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Biomedical subjects

X Chen

Publications and source records attributed to X Chen.

At least 181 records · Page 10Linked to original sources
PubMed2001

[Expression of matrix metalloproteinases in metastatic lesions of cutaneous squamous cell carcinoma].

OBJECTIVE: To investigate the expression of matrix metalloproteinases (MMPs) and its correlation with basigin/CD147 expression in metastatic lesions of cutaneous Sequamous cell carcinoma (SCC). METHODS: Expressions of MMPs and basigin/CD147 were examined by DAB and ALP immunohistochemical staining in 14 metastatic SSCs, and immunoblot analysis was used to observe the basigin/CD147 expression in metastatic samples. RESULTS: Normal skin and lymph nodes were basically negative for MMPs, but expressions of MMP-1, MMP-2, MMP-3 and MTl-MMP were increased in both tumor cells and stromal cells in metastatic SCC. Strongly positive or positive staining was observed in 4 or 8 of metastatic SCCs for basigin/CD147 in tumor cells respectively. Significant correlations were found between basigin/CD147 expression in tumor cells and MMP-1, MMP-2, MMP-3, MTl-MMP expression in surrounding stromal cells (p-values: 0.012, 0.024, 0.047 and 0.026, respectively). Immunoblot analysis revealed that basigin/CD147 expression increased in metastatic SCC. CONCLUSION: These results suggest that MMPs produced by both tumor cells and stromal cells play a role in metastasis of cutaneous SCC, and increased MMPs in stromal cells might be induced by basigin/CD147 expressed in tumor cells.

Antigens, CD↗
PubMed2001

[Effect of dextran combination with flurosemide on nephrotic syndrome].

OBJECTIVE: To compare the diuretic effect of coadministration of dextran and flurosemide with that of coadministration of Albumin and flurosemide on primary nephrotic syndrome. METHODS: In a double-blind placebo-controlled study, eighteen primary nephrotic syndrome patients on standard sodium chloride intake, random by divided into three groups and received by intravenous administration for 60 minutes for three days (a) FU (1 mg.kg-1) combination with a sham infusion, (b) FU (1 mg.kg-1) combination with 50 ml of 20% solution of Albumin, or (c) FU (1 mg/kg) combination with 250 ml dextran 40. Urinary volume, sodium and plasma atrial nartiuretic peptide concentration were assessed. RESULTS: The results showed that administration of FU alone increased mean cumulative urinary sodium and volume excretion as compared with the administration of sham infusion without treatment (P < 0.05). The administration of FU and albumin or FU and dextran 40 caused an even more marked increase of urinary sodium and volume excretion (P < 0.01), as compared with the administration of sham infusion without treatment. Plasma ANP increased significantly on both albumin infusion days and dextran 40 infusion days (P < 0.05). CONCLUSION: Coadministration of albumin and FU or dextran 40 and FU can increase the urinary volume and urinary Na and ANP significantly, dextran 40 can take the place of albumin because there was no difference between the administration of FU and albumin and FU and dextran in UV, Una and ANP.

Adolescent↗
PubMed2001

Conformational heterogeneity in the C-terminal zinc fingers of human MTF-1: an NMR and zinc-binding study.

