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Biomedical subjects

J P Yuan

Publications and source records attributed to J P Yuan.

14 recordsLinked to original sources
PubMed2007

TRPC channels: interacting proteins.

TRP channels, in particular the TRPC and TRPV subfamilies, have emerged as important constituents of the receptor-activated Ca2+ influx mechanism triggered by hormones, growth factors, and neurotransmitters through activation ofphospholipase C (PLC). Several TRPC channels are also activated by passive depletion of endoplasmic reticulum (ER) Ca2+. Although in several studies the native TRP channels faithfully reproduce the respective recombinant channels, more often the properties of Ca2+ entry and/or the store-operated current are strikingly different from that of the TRP channels expressed in the same cells. The present review aims to discuss this disparity in the context of interaction of TRPC channels with auxiliary proteins that may alter the permeation and regulation of TRPC channels.

Animals↗
PubMed2000

Structure of the Homer EVH1 domain-peptide complex reveals a new twist in polyproline recognition.

Homer EVH1 (Ena/VASP Homology 1) domains interact with proline-rich motifs in the cytoplasmic regions of group 1 metabotropic glutamate receptors (mGluRs), inositol-1,4,5-trisphosphate receptors (IP3Rs), and Shank proteins. We have determined the crystal structure of the Homer EVH1 domain complexed with a peptide from mGluR (TPPSPF). In contrast to other EVH1 domains, the bound mGluR ligand assumes an unusual conformation in which the side chains of the Ser-Pro tandem are oriented away from the Homer surface, and the Phe forms a unique contact. This unusual binding mode rationalizes conserved features of both Homer and Homer ligands that are not shared by other EVH1 domains. Site-directed mutagenesis confirms the importance of specific Homer residues for ligand binding. These results establish a molecular basis for understanding the biological properties of Homer-ligand complexes.

Animals↗
PubMed1999

Coupling of mGluR/Homer and PSD-95 complexes by the Shank family of postsynaptic density proteins.

Shank is a recently described family of postsynaptic proteins that function as part of the NMDA receptor-associated PSD-95 complex (Naisbitt et al., 1999 [this issue of Neuron]). Here, we report that Shank proteins also bind to Homer. Homer proteins form multivalent complexes that bind proline-rich motifs in group 1 metabotropic glutamate receptors and inositol trisphosphate receptors, thereby coupling these receptors in a signaling complex. A single Homer-binding site is identified in Shank, and Shank and Homer coimmunoprecipitate from brain and colocalize at postsynaptic densities. Moreover, Shank clusters mGluR5 in heterologous cells in the presence of Homer and mediates the coclustering of Homer with PSD-95/GKAP. Thus, Shank may cross-link Homer and PSD-95 complexes in the PSD and play a role in the signaling mechanisms of both mGluRs and NMDA receptors.

Adaptor Proteins, Signal Transducing↗
PubMed1999

Hydrolysis kinetics of astaxanthin esters and stability of astaxanthin of Haematococcus pluvialis during saponification.

The reaction kinetics for the hydrolysis of astaxanthin esters and the degradation of astaxanthin during saponification of the pigment extract from the microalga Haematococcus pluvialis were investigated. Different concentrations of sodium hydroxide in methanol were used for the saponification under nitrogen in darkness at ambient temperature (22 degrees C) followed by the analysis of astaxanthins and other carotenoids using an HPLC method. The concentration of methanolic NaOH solution was important for promoting the hydrolysis of astaxanthin esters and minimizing the degradation of astaxanthin during saponification. With a higher concentration of methanolic NaOH solution, the reaction rate of hydrolysis was high, but the degradation of astaxanthin occurred significantly. The rate constants of the hydrolysis reaction (first order) of astaxanthin esters and the degradation reaction (zero-order) of astaxanthin were directly proportional to the concentration of sodium hydroxide in the saponified solution. Although the concentration of sodium hydroxide in the saponified solution was 0.018 M, complete hydrolysis of astaxanthin esters was achieved in 6 h for different concentrations (10-100 mg/L) of pigment extracts. Results also indicated that a higher temperature should be avoided to minimize the degradation of astaxanthin. In addition, during saponification, no loss of lutein, beta-carotene, and canthaxanthin was found.

Chromatography, High Pressure Liquid↗
PubMed1999

Isomerization of trans-astaxanthin to cis-isomers in organic solvents.

The isomerization of trans-astaxanthin to cis-isomers in organic solvents was investigated. trans-Astaxanthin was dissolved in dimethyl sulfoxide, dichloromethane, chloroform, acetone, methanol, acetonitrile, and a mixture of dichloromethane and methanol (25:75) respectively, and heated at 35 degrees C followed by analyzing cis- and trans-astaxanthins in the solutions using HPLC. The isomerization rates of trans-astaxanthin were dependent on the solvent, and the following order was found: dichloromethane > chloroform > the mixture of dichloromethane and methanol (25:75) > methanol > acetonitrile > acetone > dimethyl sulfoxide. In different solvents, the relative contents of 9-cis- and 13-cis-astaxanthins formed during isomerization were different. In all solvents, 13-cis-isomer was the main cis-isomer from trans-astaxanthin. trans-Astaxanthin dissolved in dichloromethane or chloroform was very readily isomerized to cis-isomers, especially for dichloromethane, in which a maximum isomerization percentage was found and an equilibrium practically was reached after an appropriate time interval. Results also indicated that a higher temperature could promote markedly the isomerization of trans-astaxanthin.

