Biomedical subjects

Y L Yang

Publications and source records attributed to Y L Yang.

At least 37 records · Page 2Linked to original sources

PubMed2000

Chlorpyrifos-induced hypothermia and vasodilation in the tail of the rat: blockade by scopolamine.

Organophosphate pesticides such as chlorpyrifos reduce core temperature (Tc) in laboratory rodents. The mechanism(s) responsible for the chlorpyrifos-induced hypothermia are not well known. This study assessed the role of a key effector for thermoregulation in the rat, vasomotor control of heat loss from the tail, and its possible cholinergic control during chlorpyrifos-induced hypothermia. Tc and motor activity were monitored by telemetry in female Long-Evans rats maintained at an ambient temperature (Ta) of 25 degrees. Tail skin temperature (Tsk(t)) was measured hourly. Rats were dosed with chlorpyrifos (0 or 25 mg/kg orally). Two hr later the rats were dosed with saline or scopolamine (1.0 mg/kg intraperitoneally). Two hr after chlorpyrifos treatment there was a marked elevation in Tsk(t)) concomitant with a 0.5 degrees reduction in Tc. Scopolamine administered to control rats led to a marked elevation in Tc with little change in Tsk(t). Rats treated with chlorpyrifos and administered scopolamine underwent a marked vasoconstriction and elevation in Tc. Vasodilation of the tail is an important thermoeffector to reduce Tc during the acute stages of chlorpyrifos exposure. The blockade of the response by scopolamine suggests that the hypothermic and vasodilatory response to chlorpyrifos is mediated via a cholinergic muscarinic pathway in the CNS.

Analysis of Variance↗

PubMed1999

An integrated somatic cell hybrid, YAC, and BAC map of the Rmc1 region of mouse chromosome 1.

Rmc1, the cellular receptor for the polytropic class of murine retroviruses, determines the tissue tropism of the virus and therefore plays a critical role in the pathogenesis of polytropic virus-induced leukemia. Previously we reported the physical mapping of this gene to a 5-cM region of mouse chromosome 1 and the construction of a yeast artificial chromosome (YAC) contig across this region. In this report we describe the refinement of the Rmc1 candidate region to approximately 600 kb and the generation of an integrated somatic cell hybrid, YAC, and bacterial artificial chromosome contig spanning the region. A number of genes and loci were physically ordered along the chromosome, including a recently identified candidate for Rmc1.

Animals↗

PubMed1999

Heatstroke induces c-fos expression in the rat hypothalamus.

We induced heat stress in urethane-anesthetized rats (the animals were exposed to an ambient temperature at 42 degrees C), and monitored their colon temperature, mean arterial pressure and local cerebral blood flow. Rats 0, 20, 40 or 80 min after heat stress were sacrificed for determination of c-fos mRNA and protein expression in the paraventricular nucleus (PVN), supraoptic nucleus (SON) and preoptic nucleus (PON). The heatstroke, which appears as profound decreases in both mean arterial pressure and local cerebral blood flow and increases in colon temperature, is produced 80 min after heat stress. We show the c-fos mRNA and protein is strongly induced in all these nuclei of rat hypothalamus after the onset of heatstroke. We conclude that c-fos expression in the hypothalamus during rat heatstroke is associated with hyperthermia, arterial hypotension and cerebral ischemia.

Animals↗

PubMed1999

Ier5, a novel member of the slow-kinetics immediate-early genes.

We describe here a novel member of the slow-kinetics immediate-early gene family. Ier5 is an intronless gene, encoding a serum- and growth factor-inducible message of 2123 nucleotides that is present in a wide variety of tissues. The predicted open reading frame encodes a 308-amino-acid, highly proline-rich protein with homology to the amino terminus of the immediate-early gene pip92/Ier2/ETR101. Ier5 is predicted to be a nuclear protein and contains a PEST-like sequence, suggesting rapid protein degradation. Multiple phosphorylation sites are present. Ier5 shows growth factor induction kinetics similar to that of pip92/Ier2/ETR101, but unlike pip92/Ier2/ETR101 does not appear to require phosphokinase C activity for transcriptional activation. The sequence of the promoter region of Ier5 was determined and examined for transcription factor binding sites thought to mediate serum and growth factor response. Multiple AP-1 sites and an Ets-1 site were observed, but the CArG and CArG-like boxes of the serum response element were absent. The predicted nuclear localization of Ier5, coupled with the potential for rapid regulation by phosphorylation and/or degradation, suggests that Ier5 may play an important role in mediating the cellular response to mitogenic signals.

