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Biomedical subjects

Y H Tan

Publications and source records attributed to Y H Tan.

At least 55 records · Page 3Linked to original sources
PubMed1995

Activation of protein kinases and the inactivation of protein phosphatase 2A in tumour necrosis factor and interleukin-1 signal-transduction pathways.

We report the identification of 16 of the 30 cellular proteins which are rapidly phosphorylated in tumour-necrosis-factor-(TNF)-treated or interleukin-1-(IL-1)-treated primary human fibroblasts. Phosphorylation assays of proteins found in the cytosolic extract of human fibroblasts by in vitro assays indicate that at least 12 of these proteins are likely to be substrates for mitogen-activated protein kinase(s) (MAP kinase), mitogen-activated protein-kinase-activated protein kinase 2 (MAPKAP kinase 2), a pp60c-src-like tyrosine kinase as well as for a putative dual nucleotide protein kinase (DNK) in TNF-treated or IL-1-treated cells. Comparison of the phosphorylation of cytosolic proteins in vitro by exogenously added protein kinases with that observed in cells treated with TNF or IL-1 enabled the identification of cellular substrates of TNF-activated and IL-1-activated cellular protein kinases. Comparison of protein kinase activities of cytosolic extracts derived from TNF-treated or IL-1-treated and control fibroblasts also show the activation of MAP kinase, MAPKAP kinase 2, a putative DNK and a pp60src-like tyrosine kinase 3-19 fold. The data suggest TNF or IL-1 signal transduction may involve the phosphorylation of protein phosphatase type 2A by a pp60src-like tyrosine kinase, followed by the activation of MAP kinase, MAPKAP kinase 2 and the putative DNK. However, the activation of MAP kinase and MAPKAP kinase 2 may be independent of the earlier activation of pp60src-like tyrosine kinase and the inactivation of protein phosphatase type 2A.

Calcium-Calmodulin-Dependent Protein Kinases↗
PubMed1995

Effects of anisodamine against myocardial ischemia-reperfused injuries and antilipid peroxidation.

AIM: Anisodamine (Ani), an alkaloid first isolated in China. To study the relationship between the protective effects of Ani on myocardial cells of reperfused injuries and the antilipid peroxidation. METHODS: Coronary ligation for 15-min followed by 10 min reperfusion was performed in anesthetized rats. RESULTS: Ani 1, 3, 5 mg.kg-1 i.v. 1 min prior to reperfusion could dose-dependently lower the release of creatine kinase (282 +/- 29, 252 +/- 53, 226 +/- 50), counteract the increase of malondialdehyde content (3.3 +/- 1.3, 3.2 +/- 1.6, 3.1 +/- 1.2) in the reperfused myocardium and preserve the SOD activity (41 +/- 7, 46 +/- 8, 55 +/- 8). Ani completely abolished the drop in the contents of principal unsaturated fatty acids (oleic, linoleic, and arachidonic acids) of the membrane lipids in the reperfused myocardium. SOD 75 U.kg-1 i.v. 1 min prior to reperfusion exerted similar effects like Ani 3 mg.kg-1. CONCLUSION: It is suggested that the antilipid peroxidative effect of Ani may contribute to its protection against reperfusion-induced myocardial injuries.

Animals↗
PubMed1995

Tarsometatarsal (Lisfranc's) injuries--results of open reduction and internal fixation.

Injuries of the tarsometatarsal (Lisfranc's) joint are uncommon and are potentially associated with chronic disability. The aim of our study was to review retrospectively the results of open reduction with Kirschner wire internal fixation of tarsometatarsal injuries. In this study, 12 patients with Lisfranc's injuries treated between January 1986 and March 1993 were reviewed at an average of 36 months after the injuries. Majority of the patients suffered from type B injuries (Hardcastle's classification, 1982). There were 9 closed and 3 open injuries. All were high energy injuries sustained in motor vehicle accidents, fall from a height or crush force. All were treated with open reduction and internal fixation with Kirschner wires. Anatomical reduction was achieved and maintained. There was no postoperative redisplacement. During follow-up, most patients developed radiological evidence of post-traumatic osteoarthritic changes. However, majority of the patients were pain-free or had very little foot pain, and were able to return to their previous occupation. Our study showed that open reduction with Kirschner wire internal fixation offered satisfactory anatomical and functional results.