Kinetics↗
PubMed1998

Homer regulates the association of group 1 metabotropic glutamate receptors with multivalent complexes of homer-related, synaptic proteins.

Homer is a neuronal immediate early gene (IEG) that is enriched at excitatory synapses and binds group 1 metabotropic glutamate receptors (mGluRs). Here, we characterize a family of Homer-related proteins derived from three distinct genes. Like Homer IEG (now termed Homer 1a), all new members bind group 1 mGluRs. In contrast to Homer 1a, new members are constitutively expressed and encode a C-terminal coiled-coil (CC) domain that mediates self-multimerization. CC-Homers form natural complexes that cross-link mGluRs and are enriched at the postsynaptic density. Homer 1a does not multimerize and blocks the association of mGluRs with CC-Homer complexes. These observations support a model in which the dynamic expression of Homer 1a competes with constitutively expressed CC-Homers to modify synaptic mGluR properties.

Amino Acid Sequence↗
PubMed1998

Homer binds a novel proline-rich motif and links group 1 metabotropic glutamate receptors with IP3 receptors.

Group I metabotropic glutamate receptors (mGluRs) activate PI turnover and thereby trigger intracellular calcium release. Previously, we demonstrated that mGluRs form natural complexes with members of a family of Homer-related synaptic proteins. Here, we present evidence that Homer proteins form a physical tether linking mGluRs with the inositol trisphosphate receptors (IP3R). A novel proline-rich "Homer ligand" (PPXXFr) is identified in group 1 mGluRs and IP3R, and these receptors coimmunoprecipitate as a complex with Homer from brain. Expression of the IEG form of Homer, which lacks the ability to cross-link, modulates mGluR-induced intracellular calcium release. These studies identify a novel mechanism in calcium signaling and provide evidence that an IEG, whose expression is driven by synaptic activity, can directly modify a specific synaptic function.

Amino Acid Sequence↗
PubMed1997

Tanshinone production in Ti-transformed Salvia miltiorrhiza cell suspension cultures.

Transformed cell cultures of Salvia miltiorrhiza were established by infecting sterile plantlets with Agrobacterium tumefaciens strain C58. The transformed cells in suspension formed macroscopic clumps of cell aggregates up to 2-3 cm in size rather than homogeneous cell suspensions. These transformed cells grew well in hormone-free media. It was found that the B5 mediums supported the best growth while the 6,7-V medium promoted tanshinone production in the transformed cell suspension cultures. The effect of initial sucrose concentration on cell growth was also studied. The best growth was observed when cells were cultivated in the B5 medium containing 30 g l-1 sucrose. Although low levels of tanshinones were produced in fast growing cell cultures, there existed a rapid increase in tanshinone production when the cell aggregates were transferred to the fresh yeast-extract-containing medium. By this two-stage culture method, about 22 mg tanshinones were produced in 1 liter of medium. Green cell aggregates were formed when cells were cultured under illumination. Light was found to have an inhibitory effect on tanshinone biosynthesis. A sensitive high-performance liquid chromatographic method was developed for the measurement of tanshinones. Cryptotanshinone, tanshinone I and tanshinone IIA were identified from the transformed cultures.

Abietanes↗
PubMed1995

Developmental and regional expression pattern of a novel NMDA receptor-like subunit (NMDAR-L) in the rodent brain.

A novel NMDA receptor-like (NMDAR-L) cDNA was isolated that contained an open reading frame coding for a predicted polypeptide of 1115 amino acids that shares approximately 27% identity with NMDA receptor subunits. In situ hybridization experiments indicated that NMDAR-L mRNA was expressed in the developing rodent CNS. On postnatal day 1 (P1), NMDAR-L mRNA expression was pronounced in the entorhinal cortex, the subiculum and the thalamus, in layer V of the developing neocortex, in the superior and inferior colliculi, and various regions of the hindbrain, excluding the cerebellum. On P5, NMDAR-L mRNA was expressed in layer V of the neocortex, in the entorhinal cortex, in the subiculum, and in the thalamus. On P14, NMDAR-L mRNA was expressed in layers II-VI of the neocortex, in the entorhinal and piriform cortex, in the subiculum and CA1 field, and in the nucleus of the lateral olfactory tract. In the adult brain, NMDAR-L mRNA was detected predominately in the nucleus of the lateral olfactory tract. Injection of NMDAR-L cRNA into Xenopus oocytes did not lead to the expression of homomeric glutamate-activated channels. However, coinjection of the triple combination of NMDAR-L with NMDAR1 and NMDAR2B cRNAs led to a striking decrease in the current magnitude compared to currents obtained after coexpression of the double combination of NMDAR1 with NMDAR2B. While the function of NMDAR-L remains to be established, its developmental and regional expression pattern suggests that NMDAR-L may influence axonal outgrowth and synaptogenesis during brain development.

