Biomedical subjects

A Liu

Publications and source records attributed to A Liu.

At least 73 records · Page 4Linked to original sources

PubMed2000

NMR solution structure of the human prion protein.

The NMR structures of the recombinant human prion protein, hPrP(23-230), and two C-terminal fragments, hPrP(90-230) and hPrP(121-230), include a globular domain extending from residues 125-228, for which a detailed structure was obtained, and an N-terminal flexibly disordered "tail." The globular domain contains three alpha-helices comprising the residues 144-154, 173-194, and 200-228 and a short anti-parallel beta-sheet comprising the residues 128-131 and 161-164. Within the globular domain, three polypeptide segments show increased structural disorder: i.e., a loop of residues 167-171, the residues 187-194 at the end of helix 2, and the residues 219-228 in the C-terminal part of helix 3. The local conformational state of the polypeptide segments 187-193 in helix 2 and 219-226 in helix 3 is measurably influenced by the length of the N-terminal tail, with the helical states being most highly populated in hPrP(23-230). When compared with the previously reported structures of the murine and Syrian hamster prion proteins, the length of helix 3 coincides more closely with that in the Syrian hamster protein whereas the disordered loop 167-171 is shared with murine PrP. These species variations of local structure are in a surface area of the cellular form of PrP that has previously been implicated in intermolecular interactions related both to the species barrier for infectious transmission of prion disease and to immune reactions.

Animals↗

PubMed2000

Up-regulation of novel intermediate filament proteins in primary fiber cells: an indicator of all vertebrate lens fiber differentiation?

The early embryonic development and expression patterns of the eye lens specific cytoskeletal proteins, CP49 and CP95, were determined for the chick and were found to be similar in both human and mouse. These proteins, as well as their homologs in other species, are obligate polymerization partners which form unique filamentous structures termed "beaded filaments." CP49 and CP95 appeared as protein products after 3 days of embryonic development in the chick during the elongation of primary fiber cells. Although limited data were obtained for human embryos at these early developmental timepoints, they were consistent with the interpretation that the up-regulation of these lens specific proteins began only after the initiation of lens vesicle closure. In situ hybridization with the mouse lens confirmed that message levels for beaded filament proteins were greatly elevated in differentiating primary fiber cells. Nuclease protection assays established that mRNA levels for CP49 remained relatively constant while CP95 mRNA levels increased once the process of secondary fiber formation was under way. Although present in relatively low abundance, the mRNA for a unique splice variant of CP49, CP49(INS), was also detected early in embryonic development and into adulthood. Peptide-specific antibodies directed against unique predicted sequences were able to confirm the protein expression of CP49(INS) in both embryonic and adult chick lens cells. These data present the first detailed study of the expression of CP49 and CP95 during early lens development. They suggest that the up-regulated expression of CP49 and CP95 could serve as pan-specific markers for all vertebrate lens fiber development.

Animals↗

PubMed2000

Surgical treatment of primary midbrain gliomas.

BACKGROUND: The treatment of brainstem gliomas remains controversial. This article focuses on surgical results. METHODS: The authors retrospectively analyzed 35 patients with primary midbrain gliomas who were treated at Beijing Neurosurgical Institute from 1986 to 1997. The diagnosis was verified by histological examination. RESULT: The incidence of midbrain glioma was 10.3% (35/340) in our patients with brain stem tumors. The 35 gliomas were classified into three therapeutic groups by their locations: 7 were located in the tectal region, 8 in the aqueductal region, and 20 in the tegmental region. All of the patients underwent microsurgical treatment based on a minimally invasive approach. The operation took the form of total resection in 19 cases, subtotal resection in 12, and partial resection in 4. The operative mortality was 0. With a mean follow-up of 28 months (range, 6-48 months), 65.7% (23/35) of patients could live independently. CONCLUSION: The volume and location of midbrain tumors were highly correlated with outcome. The resection of as much tumor as possible was optimal for the treatment of midbrain gliomas and radiotherapy after operation was beneficial to patients.

Adolescent↗

PubMed2000

Otx2, Gbx2 and Fgf8 interact to position and maintain a mid-hindbrain organizer.

