Biomedical subjects

C H Yang

Publications and source records attributed to C H Yang.

At least 19 recordsLinked to original sources

PubMed1999

Thioureas differentially induce rat hepatic microsomal epoxide hydrolase and rGSTA2 irrespective of their oxygen radical scavenging effect: effects on toxicant-induced liver injury.

Thioureas have been employed as potent hydroxyl radical scavengers and also inhibit production of oxygen free radicals. The in vitro oxygen radical scavenging effect by N,N'-substituted thioureas including dimethylthiourea (DMT), diethylthiourea (DET), tetramethylthiourea (TMT) and diphenylthiourea (DPT) was assessed by the conversion of phi x-174 DNA from supercoiled DNA to the open circular form or to fragmented DNA. Addition of the N,N'-substituted thioureas to the incubation mixture significantly prevented a single strand breakage of phi x-174 DNA induced by autooxidation of benzenetriol. These thioureas were also effective in preventing degradation of phi x-174 DNA induced by autooxidation of benzenetriol in the presence of ferrous iron. In view of the in vitro radical scavenging effect by the thioureas and the role of reactive oxygen species in the induction of phase II detoxifying enzymes, expression of microsomal epoxide hydrolase (mEH) and rGSTA2 in response to these agents was investigated in the rat liver. Rats treated with each of the alkylthioureas exhibited marked increases of mEH and rGSTA2 mRNA levels with TMT being the most effective. DPT an arylthiourea, however, was minimally active in increasing the mRNAs. Time-course studies revealed that DMT, DET and TMT increased the mRNA levels to the greatest extent at 24 h after a single dose of treatment. The levels of mEH and rGSTA2 mRNA were elevated in a dose-dependent manner by the alkylthioureas. Immunoblot analysis showed that the alkylthioureas induced mEH and rGSTA2 proteins in the liver (0.6 mmol/kg per day, 3 days), which was consistent with the increases in the mRNA levels. DMT, DET or TMT enhanced CCl4-induced liver toxicity, as monitored by plasma aminotransferase activity, although each of the agents alone caused only slight increase in the alanine aminotransferase activity. In contrast to the effects of the alkylthioureas, DPT protected the liver against the toxicant-induced injury. All of the thioureas prevented decreases in the hepatic glutathione level by CCl4. Expression of cytochrome P450 2E1 and P450 2B1/2, which are implicated with metabolic activation of CCl4, was assessed after treatment with the thioureas. P450 2E1 and P450 2B1/2 were differentially induced by the alkylthioureas with the expression of P450 2E1 being inversely related with that of P450 2B1/2. These results showed that N,N'-substituted alkylthioureas were capable of inducing mEH and rGSTA2 in the liver with elevation of the mRNAs, that induction of mEH and rGSTA2 by these alkylthioureas might be mediated by production of the reactive oxygens derived from metabolic activation of the agents irrespective of their radical scavenging effect and that the agents rather enhanced toxicant-induced liver injury with the induction of P450 2E1 or P450 2B1/2.

Alanine Transaminase↗

PubMed1999

Genetic interactions of the Arabidopsis flowering time gene FCA, with genes regulating floral initiation.

The genes controlling the timing of the transition from vegetative to reproductive growth are likely candidates for regulators of genes initiating floral development. We have investigated the interaction of one particular gene controlling flowering time, FCA, with the meristem identity-genes TERMINAL FLOWER 1 (TFL1), APETALA 1 (AP1) and LEAFY (LFY) and the floral repression gene EMBRYONIC FLOWER 1 (EMF1). Double mutant combinations were generated and the phenotypes characterized. The influence of strong and intermediate fca mutant alleles on the phenotype conferred by a 35S-LFY transgene was also analysed. The results support a model where FCA function promotes flowering in multiple pathways, one leading to activation of LFY and AP1, and another acting in parallel with LFY and AP1. Only the latter pathway is predicted to be non-functional in the intermediate fca-4 allele. The results are also consistent with AP1 and TFL1 negatively regulating FCA function. Combination of Columbia fca and emf1 mutant alleles confirmed that FCA is required for the early flowering of emf1. EMF1 and FCA are therefore likely to operate in different floral pathways.

