomic RNA encapsidation to different extents in human and duck hepatitis B viruses.

To clarify the role of core protein phosphorylation in pregenomic-RNA encapsidation of human and duck hepatitis B viruses (HBV and DHBV, respectively), we have examined the phosphorylation states of different forms of intracellular HBV core protein and the phenotypic effects of mutations in the phosphorylation sites of HBV and DHBV core proteins. We show that HBV core protein is phosphorylated to similar extents in the form of protein dimers and after further assembly in pregenomic RNA-containing capsids. Individual and multiple substitutions of alanine and aspartic acid for serine in the phosphorylation sites of HBV core protein resulted in site-specific and synergistic effects on RNA encapsidation, ranging from 2-fold enhancement to more than 10-fold inhibition. Core protein variants with mutations in all phosphorylation sites exhibited dominant-negative effects on RNA encapsidation by wild-type protein. The results suggest that the presence of phosphoserine at position 162 of HBV core protein is required for pregenomic-RNA encapsidation, whereas phosphoserine at position 170 optimizes the process and serine might be preferable in position 155. Examination of the pregenomic-RNA-encapsidating capacities of DHBV core protein variants, in which four phosphorylation sites were jointly mutated to alanine or aspartic acid, suggests that phosphorylation of DHBV core protein at these sites may optimize pregenomic-RNA encapsidation but that its impact is much less profound than in the case of HBV. The possible mechanisms by which RNA encapsidation may be modulated by core protein phosphorylation are discussed in the context of the observed differences between the two viruses.

Amino Acid Sequence↗

PubMed2000

Cyclin D1 is required for transformation by activated Neu and is induced through an E2F-dependent signaling pathway.

The neu (c-erbB-2) proto-oncogene encodes a tyrosine kinase receptor that is overexpressed in 20 to 30% of human breast tumors. Herein, cyclin D1 protein levels were increased in mammary tumors induced by overexpression of wild-type Neu or activating mutants of Neu in transgenic mice and in MCF7 cells overexpressing transforming Neu. Analyses of 12 Neu mutants in MCF7 cells indicated important roles for specific C-terminal autophosphorylation sites and the extracellular domain in cyclin D1 promoter activation. Induction of cyclin D1 by NeuT involved Ras, Rac, Rho, extracellular signal-regulated kinase, c-Jun N-terminal kinase, and p38, but not phosphatidylinositol 3-kinase. NeuT induction of the cyclin D1 promoter required the E2F and Sp1 DNA binding sites and was inhibited by dominant negative E2F-1 or DP-1. Neu-induced transformation was inhibited by a cyclin D1 antisense or dominant negative E2F-1 construct in Rat-1 cells. Growth of NeuT-transformed mammary adenocarcinoma cells in nude mice was blocked by the cyclin D1 antisense construct. These results demonstrate that E2F-1 mediates a Neu-signaling cascade to cyclin D1 and identify cyclin D1 as a critical downstream target of neu-induced transformation.

Animals↗

PubMed2000

Orphan receptor COUP-TF is required for induction of retinoic acid receptor beta, growth inhibition, and apoptosis by retinoic acid in cancer cells.

Retinoic acid receptor beta (RARbeta) plays a critical role in mediating the anticancer effects of retinoids. Expression of RARbeta is highly induced by retinoic acid (RA) through a RA response element (betaRARE) that is activated by heterodimers of RARs and retinoid X receptors (RXRs). However, RARbeta induction is often lost in cancer cells despite expression of RARs and RXRs. In this study, we provide evidence that orphan receptor COUP-TF is required for induction of RARbeta expression, growth inhibition, and apoptosis by RA in cancer cells. Expression of COUP-TF correlates with RARbeta induction in a variety of cancer cell lines. In addition, stable expression of COUP-TF in COUP-TF-negative cancer cells restores induction of RARbeta expression, growth inhibition, and apoptosis by RA, whereas inhibition of COUP-TF by expression of COUP-TF antisense RNA represses the RA effects. In a transient transfection assay, COUP-TF strongly induced transcriptional activity of the RARbeta promoter in a RA- and RARalpha-dependent manner. By mutation analysis, we demonstrate that the effect of COUP-TF requires its binding to a DR-8 element present in the RARbeta promoter. The binding of COUP-TF to the DR-8 element synergistically increases the RA-dependent RARalpha transactivation function by enhancing the interaction of RARalpha with its coactivator CREB binding protein. These results demonstrate that COUP-TF, by serving as an accessory protein for RARalpha to induce RARbeta expression, plays a critical role in regulating the anticancer activities of retinoids.