3T3 Cells↗

PubMed1999

Allele-specific suppression of ColE1 high-copy-number mutants by a rpoB mutation of Escherichia coli.

We have isolated spontaneous rifampicin-resistant mutants from Escherichia coli that showed allele-specific suppression of the copy-number phenotype of ColE1 high-copy-number mutants in vivo. The key step in the regulatory circuitry of the initiation of ColE1 DNA replication is the formation of the persistent hybrid between the primer RNA and the DNA template around the replication origin. Three host-encoded enzymes, RNase H, DNA polymerase I, and RNA polymerase, are essential to the replication initiation in vitro. To decide whether the activity of RNA polymerase is involved directly in the formation of the persistent hybrid, we screened rifampicin-resistant colonies for suppressors of ColE1 copy-number mutants. Suppressor strain YY572 (rpoB572) changes the 572 residue of the beta subunit of RNA polymerase, encoded by the rpoB gene, from isoleucine to leucine. Another suppressor, YY513 (rpoB513), changes the 513 residue from glutamine to lysine. The other known rifampicin-resistant alleles located at residue 513, rpoB8 and rpoB101, did not show a significant suppression of the copy number of those ColE1 copy-number mutants as rpoB513. The suppression by rpoB513 on different ColE1 copy-number mutants showed allelic specificity. The possible roles of RNA polymerase in control of ColE1 copy number are discussed.

Alleles↗

PubMed1999

Receptors for polytropic and xenotropic mouse leukaemia viruses encoded by a single gene at Rmc1.

The onset of leukaemia caused by type C retroviruses (MLV) in mice is accelerated by the emergence of recombinant polytropic or mink cell focus-forming (MCF) viruses. Susceptibility to infection by polytropic/MCF and also by closely related xenotropic MLV has been mapped to Rmc1 on mouse chromosome 1 (refs 5-7). To identify this gene, we introduced an expression cDNA library prepared from mouse NIH3T3 fibroblasts into nonpermissive hamster cells and screened these cells for acquired susceptibility to MCF viruses encoding beta-galactosidase and G418 resistance. From hamster cell clones identified in the screen, we recovered a mouse cDNA that maps to Rmc1 and confers MCF MLV infection when expressed in nonpermissive cell lines. It encodes a membrane protein related to Syg1p (suppressor of yeast G alpha deletion; ref. 8). The receptor-binding domain of the MCF MLV envelope protein binds specifically to Xenopus laevis oocytes that express mouse Syg1, suggesting it functions as a receptor that mediates virus entry. We also obtained the cDNA encoding human SYG1. When expressed in hamster cells, it establishes infectivity by MCF MLV as well as xenotropic MLV, which do not infect laboratory mice.

3T3 Cells↗

PubMed1999

Central control of blood pressure by nitrergic mechanisms in organum vasculosum laminae terminalis of rat brain.

Experiments were carried out to explore the possible role played by the nitric oxide (NO) system in the organum vasculosum laminae terminalis (OVLT) of rat brain in arterial pressure regulation. Intracerebroventricular (ICV) or intra-OVLT administration of NO donors such as hydroxylamine, sodium nitro-prusside or s-nitro-acetylpenicillamine caused an up to 55 mmHg decrease in blood pressure (BP) but an increase in NO release (measured by porphyrin/nafion coated carbon fibre electrodes in combination with voltammetry) in the OVLT. In contrast, ICV or intra-OVLT administration of N(G)-nitro-L-arginine methyl ester (L-NAME; a constitutive NO synthase inhibitor) caused an up to 45 mmHg increase in BP but a fall in NO release in the OVLT. Compared with the BP responses induced by ICV injection of NO donors or NO synthase inhibitors, the OVLT route of injection required a much lower dose of NO donors or NO synthase inhibitors to produce a similar BP effect. The depressor effects induced by ICV or intra-OVLT administration of NO donors were attenuated by pretreatment with intra-OVLT injection of methylene blue (an inhibitor of guanylate cyclase), haemoglobin (a NO scavenger), L-NAME or spinal transection. On the other hand, the L-NAME-induced pressor effects were attenuated by pretreatment with intra-OVLT injection of L-arginine or spinal transection. The data suggest that activation of cyclic GMP-dependent NO synthase in the OVLT of rat brain causes cyclic GMP-dependent decreases in arterial pressure via inhibiting the sympathetic efferent activity.

Animals↗

PubMed1999

The immune response modifier imiquimod requires STAT-1 for induction of interferon, interferon-stimulated genes, and interleukin-6.