The human metalloregulatory transcription factor, metal-response element (MRE)-binding transcription factor-1 (MTF-1), contains six TFIIIA-type Cys(2)-His(2) motifs, each of which was projected to form well-structured betabetaalpha domains upon Zn(II) binding. In this report, the structure and backbone dynamics of a fragment containing the unusual C-terminal fingers F4-F6 has been investigated. (15)N heteronuclear single quantum coherence (HSQC) spectra of uniformly (15)N-labeled hMTF-zf46 show that Zn(II) induces the folding of hMTF-zf46. Analysis of the secondary structure of Zn(3) hMTF-zf46 determined by (13)Calpha chemical shift indexing and the magnitude of (3)J(Halpha-HN) clearly reveal that zinc fingers F4 and F6 adopt typical betabetaalpha structures. An analysis of the heteronuclear backbone (15)N relaxation dynamics behavior is consistent with this picture and further reveals independent tumbling of the finger domains in solution. Titration of apo-MTF-zf46 with Zn(II) reveals that the F4 domain binds Zn(II) significantly more tightly than do the other two finger domains. In contrast to fingers F4 and F6, the betabetaalpha fold of finger F5 is unstable and only partially populated at substoichiometric Zn(II); a slight molar excess of zinc results in severe conformational exchange broadening of all F5 NH cross-peaks. Finally, although Cd(II) binds to apo-hMTF-zf46 as revealed by intense S(-)-->Cd(II) absorption, a non-native structure results; addition of stoichiometric Zn(II) to the Cd(II) complex results in quantitative refolding of the betabetaalpha structure in F4 and F6. The functional implications of these results are discussed.

Amino Acid Sequence↗
PubMed2001

Parallel solid-phase synthesis of nucleoside phosphoramidate libraries.

Combinatorial chemistry is playing an increasingly prominent role in the process of drug discovery. A nucleic acid-based (NAB) scaffold can be engineered to create functional group and topological diversity in a library. Described herein is the parallel solid-phase synthesis of combinatorial libraries of nucleoside phosphoramidates, and the first evaluation of antiviral activity against hepatitis B virus (HBV).

Amides↗
PubMed2001

Profiling of isovalertatin family aminooligosaccharides extracted from the culture of Streptomyces luteogriseus by using liquid chromatography/electrospray ionization mass spectrometry.

A rapid and novel procedure using the liquid chromatography coupled to an electrospray ionization ion trap mass spectrometry technique was applied for the profiling of isovalertatin-family aminooligosaccharides in the extract from the culture filtrate of Streptomyces luteogriseus. The aminooligosaccharides were separated on a C-8 reversed-phase column with an acetonitrile-alkaline water gradient. The desired homologues were detected using the multiple reaction monitoring mode, and the chemical structures were confirmed by analyzing the characteristic fragment ions in their collision-induced dissociation spectra. This facile procedure led to the identification of all the five known aminooligosaccharides, isovalertatins M03, M13, M23, D03, and D23, in addition to the characterization of at least 41 novel isovalertatins, the molecular weights of which ranged from 729 to 2,793. This kind of assay should be intended as a simple and convenient way for the high-throughput analysis of screening aminooligosaccharides and potentially other structural families of natural products.

Amines↗
PubMed2001

Identification of dopamine responsive mRNAs in glial cells by suppression subtractive hybridization.

Recent studies have established that glial cells are important targets of the neurotransmitter dopamine (DA), but the regulatory effects of DA on glial cells have not been extensively studied. In the present study, we have investigated the influence of DA on gene transcription in glial cells. Two-directional (forward and backward) suppression subtraction hybridization (SSH) was performed on astrocytes cultured from rat cerebral tissues in standard media or in culture media treated with DA. PCR-select differential screening was used to further verify the differentially expressed cDNA clones, positive clones were sequenced, and the mRNAs were re-examined on Northern blots. Fourteen sequences were identified of which eleven are homologous to known genes, three are homologous to expressed sequence tags (ESTs). Three novel full-length cDNAs were isolated using the EST fragments as probes to screen a cDNA library constructed from human brain. Analysis of these sequences suggested that complex intracellular signaling pathways, involving crosstalk with growth factor pathways, steroid hormone pathways, and an interferon-regulated 2-5 A pathway, are responsive to DA in astrocytes. The responsive proteins downstream from the signaling pathways were found to fall into at least three groups, including a series of metabolic enzymes, stress proteins, transfer proteins, etc. In addition, several of them have established their relationships with specific neurodegenerative diseases, showing that there is overlap in the pathogenic mechanisms of different diseases. Our results have provided a foundation for better understanding of the molecular basis of glial cell functions in dopaminergic transmission and an approach to find possible medication for the related disorders.

