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M Choy

Publications and source records attributed to M Choy.

At least 19 recordsLinked to original sources
PubMed2001

Structural organization of the rat mitogen-activated protein kinase phosphatase 2 gene.

Mitogen-activated protein kinase (MAPK) phosphatases (MKPs) are dual specificity protein phosphatases that specifically inactivate MAPKs. Regulated expression of MKPs plays a key role in determining their physiological function. However, little is known about the molecular mechanism of the activation of MKP genes. In this study, we cloned the rat MKP-2 gene and characterized its structure. The MKP-2 gene has four exons and three introns. The organization of exons of the MKP-2 gene is very similar to that of the MKP-1 gene, suggesting that MKP-1 and MKP-2 are derived from the same ancestral gene. We identified multiple transcription start sites (TSSs) for the MKP-2 gene. There is no functional TATA motif in the 5' proximal region of the TSSs. Instead, this region is highly GC-rich and has two putative Sp1 sites. A 1.8 kb 5' flanking region of the MKP-2 gene is sufficient to mediate transcriptional activation of the luciferase reporter gene by phorbol ester in GH3 cells. These results provide essential information about structural organization and regulatory sequences of the MKP-2 gene for further investigation of the molecular mechanisms of MKP-2 induction by extracellular stimuli.

Amino Acid Sequence↗
PubMed2001

Ethanol inhibits spontaneous activity of central nucleus of the amygdala neurons but does not impair retention in the passive-avoidance task.

BACKGROUND: Behavioral studies using pharmacological manipulations that increase neuronal activity of the central nucleus of the amygdala (CeA) have implicated the CeA in enhancement of memory modulation. To date, however, there has been a dearth of studies investigating the effect of a drug that decreases CeA activity on memory modulation-a drug that inhibits the neuronal activity of the CeA might be expected to impair memory modulation. To determine whether ethanol inhibits CeA activity and, if so, whether decreased CeA activity is associated with impairment of memory modulation, this study investigated the effect of ethanol on spontaneous single-unit activity of CeA neurons and retention in the passive-avoidance task. METHODS: The effect of ethanol (0.35, 0.75, 1.5, 2.5 g/kg) was determined on spontaneously firing neurons in the CeA in urethane-anesthetized rats by use of standard in vivo single-unit electrophysiological recording techniques. Additionally, the effect of ethanol when administered immediately after training in a standard passive-avoidance task was determined on retention the following day. RESULTS: Ethanol profoundly inhibited spontaneous CeA firing rates in urethane-anesthetized rats at all doses tested. Maximal inhibition was related to dose. Each dose of ethanol significantly inhibited CeA activity within 15 min of administration; within 35 min of administration, 0.75 g/kg of ethanol inhibited CeA activity by 65.2%, and the highest dose (2.5 g/kg) produced nearly complete suppression of CeA activity (81.3%). Although ethanol markedly inhibited CeA activity, these same doses of ethanol failed to impair retention in the passive-avoidance task: 0.35, 0.75, 1.5, and 2.5 g/kg of ethanol, administered immediately after training, failed to alter latency to step-through the following day. CONCLUSIONS: These results show that ethanol profoundly inhibits spontaneous CeA activity and suggest that inhibition of the CeA is not sufficient to impair retention in the passive-avoidance task.

Amygdala↗
PubMed2000

Stromal-derived factor 1-induced megakaryocyte migration and platelet production is dependent on matrix metalloproteinases.

