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Biomedical subjects

W Ma

Publications and source records attributed to W Ma.

At least 235 records · Page 13Linked to original sources
PubMed1997

Inhibition of tumor promoter-induced activator protein 1 activation and cell transformation by tea polyphenols, (-)-epigallocatechin gallate, and theaflavins.

(-)-Epigallocatechin gallate (EGCG) and theaflavins are believed to be key active components in tea for the chemoprevention against cancer. However, the molecular mechanisms by which EGCG and theaflavins block carcinogenesis are not clear. We have used the JB6 mouse epidermal cell line, a system that has been used extensively as an in vitro model for tumor promotion studies, to examine the anti-tumor promotion effects of EGCG and theaflavins at the molecular level. EGCG and theaflavins inhibited epidermal growth factor- or 12-O-tetradecanoylphorbol-13-acetate-induced cell transformation in a dose-dependent manner. At the dose range (5-20 microM) that inhibited cell transformation, EGCG and theaflavins also inhibited AP-1-dependent transcriptional activity and DNA binding activity. The inhibition of AP-1 activation occurs through the inhibition of a c-Jun NH2-terminal kinase-dependent, but not an extracellular signal-regulated protein kinase (Erk) 1-dependent or Erk2-dependent, pathway. Because the transcription factor AP-1 is important for tumor promoter-induced neoplastic transformation, the inhibitory effects on AP-1 activation by EGCG and theaflavins may further explain the anti-tumor promotion action of these tea constituents.

Animals↗
PubMed1997

Direct stimulation of Bruton's tyrosine kinase by G(q)-protein alpha-subunit.

Heterotrimeric guanine-nucleotide-binding regulatory proteins (G proteins) transduce signals from a wide variety of cell-surface receptors to generate physiological responses. Protein-tyrosine kinases are another group of critical cellular signal transducers and their malfunction often leads to cancer. Although activation of G-protein-coupled receptors can elicit rapid stimulation of cellular protein-tyrosine phosphorylation, the mechanism used by G proteins to activate protein-tyrosine kinases is unclear. Here we show that the purified alpha-subunit of the G(q) class of G proteins (G[alpha]q) directly stimulates the activity of a purified non-receptor kinase, Bruton's tyrosine kinase (Btk), whereas purified alpha-subunits from G(il), G(O) or G(z) proteins do not. G(alpha)q can also activate Btk in vivo. Furthermore, in Btk-deficient cells, stimulation of another kinase, a p38 MAP kinase, by Gq-coupled receptors is blocked. Our results demonstrate that certain protein-tyrosine kinases can be direct effectors of G proteins.

Agammaglobulinaemia Tyrosine Kinase↗
PubMed1997

Late memory-related genes in the hippocampus revealed by RNA fingerprinting.

Although long-term memory is thought to require a cellular program of gene expression and increased protein synthesis, the identity of proteins critical for associative memory is largely unknown. We used RNA fingerprinting to identify candidate memory-related genes (MRGs), which were up-regulated in the hippocampus of water maze-trained rats, a brain area that is critically involved in spatial learning. Two of the original 10 candidate genes implicated by RNA fingerprinting, the rat homolog of the ryanodine receptor type-2 and glutamate dehydrogenase (EC 1.4.1.3), were further investigated by Northern blot analysis, reverse transcription-PCR, and in situ hybridization and confirmed as MRGs with distinct temporal and regional expression. Successive RNA screening as illustrated here may help to reveal a spectrum of MRGs as they appear in distinct domains of memory storage.

Animals↗
PubMed1997

Interferon-gamma rapidly increases peptide transporter (TAP) subunit expression and peptide transport capacity in endothelial cells.