Animals↗

PubMed2000

A vestigial X open reading frame in duck hepatitis B virus.

Duck hepatitis B virus (DHBV) appears to lack a homologue of the X protein found in mammalian hepadnaviruses. By replacing stop codons in the corresponding region of the DHBV genome, a hypothetical protein which closely matches the hydrophilicity profile of X proteins can be predicted, despite limited sequence homology. We conclude that a full-length X protein was once a common feature of the hepadnaviruses, conserved in structure but not sequence.

Amino Acid Sequence↗

PubMed2000

Distribution of glycine receptor subunits on primate retinal ganglion cells: a quantitative analysis.

This study investigates the distribution of inhibitory neurotransmitter receptors on sensory neurons. Ganglion cells in the retina of a New World monkey, the common marmoset Callithrix jacchus, were injected with Lucifer yellow and Neurobiotin and subsequently processed with antibodies against one (alpha1), or against all subunits, of the glycine receptor, or against the anchoring protein gephyrin. Immunoreactive (IR) puncta representing glycine receptor or gephyrin clusters were found on the proximal and the distal dendrites of all ganglion cell types investigated. For both parasol and midget cells, the density of receptor clusters was greater on distal than proximal dendrites for all antibodies tested. In parasol cells the average density for the alpha1 subunit of the glycine receptor was 0.087 IR puncta/microm of dendrite, and for all subunits it was 0.119 IR puncta/microm of dendrite. Thus, the majority of glycine receptors on parasol cells contain the alpha1 subunit. For parasol cells, we estimated an average of 1.5 glycinergic synapses/100 microm2 dendritic membrane on proximal dendrites and about 9.4 glycinergic synapses/100 microm2 on distal dendrites. The segregation of receptors to the distal dendrites appears to be a common feature of inhibitory neurotransmitter input to parasol and midget cells, and might be associated with the receptive field surround mechanism.

Animals↗

PubMed2000

[Iodine-125 labeled monoclonal antibody 3H11: in radioimmunoguided surgery for primary gastric cancer].

OBJECTIVE: To evaluate the clinical usefulness of iodine-125 labeled monoclonal antibody (MAb) 3H11 in radioimmunoguided surgery (RIGS) for patients with gastric cancer. METHODS: Thirty-five patients with primary gastric cancer were enrolled. Via endoscopy, iodine-125 labeled MAb 3H11 was injected into submucosa around the tumor. All patients underwent surgery 4 to 11 days after administration. Intraoperative radioimmunodetection was performed using a hand-held gamma-detecting probe. The counts of target sites were obtained, and tumor-to-normal tissue (T/NT) ratios were calculated. The T/NT ratio of 3.5:1 was taken as the lowest threshold value of positive gastric wall infiltration, and 3.0:1 for lymph node metastasis. Serial sections of those RIGS-positive lymph nodes, which were originally diagnosed as negative by routine histology, were made. Immunohistochemical staining was performed to detect the existence of lymphatic micrometastasis. RESULTS: Of thirty-five patients, 33 underwent RIGS successfully. The accuracy rate in detecting tumor infiltration of the incision margins was 97.0%, and the specificity 98.5%. In the group of patients with an interval of 6 to 8 days between injection and operation (n = 25), the RIGS results were satisfying. For the detection of lymphatic metastasis, the sensitivity of RIGS was 83.6%, the specificity 95.0%, and the accuracy 91.3%. The existence of lymphatic micrometastasis were verified immunohistochemically in 52.6% (10/19) of those RIGS positive but histologically negative lymph nodes. CONCLUSION: This study validates the use of iodine-125 labeled monoclonal antibody 3H11 for the intraoperative detection of carcinomatous lesions in gastric cancer.