Despite the discovery of thrombopoietin (TPO) and its contribution to megakaryocytopoiesis, the exact mechanisms and sites of platelet production are unknown. It has been shown that mature megakaryocytes (MKs) functionally express the stromal-derived factor 1 (SDF-1) receptor, CXCR4. SDF-1-induced migration of mature MKs through endothelial cell layers results in increased platelet production. Because the migration of polyploid MKs from the bone marrow microenvironment requires remodeling of the perivascular extracellular matrix, it was hypothesized that mature polyploid MKs may express matrix metalloproteinases (MMPs), facilitating their exit into the bone marrow extravascular space. In this report, it is demonstrated that SDF-1 induces the expression and release of gelatinase B (MMP-9) by purified mature polyploid human MKs and an adeno-CXCR4-infected megakaryocytic cell line. Neutralizing antibody to MMP-9, but not MMP-2, blocked SDF-1-induced migration of MKs through reconstituted basement membrane, suggesting that expression of MMP-9 is critical for MK migration. Incubation of mature MKs with a synthetic MMP inhibitor, 5-phenyl-1,10-phenanthrolene, resulted in the inhibition of platelet formation, suggesting that the expression of MMPs is not only critical for megakaryocyte migration but also for subsequent platelet release. Confirming these results, adeno-SDF-1 injection into normal mice resulted in increased platelet counts, a process that could be blocked by a synthetic MMP inhibitor. These results suggest mobilization of MKs involves sequential expression and activation of chemokine receptors such as CXCR4, MMP-9, followed by transendothelial migration. MMP inhibitors may have potential use in the treatment of thrombotic and myeloproliferative disorders. (Blood. 2000;96:4152-4159)

Adult↗
PubMed2000

Liposomal mediated transfection of mature rat astrocytes in vitro: a comparison of ten reagents.

Ten cationic liposomes were tested for their ability to transfect mature, astrocyte monolayers in vitro using the eucaryotic expression vector plasmid p cytomegalovirus (CMV)-beta. Liposomal agents were examined for optimum length of exposure and optimum cDNA/lipid ratios. Lipofectin demonstrated the highest transfection efficiencies of all agents tested (3.3%). When examined at 3 days following transfection, 24-h exposures yielded higher efficiencies compared to 6 h exposures (1.9%, P=0.07). Although expression appeared to decline by up to 80%, positive cells were still detected up to 2 weeks after transfection with all reagents. Lipofectin represents a useful tool for transfecting mature astrocytes for investigation of gene transfer in vitro.

Animals↗
PubMed2000

A comparative study of the ability of calcitonin gene-related peptide and adrenomedullin(13 - 52) to modulate microvascular but not thermal hyperalgesia responses.

Calcitonin gene-related peptide (CGRP), a neuropeptide, is a potent vasodilator. Adrenomedullin (ADM) is suggested to be produced by vascular cells in inflamed tissue. ADM shares some structural homology with CGRP. We have compared the ability of CGRP and ADM to modulate microvascular and thermal hyperalgesic responses in rat skin. Vasodilator activity was assessed by laser Doppler flowmetry, inflammatory oedema by the extravascular accumulation of intravenously-injected labelled albumin, and neutrophil accumulation by tissue myeloperoxidase, in dorsal skin. Hyperalgesia was assessed by a thermal hyperalgesimeter in paw skin. ADM (10-300 pmol) was 3 fold less potent than CGRP (3-100 pmol) as a direct vasodilator. CGRP (30 pmol) potentiated oedema formation induced by mediators of increased microvascular permeability, as expected (P<0.01). However, ADM (30-100 pmol) was without a potentiating effect, although ADM (300 pmol) was effective (P<0.01). By comparison ADM (100 pmol) potentiated neutrophil accumulation induced by interleukin-1beta (P<0.05), whereas CGRP (30 pmol) did not. No thermal hyperalgesia was observed to either CGRP or ADM, when given as single or repeated treatments. Thus despite a dilator activity neither CGRP nor ADM appears to mediate hyperalgesic activity in the periphery. However ADM, like CGRP, has the ability to potentiate inflammatory oedema formation and, in addition, ADM can potentiate neutrophil accumulation. ADM may, as suggested for CGRP, act as a modulator of the vascular phases of inflammation. The property of the two compounds of evoking differential microvascular responses and neutrophil accumulation may be due to differing mechanisms of action.

Adrenomedullin↗
PubMed2000

Autocrine stimulation of VEGFR-2 activates human leukemic cell growth and migration.