Human cytotoxic T lymphocytes (CTL) recognize specific complexes of HLA class I molecules and peptides, which assemble when nascent class I molecules bind peptides transported from the cytoplasm into the endoplasmic reticulum by the heterodimeric transporter associated with antigen processing (TAP). Increased class I molecule expression on the cell surface increases the efficiency of CTL lysis. The kinetics of interferon (IFN)-gamma induction of TAP, peptide transport capacity, and HLA class I molecule expression was determined in endothelial cells, which are targets of CTL following transplantation or viral infection. TAP mRNAs are induced rapidly, increasing 20-fold (TAP1) or 10-fold (TAP2) by 12 h, whereas HLA class I mRNA is induced more slowly, increasing 10-fold in 24 h. TAP1 and TAP2 proteins are also induced rapidly, increasing 10-fold in 24 h, whereas HLA class I heavy chain proteins and surface expression increase more slowly. Peptide transport capacity in endothelial and HeLa cells increases within 6 h of IFN-gamma treatment, suggesting that the IFN-gamma-induced TAP heterodimers are functional. Therefore, the IFN-gamma-induced increase in TAP proteins is accompanied by an increased peptide transport capacity, which may be important in supporting the subsequent rise in HLA class I protein expression.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1997

Signal transduction through atypical PKCs, but not the EGF receptor, is necessary for UVC-induced AP-1 activation in immortal murine cells.

The exposure of mammalian cells to ultraviolet (u.v.) irradiation leads to activation of transcription factors, such as AP-1 and NFkappaB. It is postulated that the EGF receptor but not protein kinase C (PKC) is the major membrane mediator in UVC-induced signal transduction. We demonstrate here that the antisense oligonucleotides of PKC zeta and the dominant negative mutant of PKC lambda/iota as well as dominant negative PKC zeta markedly blocked UVC-induced AP-1 activity. In contrast, UVC-induced AP-1 activity in cells devoid of the EGF receptor (B82), is not significantly different from that of the stable transfectants with a kinase-deficient EGF receptor (B82M721), or wild-type EGF receptor (B82L). This was found at all UVC irradiation doses and time courses studied, while high levels of EGF-induced AP-1 activity were observed in B82L cells but not in B82 cells. This evidence strongly suggests that atypical PKCs, but not the EGF receptor, is necessary for UVC-induced AP-1 activation in JB6 and B82 cells.

Animals↗
PubMed1997

GABA induces GABAergic MSCs in cultured embryonic rat thalamic neurons.

Application of 0.1-10 microM GABA in the vicinity of cultured embryonic rat thalamic neurons recorded with patch pipettes in the presence of 2 microM TTX induced or increased the frequency of miniature synaptic currents (MSCs) that reversed polarity at the Cl- equilibrium potential. These MSCs were blocked by the GABAA receptor antagonist bicuculline and exhibited exponential decay kinetics that closely paralleled those estimated from fluctuation analysis of Cl- channels activated pharmacologically by applying 1-10 microM GABA to the same cells. We conclude that the MSCs are mediated by GABA. Application of the GABAA receptor agonist muscimol activated Cl- current but failed to induce GABAergic MSCs while submicromolar concentrations of GABA evoked GABAergic MSCs but did not activate Cl- channels. The GABAB receptor agonist (-)baclofen did not mimic GABA in inducing MSCs. Induction of GABAergic MSCs by GABA required extracellular Ca2+. Verapamil and Co2+, which block voltage-dependent calcium channels, completely blocked GABA-induced MSCs independent of their effects on the direct activation of a Cl- current response. The results indicate that GABA can trigger GABAergic Cl(-)-dependent MSCs in a Cao(2+)-dependent manner. The mechanism may involve a novel receptor and/or signal transduction pathway.

Animals↗
PubMed1997

Minisatellite DNA markers reveal hybridisation between the endangered black robin and tomtit.

We have used multilocus minisatellite DNA profiling to assess genetic variation in the endangered and highly inbred black robins and the closely related tomtits. These species are restricted to wild populations on the Chatham Islands, off the east coast of New Zealand. DNA profiles revealed a remarkable degree of genetic similarity among black robins, as well as among the tomtits sampled, although the typical profiles of these two species were clearly distinct. The parentage of two putative hybrid chicks and one putative hybrid adult was established for a 'black robin' adult male and an adult tomtit female which were found nesting together. The 'black robin' male, despite being morphologically a typical black robin, was found to possess a number of minisatellite-containing restriction fragments not recorded from the black robin population (n = 103). These fragments were however detected in tomtits. Consequently, this bird appeared to be an F1 hybrid and his three offspring were F2 hybrids. Mitochondrial DNA sequencing of members of this family showed that the 'black robin' male had cytochrome b and 16S of black robin, rather than tomtit, haplotypes. This indicates that the black robin adult male hybrid was the result of a black robin female mating with a tomtit male. These findings are particularly important since tomtits had been used as cross-foster parents for black robins, as part of an earlier conservation recovery program. The existence of any hybrids thus detected would have important implications for cross-fostering programs generally, since may such programs are now being implemented in conservation programs worldwide.