Alleles↗

PubMed1999

Inappropriate sexual behaviors in dementia: a preliminary report.

We investigated types of inappropriate sexual behavior (ISB) and patient characteristics in geriatric patients with dementia. The study group consisted of 133 consecutive geropsychiatric demented patients admitted to our ward. All patients underwent standardized diagnostic procedures for dementia, and ISB was assessed by a questionnaire completed by patients' caregivers and records during hospitalization. Patients were then subdivided on the basis of the presence or absence of ISB. Of the 133 demented patients, 20 (15.0%) were reported to demonstrate ISB at home or during hospitalization. Patients with ISB had various types of dementia. There were no significant differences in patients with and without ISB in regard to age, age of onset, gender, educational level, or Mini-Mental State Examination scores. ISB is not unusual in dementia patients and can be found in different types of dementia. Medical care providers need to be trained to discuss sexual issues with caregivers and offer ideas and training to help cope with patients with ISB.

Aged↗

PubMed1999

Power spectral analysis of arterial and central venous pressure signals during graded hemorrhage in anesthetized rats.

Based on simultaneous power spectral analysis of systemic arterial pressure (SAP) and central venous pressure (CVP) signals in rats anesthetized with pentobarbital sodium, we assessed the hypotheses that subtle changes in the SAP spectrum exist during hemorrhagic shock, and that the CVP spectrum is a feasible index for central blood volume during acute graded blood loss. During Stage I hemorrhagic shock seen after reduction in 10% of total blood volume (TBV), there was a significant increase in the power of both the very low frequency (VLF, 0-.25 Hz) and low frequency (LF, .25-.8 Hz) components, along with a moderate decrease in the very high frequency (VHF, 5-9 Hz) component, of SAP signals. Substantial reduction in VLF, LF, and VHF components in the SAP spectrum occurred after a blood loss of 25% of TBV (Stage II), which persisted during Stage III hemorrhagic shock when the withdrawn blood reached 50% of TBV and the mean SAP maintained at 40 mm Hg. The depressed SAP-VLF and SAP-LF components sustained the period of spontaneous recovery and subsequent retransfusion of shed blood, although the power of SAP-VHF component gradually elevated during these two periods. The power of the high-frequency (HF, .8-2.4 Hz) component of SAP signals increased discernibly only during Stage III, became significant on spontaneous recovery, and declined during retransfusion. Although CVP and CVP-VHF component progressively declined, the power of the CVP-HF component manifested a gradual increase that was significantly and reversely correlated with the reduction in TBV. We conclude that differential changes in individual components of the SAP spectrum occur during hemorrhagic shock, and that the CVP-HF component may be a reliable indicator for central blood volume during acute graded blood loss.

Algorithms↗

PubMed1999

Case of sepsis caused by Bifidobacterium longum.

We report a case of sepsis caused by Bifidobacterium longum in a 19-year-old male who had developed high fever, jaundice, and hepatomegaly after acupuncture therapy with small gold needles. Anaerobic, non-spore-forming, gram-positive bacilli were isolated from his blood and finally identified as B. longum. He recovered completely after treatment with ticarcillin and metronidazole. To our knowledge, this is the first report of incidental sepsis caused by B. longum.

Actinomycetales Infections↗

PubMed1999

EGF induces nuclear translocation of STAT2 without tyrosine phosphorylation in intestinal epithelial cells.

Signal transducers and activators of transcription (STATs) are cytoplasmic proteins that bind to activated membrane receptors, undergo ligand-dependent phosphorylation on tyrosine residues, and translocate to the nucleus, where they induce transcription of specific genes in response to a variety of ligands, including cytokines and some growth factors. Using immunocytochemical and biochemical techniques, we investigated the localization and responses of STAT1 and STAT2 to epidermal growth factor (EGF) stimulation in IEC-6 intestinal epithelial cells and HeLa cells. These studies provide the first description of STAT activation and localization in response to EGF in intestinal epithelial cells and some novel findings regarding the activation and localization of STATs in general. These include the following. First, EGF promoted the tyrosine phosphorylation of STAT1 in IEC-6 cells and caused its translocation to the nucleus. Second, in the absence of EGF stimulation both STAT1 and STAT2 were localized to the Golgi apparatus in IEC-6 cells. Third, EGF caused the translocation of STAT2 to the nucleus in both IEC-6 and HeLa cells without inducing the tyrosine phosphorylation of STAT2.