Imiquimod is an oral inducer of interferon (IFN) and several other proinflammatory cytokines and has been successfully used topically as an antiviral agent for the treatment of genital warts. We have investigated the molecular mechanisms by which imiquimod induces the expression of IFNs, IFN-stimulated genes (ISGs), and proinflammatory cytokines in vivo, using mice deficient in various components of the IFN signaling system. Mice deficient in the transcription factor interferon regulatory factor 1 (IRF-1) or in the serine/threonine protein kinase PKR responded normally to imiquimod, producing high levels of circulating IFN and induction of several ISGs. On the other hand, when mice deficient in STAT-1 were treated, a 32-fold reduction in the level of circulating IFN was observed, together with a lack of induction of 2-5 oligo adenylate synthetase (2-5 OAS) and IRF-1 genes. Interestingly, there was also a lack of induction of interleukin-6 (IL-6) gene expression, although tumor necrosis factor was induced and readily detected in serum. In mice deficient in the type I IFN receptor, imiquimod induced levels of IFN similar to those in control mice, but again, neither 2-5 OAS, IRF-1, nor IL-6 genes were induced in mutant mice. Our results suggest that STAT-1 plays a critical role in the mechanism of gene activation by imiquimod. Moreover, induction of IL-6 gene expression appears to be dependent on components of the IFN signaling cascade.

Administration, Oral↗

PubMed1999

Heat shock protein expression protects against cerebral ischemia and monoamine overload in rat heatstroke.

This study attempted to ascertain whether the ischemic damage to neurons and monoamine overload in brain that occur during rat heatstroke can be attenuated by heat shock protein (HSP) 72 induction. Effects of heatstroke on mean arterial pressure (MAP), cerebral blood flow (CBF), brain dopamine (DA) and serotonin (5-HT) release, and neural damage score were assayed in rats 0, 16, or 48 h after heat shock (42 degrees C for 15 min) or chemical stress (5 mg/kg sodium arsenite ip). Brain HSP 72 in rats after heat shock or chemical stress was detected by Western blot, and brain monoamine was determined by a microdialysis probe combined with high-performance liquid chromatography. Heatstroke was induced by exposing the animal to a high ambient temperature (43 degrees C); the moment at which MAP and CBF decreased from their peak values was taken as the time of heatstroke onset. Prior heat shock or chemical stress conferred significant protection against heatstroke-induced hyperthermia, arterial hypotension, cerebral ischemia, cerebral DA and 5-HT overload, and neural damage and correlated with expression of HSP 72 in brain at 16 h. However, at 48 h, when HSP 72 expression returned to basal values, the above responses that occurred during the onset of heatstroke were indistinguishable between the two groups (0 h vs. 48 h). These results lead to the hypothesis that the brain can be preconditioned by thermal or chemical injury, that this preconditioning will induce HSP 72, and that HSP 72 induction will correlate quite well with anatomic, histochemical, and hemodynamic protection in rat heatstroke.

Animals↗

PubMed1999

R-dl-verapamil downmodulates multidrug resistance of KBv200 cells to vincristine and doxorubicin.

AIM: To study the attenuation of multidrug resistance (MDR) by R-dl-verapamil (R-Ver) and the acute animal toxicity of R-Ver, and to compare these results of R-Ver with the results of dl-verapamil (Ver). METHODS: Cytotoxicity was determined by tetrazolium (MTT) assay. Cellular accumulation of doxorubicin (Dox) was measured by fluorescence spectrophotometry. Acute animal toxicity was tested by i.p. drug administration in BALB/c mice. RESULTS: R-Ver attenuated MDR of KBv200 cells to vincristine (VCR) and Dox. This attenuation ability was dose-related, and was also dependent on drug exposure time. R-Ver 1.25 mumol.L-1 increased the sensitivity of KBv200 cells to VCR (P < 0.01) with a 24-h period of drug exposure. R-Ver downmodulated MDR and increased cellular Dox accumulation of KBv200 cells as effectively as Ver, but possessed lower acute toxicity in BALB/c mice. While LD50 of Ver was 60 (49-73) mg.kg-1, LD50 of R-Ver was 166 (137-202) mg.kg-1. CONCLUSION: R-Ver downmodulated the MDR to VCR and Dox at 1.25 mumol.L-1, and this effect on VCR can be realized with drug exposure duration of 24 h.

Animals↗

PubMed1998

Heat shock protein expression protects against death following exposure to heatstroke in rats.

