Biomedical subjects

S Chen

Publications and source records attributed to S Chen.

At least 361 records · Page 20Linked to original sources

PubMed2000

TIA-1 is a translational silencer that selectively regulates the expression of TNF-alpha.

TIA-1 and TIAR are related proteins that bind to an AU-rich element (ARE) in the 3' untranslated region of tumor necrosis factor alpha (TNF-alpha) transcripts. To determine the functional significance of this interaction, we used homologous recombination to produce mutant mice lacking TIA-1. Although lipopolysaccharide (LPS)-stimulated macrophages derived from wild-type and TIA-1(-/-) mice express similar amounts of TNF-alpha transcripts, macrophages lacking TIA-1 produce significantly more TNF-alpha protein than wild-type controls. The half-life of TNF-alpha transcripts is similar in wild-type and TIA-1(-/-) macrophages, indicating that TIA-1 does not regulate transcript stability. Rather, the absence of TIA-1 significantly increases the proportion of TNF-alpha transcripts that associate with polysomes, suggesting that TIA-1 normally functions as a translational silencer. TIA-1 does not appear to regulate the production of interleukin 1 beta, granulocyte-macrophage colony-stimulating factor or interferon gamma, indicating that its effects are, at least partially, transcript specific. Mice lacking TIA-1 are hypersensitive to the toxic effects of LPS, indicating that this translational control pathway may regulate the organismal response to microbial stress.

3' Untranslated Regions↗

PubMed2000

Bioactivation of 5-(aziridin-1-yl)-2,4-dinitrobenzamide (CB 1954) by human NAD(P)H quinone oxidoreductase 2: a novel co-substrate-mediated antitumor prodrug therapy.

A novel prodrug activation system, endogenous in human tumor cells, is described. A latent enzyme-prodrug system is switched on by a simple synthetic, small molecule co-substrate. This ternary system is inactive if any one of the components is absent. CB 1954 [5-(aziridin-1-yl)-2,4-dinitrobenzamide] is an antitumor prodrug that is activated in certain rat tumors via its 4-hydroxylamine derivative to a potent bifunctional alkylating agent. However, human tumor cells are resistant to CB 1954 because they are unable to catalyze this bioactivation efficiently. A human enzyme has been discovered that can activate CB 1954, and it has been shown to be commonly present in human tumor cells. The enzyme is NQO2 [NAD(P)H quinone oxidoreductase 2], but its activity is normally latent, and a nonbiogenic co-substrate such as NRH [nicotinamide riboside (reduced)] is required for enzymatic activity. There is a very large (100-3000-fold) increase in CB 1954 cytotoxicity toward either NQO2-transfected rodent or nontransfected human tumor cell lines in the presence of NRH. Other reduced pyridinium compounds can also act as co-substrates for NQO2. Thus, the simplest quaternary salt of nicotinamide, 1-methyl-3-carboxamidopyridinium iodide, was a co-substrate for NQO2 when reduced to the corresponding 1,4-dihydropyridine derivative. Increased chain length and/or alkyl load at the 1-position of the dihydropyridine ring improved specific activity, and compounds more active than NRH were found. However, little activity was seen with either the 1-benzyl or 1-(2-phenylethyl) derivatives. A negatively charged substituent at the 3-position of the reduced pyridine ring also negated the ability of these compounds to act as cosubstrates for NQO2. In particular, 1-carbamoylmethyl-3-carbamoyl-1,4dihydropyridine was shown to be a co-substrate for NQO2 with greater stability than NRH, with the ability to enter cells and potentiate the cytotoxicity of CB 1954. Furthermore, this agent is synthetically accessible and suitable for further pharmaceutical development. NQO2 activity appears to be related to expression of NQO1 (DT-diaphorase), an enzyme that is known to have a favorable distribution toward certain human cancers. NQO2 is a novel target for prodrug therapy and has a unique activation mechanism that relies on a synthetic co-substrate to activate an apparently latent enzyme. Our findings may reopen the use of CB 1954 for the direct therapy of human malignant disease.