Animals↗

PubMed1998

Bcl-2 prevents topoisomerase II inhibitor GL331-induced apoptosis is mediated by down-regulation of poly(ADP-ribose)polymerase activity.

Poly (ADP-ribose) polymerase (PARP), a nuclear enzyme responsible for DNA strand breaks, has been recently suggested to be crucial for apoptosis induced by a number chemotherapeutic drugs. In this study, we demonstrated that the PARP activity could be evidently elevated with a peak at 6 h when HL-60 cells were treated with a new anticancer drug GL331. Coincident with the peak of PARP activity, an apparent DNA fragmentation and apoptotic morphology were observed in cells treated with GL331. The subsequent apoptotic DNA fragmentation induced by GL331 could be completely blocked by transfecting cells with anti-sense PARP retroviral vector or by treating cells with PARP inhibitor, 3-aminobenzamide (3-AB). This blocking effect thus suggests that activation of PARP was critically involved in GL331-induced apoptosis. The fact that Bcl-2 has been found to antagonize cell death induced by a wide variety of agents, accounts for why we examined whether if Bcl-2 could antagonize GL331 effects. Interestingly, ectopic overexpression of Bcl-2 in either HL-60 or U937 cells caused in resistance towards GL331-elicited DNA fragmentation and cytotoxic effect. Additionally, Bcl-2 also attenuated the poly(ADP-ribosyl)ation of PARP itself as well as Histone H1 at the early period of drug treatment. However, Bcl-2 did not influence the extent of DNA strand breaks induced by GL331 in either control or Bcl-2-overexpressing cells. In addition, analysis of basal PARP activity in control and several Bcl-2 overexpressing clones revealed that Bcl-2 down-regulated PARP activity under the condition without DNA damages. Above findings suggest that poly(ADP-ribosyl)ation of nuclear targets is important for apoptosis induced by DNA-reactive anticancer drugs.

Antineoplastic Agents↗

PubMed1998

Inhibition of fos-jun-DNA complex formation by dihydroguaiaretic acid and in vitro cytotoxic effects on cancer cells.

The effect of dihydroguaiaretic acid (DHGA), isolated from the aryls of Myristica fragrans, on the transcription factor (fos-jun dimer) action was investigated via in vitro assay. DHGA showed an inhibitory effect against the complex formation of the fos-jun dimer and the DNA consensus sequence with an IC50 value of 0.21 micromol. Nordihydroguaiaretic acid (NDGA) and curcumin also inhibited fos-jun dimer action showing IC50 values of 7.9 and 6.9 nmol, respectively. DHGA and NDGA suppressed leukemia, lung cancer and colon cancer in an in vitro bioassay. The in vitro experiment suggested that inhibition of fos-jun-DNA complex formation could be due to the direct interference of fos-jun dimer binding onto the DNA consensus sequence by NDGA and curcumin.

Dimerization↗

PubMed1998

STAT3 complements defects in an interferon-resistant cell line: evidence for an essential role for STAT3 in interferon signaling and biological activities.

STAT proteins play critical roles in the signal transduction pathways for various cytokines. The type I interferons (IFNalpha/beta) promote the DNA-binding activity of the transcription factors STAT1, STAT2, and STAT3. Although the requirement for STAT1 and STAT2 in IFNalpha/beta signaling and action is well documented, the biological importance of STAT3 to IFN action has not yet been addressed. We found that STAT3 plays a critical role in signal transduction by IFNalpha/beta. A human cell line that is resistant to the antiviral and antiproliferative activities of IFN but is still IFN-responsive by virtue of STAT1 and STAT2 activation was found to be defective in STAT3 activation and in induction of NF-kappaB DNA-binding activity. Expression of STAT3 in these resistant cells complemented these signaling defects and also markedly increased cellular sensitivity to the antiviral and antiproliferative effects of IFN. Because STAT3 is involved in the induction of NF-kappaB DNA-binding activity and in the induction of antiviral and antiproliferative activity, our results place STAT3 as an important upstream element in type I IFN signal transduction and in the induction of biological activities. Therefore, our results indicate that STAT1 and STAT2 are not the only STATs required for the expression of the key biological activities of IFNalpha/beta.