Emerging data suggest that VEGF receptors are expressed by endothelial cells as well as hematopoietic stem cells. Therefore, we hypothesized that functional VEGF receptors may also be expressed in malignant counterparts of hematopoietic stem cells such as leukemias. We demonstrate that certain leukemias not only produce VEGF but also express functional VEGFR-2 in vivo and in vitro, resulting in the generation of an autocrine loop that may support leukemic cell survival and proliferation. Approximately 50% of freshly isolated leukemias expressed mRNA and protein for VEGFR-2. VEGF(165) induced phosphorylation of VEGFR-2 and increased proliferation of leukemic cells, demonstrating these receptors were functional. VEGF(165) also induced the expression of MMP-9 by leukemic cells and promoted their migration through reconstituted basement membrane. The neutralizing mAb IMC-1C11, specific to human VEGFR-2, inhibited leukemic cell survival in vitro and blocked VEGF(165)-mediated proliferation of leukemic cells and VEGF-induced leukemic cell migration. Xenotransplantation of primary leukemias and leukemic cell lines into immunocompromised nonobese diabetic mice resulted in significant elevation of human, but not murine, VEGF in plasma and death of inoculated mice within 3 weeks. Injection of IMC-1C11 inhibited proliferation of xenotransplanted human leukemias and significantly increased the survival of inoculated mice. Interruption of signaling by VEGFRs, particularly VEGFR-2, may provide a novel strategy for inhibiting leukemic cell proliferation.

Animals↗
PubMed1999

Reactivity and assay restriction profiles of monoclonal and polyclonal antibodies to acid phosphatases: a preliminary study.

The development of secure diagnostic immunoassays requires, among others, rigorous characterisation of potential antibody reagents. The reactivity profiles of seven antibodies (six monoclonal [MAb] and one polyclonal [PAb]) with putative specificity for tartrate-resistant acid phosphatase (TRAP) and/or osteoclasts were evaluated in enzyme-linked immunosorbent assay (ELISA) and/or immunocytochemistry. MAbs 2H1, 4E6 and 5Cl demonstrated assay restriction: exhibiting reactivity only in ELISA. The remaining three MAbs (G211D, G312G and V35B) and the PAb 8023 recognised recombinant TRAP (rTRAP) in ELISA and native acid phosphatases in selected tissues and cell lines. The latter were cytochemically assessed for both tartrate-sensitive acid phosphatase (TSAP) and TRAP. V35B showed reactivity against the monocytic leukaemia cell line U937 and guinea pig kidney tissue (both TSAP+ and TRAP+) and ECV304 (TSAP+) cells. Interestingly, the reactivity of MAb G211D co-localised with TRAP activity in the membrane of osteoclasts but also detected cytoplasmic components in U937 cells and human embryonic lung fibroblasts (TRAP+ and TRAP+). G211D exhibited immunoreactivity against placental trophoblasts (positive for total AP). Intriguingly, MAbs 2H1, 4E6, 5Cl and PAb 8023 cross-reacted with potato acid phosphatase in ELISA, suggesting reactivity to conformationally similar epitopes. Thus, some of these reagents could be used in the development of standardised diagnostic immunoassays or as drug-targeting agents for conditions in which the pathological process involves bone resorption, the MAbs G211D, 2H1, 4E6, 5Cl and PAb 8023 being useful in ELISA but not immunocytochemical detection of TRAP.

Acid Phosphatase↗
PubMed1999

Bisdiamine inhibits extracellular matrix formation and cell proliferation of atrioventricular mesenchyme from developing chick heart valves.

Abnormalities of the cushion tissues lead to atrioventricular septal defects (AVSD) and truncus arteriosus (TA). Bisdiamine exposure in the embryo frequently causes AVSD and TA in the newborn chick, mouse, or rat. We studied the effects of bisdiamine on mesenchymal cells grown in aggregate culture isolated from the developing atrioventricular valves of the stage-36 chick embryo. Fibronectin extracellular matrix formation and cell proliferation in the aggregates were assessed in various media. Chick serum stimulated the cells to produce an extracellular matrix and to divide, and the inclusion of bisdiamine inhibited both responses. If we isolated an extracellular matrix from a monolayer of mesenchymal cells and added the sonicated matrix to the medium containing serum and bisdiamine, the matrix incorporated into the aggregates and the cells entered the mitotic cycle. Our previous work established that cells need to attach to an intact extracellular matrix to begin cell division. Thus, we suggest that bisdiamine inhibits the normal formation of the extracellular matrix, leading to reduced cell proliferation, but it does not affect matrix-cell interaction. The lack of cushion growth in situ may be the cause of AVSD or TA.

Animals↗
PubMed1998

Comparing a mass-balance algorithm with a Bayesian regression analysis computer program for predicting serum phenytoin concentrations.