Aging↗
PubMed1990

[Pulmonary Pseudomonas infections].

145 strains of pathogenic pseudomonas had been isolated from the sputum or bronchoscopic aspirate of 1423 patients with pulmonary infections. They were classified into 8 types, among which 31.7% was pseudomonas aeruginosa. Pseudomonas aeruginosa was the dominant causative organism in pulmonary infections of the aged while in presenile ones the organism was mainly Pseudomonas fetid. The incidence of nosnocomial pseudomonas infection in patients of COPD with respiratory failure was 40%, of COPD with pulmonary infection 9.1% and of others 6.6%. 24 pseudomonas carriers with COPD (colonies less than or equal to 10(6)/ml in sputum) had been followed up. 16 out of them became negative in sputum culture without any treatment, while the remaining 8 developed pulmonary pseudomonas infections. 21 patients (14.5%) were found to have other types of pseudomonas infections during antibiotic treatment. Sensitivity tests showed that third-generation cephalosporins and aminoglycosides had definite antimicrobial activity against pseudomonas, the former being more stable and effective than the latter.

Adult↗
PubMed1989

Ciclosporin and thyroid-stimulating immunoglobulins in endocrine orbitopathy.

The study investigated whether ciclosporin (C) affected the thyroid-stimulating immunoglobulins (TSI) in serum of patients with endocrine orbitopathy (EO). The effect of C was compared with that of prednisone (P). Fifteen patients with EO classes III-V received C (n = 7) or P (n = 8). In addition to the immunosuppressants, five patients with Graves' disease in each group received methimazole (MMI). The stimulation of the cAMP levels in the medium of thyrocyte cultures was determined as a parameter of TSI. The TSI levels were markedly lowered in both groups during and after therapy. C group: before therapy 6.2 pmol/ml +/- 1.63 (100%, mean +/- SEM), during treatment 4.6 pmol/ml +/- 2.28 (74%), after treatment 4.1 pmol/ml +/- 1.33 (66%). P group: before treatment 9.1 pmol/ml +/- 3.42 (100%), during treatment 5.9 pmol/ml +/- 2.90 (65%), after treatment 3.7 pmol/ml +/- 1.20 (41%). There is neither a significant difference between the two groups nor between the patients who received the combined therapy (MMI + immunosuppressants) or only received immunosuppressants (P more than 0.05). The mean cAMP value of the healthy reference group (n = 19) is 0.4 pmol/ml +/- 0.03. There is a significant difference between this value and the cAMP values of the patients both before and after therapy (P less than 0.01). Thus, both C and P markedly lower the TSI titers of patients with EO.

Adult↗
PubMedDate not supplied

Activation of NMDA receptor-channels in human retinal Müller glial cells inhibits inward-rectifying potassium currents.

Although it is well known that neurotransmitters mediate neuron-to-neuron communication, it is becoming clear that neurotransmitters also affect glial cells. However, knowledge of neuron-to-glial signalling is limited. In this study, we examined the effects of the glutamate agonist N-methyl-D-aspartate (NMDA) on Müller cells, the predominant glia of the retina. Our immunocytochemical studies and immunodetection by Western blotting with monoclonal antibodies specific for the NMDAR1 subunit provided evidence for the expression by human Müller cells of this essential component of NMDA receptor-channels. Under conditions in which potassium currents were blocked, NMDA-induced currents could be detected in perforated-patch recordings from cultured and freshly dissociated human Müller cells. These currents were inhibited by competitive and non-competitive blockers of NMDA receptor-channels. Extracellular magnesium reduced the NMDA-activated currents in a voltage-dependent manner. However, despite a partial block by magnesium, Müller cells remained responsive to NMDA at the resting membrane potential. Under assay conditions not blocking K+ currents, exposure of Müller cells to NMDA was associated with an MK-801 sensitive inhibition of the inward-rectifying K+ current (IK(IR)), the largest current of these glia. This inhibitory effect of NMDA appears to be mediated by an influx of calcium since the inhibition of IK(IR) was significantly reduced when calcium was removed from the bathing solution or when the Müller cells contained the calcium chelator, BAPTA. Inhibition of the Müller cell KIR channels by the neurotransmitter glutamate is likely to have significant functional consequences for the retina since these ion channels are involved in K+ homeostasis, which in turn influences neuronal excitability.

Cell Communication↗
PubMedDate not supplied

Expression of bcl-2 and Bax in EGFR-antisense transfected and untransfected glioblastoma cells.

Glioblastomas are the most frequent and most malignant astrocytic gliomas. The epidermal growth factor receptor (EGFR) gene is the most frequently amplified and overexpressed in glioblastomas. The expression of bcl-2 and Bax in EGFR-antisense transfected and un-transfected glioblastoma cell line, U87E and U87V was studied by immunohistochemistry and western blotting. Our results show that the expression of Bax was stronger and bcl-2 was weaker in EGFR-antisense transfected cell line than the untransfected control. Bcl-2 and Bax genes are probably involved in the reduction of malignancy of glioblastoma cell caused by the introduction of EGFR-antisense into these tumor cells.

Apoptosis↗