Antiviral Agents↗

PubMed1998

Crystallization and preliminary X-ray studies of hORF6, a novel human antioxidant enzyme.

HORF6 is a member of the novel antioxidant enzyme family found in humans. A recombinant form of hORF6 expressed and purified from E. coli has been crystallized by the hanging-drop method using various PEG's as precipitating agents. HORF6 crystallizes in two different monoclinic space groups, P21 and C2. The P21 crystals have unit-cell dimensions of a = 47.85, b = 75.17, c = 63.30 A and beta = 110.21 degrees and contain two monomers per asymmetric unit, while the C2 crystals have unit-cell dimensions of a = 165.27, b = 95.44, c = 166.44 A and beta = 128.97 degrees and contain more than six monomers per asymmetric unit. The P21 crystals with the smaller unit cell diffract X-rays better and behave well for the X-ray analysis. A native data set from a single crystal of the P21 space group gas been collected to 2.0 A resolution.

Antioxidants↗

PubMed1998

Differences in activity between alpha and beta type I interferons explored by mutational analysis.

Type I interferon (IFN) subtypes alpha and beta share a common multicomponent, cell surface receptor and elicit a similar range of biological responses, including antiviral, antiproliferative, and immunomodulatory activities. However, alpha and beta IFNs exhibit key differences in several biological properties. For example, IFN-beta, but not IFN-alpha, induces the association of tyrosine-phosphorylated receptor components ifnar1 and ifnar2, and has activity in cells lacking the IFN receptor-associated, Janus kinase tyk2. To define the structural basis for these functional differences we produced human IFN-beta with point mutations and compared them to wild-type IFN-beta in assays that distinguish alpha and beta IFN subtypes. IFN-beta mutants with charged residues (N86K, N86E, or Y92D) introduced at two positions in the C helix lost the ability to induce the association of tyrosine-phosphorylated receptor chains and had reduced activity on tyk2-deficient cells. The combination of negatively charged residues N86E and Y92D (homologous with IFN-alpha8) increased the cross-species activity of the mutant IFN-betas on bovine cells to a level comparable to that of human IFN-alphas. In contrast, point mutations in the AB loop and D helix had no significant effect on these subtype-specific activities. A subset of these latter mutations did, however, reduce activity in a manner analogous to IFN-alpha mutations. The effects of these mutations on IFN-beta activity are discussed in the context of a family of related ligands acting through a common receptor and signaling pathway.

Amino Acid Sequence↗

PubMed1998

Induction of Jak/STAT signaling by activation of the type 1 TNF receptor.

Cellular responses to TNF are initiated by either of two cell surface receptors, the type 1 TNF receptor (TNFR1) and the type 2 TNF receptor (TNFR2). Although neither receptor contains an intrinsic protein tyrosine kinase, such activity has been implicated in TNF action. In this study, we show that murine TNF induces the tyrosine phosphorylation and activation of the intracellular Janus tyrosine kinases Jak1, Jak2, and Tyk2 in murine 3T3-L1 adipocytes. Activation of Jak kinases by TNF was associated with tyrosine phosphorylation of STAT1, STAT3, STAT5, and STAT6, but not STAT2 or STAT4, showing that TNF acts on a specific subset of these latent cytoplasmic transcription factors in 3T3-L1 adipocytes. Agonist antiserum to TNFR1 induced Jak kinase and STAT protein phosphorylation. Phosphorylation of Jak proteins was also induced by human TNF, which selectively binds to TNFR1 on murine cells. 35S-labeled Jak kinases were precipitated from a cell-free system and from lysates of 3T3-L1 adipocytes by a glutathione S-transferase fusion protein containing the cytoplasmic domain of TNFR1. These results suggest that the cytoplasmic domain of TNFR1 can directly interact with and form signaling complexes with Jak kinases. Jak2 was precipitated from HeLa cells by antiserum to TNFR1, directly demonstrating their association in vivo. Thus, TNF activates a Jak/STAT signal-transduction cascade by acting through TNFR1.