A decade ago, chick-quail transplantation studies demonstrated that the junction between the midbrain and hindbrain has the properties of an organizing center capable of patterning the midbrain and cerebellum. Many of the genes that function to pattern these tissues have been identified and extensively studied. Recent experiments have shown that Otx2, Gbx2 and Fgf8 genes play a major role in the positioning and functioning of this organizing center.

Animals↗

PubMed2000

Substituted benz[a]acridines and benz[c]acridines as mammalian topoisomerase poisons.

Coralyne and several other synthetic benzo[a,g]quinolizium derivatives related to protoberberine alkaloids have exhibited activity as topoisomerase poisons. These compounds are characterized by the presence of a positively charged iminium group, which has been postulated to be associated with their pharmacological properties. The objective of the present study was to devise stable noncharged bioisosteres of these compounds. Several similarly substituted benz[a]acridine and benz[c]acridine derivatives were synthesized and their relative activity as topoisomerase poisons was determined. While the benz[c]acridine derivatives evaluated as part of this study were devoid of topoisomerase poisoning activity, several dihydrobenz[a]acridines were able to enhance DNA cleavage in the presence of topo I. In contrast to certain protoberberine derivatives that did exhibit activity as topo II poisons, none of the benz[a]acridines derivatives enhanced DNA cleavage in the presence of topo II. Among the benz[a]acridines studied, 5,6-dihydro-3,4-methylenedioxy-9,10-dimethoxybenz[a]acridine, 13e, was the most potent topo I poison, with comparable potency to coralyne. These data suggest that heterocyclic compounds structurally related to coralyne can exhibit potent topo I poisoning activity despite the absence of an iminium cation within their structure. In comparison to coralyne or other protoberberine derivatives, these benz[a]acridine derivatives possess distinctly different physicochemical properties and represent a novel series of topo I poisons.

Acridines↗

PubMed2000

2"-Substituted 5-phenylterbenzimidazoles as topoisomerase I poisons.

5-Phenylterbenzimidazole (1) is active as a topoisomerase I poison (topo I) and is cytotoxic to human tumor cells. No cross-resistance was observed for 1 when it was evaluated against the camptothecin-resistant cell line, CPT-K5. Derivatives of 1 substituted at the 2"-position, however, did exhibit cross-resistance to this cell line. The basis for the resistance of this cell line towards CPT is that it possesses a mutant form of topo I. These results suggest that substituents at the 2"-position may be in proximity to the wild-type enzyme. Therefore, we hypothesized that terbenzimidazoles with 2"-substituents could be capable of interacting with the enzyme and thereby influence activity within this class of topo I poisons. 5-Phenylterbenzimidazoles with a hydroxy, hydroxymethyl, mercapto, amino, N-benzoylaminomethyl, chloro, and trifluoromethyl group at the 2"-position were synthesized. In addition, several 2"-ethyl-5-phenylterbenzimidazoles were prepared containing either a methoxy, hydroxy, amino, or N-acetylamino group at the 2-position of the ethyl side-chain. These 2"-substituted 5-phenylterbenzimidazoles were evaluated as topo I poisons and for cytotoxic activity. The presence of a strong electron-withdrawing group at the 2"-position, such as a chloro or trifluoromethyl group, did enhance both topo I poisoning activity and cytotoxicity. Studies on the relative DNA binding affinity of 1 to its 2"-amino and 2"-trifluoromethyl derivatives did exhibit a correlation with their relative differences in biological activity.

Antineoplastic Agents↗

PubMed2000

Topoisomerase I inhibition and cytotoxicity of 5-bromo- and 5-phenylterbenzimidazoles.

