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Biomedical subjects

D Chen

Publications and source records attributed to D Chen.

At least 631 records · Page 35Linked to original sources
PubMed1995

Deer antler tissue contains two types of bone morphogenetic protein 4 mRNA transcripts.

Previously we isolated a bone morphogenetic protein 4 (BMP-4) cDNA from human prostate cancer cells and found that the 5' noncoding exon 1 of this BMP-4 cDNA was different from that of human bone cell BMP-4 cDNA. Recently we identified two alternate exon 1s, 1A and 1B, for BMP-4 gene by reverse transcription-polymerase chain reaction (RT-PCR) assays from fetal rat calvarial osteoblasts. In order to further examine alternate exon 1 usage in the BMP-4 gene, we screened deer antler tissue cDNA library. We isolated two types of cDNA clones encoding BMP-4 from this deer antler cDNA library. Sequencing of these clones have revealed a single open reading frame encoding a 408 amino acid protein. Comparison of 5' noncoding exon 1 portion of these cDNA sequences with those of human bone and prostate BMP-4 cDNA sequences and mouse BMP-4 genomic DNA sequence demonstrated that deer antler tissue expresses both exon 1A and 1B containing BMP-4 mRNA transcripts. This suggests that BMP-4 gene may contain alternate promoters or alternate splicing sites in deer antler tissue.

Amino Acid Sequence↗
PubMed1995

Antinociceptive activity of calcitonin and central cholinergic system: behavioural and neurochemical analyses.

Behavioural and neurochemical analyses were carried out to investigate the relationship between the antinociceptive activity of porcine calcitonin (pCT) and central cholinergic system in mice and rats. Behavioural studies revealed that the antinociceptive activity of pCT encapsulated in sulphatide-containing liposomes injected intravenously into mice was significantly inhibited by atropine sulphate, but not by atropine methylnitrate, and potentiated by physostigmine, but not by neostigmine. Neurochemical studies using rat brain synaptosomes showed that pCT stimulated synaptosomal sodium-dependent high-affinity choline uptake, which was found to be closely associated with acetylcholine (ACh) synthesis (50-60%). This effect was concentration-dependent. In addition, pCT elicited a biphasic effect on ACh release from synaptosomes with an initial brief period of stimulation and subsequent prolonged inhibition. This stimulation was not affected by atropine sulphate, but markedly reduced by incubation in the presence of diltiazem or in a calcium-free medium, indicating that the modulation of ACh release by the peptide may be mediated by calcium fluxes across the synaptosomal membrane independent of cholinergic receptor activation. However, pCT does not affect the activity of synaptosomal acetylcholinesterase. Therefore, the behavioural study in vivo with the neurochemical analysis in vitro suggests that the central cholinergic system may be involved in the antinociceptive activity of calcitonin.

Acetylcholine↗
PubMed1995

Expression of gax, a growth arrest homeobox gene, is rapidly down-regulated in the rat carotid artery during the proliferative response to balloon injury.

gax is a recently described homeobox gene whose expression in the adult is largely confined to cardiovascular tissues, gax has been shown to be rapidly down-regulated in cultured vascular smooth muscle cells (VSMC) upon stimulation by serum or platelet-derived growth factor. The temporal profile of gax expression in vitro matches that of two families of growth arrest genes: the gas genes and the gadd genes. All of these genes are expressed at their highest levels in quiescent cells and are down-regulated following mitogen activation. Here we report that gax is also down-regulated in vivo in the vascular wall in response to endothelial denudation by balloon angioplasty. The reduction in steady state levels of gax mRNA is transient and occurs with a similar time course to that seen in vitro. The down-regulation of gax in response to balloon injury mirrors the up-regulation seen in a number of early response genes such as c-myc and c-fos. This report is the first to document the in vivo expression of a growth arrest gene which regulates proliferation of vascular smooth muscle cells. In addition, in contrast with previous reports which have demonstrated up-regulation of several genes following balloon injury and/or angioplasty, the present report demonstrates the down-regulation of a regulatory gene within hours of balloon injury. The characteristics of gax suggest it may be required to maintain the gene expression of proteins in VSMC that are associated with the nonproliferative or contractile phenotype in smooth muscle cells.