Rats 0, 16, or 48 h after heat shock (42 degrees C core temperature for 15 min) or chemical stress (5 mg/kg sodium arsenite, i.p.) were exposed to a high ambient temperature (43 degrees C) to induce heatstroke onset. The moment in which the mean arterial pressure and cerebral blood flow began to decrease from their peak values was taken as the onset of heatstroke. Prior heat shock or chemical stress conferred significant protection against heatstroke-induced arterial hypotension, cerebral ischemia, cerebral neuronal damage and death, and correlated with expression of HSP72 in brain, heart, liver and kidney at 16 h. However, at 48 h, when HSP72 expression returned to basal values, the above responses that occurred after the onset of heatstroke of two groups (0 h group VS 48 h group) were indistinguishable. The data suggest that HSP72 presence increases survival in rat heatstroke by attenuating arterial hypotension, cerebral ischemia and neuronal damage.

Animals↗

PubMed1998

Striatal glutamate release is important for development of ischemic damage to striatal neurons during rat heatstroke.

This study attempted to ascertain whether heatstroke-induced ischemia is associated with augmented striatal glutamate release and can be attenuated by NMDA receptor antagonists. Mean arterial pressure (MAP), striatal cerebral blood flow (CBF), striatal glutamate release and striatal neuronal damage score were assessed in saline-treated rats and in rats treated with NMDA receptor antagonists. Heatstroke was induced by exposing the animals to a high ambient temperature; the moment at which MAP and CBF began to decrease from their peak levels was taken as the onset of heatstroke. During onset of heatstroke, rats displayed higher values of colonic temperature, striatal glutamate release and striatal neuronal damage score, and lower values of MAP and striatal blood flow compared with normothermic control rats. The decreased MAP, the diminished striatal blood flow, the augmented striatal glutamate release and the increased striatal neuronal damage score during onset of heatstroke were significantly attenuated by pretreatment with an NMDA receptor antagonist such as MK-801 or ketamine. In addition, the survival time (interval between onset of heatstroke and death) of the rats was extended by pretreatment with one of these two NMDA receptor antagonists. These results suggest that marked accumulation of glutamate in the striatum is important for the development of ischemic damage to striatal neurons during the onset of heatstroke.

Animals↗

PubMed1998

Enzymatic hydrolysis of organic cyclic carbonates.

Ethylene carbonate, a cyclic organic carbonate widely used industrially, is toxic when metabolically converted to ethylene glycol. A rat liver enzyme active in catalyzing the ring opening has been purified to electrophoretic homogeneity and found to be active in the hydrolysis of ethylene, vinylene, and propylene carbonates to CO2 and the respective glycols. Neither thiocarbonates nor open chain carbonates served as substrate nor did a variety of esters, lactams, lactones, and related heterocycles. The enzyme was active, however, with imides and appears to be identical to rat liver imidase. The identification was confirmed by copurification of enzyme activities, by similarities in the pattern of inhibition, and by the reactivity with a polyclonal antibody directed against the enzyme purified here.

Amidohydrolases↗

PubMed1998

The telomeres of Streptomyces chromosomes contain conserved palindromic sequences with potential to form complex secondary structures.

The chromosomes of the gram-positive soil bacteria Streptomyces are linear DNA molecules, usually of about 8Mb, containing a centrally located origin of replication and covalently bound terminal proteins (which are presumably involved in the completion of replication of the telomeres). The ends of the chromosomes contain inverted repeats of variable lengths. The terminal segments of five Streptomyces chromosomes and plasmids were cloned and sequenced. The sequences showed a high degree of conservation in the first 166-168bp. Beyond the terminal homology, the sequences diverged and did not generally cross-hybridize. The homologous regions contained seven palindromes with a few nucleotide differences. Many of these differences occur in complementary pairs, such that the palindromicity is preserved. Energy-optimized modelling predicted that the 3' strand of the terminal palindromes can form extensive hairpin structures that are similar to the 3' ends of autonomous parvovirus genomes. Most of the putative hairpins have a GCGCAGC sequence at the loop, with the potential to form a stable single C-residue loop closed by a sheared G:A pairing. The similarity between the terminal structures of the Streptomyces replicons and the autonomous parvoviral genomes suggests that they may share some structural and/or replication features.

Base Sequence↗

PubMed1998

Interaction between high glucose and TGF-beta in cell cycle protein regulations in MDCK cells.