Topoisomerase I is an enzyme that is essential for maintaining the three-dimensional structure of DNA during the processes of transcription, translation and mitosis. With the introduction of new clinical agents that are effective in poisoning topoisomerase I, this enzyme has proved to be an attractive molecular target in the development of anticancer drugs. Several terbenzimidazoles have been identified as potent topoisomerase I poisons. Structure-activity data on various terbenzimidazoles have revealed that the presence of lipophilic substituents at the 5-position of various terbenzimidazoles correlates with enhanced cytotoxicity. While the effect of having substituents at both the 5- and 6-positions had not been evaluated, previous studies did indicate that the presence of a fused benzo-ring at the 5,6-position results in a significant decrease in topoisomerase I poisoning activity and cytotoxicity. In the present study we investigated whether substituents at both the 5- and 6-positions of varied terbenzimidazoles would allow for retention of topo I poisoning activity. The 6-bromo, 6-methoxy, or 6-phenyl derivatives of both 5-bromo- and 5-phenylterbenzimidazole were synthesized and evaluated for topo I poisoning activity, as well as their cytotoxicity toward human lymphoblastoma cells. The data indicate that such derivatives do retain similar topo I poisoning activity and possess cytotoxicity equivalent to either 5-bromo- or 5-phenylterbenzimidazole. Significant enhancement in the topoisomerase I poisoning activity and cytotoxicity of 5-phenylterbenzimidazole is observed when the 2"-position is substituted with either a chloro or trifluoromethyl substituent. The influence of such substituents on the biological activity of 5.6-dibromoterbenzimidazole (6a) was also explored. In the case of either 2"-chloro-5,6-dibromoterbenzimidazole (6b) or 2"-trifluoromethyl-5,6-dibromoterbenzimidazole (6c), topoisomerase I poisoning was not enhanced relative to 6a. While cytotoxicity toward RPMI 8402 was also not significantly affected, comparative studies performed against several solid human tumor cell lines did reveal a significant increase in cytotoxicity observed for 6c as compared to 6a.

Benzimidazoles↗

PubMed2000

Cold storage of Halotydeus destructor (Acari: Penthaleidae) for use in experiments.

Survival of medium sized nymphal stages of redlegged earth mite Halotydeus destructor (Tucker) (mainly tritonymphs and deutonymphs) stored under low temperature (1.5 degrees C) in sealed plastic boxes remained more than 50% after 12 days of storage, with some mites surviving for up to eight weeks. Adding fresh subclover leaves into the storage box increased the survival rate of mites from 12% to 28%, 19 days after the storage started. Mites stored for two weeks at low temperatures showed feeding activity in a screening experiment similar to mites collected directly from the field. This indicated that cold storage of redlegged earth mite can be used to build up mite numbers for large screening experiments, or to extend the period of availability of mites collected from the field. However, their reproductive ability was greatly reduced after three weeks at low temperature. Thus, care should be taken when using mites for experiments measuring reproduction. The implications of low temperatures for reducing field populations of mites in midwinter are also discussed.

Animals↗

PubMed2000

NMR experiments for resonance assignments of 13C, 15N doubly-labeled flexible polypeptides: application to the human prion protein hPrP(23-230).

A combination of three heteronuclear three-dimensional NMR experiments tailored for sequential resonance assignments in uniformly 15N, 13C-labeled flexible polypeptide chains is described. The 3D (H)N(CO-TOCSY)NH, 3D (H)CA(CO-TOCSY)NH and 3D (H)CBCA(CO-TOCSY)NH schemes make use of the favorable 15N chemical shift dispersion in unfolded polypeptides, exploit the slow transverse 15N relaxation rates of unfolded polypeptides in high resolution constant-time [1H, 15N]-correlation experiments, and use carbonyl carbon homonuclear isotropic mixing to transfer magnetization sequentially along the amino acid sequence. Practical applications are demonstrated with the 100-residue flexible tail of the recombinant human prion protein, making use of spectral resolution up to 0.6 Hz in the 15N dimension, simultaneous correlation with the two adjacent amino acid residues to overcome problems associated with spectral overlap, and the potential of the presently described experiments to establish nearest-neighbor correlations across proline residues in the amino acid sequence.

Carbon Isotopes↗

PubMed2000

Sensitivity enhanced NMR spectroscopy by quenching scalar coupling mediated relaxation: application to the direct observation of hydrogen bonds in 13C/15N-labeled proteins.

In this paper, we demonstrate that the sensitivity of triple-resonance NMR experiments can be enhanced significantly through quenching scalar coupling mediated relaxation by using composite-pulse decoupling (CPD) or.an adiabatic decoupling sequence on aliphatic, in particular alpha-carbons in 13C/15N-labeled proteins. The CPD-HNCO experiment renders 50% sensitivity enhancement over the conventional CT-HNCO experiment performed on a 12 kDa FK506 binding protein, when a total of 266 ms of amide nitrogen-carbonyl carbon defocusing and refocusing periods is employed. This is a typical time period for the direct detection of hydrogen bonds in proteins via trans-hydrogen bond 3hJ(NC') couplings. The experimental data fit theoretical analysis well. The significant enhancement in sensitivity makes the experiment more applicable to larger-sized proteins without resorting to perdeuteration.