Angioplasty, Balloon↗
PubMed1995

Regulation of phosphatidylinositol 3'-kinase by tyrosyl phosphoproteins. Full activation requires occupancy of both SH2 domains in the 85-kDa regulatory subunit.

Phosphatidylinositol 3'-kinase (PI 3'-kinase) is activated in insulin-stimulated cells by the binding of the SH2 domains in its 85-kDa regulatory subunit to insulin receptor substrate-1 (IRS-1). We have previously shown that both tyrosyl-phosphorylated IRS-1 and mono-phosphopeptides containing a single YXXM motif activate PI 3'-kinase in vitro. However, activation by the monophosphopeptides was significantly less potent than activation by the multiply phosphorylated IRS-1. We now show that the increased potency of PI 3'-kinase activation by IRS-1 relative to phosphopeptide is not due to tertiary structural features IRS-1, as PI 3'-kinase is activated normally by denatured, reduced, and carboxymethylated IRS-1. Furthermore, activation of PI 3'-kinase by bis-phosphorylated peptides containing two YXXM motifs is 100-fold more potent than the corresponding mono-phosphopeptides and similar to activation by IRS-1. These data suggest that tyrosyl-phosphorylated IRS-1 or bis-phosphorylated peptides bind simultaneously to both SH2 domains of p85. However, these data cannot differentiate between an activation mechanism that requires two-site occupancy for maximal activity as opposed to one in which bivalent binding enhances the occupancy of a single activating site. To distinguish between these possibilities, we produced recombinant PI 3'-kinase containing either wild-type p85 or p85 mutated in its N-terminal, C-terminal, or both SH2 domains. We find that mutation of either SH2 domains significantly reduced phosphopeptide binding and decreased PI 3'-kinase activation by 50%, whereas mutation of both SH2 domains completely blocked binding and activation. These data provide the first direct evidence that full activation of PI 3'-kinase by tyrosylphosphorylated proteins requires occupancy of both SH2 domains in p85.

Amino Acid Sequence↗
PubMed1995

The varicella-zoster virus origin-binding protein can substitute for the herpes simplex virus origin-binding protein in a transient origin-dependent DNA replication assay in insect cells.

We isolated two recombinant baculoviruses each of which expresses a varicella-zoster virus (VZV) homolog of one of the seven herpes simplex virus type 1 (HSV-1) genes required for DNA replication. We performed transient origin-dependent DNA replication assays in insect cells in which we substituted a baculovirus which expresses a VZV protein for a baculovirus which expresses its HSV homolog. VZV gene 51 protein was found to be able to support origin-dependent DNA synthesis when it was substituted for UL9, the HSV-1 origin-binding protein (OBP). This occurred whether an HSV-1 or a VZV origin-containing plasmid was used in the assay. These results suggest that VZV gene 51 protein is able to interact with the HSV replication machinery, and in light of the extensive structural divergence of these proteins, it suggests that initiation of VZV and HSV-1 DNA synthesis may involve a limited number of interactions between the OBP and other replication factors. Substitution of infected-cell protein 8 (ICP8), the major single-stranded DNA-binding protein of HSV-1, with VZV gene 29 protein, however, did not result in amplification of plasmids containing either an HSV-1 or a VZV origin. In the absence of ICP8, addition of both VZV gene 51 protein and gene 29 protein was also negative for origin-dependent replication whether or not UL9 was present. Although demonstration that our baculovirus-expressed VZV gene 29 protein is functional for DNA replication will await development of a VZV replication system, our results suggest that VZV gene 29 protein is unable to interact functionally with one or more of the HSV replication proteins. This approach should contribute to efforts to define the interactions among the alphaherpesvirus DNA replication proteins.

Animals↗
PubMed1995

Increasing neuroforaminal volume by anterior interbody distraction in degenerative lumbar spine.