Accidental Falls↗
PubMed1994

Differential induction of the interleukin-6 gene by tumor necrosis factor and interleukin-1.

Although tumor necrosis factor (TNF) and interleukin-1 (IL) induce the expression of the IL-8, TNF-stimulated gene 6, and plasminogen activation inhibitor-2 genes and the activation of NF-kappa B with nearly identical kinetics, the two cytokines differ significantly in the induction of the IL-6 gene in all primary fibroblasts tested. IL-1 induces IL-6 gene expression after 30 min of IL-1 treatment, reaching a maximum level by 7 h, and is sustained for up to 14 h. TNF also induces the IL-6 gene expression at 30 min but the induction was low. A similar differences in the amount of IL-6 secreted was observed in the IL-1/TNF-treated cells. Measurement of IL-6 gene transcription by nuclear run-on transcription assays indicated a 4-fold higher rate of IL-6 gene transcription in IL-1-treated than in TNF-treated cells. The IL-1-induced IL-6 mRNA has a significantly longer half-life (> 6 h) compared to 30 min for TNF-treated cells. These results suggest that the induction of the IL-6 gene expression in primary human fibroblasts by TNF and IL-1 is differentially regulated at the transcriptional as well as at the post-transcriptional level.

Dactinomycin↗
PubMed1994

Dephosphorylation of the small heat shock protein Hsp27 in vivo by protein phosphatase 2A.

The phosphorylation of the Hsp27 complex is rapidly altered in MRC-5 cells when they are exposed to mitogens, cytokines, stress, or serine/threonine protein phosphatase inhibitors. Here we performed experiments to identify which cellular protein phosphatase (PP1, PP2A, or PP2B) is responsible for the in vivo phosphorylation/dephosphorylation of Hsp27. In their purified forms, PP2A dephosphorylates Hsp27 more effectively than PP2B, whereas PP1 is weakly active. Measurements of enzyme activity of lysates derived from inhibitor-treated cells indicated that Hsp27 phosphatase activity is equally sensitive to okadaic acid (PPI/PP2A inhibitor) and cyclosporin (PP2B inhibitor) and that both okadaic acid and cyclosporin treatment inhibited Hsp27 phosphatase activity additively. Together the in vitro data suggest that both PP2A and PP2B can dephosphorylate Hsp27. However, the phosphorylation of Hsp27 in vivo is only affected when cells are treated with PP1 and PP2A inhibitors (okadaic acid, calyculin A) or cantharidin (PP2A inhibitor), but not the PP2B inhibitor, cyclosporin A, suggesting PP2A to be the main enzyme dephosphorylating Hsp27 in the cells. Purification and immunoblotting of Hsp27 phosphatase from MRC-5 cells also suggest it to be PP2A and not PP1 or PP2B. The ability of PP2A to dephosphorylate Hsp27 is shown to be regulated by the phosphorylation state of PP2A itself.

Amino Acid Sequence↗
PubMed1994

Effects of berberine on delayed afterdepolarizations in ventricular muscles in vitro and in vivo.

The effects of berberine on delayed afterdepolarizations in ventricular muscles in vitro and in vivo were investigated to help explain the mechanisms for its antiarrhythmic action. Berberine 3 mumol reduced the amplitude of delayed afterdepolarizations induced by ouabain or posthypoxic reoxygenation and abolished subsequent triggered activity in isolated guinea pig right ventricular papillary muscles. At 30 mumol, it decreased the incidence of delayed afterdepolarizations, associated with a further decrease in the amplitude of delayed afterdepolarizations. In rabbit left ventricular (LV) muscles in vivo, berberine 1 mg/kg intravenously (i.v.) decreased the amplitude of delayed afterdepolarizations evoked by ouabain and calcium gluconate from 9.6 +/- 1.9 to 6.8 +/- 0.8 mV and left stellate ganglion stimulation from 9.4 +/- 2.1 to 6.2 +/- 0.7 mV and blocked ventricular arrhythmias. After a 4-mg/kg i.v. bolus, the drug inhibited and even completely abolished development of delayed afterdepolarizations, yet still reduced maximal velocity of depolarization in isolated and in vivo ventricular muscles. Therefore, one of the important mechanisms for antiarrhythmic action of berberine may be suppression of delayed afterdepolarizations, which may be attributable in part to a decrease in Na+ influx.