Carbon Isotopes↗

PubMed2000

Detection of very weak side chain-main chain hydrogen bonding interactions in medium-size 13C/15N-labeled proteins by sensitivity-enhanced NMR spectroscopy.

We describe the direct observation of very weak side chain-main chain hydrogen bonding interactions in medium-size 13C/15N-labeled proteins with sensitivity-enhanced NMR spectroscopy. Specifically, the remote correlation. between the hydrogen acceptor side chain carboxylate carbon 13CO2delta of glutamate 54 and the hydrogen donor backbone amide 15N of methionine 49 in a 12 kDa protein, human FKBP12, is detected via the trans-hydrogen bond 3hJ(NCO2delta) coupling by employing a novel sensitivity-enhanced HNCO-type experiment, CPD-HNCO. The 3hJ(NCO2delta) coupling constant appears to be even smaller than the average value of backbone 3hJ(NC') couplings, consistent with more extensive local dynamics in protein side chains.

Carbon Isotopes↗

PubMed2000

NMR detection of side chain-side chain hydrogen bonding interactions in 13C/15N-labeled proteins.

We describe the direct observation of side chain-side chain hydrogen bonding interactions in proteins with sensitivity-enhanced NMR spectroscopy. Specifically, the remote correlation between the guanidinium nitrogen 15Nepsilon of arginine 71, which serves as the hydrogen donor, and the acceptor carboxylate carbon 13CO2gamma of aspartate 100 in a 12 kDa protein, human FKBP12, is detected via the trans-hydrogen bond 3h JNepsilonCO2gamma coupling by employing a novel HNCO-type experiment, soft CPD-HNCO. The 3h JNepsilonCO2gamma coupling constant appears to be even smaller than the average value of backbone 3h JNC' couplings, consistent with more extensive local dynamics in protein side chains. The identification of trans-hydrogen bond J-couplings between protein side chains should provide useful markers for monitoring hydrogen bonding interactions that contribute to the stability of protein folds, to alignments within enzyme active sites and to recognition events at macromolecular interfaces.

Animals↗

PubMed2000

MtDNA and Y chromosome polymorphisms in Hungary: inferences from the palaeolithic, neolithic and Uralic influences on the modern Hungarian gene pool.

Magyars imposed their language on Hungarians but seem not to have affected their genetic structure. To better investigate this point, we analysed some mtDNA and Y chromosome polymorphisms in a sample of the Hungarian Palóc who, for historical reasons, could have retained genetic traces of Magyars more than other groups. In addition, we examined a mixed sample from Budapest. About 100 individuals were tested for the markers defining all the European and Asian mtDNA haplogroups and about 50 individuals for some Y chromosome markers, namely the 12f2 and 49a,f/TaqI RFLPs, the YAP insertion, the microsatellites YCAIIa, YCAIIb, DYS19 and the Asian 50f2/C deletion. In the mtDNA analysis only two subjects belonged to the Asian B and M haplogroups. The Y chromosome analyses showed that the Palóc differed from the Budapest sample by the absence of YAP+ allele and by the DYS19 allele distribution; that the proto-European 49a,f Ht 15 and the neolithic 12f2-8Kb were rather uncommon in both groups; that there is a high prevalence of the 49a,f Ht 11 and the YCAII a5-b1; and that the Asian 50f2/C deletion is absent. These results suggest that the influence of Magyars on the Hungarian gene pool has been very low through both females and males and the Hungarian language could be an example of cultural dominance. Alternative explanations are discussed. An expansion centred on YAP-, 49a,f Ht 11 is revealed by the median network based on compound haplotypes. 49a,f Ht 11 could represent either a paleolithic marker of eastern Europe which underwent expansion after the last glacial period, or a marker of the more recent spread of the Yamnaia culture from southern Ukraine.

Alu Elements↗

PubMed2000

Evidence for linkage of a tandem duplication polymorphism upstream of the dopamine D4 receptor gene (DRD4) with attention deficit hyperactivity disorder (ADHD).