STUDY DESIGN: This study quantified changes in the size of the stenotic neuroforamen in degenerative lumbar spines. The volume and area of the neuroforamen were measured before and after the application of anterior distraction using the BAK interbody fusion system. OBJECTIVE: To quantitatively assess the neuroforaminal area and volume when the BAK interbody fusion system is applied to lumbar spines with neuroforaminal stenosis. SUMMARY OF BACKGROUND DATA: The spatial relationship between the nerve root and the osseous and nonosseous elements of the neuroforamen is clinically important. Few studies have focused on changes in neuroforaminal size in the lumbar spine after anterior interbody distraction. No previous study has assessed the neuroforaminal volume. METHODS: The BAK instrumentation system was applied anteriorly at L4-L5 and L5-S1 intervertebral discs in nine degenerative cadaver lumbar spines. The neuroforaminal volumes of L4-L5 and L5-S1 were measured from silicon molds taken of the neuroforamen. In addition, computed tomography and circular blunt probes were used to determine the neuroforaminal areas. The disc height was recorded from lateral radiographs. RESULTS: After the BAK instrumentation, the volume of the neuroforamen increased significantly--by 22.9% for L4-L5 and 21.5% for L5-S1. The posterior disc height increased by 37.1% at L4-L5 and 45.1% at L5-S1. The neuroforaminal areas significantly increased--by 29.0% at L4-L5 and 33.8% at L5-S1. There was good correlation between the volume and the posterior disc height (R2 = 0.50) and the volume and the area of the narrowest portion of neuroforamen (R2 = 0.56). CONCLUSIONS: The results indicated that anterior systems such as the BAK system, which increase disc heights, can significantly increase neuroforaminal volume and area, providing adequate space for the nerve root and improving neuroforaminal stenosis.

Aged↗
PubMed1995

Rhabdomyosarcoma of the vagina in a postmenopausal woman: report of a case and review of the literature.

Most rhabdomyosarcomas (RMSs) of the female genital tract occur in infants and young children as sarcoma botryoides. Vaginal RMS occurring in a postmenopausal woman is extremely rare. To our knowledge, only three vaginal RMSs have been reported in patients who were over 50 years of age. Herein, the first case in Taiwan and the fourth case in the world is reported, and the pertinent literature is briefly reviewed. A 63-year-old woman complained of a few days of abnormal vaginal bleeding. Vaginal examination demonstrated two black polypoid tumors located at the left-lateral and posterior wall of the vagina. The patient had previously undergone a vaginal total hysterectomy for rectocele and urine incontinence, so surgical treatment including local wide excision and bilateral salpingo-oophorectomy were performed under the diagnosis of malignant vaginal tumor. The clinical, histopathological, and immunohistochemical studies revealed a group Ia pleomorphic RMS. Postoperative radiotherapy was performed. The patient remains alive and well 12 months after a combined therapy.

Combined Modality Therapy↗
PubMed1995

MCF-7 breast cancer cells overexpressing transfected c-erbB-2 have an in vitro growth advantage in estrogen-depleted conditions and reduced estrogen-dependence and tamoxifen-sensitivity in vivo.

A c-erbB-2 expression vector was transfected into the estrogen receptor positive (ER+) MCF-7 human breast cancer cell line to determine if overexpression of this transmembrane tyrosine kinase could increase the malignant phenotype of this cell line. Loss of transfected c-erbB-2 expression was observed when cells were carried in medium containing estrogen. Homogeneous populations stably overexpressing levels of the 185 kDa c-erbB-2 observed in the SKBR-3 a breast cancer cell line which overexpresses c-erbB-2 as a result of gene amplification could be obtained by continually maintaining the transfected cell lines in estrogen-free conditions. Levels of constitutively activated c-erbB-2 varied among clonal isolates. Whereas some overexpressing lines did acquire the ability to form transient tumor nodules in ovariectomized nude mice without estrogen supplementation, as well as in mice that received the antiestrogen tamoxifen, one cell line that exhibited the highest levels of constitutively activated c-erbB-2 was able to form static tumors of a larger size under both conditions. This same cell line formed progressively growing tumors in estrogen-supplemented mice that were much larger than observed in mice injected with control cell lines, and also showed reduced sensitivity to antiestrogens in vitro, but it continued to have a low metastatic phenotype. These results suggest that signal transduction mediated by the c-erbB-2 tyrosine kinase can partially overcome the estrogen dependence of ER+breast cancer cells for growth and that c-erbB-2 overexpression confers a selective advantage to such cells in the absence of estrogen.

Blotting, Western↗
PubMed1995

Heterologous expression systems for P-glycoprotein: E. coli, yeast, and baculovirus.