Transforming growth factor-beta (TGF-beta) may mediate high glucose effects in renal cells. Thus, Madin-Darby canine kidney cells were studied for the modulation of cell cycle regulatory proteins by high glucose (27.5 mM) and TGF-beta1. We showed that unlike other renal cells, TGF-beta1 mRNA and its bioactivity were not induced by high-glucose culture. Furthermore, high glucose per se increased cellular proliferation without alterations in cell size. High glucose also increased the percentage of cells in the G2/M phase while decreasing cells in the G0/G1 phase of the cell cycle. In contrast, TGF-beta1 dose dependently (1 to 4 ng/ml) decreased cellular mitogenesis while increasing hypertrophy in the cells, especially in the presence of high glucose. TGF-beta1 also increased the percentage of cells arrested in the G0/G1 phase while decreasing cells in the G2/M phase of the cell cycle. Regarding two of the cell cycle regulatory proteins, high glucose increased cdc2 kinase activity and retinoblastoma protein (pRb) phosphorylation. In contrast, TGF-beta1 decreased cdc2 kinase activity and pRb phosphorylation, especially in the presence of high glucose. Additionally, glucose dose dependently (5.5, 16.5, 27.5, and 38.5 mM) increased type I and II TGF-beta receptor protein expression. In conclusion, changes in cdc2 kinase activity and pRb phosphorylation were correlated with high glucose and TGF-beta1-induced growth effects in a cell cycle-dependent manner in the Madin-Darby canine kidney cells. Furthermore, high glucose may potentiate TGF-beta1-induced effects by enhancing TGF-beta receptor protein expression.

Animals↗

PubMed1997

Dexamethasone administered into organum vasculosum laminae terminalis of rabbits induced antipyresis via inhibiting nitric oxide pathway in situ.

Direct administration of lipopolysaccharide (LPS) into the organum vasculosum laminae terminalis (OVLT) increased the amount of nitric oxide (NO) release and inducible NO synthase expression. These increases paralleled the increase in deep body temperature in unanesthetized rabbits. Pretreatment with dexamethasone, a synthetic glucocorticoid, not only reduced the fever but also attenuated the NO release and the inducible NO synthase expression in the OVLT following an intra-OVLT dose of LPS. The data suggest that steroids such as dexamethasone exert their antipyresis by inhibiting the NO pathway in the OVLT of rabbit brain.

Analgesics, Non-Narcotic↗

PubMed1997

A double-stranded RNA-activated protein kinase-dependent pathway mediating stress-induced apoptosis.

Apoptosis occurs in response to different cellular stresses, including viral infection, inflammatory cytokines, growth factor deprivation, and UV light, but it is unclear whether these inducers share a common mechanism of induction. The interferon-induced, double-stranded RNA-activated protein kinase (PKR) has been implicated in processes that rely on apoptosis as control mechanisms in vivo, including antiviral activities, cell growth regulation, and tumorigenesis. Here we report that mouse embryo fibroblasts from mutant mice containing homozygous deletions in the PKR gene (Pkr(0/0) mice) were resistant to apoptotic cell death in response to double-stranded RNA, tumor necrosis factor-alpha, or lipopolysaccharide. The mechanism underlying the suppression of apoptosis in the Pkr(0/0) cells could be attributed to defects in the activation of DNA-binding activity for the transcription factor interferon regulatory factor-1 and in Fas mRNA induction. Thus, these results provide genetic evidence implicating a requirement for PKR in mediating different forms of stress-related apoptosis.

Animals↗

PubMed1997

Physical association between STAT1 and the interferon-inducible protein kinase PKR and implications for interferon and double-stranded RNA signaling pathways.

The interferon-inducible double-stranded RNA protein kinase PKR controls protein synthesis through the phosphorylation of eukaryotic translation initiation factor (eIF)-2. In addition to its demonstrated role in translational control, several reports have suggested a transcriptional role for PKR. Here we report that PKR is involved in IFN- and dsRNA-signaling pathways by modulating the function of the signal transducer and activator of transcription STAT1. We also show that PKR associates with STAT1 in mouse and human cells. The association is not a kinase-substrate interaction since STAT1 phosphorylation is not modified by PKR in vitro or in vivo. In addition, the formation of the PKR-STAT1 complex is not dependent upon the enzymatic activity of PKR but does require the dsRNA-binding domain of PKR. Moreover, there is a concomitant decrease in PKR-STAT1 interaction and increase in STAT1 DNA binding in response to IFNs or dsRNA. These findings suggest that PKR plays an important role in IFN and dsRNA-signaling pathways by modulating the transcriptional function of STAT1.

3T3 Cells↗