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Biomedical subjects

Q Zhu

Publications and source records attributed to Q Zhu.

At least 181 records · Page 10Linked to original sources
PubMed1998

[The high resolution spectroscopy of CH35 Cl3 and CH35Cl2(37) V = 3 stretching overtone].

The Fourier transform spectrometer (FTS) is used to record the high resolution spectrum of V = 3 stretching overtone for two isotopic species: CH35Cl3 and CH35Cl2(37)Cl. The rotational constants of CH35Cl2(37) Cl are calculated approximately from its isotope, CH35Cl3. The ground states combination difference method is used to assign the observed transitions. Because of the relatively small rotational constant, the resolution of 0.02 cm(-1) is still not enough to resolve the rotational K structure of CHCl3. So, all the observed transitions are assigned as parallel band transitions arising from the k = 0 rotational states. A weighted non-linear least-square fitting program is developed to fit the assigned transitions and derive the rotational constants. The result of the fitting for the CH35Cl2(37)Cl spectrum indicates that it is reasonable and reliable to derive the spectroscopic parameters using the isotopic effect.

English Abstract↗
PubMed1997

Comparative molecular field analysis of a series of paclitaxel analogues.

A series of 94 paclitaxel analogues exhibiting antitumor activity by promoting the assembly of microtubules and inhibiting the disassembly process of microtubules to tubulin were investigated using the comparative molecular field analysis (CoMFA) method. These compounds belonging to 10 structural classes were randomly divided into a training set of 80 compounds and a test set of 14 compounds. Since the three-dimension structure of ligand--receptor complex is unknown, from X-ray and NMR data we rationally selected the three-dimension structure of paclitaxel in a polar solution as the active conformation and starting structure for molecule modeling, the other molecules were aligned using this molecule model as the template. The most optimal CoMFA yielded a two-components model, with significant cross-validation r2cv of 0.640 and conventional r2 of 0.868. The predictive ability of training set model was tested on the test set of 14 compounds. The tests not only revealed the robustness of the CoMFA model but demonstrated that for our model r2pred based on the mean activity of test set compounds can accurately estimate external predictivity but r2pred based on the mean activity of training set compounds overestimated the model. The CoMFA model explained why the activity of taxoid is sensitive to the stereochemistry of the atoms at C-2' and C-3' positions and the presence of hydroxyl group at C-2' position. The other factors affecting activity were also elucidated according to standard coefficient contour maps of steric and electrostatic fields derived from the CoMFA model.

Antineoplastic Agents↗
PubMed1997

Wiskott-Aldrich syndrome/X-linked thrombocytopenia: WASP gene mutations, protein expression, and phenotype.

Wiskott-Aldrich syndrome (WAS) and X-linked thrombocytopenia (XLT), caused by mutations of the WAS protein (WASP) gene, represent different phenotypes of the same disease. To demonstrate a phenotype/genotype correlation, we determined WASP gene mutations in 48 unrelated WAS families. Mutations included missense (20 families) and nonsense (eight) mutations located mostly in exons 1 to 4, and splice-site mutations (seven) and deletions and insertions (13) located preferentially in exons 7 to 11. Both genomic DNA and cDNA were sequenced and WASP expression was measured in cell lysates using peptide-specific rabbit anti-WASP antibodies. WASP was expressed in hematopoietic cell lines including bone marrow-derived CD34+ cells. Missense mutations located in exons 1 to 3 caused mild disease in all but one family and permitted WASP expression, although frequently at decreased concentration. Missense mutations affecting exon 4 were associated with classic WAS and, with one exception, barely detectable WASP. Nonsense mutations caused classic WAS and lack of protein. Insertions, deletions, and splice-site mutations resulted in classic WAS and absent, unstable, truncated, or multiply spliced protein. Using affinity precipitation, WASP was found to bind to Src SH3-containing proteins Fyn, Lck, PLC-gamma, and Grb2, and mutated WASP, if expressed, was able to bind to Fyn-glutathione S-transferase (GST) fusion protein. We conclude that missense mutations affecting the PH domain (exons 1 to 3) of WASP inhibit less important functions of the protein and result in a mild phenotype, and that missense mutations affecting exon 4 and complex mutations affecting the 3' portion of WASP interfere with crucial functions of the protein and cause classic WAS.