Animals↗
PubMed2001

Regulation of CSF1 promoter by the SWI/SNF-like BAF complex.

The mammalian BAF complex regulates gene expression by modifying chromatin structure. In this report, we identify 80 genes activated and 2 genes repressed by the BAF complex in SW-13 cells. We find that prior binding of NFI/CTF to the NFI/CTF binding site in CSF1 promoter is required for the recruitment of the BAF complex and the BAF-dependent activation of the promoter. Furthermore, the activation of the CSF1 promoter requires Z-DNA-forming sequences that are converted to Z-DNA structure upon activation by the BAF complex. The BAF complex facilitates Z-DNA formation in a nucleosomal template in vitro. We propose a model in which the BAF complex promotes Z-DNA formation which, in turn, stabilizes the open chromatin structure at the CSF1 promoter.

Base Sequence↗
PubMed2001

Measurement of the rate of nu(e) + d --> p + p + e(-) interactions produced by (8)B solar neutrinos at the Sudbury Neutrino Observatory.

Solar neutrinos from (8)B decay have been detected at the Sudbury Neutrino Observatory via the charged current (CC) reaction on deuterium and the elastic scattering (ES) of electrons. The flux of nu(e)'s is measured by the CC reaction rate to be straight phi(CC)(nu(e)) = 1.75 +/- 0.07(stat)(+0.12)(-0.11)(syst) +/- 0.05(theor) x 10(6) cm(-2) s(-1). Comparison of straight phi(CC)(nu(e)) to the Super-Kamiokande Collaboration's precision value of the flux inferred from the ES reaction yields a 3.3 sigma difference, assuming the systematic uncertainties are normally distributed, providing evidence of an active non- nu(e) component in the solar flux. The total flux of active 8B neutrinos is determined to be 5.44+/-0.99 x 10(6) cm(-2) s(-1).

Journal Article↗
PubMed2001

Pro-survival function of Akt/protein kinase B in prostate cancer cells. Relationship with TRAIL resistance.

Tumor necrosis factor superfamily member TRAIL/Apo-2L has recently been shown to induce apoptosis in transformed and cancer cells. Some prostate cancer cells express constitutively active Akt/protein kinase B due to a complete loss of lipid phosphatase PTEN gene, a negative regulator of phosphatidylinositol 3-kinase pathway. Constitutively active Akt promotes cellular survival and resistance to chemotherapy and radiation. We have recently noticed that some human prostate cancer cells are resistant to TRAIL. We therefore examined the intracellular mechanisms of cellular resistance to TRAIL. The cell lines expressing the highest level of constitutively active Akt were more resistant to undergo apoptosis by TRAIL than those expressing the lowest level. Down-regulation of constitutively active Akt by phosphatidylinositol 3-kinase inhibitors, wortmannin and LY294002, reversed cellular resistance to TRAIL. Treatment of resistant cells with cycloheximide (a protein synthesis inhibitor) rendered cells sensitive to TRAIL. Transfecting dominant negative Akt decreased Akt activity and increased TRAIL-induced apoptosis in cells with high Akt activity. Conversely, transfecting constitutively active Akt into cells with low Akt activity increased Akt activity and attenuated TRAIL-induced apoptosis. Inhibition of TRAIL sensitivity occurs at the level of BID cleavage, as caspase-8 activity was not affected. Enforced expression of anti-apoptotic protein Bcl-2 or Bcl-X(L) inhibited TRAIL-induced mitochondrial dysfunction and apoptosis. We therefore identify Akt as a constitutively active kinase that promotes survival of prostate cancer cells and demonstrate that modulation of Akt activity, by pharmacological or genetic approaches, alters the cellular responsiveness to TRAIL. Thus, TRAIL in combination with agents that down-regulate Akt activity can be used to treat prostate cancer.

Androstadienes↗
PubMed2001

Activation of mitogen-activated protein kinase by membrane-targeted Raf chimeras is independent of raft localization.