3T3 Cells↗

PubMed1998

The antiviral action of interferon is potentiated by removal of the conserved IRTAM domain of the IFNAR1 chain of the interferon alpha/beta receptor: effects on JAK-STAT activation and receptor down-regulation.

The first cloned chain (IFNAR1) of the human interferon-alpha (IFN alpha) receptor acts as a species-specific transducer for type 1 IFN action when transfected into heterologous mouse cells. Stably transfected mouse L929 cell lines expressing truncation mutants of the intracellular domain of the human IFNAR1 chain were tested for biological responses to human IFN alpha. Deletion of the intracellular domain resulted in a complete loss of sensitivity to the biological activity of human IFN but markedly increased IFNAR1 cell surface expression, demonstrating that the intracellular domain is required for biological function and contains a domain that negatively regulates its cell surface expression. Removal of the conserved membrane distal 16-amino-acid IRTAM (Interferon Receptor Tyrosine Activation Motif) sequence: (1) increased sensitivity to IFN alpha's antiviral activity, (2) increased the rapid IFN alpha-dependent formation of STAT-containing DNA-binding complexes, (3) prolonged tyrosine phosphorylation kinetics of the JAK-STAT pathway, and (4) blocked the IFN-dependent down-regulation of the IFNAR1 chain. These results indicate that the IRTAM negatively regulates signalling events required for the induction of IFN's biological actions via regulating receptor down-regulation.

Amino Acid Sequence↗

PubMed1998

Homozygous deletions of the CDKN2 gene and loss of heterozygosity of 9p in primary hepatocellular carcinoma.

To elucidate the alterations of CDKN2 in hepatocarcinogenesis, we performed a loss of heterozygosity (LOH) study using eight polymorphic markers surrounding the CDKN2 gene and analyzed the homozygous deletions and mutations of the CDKN2 gene in 41 primary hepatocellular carcinomas (HCCs). Frequent LOH (27.8-44%) was found in the eight loci on chromosome 9p, however, no intragenic mutations of CDKN2 were observed by PCR-SSCP analysis. Homozygous deletions were detected in 25 of 41 HCCs (61%) by a comparative multiplex PCR. No expression of the CDKN2 protein was noted in five out of nine available HCCs by Western blot analysis. These results suggest that inactivation of the CDKN2 gene in HCC is a frequent event in which homozygous deletions are the most common mechanism of CDKN2 inactivation.

Carcinoma, Hepatocellular↗

PubMed1998

Serological characterization of the 3'-proximal encoded proteins of beet yellows closterovirus.

The 3'-proximal open reading frames (ORFs) of beet yellows closterovirus, California isolate (BYV-CA), were sequenced and the expression of the corresponding proteins analyzed. The nucleotide sequence of ORF 5 (coding for p24) was most conserved compared with ORF 7 (coding for p20) and ORF 8 (coding for p21) among the isolates analyzed. Polyclonal antisera were produced to GST fusion proteins of p24, p20, and p21. Accumulation of p24, CP, p20 and p21 was studied in infected Tetragonia expansa plants and Chenopodium quinoa protoplasts. All four proteins were expressed in all tissues (old leaves, young leaves and stems), and most abundantly in young leaves. The subcellular localization of each protein in different tissues showed that compared with p24, CP and p21, p20 accumulated less in transfected protoplasts. Immunogold labeling in sugarbeet with p24 and CP antisera demonstrated co-localization of p24 and CP in vascular petiole tissues. In infectivity neutralization tests, antisera against p24 and CP greatly reduced transmission of BYV by viruliferous aphids compared with viruliferous aphids fed on preimmune serum or antiserum to p21.

Amino Acid Sequence↗

PubMed1998

Chromosomal localization of the murine RFC-1 gene encoding a folate transporter and its amplification in an antifolate resistant variant overproducing the transporter.