Animals↗

PubMed2000

Characterization of glucosinolate uptake by leaf protoplasts of Brassica napus.

The uptake of radiolabeled p-hydroxybenzylglucosinolate (p-OHBG) by protoplasts isolated from leaves of Brassica napus was detected using silicone oil filtration technique. The uptake was pH-dependent with higher uptake rates at acidic pH. Imposition of a pH gradient (internal alkaline) across the plasma membrane resulted in a rapid uptake of p-OHBG, which was inhibited in the presence of carbonyl cyanide m-chlorophenylhydrazone, indicating that the uptake is dependent on a proton motive force. Dissipation of the internal positive membrane potential generated a small influx as compared with that seen for pH gradient (DeltapH). Kinetic studies demonstrated the presence of two uptake systems, a saturable and a linear component. The saturable kinetics indicated carrier-mediated translocation with a K(m) of 1.0 mm and a V(max) of 28.7 nmol/microl/h. The linear component had very low substrate affinity. The carrier-mediated transport had a temperature coefficient (Q(10)) of 1.8 +/- 0.2 in the temperature range from 4-30 degrees C. The uptake was against a concentration gradient and was sensitive to protonophores, uncouplers, H(+)-ATPase inhibitors, and the sulfhydryl group modifier p-chloromercuriphenylsulfonic acid. The carrier-mediated uptake system had high specificity for glucosinolates because glucosinolate degradation products, amino acids, sugars, or glutathione conjugates did not compete for p-OHBG uptake. Glucosinolates with different side chains were equally good competitors of p-OHBG uptake, which indicates that the uptake system has low specificity for the glucosinolate side chains. Our data provide the first evidence of an active transport of glucosinolates by a proton-coupled symporter in the plasma membrane of rape leaves.

Brassica↗

PubMed2000

12-O-tetradecanoylphorbol-13-acetate (TPA)-induced c-Jun N-terminal kinase (JNK) phosphatase renders immortalized or transformed epithelial cells refractory to TPA-inducible JNK activity.

c-Jun N-terminal kinase (JNK) regulates gene expression in response to various extracellular stimuli. JNK can be activated by the tumor promoting agent, 12-O-tetradecanoylphorbol-13-acetate (TPA) in normal human oral keratinocytes but not in human keratinocytes that have been immortalized (HOK-16B and HaCaT) or transformed (HOK-16B-Bap-T) nor in a cervical carcinoma cell line (HeLa). The refractory JNK activation response to TPA is not due a defect in the JNK pathway, because JNK can be activated by other stimuli, e.g. UV irradiation and an alkylating agent N-methyl-N'-nitrosoguanidine in these immortalized or transformed cells. More importantly, the refractory JNK and JNKK activation response to TPA can be restored by treatment of the cells with a combination of TPA and a protein-tyrosine phosphatase inhibitor, sodium orthovanadate. Furthermore, pretreatment of cells with TPA partially inhibited UV- or N-methyl-N'-nitrosoguanidine-induced JNK activity. These results suggest that a TPA-inducible, orthovanadate-sensitive protein-tyrosine phosphatase may specifically down-regulate JNK signaling pathway in these immortalized/transformed epithelial cells. In contrast, ERK and p38/Mpk2 are not regulated by this TPA-induced phosphatase. This putative protein-tyrosine phosphatase appears to be JNK pathway-specific.

Amino Acid Sequence↗

PubMed2000

Two-body B meson decays to eta and eta('): observation of B --> eta K*.

In a sample of 19 x 10(6) produced B mesons, we have observed the decays B-->eta K(*) and improved our previous measurements of B-->eta'K. The branching fractions we measure for these decay modes are B(B+-->eta K(*+)) = (26.4(+9.6)(-8.2)+/-3.3)x10(-6), B(B(0)-->eta K(*0)) = (13.8(+5.5)(-4.6)+/-1.6)x10(-6), B(B(+)-->eta'K(+) = (80(+10)(-9)+/-7)x10(-6), and B(B(0)-->eta'K0) = (89(+18)(-16)+/-9)x10(-6). We have searched with comparable sensitivity for related decays and report upper limits for these branching fractions.