Amino Acid Sequence↗
PubMed1997

The contribution of GSH peroxidase-1, catalase and GSH to the degradation of H2O2 by the mouse lens.

Utilizing cultured lenses from normal and homozygous glutathione peroxidase (GSHPx-1) knockout mice and inhibitors for GSSG Reductase (GSSG Red), 1,3-bis(2-chlorethyl)-1-nitrosourea (BCNU) and catalase (Cat), 3-aminotriazole (3-AT), the ability to degrade H2O2 was examined at two H2O2 concentrations, 300 microM and 80 microM. It was found that GSHPx-1 contributed about 15% to the H2O2 degradation. The Cat contribution was concentration dependent being about 30% at 300 microM H2O2 and approximately 8% to 15% at 80 microM H2O2. GSH loss measured as nonprotein thiol (NP-SH) was shown to be linked to most of the remaining H2O2 degradation accounting for about 54% to 72% of the H2O2 degradation at 300 microM and 80 microM, respectively. However, based on evaluation of the ability of GSH to nonenzymatically degrade H2O2, it can only account for about 36% at 300 microM and 19% at 80 microM H2O2 of the observed lens H2O2 degradation. It is, therefore, concluded that lens GSH must be involved in other reactions either directly or indirectly related to H2O2 degradation.

Amitrole↗
PubMed1997

Microperoxidases catalytically degrade reactive oxygen species and may be anti-cataract agents.

microPx-11, a ferriheme undecapeptide proteolytic degradation product of cytochrome C is shown to be a peroxidase with broad specificity degrading H2O2 and tertiary butyl hydroperoxide. It is also capable of effectively eliminating superoxide and hydroxyl radical. The peroxidase loses activity in the presence of peroxide unless it is stabilized by ascorbate (Asc) or solutions such as aqueous humor or medium 199. While thiol but not disulfides inactivates the microPx-11, it is not inhibited in the presence of the rat lens which has a high GSH content. microPx-11 at concentrations 10 to 50 fold greater than are required to achieve good protective activity exhibits no toxicity based on cell viability, ATP levels and lens transparency after long-term incubations of alpha TN4-1 cells or cultured rat lens. The peroxidase is capable of protecting cultured rat lenses from photochemical stress where H2O2, O2.- and OH. are generated based on transparency, choline transport, epithelial cell viability and protein integrity as indicated by SDS-PAGE of the rat lens protein. In the absence of the peroxidase, extensive epithelial cell death and other degradative changes are observed. The DNA of alpha TN4-1 cells can also be protected from H2O2 induced single strand breaks by the microPx-11. The overall results suggest that a number of cytochrome C proteolytic degradation products are peroxidases which may be effective anti-cataract agents protecting the lens from oxidative stress.

Animals↗
PubMed1997

Restriction of viral population by intravaginal infection of simian immunodeficiency viruses in macaque monkeys.

In order to examine whether the viral population is affected by intramucosal transmission, we analyzed the viral genotypes first detected in peripheral blood mononuclear cells (PBMCs) after intravaginal inoculation, before virus antibodies were detectable, and compared them with those in the inoculum. Three female cynomolgus macaques were inoculated intravaginally and a fourth was inoculated intravenously with polyclonal simian immunodeficiency viruses (SIVmac32H). The provirus genomes which first appeared in PBMC were sequenced in the V1 to V2 region of the SIV envelope gene. A comparison of the sequences obtained from each monkey revealed a homogeneous or heterogeneous viral population depending on the infection route. In the intravenously inoculated monkey, the viral population was heterogenous and was similar to that in the virus inoculum. On the other hand, in the intravaginally inoculated monkeys, single genotypes (in two monkeys) and one genotype with a slight variation (in one monkey) were found, but they were different from each other, having no characteristic sequences in the V1 to V2 region in common. None of the genotypes found in the PBMC were major genotypes in the virus inoculum. These results suggest that some selective mechanism, which differs among individuals, restricts the viral population during mucosal transmission.