Adult↗

PubMed1999

Prostate-localized and androgen-regulated expression of the membrane-bound serine protease TMPRSS2.

Genes regulated by androgenic hormones are of critical importance for the normal physiological function of the human prostate gland, and they contribute to the development and progression of prostate carcinoma. We used cDNA microarrays containing 1500 cDNAs to profile transcripts regulated by androgens in prostate cancer cells and identified the serine protease TMPRSS2 as a gene exhibiting increased expression upon exposure to androgens. The TMPRSS2 gene is located on chromosome 21 and contains four distinct domains, including a transmembrane region, indicating that it is expressed on the cell surface. Northern analysis demonstrated that TMPRSS2 is highly expressed in prostate epithelium relative to other normal human tissues. In situ hybridization of normal and malignant prostate tissues localizes TMMPRSS2 expression to prostate basal cells and to prostate carcinoma. These results suggest that TMPRSS2 may play a role in prostate carcinogenesis and should be investigated as a diagnostic or therapeutic target for the management of prostate cancers.

Androgens↗

PubMed1999

Mutational analyses of the putative calcium binding site and hinge of the turnip crinkle virus coat protein.

The turnip crinkle carmovirus (TCV) coat protein (CP) is folded into R (RNA-binding), S (shell), and P (protruding) domains. The S domain is an eight-stranded beta barrel common to the coat protein subunits of most RNA viruses. A five-amino-acid hinge connects the S and P domains. In assembled particles, each pair of CP subunits is thought to bind a single calcium ion through interactions with three residues of one subunit and two residues of a neighboring subunit. These five residues comprise the putative calcium-binding site (CBS). The putative CBS and hinge are adjacent to one another. Mutations were introduced into the putative CBS or hinge in an effort to further determine the biological functions of TCV CP. One putative CBS mutant, TCV-M32, exhibited wild-type cell-to-cell movement but failed to move systemically in Nicotiana benthamiana, and particles were not detected. Another putative CBS mutant, TCV-M23, exhibited deficient cell-to-cell movement but particles accumulated in isolated protoplasts. Two other putative CBS mutants, TCV-M22 and -M33, showed wild-type cell-to-cell and systemic movement but elicited mild systemic symptoms that were somewhat delayed. All of the hinge mutants exhibited wild-type movement but some elicited non-wild-type symptoms. Point mutations in the putative CBS or hinge appear to alter virus-ion interactions, secondary structure, or particle conformation, thereby affecting interactions between the CP and plant hosts.

Binding Sites↗

PubMed1999

Transmembrane topology of human glucose 6-phosphate transporter.

Glycogen storage disease type 1b is caused by a deficiency in a glucose 6-phosphate transporter (G6PT) that translocates glucose 6-phosphate from the cytoplasm to the endoplasmic reticulum lumen where the active site of glucose 6-phosphatase is situated. Using amino- and carboxyl-terminal tagged G6PT, we demonstrate that proteolytic digestion of intact microsomes resulted in the cleavage of both tags, indicating that both termini of G6PT face the cytoplasm. This is consistent with ten and twelve transmembrane domain models for G6PT predicted by hydropathy analyses. A region of G6PT corresponding to amino acid residues 50-71, which constitute a transmembrane segment in the twelve-domain model, are situated in a 51-residue luminal loop in the ten-domain model. To determine which of these two models is correct, we generated two G6PT mutants, T53N and S55N, that created a potential Asn-linked glycosylation site at residues 53-55 (N53SS) or 55-57 (N55QS), respectively. N53SS or N55QS would be glycosylated only if it is situated in a luminal loop larger than 33 residues as predicted by the ten-domain model. Whereas wild-type G6PT is not a glycoprotein, both T53N and S55N mutants are glycosylated, strongly supporting the ten-helical model for G6PT.