Amino Acid Sequence↗
PubMed1997

RF2a, a bZIP transcriptional activator of the phloem-specific rice tungro bacilliform virus promoter, functions in vascular development.

Rice tungro bacilliform virus (RTBV) replicates only in phloem cells in infected rice plants and its promoter drives strong phloem-specific reporter gene expression in transgenic rice plants. We isolated a cDNA encoding a basic leucine zipper (bZIP) protein, RF2a, which binds to the Box II cis element that is important for expression from the promoter. RF2a, which stimulates Box II-dependent transcription in a homologous in vitro transcription system, accumulates in nuclei of phloem and certain other cell types in shoots, but is found at only very low levels in roots. Transgenic antisense plants in which RF2a accumulation was suppressed had normal roots but stunted, twisted leaves with small, disorganized vascular bundles, an enlarged sclerenchyma and large air spaces. We propose that the RTBV promoter exploits a host transcription factor that is critical for leaf tissue differentiation and vascular development for its expression.

Amino Acid Sequence↗
PubMed1997

The cluA- mutant of Dictyostelium identifies a novel class of proteins required for dispersion of mitochondria.

The cluA gene of Dictyostelium discoideum encodes a novel 150-kDa protein. Disruption of cluA results in clustering of mitochondria near the cell center. This is a striking difference from normal cells, whose mitochondria are dispersed uniformly throughout the cytoplasm. The mutant cell populations also exhibit an increased frequency of multinucleated cells, suggesting an impairment in cytokinesis. Both phenotypes are reversed by transformation of cluA- cells with a plasmid carrying a constitutively expressed cluA gene. The predicted sequence of the cluA gene product is homologous to sequences encoded by open reading frames in the genomes of Saccharomyces cerevisiae and Caenorhabditis elegans, but not to any known protein. The only exception is a short region with some homology to the 42-residue imperfect repeats present in the kinesin light chain, which probably function in protein-protein interaction. These studies identify a new class of proteins that appear to be required for the proper distribution of mitochondria.

Amino Acid Sequence↗
PubMed1997

Lanthionine-somatostatin analogs: synthesis, characterization, biological activity, and enzymatic stability studies.

A series of cyclic somatostatin analogs containing a lanthionine bridge have been subjected to studies of structure-activity relationships. A direct synthesis of the thioether bridged analog (1) of sandostatin (SMS 201,995) and several lanthionine hexa-, hepta-, and octapeptides was carried out by using the method of cyclization on an oxime resin (PCOR) followed by condensation reactions in solution. The structures of the target peptides were analyzed by liquid secondary ion mass spectrometry (LSIMS) and subjected to high-energy collision-induced dissociation (CID) studies after opening of the peptide ring by proteolytic cleavage. The biological activities of these compounds have been evaluated by assaying their inhibitory potencies for the release of growth hormone (GH) from primary cultures of rat anterior pituitary cells, as well as by their binding affinities to cloned somatostatin receptors (SSTR1-5). The structural modification of sandostatin by introducing a lanthionine bridge resulted in a significantly increased receptor binding selectivity. The lanthionine octapeptide with C-terminal Thr-ol (1) showed similar high affinity for rat SSTR5 compared to somatostatin[1-14] and sandostatin. However, it exhibits about 50 times weaker binding affinity for mSSTR2b than sandostatin. Similarly, the lanthionine octapeptide with the C-terminal Thr-NH2 residue (2) has higher affinity for rSSTR5 than for mSSTR2B. Both peptides (compounds 1 and 2) have much lower potencies for inhibition of growth hormone secretion than sandostatin. This is consistent with their affinities to SSTR2, the receptor which is believed to be linked to the inhibition of growth hormone release by somatostatin and its analogs. The metabolic stability of lanthionine-sandostatin and sandostatin have been studied in rat brain homogenates. Although both compounds have a high stability toward enzymatic degradation, the lanthionine analog has a 2.4 times longer half-life than sandostatin. The main metabolites of both compounds have been isolated and identified by using an in vivo technique (cerebral microdialysis) and mass spectrometry.