Journal Article↗

PubMed2000

Measurement of charge asymmetries in charmless hadronic B meson decays.

We search for CP-violating charge asymmetries (alpha(CP)) in the B meson decays to K(+/-)pi(-/+), K(+/-)pi(0), K(0)(S)pi(+/-), K(+/-)eta('), and omega pi(+/-). Using 9.66 million upsilon(4S) decays collected with the CLEO detector, the statistical precision on alpha(CP) is in the range of +/-0.12 to +/-0.25 depending on decay mode. While CP-violating asymmetries of up to +/-0.5 are possible within the standard model, the measured asymmetries are consistent with zero in all five decay modes studied.

Journal Article↗

PubMed2000

Molecular and functional heterogeneity of hyperpolarization-activated pacemaker channels in the mouse CNS.

The hyperpolarization-activated cation current (termed I(h), I(q), or I(f)) was recently shown to be encoded by a new family of genes, named HCN for hyperpolarization-activated cyclic nucleotide-sensitive cation nonselective. When expressed in heterologous cells, each HCN isoform generates channels with distinct activation kinetics, mirroring the range of biophysical properties of native I(h) currents recorded in different classes of neurons. To determine whether the functional diversity of I(h) currents is attributable to different patterns of HCN gene expression, we determined the mRNA distribution across different regions of the mouse CNS of the three mouse HCN genes that are prominently expressed there (mHCN1, 2 and 4). We observe distinct patterns of distribution for each of the three genes. Whereas mHCN2 shows a widespread expression throughout the CNS, the expression of mHCN1 and mHCN4 is more limited, and generally complementary. mHCN1 is primarily expressed within neurons of the neocortex, hippocampus, and cerebellar cortex, but also in selected nuclei of the brainstem. mHCN4 is most highly expressed within neurons of the medial habenula, thalamus, and olfactory bulb, but also in distinct neuronal populations of the basal ganglia. Based on a comparison of mRNA expression with an electrophysiological characterization of native I(h) currents in hippocampal and thalamic neurons, our data support the idea that the functional heterogeneity of I(h) channels is attributable, in part, to differential isoform expression. Moreover, in some neurons, specific functional roles can be proposed for I(h) channels with defined subunit composition.

Animals↗

PubMed2000

Long-term prevention of renal insufficiency, excess matrix gene expression, and glomerular mesangial matrix expansion by treatment with monoclonal antitransforming growth factor-beta antibody in db/db diabetic mice.

Emerging evidence suggests that transforming growth factor-beta (TGF-beta) is an important mediator of diabetic nephropathy. We showed previously that short-term treatment with a neutralizing monoclonal anti-TGF-beta antibody (alphaT) in streptozotocin-diabetic mice prevents early changes of renal hypertrophy and increased matrix mRNA. To establish that overactivity of the renal TGF-beta system mediates the functional and structural changes of the more advanced stages of nephropathy, we tested whether chronic administration of alphaT prevents renal insufficiency and glomerulosclerosis in the db/db mouse, a model of type 2 diabetes that develops overt nephropathy. Diabetic db/db mice and nondiabetic db/m littermates were treated intraperitoneally with alphaT or control IgG, 300 microgram three times per week for 8 wk. Treatment with alphaT, but not with IgG, significantly decreased the plasma TGF-beta1 concentration without decreasing the plasma glucose concentration. The IgG-treated db/db mice developed albuminuria, renal insufficiency, and glomerular mesangial matrix expansion associated with increased renal mRNAs encoding alpha1(IV) collagen and fibronectin. On the other hand, treatment with alphaT completely prevented the increase in plasma creatinine concentration, the decrease in urinary creatinine clearance, and the expansion of mesangial matrix in db/db mice. The increase in renal matrix mRNAs was substantially attenuated, but the excretion of urinary albumin factored for creatinine clearance was not significantly affected by alphaT treatment. We conclude that chronic inhibition of the biologic actions of TGF-beta with a neutralizing monoclonal antibody in db/db mice prevents the glomerulosclerosis and renal insufficiency resulting from type 2 diabetes.