Amino Acid Sequence↗

PubMed1999

Protein extravasation and cellular uptake after high-dose human-albumin treatment of transient focal cerebral ischemia in rats.

Treatment with human albumin administered intravenously in the immediate post-ischemic period following a 2-h period of transient focal cerebral ischemia leads to a reduction of cortical infarction in rat. Immunohistochemistry with antibodies to rat immunoglobulins (IgG), rat albumin and (exogenous) human albumin was used to study blood-brain barrier changes. The degree of IgG extravasation was not changed by human-albumin treatment. Diffuse signals and uptake into necrotic neurons was seen in cortex of saline animals. In animals treated with human albumin, cortical neurons with preserved structural features had taken up human albumin. Treatment with human albumin may provide direct neuronal protection.

Albumins↗

PubMed1999

Accumulation of glycolipids in mutant Chinese hamster ovary cells (Z65) with defective peroxisomal assembly and comparison of the metabolic rate of glycosphingolipids between Z65 cells and wild-type CHO-K1 cells.

The influence of peroxisomal dysfunction on glycosphingolipid metabolism was investigated using mutant Chinese hamster ovary (CHO) cells (Z65) with defective assembly of the peroxisomal membranes. In accordance with previous observations, the concentration of very long chain fatty acid (C24:0) was shown to be higher in Z65 cells than in control cells. We then compared the composition of glycolipids in Z65 cells with that in CHO-K1 cells, which are wild-type Chinese hamster ovary cells with intact peroxisomes, and found significantly increased concentrations of ceramide monohexoside (CMH) and ganglioside GM3 in Z65 cells. However, there were no differences in the concentrations of glycerophospholipids, triglycerides, free fatty acids and cholesterol between Z65 and CHO-K1 cells. Further, to investigate the metabolic rate of the major lipids, Z65 and CHO-K1 cells were pulse-labeled with [3-14C]serine. [3-14C]Serine was incorporated into phosphatidylserine, phosphatidylethanolamine and sphingomyelin more quickly in CHO-K1 than in Z65 cells. However, after 48 h, the radioactivity incorporated into those lipids, including CMH, was greater in Z65 cells than in CHO-K1 cells. Thus, the altered metabolism of glycosphingolipids, probably due to peroxisomal dysfunction, was thought to be responsible for the change in glycosphingolipid composition in Z65 cells.

Animals↗

PubMed1999

Pteridine analysis in urine by capillary electrophoresis using laser-induced fluorescence detection.

Pteridines are a class of compounds excreted in urine, the levels of which are found to elevate significantly in tumor-related diseases. For the first time, we have developed a method, based on high-performance capillary electrophoresis (HPCE) and laser-induced fluorescence (LIF) detection, to monitor the pteridine levels in urine. HPCE provides better separation than high-performance liquid chromatography and the LIF detector enables us to detect minute amounts of pteridines in body fluid. Eight different pteridine derivatives were well separated in 0.1 M Tris-0.1 M borate-2 mM EDTA buffer (pH 8.75) using a 60-cm fused-silica capillary (50-micron i.d., 35-cm effective length), six of which were detected and characterized in urine samples from normal persons and different cancer patients. The detection limits of these pteridines are under 1 x 10(-10) M. The levels of neopterin, pterine, xanthopterin, and pterin-6-carboxylic acid were found to be significantly elevated in urine excreted by cancer patents, while the level of isoxanthopterin dropped in these patients. No significant change of biopterin level was found between healthy individuals and cancer patients. This method can be used in clinical laboratories either for cancer monitoring or for precancer screening.

Electrophoresis, Capillary↗

PubMed1999

Inactivation of the glucose 6-phosphate transporter causes glycogen storage disease type 1b.

Glycogen storage disease type 1b (GSD-1b) is proposed to be caused by a deficiency in microsomal glucose 6-phosphate (G6P) transport, causing a loss of glucose-6-phosphatase activity and glucose homeostasis. However, for decades, this disorder has defied molecular characterization. In this study, we characterize the structural organization of the G6P transporter gene and identify mutations in the gene that segregate with the GSD-1b disorder. We report the functional characterization of the recombinant G6P transporter and demonstrate that mutations uncovered in GSD-1b patients disrupt G6P transport. Our results, for the first time, define a molecular basis for functional deficiency in GSD-1b and raise the possibility that the defective G6P transporter contributes to neutropenia and neutrophil/monocyte dysfunctions characteristic of GSD-1b patients.