Alanine↗
PubMed1997

A refined model for the somatostatin pharmacophore: conformational analysis of lanthionine-sandostatin analogs.

We report the conformational analysis of a series of analogs of sandostatin (octreotide, D-Phe1-c[Cys2-Phe3-D-Trp4-Lys5-Thr6-Cys 7]-Thr8-ol) using 1H NMR spectroscopy and molecular modeling. Two active compounds in which the disulfide group is replaced by a monosulfide (lanthionine) bridge (D-Phe1-c[AlaL2-Phe3-D-Trp4-Lys5-Thr6-A laL7]-Thr8-ol and D-Phe1-c[AlaL2-Phe3-D-Trp4-Lys5-Thr6-Al aL7]-Thr8-NH2, where AlaL denotes each of the lanthionine amino acid ends linked by the monosulfide bridge) show different mSSTR2b/rSSTR5 receptor selectivities as compared to sandostatin. These new results have enabled us to reveal features of the somatostatin pharmacophore common to the model previously proposed in our laboratory on the basis of main chain and side chain chiral methylation studies. In addition, our studies provide new insight into the role of the disulfide bridge and of Thr8 in binding potency. We also show that the lanthionine group is a good mimetic of beta-VI turns and can be incorporated in sandostatin analogs maintaining the essential secondary structural features of sandostatin. These results facilitate the design of new sandostatin peptidomimetics.

Alanine↗
PubMed1997

Mitogenic stimulation of resting T cells causes rapid phosphorylation of the transcription factor LSF and increased DNA-binding activity.

The mammalian transcription factor LSF (CP2/LBP-1c) binds cellular promoters modulated by cell growth signals. We demonstrate here that LSF-DNA-binding activity is strikingly regulated by induction of cell growth in human peripheral T lymphocytes. Within 15 min of mitogenic stimulation of these cells, the level of LSF-DNA-binding activity increased by a factor of five. The level of LSF protein in the nucleus remained constant throughout this interval. However, a rapid decrease in the electrophoretic mobility of LSF, attributable to phosphorylation, correlated with the increase in DNA-binding activity. pp44 (ERK1) phosphorylated LSF in vitro on the same residue that was phosphorylated in vivo, specifically at amino acid position 291, as indicated by mutant analysis. As direct verification of the causal relationship between phosphorylation and DNA-binding activity, treatment in vitro of LSF with phosphatase both increased the electrophoretic mobility of the protein and decreased LSF-DNA-binding activity. This modulation of LSF-DNA-binding activity as T cells progress from a resting to a replicating state reveals that LSF activity is regulated during cell growth and suggests that LSF regulates growth-responsive promoters.

Calcium-Calmodulin-Dependent Protein Kinases↗
PubMed1997

Calreticulin-integrin bidirectional signaling complex.

Calreticulin has multiple functions, diverse cellular locations, and putative isoforms. It likely maintains integrin avidity by binding alpha integrin cytoplasmic tails and is a surface lectin which triggers cell spreading. In the present study, we have immunocaptured a cell surface complex from B16 mouse melanoma cells which contains alpha 6 beta 1 integrin, two molecular forms of calreticulin, and KDEL docking protein (KDEL-R). One of the calreticulins, "endocalreticulin", a 52 kDa protein, does not become surface biotinylated, and is probably bound to alpha integrin cytoplasmic tails; it disappears when B16 cells adhere to laminin, and two ubiquitinated calreticulins appear. One ubiquitinated species, a 125 kDa protein, is restricted to focal contacts whereas a second species, a 75 kDa protein, is in focal contacts and surrounding plasma membrane; it also arises when cells bind non-specific surfaces. The other calreticulin, "ectocalreticulin", a 62 kDa protein, becomes surface biotinylated, is probably anchored to surface KDEL-R, and cooperates with alpha 6 beta 1 integrin, triggering cell spreading. The present results suggest a model in which calreticulin-integrin surface complex functions as a symbiotic unit, transmitting information in both directions across the plasma membrane.

Animals↗
PubMed1997

Multiconformational NMR analysis of sandostatin (octreotide): equilibrium between beta-sheet and partially helical structures.