Binding of proteins to the plasma membrane can be achieved with various membrane targeting motifs, including combinations of fatty acids, isoprenoids, and basic domains. In this study, we investigate whether attachment of different membrane targeting motifs influences the signaling capacity of membrane-bound signal transduction proteins by directing the proteins to different membrane microdomains. We used c-Raf-1 as a model for a signaling protein that is activated when membrane-bound. Three different membrane targeting motifs from K-Ras, Fyn, and Src proteins were fused to the N or C terminus of Raf-1. The ability of the modified Rafs to initiate MAPK signaling was then investigated. All three modified Raf-1 constructs activated MAPK to nearly equivalent levels. The extent of localization of the Raf-1 constructs to membrane microdomains known as rafts did not correlate with the level of MAPK activation. Moreover, treatment of cells with the raft disrupting drug methyl-beta-cyclodextrin (MbetaCD) caused activation of MAPK to levels equivalent to those achieved with membrane-targeted Raf constructs. The use of pharmacological agents as well as dominant negative mutants revealed that MAPK activation by MbetaCD proceeds via a phosphoinositide 3-kinase-dependent mechanism that is Ras/Raf-independent. We conclude that cholesterol depletion from the plasma membrane by MbetaCD constitutes an alternative pathway for activating MAPK.

Animals↗
PubMed2001

Structure of an RNA hairpin from HRV-14.

The 5' noncoding region of the picornaviral genome begins with a cloverleaf which is required for viral replication, due at least in part to an interaction with the viral RNA polymerase as part of a fusion with the predominant viral protease. The necessary region of the cloverleaf has previously been narrowed to a highly conserved stem-loop. The solution structure of a 14-nucleotide RNA hairpin, which is part of the conserved stem-loop from human rhinovirus isotype 14, is presented here. The secondary structure of the hairpin is identical to predictions: a five base pair stem is bounded by a triloop with sequence UAU. However, the fold of the triloop is novel, with stacking of the second loop base onto the closing base pair of the stem, and deviations from A form geometry are introduced into the stem regions bordering the triloop, particularly on the 3' side. These deviations and the associated triloop structure could help to explain the distinct sequence conservation and mutational analysis data observed for the stem region of the hairpin, as compared to a second sequentially similar stem in the intact stem-loop.

5' Untranslated Regions↗
PubMed2001

p73 cooperates with DNA damage agents to induce apoptosis in MCF7 cells in a p53-dependent manner.

p73, a member of the p53 family, can induce apoptosis in cancer cells. Since p53-mediated apoptosis can be augmented by various cancer chemotherapeutic agents, it has been hypothesized that the status of the endogenous p53 gene in cancer cells is a key determinant in the outcome of cancer therapy. To determine whether p73 can sensitize cancer cells to apoptosis by DNA damage agents, several MCF7 adenocarcinoma cell lines that inducibly express p73 or p53 under a tetracycline-regulated promoter were generated. We found that at relevant physiological levels, p73, but not p53, is capable of sensitizing MCF7 cells to apoptosis induced by chemotherapeutic agents. In addition, we found that p73 can cooperate with the DNA damaging agent camptothecin to activate the initiator caspase 2. Furthermore, we found that p73 can cooperate with DNA damaging agents or p53 to induce some p53 target genes and activate their promoters. In contrast, in MCF7E6 cells that ectopically express the human papillomavirus E6 oncogene and are functionally p53-null, the ability of p73 to sensitize cells to apoptosis is abrogated. Taken together, these results suggest that a functional interaction between p53 and p73 in MCF7 cells leads to enhanced induction of apoptosis.

Adenocarcinoma↗
PubMed2001

Low concentration N-methyl-N'-nitro-N-nitrosoguanidine activates DNA polymerase-beta expression via cyclic-AMP-protein kinase A-cAMP response element binding protein pathway.