Attention deficit hyperactivity disorder (ADHD) is a common childhood-onset neurodevelopmental disorder. Evidence from twin, adoption, and family studies provide support for a genetic contribution to the etiology of ADHD. Several candidate gene studies have identified an association between a 7-repeat variant in exon 3 of the dopamine 4 receptor gene (DRD4) and ADHD. However, in spite of the positive reports finding association of the exon 3 VNTR with ADHD, several other polymorphisms within DRD4 have been identified that conceivably could contribute to risk for ADHD. Recently, another common polymorphism of the DRD4 gene has been described involving a 120-bp repeat element upstream of the 5' transcription initiation site. In this report, we describe results of analysis of the DRD4 120-bp repeat promoter polymorphism in a sample of 371 children with ADHD and their parents, using the transmission disequilibrium test (TDT). Results showed a significant preferential transmission of the 240-bp (long) allele with ADHD. Exploratory analyses of the Inattentive phenotypic subtype of ADHD strengthened the evidence for linkage. These data add further support for the role of DRD4 variants conferring increased risk for ADHD, and imply that additional studies of DRD4 and other related genes are needed.

Adolescent↗

PubMed2000

Modulation of hypothalamic NMDA receptor function by cyclic AMP-dependent protein kinase and phosphatases.

In the present study we investigated the modulation of hypothalamic NMDA receptor-mediated currents by cyclic AMP-dependent protein kinase (PKA) using the two-electrode voltage-clamp technique in Xenopus oocytes injected with rat hypothalamic mRNA. Application of forskolin, which activates PKA by means of cyclic AMP stimulation, caused a transient increase of NMDA-induced currents, whereas the inactive forskolin analogue 1,9-dideoxyforskolin had no effect. Incubation of oocytes with a membrane-permeable analogue of cyclic AMP, 8-bromoadenosine 3',5' -cyclic monophosphate, potentiated NMDA responses even more prominently than with forskolin. NMDA-induced currents recorded from Xenopus oocytes injected with cRNA encoding the NMDA receptor subunits NR1, NR2A, and/or NR2B, mainly found in rat hypothalamus, were not affected by PKA activation but were increased by protein kinase C (PKC) stimulation. It is interesting that inhibition of endogenous protein phosphatase 1 and/or 2A by calyculin A resulted in a similar enhancement of hypothalamic NMDA-induced currents. Preinjection of oocytes with calyculin A impeded the PKA- but not the PKC-mediated potentiation of hypothalamic NMDA-induced currents. We propose the involvement of an additional third messenger in the PKA effect, which acts most likely via the inhibition of tonically active protein phosphatase 1 and/or 2A.

8-Bromo Cyclic Adenosine Monophosphate↗

PubMed2000

Expression and function of angiopoietin-1 in breast cancer.

Angiopoietin-1 (Ang1) has been shown to act as an angiogenic promoter in embryonic angiogenesis by promoting vascular branching, pericyte recruitment and endothelial survival. We have investigated the role of Ang1 in tumour neovascularization under clinical conditions and in animal models. The expression of Ang1 in clinical breast cancer specimens was analysed by using laser-capture microdissection and reverse transcriptase-linked polymerase chain reaction (RT-PCR) on RNA isolated from the samples. Despite the expression of Ang1 in many human breast cancer cell lines, the gene was expressed in only three of 21 breast cancer clinical specimens, even though its receptor, Tie2, is abundant in the vasculature of all of these tumours. Ang1 was then overexpressed in a human breast cancer cell line (MCF-7) on its own and in conjunction with FGF1, an angiogenic factor shown to be able to increase the tumorigenicity of MCF-7 cells. High concentrations of Ang1 were produced in the conditioned media of the transfected cells (range 156-820 ng ml(-1)). However, in contrast to its physiological role as promoter of angiogenesis, overexpression of Ang1 did not enhance tumour growth, but instead caused up to a 3-fold retardation of tumour growth (P = 0.003).

Angiopoietin-1↗

PubMed2000

Generation of dendritic cells from adherent cells of cord blood by culture with granulocyte-macrophage colony-stimulating factor, interleukin-4, and tumor necrosis factor-alpha.