This paper reports a detailed conformational analysis by 1H NMR (DMSO-d6, 300 K) and molecular modeling of the octapeptide D-Phe1-Cys2-Phe3-D-Trp4-Lys5-Thr6-Cys7+ ++-Thr8-ol (disulfide bridged) known as sandostatin (or SMS 201-995 or octreotide) with both somatostatin-like and opioid-like bioactivities. This is the initial report on sandostatin showing that attempts to explain all NMR data using a single average conformation reveal several important inconsistencies including severe violations of mutually exclusive backbone-to-backbone NOEs. The inconsistencies are solved by assuming an equilibrium between antiparallel beta-sheet structures and conformations in which the C-terminal residues form a 3(10) helix-like fold (helical ensemble). This conformational equilibrium is consistent with previous X-ray diffraction investigations which show that sandostatin can adopt both the beta-sheet and the 3(10) helix-like secondary structure folds. In addition, indications of a conformational equilibrium between beta-sheet and helical structures are also found in solvent systems different from DMSO-d6 and for other highly bioactive analogs of sandostatin. In these cases a proper multiconformational NMR refinement is important in order to avoid conformational averaging artifacts. Finally, using the known models for somatostatin-like and opioid-like bioactivities of sandostatin analogs, the present investigation shows the potentials of the proposed structures for the design of novel sandostatin-based conformationally restricted peptidomimetics. These analogs are expected to refine the pharmacophore models for sandostatin bioactivities.

Hormones↗
PubMed1997

Photo-irradiation improved functional preservation of the isolated rat heart.

BACKGROUND AND OBJECTIVE: Photo-irradiation causes a variety of effects in different cells and tissues. We hypothesized that photo-irradiation may improve cardiac preservation based on these observations. STUDY DESIGN/MATERIALS AND METHODS: For pre-storage treatment (Pre), the heart in an anesthetized open-chest rat was irradiated using an Argon-dye laser with a wavelength of 660 nm at a fluence of 16.8 J/cm2 or sham-operated. The heart was excised, perfused with Krebs-Henseleit Buffer, cardioplegically arrested, and stored by immersion at 0 degree C for 18 hrs. Functional recovery was evaluated by working reperfusion for 30 min. For post-storage treatment (Post), the isolated hearts were stored for 18 hrs at 0 degree C; laser irradiation at a fluence of 36 J/cm2 was administered during working reperfusion. Hearts which did not receive irradiation during reperfusion served as control. Furthermore, isolated cardiomyocytes were used to study laser effect on cellular ATP content, catalase activity, and nitric oxide (NO) release. RESULTS: Both Pre and Post groups showed significant improvement in recovery of aortic flow, cardiac output, and work compared to the corresponding control groups (P < 0.05). Combined Pre/Post laser treatment did not improve function. Investigation using isolated rat cardiomyocytes found that both end-storage ATP and end-reperfusion catalase activity in the laser-treated group were significantly higher than those in the untreated cells (P < 0.05). NO release increased by 15% in the laser group after 18 hrs of 37 degrees C incubation. CONCLUSION: Photo-irradiation improves functional recovery of the cold-stored rat heart possibly via conservation of ATP and antioxidant enzyme activity.

Adenosine Triphosphate↗
PubMed1997

Delayed maturation of regenerating myelinated axons in mice lacking neurofilaments.

Using the technique of homologous recombination in embryonic stem cells, we generated mice bearing a targeted disruption of the gene encoding the neurofilament light (NF-L) protein. The absence of NF-L protein in mice resulted in dramatic declines of approximately 20-fold in the levels of neurofilament medium and heavy proteins in the brain and sciatic nerve while increases were detected for other cytoskeletal proteins such as tubulin and GAP-43. Despite a lack of neurofilaments and hypotrophy of axons, the NF-L knockout mice develop normally and do not exhibit overt phenotypes. However, in both NF-L -/- and NF-L +/- mice, the regeneration of myelinated axons following crush injury of peripheral nerves was found to be abnormal. In the second week after axotomy, the number of newly regenerated myelinated axons in the sciatic nerve and facial nerve of NF-L -/- mice corresponded to only approximately 25 and approximately 5% of the number of myelinated axons found in normal mice, respectively. At this early postaxotomy stage, electron microscopy of nerve segments distal to the crush site in NF-L -/- mice revealed abundant clusters of axonal sprouts that were indicative of retarded maturation of regenerating fibers. The analysis of the distal sciatic nerve at 2 months after crush indicated that neurofilament-deficient axons have the capacity to regrow for a long distance and to remyelinate, albeit at a slower rate. These results provide the first direct evidence for a role of neurofilaments in the maturation of regenerating myelinated axons.