The ability of a mass-balance algorithm to predict non-steady-state phenytoin concentrations in neurosurgery patients was compared with that of Phenda, a computerized Bayesian regression analysis program. Fifty neurosurgery patients who had had two or more initial phenytoin serum concentrations measured at least 60 hours apart and at least 1 hour after any i.v. doses, with the second concentration being not more than twice and not less than half of the first, and who had had a third or final phenytoin measurement (for use in a prediction analysis) were evaluated. The patients' maximum rates of metabolism were calculated by using the two initial phenytoin concentrations and a mass-balance algorithm, and the third phenytoin concentration was predicted. The patients' demographics and phenytoin dosages and concentrations were entered into Phenda, which was used to predict the third phenytoin concentration. The ability of the two methods to predict the third concentration was evaluated by the method of Sheiner and Beal. Fifty observations from 48 patients were evaluated. The mass-balance algorithm had a positive prediction bias of 2.52 mg/L and a precision error of 5.08 mg/L, compared with 2.30 and 5.30, respectively, for Phenda. The difference in the results between the two methods was not significant. There was no significant difference between the mass-balance algorithm and Phenda in the ability to predict phenytoin concentrations.

Algorithms↗
PubMed1996

Fibroblast growth factor-2 stimulates embryonic cardiac mesenchymal cell proliferation.

The proliferation response of stage 36 chick atrioventricular valve mesenchymal cells to fibroblast growth factor-2 (FGF-2) was studied in the tissue-like environment of three-dimensional cell aggregates maintained in organ culture. The mitogenic effects of FGF-2 on mesenchymal tissue depended on the FGF-2-stimulated formation of a fibronectin-containing extracellular matrix. The matrix was absent in unstimulated aggregates, and co-localized with regions of actively proliferating cells in stimulated aggregates. Inhibition of fibronectin matrix formation by the inclusion of Arg-Gly-Asp-containing peptides, which compete with fibronectin for binding to the cell surface alpha 5 beta 1 integrin receptors, abolished the proliferation effects of FGF-2. Inhibition of sulfation of cell surface glycosaminoglycans by treatment with sodium chlorate significantly reduced both the formation of the fibronectin matrix and cell proliferation in response to FGF-2, suggesting an involvement of the low-affinity sulfated glycosaminoglycan FGF receptor system. Thus, the FGF-stimulated growth of embryonic atrioventricular valve mesenchyme in vitro involves the production of a fibronectin matrix. We suggest that the stimulation of the fibronectin matrix represents an essential element in growth factor signaling of mesenchymal tissue, with the matrix serving as an anchorage substratum for the proliferating cells.

Animals↗
PubMed1994

Fecal occult blood testing for colorectal cancer in an ethnically diverse population.

Fecal occult blood test kits were distributed throughout the ethnically diverse Hawaiian Islands during a 3-week period in 1989. Occult blood was detected in 1,631 persons (11.8%). At least 83% of the participants with positive tests sought medical advice. Subsequently, 76 (4.7%) were diagnosed as having colorectal adenomas and an additional 1.4% had malignant neoplasms (3 gastric and 20 colorectal adenocarcinomas). Three quarters of the colorectal cancers were localized and node-negative. Participation in this program and the type of diagnostic studies done on participants with positive tests varied according to sex and ethnicity. Therefore, these demographic variables must be considered in designing fecal occult blood screening programs.

Adolescent↗
PubMed1993

Fibroblast behavior in the embryonic chick heart.

Intracardiac fibroblasts (mesenchymal cells) of Hamburger and Hamilton stage 36 chick heart reside in the epicardium and atrioventricular valves. The characteristics of the epicardial fibroblasts include segregation from the myocytes of the heart wall myocardium, voluminous extracellular matrix production, and some cell proliferation activity. The atrioventricular fibroblasts intermingle with myocytes at the mutual border between these tissues, produce smaller amounts of extracellular matrix, and show very active cell proliferation. Is the behavior of each population of fibroblasts predetermined or is each responding in a reversible fashion to local environment? A cell aggregate culture system, which permits 3-dimensional cell-cell and cell-matrix interactions, is used to study the behavior of each isolated population of fibroblasts in vitro. In the presence of serum-free medium, each population produces very little extracellular matrix, has relatively low mitotic activity, and does not segregate from myocytes when the aggregate is composed of randomly intermixed myocytes and fibroblasts. In the presence of chicken serum, each population increases matrix production, increases cell proliferation, and sorts from myocytes. Thus, we suggest that the two populations of fibroblasts in the developing heart are responding to local environments and the differences observed in vivo are not the consequence of irreversible states of cellular differentiation.