Amino Acid Sequence↗
PubMed1997

Substance P and enkephalin immunoreactivities in axonal boutons presynaptic to physiologically identified dorsal horn neurons. An ultrastructural multiple-labelling study in the cat.

A combination of intracellular electrophysiological recording and injection of horseradish peroxidase with ultrastructural immunocytochemistry was used to investigate the synaptic interplay between substance P- and enkephalin-immunoreactive axonal boutons and three types of functionally characterized dorsal horn neurons in the cat spinal cord. The dorsal horn neurons were classified as nociceptive specific, wide dynamic range and non-nociceptive based on their responses to innocuous and noxious stimuli. Most of the nociceptive neurons (either nociceptive specific or wide dynamic range) contained enkephalin immunoreactivity, but none of the non-nociceptive neurons were positive for enkephalin. Three types of immunoreactive boutons were found in contact with the functionally characterized dorsal horn neurons. These boutons were positive for either substance P, enkephalin, or substance P+enkephalin. Quantitative analysis revealed that the percentages of substance P-immunoreactive boutons apposed to the cell bodies, proximal dendrites and distal dendrites of nociceptive neurons were significantly higher than those of non-nociceptive neurons. Furthermore, the percentages of substance P+enkephalin-immunoreactive axonal boutons apposed to the distal dendrites of nociceptive neurons were significantly higher than those of non-nociceptive neurons and the percentages of enkephalin-immunoreactive boutons apposed to the cell bodies and proximal dendrites of nociceptive neurons were significantly higher than in non-nociceptive neurons. Finally, neither enkephalin-immunoreactive nor substance P+enkephalin-immunoreactive boutons were ever seen presynaptic to substance P-immunoreactive boutons. These results provide evidence of an anatomical substrate within the dorsal horn for the interaction of substance P-mediated with enkephalin-mediated mechanisms. The data support the idea that the modulation of nociceptive input in the dorsal horn by enkephalinergic neurons occurs mainly via a postsynaptic mechanism, and thus suggest that dorsal horn enkephalinergic neurons participate in a local inhibitory feedback loop in a distinct pathway from the previously postulated opioid-mediated depression of substance P release from primary afferent terminals.

Animals↗
PubMed1997

Differential expression of galanin immunoreactivities in the primary sensory neurons following partial and complete sciatic nerve injuries.

Neuropeptide expression in primary sensory neurons is highly plastic in response to peripheral nerve axotomy. While neuropeptide changes following complete sciatic nerve injury have been extensively studied, much less is known about the effects of partial sciatic nerve injuries on neuropeptide plasticity. Galanin. a possible endogenous analgesic peptide, was up-regulated in primary sensory neurons following complete sciatic nerve injury. We investigated the effects of partial sciatic nerve injuries on galanin expression in primary sensory neurons, and compared this effect with that after complete sciatic nerve injury. Complete transection, partial transection and chronic constriction injury were made, respectively, on the sciatic nerves of three groups of rats at high thigh level. Animals were allowed to survive for four and 14 days before being killed. L4 and L5 dorsal root ganglia, L4 5 spinal cord and lower brainstem were processed for galanin immunocytochemical staining. After all three types of sciatic nerve injuries, galanin-immunoreactive neurons were significantly increased in the ipsilateral dorsal root ganglia, and galanin-immunoreactive axonal fibres were dramatically increased in the superficial laminae of the dorsal horn and the gracile nuclei, compared to the contralateral side. However, in partial injury models, the percentages of galanin-immunoreactive dorsal root ganglion neurons were significantly higher than in complete nerve transection. Size frequency distribution analysis detected that more medium- and large-size galanin-immunoreactive dorsal root ganglion neurons were present after partial nerve transection and constriction injury than after complete nerve transection. Using a combined approach of retrograde tracing of flurorescent dyes and galanin immunostaining, we found that a partial transection increased the proportions of galanin-immunoreactive neurons among both axotomized and non-axotomized neurons. Galanin-immunoreactive axonal fibres were not only detected in the superficial laminae, but also in the deeper laminae of the dorsal horn of partial injury animals. Furthermore, more galanin-immunoreactive axonal fibres were observed in the ipsilateral gracile nuclei of partially injured rats than in completely injured rats. We conclude that partial sciatic nerve injuries induced greater galanin up-regulation in medium- and large-size dorsal root ganglion neurons than complete sciatic nerve injury. Galanin expression in primary sensory neurons seems to be differentially regulated following partial and complete sciatic nerve injuries.