Animals↗

PubMed2000

Ion-induced interfacial dynamics of phospholipid monolayers.

Ion-induced interfacial dynamics of phospholipid monolayers were studied by various electrochemical techniques. The lipid monolayers were constructed by using the mercapto derivatives of natural lipids that were self-assembled directly onto gold electrode surfaces in a tails-down fashion. The supported lipid assemblies appeared to act as rather effective electron-tunneling barriers with K3Fe(CN)6 as the redox probe, despite a relatively low surface coverage and/or a disordered surface structure. Upon the stimulation by alkaline-earth ions, the lipid layers appeared to undergo surface reorganization, exposing part of the electrode surface which resulted in the formation of microscopic mass-transfer lipid channels. The dimensions and/or the number of these channels increased with increasing ion concentrations, and this ion-gate effect appeared to be quite selective, with the most pronounced effects observed among the series of alkaline-earth ions with Ca2+.

Electrochemistry↗

PubMed2000

A gender-specific mRNA encoding a cytotoxic ribonuclease contains a 3' UTR of unusual length and structure.

A cDNA (2855 nt) encoding a putative cytotoxic ribonuclease (rapLR1) related to the antitumor protein onconase was cloned from a library derived from the liver of gravid female amphibian Rana pipiens. The cDNA was mainly comprised (83%) of 3' untranslated region (UTR). Secondary structure analysis predicted two unusual folding regions (UFRs) in the RNA 3' UTR. Two of these regions (711-1442 and 1877-2130 nt) contained remarkable, stalk-like, stem-loop structures greater than 38 and 12 standard deviations more stable than by chance, respectively. Secondary structure modeling demonstrated similar structures in the 3' UTRs of other species at low frequencies (0.01-0.3%). The size of the rapLR1 cDNA corresponded to the major hybridizing RNA cross-reactive with a genomic clone encoding onconase (3.6 kb). The transcript was found only in liver mRNA from female frogs. In contrast, immunoreactive onconase protein was detected only in oocytes. Deletion of the 3' UTR facilitated the in vitro translation of the rapLR1 cDNA. Taken together these results suggest that these unusual UFRs may affect mRNA metabolism and/or translation.

3' Untranslated Regions↗

PubMed2000

Observation of phase-matched relativistic harmonic generation

Phase-matched relativistic harmonic generation in plasmas is observed for the first time. Third-harmonic light is detected and discriminated spectrally and angularly from the harmonics generated from competing processes. Its angular pattern is a narrow forward-directed cone, which is consistent with phase matching of a high-order transverse mode in a plasma. The signal level is found to be on the same order of magnitude for a circularly polarized pump pulse as for a linearly polarized pump pulse.

Journal Article↗

PubMed2000

Echocardiographic destruction of albumin microbubbles directs gene delivery to the myocardium.

BACKGROUND: The noninvasive, tissue-specific delivery of therapeutic agents to the heart would be a valuable clinical tool. This study addressed the hypothesis that albumin-coated microbubbles could be used to effectively deliver an adenoviral transgene to rat myocardium by ultrasound-mediated microbubble destruction. METHODS AND RESULTS: Recombinant adenovirus containing beta-galactosidase and driven by a constitutive promoter was attached to the surface of albumin-coated, perfluoropropane-filled microbubbles. These bubbles were infused into the jugular vein of rats with or without simultaneous echocardiography. Additional controls included ultrasound of microbubbles that did not contain virus, virus alone, and virus plus ultrasound. One group underwent ultrasound-mediated destruction of microbubbles followed by adenovirus infusion. Rats were killed after 4 days and examined for beta-galactosidase expression. The hearts of all rats that underwent ultrasound-mediated destruction of microbubbles containing virus showed nuclear staining with 5-bromo-4-chloro-3-indolyl-beta-D-galactopyranoside substrate, indicating expression of the transgene. None of the control animals showed myocardial expression of the beta-galactosidase transgene. By quantitative analysis, beta-galactosidase activity was 10-fold higher in the treated group than in controls (P<0.0001). CONCLUSIONS: Ultrasound-mediated destruction of albumin-coated microbubbles is a promising method for the delivery of bioactive agents to the heart.