Animals↗
PubMed1994

Presynaptic histamine H1- and H3-receptors modulate sympathetic neurotransmission in isolated guinea pig vas deferens.

The action of (R)-alpha-methylhistamine (alpha-MeHA), a selective H3-receptor agonist, on field stimulation induced contraction of guinea pig vas deferens was composed of 2 components: the "inhibition" (0.1-100 nmon.L-1) and the "enhancement" (1-10 mumol.L-1). In the presence of histamine H1 antagonist, chlorpheniramine (1 mumol.L-1), alpha-MeHA (0.1 nmol.L-1-10 mumol.L-1) showed only a concentration-dependent inhibition. Selective histamine H3-receptor antagonist, thioperamide (1 nmol.L-1-10 mumol.L-1) antagonized the inhibitory effect of alpha-MeHA and increased the contractile amplitude of vas deferens elicited by field pulses when thioperamide was used alone. alpha-MeHA 10 mumol.L-1 enhanced the contractile amplitude, which was reversed by chlorpheniramine 1 mumol.L-1, but not by ranitidine (1 mumol.L-1). Pyridelethylamine, an H1-receptor agonist, facilitated concentration-dependently the contractile response of vas deferens. The effect was antagonized by chlorpheniramine, but not by ranitidine. Dimaprit, an H2-receptor agonist had no effect on the field stimulation induced sympathetic response. Both alpha-MeHA and pyridelethylamine failed to influence the contraction of vas deferens elicited by direct field stimulation in smooth muscle or by exogenously applied norepinephrine. It was concluded that histamine H1- and H3-receptors existed in sympathetic terminals of guinea pig vas deferens and facilitated or inhibited the sympathetic neurotransmission.

Animals↗
PubMed1994

Inhibition of sympathetic neurotransmission via NEM-sensitive H3-receptors in the guinea pig vas deferens.

The influence of N-ethylmaleimide (NEM) on sympathetic neurotransmission induced by field stimulation on the isolated guinea pig vas deferens was studied. Application of (R)-alpha-methylhistamine (0.1 mcmol/l) significantly inhibited the sympathetic response by 26.0%, while thioperamide facilitated the sympathetic contraction of vas deferens evoked by field pulses by 221.1%. Pretreatment of vas deferens with NEM (60 mcmol/l) for 15 min abolished both the inhibitory and facilitatory effects. Attenuation of thioperamide facilitatory effect by NEM was not significantly altered when the H3-receptors were occupied by thioperamide prior to and during NEM treatment. The results suggest that effects mediated by H3-receptors in the guinea pig vas deferens were NEM-sensitive and possibly transmitted by Gi or Go proteins.

Animals↗
PubMed1994

High concentrations of mannitol in the shiitake mushroom Lentinula edodes.

A quantitative analysis of mannitol, using gas-liquid chromatography (GLC), was carried out in the various tissues of Lentinula edodes (Berk.) Pegler in comparison with Agaricus bisporus (Lge) Imb. and Coprinus cinereus (Schaeff.: Fr.) S. F. Gray. Mycelia of L. edodes had a low level of mannitol (ca 1% on a dry wt basis) compared with the fruit body stipe and pileus (20-30%). The highest level of mannitol was observed in the pileus of A. bisporus (close to 50%). These observations of similar levels of accumulation of mannitol suggest that glucose catabolism in L. edodes and A. bisporus are similar. No mannitol was detectable in the pileus of C. cinereus.

Agaricus↗
PubMed1993

Differential induction of nuclear NF-kappa B by protein phosphatase inhibitors in primary and transformed human cells. Requirement for both oxidation and phosphorylation in nuclear translocation.