Animals↗

PubMed1999

Bilirubin-human serum albumin interaction monitored by capillary zone electrophoresis.

Capillary zone electrophoresis was used to monitor the interaction between bilirubin and human serum albumin. Cord blood serum samples were injected directly into an uncoated fused-silica capillary (30 cm x 50 microns i.d.) and separation was accomplished within 4 min without extensive sample pretreatment. The most suitable running buffer to separate free bilirubin from albumin bound bilirubin was found to contain 1.0 mmol/L EDTA, 5% acetonitrile and 15 mmol/L phosphate with pH adjusted to 8.4. Approximately two bilirubin dianions could be bound per human serum albumin molecule in the cord blood serum. The binding constant was estimated to be 1.1 x 10(5) (L/mol) at 25 degrees C and pH 8.4. The peak area ratio of free bilirubin to total bilirubin can be used to determine the bilirubin binding capacity of cord blood serum for the concentration range of total bilirubin from 204 to 340 mumol/L using 1:5 diluted cord blood seras.

Bilirubin↗

PubMed1999

Application of capillary nongel sieving electrophoresis for gene analysis.

Capillary electrophoresis (CE) has proved to be a strong tool for DNA analysis and has found abundant applications in the fields of restriction fragment sizing, mutation screening, polymerase chain reaction (PCR) product characterizing and forensic identifying. CE may be the main alternative to slab gel electrophoresis. Capillary nongel electrophoresis is the most favorable mode when aiming for this purpose because of its advantages of long lifetime, easy operation, good reproducibility, and low expense. In this paper, a new kind of sieving matrix, with mannitol as the additive for capillary electrophoresis, as well as related methods and their application for gene analysis were reported. Nine DNA fragments amplified by multiplex PCR from a normal dystrophin gene were well separated by this system. Three different deletions were found in Duchenne muscular dystrophy (DMD) patients. Three to four copies of the sex-determination region of the Y chromosome (SRY) gene, as well as the phenylalanine hydroxylase (PAH) gene, could be detected in mixed samples. The frequencies of short tandem repeats (STR) in PAH genes was analyzed in 61 normal Chinese individuals and 6 phenylketonuria families. One case of prenatal gene diagnosis was performed. By using this matrix, CE coupled with reverse transcription PCR (RT-PCR), the analysis of the alternative splicing expression pattern of the fragile X mental retardation 1 (FMR1) gene in adult lung tissue was achieved.

Adult↗

PubMed1999

Study of enantioselective interactions between chiral drugs and serum albumin by capillary electrophoresis.

The separation of the enantiomers of three basic drugs, i.e., ofloxacin, propranolol and verapamil, was achieved by affinity capillary electrophoresis (ACE), with human serum albumin (HSA) and bovine serum albumin (BSA) as chiral selectors in phosphate buffer at pH 7.4. Ofloxacin was only separated in the presence of BSA, and verapamil only with HSA, while propranolol was separated with either HSA or BSA. The effects of protein concentration and column wall adsorption on the degree of separation were investigated. Two displacers, ketoprofen and warfarin, respectively, when added to the protein containing buffer, both showed significant effects on the separation behavior. From these data it was argued that verapamil may bind to HSA at both locations known, the warfarin binding site (I) and the ketoprofen binding site (II). While with BSA, binding of ofloxacin may also occur at site I, the preferential binding site for propanolol remains controversial. A drug-drug interaction between propranolol and ketoprofen due to opposite charges was concluded from the increase in migration time in BSA solution. The unbound concentration of verapamil enantiomers in solution in the presence of HSA, as estimated from CD-modified capillary zone electrophoresis, was triggered not only by the HSA concentration but also by the coadditive concentration.

Adsorption↗