Animals↗
PubMed1997

Expression, purification, and functional analysis of the TyrR protein of Haemophilus influenzae.

The gene that was inferred to encode the TyrR protein of Haemophilus influenzae Rd was synthesized by polymerase chain reaction and inserted into a T7-based expression vector. Methods were developed to overexpress the TyrR protein of H. influenzae in Escherichia coli and to purify the protein on a large scale. Both in vitro and in vivo functional comparisons of the H. influenzae and E. coli TyrR proteins were carried out. The TyrR protein of H. influenzae was able to bind in vitro to an operator target upstream of the aroF-tyrA gene of E. coli. In the presence of [gamma-S]ATP, the DNA binding ability of the H. influenzae TyrR protein was drastically reduced. Despite the much shorter peptide chain length (318 amino acid residues vs 513), the TyrR protein of H. influenzae was as active in repressing the aroF promoter as the TyrR protein of E. coli. Repression by both proteins was enhanced in the presence of tyrosine; however, the transcriptional activation function associated with the TyrR protein of E. coli could not be detected when the H. influenzae TyrR protein was expressed in E. coli. By computer analysis, at least five operator targets for TyrR were identified within the genomic DNA of H. influenzae. These observations show that the assignment of function to the tyrR gene of H. influenzae was correctly made. Further studies of the H. influenzae TyrR protein in comparison to its E. coli counterpart should provide valuable mechanistic information on transcriptional regulation in this system.

Amino Acid Sequence↗
PubMed1997

Enzymic analysis of the structure of oxidized potato starches.

The possibility to use enzymic methods for the analysis of the positions of carboxyl and carbonyl groups in sodium hypochlorite oxidized (HO) and hydrogen peroxide oxidized (PO) potato starches was investigated. The HO-starch, that contained more modified glucosyl residues, possessed a lower beta-amylolysis limit and all of the polymer components were resistant to complete hydrolysis as judged from gel-permeation chromatograms. In contrast, the PO-starch contained 24% of apparently unmodified, linear chains that were hydrolysed by beta-amylase. After debranching, approximately 30% of the chains in the HO-sample and approximately 20% in the PO-sample remained partly resistant to successive beta-amylolysis.

Amylopectin↗
PubMed1997

The assessment of proliferating cell nuclear antigen (PCNA) immunostaining in human benign and malignant epithelial lesions of the parotid gland.

Immunoreactivity of proliferating cell nuclear antigen (PCNA) was assessed in formalin-fixed, paraffin-embedded sections from human normal parotid gland (N; n = 12), chronic sialadenitis (CS; n = 8), Warthin's tumour (W; n = 10), benign pleomorphic adenoma (BPA; n = 11), mucoepidermoid carcinoma (MEC; n = 14), carcinoma in pleomorphic adenoma (CPA; n = 10) and adenoid cystic carcinoma (ACC; n = 12) of the parotid gland, using the monoclonal antibody PC 10. The morphometric parameters measured comprised PCNA labelling induces (PI = the numerical percentage of PCNA positive nuclei) and volume densities of PCNA positive nuclei(VV, PEP = the relative volume of positive nuclei per unit volume of reference epithelium). All parameters were expressed in relation to total positive, as well as to strongly- and weakly-positive nuclei. In general, the values of PCNA parameters increased progressively in benign lesions in comparison with the N group, and in malignant neoplasms in comparison with non-neoplastic groups and benign lesions. The strongly-positive parameters showed more statistically significant differences than weakly-positive ones, suggesting that weakly-stained nuclei may include some non-cycling cells and, therefore, that weakly-positive parameters may not be reliable proliferation markers. Values for all parameters in CPA were significantly higher than those in BPA, suggesting that these parameters may be used as diagnostic discriminators. Spearman rank correlation analysis showed a highly positive correlation between the morphometric parameters and the severity of the lesions. Furthermore, the mean values of PISP were significantly higher in patients who died of the malignant tumours than in those patients who survived. Our results indicate that PCNA indices might be useful markers for discriminating between benign (BPA) and malignant tumours of the parotid gland and that the parameter PISP may have prognostic applications.