Phosphoseryl/threonyl protein phosphatase inhibitors, viz. okadaic acid and calyculin-A, failed to induce nuclear factor-kappa B (NF-kappa B) nuclear translocation in several primary human cells although a marked and rapid induction was observed in their simian virus 40 transformed counterparts. Inability to induce NF-kappa B cannot be due to a non-activatable system since NF-kappa B was strongly activated by tumor necrosis factor in all the five primary cell types tested. It is also unlikely that the differential induction was due to differential sensitivity of primary and transformed cells to phosphatase inhibitors as the intracellular phosphatase activities of both cell types were equally inhibited by these inhibitors. However, pretreatment with hydrogen peroxide or buthionine sulfoximine, chemicals known to directly or indirectly elevate the intracellular free-radical levels, enabled okadaic acid to induce nuclear translocation of NF-kappa B in primary cells. Conversely cysteine, an antioxidant and precursor of the free radical scavenger, glutathione, inhibited the induction of NF-kappa B by tumor necrosis factor in primary cells, and by okadaic acid or tumor necrosis factor in transformed cells. These data, taken together, suggest that free radical-dependent oxidation and protein phosphorylation are not independent modes of NF-kappa B induction, but are both required for the release of NF-kappa B from I kappa B. Furthermore, the differential induction of NF-kappa B nuclear translocation by okadaic acid in primary and transformed human cells, reported herein, reflects intrinsic differences in the intracellular oxidative state between the two groups of cells. The induction of NF-kappa B by tumor necrosis factor in primary cells suggests that this cytokine fulfills the requirement for oxidation, possibly by inducing the production of free radicals.

Amino Acid Sequence↗
PubMed1993

Detection and characterization of cellular EGR-1 binding to its recognition site.

Most of what is known of the Egr-1 DNA binding site GCGGGGGCG was originally identified by experiments using DNA sequences and bacterially expressed or in vitro translated EGR-1 protein. Here we report the binding of cellular EGR-1 protein derived from HeLa, mouse and human fibroblasts to its consensus sequence. Binding is strongly but transiently stimulated in these cells by serum, phorbol ester, or by okadaic acid, an inhibitor of protein serine/threonine phosphatases 1 and 2A, suggesting the regulation of this gene expression and its DNA binding activity to be under the control of protein kinase(s) and phosphatase(s). When EGR-1 synthesis is stimulated under the above conditions, binding of the transcription factor Sp1 to its recognition site in the Egr-1 promoter is reduced with a concomitant appearance of EGR-1 DNA binding. This is likely a result of competition between Sp1 and the newly synthesized EGR-1, since there is a partial overlap in the binding sequences recognized by these proteins. In cotransfection experiments EGR-1 activated transcription through multiple copies of GCGGGGGCG 5' to a minimum promoter of c-fos. Interestingly, EGR-1 is shown to down-regulate the transcription of its own gene expression, whereas Sp1 activated Egr-1 gene expression. The detection of cellular EGR-1 binding to the Egr-1 consensus sequence in the different cell types provides a model for studying the mechanism by which an immediate-early gene is regulated by various ligands.

3T3 Cells↗
PubMed1993

Inactivation of a redox-sensitive protein phosphatase during the early events of tumor necrosis factor/interleukin-1 signal transduction.

Isoforms of heat shock protein (Hsp) 27 were used as intracellular markers to study tumor necrosis factor/interleukin-1 (TNF/IL-1) regulation of protein phosphatases in primary human fibroblasts. These isoforms were rapidly phosphorylated to varying degrees when fibroblasts were treated with either TNF, IL-1, okadaic acid, calyculin A, ARS, epidermal growth factor, fibroblast growth factor, H2O2, buthionine sulfoximine, N-ethylmaleimide, diethylmaleimide, or iodoacetate. However, inhibitors of protein kinases A and C, tyrosyl protein kinases, and general protein kinases had no effect on the enhanced phosphorylation of these isoforms in TNF, IL-1, okadaic acid, or calyculin A-stimulated cells, suggesting that the activation of protein kinases by itself is insufficient to produce these changes. Isoforms of 32P-labeled Hsp27 were dephosphorylated during cold-chases with excess phosphate in the absence but not in the presence of TNF/IL-1 or inhibitors of protein phosphatases suggesting that inactivation of protein phosphatase(s) plays a role in TNF/IL-1 signal transduction. Assays of phosphatase activity of cytosolic fractions from TNF or okadaic acid treated human fibroblasts showed an inactivation of protein phosphatase activity against the 32P-labeled Hsp27 protein substrates. In vitro assays of partially purified phosphatase activity from primary human fibroblasts with Hsp27 substrate also showed the protein phosphatase activity to be inhibited by ARS. Like okadaic acid, ARS mimics TNF in inducing specific patterns of cellular protein phosphorylation. Taken together these findings are consistent with the hypothesis that a SH-dependent protein phosphatase is inactivated during the early events of TNF/IL-1 signal transduction, hence inhibitors of protein phosphatases and SH modifying compounds can mimic the early effects of TNF/IL-1 on cells.