Ultraviolet light (UV), ionizing-radiation or alkylating agents are known as carcinogens, mostly because of their ability to damage DNA directly. However, they may also play a diverse role in activating the signal pathways and altering the gene expression. We have shown previously that N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) of 0.2 microM can increase the transcription of DNA polymerase-beta gene, which has a cyclic AMP response element (CRE) motif in its promoter. Using the CRE report vector, we show here, such treatment can stimulate the CRE-driven gene expression by approximately 1.5-fold compared with control. Consistent with it, the proportion of ser-133 phosphorylated CRE binding protein (CREB), the related transcription factor was 2.08-fold higher versus control in vero cells after 60 min of MNNG treatment. Although CREB has many putative kinases for its phosphorylation, such as p38 mitogen-activated protein kinase (p38 MAPK), Ca(2+)/calmodulin-dependent protein kinase Pi (CaMK Pi) and protein kinase C (PKC), we found the protein kinase A (PKA) was activated and its activation peaked when cells were treated for 60 min (with arbitrary activity unit of 11.03+/-2.80 and 0.86+/-0.43 in treatment and control, respectively), this phasic character was similar to that of the CREB phosphorylation. We also determined the intracellular cyclic AMP (cAMP) levels and it was found that the cAMP concentration was elevated after 60 min treatment (1.53-fold higher). However, to our surprise, we did not find any accompanying cAMP elevation in cells treated by MNNG for 30 min, in which PKA was activated significantly. These findings, together with other observations, suggest that cAMP-PKA-CREB signaling pathway mediates the low concentration MNNG induced pol-beta expression. In addition to elevated cAMP, there might exist a cAMP-independent PKA activation manner in this course.

Animals↗
PubMed2001

Rapid characterization of DNA oligomers and genotyping of single nucleotide polymorphism using nucleotide-specific mass tags.

Using currently available MS-based methods, accurate mass measurements are essential for the characterization of DNA oligomers. However, there is a lack of specificity in mass peaks when the characterization of individual DNA species in a mass spectrum is dependent solely upon the mass-to-charge ratio (m/z). Here, we utilize nucleotide-specific tagging with stable isotopes to provide internal signatures that quantitatively display the nucleotide content of oligomer peaks in MS spectra. The characteristic mass-split patterns induced by the partially (13)C/(15)N-enriched dNTPs in DNA oligomers indicate the number of labeled precursors and in turn the base substitution in each mass peak, and provide for efficient SNP detection. Signals in mass spectra not only reflect the masses of particular DNA oligomers, but also their specific composition of particular nucleotides. The measurements of mass tags are relative in the mass-split pattern and, hence, the accuracy of the determination of nucleotide substitution is indirectly increased. For high sample throughput, (13)C/(15)N-labeled sequences of interest have been generated, excised in solution and purified for MS analysis in a single-tube format. This method can substantially improve the specificity, accuracy and efficiency of mass spectrometry in the characterization of DNA oligomers and genetic variations.

Base Composition↗
PubMed2001

Possible mechanism of hypothermia induced by intracerebroventricular injection of orphanin FQ/nociceptin.