Adenocarcinoma↗
PubMed1997

An extensive repeat structure down-regulates human monoamine oxidase A promoter activity independent of an initiator-like sequence.

The 5' flanking sequence of the human monoamine oxidase A (MAO A) gene consists of an extensive repeat structure. Two 90-bp repeats (I and II) were found in the core promoter (the 0.24-kb PvuII/DraII fragment), each containing two Sp1 binding sites. An additional six repeats were found, five of which (III-VII) were upstream and one (-I) downstream of the core promoter. Using transient transfection assay with a human growth hormone reporter gene, we found that the upstream repeating units III-VII (in a 0.78-kb BamHI/DraII fragment) down-regulate core promoter activity to 13 +/- 10% in a human glioma cell line (1242 MG) and 2 +/- 1% in a cervical carcinoma cell line (HeLa), respectively. The 0.24-kb core promoter activity was taken as 100%. Addition of the initiator (Inr)-like sequence to this 0.78-kb fragment (0.82-kb BamHI/-17 fragment) still showed decreased promoter activity (10 +/- 9% in 1242 MG cells and 8 +/- 1% in HeLa cells). Thus, the upstream sequence down-regulates promoter activity with or without the Inr-like sequence. When the Inr-like sequence was added to the core promoter (0.28-kb PvuII/-17 fragment), the promoter activity decreases significantly in both 1242 MG (55 +/- 6%) and HeLa (60 +/- 10%) cells. These results suggest that although the Inr-like sequence is present in the human MAO A promoter, it acts as a negative cis element instead of a transcription initiator.

Base Sequence↗
PubMed1997

The matrix attachment region-binding protein SATB1 participates in negative regulation of tissue-specific gene expression.

The nuclear matrix has been implicated in several cellular processes, including DNA replication, transcription, and RNA processing. In particular, transcriptional regulation is believed to be accomplished by binding of chromatin loops to the nuclear matrix and by the concentration of specific transcription factors near these matrix attachment regions (MARs). A number of MAR-binding proteins have been identified, but few have been directly linked to tissue-specific transcription. Recently, we have identified two cellular protein complexes (NBP and UBP) that bind to a region of the mouse mammary tumor virus (MMTV) long terminal repeat (LTR) previously shown to contain at least two negative regulatory elements (NREs) termed the promoter-proximal and promoter-distal NREs. These NREs are absent from MMTV strains that cause T-cell lymphomas instead of mammary carcinomas. We show here that NBP binds to a 22-bp sequence containing an imperfect inverted repeat in the promoter-proximal NRE. Previous data showed that a mutation (p924) within the inverted repeat elevated basal transcription from the MMTV promoter and destabilized the binding of NBP, but not UBP, to the proximal NRE. By using conventional and affinity methods to purify NBP from rat thymic nuclear extracts, we obtained a single major protein of 115 kDa that was identified by protease digestion and partial sequencing analysis as the nuclear matrix-binding protein special AT-rich sequence-binding protein 1 (SATB1). Antibody ablation, distamycin inhibition of binding, renaturation and competition experiments, and tissue distribution data all confirmed that the NBP complex contained SATB1. Similar types of experiments were used to show that the UBP complex contained the homeodomain protein Cux/CDP that binds the MAR of the intronic heavy-chain immunoglobulin enhancer. By using the p924 mutation within the MMTV LTR upstream of the chloramphenicol acetyltransferase gene, we generated two strains of transgenic mice that had a dramatic elevation of reporter gene expression in lymphoid tissues compared with reporter gene expression in mice expressing wild-type LTR constructs. Thus, the 924 mutation in the SATB1-binding site dramatically elevated MMTV transcription in lymphoid tissues. These results and the ability of the proximal NRE in the MMTV LTR to bind to the nuclear matrix clearly demonstrate the role of MAR-binding proteins in tissue-specific gene regulation and in MMTV-induced oncogenesis.

Amino Acid Sequence↗