Albumins↗

PubMed2000

Kinetic glass transition in a micellar system with short-range attractive interaction

We show that percolation and structural arrest transitions coexist in different regions of the phase diagram of a copolymer-micellar system and relate them to short-range intermicellar attraction. The intermediate scattering function shows a nonergodic transition along a temperature and concentration dependent line. Analyses show a logarithmic time dependence, attributed to a higher-order glass transition singularity predicted by mode-coupling theory, followed by a power law.

Journal Article↗

PubMed2000

CD59 expressed on a tumor cell surface modulates decay-accelerating factor expression and enhances tumor growth in a rat model of human neuroblastoma.

It has been hypothesized that complement inhibitors expressed on the surface of tumor cells prevent effective immune-mediated clearance. Whereas there are in vitro data to support this hypothesis, the species-selective activity of complement inhibitors has been a hindrance to investigating the role of membrane-bound complement inhibitors in rodent models of human cancer. The CD59-positive LAN-1 human neuroblastoma cell line was significantly more sensitive to lysis by rat complement than by human complement, illustrating the species selectivity of endogenously expressed complement inhibitors. Transfection of LAN-1 cells with rat CD59, an inhibitor of the terminal cytolytic membrane attack complex, effectively protected the cells from lysis by rat complement in vitro. When LAN-1 cells stably expressing rat CD59 were inoculated into immune-deficient rats, the onset of tumor growth and the rate of tumor growth were significantly enhanced compared with those of control-transfected LAN-1 cells. These data show directly that the expression of a complement inhibitor on a tumor cell promotes tumor growth. Flow cytometric analysis revealed that the endogenous expression of decay-accelerating factor (DAF), an inhibitor of complement activation, was up-regulated on the surface of cells after in vivo growth. Of further interest, higher levels of DAF were present on CD59-transfected cells than on control-transfected cells derived from tumors. Increased DAF expression correlated with decreased complement deposition on the tumor cell surface. These results show that expression of complement inhibitors on a tumor cell has functional consequences with regard to complement deposition in vivo and indicate that CD59 can indirectly effect complement activation and C3 deposition in vivo via a link between CD59 and DAF expression.

Animals↗

PubMed2000

Coactivator-vitamin D receptor interactions mediate inhibition of the atrial natriuretic peptide promoter.

We have discovered a role for coactivators binding to the AF-2 surface of the vitamin D receptor (VDR) in its negative effects on gene transcription. We tested nine amino acid residues (Ser(235), Ile(242), Lys(246), Asp(253), Ile(260), Leu(263), Leu(417), Leu(419), and Glu(420)) in human VDR which, based on homology to the human thyroid hormone receptor, would be predicted to lie in or near the coactivator-binding site. Mutation of six of these residues in VDR resulted in loss of both the activation (assessed with a transfected DR3 TK luciferase reporter) and inhibition (assessed with an hANPCAT reporter) functions of the receptor when tested in cultured neonatal rat atrial myocytes and HeLa cells. Collectively, these mutations also suppressed association of VDR with the coactivators GRIP1 and steroid receptor coactivator 1 in vitro but had little or no effect on ligand binding, heterodimerization with the retinoid X receptor, or association with a VDR-specific DNA recognition element. Co-transfection with GRIP1 or steroid receptor coactivator 1 amplified both the positive and negative responses to wild type VDR but had little or no effect on the functionally impaired mutants described above. The interaction between VDR and GRIP1 proved to be heavily dependent upon the integrity of nuclear box III in the latter protein. Mutations in this region of GRIP1 impaired its ability to associate with VDR in vitro and to amplify VDR activity in intact cells. These studies establish a role for coactivators recruited to the same receptor surface in both the activating and inhibitory activity of the liganded receptor.