Animals↗
PubMed1993

Cardiomyopathy induced by phenylpropanolamine.

A 14-year-old girl had evidence of an acute cardiomyopathy after a minimal overdose of phenylpropanolamine. She had myocardial dysfunction, ventricular dysrhythmia, and secondary pulmonary edema without any associated systemic hypertension. The cardiomyopathy resolved after several days.

Adolescent↗
PubMed1992

Fate of the atrioventricular endocardial cushions in the developing chick heart.

To determine the fate of the atrioventricular endocardial cushions in cardiac development, we used staining methods for extracellular fibronectin, which is abundant in the endocardial cushions, and actin, which is abundant in the myocytes. White Leghorn chick embryo hearts were harvested at Hamburger and Hamilton stages 26 to 36, and serial sections of the atrioventricular valve region were stained. Before atrioventricular valve formation, fibronectin and actin staining reveal separation between the fibronectin-rich endocardial cushions and the actin-rich myocardial layer. The developing mitral valve leaflets at all of the observed stages contain a fibronectin-rich matrix but no actin-rich myocytes. In contrast, the tricuspid band includes both fibronectin matrix and actin-rich cells. We conclude that the mitral valve leaflets in the chick form predominantly from the endocardial cushion tissue, and the tricuspid band receives contributions from both the endocardial cushions and surrounding myocardium.

Actins↗
PubMed1992

Properties of human thymic B cells.

B cells, distinct from those seen in myasthenia gravis, are present in normal human thymic medulla, concentrated around the Hassall's corpuscles. We have shown that they constitute 33 +/- 4.8% of the total cells in the thymic medulla. In tissue sections they were often seen to have rosettes of thymocytes around them, a relationship which was maintained when the cells were isolated from the thymus. Thymic B cells expressed cytoplasmic immunoglobulins IgD, IgM and IgG but only rarely IgA. Unlike murine thymic B cells, human thymic B cells were CD5-. Freshly isolated thymic B cells were activated cells, but they rapidly became quiescent and died in culture over a 10-day period unless stimulated with mitogens. Thymic B cells responded to polyclonal B-cell activators SAC and TPA and when stimulated, maintained their relationship with thymocytes. Electron microscopic studies showed that two morphologically different thymocyte populations associated with the B cells. The plasma membranes of larger thymocytes were juxtaposed to the B-cell membrane, but smaller thymocytes with darker cytoplasm were associated with the B cells via cytoplasmic strands. Studies in mice have suggested that B cells are involved in thymic negative selection. The close association between activated B cells and thymocytes observed in this study supports this hypothesis.

B-Lymphocytes↗
PubMed1991

Transforming growth factor-beta 1 localized within the heart of the chick embryo.

Transforming growth factor-beta 1 is a pleiotropic peptide mediator of growth, differentiation, and extracellular matrix synthesis. In the embryonic chick heart prior to the formation of the endocardial cushions, evidence from in vitro experiments suggests that transforming growth factor-beta 1 may be an inducer of the differentiation of atrioventricular endothelial cells into endocardial cushion mesenchyme. Further in vitro evidence suggests that the factor stimulates mesenchymal cell proliferation, and, thus, growth of the cushions. Using an antibody made against a peptide duplicating the aminoterminal 30 amino acid sequence of transforming growth factor-beta 1, we stained sections of stage 11, 18, 23, 26, and 36 chick hearts by an in situ immunofluorescence technique. Transforming growth factor-beta 1 staining localized to the endocardial surface and epicardial surface of the stage 11 heart, but it decreased from these locations in later stages. The cardiac jelly (stage 11), endocardial cushions (stage 18, 23, and 26), and, subsequently, the heart valve leaflets (stage 36) stained intensely for the growth factor.

Animals↗