Animals↗
PubMed1997

Variations of equine urinary volatile compounds during the oestrous cycle.

Equine urine was analysed by capillary gas chromatography. The volatile profiles from oestrous and dioestrous samples were compared to establish any qualitative or quantitative difference that may have potential value in olfactory communication. Forty-five different volatile compounds were detected. Of these, 17 major compounds were common to all chromatograms. The chemical profile of oestrous urine was distinguished by the presence of a unique peak that was not present in dioestrous samples. Numerous constituents exhibited endocrine dependence: while the concentrations of seix peaks increased at oestrus, the concentrations of another five peaks decreased at the same time. Since oestrous urine, but not dioestrous urine, has been shown to elicit sexual behaviour in the stallion, the unique peak, together with the peaks that were present in increased concentration at oestrus, may represent important chemical signals that stallions use to detect urinary 'oestrous odours'. Statistical analyses also indicated that the relative ratios (normalized peak areas) of many peaks changed significantly across the oestrous cycle: the rations increased in nine peaks, decreased in six peaks, and remained constant in two peaks at oestrus.

Analysis of Variance↗
PubMed1997

Inhibitory effects of topical application of low doses of curcumin on 12-O-tetradecanoylphorbol-13-acetate-induced tumor promotion and oxidized DNA bases in mouse epidermis.

The effects of topical applications of very low doses of curcumin (the major yellow pigment in turmeric and the Indian food curry) on 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced oxidation of DNA bases in the epidermis and on tumor promotion in mouse skin were investigated. CD-1 mice were treated topically with 200 nmol of 7,12-dimethylbenz[a]anthracene followed one week later by 5 nmol of TPA alone or together with 1, 10, 100 or 3000 nmol of curcumin twice a week for 20 weeks. Curcumin-mediated effects on TPA-induced formation of the oxidized DNA base 5-hydroxymethyl-2'-deoxyuridine (HMdU) and tumor formation were determined. All dose levels of curcumin inhibited the mean values of TPA-induced HMdU formation in epidermal DNA (62-77% inhibition), but only the two highest doses of curcumin strongly inhibited TPA-induced tumor promotion (62-79% inhibition of tumors per mouse and tumor volume per mouse). In a second experiment, topical application of 20 or 100 nmol (but not 10 nmol) of curcumin together with 5 nmol TPA twice a week for 18 weeks markedly inhibited TPA-induced tumor promotion. Curcumin had a strong inhibitory effect on DNA and RNA synthesis (IC50 = 0.5-1 microM) in cultured HeLa cells, but there was little or no effect on protein synthesis.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed1997

Anatomical gradients in proliferation and differentiation of embryonic rat CNS accessed by buoyant density fractionation: alpha 3, beta 3 and gamma 2 GABAA receptor subunit co-expression by post-mitotic neocortical neurons correlates directly with cell buoyancy.