Amino Acid Sequence↗
PubMed1993

[Indirect testimony of stress conduction from mandible to skull in maxillofacial trauma: morphological changes of temporomandibular joint disc]

There were cerebral injuries accompanied in maxillofacial high velocity projectile wound.Owing to the special anatomic relationship between skull and facial bones,the stress conduction of bone was an important factor of cerebral injury in maxillofacial wound.In this experiment,the canine mandibular regions were wounded by steel spheres,which weight 1.03g,impacting velocity at 1400m/s,to produce severely maxillofacial firearm wounds.The morphological and pathological changes of temporomandibular joint disc of wounded side were observed with light and electron microscopes.The microscopic injuries of disc,including arrangement disorder of figre,spotty edema and some fibrous dissolution,etc,were found.These results have provided an indirect evidence of injurous mechanism of the cerebral injury accompaning maxillofacial high enery misslle wound.

Journal Article↗
PubMed1993

Effects of 3,6-dimethamidodibenzopyriodonium citrate on slow inward calcium current in isolated guinea pig ventricular cells.

The effects of 3,6-dimethamidodibenzopyriodonium citrate (I-65) on action potentials and slow inward calcium current (I(si)) were examined on isolated guinea pig ventricular myocardial cells. I-65 (30-100 mumol.L-1) depressed the action potential duration at 20% repolarization (APD20) and, under voltage-clamp conditions, reduced the amplitude of I(si) without changing the I-V relations. I-65 also showed use-dependent effects on I(si). These suggest that I-65 may block I(si) by acting on the inactivated state of Ca channels.

Action Potentials↗
PubMed1993

[Effects of 3,6-dimethylamino-dibenzopyriodonium formiate on action potential and slow inward calcium current in isolated guinea pig ventricular myocytes].

The effects of 3,6-dimethylamino-dibenzopyriodonium formiate (IHC-64) on action potential and slow inward calcium current (I(si)) were investigated in isolated guinea pig ventricular myocytes using whole cell voltage clamp recording. IHC-64 (20 and 200 mumol/L) was shown to markedly decrease APD20 and APD90. However, in the presence of nisoldipine, no obvious effects of IHC-64 on APD20 could be detected. Under voltage clamp conditions, IHC-64 (20 and 200 mumol/L) caused a significant decrease in I(si). The results indicate that IHC-64 can block the calcium channels in isolated guinea pig ventricular myocytes.

Action Potentials↗
PubMed1992

Characteristics of depressing effect of cycloprotobuxine-A on the maximal velocity of depolarization in myocardium.

The characteristics of the depressing effect of cycloprotobuxine-A on Vmax in isolated guinea pig myocardium were investigated with a standard microelectrode technique. Cycloprotobuxine-A 3-30 mumol/l produced a concentration-dependent decrease in Vmax, associated with a prolongation of the action potential duration. At 3 mumol/l, a small resting block of Vmax, but a pronounced use-dependent block was found. This use-dependent block increased progressively as stimulation frequency increased from 0.5 to 4.0 Hz. The time constant and rate for onset of use-dependent block were 2.0-7.3 s and 0.11-0.25 AP-1 (reciprocal action potential number), respectively. The time constant and half-life for recovery from use-dependent block were 11.8 and 8.1 s. Thus, the kinetics of the depressing effect of cycloprotobuxine-A on Vmax were intermediate. In muscles depolarized by high [K+]0, the resting block was enhanced slightly, while use-dependent block was greatly augmented. These results suggested that cycloprotobuxine-A could have a low affinity for resting Na+ channels but a much higher affinity for activated and/or inactivated Na+ channels, and that the use-, frequency- and voltage-dependent effects of cycloprotobuxine-A on Vmax may play an important role in preventing the development of cardiac arrhythmias.

Action Potentials↗