Although dendritic cells (DC) can be cultured from cord blood (CB) CD34+ progenitor cells, the generation of DC from CB monocytes has not been reported. In this paper, we explored the generation of DC from CB monocytes to establish the simplest way to obtain a substantial number of DC from CB. We isolated monocytes from CB mononuclear cells (CB-MNC) by the plastic adherence method. These adherent cells (monocyte-rich cells) were cultured in RPMI 1640 medium supplemented with 10% fetal bovine serum (FBS) or in serum-free X-VIVO 15 medium (SFM) for 7 days, both of which contained 100 ng/ml granulocyte-macrophage colony-stimulating factor (GM-CSF) and 10 ng/ml interleukin-4 (IL-4) with or without 10 ng/ml tumor necrosis factor-alpha (TNF-alpha) (added at day 5). In the presence of GM-CSF and IL-4, CB-adherent cells became nonadherent, acquired DC morphology, and showed increased expression of CD1a, CD80, CD86, and HLA-DR; they lost membrane CD14 and some cells with the expression of CD83 and CMRF-44 were generated. With the addition of TNF-alpha to these cultures and culturing for further 2 days, the proportion of CD83+ cells was elevated in both the FBS and SFM culture systems, compared with the culture without TNF-alpha. In the culture with TNF-alpha, cells expressing CD1a, CD80, CD86, HLA-DR, and HLA-DQ were markedly increased. TNF-alpha-treated cells were demonstrated to be stronger stimulators for proliferation of both allogeneic CB lymphocytes and PB lymphocytes than were cells not treated with TNF-alpha. The yield of CD83+ DC at day 7 of cultures was 4.9 +/- 1.1 x 10(5) or 3.0 +/- 0.5 x 10(5) per 1.2 x 10(7) CB-MNC plated initially when cultured in FBS or SFM, respectively. These results have shown that a substantial number of mature DC could be generated from CB-adherent cells even by serum-free culture. We then compared these CB-adherent cell-derived DC (CB-DC) with peripheral blood (PB)-adherent cell-derived DC (PB-DC) in cell-surface phenotype and function. We found day 7 CB-DC have lower expression of CD80, CD1a, CD83, and CMRF-44 than day 7 PB-DC, but CB-DC have a similar capacity to stimulate the proliferation of both allo-CB lymphocytes and PB lymphocytes, compared with PB-DC. CB-DC cultured with GM-CSF and IL-4 have almost identical capacity of phagocytosis to take up fluorescein isothiocyanate (FITC)-dextran and Lucifer yellow (LY), compared with PB-DC. In summary, our findings suggest CB adherent cells, when cultured with GM-CSF, IL-4, and TNF-alpha, are a potent source of functional DC. Thus, CB-DC as well as PB-DC may become valuable tools for immunotherapy.

Cell Adhesion↗

PubMed2000

Familial clustering of symptoms and disruptive behaviors in multiplex families with attention-deficit/hyperactivity disorder.

OBJECTIVE: To examine familial clustering of attention-deficit/hyperactivity disorder (ADHD), ADHD subtypes, symptoms, and oppositional behaviors in affected sibling pairs (ASPs) and their parents. METHOD: One hundred thirty-two ASPs, ranging in age from 5 to 25 years and ascertained through clinic and volunteer referrals, were examined for DSM-IV ADHD subtypes, oppositional defiant disorder (ODD), and conduct disorder (CD) with the Schedule for Affective Disorders and Schizophrenia for School-Age Children-Present and Lifetime version (K-SADS-PL). Two hundred fifty-six parents in these families were assessed by means of the SADS-Lifetime version, Modified for the Study of Anxiety Disorders, Updated for DSM-IV (SADS-LA-IV), and the Behavioral Disorders supplement of the K-SADS-PL to determine ADHD, ODD, and CD. RESULTS: Fifty-five percent of families ascertained through an ASP have at least one parent with a lifetime diagnosis of ADHD. The frequency of ADHD in at least one parent was higher in families with at least one affected girl (63%) than in families with only affected boys (45%) (p = .02). There was no evidence that affected siblings or parents within ASP families showed similar patterns of ADHD symptoms, such as ADHD subtype classification. In contrast, CD significantly clustered in ASP families. CONCLUSIONS: The sex difference in prevalence of ADHD among ASPs is consistent with a model of inheritance in which girls require a greater loading of familial influences to develop ADHD. The lack of familial clustering of ADHD symptoms within ASP families suggests that hyperactive and inattentive symptoms reflect common familial underpinnings and not unique familial effects. In contrast, CD seems to reflect unique familial underpinnings distinct from those underlying ADHD.

Adolescent↗