Development of the CNS occurs as a complex cascade of pre-programmed events involving distinct phases of cell proliferation and differentiation. Here we show these phases correlate with cells of specific buoyant densities which can be readily accessed by density gradient fractionation. Sprague-Dawley dams were pulse-labelled with bromodeoxyuridine (BrdU) and selected regions of embryonic (E) CNS tissues at E11-22 dissociated with papain into single-cell suspensions. Proliferative cell populations were assessed by anti-BrdU and propidium iodide staining using flow cytometry. Cell differentiation was evaluated using molecular and immunocytochemical probes against mRNAs and antigens differentiating the neuroepithelial, neuronal and glial cell lineages. The results show the emergence of distinctive spatiotemporal changes in BrdU+ populations throughout the CNS during embryonic development, which were followed by corresponding changes in the cellular distributions of antigens distinguishing specific cell types. Fractionation of neocortical cells using discontinuous Percoll gradients revealed that an increasing number of cells increase their buoyancy during corticogenesis. Immunocytochemical and molecular characterization showed that the proliferative and progenitor cell populations are for the most part associated with lower buoyancy or higher specific buoyant densities (> 1.056 g/ml) whereas the post-mitotic, differentiated neurons generally separated into fractions of higher buoyancy or lower specific buoyant densities (< 1.043 g/ml). Immunostaining with antibodies against several GABAA receptor subunits (alpha 3, beta 3, gamma 2) revealed that the highest percent (70-90%) of immunopositive cells could be identified in the most buoyant, differentiating neurons found in the cortical plate/subplate regions, with the lowest percent of the immunopositive cells found in the least buoyant, proliferative and progenitor cell populations originating from the ventricular/subventricular zones. Taken together, these results indicate that buoyant density is a distinguishing characteristic of embryonic CNS cells transforming from primarily proliferative to mainly differentiating, and that fractionation of these cells according to their buoyant densities provides rapid access to the properties of specific cell lineages during the prenatal period of CNS development.

Animals↗
PubMed1997

Neurotrophins stimulate chemotaxis of embryonic cortical neurons.

During mammalian cortical development, neuronal precursors proliferate within ventricular regions then migrate to their target destinations in the cortical plate, where they organize into layers. In the rat, most cortical neuronal migration occurs during the final week of gestation (Bayer et al, 1991; Jacobson, 1991). At this time (E15-E21), reverse transcriptase-polymerase chain reaction demonstrated that cortical homogenates contain mRNA encoding brain derived neurotrophic factor (BDNF) and the catalytic form of its high-affinity receptor, TrkB. Immunocytochemistry and in situ hybridization of sections revealed that the catalytic TrkB receptors predominantly localize to regions containing migratory cells. Many TrkB+ cells exhibited the classic morphology of migrating neurons, suggesting that TrkB ligands play a role in cortical neuronal migration. We analysed whether TrkB ligands influence the motility of embryonic cortical cells (from E15-E21) using a quantitative in vitro chemotaxis assay. High-affinity TrkB ligands (BDNF and NT4/5) stimulated chemotaxis (directed migration) of embryonic neurons at concentrations ranging from 1 to 100 ng/ml. NT-3, a low-affinity TrkB ligand, only stimulated significant migration at high concentrations (> or =100 ng/ml). Peak migration to BDNF was observed at gestational day 18 (E18). BDNF-induced chemotaxis was blocked by either tyrosine kinase inhibitor, K252a, or the Ca2+-chelator, BAPTA-AM, suggesting that BDNF-induces motility via autophosphorylation of TrkB receptor proteins and involves Ca2+-dependent mechanisms. BDNF-stimulation of increased cytosolic Ca2+ was confirmed with optical recordings of E18 cortical cells loaded with Ca2+ indicator dye. Thus, signal transduction through the TrkB receptor complex directs neuronal migration, suggesting that, in vivo, BDNF exerts chemotropic effects that are critical to morphogenesis of the cortex.

Animals↗
PubMed1997

[Investigation on hepatitis G virus (HGV) infection among different populations in Shenzhen].

A reverse transcription polymerase chain reaction assay with nested primers (RT-nested PCR) deduced from the 5' untranslated region of HGV genome was established to detect HGV RNA. By using this assay, we tested the serum samples of 106 paid blood donors, 80 intravenous drug users and 168 cases with viral hepatitis in Shenzhen, China. The positive rates of HGV RNA were 8.5%, 46.3% and 7.7%, respectively. The positive rates of HGV RNA in 61 cases with chronic hepatitis B and 33 cases with chronic hepatitis C were 8.2% and 21.2%. Among the 33 cases with chronic hepatitis C, the positive rate of HGV RNA in 15 cases infected with HCV by blood or blood products was 40.0%, compared with 1.7% in 18 cases without exposure to blood or blood products (P<0.05). The results of this study suggest that HGV infection is common in paid blood donors; the intravenous drug user is the population at high risk for HGV infection; the patients with post-transfusion chronic hepatitis C are often supperinfected with HGV.

Adult↗