A variant of the L1210 cell (L1210/R83) selected in the presence of the lipophilic antifolate, metoprine, and a concentration of the natural diastereoisomer of 5-formyltetrahydrofolate, lL5CHO-folateH4, suboptimum for growth exhibited a 35-fold increase compared to parental L1210 cells in one-carbon, reduced folate transport. This was evidenced by the increase in Vmax for [3H]MTX (methotrexate) influx and a commensurate increase in the amount of the 46 kilodalton (kDa) transport protein and reduced folate carrier (RFC-1) mRNA. The variant is resistant to lipophilic antifolates, but shows collateral sensitivity to classical folate analogues. Karyotype analysis of L1210/R83 cells revealed the presence of several new chromosome abnormalities. One of these was a large, submetacentric marker chromosome comprising a normal #10 and a longer, abnormally banded arm of uncertain origin which exhibited an interstitial, palely staining, HSR-like segment. The results of Southern and Northern blotting showed that the RFC-1 gene copy number and RNA transcript level were markedly increased (30-35 fold) in L1210/R83 cells. Fluorescence in situ hybridization (FISH) analysis revealed that the HSR-like segment in these cells was the site of amplified RFC-1 genes. Independent revertant subclones, obtained following growth in the absence of selection pressure, showed four- to 12-fold decreases in [3H]MTX influx Vmax and in amount of NHS (N-hydroxysuccinimide)-[3H]MTX affinity labeled one-carbon, reduced folate transporter compared to L1210/R83 cells. RFC-1 gene copy number also decreased, and the mean length of the HSR in these revertants declined 1.6- to 5-fold. Based upon genomic nucleotide sequencing, the RFC-1 gene in the normal mouse genome was localized to chromosome 10 in close association with the alpha 1 (Col18a1) collagen gene at 10B3(locus 41cM). The close association of these genes was confirmed by other data showing that the alpha 1 collagen gene was co-amplified in L1210/R83 cells. These results document the amplification at the site of a putative HSR in an L1210 cell variant of the RFC-1 gene regulating expression of the one-carbon, reduced folate transporter.

Animals↗

PubMed1998

Striatal dopamine dynamics are altered following an intranigral infusion of iron in adult rats.

In vivo electrochemical detection was employed to examine iron-induced oxidative injury on dopamine dynamics in the nigrostriatal system of urethane-anesthetized rats. Seven days after an intranigral infusion of iron, oxidative stress was confirmed by an elevated lipid peroxidation in lesioned substantia nigra (SN). Local application of potassium (K+) evoked dopamine releases from the dopamine-containing nerve terminals in the striatum. Both amplitude and rate of clearance (Tc) of evoked dopamine releases were lower in striatum with lesioned SN; however, the time course parameters of dopamine release in the lesioned group were not different from those of the intact group, indicating a reduction in dopamine clearance. Indeed, iron-induced oxidative stress attenuated the effect of nomifensine, a high-affinity dopamine uptake blocker, on dopamine clearance. In striatum with intact SN, the amplitude and time course parameters of signals by exogenous dopamine were increased and Tc was decreased by nomifensine. In contrast, nomifensine did not significantly alter the dopamine signals of the lesioned group. Taken together, in addition to the increased lipid peroxidation in SN, our in vivo electrochemical data demonstrates that iron-induced oxidative injury attenuates K+-evoked dopamine release and dopamine uptake in the ipsilateral striatum. The diminished nomifensine effect implies a lack of high-affinity dopamine uptake sites.

Animals↗

PubMed1998

A possible hydrolysis mechanism of beta-naphthyl acetate catalyzed by antibodies.

The mechanism of ester hydrolysis has been extensively studied; however, the precise function of active-site residues in promoting catalysis is unclear. We describe here the structural models for the complex of a catalytic antibody Fv fragment with a phosphonate transition-state analogue, constructed by using gene cloning, sequencing and molecular modeling, mainly based on a known X-ray structure of a catalytic antibody. Hydrophobic and electrostatic analyses of the Fv/analog and Fv/substrate interaction suggest the hydrolysis mechanism: Tyr L91 and Tyr H97 play important roles to stabilize the beta-naphthyl group of hapten through pi-stack; His H35 donates a pair of free electrons at the atom NE2 to an active water and let it to be a partial hydroxide, which attacks the carbon atom of the carbonyl group of the substrate. Both His H35 and Arg L96 can form hydrogen bonds and stabilize the anionic tetrahedral intermediate formed during turnover. This mechanism emphasizes that an active water bridge may be formed during hydrolysis process.

Amino Acid Sequence↗