Chemotherapy, though it remains one of the front-line weapons used to treat human cancer, is often ineffective due to drug resistance mechanisms manifest in tumor cells. One common pattern of drug resistance, characterized by simultaneous resistance to multiple amphipathic, but otherwise structurally dissimilar anticancer drugs, is termed multidrug resistance. Multidrug resistance in various model systems, covering the phylogenetic range from bacteria to man, can be conferred by mammalian P-glycoproteins (PGPs), often termed multidrug transporters. PGPs are 170-kD polytopic membrane proteins, predicted to consist of two homologous halves, each with six membrane spanning regions and one ATP binding site. They are members of the ATP-binding cassette (ABC) superfamily of transporters, and are known to function biochemically as energy-dependent drug efflux pumps. However, much remains to be learned about PGP structure-function relationships, membrane topology, posttranslational regulation, and bioenergetics of drug transport. Much of the recent progress in the study of the human and mouse PGPs has come from heterologous expression systems which offer the benefits of ease of genetic selection and manipulation, and/or short generation times of the organism in which PGPs are expressed, and/or high-level expression of recombinant PGP. Here we review recent studies of PGP in E. coli, baculovirus, and yeast systems and evaluate their utility for the study of PGPs, as well as other higher eukaryotic membrane proteins.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1995

Cholecystokinin-B receptor ligands of the dipeptoid series act as agonists on rat stomach histidine decarboxylase.

BACKGROUND & AIMS: The effect of gastrin on the enterochromaffin-like cells in the rat stomach is mediated by cholecystokinin (CCK)-B receptors and manifested as activation of histidine decarboxylase (HDC). The dipeptoids PD 136450, PD 135158, and PD 134308 are thought to be selective CCK-B receptor antagonists. The effects of the dipeptoids and of gastrin-17 and sulfated CCK-8 on rat stomach HDC activity were examined. METHODS: Drugs were infused intravenously or subcutaneously to fasted rats, and the HDC activity was determined. RESULTS: The dipeptoids activated HDC with maximal responses (50%-60% of the maximal response to gastrin) at 1 mumol.kg-1.h-1. Rat gastrin-17 activated HDC maximally at 3 nmol.kg-1.h-1, and sulfated CCK-8 produced maximal response at 20 nmol.kg-1.h-1. The CCK-B receptor antagonist L-365,260 inhibited the HDC activation induced by gastrin, sulfated CCK-8, or the dipeptoids. The dipeptoids did not inhibit the gastrin-induced HDC activation. CONCLUSIONS: Gastrin, sulfated CCK-8, and the dipeptoids activated rat stomach HDC. L-365,260 but not devazepide inhibited the HDC activation. Thus, the dipeptoids, which failed to inhibit the gastrin-induced HDC activation, act as CCK-B receptor agonists and not as antagonists. It is important to recognize this to ensure appropriate interpretation of data obtained with these drugs.

Animals↗
PubMed1995

Circulating pancreastatin is a marker for the enterochromaffin-like cells of the rat stomach.

BACKGROUND/AIMS: Peptides of the chromogranin family occur in peptide hormone-producing cells throughout the body. One source of such peptides is the enterochromaffin-like (ECL) cells, which constitute the predominant population of endocrine cells in the fundus (the acid-producing part) of the rat stomach. The purpose of this study was to examine whether ECL cells, which are controlled by gastrin, represent a major source of circulating pancreastatin, a fragment of chromogranin A. METHODS: Rats underwent surgical procedures and treatments in which the ECL cells could be manipulated. The procedures included antrectomy, fundectomy, and gastrectomy (and adrenalectomy), and the treatments included fasting or feeding, gastrin-17 infusion, and administration of omeprazole or ranitidine. The concentrations of pancreastatin-like immunoreactivity (LI) and gastrin in the serum were determined by radioimmunoassay. RESULTS: The serum pancreastatin-LI concentration was lowered by about 80% by fundectomy and gastrectomy; both of these procedures eliminated the ECL cell population. Adrenalectomy had no effect on the serum pancreastatin-LI concentration. Gastrin infusion, which activates the ECL cells, promptly increased serum pancreastatin-LI concentration. Refeeding after fasting and administration of omeprazole or ranitidine increased the serum pancreastatin-LI concentrations; these responses were prevented by antrectomy. CONCLUSIONS: The concentration of circulating pancreastatin-LI reflects the activity of the ECL cells and the size of the ECL cell population in the rat stomach.

Adrenalectomy↗