Amino Acid Sequence↗

PubMed2000

Characterization of the human EPLIN (Epithelial Protein Lost in Neoplasm) gene reveals distinct promoters for the two EPLIN isoforms.

EPLIN is a novel LIM domain protein that co-localizes to the actin stress fibers and focal adhesion plaques. We previously have demonstrated that two isoforms, the 600aa EPLIN-alpha and the 759aa EPLIN-beta, are generated from a single gene. In the majority of human breast and prostate cancer cell lines, the expression of EPLIN-alpha is significantly reduced, while the expression of EPLIN-beta is either up-regulated or unchanged. To understand the basis of this differential regulation, we have determined the organization of the human EPLIN gene. The human EPLIN100kb and consists of 11 exons. The EPLIN-beta mRNA requires all 11 exons, while the EPLIN-alpha mRNA requires Exons 4-11. The transcriptional start sites of EPLIN-alpha were mapped within the third intron by 5' RACE and S1 nuclease protection. Similarly, the 5' ends of EPLIN-beta were mapped upstream of Exon 1. The DNA sequences flanking the EPLIN-alpha or EPLIN-beta transcriptional start sites were capable of stimulating the expression of promoter reporter constructs. Interestingly, the endogenous transcription of EPLIN-alpha, but not EPLIN-beta, could be stimulated by serum, indicating that the expression of two EPLIN isoforms can be independently regulated. A consensus serum response element was present within 100bp upstream of the transcriptional start sites of EPLIN-alpha. The activity of 0.7kb EPLIN-alpha promoter reporter construct could be enhanced by activated RhoA, indicating that this serum response element is functional.

3T3 Cells↗

PubMed2000

Two cases of AML (M2) with a t(8;19)(q22;q13): a new cytogenetic variant.

"Simple" variants of the t(8;21) translocation involving chromosome 8 and a chromosome other than number 21 are rare. To our knowledge, only t(3;8)(q29;q22), t(8;11)(q22;q13), t(8;16)(q22;q24), t(8;20)(q22;p13), and t(8;22) have been reported in the literature. This paper describes for the first time two patients with acute myelogenous leukemia with a consistent t(8;19)(q22;q13) translocation. Their myelograms were compatible with the FAB-M2 subtype. The blasts from case 2 expressed CD34, CD33, CD13, and CD19. Karyotype analyses were performed on bone marrow cells using R- and G-banding at presentation. A t(8;19)(q22;q13) translocation was found in 28/30 metaphases for case 1 and in 23/25 metaphases for case 2. The latter case also had a deletion of chromosome 9, del(9)(q12q22) as an additional abnormality. Reverse transcriptase-polymerase chain reaction study revealed no AML1/ETO fusion transcript in case 2. Dual-color fluorescence in situ hybridization (FISH) assay using two probes (BAC92 and YAC412A4) convincingly demonstrated that the chromosomal material from 8q was translocated onto 19q rather than 19p in case 2. Thus, we consider t(8;19)(q22;q13) a true "simple" variant of t(8;21), and assume that a fusion gene resulting from the t(8;19) may contain the ETO gene located at 8q22 and an unknown partner gene from 19q13, which probably is a new transcription factor, whose molecular entity warrants further study.

Adolescent↗

PubMed2000

Activation of metabotropic GABAB receptors inhibited glutamate responses in spiral ganglion neurons of mice.

The lateral olivocochlear efferent (LOC) fibers form axodendritic synapses with auditory nerve dendrites synapsing on inner hair cells to affect postsynaptic responses GABA is one of the primary transmitters used by the LOC efferent. However, the molecular nature and developmental expression of the GABA receptors in spiral ganglion (SG) neurons are poorly understood. We have identified the GABAB receptors in SG neurons of mice by pharmacological criteria and polymerase chain reaction (PCR) detection. Applications of GABA or baclofen increased intracellular Ca2+ concentrations and inhibited glutamate responses. The responses were blocked by saclofen, but not by bicuculline. Relative-quantitative PCR showed that GABAB receptors were expressed prenatally, and their levels did not change significantly during the maturation of SG neurons.

Age Factors↗