Orphanin/nociceptin (OFQ/N), a 17-amino-acid peptide, is an endogenous peptide, the receptor for which is similar to mu-, delta- and kappa-opioid receptors ( approximately 65% homology). Reports indicate that OFQ/N can block the antinociception induced by mu-, delta- and kappa-opioid agonists in the rat and in the mouse, indicating that there is a functional interaction between opioid receptors and OFQ/N receptors in the nervous system. It is well known that activation of the mu- and kappa-opioid receptors results in hyperthermia and hypothermia, respectively, in Sprague-Dawley rats. The present studies were designed to examine effects of OFQ/N on body temperature (Tb) and explore whether the mechanism of T(b) change induced by OFQ/N involved the opioid system. The results show that (1) i.c.v. injection of a high dose of OFQ/N (9-18 micro g) produces hypothermia in adult rats; (2) OFQ/N (1.8 micro g, i.c.v., t=+30 s after morphine) can decrease morphine-induced hyperthermia; (3) neither the opioid receptor antagonist, naloxone (10 mg/kg, s.c., t=-15 s before OFQ/N) nor the kappa-opioid receptor antagonist nor-BNI (1 micro g/5 microl, i.c.v., t=-30 s before OFQ/N) reduces the hypothermia induced by i.c.v. injection of OFQ/N at dose of 18 micro g (P>0.05); (4) 60 micro g/5 microl AS oligo (i.c.v. treatment on days 1, 3 and 5) against OFQ/N receptors significantly reduces the hypothermia induced by i.c.v. injection of 9 micro g OFQ/N (P<0.01). These results suggest that the hypothermia induced by i.c.v. injection of a high dose of OFQ/N (9 or 18 micro g) is mediated, at least partially, by its own receptor, independent or downstream of opioid receptors in the rat brain and that OFQ/N probably acts as a physiological antagonist to reduce morphine-induced hyperthermia.

Animals↗
PubMed2001

The absorption edge of protein-bound mercury and a double-edge strategy for HgMAD data acquisition.

The L(III) absorption edge of protein-bound mercury (Hg) has been experimentally determined using X-ray data collection from a crystal. This absorption edge is 12 291 eV, 4 eV higher than the theoretical value of elemental Hg. Considering the possible shift of the Hg absorption edge with the chemical environment in different protein crystals, a double-edge strategy for multiwavelength anomalous diffraction (MAD) data collection has been developed. The approach provides a convenient way to optimize the dispersive signal between a remote wavelength and two edge wavelengths separated from each other by 4 eV. The dispersive signals derived from both edges are used, along with anomalous signals, in MAD phasing and phase refinement. This approach has been used in the crystal structure determination of three proteins containing one Hg atom per 186-196 amino-acid residues at 2.0, 2.6 and 2.7 A resolution. A set of four wavelengths is recommended for HgMAD data acquisition: 1.0087 A (12 291 eV, edge1), 1.0084 A (12 295 eV, edge2), 1.0064 A (12 320 eV, peak) and 0.9918 A (12 500 eV, remote). Although it is no longer necessary to determine the L(III) absorption edge of protein-bound Hg experimentally, an initial fluorescence scan on the crystal for data collection is still necessary to verify the existence of Hg in the crystal.

Crystallography, X-Ray↗
PubMed2001

Effects of low intensity radiofrequency electromagnetic fields on electrical activity in rat hippocampal slices.

Slices of rat hippocampus were exposed to 700 MHz continuous wave radiofrequency (RF) fields (25.2-71.0 V m(-1), 5-15 min exposure) in a stripline waveguide. At low field intensities, the predominant effect on the electrically evoked field potential in CA1 was a potentiation of the amplitude of the population spike by up to 20%, but higher intensity fields could produce either increases or decreases of up to 120 and 80%, respectively, in the amplitude of the population spike. To eliminate the possibility of RF-induced artefacts due to the metal stimulating electrode, the effect of RF exposure on spontaneous epileptiform activity induced in CA3 by 4-aminopyridine (50-100 microM) was investigated. Exposure to RF fields (50.0 V m(-1)) reduced or abolished epileptiform bursting in 36% of slices tested. The maximum field intensity used in these experiments, 71.0 V m(-1), was calculated to produce a specific absorption rate (SAR) of between 0.0016 and 0.0044 W kg(-1) in the slices. Measurements with a Luxtron fibreoptic probe confirmed that there was no detectable temperature change (+/- 0.1 degrees C) during a 15 min exposure to this field intensity. Furthermore, imposed temperature changes of up to 1 degrees C failed to mimic the effects of RF exposure. These results suggest that low-intensity RF fields can modulate the excitability of hippocampal tissue in vitro in the absence of gross thermal effects. The changes in excitability may be consistent with reported behavioural effects of RF fields.

Action Potentials↗